Download – Piezoelectric Nanowires – Group 11 Project Specification

Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
1. Revision History
Rev #
Date
October 30, 2008
1
2
3
October 30, 2008
October 30, 2008
October 31, 2008
4
5
6
7
8
November 1, 2008
November 2, 2008
November 2, 2008
November 2, 2008
9
November 3, 2008
Description
Introduction, Customer
Requirements and Project Background
(Sections 2, 2.1)
Blocks, Interface Definitions
(Sections 2.2.2, 4.1.1)
Block Diagrams
(Sections 4, 4.1)
Compile Project Research and
Technology Review Analysis from
Individual Reports
(Sections 2.2, 2.2.1)
Implementation Approaches
(Section 3.1)
Revision of Blocks
(Section 2.2.2)
Absolute Minimum Requirements,
Desired Feature Set
(Sections 2.3.1, 2.3.2)
Fix Citations throughout document
Revision of Block Diagram and Blocks
(Sections 2.2.2, 4.1)
Revision of Glossary and Citations,
Color Coding, Formatting Details, Edit
Absolute Minimum Requirements and
Desired Feature Set, Testing
(Appendices, Sections 2.3.1, 2.3.2, 6)
Additional Block Descriptions, Add to
Blocks Section
(Section 2.2.2)
Contributor(s)
Ashley Mason, Todd Waggoner
Adam Stone
Todd Waggoner
Ashley Mason
Todd Waggoner
Adam Stone
Ashley Mason
Ashley Mason, Adam Stone,
Todd Waggoner
Ashley Mason
10
November 3, 2008
11
November 18, 2008
Font Change, Grammatical Revisions
Todd Waggoner
12
November 26, 2008
Block Interfaces and Operations
(Sections 5.4, 5.5)
Todd Waggoner
13
November 27, 2008
Block Interfaces and Operations
(Sections 5.1, 5.2, 5.3)
Ashley Mason
14
November29, 2008
Block Interfaces and Operations
(Sections 5.6, 5.7)
Adam Stone
15
November 30, 2008
Block Interfaces and Operations
(Sections 5.1 – 5.7)
16
December 5, 2008
Fix font, Label figures and tables,
Block Interfaces and Operations
(Sections 5.1 – 5.3),
Development Plan (Section 8),
Testing (Section 6)
Additional Seed Layer Comparison Table
Todd Waggoner
Ashley Mason, Adam Stone,
Todd Waggoner
Ashley Mason
Page 1 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
December 6, 2008
Revision of Block Interface and
Operations
(Sections 5.4, 5.5),
Updated Block Diagram
(Section 5)
Todd Waggoner
December 6, 2008
Revision of Block Interface and
Operations
(Sections 5.6, 5.7)
Additional Actuator Comparison Table
Bill of Materials for Actuator
Adam Stone
19
December 6, 2008
General Interface Definition
(Section 4.1.1)
Overall Review of Paper
Fix Remaining Suggestions from TA
Add Terms to Glossary
Ashley Mason, Adam Stone,
Todd Waggoner
20
December 7, 2008
Added Mechanical Test Platform Block
Descriptions
(Section 5.8)
Ashley Mason, Todd Waggoner
17
18
Page 2 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
2. Introduction
This project stems out of research from Georgia Tech [1]. Previous experiments showed that small amounts
of energy could be harvested by coating Kevlar strands with ZnO (zinc oxide) nanowires. When the ZnO
nanowires are stressed by linear tension and compression or axial bending they create an electric potential. This
piezoelectric property of the ZnO wires is utilized by wrapping together two separate strands of Kevlar coated
with these wires. The experimental set-up from Georgia Tech is shown in Fig. 1. A motor is used to pull on a
string and actuate the Kevlar strands. On
the other end is a spring that returns the
strands to equilibrium between pulls. The
details of the electrical connections are not
shown.
The project entails the design of
three major sub-systems:
synthesis of the nanowires the
Fig. 1: Basic Experimental Set-up from Georgia Tech Review Article [1]. The
electrical measurement circuit and
important things to notice in this image are the wrapping of the fibers and the
the mechanical actuation system.
coatings on each of the Kevlar strands.
For the growth of the wires,
hydrothermal, solution-based methods will be pursued in order to allow the use of non-traditional substrates that
would be destroyed by traditional furnace growths. Instead of temperatures approaching 1000° C, these
nanowires are produced at less than 100° C. Following some initial research in this area by Zhong Wang at
GeorgiaTech, the initial substrates of interest are Kevlar strands of fiber [1]. Since these decompose around
400° C, this low-temperature growth method essential.
There are multiple steps to the growth process. To successfully grow the nanowires, a seed layer must be
deposited. Given the capabilities at Oregon State University, the deposition can be done via Atomic Layer
Deposition (ALD), RF magnetron sputtering, or a sol-gel approach. ALD will be the standard method due to
having excellent reproducibility and uniform coverage across the entire substrate. Other methods may be used
for comparisons to determine which processes yield the best nanowire for piezoelectric energy harvesting
purposes.
Once the wires are grown, they must be assembled into an actual energy harvesting system. Functionalized
Kevlar strands need to be intertwined in order to provide contact between nanowires that will cause a mechanical
stress essential to piezoelectric generation. To ensure a net flow of electricity, current should only flow in one
direction. This is accomplished by coating one of the Kevlar fibers with a metal such as Al or Au. The
difference in Fermi level of the metal and the conduction band of the semiconductor will produce a Schottky
barrier that will act like a diode.
Next, an electrical test system must be designed to measure the electrical output and ensure electricity is being
generated. Due to the expected amounts that will be produced, a picoammeter must be used. This ensures that
any small amount of current produced will be successfully detected.
To apply an external force to the functionalized Kevlar circuit, a mechanical actuator will be designed. This
will reproducibly pull at the Kevlar, causing the nanowires on its surface to interact and bend relative to each
other. This bending causes a stress on the lattice and creates a voltage via the direct piezoelectric effect.
Although this test bench is being designed around a certain experiment, the objective is to make the system
alterable so that alternative materials can be used (such as polyethylene fibers instead of Kevlar, or a different
piezoelectric in place of ZnO). Depending on initial measurements, the need to study alternative materials could
become prevalent, and the actuation and measurement systems could be used to characterize multiple
alternatives.
This project is important because piezoelectric energy harvesting could be utilized to power small sensors or
medical devices which should not be powered off of batteries. In theory, with enough of the ZnO enhanced
Kevlar fibers, portable devices could be powered as well. For example, an exercise shirt could power an iPod.
Power sources have been a weak point of electronic devices since the time of their origin. Smaller and lighter
voltage sources such Lithium ion batteries and ultracapacitors can greatly increase the mobility of electronic
Page 3 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
devices. Their major limitation is the need to be recharged often. Piezoelectric nanowires are different from
other alternatives because they are an energy source, not an energy storage device.
Another reason that this project is important to the research professor and sponsor is that it is a very
controversial topic. Since the original results from Georgia Tech were published, other groups have tried to
reproduce the original experiments and have been suspicious about where the power output is coming from.
Researchers at the Max Plank Institute believe that the output is actually coming from the measurement circuit,
rather than the ZnO wires themselves. Currently, no other data refuting the Georgia Tech claims has been
published, so contributing to this research cause is critical.
2.1 Customer Requirements and Project Background
The proposed platform will be used in order to study the accuracy of previous studies and to try and soothe
some of the controversy around the originally published results from Georgia Tech. Since this project’s funding
coming from a research grant, the various systems encompassing the project must be made to scientifically prove
(or disprove) that piezoelectric energy harvesting is possible from nanowires. Because of research requirements,
it is essential that everything made is well documented and can stand up to academic scrutiny for publication.
The most important part of this design is that all steps must be repeatable and reliable between runs. There
are also strict noise constraints because the measurements of interest are expected to be in the pA range. Ideally,
the system should be small enough to be mobile, although this may not be critical because the bench should only
be used in a low-noise environment. If needed, the entire apparatus should be able to fit into a dark box or
Faraday cage to eliminate outside interference and generation of photocarriers within the semiconductor. For
instance, moving the measurement equipment to Kelley Engineering Center for the Engineering Expo is
probably not critical because of the noise that would be introduced by the surrounding projects.
Instead of mobility, emphasis should be placed on the ease of building the system. Since other researchers
should be able to utilize this test bench design, the building and analytical processes should be as simple as
possible, low cost and well documented. This system should be able to function on its own rather than be part of
a larger system. Results should be analyzed in-depth and be documented well enough to be published in peerreviewed journals. A reliable test system made within a short amount of time which is easy to build and highly
accurate can resolve some confusion in the research world. As with a more conventional market, the research
market is very competitive as far as publishing and the timelines that are associated with projects and results.
The trade-offs to be cautious about here are the creation and evaluation of an accurate system and being prepared
to publish in a reasonable time period.
Lastly, the final materials used in the fibers and materials should be as easy to synthesize as possible.
Working with chemicals can be a dangerous process, especially depending on the availability of required safety
equipment. Since repeatability is critical for this system, the chemical processes will be under review.
2.2 Project Research
While studying this specific research interest, it is important to review other similar technologies. One
technology that can be used for the same purpose is that of thermopiles. Thermopiles are a collection of many
thermocouples. Thermopiles generate an electric potential by drawing energy from heat. They only work where
there is a thermal gradient. Thermoelectric generators have been developed for the human body. These can
theoretically power devices indefinitely. By using the heat from the human body (most commonly the forehead)
the thermoelectric generators can generate enough power to individually sustain some devices like a brainwave
monitor [2]. The thermocouples are made of a silicon and germanium compound, poly-SiGe. This material was
chosen to take advantage of the Thomson effect. Thermoelectrics use a temperature gradient created by heating
one side and cooling the other to induce an electric potential. SiGe is a commonly used thermoelectric that is
manufactured with an air gap in the center. The size of the gap is selected so that heat flow through the gap and
through the SiGe is the same, ensuring maximum power output [3]. The SiGe is attached on either side by a
silicon plate, one for the cooler side and one for the hot side as shown in Fig. 2.
Page 4 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
Fig. 2: SiGe thermocouple system [3]
An efficient way to link many of these is in a rim shape. This topology creates an efficient thermal circuit
where air can flow from the center outwards much like a desktop chassis. With current designs thermopiles can
generate power in the milliwatt range indefinitely with a human heat source.
Another interesting nanowire energy harvesting project are the photosensitive nanowires created by Harvard
chemists. These wires are made of layers of three different types of silicon. With the different electrical
properties of these different types of silicon the wires are photovoltaic. These can convert 3.4% of the energy
from sunlight into electricity with up to a 5% efficiency [4]. Sunlight is one of the least power dense sources
available, especially considering the low efficiencies of current photovoltaic devices. Harvard chemists believe
they will be able to increase the efficiency of the nanowires by researching alternate internal structures for the
nanowires.
Another method of energy harvesting would be to use a micro-electro-mechanical system (MEMS) in the
form of a linear inertial energy scavenger, Fig. 3.
Fig. 3: MEMS Energy Harvester [6]
If the MEMS uses an electromagnetic energy conversion system there would be a coil on the proof mass.
Dampening changes the vibrational energy of the device into an electrical potential. The power output of such a
device is highly dependent on the frequency of vibration, a drawback that piezoelectric nanowires do not have.
These take a fairly complex system of micromachining to fabricate and cannot be made much smaller than the
mm range with current technology [6].
The most important project to refer to would be the ZnO nanowire research that the Georgia Institute of
Technology conducted recently. This research is somewhat different than other nanowire energy sources in that
the nanowires are not meant to be stretched or compressed, but bent. The core of the fiber is Kevlar, for its
strength and flexibility. There are 5 layers to each fiber: the inner-most being the Kevlar core, next is a layer of
tetraethoxysilane (TEOS), a ZnO seed layer, another TEOS layer, and finally the ZnO nanowires. The outer
surface is covered in radially grown ZnO nanowires. The TEOS layers help form better quality bonds with the
other layers and improve the bending performance of the surface ZnO nanowires. Fig. 4 gives a diagram of the
cross section of a fiber and shows SEM images of the ZnO nanowires.
Page 5 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
The method of energy harvesting is to coat
one fiber with a surface of gold (Au) and
intertwine it with another fiber without Au. The
gold creates a Schottky junction so that current
is allowed to flow from the gold surface to the
ZnO nanowire. As linearly axial vibrations are
induced on the pair of fibers the ZnO fibers will
be bent with respect to the gold coated fiber and
generate an electric potential due to its
piezoelectric properties. The efficiency of ZnO
wires was found to be 17 – 30% [7]. These
were tested and found to give a current output
of ~5pA. The Georgia Tech researchers believe
that the output current is smaller than expected,
due to cracks in the seed layer. This damage
significantly increases the fiber's inner
resistance. The open circuit voltage was also
measured to be ~1 – 3mV. This would mean the
power output of a single fiber would be
~1 – 15fW (femptoWatts). In an attempt to
increase power output, the researchers
deposited a conducting layer onto the fiber
before the ZnO layer, which decreased the inner
resistance from 1GΩ to 1kΩ. The output current
Fig. 4: ZnO nanowire cross section and SEM images [1]
was found to increase from ~4pA to ~4nA,
a factor of 1000. This shows that the inner resistance of the fiber is about linearly proportional to the power
output. This means any method of reducing the inner resistance could significantly improve power output. The
size, durability, and flexibility of these nanowires provide the ability to use them on clothing [8].
One issue with human-powered energy devices is where to place them for maximum efficiency. During
different types of activities, the efficiency can change dramatically. It would be advisable to map out
accelerations of different body parts for each of these activities by using accelerometers. This data could be used
to find where to place piezoelectric nanogenerators to produce the most energy [9].
ZnO-coated Kevlar will be used as nanogenerators in this project because growth processes are wellresearched. As time allows, other materials outside of the original scope of the design project will also be
studied. There are multiple methods to grow nanowires, and these methods become more complicated
depending on the target type of wires as well as the substrate which the wires are being grown on. Although
ZnO nanowires are most commonly made by gas-phase approaches, these methods require temperatures of 450 –
900 oC. Because of the needed non-traditional substrate, a different method must be explored [10].
Table 1 is a summary of different types of nanowires and their associated most common growth methods [11].
Because of the types of materials being looked at (piezoelectric growth species and Kevlar substrate), material
options and processing temperatures are limited. There seem to be three main options if other materials are to be
explored. The easiest would be continuing to use ZnO because this material is commonly worked with due to its
many useful properties as a wide band-gap semiconductor. Not only is ZnO piezoelectric, but it is also used for
its conductivity, high voltage-current non-linearity, sensitivity to various gases and chemicals, optical properties
and catalytic activity [12]. ZnO has three key advantages over other related materials: it exhibits both
piezoelectric and semiconducting properties (useful for sensors and transducers), this material is biosafe (can be
used in medical applications with little toxicity) and ZnO exhibits the most diverse nanostructure configurations
including nanowires, nanobelts, nanosprings, nanorings, nanobows and nanohelices [13]. One reason this project
will initially use ZnO is due to the amount of synthesis research that has been done with ZnO over other
materials. In a research sense, it could be more beneficial to explore these other options, but this
experimentation may be outside the scope of this project. The benefits of BaTiO3 or PZT would be their
increased charge constant (piezoelectric constant) in comparison to ZnO. BaTiO3 wires can traditionally be
prepared in a “salt-assisted high-temperature solid-state chemical reaction”, which causes problems if Kevlar
Page 6 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
strands are chosen as a growth substrate [14]. Either alternative growth methods of the BaTiO3 need to be
examined or a replacement for the Kevlar that can withstand higher temperatures needs to be found for this
synthesis [5].
Table 1: Materials and Methods Summary Table [10]
Another aspect of this project is to examine multiple methods of measuring possible piezoelectric output.
Many different picoammeters already exist on the market. The price ranges starts from as little as a few hundred
dollars to over a thousand. This is a viable option, since the product is guaranteed to measure in the desired
current range and has the least amount of uncertainty.
Page 7 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
Alternatively, Oregon State University has a number of older semiconductor parameter analyzers and
picoammeters in Owen. These tools can likely be made to work, but are obviously a shared resource. Any
connections to the equipment must be very temporary (based on BNC connections) so that other students may
continue to utilize the devices as needed. In the electrical characterization lab on the third floor of Owen, the
equipment includes: HP 4140B picoammeter and DC Voltage source, HP 4192A LF impedance analyzer, HP
4145B semiconductor parameter analyzer, and an Agilent 4156C precision semiconductor parameter analyzer.
The HP 4140B is primarily used for dielectric breakdown testing and a control interface would most likely be
necessary in order to take and store desired measurements. The 4145B and 4156C are currently attached to
probe stations inside of dark boxes. Design considerations must be taken to bypass the probe stations without
interfering with anyone else’s future measurements. Additionally, the 4145B and 4156C use a Source Monitor
Unit (SMU) to apply a voltage through a semiconducting device and measuring current response. It’s currently
unclear if these will read desired currents without an applied voltage bias.
The last option is to design and build something in-house. A few sample picoammeter circuits are available
online, but SPICE analysis would be necessary to determine possible viability. Building something has the least
guarantee to work, but gives the most customizability. There are current Opamps in the marketplace designed
for use within picoammeters, such as the CA3420 from Intersil [15]. In general, picoammeter circuits are very
similar to a standard Digital Multi-Meter (DMM). The main difference is in a burden voltage. This is the
voltage drop across the measurement device, and should be as low as possible. Input current is another
important consideration for amplifiers in a picoammeter circuit. The CA3420 has a fairly constant input current
of 1 pA, an important consideration in this case.
Fig. 5: Low Noise Opamp Circuit [15]
Page 8 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
2.2.1 Technology Review Analysis – Systems
Overall Comparision
The following table is a comparison between ZnO energy harvesting technology and other alternative
energy sources, a brief summary can be found after the tables. The relative terms in this table (large, medium,
small, easy, difficult, etc.) are used to compare different technologies. Although these terms are not
quantifiable the comparison chosen is sufficient for this overview.
Table 2: Similar Technology Comparison Table
Technology
Efficiency
Ease of manufacturing
Size (relative)
17-30%
Power Output
Relative
nW range (small)
ZnO nanowires
Medium
Very small
Photoelectric
nanowires
Thermo couples
3.40%
pW range (very small)
Medium
Very small
3-7%
Medium
Medium
MEMS
electromagnetic
MEMS electrostatic
~20%
mW range (relatively
high)
nW range (small)
Medium-difficult
Medium
~20%
nW range (small)
Medium-difficult
Medium
MEMS piezoelectric
~20%
nW range (small)
Medium-difficult
Medium
Wind
~50%
W range for vehicle
adapted wind
Easy
Very large
Solar cells
30-60%
mW range per cell
Easy-medium
Large
EM converters
~60%
pW range (very small)
Medium
Large
Technology
Effect on
movement
Durability
Reliability of application
Lifetime
Environmental
Impact
ZnO nanowires
Negligible
Durable
Dependent on frequency of
stress
Undetermined
Unknown
Photoelectric
nanowires
Negligible
Less than
ZnO
Dependent on light
Undetermined
Unknown
Thermo couples
Slight
Very durable
Very reliable with a human
source
Long
Recyclable
MEMS
electromagnetic
Slight
Somewhat
durable
Dependent on frequency of
stress
Medium
Recyclable
MEMS electrostatic
Slight
Somewhat
durable
Dependent on frequency of
stress
Medium
Recyclable
MEMS piezoelectric
Slight
Somewhat
durable
Dependent on frequency of
stress
Medium
Recyclable
Wind
Noticeable
Reliable
Short
Recyclable
Solar cells
Noticeable
Dependent on light
Medium
Recyclable
EM converters
Slight
Somewhat
durable
Somewhat
durable
Durable
Reliable depending on
location
Long
Recyclable
Page 9 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
ZnO nanowires: Some strengths are that they are very small and light and can be attached to the surface of clothing.
Also, they are not noticeable in weight to the wearer. The power conversion efficiency is also very good. The Kevlar
core of the fibers ensures excellent durability and flexibility. The best point about this technology is that it is exactly
what is trying to reproduced. Some of the difficulties are growing wires with consistent structures. There are also
questions on the validity of this technology.
Photoelectric nanowires: Some of the positive things about this are that they can be interwoven with clothing, and are
negligible to the wearer. Some of the drawbacks are that they are less durable than the ZnO nanowires because of the
3 layers of silicon that make up the wire. It also has a low efficiency. This coupled with the fact that its power source
is relatively low in power density (sunlight) results in its low power output.
All three MEMS devices can be described here. The positive aspects are that they have a higher power output ratio per
device than any of the nanowires. Another is that they are a proven technology and already in the marketplace. Some
drawbacks are that they have a shorter lifetime than other technologies because of their moving parts. Also it takes a
significant amount of micromachining to create each device.
Wind: Mobile versions of wind power have mostly been developed for vehicles. It has not been very popular due to
competition with other technologies, its size, and also can have a noticeable drag effect depending on the way it is
designed. The positives are that it can have a higher power output than other energy harvesting techniques.
Solar cells: Positives are that they have good efficiency compared to other methods, and easy to manufacture. They
have a significant size which severely limits their mobility.
EM converters: Small size and micromachining requirements are limited. Power source density is low, which results
in a low power output.
Page 10 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
Method Comparison
The following tables are a comparison between different growth mechanisms for nanowire synthesis.
Table 3: Method Comparison Table
Wire
Length
Wire alignment
Aspect Ratio
Density
Process Time
Hydrothermal using
Hot Plate [1,10,11]
1.5 – 2 µm
Can obtain good
alignment, (± 10o
from
perpendicular)
Wires are usually
grown pretty
dense, hopefully
should still allow
enough space for
bending
Typically 10 – 12
hours, can see growth
in as little as 2 hours
Vapor-Solid [25]
VLS [24]
3 – 10 µm
~ 20 µm
Aligned
Aligned
Using Zinc Nitrate
and HMTA can
only get ratios of
up to ~50, can
introduce extra
items into solution
to help with this
problem
~ 100
25 – 75
~ 1 hour
1 – 1.5 hours
Hydrothermal using
Microwave [26]
~ 300 nm
Can obtain good
alignment, (± 10o
from
perpendicular)
Sparse
Depends on
patterning of
catalyst
nanobeads
Same as with
Hydrothermal
~3
3 – 15 minutes
Temperature
Uniformity
Method Difficulty
Level
Required Equipment
Hydrothermal using
Hot Plate [1,10]
~ 80 oC
Fairly simple
Vapor-Solid [25]
600 – 1000 oC
Hotplate, solution, Zinc
Nitrate, HMTA,
thermometer, stirrer
Furnace, Gases, Precursors,
deposition tool for seed layer
VLS [24]
600 – 1000 oC
Good uniformity,
problems stem from
cracks in seed layer
Good uniformity
within only a few cm
range in furnace
Uniformity depends
on catalyst
Hydrothermal using
Microwave [26]
~ 80 – 100 oC
Good
Fairly simple
Moderately simple,
requires patterning of
gold catalyst
Easy
Furnace, Gases, Precursors,
deposition tool for gold
catalyst
Solution and microwave
For this project, available choices are mainly between the Hydrothermal Hot Plate and Hydrothermal
Microwave methods because of the breakdown temperature of the Kevlar. The Hot Plate method has been
known to give a better aspect ratio, but the Microwave method takes significantly less time.
Page 11 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
Material Comparison
The following tables are a comparison between piezoelectric materials which could potentially be used for
this project.
Table 4: Material Comparison Table
Crystalline
Structure
Toxicity
Ease of
Processing
Cost
of Production
Other applications
ZnO [10, 16]
Wurzite
Easy, massproduced
Cheap, easily made
precursors
Laser diodes, LEDs
BaTiO3
[5, 17, 18]
Perovskite
Easy in smaller
quantities
Moderate
Capacitor dielectric,
Thermal switches
PZT [19]
Perovskite
Biosafe, safe
except for ZnO
fumes
Usual
warnings with
handle (do not
inhale, wear
gloves, etc.)
Lead
poisoning, not
fully
investigated
Moderate, hard to
control Zr/Ti ratio
Cheap in small
quantities
FRAM, ceramic
resonators
GaN [20]
Wurzite
LEDs, solar cells
Wurzite
Difficult, requires
sapphire, ZnO or
SiC substrates for
highly crystalline
material, hard to
scale up
Mass-produced,
easy to form
Expensive
substrates, normal
crystals can be
cheaply produced
CdS
[21, 22, 23]
Not fully
investigated,
dust is
irritating to
skin, lungs and
eyes
Toxic to
kidneys, lungs,
liver,
suspected
carcinogen
Cheap
Solar cells, photoresistors
Piezoelectric
Constant
Lattice Constant (at
300 K, in Å)
Seed Layer Growth
Amount of Research
ZnO [5, 16, 21]
BaTiO3
[6, 18, 18]
Low
High
4.580
4.020
Sputtering, CVD, ALD
Sintering BaCO3 and
TiO2,
Hydrothermal
PZT [5, 19]
High
a=3.992; c = 4.108
CVD, Sol-Gel
GaN [5, 20]
Low
a=3.189; c=5.185
MBE, MOCVD
CdS
[21, 22, 23]
Moderate
a=4.160; c=6.756
MOCVD, Sputtering,
Sol-Gel
Most common for nanowires
Research into variance of
refractive index, research
switched to PZT when it was
discovered
Some for MEMS, AFM
cantilevers
Well researched for blue LEDs,
lasing
Well researched in alternative
applications, nanowire research
less common
Page 12 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
Seed Layer Coating Comparison
The following table describes three different methods which can be used for thin-film deposition. In this
project these techniques are being compared to determine the best option for the seed layer coating. Only
relative terms (short, medium, high, low, etc.) are needed in this comparison.
Table 5: Seed Layer Coating Comparison Table
Sputtering
ALD
Sol-Gel
Precursors or Sources
Solid target of deposition
material is used
Non-reactive argon plasma
Chemicals in gas phase
Substrate Limitations
Works for flat substrates
Vacuum Condition
High vacuum
required
Processing Time
Medium
Works for all substrates
Long
Chemicals in liquid
solution
Works for all substrates
Low vacuum
required
Vacuum not
required
Short
Measurement Comparison
The following tables are comparisons of possible measurement technologies which could be utilized.
Table 6: Measurement Technology Comparison Table
Resolution
HP 4140B [3]
HP 4145B [4]
Agilent 4156C [5]
CA3420 [27]
Keithley 6485[7]
Keithley 6487
[8,9]
1 fA
50 fA
1 fA
Unknown
10 fA
10 fA
Minimum
Range (+/-)
1 pA
1000 pA
10 pA
1.5 pA
2 nA
2 nA
AD795 [10,11]
Teltron 2808 [12]
Transimpedance
Amplifier [13]
1 pA
Unknown
0.1 pA
4 nA
200 pA
204.6 pA
Integration Time
HP 4140B [3]
HP 4145B [4]
Agilent 4156C [5]
CA3420 [27]
Keithley 6485 [7]
Keithley 6487
[8,9]
133 ms
3.6 ms
Unknown
2 µs
1 ms
1 ms
AD795 [10,11]
Teltron 2808 [12]
Transimpedance
Amplifier [13]
100 µs
Unknown
120 µs
Accuracy @
Min. Range
5%
1%
4%
Unknown
0.4%
0.3%
Unknown
Unknown
Unknown
Voltage Burden
Estimated Cost
Free
Free
Free
Obsolete
Need Quote
$2995
~$10 with sampling IC
$355
~$25
Display (digits)
<10µV
Unknown
Unknown
Unknown
<200µV
<200µV
3½
N/A
N/A
*
5½
5½
Unknown
Unknown
Unknown
*
*
4½
Portability
Minimal
Minimal
Minimal
Good
Medium
Medium
Good
Good
Good
Utility Beyond
Original Project
Good
Good
Good
Little
Medium
Medium
Little
Poor
Medium
*Need DMM or some other measurement device to obtain output.
Page 13 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
The transimpedance amplifier shown in Fig. 6 uses an integrator, switching a large feedback resistor for a
capacitor and using hold or reset switches. In the specific example cited, it also uses a LM555, EPROM, and
LCD display. The LM555 handles timing for integration and the EPROM holds look-up tables to match the
voltage output to a corresponding four-digit picoamp equivalent. This look-up is done based upon an A/D
converter's output. The EPROM data is then output to an LCD driver and displayed for the user.
Fig. 6: Fast-Settling Picoammeter [33]
For this project, one of the most important parts will be to test the nanowires. Therefore, a test bed needs to
be created to accurately measure the induced voltage of a stressed wire. The stressing of the wire also needs to
be very accurate. Although project goals include looking for a way to test the functionalized Kevlar strands, a
starting place could be testing a single wire. One possible setup could be one that researchers at the University
of Illinois used to apply tension to BaTiO3 nanowires [5]. The setup is illustrated in Fig. 7.
Fig. 7: Testing setup from University of Illinois for testing a single BaTiO3 nanowire [5]
The piezostack is used to apply tension to the mobile base at low frequencies (~30Hz). In this experiment the
energy harvested was in the attojoule range so the charge amplifier (in this case the A250F, Amptek, Inc.) is
needed to amplify the current to a level of magnitude high enough to accurately measure it. The nanowire was
Page 14 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
fixed at both ends using a localized electron beam to deposit platinum (Pt) inside a scanning electron microscope
(SEM). Fig. 8 shows the amplification circuit in schematic form.
Fig. 8: Schematic representation of testing system [5]
The current source represents the nanowire under stress generating an electric current. Rnw is the total
resistance of the nanowire and Cnw is the total capacitance, including parasitic capacitance, of the wire. The
current can be modeled by:
i is the current, d is the charge constant, and E is the Young’s modulus of the piezoelectric element, F
(1)
is the applied load, A is the load area, and epsilon is the resulted strain [5].
The project will require development of a mechanical actuation system. Although the procedure described
above is helpful in intermediate testing the final product will have to be different. Fundamentally, this actuation
device will be used to stretch the Kevlar strands relative to one another. In order to have the best design for this
project, each piece needs to be examined separately and the best choice for that part should be made.
Actuation Technology Comparison
A comparison table for actuating technologies is shown below in Table 7.
Table 7: Actuation Technology Comparison Table
Positional Accuracy
Range
Speed (max)
Cost
Power
VCS-10H [38]
±200nm
10mm
20,000mm/s
$1500
±12V to ±24V DC
T-LA13 [43]
±0.1μm
13mm
4mm/s
$782
15V DC
FA-MS-8-12-4"
[44]
Unknown
4inches
44.45mm/sec
$75
12V DC
Mini 0 [45]
Unknown
100mm
40mm/s
Unknown
24V DC
Pro165 Linear
Stage [46]
±6μm
600mm
300mm/s
“low”; otherwise
unspecified
Unknown
Page 15 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
2.2.2 Technology Review Analysis – Blocks
[B1] Seed Layer Coating:
This block is required to produce a ZnO seed layer. The seed layer is a thin film, coating the entire Kevlar strand
and provides nucleation sites for nanowire growth to begin. Without the seed layer, nanowires would not grow on the
surface because there is no compatible crystalline structure on the bare Kevlar. The seed layer can be deposited in a
number of ways at Oregon State University and is tabulated below in sub-blocks B1B, B1C, and B1D:
[B1A] TEOS:
TEOS
Attributes
Enhances bonding strength between Kevlar substrate and seed layer
Improves mechanical performance of fiber
Cross linked chains bind the bases of the nanowires together with more strength
Without the TEOS layer there were problems with the bonding between Kevlar and the ZnO seed layer.
TEOS not only enhances the bond strength, but also binds the bases of the nanowires together so that the fiber
can be flexed and bent at greater angles.
[B1B], [B1C], [B1D] Seed Layer Deposition:
Methods
Strengths
Sputtering
Evenly distributed across
sputtering surface
Accurate thickness of deposition
layer
Atomic Layer Deposition (ALD) Very uniform deposition surface
Do not have to rotate Kevlar
Sol-Gel
Solution based
Weaknesses
Requires high vacuum
Requires rotation of Kevlar
strand for uniform coverage
Slow
Expensive, flammable precursors
Non-uniform deposition layer for
a cylindrical substrate
Low temperature
Sputtering and ALD both produce very even deposition layers. ALD will be used because the Kevlar strand
does not have to be rotated and the tool is owned by the research professor.
Page 16 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
[B2] Hydrothermal Nanowire Growth:
This block is the single most important piece of the entire system. This project is research based, trying to find an
optimal method and procedure for ZnO nanowire growth. The nanowires must be of sufficient size to ensure proper
contact between Kevlar strands.
Methods
Microwave
Hot plate
Strengths
Temperatures do not exceed
Kevlar breakdown temp.
Equipment needed is readily
available and generally
inexpensive
Growth time is 3 to 15 minutes
Lengths and widths of
nanowires close to desired
values
Inexpensive equipment
Weaknesses
Shorter and wider nanowires than other methods
Unwanted crystal deposition during growth
process
Much more growth time than other methods
Uses more power than microwave
Kevlar makes a good substrate due to its very high tensile strength and flexibility. Unfortunately, it breaks down at
temperatures needed for other growth methods. The only remaining growth options for a Kevlar core are hydrothermal
growth methods. Growth time is significantly longer for the Hot Plate method than the other method, but lengths and
aspect ratios are closer to the desired results. The Microwave method cuts down the growth time significantly, but the
process seems to be very length limited. There are other agents that can be added to the chemical solution to limit
growth in one direction and increase aspect ratio. In both of these methods unwanted crystal deposition can be
remedied with sonication. Although the bonding between the Kevlar core and the seed layer is not ideal, it has been
improved using a TEOS layer.
[B3] Wound Kevlar:
Au coated Kevlar Strand
Coated with layer of Au ~300nm thick
Au acts as Schottky barrier allowing current to
only flow one way
Movement of Au coated nanowires is considered
negligible
Kevlar Strand
Nanowires on the Kevlar strand act as cathode for
the Schottky junction with the Au coated nanowires
Nanowires are bent from pressure from the Au
coated nanowires
The piezoelectric properties of the ZnO nanowires
generates an electric current
The functionalized Kevlar strand pairs act together to form a voltage potential across the surface. When the gold
coated wires press against the uncoated wires, both will bend. This causes a voltage potential across a nanowire’s
diameter to be produced from the strain on the crystal lattice. The gold has a sufficiently different work function to
create a Schottky barrier. This prevents current from flowing as the Kevlar strands move back to equilibrium when the
nanowires would be bent the other way. In essence, the gold is essential to creating a rectifier that ensures a net
current.
Page 17 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
[B4] Picoammeter:
The picoammeter block allows for testing of any piezoelectric power generation from the actuated Kevlar strands.
The data provided by this block is what will actually be analyzed to determine the usefulness of this novel approach of
energy harvesting. Without it, there is no quantifiable information to propose and support a theory with.
Device
Existing devices on OSU campus
Implement custom design
Purchase an existing one
Advantages
No cost, local, no design or build
time
Able to design to custom specs
No design or build time, accurate
and reliable measurements
Disadvantages
May not fit project needs, may
not be able to get access to it
Time to design, acquire
materials, and build
Cost, finding one with enough
accuracy
The most ideal situation would have been to use the equipment that is on campus. This equipment would have the
advantage of no cost, no design and build times, and accurate results. A limiting factor is that the integration time for
sampling may be too long, and something that samples faster might have to be pursued. The equipment already on
campus would have been able to meet the requirements of the original project. Recent redesigns have made the design
of a picoammeter circuit in parallel ideal. One of the desired requirements for this project is having a working display
at the engineering expo. Since the picoammeter on campus is a public piece of equipment, it cannot be removed from
Owen. The design of a picoammeter circuit will allow the creation of a portable display.
[B4A] Probes:
Probes
Features
Sense voltage across stressed fiber
Fixed positioning
Concerns
Capacitance added to the circuit due to the
probes
EM noise coupling
Probes are needed to detect any induced voltage across the fibers. Capacitance added to the circuit by the
probes could be significant because of the very low power levels expected. The length of the probes could be
a problem — if too much EM noise couples onto them. This could greatly distort the outcome of the
measurements.
[B4B] Amplifier:
Amplifier
Features
Amplifies induced voltage to attain
clear measurements
Low noise opamp
Concerns
Enough gain to detect picoamp signals
EM noise
The purpose of the amplifier is to boost the signal to a measurable quantity. Opamps are usually a
significant source of noise at such low currents. To get around this, more expensive BiCMOS or JFET
technologies can be used to produce a very low-noise opamp. No matter what is done to make a more ideal
amplifier, input impedance and noise will be the primary factors that could limit useful measurement ranges.
Page 18 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
[B5] Computer Processing:
This block allows for logging data measurements and performing calculations on the measured data. It is
essential to fit measured data to the input frequency and amplitude of actuation to see if there is any actual
energy harvesting. Logged data can either be input directly or with a USB thumb drive. If it were to be
input directly through a port, this would require an additional ADC circuit to convert the analog voltage
output of the picoammeter into a digital value. To use a thumb drive, all that would be required is a digital
oscilloscope with the capability to save logged data to such a thumb drive.
Useful Programs
Excel
HyperTerminal
Windows XP
Advantages
Allows for data logging
Familiar and very customizable
interface
Easily interchangeable and
upgradeable
[B5A] I/O:
I/O Devices
Keyboard
Mouse
Monitor
Flash drives
Standard USB interface
Standard USB interface
Standard LCD
Removable
This is the general I/O interface with the PC. Standard I/O capabilities for user input, data storage, and
viewing are required.
[B5B] PC:
Features
Able to interface with various equipment such as
picoammeter or motor controller
Programming of the controller
Stores Results
Software to record measurements
Inexpensive
This will be a basic computer setup with measurement software, and an interface to the controller. Must be
able to run and compile C programs. This is what will be used to program the controller.
[B6] Actuator:
The actuator is essential to providing the needed strain on piezoelectric nanowires for voltage generation. Without it
there would be no test to see if the nanowires are suitable for piezoelectric energy harvesting. The block must also be
flexible enough to allow for a variety of input frequencies and amplitudes in order to find the most ideal test
conditions.
Strengths
Voice coil provides unrivaled speed and position
resolution
Allows for simple attachment of Kevlar
Controlled with microprocessor for control
Weaknesses
Motor coil will need to be shielded to lower
inductive noise with measurement circuit
Maximum stroke of 10 mm
Page 19 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
This actuator uses a simple voice coil motor that simply pushes or pulls a coil of wire. The actuator may be
problematic due to using an electric motor since it will inherently generate noise. This must be overcome with
adequate shielding and distance from the actual Kevlar. The actuator must also allow for the easy attachment of the
Kevlar strands to be tested. Since the Kevlar has a diameter of 14 µm, it must be able to apply strain without
damaging the Kevlar or interfering with the electrical measurements of the Kevlar.
[B6A] Spring:
Strengths
Simple
Replaceable or Upgradeable
Weaknesses
Possible to overstretch
Force constant must be compatible with motor (<
1.5 lbs/ 10 mm)
Potential for oscillations
The spring allows for one side to remain firmly attached and helps prevent applying too much force on the
Kevlar. The spring also helps return the Kevlar to equilibrium, although it is possible oscillations will cause
the Kevlar to slacken and unwind in some way to affect uniform measurements. Note that this might not
appear in the final design if it is determined to be unnecessary.
[B6B] Mounting Brackets:
Strengths
Simple and reusable
Interchangeable
Weaknesses
Might damage seed layer and affect conductivity of
Kevlar
Potential to interfere with electrical measurements
by adding unknown capacitive effects
Constant location for ensuring equal test lengths
between different samples
Mounting brackets will be used to attach the Kevlar to the voice coil and spring. This allows for it to remain
in tension during testing. The specific design is not finalized due to concerns about lowering the overall
conductivity of the Kevlar and interfering with the electrical connection to the picoammeter.
[B6C] Voice Coil:
Strengths
Simple design
Built-in positional feedback circuit
Maximum bandwidth of 1 kHz
Weaknesses
Limited to 10 mm stroke
Low constant force (1.5 lbs.)
200 nm repeatability which is higher than the
associated controller for it
Sub-micron positioning resolution (150 nm)
No commutator
Voice coil motors are one of the most simplistic types of motors. By applying a current to a coil, a magnetic
field will be created that attracts it toward or repels it away from a permanent magnet that surrounds the coil.
Altering the magnitude and direction of the current, this coil can be easily made to move backwards and
forwards at a given frequency. A coil is also simple enough that it is easy to control its position relative to the
magnetic stator. By attaching the strand of Kevlar to this motor, the desired actuation can occur that will
affect the piezoelectric nanowires.
Page 20 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
[B7] Controller:
This block handles all commands to the linear actuator. It ensures that actuation of the Kevlar fiber remains
consistent in both amplitude and frequency during testing. The block is programmed by a PC which allows for a
simple interface with no learning curve. This block is essential to ensuring a repeatable test that can be performed on
any number of Kevlar strands.
Strengths
16-bit A/D Converter allowing for 150 nm
resolution with specified voice coil
Programmable through standard RS-232
connection
Can be programmed to produce accurate sine
waves
Weaknesses
Extra piece of equipment with associated cost
Limited programmability
Needs external power supply
The controller will be used to hand I/O for the voice coil motor [B6]. This allows for very accurate and precise
control over the position of the motorized stage. Additionally, it will protect the motor in case it draws too much
current or overheats. Since it can be programmed via HyperTerminal, accurately varying the frequency and amplitude
of motion will be easy to accomplish up to 10 kHz, far beyond the desired range for this project.
[B7A] Motor Power Supply:
Strengths
±12V to ±35V DC
10 A peak
Current limiting
Internal current amplifier
Weaknesses
Built-in, so no adjustments can be made
Poorly defined in datasheet
Single-phase output (No AC Motors)
Requires interface with PC
The SCA 814 Servo Controller includes a ±12V to ±35V DC current amplifier with a 10 A max supply.
This allows for complete control over the motor to come from the controller, without worrying about
connecting another power supply for the motor. This will also act as a current limiter to prevent damage to the
motor while still ensuring it can supply necessary peak current during actuation.
[B7B] A/D Converter:
Strengths
16-bit
150 nm resolution with 10 mm stroke motor
Weaknesses
Resolution dependant on full stroke of motor
Poorly defined in datasheet
A 16-bit converter allows for superior measurement capabilities. The control this offers is greater than
desired, but this allows for finely tuning the amplitude of actuation on the Kevlar strands. It also ensures that
every cycle has uniform amplitude and consistent timing.
[B7C] Microprocessor:
Strengths
RISC
Upgradeable
Weaknesses
Limited access to programmability
Uncertain of specific capabilities
RISC architecture allows for an inexpensive processor to easily interface with the I/O of the controller. It is
also programmable so that any sort of desired waveform may be produced and output to the motor. The
processor ensures that the voice coil goes to a desired location without going too far.
Page 21 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
2.3 Feature Set
2.3.1 Absolute Minimum Requirements
The following list of minimum requirements is necessary to ensure that the project is working properly. In
order to pursue this project, the system must be well-characterized and proven so that no doubts are cast upon the
measurements taken. Each piece of the project must be strong both on its own and on a system level. There are
specific requirements for the grown nanowires to give the best chances for piezoelectric generation. Constraints
should be put on both the mechanical actuation system and the electrical measurement circuit so that the designs
are carefully contemplated. By meeting all of the requirements, 100 points will be received. Each requirement
is weighted by relative importance.












Well-defined method of nanowire production that repeatedly produces aligned ZnO nanowires. *
(7 points)
Nanowire at least 1 µm in length and have an aspect ratio of at least 10:1. (7 points)
Nanowire density must be low enough to allow movement in the wires but high enough to ensure
enough output that it is detectable (10 – 50 µm-2). (7 points)
Adhesion of seed layer to Kevlar can withstand actuation for 100 cycles without showing signs of
separation. This ensures durability of the seed layer and uniform wire coverage on the Kevlar.
(15 points)
Picoammeter circuit must accurately be able to measure in 50 pA quantities to adequately test
nanowires output. (15 points)
Sample rate of electrical measurements must be a minimum of 1 kHz. This ensures sampling at a
rate much greater than the input frequency from the actuator. (7 points)
Kevlar attachment to mechanical actuator must allow for replacement of different samples.
(15 points)
Mechanical actuator must have positional precision of at least 0.1 mm so as to make a repeatable
set of input forces. (5 points)
Mechanical system should not interfere with electrical measurements, ie. any noise from a motor
should be filtered out. * (7 points)
Pull on Kevlar should be adjustable (from 0.1 to 5 mm if necessary) to find an optimal stroke that
stresses system without permanently damaging the Kevlar and nanowires. * (5 points)
Mechanical actuation system must have a variable frequency of 1 – 20 Hz. (5 points)
Analysis and theory of results. * (5 points)
* Certain requirements cannot be firmly quantified. Whether these requirements have been
met will be evaluated by the research professor.
Page 22 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
2.3.2 Desired Feature Set
The following goals are those that have been deemed less critical to success. Given time and resources, an
effort to achieve these goals shall be made over the course of the project. Failure to achieve some or all of
these points not affect the basic ability to characterize as-grown ZnO nanowires. The desired requirements can
be worth a total of 50 extra credit points.






Examine possible alternative materials such as polyethylene fibers instead of Kevlar, other piezo materials
rather than ZnO, aluminum rather than gold for a Schottky barrier, etc. * (10 points)
Compare results from piezoelectric and non-piezoelectric growth materials. * (5 points)
Nanowires should be 3µm long with an aspect ratio over 100:1. These would most likely improved
results. (10 points)
Electrical measurements sampled at 0.5 MHz or higher. This will better show any spikes in current as
the system tries to reach equilibrium. (5 points)
Entire system portable and stable enough to exhibit a working test procedure at Engineering Expo.
(15 points)
Change mechanical actuation frequency to 100 – 200 Hz and determine the effects of higher
frequencies on material breakdown. (5 points)
* Certain requirements cannot be firmly quantified. Whether these requirements have been
met will be evaluated by the research professor.
3. Architectural Overview
The piezoelectric energy harvesting project entails the growth and characterization of piezoelectric
nanowires. ZnO nanowires will primarily be used, though other materials are of interest if time allows. ZnO
was chosen primarily for having a well-characterized growth method compatible with the chosen substrate
material. Most methods of growing nanowires involve a furnace at temperatures approaching 1000° C. Since
Kevlar is used as a substrate, it decomposes above 400° C and a low-temperature method is needed.
Hydrothermally grown ZnO allows for nanowires to be deposited in a solution of water, below its boiling point
of 100° C.
The Kevlar substrates must be functionalized with nanowires, and the nanowires must be suited for
piezoelectric purposes. The growth method must be tailored to produce single-crystalline [0001] ZnO nanowires
of at least 1 μm in length. Additionally, the wires must be aligned normal to the Kevlar's surface.
To test the nanowire structure, an actuator must be used to apply an external modulus. The Kevlar attached to
this actuator must be consistently wound between samples to ensure consistency. In addition, the linear actuator
must be controlled with a precision down to 0.1mm. The actuation system must also allow for easy connections
of an electrical measurement circuit to the Kevlar strands.
The electrical test circuit will consist of a picoammeter designed to measure currents down to 1 pA. This
system must be able to measure data over time at a sampling rate of at least 1 kHz. Any noise on the circuit
should be tested and accounted for. Any output from the functionalized Kevlar must be significantly larger than
the background levels of noise. The measured data should be stored for analysis and comparisons between
different experimental trials as well as for control runs.
Page 23 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
3.1 Implementation Approaches
Option 1:
 Microwave Growth of ZnO Nanowires
 HP 4140B Picoammeter and DC Voltage Source
 CA3420 Opamp picoammeter circuit
 Equipment Solutions VCS10H [38]
 Equipment Solutions SCA814 Linear Servo Controller [39]
Producing ZnO nanowires with a microwave was chosen because of its growth time. The nanowires can be
made in as little as five minutes, making it possible to produce as many test samples as required. Microwaves
are inexpensive and easy to attain, which makes the process cost-effective. The HP 4140B was chosen because
of its availability in the EECS Electrical Characterization Lab in Owen Hall. Its datasheet suggests being able to
measure down to 1 fA. This is mostly likely due to a voltage burden of less than 10 µV, which is the best of all
researched possibilities. A picoammeter circuit using the CA3420 opamp is being designed so a portable display
can be at the expo. The HP 4140B will still be necessary to characterize the designed circuit. A voice coil motor
was chosen because of its simplicity in design, fast response time for attaining higher frequencies, and positional
resolution. A controller is attached to the voice coil to ensure consistent timing and position of the voice coil.
Option 2:
 Hot Plate Growth of ZnO Nanowires
 Agilent 4156C Precision Semiconductor Parameter Analyzer
 Firgelli PQ12S Linear Actuator
Hot plate growth uses the same reactants as the preferred microwave method. The only difference is that heat
is applied to the solution via a hot plate instead of microwaves. Initial microwave results showed shorter and
broader NWs than obtained from a hot plate. If this cannot be improved, hot plate growth will most likely
provide the best wires for testing. Since growths take a minimum of 12 hours, development of this method
should be done in parallel to microwave growths. The Agilent 4156C was chosen because it has a better
integration time than the picoammeter, meaning it can sample more quickly. The resolution will suffer slightly
as a result, but should still be acceptable depending upon input noise. Noise might be a factor because
semiconductor parameter analyzers use a Source Measure Unit (SMU) that generally sources voltage to a
semiconductor and measures current response. Actuation can be accomplished with a Firgelli PQ12S Linear
Actuator. The unit has small size, but is not as responsive or accurate as a voice coil. Motor noise will be less of
a problem, and the control could be as simple as applying a sinusoidal waveform through an amplifier to power
the actuator.
Option 3:
 AD795 Precision FET Opamp
 Microwave Growth of ZnO Nanowires
 Futaba S148 Analog Rotary Servo [40]
 Linear Servo Conversion Kit [41]
The AD795 IC provides very low input current and sampling of up to 0.5 MHz. The associated circuit has a
maximum bias current of 1 pA and the faster sampling rate should help to reduce noise in the circuit. A
potentially inexpensive alternative for actuation uses a Futaba S148 rotary servo converted to a linear servo.
This provides accurate control but servos tend to be much slower and this may limit the actuation frequency
range. There are only two options for growth methods, so the more efficient method is chosen.
Page 24 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
Option 1 is chosen because of its quick approach to characterization. Microwave-based growth provides the
quickest method of nanowire synthesis. This allows for many growth runs in a shorter amount of time, making it
much faster to begin characterization and process optimization. The picoammeter is ready to be used in Owen,
although different probes will be used for this sensing application. The HP 4140B can also be used to
characterize an additional designed circuit. A picoammeter circuit using the CA3420 opamp is being created so
a portable display can be at the expo.
Using a voice coil motor provides simplistic operation, especially when coupled with the servo controller.
Since the microcontroller is from the same company, compatibility is assured. The voice coil will provide the
most positional precision of any other alternative as well as the largest frequency range. Given possible
shortcomings of this option (nanowire lengths will possibly remain too short, picoammeter cannot sample fast
enough, etc.), hot plate growth and an alternative picoammeter circuit will continue to be researched in parallel.
4. Top Level Description
The goal of this project is to develop a testbed for piezoelectric nanowires. Fig. 9 shows a very high level
block diagram which will be explained deeper in Section 4.1. The important thing to notice is that only one
input, power to the system, is planned for. From there, the goal of the project is to get reasonable data of a welldesigned evaluation platform.
Fig. 9: Top Level Block Diagram
Page 25 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
4.1 Top Level Block Diagram
Fig. 10: Top Level Block Diagram
Page 26 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
4.1.1 Top Level Interface Definition
Signals
Kevlar
Seed layer adhesion
Chemicals
Description
Core of fibers
TEOS used to strengthen bond
between Kevlar and seed-layer
Used in DI Water solution to form
ZnO nanowires
Temperature
Necessary temperature for growth
Growth Time
Amount of time to form correctly
dimensioned nanowires, varies
depending on method
Seed layer is applied to Kevlar to
promote self-assembly of nanowires
ZnO nanowires with desired
dimensions for piezoelectric energy
harvesting
Used to form a Schottky junction
with the uncoated wires
Cleans fibers after hydrothermal
growth
Kevlar w/ seed layer
Nanowires
Gold Evaporation
Sonication
Functionalized Kevlar
strands
Strands to be used for actuation to
measure possible output current
Current
Output from the nanowires
Voltage
Unamplified voltage from the
functionalized Kevlar strand
.csv file used for programming
position of actuator
Computer communication bus
Mechanically applied using voice
coil
Code
Data
Actuation
Position
Vbb
Vcc
Vdd
Power
Used in actuation length settings
Power for computer processing
block
Power for controller block
Power for picoammeter block
Power for actuator from controller
block
Feedback
Control signal for microprocessor
Command
Correction instruction from
feedback signal
RS-232
Probes
Interface for controller
Low noise probes used to connect
picoammeter circuit to the system
Measure
Amplified current output from
functionalized Kevlar strands
converted into a voltage
Details
High tensile and shearstrength
Tetraethyl orthosilicate
Attributes
Flexible
Zinc nitrate Zn(NO3)2
Hexamethylene tetramine (HMTA)
Polyethylene imine
Room temp. (Stage1)
(80-95)˚C (Stage2)
150˚C (Stage3)
10 to 12 hours for hotplate
3 to 15 minutes for microwave
Kevlar thoroughly cleaned
Surface coating of TEOS
Length of at least 1 μm
Aspect ratio of at least 10:1
~300nm thick gold layer on the
nanowires
Ultrasonic frequencies
(20 kHz – 40 kHz sweep)
Duration of sonication can be altered
Uniform wire density on surface
One strand coated with ZnO
nanowires and evenly distributed
Au layer
One strand only covered with
ZnO nanowires
Expected values in picoampere range
(> 50pA)
Frequency control algorithms
Between PC and I/O
Variable force and distance
Variable frequency
(1 – 20 Hz)
Set with software
120 V AC rms
15 A
± 12 – 35 V DC
± 6V DC
±12 – 24V AC
Voltage varies depending on
frequency and length
15 A peak current
2.86 A max current
12 A peak current
16 – bit signal
(0 – 5V DC)
Varies depending on load
Control signal for the motor power
supply (changes actuator position)
(0 – 5V DC)
Varies depending on load
9 pin, serial, 5V DC
BNC Connectors
0 – 50µA current
Current depends on voltage which
varies with load
0 – 50µA current
Current depends on voltage which
varies with load
Less than 20 pF capacitance
Page 27 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
5. Block Descriptions
5.1. Seed Layer Coating Diagram
Fig. 11: Seed Layer Coating Diagram
5.1.1 Seed Layer Coating Interface Definition
Signals
Kevlar
Seed Layer Adhesion
Input/Output
Input
Intermediate
Surface
Texture similar to plastic
Kevlar coated with TEOS
Kevlar with Seed Layer
Output from Seed Layer
Creating Mechanism
Plastic is now covered
with more growth favoring
ZnO seed layer
Diameter
14 µm
14 µm
Thin layer of TEOS
14 µm from Kevlar
(20 nm thick seed layer)
Conductivity
None
None
Semiconducting seed
layer
5.1.2 Seed Layer Coating Operation
A seed layer is needed to begin the process of growth utilizing self-assembly principles. The seed layer
will create an energetically favorable growth environment for the ZnO nanowires. Possible output currents
from the piezoelectric nanowires will use the seed layer for conduction. This seed layer needs to be firmly
attached to the seed layer, and TEOS will be used to ensure a strong bond between the Kevlar and seed
layer.
5.1.2A TEOS
Tetraethyl orthosilicate (TEOS) is a chemical that is used to create a surface more favorable for
growth of the zinc oxide seed layer. To make a comparison, when depositing films on silicon wafers,
the wafer will already have a natural oxide (silicon dioxide) which will make the surface more
favorable for growth because of free hydroxyl groups to bond to. Since Kevlar is a plastic-like
material, using TEOS will create this oxide layer and promote growth of zinc oxide.
5.1.2B Sputtering
Deposition using sputtering is facilitated by heating a target and bombarding it with a non-reactive
material (usually argon plasma). Because this takes place in high vacuum, particles freed from the
target can deposit directly onto the desired substrate surface. This is a line-of-sight deposition, so to
coat a strand of Kevlar it would need to be mounted in such a way to rotate evenly. For zinc oxide
deposition, a zinc target is used and a small amount of oxygen flows over the substrate.
Page 28 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
5.1.2C ALD
Atomic Layer Deposition is used for deposition of thinner films. Multiple precursors are introduced
to the chamber individually. Although ALD is similar to more traditional Chemical Vapor Deposition
(CVD), the chemical reactions are split into half-reactions by separating the administration of each
precursor. By keeping these precursors separate, thinner films can be achieved. Additionally, each
reaction is self-limiting which means that thickness can be controlled down to a single layer of atoms.
Unlike sputtering, this has the added advantage of coating the entire substrate surface without rotation.
5.1.2D Sol-Gel
A chemical solution method can be used to create materials as well. Usually used for metal oxides,
a gel is formed and then deposited onto the substrate by either dip-coating or spin-coating. This is a
low-cost and low-temperature method, and doping or adding extra components is simple. The
chemical slurry that is formed allows for uniform coverage and dispersion over smoothly polished
substrates. For a non-traditional substrate such as Kevlar, Sol-Gel deposition methods are limited by
the cylindrical shape. To illustrate, when spin-coating, the gel would only be able to cover a certain
amount of the substrate. In the case of dip-coating, a thickness gradient would occur in the seed layer
from pulling the substrate out of the solution. Although pulling at a slow and steady rate would allow
for a uniform film, Atomic Layer Deposition still produces a more conformal seed layer.
5.2 Hydrothermal Nanowire Growth Diagram
Fig. 12: Hydrothermal Nanowire Growth Diagram
5.2.1 Hydrothermal Nanowire Growth Interface Definition
Signals
Kevlar with Seed Layer
Input/Output
Input
Materials
Plastic covered ZnO seed layer
Process Details
N/A
Conductivity
Semiconducting seed layer
Chemicals
Input
N/A
N/A
Temperature
Input
Hexamethylene tetramine
Polyethylene imine
Zinc Nitrate Hydrate
DI Water
N/A
Range of 80 – 90 C
N/A
Growth Time
Input
N/A
N/A
Nanowires
Output
Zinc Oxide
Varies with Hydrothermal
method choice
N/A
To be determined
Page 29 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
5.2.2 Hydrothermal Nanowire Growth Operation
Two options for hydrothermal growths exist. Attributes of each method are discussed in the following
sections. Both of these methods utilize a mixture of hexamethylene tetramine, zinc nitrate hydrate,
polyethylene imine and DI water. The heating mechanisms of each method lead to variances in nanowire
properties. Currently, the two most significant variables are growth time and aspect ratio. When studying
material properties later in the project, one method may yield nanowires with better electrical conductivity.
5.2.2A Microwave
Kevlar breaks down at approximately 400 °C, limiting growth methods to hydrothermal options
because of the higher processing temperatures (~ 900 °C) required for other methods. Hydrothermal
growth utilizing a microwave would be preferable because growth times are on the order of 5 – 10
minutes. An additional advantage from shorter growth time is that any crystals that happen to form in
solution do not have enough time to grow to sufficient sizes and deposit on the Kevlar surface. If
crystals are still present, their smaller size would make sonication faster. One issue that has been
noticed with this method is the length limitation. Nanowire lengths currently attained from this
method are on the order of 300 nm rather than the desired lengths of ~ 3um.
5.2.2B Hot Plate
Average growth times for this method are about 10 – 12 hours. The longer growth times are
undesirable. Average lengths for the hot plate hydrothermal method up to this point are approximately
1 µm, which is a three-fold increase over the microwave method.
5.3 Wound Kevlar Diagram
Fig. 13: Wound Kevlar Diagram
5.3.1 Wound Kevlar Interface Definition
Signals
Nanowires
Input/Output
Input
Purpose
Piezoelectric energy harvesting
Material
Zinc Oxide
Sonication
Input
Used to remove large crystal
growths (dendrites)
Acetone or Isopropyl alcohol
Gold Evaporation
Input
Gold
Current
Output
Gold will be evaporated onto ZnO
coated Kevlar strand
Main output under study
Functionalized
Kevlar Strands
Output
Complete electrical circuit
generated by bending of
nanowires
Kevlar coated with Zinc Oxide
nanowires, one strand with Au
coating, one without
N/A
Desired Features
Aspect ratio of 10:1
Length of ~3 µm
Variable frequency and
variable duration
Uniform coverage of
nanowires
Study possible output to
beyond a reasonable
doubt
Consistent winding
between samples
Page 30 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
5.3.2 Wound Kevlar Operation
The expected output current will come from the interaction of the two functionalized strands of Kevlar.
The relative motion between the two strands will bend the ZnO nanowires while the Au coated nanowire
will act as a negative electrode.
5.3.2A Au Coated Kevlar Strand
One of the Kevlar strands with zinc oxide nanowires will be coated with gold. Gold is used because
of a large work function at 5.1 eV when compared to the bandgap of ZnO at 3.3 eV [42]. Two strands
are wound together to form a Schottky barrier, forcing current to flow through a loop from the bent
zinc oxide wires to the Au coated wires. The flow of the current is shown in Fig. 14.
Fig. 14: Nanowire Current Generation Circuit
5.3.2B Kevlar Strand
This Kevlar strand is only coated with zinc oxide wires. In order to complete the circuit described
above, both are necessary to wind around the other. This ensures that nanowires strain other
nanowires, taking advantage of their piezoelectric properties. Consistent winding techniques need to
be developed to reduce major sources of human error.
5.4 Picoammeter Diagram
Fig. 15: Picoammeter Block Diagram
Page 31 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
Fig. 16: Amplifier and Power Diagram
5.4.1 Picoammeter Interface Definition
Signals
Vdd
Input/Output
Input
Description
Common Supply
Voltage
Picoammeter Equipment
Voltage: 120 VAC
Current: 10 A Max
Current
Input
Output from the
nanowires
Voltage: Not yet determined
(Depends on magnitude of
nanowire strain)
Current: 0-100 pA
Type: Analog
Voltage
Intermediate
Voltage to be
amplified
Measure
Output
Amplified signal used
for measurement
Voltage: Attenuated from
input current due to probe
length
Current: 0-100 pA
Type: Analog
Voltage: 0 – 5V
Current: 50 µA
Type: Digital
Picoammeter Circuit
Voltage: ±6 V from
batteries
Current: 2.86 A Max
Voltage: Not yet
determined (Depends on
magnitude of nanowire
strain)
Current: 0-100 pA
Type: Analog
Voltage: Attenuated from
input current due to probe
length
Current: 0-100 pA
Type: Analog
Voltage: -1.5 – 1.5V
Current: 15 µA
Type: Digital
5.4.2 Picoammeter Operation
The picoammeter is essential for actually measuring data. Due to the amounts of current
expected (around 50 pA), this circuit has the tightest design constraints compared to every other
block. This picoammeter functions around the CA3420 opamp from Intersil. It has low-noise and
high gain properties that make it work well for this application, although high gain also limits its
unity-gain bandwidth to 500 kHz. By having a high input impedance of the circuit, combined with
a low bias current of the opamp, very little of the current from the nanowires is wasted and a
voltage associated with this current will appear across the inputs of the amplifier. This is amplified
100,000x so the current can be more readily measured.
The selected circuit also has a potentiometer to compensate for any voltage offset caused by
process variations. This allows for the amplifier to be tuned so that 0 pA actually outputs 0 mV.
There is also another variable resistor in the resistor network to compensate for any variations in the
1% tolerance resistors.
5.4.2A Probes
When connecting probes to functionalized Kevlar, a method needs to be developed to minimize
damage to the ZnO seed layer. Since the seed layer conducts the desired current, it is essential to have
a good Ohmic contact with the probes. The actual probe model has yet to be determined. Probes will
either be connected directly to the Kevlar or to clamps which will attach the Kevlar to the voice coil
actuator.
BNC connectors will be utilized because coaxial shielding in the wires will reduce noise. Also,
available current sensing equipment utilizes the same connections. Probes for this application are
typically around 20 pF, although it is possible to get active probes that reduce the capacitance further.
Page 32 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
Because of the low frequencies that are expected, this should not have a major influence and can most
likely be ignored.
5.4.2B Amplifier
Two amplifier options will be explored in parallel. This approach will help clarify if amplifier noise
is responsible for previous results from Georgia Tech. The HP 4140B picoammeter is available in
Owen Hall and can be used as a control for studying the picoammeter circuit. The HP 4140B will also
be used for initial characterization of the ZnO nanowires until completion of the alternative circuit.
The picoammeter circuit will utilize a low-noise opamp to provide amplification. The initial
schematic is shown in Fig. 17. Alterations may be made to the schematic based upon SPICE results of
the proposed design. The specified CA3420 opamp from Intersil will be modeled in SPICE based
upon its datasheet and then the entire circuit will be simulated. Modifications will be made as
necessary to ensure design specifications are met.
Initial SPICE analysis was done by assuming the opamp is ideal with a single pole. The measured
output is always at M, and the circuit is tunable by adjusting where the feedback of the opamp is
connected in a resistor network. In Fig. 18, the output is graphed against a sweeping input current and
the feedback is attached to the ±5 pA tap. Fig. 19 shows the same thing but attached to the ±50 pA
tap. These simulations suggest good linearity between input current and output voltage.
These output voltages will be read by an ADC and then sent to the computer. Alternatively, a
digital oscilloscope could be used to log data and transfer it to PC with a USB thumb drive. This is
attractive because it would eliminate any switching noise from the device as well as simplify the
circuit.
To power the measurement circuit, two 6V lantern batteries will be used when taking
measurements. For testing purposes, the circuit can be connected directly to a benchtop power supply.
The batteries are used because of both portability and isolation. Rectifying power from a wall outlet
will always have some amount of ripple voltage that can skew results. A pair of low dropout (LDO)
linear regulators will be used to power the +1.5V and -1.5V supply rails to the opamp. Ideally, these
LDOs will be combined onto a single IC with a connection for ground as well. This would make sure
that any ripples seen on the positive or negative voltage rails would be minimized.
Fig. 17: Low Noise Opamp Circuit [27]
Page 33 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
Fig. 18: 5 pA Tap on Circuit
Fig. 19: 50 pA Tap on Circuit
Page 34 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
5.5 Computer Processing Diagram
Fig. 20: Computer Processing Block Diagram
5.5.1 Computer Processing Interface Definition
Signals
Vbb
Input/Output
Input
Description
Common Supply Voltage
Interface
Wall outlet
Measure
Output from picoammeter
circuit
Amplified signal used for
measurement
Display
Output
VGA Monitor Output
Depends on picoammeter
choice:
Existing equipment uses
RS-232
Picoammeter circuit
interface still needs to be
studied
RGB or DVI output
User Input
Input
Keyboard and Mouse
USB peripherals
Data
Intermediate
Data for processing and
then output
Internal system bus
Signal Details
Voltage: 120 VAC
Current: 15 A Max
Voltage: -1.5 – 1.5V
Current: 15 µA
Type: Digital
Voltage: 0 – 5V
Current: 50 µA
Type: Digital
Voltage: 0 – 5V
Current: 50 µA
Type: Digital
Voltage: 0 – 5V
Current: 50 µA
Type: Digital
5.5.2 Computer Processing Operation
Computer Processing is implemented with a standard PC running Windows XP. This allows for any
computer equipped with a RS-232 serial port to interface with the rest of the system. The PC will handle
programming of the voice coil controller’s microprocessor and collecting measurements from the
picoammeter. The microprocessor will be controlled by outputting a .csv file containing positional data.
The positional data is in the form of a sine wave, so the voice coil can be actuated as desired.
The computer also handles the logging and analysis of experimental data. By characterizing noise, the
average noise level should be able to be mathematically removed from actual measurements from actuated
Kevlar. Each set of data taken can be used to find the most optimal conditions for piezoelectric generation.
Page 35 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
5.5.2.A I/O
The I/O block handles any general inputs and outputs for the PC. This includes any logged data
through the USB or RS-232 ports. It also includes VGA output to a monitor for displaying
information. USB and RS-232 are standardized port configurations, so there is no chance of
incompatibility between devices that use these. USB is used for user input devices such as the
keyboard and mouse. It can also handle data transfer from a portable flash memory stick.
The I/O block handles communicates with the picoammeter and controller blocks. The
picoammeter collects data that is then transferred to the computer through this block. The controller
interfaces with the computer processor via the RS-232. This allows a user to program the actuator
block for any sort of positional input.
5.5.2.B PC
PC processes all incoming and outgoing data. It also provides a platform for the user to interface
with for calculations, analysis, and voice coil programming. The PC runs a Windows-based operating
system of either XP or Vista. The main programs the user will use in this project are Excel and
HyperTerminal. Excel allows for easy manipulation of data arrays. This is useful to easily make a
positional waveform and save to a .csv file. It also is a useful tool for storing, calculating, and
graphing data. HyperTerminal is used to communicate with the controller block for programming.
5.6 Actuator Diagram
Fig. 21: Actuator Block Diagram
5.6.1 Actuator Interface Definition
Signals
Functionalized Kevlar
Strands
Input/Output
Input
Description
Wound Kevlar strands
(one covered with zinc
oxide wires, one covered
with zinc oxide wires
coated with gold)
Power
Input
Power supplied from voice
coil motor controller
Position
Input/Output
Position of voice coil will
be read and programmed
by the motor controller
Accuracy: ±200nm
Interface
Need to determine final
design
Need to clamp or bond
Kevlar to actuator while
still allowing easy
interchangeability
High Density DB-15 style
connection.
High Density DB-15 style
connection.
Signal Details
N/A
Power range: ±12 – 24 V
Current: 12A
Type: AC
Voltage: 0 – 5V
Current: 50 µA
Type: Analog
Page 36 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
5.6.2 Actuator Operation
The voice coil acts as the actuation mechanism in the mechanical system. Power is an input which gives
the inner coil enough energy to accelerate relative to the rest of the stage. The chosen voice coil has a built
in position sensor which allows positional data to be read by another device (therefore the “Position” signal
is an output of the Actuator block). Actuation acts an input and output to the voice coil. This is because the
coil is fed frequency and magnitude actuation data to which it responds to. There is also a feedback loop on
the actuator output intended for the actuation motion to self correct errors; in this way it is also an input.
5.6.2A Spring
To return the actuated Kevlar back to its original position while retaining tension, a spring will be
used. This spring will be attached to a static surface and the side of the Kevlar fiber, which is not
being actuated. The actual spring to be utilized has not yet been determined.
5.6.2B Mounting Brackets
Mounting brackets are required to attach the voice coil to a solid surface to prevent the entire device
moving from applying stress on the fibers. The final design of these brackets, or some other mounting
mechanism, is still to be determined. The critical design considerations are that the Kevlar samples
need to be easy to exchange, the Kevlar needs to be firmly connected and the brackets cannot damage
the strands.
5.6.2C Voice Coil
The voice coil is a single piece of equipment that will be purchased from Equipsolutions. The
Kevlar strands will be attached to the head of the voice coil, and the coil (while powered) will induce
the mechanical stress on the fibers. The VCS-10H voice coil takes an input voltage of ±12V to ±24V.
As the current used will go to the conduction coil, the actual power is a function of the current (which
will be sinusoidal). The voice coil will be programmed so that the position of the head can be known
at any point in its period to ±200nm of accuracy.
5.7 Controller Diagram
Fig. 22: Controller Block Diagram
Fig. 23: Microprocessor Sub-Block Diagram
Page 37 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
5.7.1 Controller Interface Definition
Signals
Vcc
Input/Output
Input
Description
Powers controller
Interface
Four circuit Mini-Fit Jr.
RS-232
Input
Communication from
computer
RS-232
Position
Input/Output
Motor controller will
position voice coil Accuracy:
High Density DB-15 style
connection, pin 2.
Power
Output
Powers voice coil
High Density DB-15 style
connection.
Programming
Intermediate
Allows the processor to
execute instructions
specified by a user
System bus
±200nm
Signal Details
Power range: ±12 – 35 V
Peak Current: 15 A
Type: DC
Power range: ±5V
Current: 50 µA
Type: DC
Power range: ±5V
Current: 50 µA
Type: DC
Power range: ±12 – 24 V
Peak Current: 12A
Type: AC
Power: 5V
Current: 50μA
Type: DC
5.7.2 Controller Operation
A control system is required to operate and give parameters to the voice coil. Vcc ranges from ±12V to
±35V DC and powers the controller. RS-232, a standard serial connection, will be used in conjunction with
a PC to program the controller. The outputs of this block are position and power. The power is used as the
power input for the voice coil. The controller has an onboard current amplifier so the controller is capable of
supplying the required current. The position output consists of programmed values on the controller.
5.7.2A Motor Power Supply
The motor power supply is used to power the voice coil. The main component of this is a built-in
current amplifier. This component is part of the controller and will supply an output voltage of
±12 – 24 V, and a maximum output current of 12A.
5.7.2B A to D Converter
The function of this block is to transform analog positional information from the voice coil and
convert it into a digital format for the microprocessor. This 16-bit analog to digital converter is built
into the controller. This is ideal because it enables users to get a 200nm resolution. The voltage range
of this feedback signal is 0-5V AC.
5.7.2C Microprocessor
The microprocessor aids in the control of the voice coil during actuation by transforming userspecified positional data into a control signal. The voice coil’s current position is fed back to the
processor through the A to D converter. With this information, the control signal to the power supply
allows for output waveform modification. In Fig. 23, the microprocessor is broken down into two
more sub-blocks.
5.7.2C.i RISC
The RISC chip processes user-supplied code and positional data from the voice coil. From
this information, it outputs data to the power supply. The power supply utilizes this data by
altering its output as needed so that the voice coil moves to a new position. New positional
data is read, further adjusting output so that the coil can quickly and accurately arrive at the
correct position.
Page 38 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
5.7.2C.ii Code
The user-supplied code is entered as a .csv file containing positional data. This will be in
the form of a sine wave for voice coil actuation. Pseudo-code for these operations follows:
Loop
Goto position x = sin(f*t) //f is frequency
Delay(0.001 seconds) // because of 1kHz bandwidth
Until (0>1) //infinite loop until turned off
5.8 Mechanical Test Platform Diagram
Fig. 24: Mechanical Test Platform Diagram
Page 39 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
5.8.1 Mechanical Test Platform Diagram
Signals
Vcc
Input/Output
Input
Description
Powers controller
Interface
Four circuit Mini-Fit Jr.
Vdd
Input
Common Supply Voltage
Power cord
RS-232
Input
Communication from
computer
RS-232
Position
Intermediate
Motor controller will
position voice coil Accuracy:
High Density DB-15 style
connection, pin 2.
Power
Intermediate
Powers voice coil
High Density DB-15 style
connection.
Current
Intermediate
System bus
Measure
Intermediate
Allows the processor to
execute instructions
specified by a user
Amplified signal used for
measurement
Functionalized Kevlar
Strands
Intermediate
N/A
Nanowires
Input
Kevlar coated with Zinc
Oxide nanowires, one strand
with Au coating, one without
Zinc oxide nanowires
Signal Details
Power range: ±12 – 35 V
Peak Current: 15 A
Type: DC
Voltage: ±6 V from
batteries
Current: 2.86 A Max
-ORVoltage: 120 VAC
Current: 10 A Max
Power range: ±5V
Current: 50 µA
Type: DC
Power range: ±5V
Current: 50 µA
Type: DC
Power range: ±12 – 24 V
Peak Current: 12A
Type: AC
Power: 5V
Current: 50μA
Type: DC
Voltage: -1.5 – 1.5V
Current: 15 µA
Type: Digital
-ORVoltage: 0 – 5V
Current: 50 µA
Type: Digital
N/A
N/A
N/A
±200nm
RS-232
-ORUSB
5.8.2 Mechanical Test Platform Operation
The mechanical test platform is the base for all of the measurement blocks to be placed on. This block
symbolizes how individual blocks will come together once each functions properly. The four pieces that
make up this block are the wound Kevlar, picoammeter, actuator and controller. Each block has been
individually described in previous sections.
Page 40 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
6. Testing
6.1 Minimum Requirements Testing
Successful Nanowire Synthesis
 Well-defined method of nanowire production that repeatedly produces aligned ZnO nanowires. *
1. Prepare 5 samples from different growth batches using chosen growth parameters.
2. Properly mount samples for high quality SEM images. Previous mounting steps were as follows:
i. Firmly attach copper grounding straps to SEM stage.
ii. Apply carbon tape to stage on top of copper grounding straps.
iii. Attach sample to carbon tape and press firmly on Kapton tape which is still connected to ends of
samples.
iv. Firmly attach additional copper grounding straps covering Kapton tape to keep samples from
drifting during imaging.
v. Coat entire stage with carbon to hopefully decrease charging of the sample.
vi. Follow proper steps for traditional SEM equipment use and imaging.
3. Take images of samples. The images should not be corrupted due to charging effects, that
comparisons will have to be performed at consistent magnification and that images must be
representative of the sample.
4. Evaluate images.
Pass: Research professor signs off below that there is sufficient evidence provided through SEM images
that the chosen process parameters yield consistent samples.
Fail: Not enough evidence is provided to convince the research professor that consistency between
samples was achieved.

Nanowire at least 1 µm in length and have an aspect ratio of at least 10:1
1. Prepare sample using chosen growth parameters.
2. Properly mount samples for high quality SEM images. Previous mounting steps were as follows:
i. Firmly attach copper grounding straps to SEM stage.
ii. Apply carbon tape to stage on top of copper grounding straps.
iii. Attach sample to carbon tape and press firmly on Kapton tape which is still connected to ends of
samples.
iv. Firmly attach additional copper grounding straps covering Kapton tape to keep samples from
drifting during imaging.
v. Coat entire stage with carbon to hopefully decrease charging of the sample.
vi. Follow proper steps for traditional SEM equipment use and imaging.
3. Take images of samples. The images should not be corrupted due to charging effects, that
comparisons will have to be performed at consistent magnification and that images must be
representative of the sample.
4. Study images. Use measurement tools to show length and widths of nanowires on SEM images.
Pass: SEM images show that nanowires are longer than 1 µm AND that the aspect ratio is greater
10:1.
than
Fail: Nanowires are less than 1 µm long OR the aspect ratio is less than 10:1.
Page 41 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec

Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
Nanowire density must be low enough to allow movement in the wires but high enough to ensure
enough output that it is detectable. (~10 – 50 µm-2)
1. Prepare sample using chosen growth parameters.
2. Properly mount samples for high quality SEM images. Previous mounting steps were as follows:
i. Firmly attach copper grounding straps to SEM stage.
ii. Apply carbon tape to stage on top of copper grounding straps.
iii. Attach sample to carbon tape and press firmly on Kapton tape which is still connected to ends of
samples.
iv. Firmly attach additional copper grounding straps covering Kapton tape to keep samples from
drifting during imaging.
v. Coat entire stage with carbon to hopefully decrease charging of the sample.
vi. Follow proper steps for traditional SEM equipment use and imaging.
3. Take five representative images of sample. The images should not be corrupted due to charging
effects, that comparisons will have to be performed at consistent magnification and that images must
be representative of the sample.
4. Study images. Use Paint to analyze the density of the nanowires over the surface of the samples:
i. Use scale bar on image to determine the conversion factor between pixels and µm.
ii. Draw a unit square (size will vary with image magnification) and count the number of nanowires
within the square.
iii. Average density values from the five images.
Pass: SEM images and analysis show that average nanowire density is between 10 – 50 µm-2.
Fail: SEM images and analysis are not conclusive OR average nanowire density is less than
10 µm-2 OR greater than 50 µm-2.

Adhesion of seed layer to Kevlar can withstand actuation for 100 cycles without showing signs of
separation. This ensures durability of the seed layer and uniform wire coverage on the Kevlar. *
1. Take images of seed layer of one Kevlar sample from growth batch.
2. Use another Kevlar strand to be actuated for 100 cycles.
3. Prepare actuated sample for SEM imaging.
4. Properly mount samples for high quality SEM images. Previous mounting steps were as
follows:
i. Firmly attach copper grounding straps to SEM stage.
ii. Apply carbon tape to stage on top of copper grounding straps.
iii. Attach sample to carbon tape and press firmly on Kapton tape which is still connected to ends of
samples.
iv. Firmly attach additional copper grounding straps covering Kapton tape to keep samples from
drifting during imaging.
v. Coat entire stage with carbon to hopefully decrease charging of the sample.
vi. Follow proper steps for traditional SEM equipment use and imaging.
5. Take images of samples. The images should not be corrupted due to charging effects, that
comparisons will have to be performed at consistent magnification and that images must be
representative of the sample.
6. Study images. Seed layer should be firmly attached to Kevlar.
Pass: SEM images and analysis show no damage to the seed layer (peeling, cracking, etc.)
Fail: SEM images and analysis show damage to the seed layer (peeling, cracking, etc.)
Page 42 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
Accurate Electrical Measurements
 Picoammeter circuit must accurately be able to measure in 50 pA quantities to adequately test
nanowires output.
1. Create current source circuit which can produce a reliable output.
2. Connect circuit to picoammeter in series.
3. Measure output.
4. Compare experimental results with expected output current from circuit and HP 4140B.
Pass: The picoammeter can successfully measure currents in 50 pA quantities.
Fail: The picoammeter cannot successfully measure currents in 50 pA quantities.

Sample rate of electrical measurements must be a minimum of 1 kHz. This ensures sampling at a rate
much greater than the input frequency from the actuator.
1. Connect measurement circuit to the current generator described in the previous test.
2. Take measurements for one minute.*
3. From waveform, count number of acquired data points and confirm that data was sampled at a rate of
at least 1kHz.
* Measurements will be tracked by using an oscilloscope.
Pass: Sampling frequency is calculated to be at least 1 kHz.
Fail: Sampling frequency is calculated to be less than 1 kHz.
Robust Mechanical System Design
 Kevlar attachment to mechanical actuator must allow for replacement of different samples.
1. Detach electrical measurement probes from the testing apparatus.*
2. Unclamp the Kevlar sample and remove from testing apparatus.
3. Securely clamp new Kevlar fiber onto the actuation head.
4. Attach electrical measurement probes to the Kevlar samples.*
* This will not be necessary if electrical measurement probes do not connect directly to Kevlar.
Pass: Complete replacement of Kevlar in one hour or less.
Fail: Fail to replace Kevlar sample in the one hour time frame.

Mechanical actuator must have positional precision of at least 0.1 mm so as to make a repeatable set of
input forces.
Voice Coil:
1. Use software to program voice coil positions.
2. Analyze logged data and check bits to ensure 0.1mm or better accuracy.
-OR-
Page 43 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
General Positional Accuracy:
1. Set actuation device to predetermined position.
2. Set a block using calipers at 0.1mm greater than a position for the actuator to move to.
3. Move the actuator to the new position.
4. Use calipers to determine distance from the block.
Pass: Actuator performs functions as programmed.
Fail: Actuator does not perform a programmed function as expected.

Mechanical system should not interfere with electrical measurements, ie. any noise from a motor
should be filtered out. *
1. Prepare two Kevlar fiber samples with a zinc oxide seed layer, but without nanowire growth.
2. Clamp this pair of fibers to the actuation mechanism.
3. Attach electrical measurement probes to the Kevlar.
4. Program an actuation sequence.
5. Analyze any observed current waveform.
6. Characterize noise produced by zinc oxide coated sample using three test runs.
7. As a second test, prepare copper wire for actuation.
8. Repeat steps 2 through 6 for the copper wire.
Pass: Research professor signs off that the observed waveform is negligible OR can be mathematically
removed during analysis.
Fail: Research professor does not sign off observed waveform is not negligible OR cannot be
mathematically removed during analysis.

Pull on Kevlar should be adjustable (from 0.1 to 5 mm if necessary) to find an optimal stroke that
stresses system without permanently damaging the Kevlar and nanowires. *
1. Set a block using calipers a distance of 0.2 mm from the actuation head.
2. Move the actuation head to the 0.2 mm point.
3. Verify the actuator position using calipers.
4. Set a block using calipers a distance of 5 mm from the actuation head.
5. Move the actuation head to the 5 mm point.
6. Verify actuator position using calipers.
7. Properly mount samples for high quality SEM images. Previous mounting steps were as follows:
i. Firmly attach copper grounding straps to SEM stage.
ii. Apply carbon tape to stage on top of copper grounding straps.
iii. Attach sample to carbon tape and press firmly on Kapton tape which is still connected to ends of
samples.
iv. Firmly attach additional copper grounding straps covering Kapton tape to keep samples from
drifting during imaging.
v. Coat entire stage with carbon to hopefully decrease charging of the sample.
vi. Follow proper steps for traditional SEM equipment use and imaging.
8. Take images of samples. The images should not be corrupted due to charging effects, that
comparisons will have to be performed at consistent magnification and that images must be
representative of the sample.
9. Evaluate images.
Page 44 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
Pass: Actuation device is able to vary the pulling distance from 0.2 mm to 5 mm. The Kevlar and zinc
oxide seed layer are not damaged at optimized stroke.
Fail: Actuation device is unable to vary the pulling distance of 0.2mm to 5 mm OR an optimal stroke
cannot be found.

Mechanical actuation system must have a variable frequency of 1 – 20 Hz.
1. Design a sensor circuit which will measure each wave cycle of an actuation sequence.
2. Build the fore mentioned circuit.
3. Orient the sensor so as to detect the actuation waveform.
4. Program the actuator for frequencies of 1 and 20 Hz.
5. Activate the actuation device and run for 1 minute at each frequency.
6. Analyze the output waveforms from the sensor circuit.
Pass: Mechanical actuation system is able to perform actuation at frequencies of 1and 20 Hz.
Fail: Mechanical actuation system does not have a variable frequency OR is unable to actuate with
frequencies of 1and 20 Hz.
Adequate Analysis of Results
 Analysis and theory of results. *
1. If a current output is measured, provide a convincing argument that this current is coming from the
wires.
2. If there is no output current measured, explain why this is occurring.
3. Data should be sufficient enough to back-up theory and analysis.
Pass: Research professor finds analysis of results accurate and adequate.
Fail: Research professor does not find analysis complete or satisfactory.
* Certain requirements cannot be firmly quantified. Whether these requirements have been
met will be evaluated by the research professor.
6.2 Desired Requirements Testing
 Examine possible alternative materials such as polyethylene fibers instead of Kevlar, other piezo materials
rather than ZnO, aluminum rather than gold for a Schottky barrier, etc. *
1. Growth methods for different substrate or nanowires materials are detailed.
2. Test results exist for any additional materials that were explored.
3. Comparisons have been made between ZnO Kevlar with Au Schottky and the alternative.
Pass: Alternative materials have been explored and tested to the satisfaction of research
professor.
Fail: No alternatives were explored OR they were not explored sufficiently and to the satisfaction of
research professor.

Compare results from piezoelectric and non-piezoelectric growth materials. *
1. Non-piezoelectric material chosen with a known method of nanowires growth compatible with Kevlar
substrate.
2. Growth method characterized, samples from method are made.
3. Test using identical procedures that were developed for ZnO-coated Kevlar.
4. Analysis has been completed with identical figures of merit to ZnO-coated Kevlar.
Page 45 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
5. Conclusions from analysis can be used to either support or disprove ZnO nanowires can generate
energy from piezoelectric strain.
Pass: Non-piezoelectric material was tested. Research professor believes results are conclusive.
Fail: No tests on non-piezoeletric material performed OR results inconclusive to research professor.

Nanowires should be 3µm long with an aspect ratio over 100:1. These would most likely improved
results.
1. Prepare sample using chosen growth parameters.
2. Properly mount samples for high quality SEM images. Previous mounting steps were as follows:
i. Firmly attach copper grounding straps to SEM stage.
ii. Apply carbon tape to stage on top of copper grounding straps.
iii. Attach sample to carbon tape and press firmly on Kapton tape which is still connected to ends of
samples.
iv. Firmly attach additional copper grounding straps covering Kapton tape to keep samples from
drifting during imaging.
v. Coat entire stage with carbon to hopefully decrease charging of the sample.
vi. Follow proper steps for traditional SEM equipment use and imaging.
3. Take images of samples. The images should not be corrupted due to charging effects, that
comparisons will have to be performed at consistent magnification and that images must be
representative of the sample.
4. Study images. Use measurement tools to show length and widths of nanowires on SEM images.
Pass: SEM images show that nanowires are longer than 1 µm AND that the aspect ratio is greater
100:1.
than
Fail: Nanowires are less than 3 µm long OR the aspect ratio is less than 100:1.

Electrical measurements sampled at 0.5 MHz or higher. This will better show any spikes in current as
the system tries to reach equilibrium.
1. Connect measurement circuit to the current generator described in the previous test.
2. Take measurements for one minute.*
3. From waveform, count number of acquired data points and confirm that data was sampled at a rate of
at least 1kHz.
* Measurements will be tracked by using an oscilloscope.
Pass: Sampling frequency is calculated to be at least 0.5 MHz.
Fail: Sampling frequency is calculated to be less than 0.5 MHz.

Change mechanical actuation frequency to 100 – 200 Hz and determine the effects of higher
frequencies on material breakdown.
1. Orient the sensor from minimum requirements so as to detect the actuation waveform.
2. Program the actuator for frequencies 100 and 200 Hz.
3. Activate the actuation device and run for 1 minute at each frequency.
4. Analyze the output waveforms from the sensor circuit.
Page 46 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
Pass: Mechanical actuation system is able to perform actuation at frequencies of
100 and 200 Hz.
Fail: Mechanical actuation system does not have a variable frequency OR is unable to actuate with
frequencies of 100 and 200 Hz.

Entire system portable and stable enough to exhibit a working test procedure at Engineering Expo.
1. Each system component shall weigh no more than 35 lbs.
2. Perform standard test procedure in any room specified by course instructor.
Pass: System components weight less than 35 lbs. AND test results do not disagree with previous results
in controlled environment.
Fail: One or more system components weigh 35 lbs. OR test results disagree with previous results.
* Certain requirements cannot be firmly quantified. Whether these requirements have been
met will be evaluated by the research professor.
Page 47 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
7. Bill of Materials
Block
Description
Manufacturer
Voice Coil
Actuation
mechanism
Control of
voice coil
Linear Power
Supply
TEOS
Equipment
Solutions
Equipment
Solutions
Equipment
Solutions
Alfa Aesar
Hydrothermal
Nanowire
Growth
Hydrothermal
Nanowire
Growth
Hydrothermal
Nanowire
Growth
Hydrothermal
Nanowire
Growth
Hydrothermal
Nanowire
Growth
Seed Layer
Coating
Picoammeter
Hexamethylene
tetramine
Picoammeter
Manufacturer
Part #
VCS-10H
Supplier
Supplier
Part #
VCS10H
SCA814
Availability
Quantity
Available
Unit
Cost
$1,500
1
Total
Cost
$1,500
Available
$950
1
$950
LPS24
Available
$275
1
$275
40251
Available
500g
$43.50
1kg
$22.60
100g
$62.40
500g
$33.40
1
$468.53
40251
Equipment
Solutions
Equipment
Solutions
Equipment
Solutions
Alfa Aesar
Alfa Aesar
A17213
Alfa Aesar
A17213
Available
Polyethylene
imine
Alfa Aesar
40527
Alfa Aesar
40527
Available
Zinc Nitrate
Hydrate
Alfa Aesar
12313
Alfa Aesar
12313
Available
Hot Plate
VWR
12365-480
VWR
12365480
Available
$43.50
for
500g
$22.60
for
1kg
$62.40
for
100g
$33.40
for
500g
$468.53
Low Static
Kapton Tape
3M
5419 GOLD
1/2IN X 36YD
Digi-Key
3M5919
12-ND
Available
$29.35
1
$29.35
Kevlar
DuPont
-----
Available
-----
1.5kΩ ± 1%
Resistor
Vishay/Dale
CMF551K500
0FHEB
Digi-Key
Available
5
$0
Sample
$0.85
430Ω ± 1%
Resistor
150Ω ± 1%
Resistor
Vishay/BC
Components
Vishay/Dale
SFR250000430
0FR500
CMF55150R00
FHEB
Digi-Key
Available
$0.19
5
$0.95
Available
$0.17
5
$0.85
Picoammeter
11kΩ ± 1%
Resistor
Vishay/Dale
CMF5511K00
0FHEB
Digi-Key
Available
$0.17
5
$0.85
Picoammeter
68Ω ± 1%
Resistor
1kΩ
potentiometer
Panasonic ECG
CTS
Corporation
Electro
components
CTS
Corporation
Electro
components
EPCOS Inc
EROS2PHF68R0
296UD102B1
N
Digi-Key
CMF1.5
0KHFCT
-ND
PPC430
YCT-ND
CMF150
HFCTND
CMF11.
0KHFCT
-ND
P68.0CA
CT-ND
CT2262ND
$0
Sample
$0.17
Available
$0.171
10
$1.71
2,738
Available
$1.51
2
$3.02
296UD103B1
N
Digi-Key
CT2265ND
5,112
Available
$1.51
2
$3.02
B37979N1100J
000
CMF551M000
0FHEB
Digi-Key
P4837ND
CMF1.0
0MHFC
T-ND
PPCHF1
0MCTND
588HVF120
6T1008J
E
27,150
Available
Available
$0.23
2
$0.46
$0.17
5
$0.85
Available
$0.798
5
$3.99
Available
$3.95
2
$7.90
Controller
Controller
Seed Layer
Coating
Picoammeter
Picoammeter
SCA814
LPS24
-----
DuPont
Digi-Key
Digi-Key
Picoammeter
10kΩ
potentiometer
Picoammeter
10 pF capacitor
Picoammeter
1MΩ
Resistor
Vishay/Dale
Picoammeter
10MΩ
Resistor
Vishay/BC
Components
HVR37000010
05FR500
Digi-Key
Picoammeter
10 GΩ Resistor
Ohmite
HVF1206T100
8JE
Mouser
Digi-Key
Page 48 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
Picoammeter
AA Batteries
Panasonic-BSG
LR-6PA/2SB
Digi-Key
Picoammeter
CA3420
Intersil
CA3420EZ
Intersil
Picoammeter
1.5V fixed
regulator
Rohm
BA15BC0T
Digi-Key
P107ND
CA3420
EZ
BA15BC
0T-ND
In Stock
$0.54
4
$2.16
In Stock
$0
Sample
$1.02
2
$0
Sample
$2.04
In Stock
2
Page 49 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
8. Development Plan
The next few paragraphs describe the timeline of this project and the associated tasks as well as their
dependency on one another. Although set-backs cannot always be planned for, a better understanding of how
the tasks are related to one another can help ease the stress of the critical path.
Over the break each team member will be taking days off, but the goal is to still keep making progress on the
project. For example, parts can be ordered so that the lead times associated with each piece will not be an issue
Winter term. Different parts of the project each have associated goals and deadlines so the plans for each piece
are described in sections below, with a final project plan as a summary.
8.1 Materials
Although the functionalized Kevlar strands are needed for the project, improvements of growth
consistency and experiments around altering growth parameters will not disrupt the development of the
other sub-blocks. The main issue for the materials part of the project is getting proper access to a high
quality scanning electron microscope and reserving sufficient tool time. Hewlett-Packard Corvallis has
generously donated visitor access to their Analytical and Development Labs and the time of an experienced
technician. After working through the logistics between the legal departments of OSU and HP, the
paperwork has been signed and site visits will begin after January 1, 2009.
There are two different growth mechanisms that can be used; each method needs to be studied in parallel.
The hot plate method produces longer wires, but growth times are significantly longer. On the contrary, the
microwave method has the benefit of a significantly shorter growth time but the wires are much shorter.
The microwave method is the more favorable method because of the shorter growth time, but both methods
need to be improved so that required nanowire dimensions can be achieved.
8.2 Electrical Measurements
There are two options for taking electrical measurements. The HP 4140B is available for use in Owen,
but one of the desired requirements is to have a working display at the expo. The equipment in Owen is for
use in Owen and is not located in a low-noise area. One of the very large issues with the electrical
measurements is noise. Not only is a very low-noise environment needed, but the noise that is present has
to be well characterized so that it can be subtracted from the performed measurements. One of the more
challenging pieces of this part of the project is the design of the picoammeter. There are different options
which need to be considered and the members of this team do not have the required specialty in circuit
design. For this piece of the project, parts should be ordered over break. There have been some problems
with the progress of the actual design so the schedule is already getting tighter.
8.3 Mechanical Actuator
The current plan for the mechanical actuator is using a voice coil. The idea behind this is that not only is
the voice coil bi-directional but there is also a controller which can be used to track the position of the
actuator to an accuracy of 200nm. Since this research project is in the center of a large controversy using
the most accurate equipment as possible is vital. Over break, ways that the Kevlar should attach to the voice
coil need to be examined. Another good time investment would be ordering the voice coil and controller.
Time off of school should be utilized to get more familiar with the voice coil software.
8.4 Project Approach Summary
The general approach to this project is to develop each of the subsystems individually. After each piece
is completed and verified the project as a whole can be further developed. The design of each system will
be performed in accordance with the overall project objectives. Testing is broken up by the subsystem so
that if a particular block is not functioning properly, the rest of the project will not be categorized as nonfunctioning. A pass condition exists for each subsystem and failure of one test will not create a domino
effect. If proper design considerations are taken, only a few weeks will be needed for complete system
integration.
Page 50 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Appendix A.
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
References
[1] Y. Qin, X. Wang, and Z. L. Wang, “Microfibre–nanowire Hybrid Structure for Energy Scavenging”, Nature, vol.
451, pp. 809 – 814, February 2008.
[2] Interuniversity Microelectronics Centre, "Thermopiles in Headband Power Wireless EEG Sensor and 2.4 GHz
Transmitter," Wearable Smart Sensors, October 2007. [Online]. Available:
http://www.wearablesmartsensors.com/energy_sources.html. [Accessed: November 2, 2008].
[3] Z. Wang, V. Leonov, P. Fiorini, and C. Van Hoof IMEC vzw, Kapeldreef 75, B-3001, Leuven, Belgium,
“Micromachined Polycrystalline SiGe-Based Thermopiles for Micropower Generation on Human Body,”
Symposium on Design, Test, Integration and Packaging of MEMS/MOEMS, DTIP 2007, Stresa, lago Maggiore,
Italy, 284-289.
[4] A. Powell, "Nanowire Generates Its Own Electricity," ScienceDaily, October 2007. [Online]. Available:
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Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
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Page 52 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
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Page 53 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Appendix B.
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
Naming Conventions and Glossary
Analog Digital Converter (ADC)
A device used to convert an analog signal to digital bit values. This allows an arbitrary signal to be
read by a computer or microprocessor for processing.
Aspect ratio
Term used to define nanowire dimensions. Formally defined as length over width.
Atomic Layer Deposition (ALD)
A method of depositing thin films one monolayer of atoms at a time. This is done in an inert gas
environment where one material is introduced to the substrate, purged, and then followed by a second.
By repeating this process multiple times, a thin film is grown.
AttoSI prefix meaning 1*10-18
Au
Gold (periodic table abbreviation)
Autoclave
Closes heating system to contain water so that solution can be heated above boiling point.
Block
A block is the basic element of a system. It is a standalone object that performs some function in the
system. A block should be ‘small’ enough that everything contained inside of it can be fully
understood as a whole, or the contents can be purchased as a whole.
Customer Requirement
A requirement that may or may not be able to be tested as is. A requirement supplied by the customer,
sponsor, or mentor.
CVD
Chemical Vapor Deposition
DI water
Deionized water is purified water that has had its mineral cations (eg. sodium, calcium, iron or copper)
and anions (eg. chloride or bromide) removed.
Dip-coating
The substrate is submerged in the coating solution and is slowly pulled out of the solution allowing the
solution to cover the substrate. The substrate is then dried to finish creating the thin-film.
Discipline Decomposition
The process of dividing a system into blocks based on the primary knowledge used in defining each
block. (e.g. computer science, electrical, mechanical)
Engineering Requirements
A requirement that can be tested and evaluated through a step by step process. Usually a numerical
specification is included.
Page 54 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
Environment
The set of influences that the system will be operating within. These could include temperature,
humidity, immersion, vacuum, etc…
EPROM
Erasable Programmable Read-Only Memory. A non-volatile memory that will store data even without
being powered.
Functional Decomposition
The process of dividing a system into blocks that represent the required functions. See discipline
decomposition, locality decomposition
Half-reaction
Can be either the oxidation or reduction reaction component of a redox reaction. In order to obtain a
half reaction the change in oxidation state of the individual substances is considered.
Hydroxyl Group
A grouping of chemicals describing molecules which consist of an oxygen atom and a hydrogen atom
connected by a covalent bond.
Integrated Circuit (IC)
A silicon chip encased in a hard plastic with a various number of input and output pins to make
connections. The silicon has a circuit made on it with numerous transistors and other components,
made together to perform some function.
Interface Characteristics
Every connection between blocks is defined by a unique name and a list of interface characteristics.
These characteristics define an interface to the degree that a block can be built without knowledge of
other blocks in the system
Photosensitive Nanowires
Nanowires acting as antennae that can absorb wavelengths of visible light.
Photovoltaic
A material characteristic that causes a voltage potential to be produced when light is shown onto the
material’s surface.
Piezoelectricity
A material property where a voltage potential is created from mechanical stress.
Platform
Used to describe the project as a whole, in its physical aspects and the necessary application functions.
Locality Decomposition
The process of dividing a system into blocks based on the similarity (locality) of blocks. (e.g. all
inputs together, all outputs together)
Low Dropout Regulator
Linear DC voltage regulator used to create a different input voltage than what is provided by a power
supply or batteries.
Page 55 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
Molecular Beam Epitaxy (MBE)
Slow deposition method which allows crystals to grow epitaxially in a vaccuum
MOCVD
Metal Organic Chemical Vapor Deposition
Ohmic Contact
A near-ideal metal-semiconductor interface that allows electrons to flow between the two materials
with no voltage drop.
RISC
Reduced Instruction Set Computing. Simpler instructions are used to increase the speed of specified
actions.
Scanning Electron Microscope (SEM)
A type of electron microscope used to image samples by accelerating electrons toward the sample.
Because electrons have a much smaller wavelength than visible light, much smaller features can be
seen on the sample.
Schottky Junction
A Schottky Junction uses a metal-semiconductor interface instead of semiconductor-semiconductor
interfaces seen in p-n junctions. Due to a difference between the metal’s work function and the
semiconductor’s band gap, a diode is formed that only allows current to flow in a single direction.
Spin-coating
Used to apply uniform thin films to flat substrates. First, an excess amount of a solution is
placed on the substrate. The substrate is then rotated at high speed in order to spread the fluid
by centrifugal force.
Strain
Magnitude of deformation in a material under stress.
Sub-System
This is a grouping of one or more blocks that function together to perform some task. (e.g. a motor and
a motor controller perform the task of motion.)
System
The complete system being designed to study and test piezoelectric nanowires. This includes all
blocks in your design.
Test bench
This phrase is used to describe the combination of the mechanical actuator and electrical measurement
systems.
Thermopile
A stack of alternating types of metal wires. A voltage difference is produced across the wires when
heat is applied. By stacking them in series, a higher potential can be produced to power a device.
Thomson Effect
Describes the heating or cooling of a current-carrying conductor with a temperature gradient.
Page 56 of 57
Project Specification – Piezoelectric Nanowires
Adapted from ECE 322 Project Spec
Ashley Mason, Adam Stone, Todd Waggoner – Group 11
Copyright 2008 – Oregon State University
December 7, 2008
Top-Level
This refers to the system block diagram containing all blocks in the system.
VLS
Vapor Liquid Solid growth mechanism
Young's Modulus
The measure of the stiffness of an isotropic elastic material. Defined as uniaxial stress over uniaxial
strain.
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