Download Lecture 1-1 Introduction to Micro Tranducers

NTHU ESS5841
F. G. Tseng
The Principles and Applications of Micro Transducers
Spring/2001, 1-1, p1
Lecture 1-1 Introduction to Micro Transducers
 Position of This Course
大三
微系統概論一
微系統概論二
微機電系統導論
大四
微系統製程與實驗
一I
微系統工程原理
微機械熱流學
碩一
高等微系統製程與實驗
II II
微機電系統分析
與量測
微機電構裝技
術及可靠度
微系統設計/
微機電系統
分析與設計
微系統材料
微磨潤學
碩一下/
碩二
微機電系統分析
與量測實驗
電磁式微
機電實驗
深刻模造技術
微感測器及量測
系統之訊號處理
微轉換器原理及應用
/微機電傳感器
生醫微機電
及奈微微流
體系統
電磁波微系
統
 Scope of This Course:
Introduction of the principles and applications of micro- mechanical,
thermal, fluidic, optical, electrical, magnetic, and
chemical/bio-chemical Transducers.
Goal:
To help on your micro system design in choosing right principles and
applications from the systematic study on broad fields of micro
transducers.
 Definition of Transducers:
NTHU ESS5841
F. G. Tseng
The Principles and Applications of Micro Transducers
Spring/2001, 1-1, p2
Transducers: Convert one form of energy into another,
including sensors and actuators.
Sensors: measure signals from the environment and transfer
them into an output which can be readout.
Actuators: Perform useful work on the environment in response
to a command or a control signal.
 Components of Transducers Systems
 Why Micromachined?
1. When to use micromachine?
If there is no other way (enabling technology), or there are clear
advantages, micro machining can be a very powerful
technique. —Kurt Petersen, Transducers'95.
2. Scaling and performance (problem or benefit?)
Consider the following physical properties:
Thermal transport properties (can be locally highly coupled or
NTHU ESS5841
F. G. Tseng
The Principles and Applications of Micro Transducers
Spring/2001, 1-1, p3
isolated)
Mass transport properties (greatly enhanced in small scale, applied
in electrochemical microelectrodes)
Surface area to Volume ratio (increased in small scale, applied in
separation)
Capillary force (driving or dragging force?)
Power dissipation (large in small scale)
We should treat scaling issues wisely and properly!!!
3.Cost reduction issues:
MEMS can reduce fabrication cost, however, Testing and
Packaging may cost lots more than we think.
Mass-market drivers must be found to ensure the cost done
by volume production.
To move up the transducers level to better performance,
which the old devices cannot approach.
Disposable devices are increasing importance in chemical
and biomedical applications than durable devices in like
automobile industry.
4. Complexity of System:
Yield decreases with the increasing of system complexity
Not all the components have been miniaturized (power source,
gas pump)
Biocompatibility issues-limit material selections
Some systems work better in MESOSCOPIC (cm2-10cm2,
chemical reactor, synthesizers, analyzers, heating and cooling
units, combustors and fuel cells).
NTHU ESS5841
F. G. Tseng
The Principles and Applications of Micro Transducers
Spring/2001, 1-1, p4
Interconnection and packaging methods are very important!!
5. Flow chart for the design concerns of micro transducers:
Commercial or research need
Basics physics and scale laws
Literature/nature survey
Integration issue
Fabrication process
Packaging issues
Testing methods
Final cost estimation
How to improve performance
in the future?
Make decision
NTHU ESS5841
F. G. Tseng
The Principles and Applications of Micro Transducers
Spring/2001, 1-1, p5
 Sensor characteristics
Transfer function
An idea or theoretical output-stimulus relationship.
The function can be: linear, logarithmic, exponential or
power function:
S  a  bs , S: output signal, s: stimulus, a: output at zero
input, b: sensitivity.
Or
S  a  b ln s
S  ae ks
S  a0  a1s k
S  a0  a1s  a2 s 2  
In many cases, a nonlinear sensor may be considered
linear over a limited range, or use piece-wise approximation.
Span (input)
A dynamic range of stimuli which may be converted by a
sensor. Also called input full scale (FS). It represents the
highest possible input value which can be applied to the
sensor without causing unacceptably large inaccuracy.
For broad band and nonlinear response, the dynamic
range of the input stimuli is often expressed in decibels:
NTHU ESS5841
F. G. Tseng
The Principles and Applications of Micro Transducers
Spring/2001, 1-1, p6
dB  10 log
P2
P1 , P: power
dB  20 log
s2
s1 , s: force, current, or voltage
for example: P2/P1=100 => 20dB, s2/s1=10 => 20 dB.
Full scale output
The difference between the output signals measured with
maximum input stimulus and the lowest input stimulus
applied.
Accuracy
A ratio of the highest deviation of a value represented by
the sensor to the ideal value.
It can be in terms of :
1. Directly measured value ()
2. In % of input span (full scale)
3. In terms of output signal
For example:
 FSO (%)  100(Sr  Si ) / S FSO
Si: idea value, Sr: real value, FSO: full scale of output
The difference between Permissive limits and ideal
transfer function: ±
The difference between real and ideal functions: ±
NTHU ESS5841
F. G. Tseng
The Principles and Applications of Micro Transducers
Spring/2001, 1-1, p7
Accuracy is effected by part-to-part variation, hysteresis,
dead band, calibration and repeatability errors. Use
worst-case analysis to determine the worst possible
performance of the system.
To reduce the error from part-to-part variation, a
multiple-point calibration is required, as shown in the right
hand side figure. Thus the permissive limits become
narrower.
Calibration error
An inaccuracy permitted by a manufacture when a
sensor is calibrated in the factory. The error is a systematic
nature, and it shifts the accuracy of transduction for each
stimulus point by a constant. Note: it is not necessary
uniform.
For example:
NTHU ESS5841
F. G. Tseng
The Principles and Applications of Micro Transducers
Spring/2001, 1-1, p8
Intercept error:
 a  a1  a 
Slop error:
b  

s2  s1

s1
s2  s1
NTHU ESS5841
F. G. Tseng
The Principles and Applications of Micro Transducers
Spring/2001, 1-1, p9
Hysteresis
A deviation of the sensor’s output at a specified point of input
signal when it is approached from opposite directions.
Nonlinearity
The maximum deviation (L) of the real transfer function
from the approximation straight line.
The approximation straight line can be determined by:
Terminal points (line 1 in figure), least squares (line 2),
tangent line to the point of interest (line 3).
Independent linearity: referred to “best straight line”,
which is a line midway between two parallel straight lines
closest together and enveloping all output values on the real
transfer function.
Note: manufactures often publish smallest possible
NTHU ESS5841
F. G. Tseng
The Principles and Applications of Micro Transducers
Spring/2001, 1-1, p10
number to specify nonlinearity, without defining what
method was used.
Saturation
at some levels of the input stimulus, the output signal no
longer will be responsive.
NTHU ESS5841
F. G. Tseng
The Principles and Applications of Micro Transducers
Spring/2001, 1-1, p11
Repeatability(reproducibility)
The inability of a sensor to represent the same value
under identical conditions. Expressed as the maximum
difference between output readings as determined by two
calibrating cycles.
r 

100%
FS
Possible source: thermal noise, build up charge, material
plasticity, etc.
Dead band
The insensitivity of a sensor in a specific range of input
signals.
Resolution
Smallest increments of stimulus which can be sensed.
NTHU ESS5841
F. G. Tseng
The Principles and Applications of Micro Transducers
Spring/2001, 1-1, p12
For example:
1. Minimum equidistant displacement: a minimum
angle of 0.5
2. Percents of full scale(FS): an angular sensor has a
full scale 270, 0.5 resolution may be specified as
0.181% of FS.
3. Number of bits: 8-bit resolution.
The resolution may be specified as typical, average, or
worst. When there is no measurement steps in the output
signal, is said that the sensor has continuous or infinitesimal
resolution.
Output impedance
When interface a sensor with the electronic circuit, output
impedance is important.
See the figure for parallel (left) and serial (right) connections
of the output to the circuit input.
NTHU ESS5841
F. G. Tseng
The Principles and Applications of Micro Transducers
Spring/2001, 1-1, p13
To minimize output signal distortions,
voltage connection (A): Zout low, Zin High.
current connection(B) : Zout high, Zin low.
Excitation
The signal needed for the active transducer operation,
usually specified as a range of voltage or current (sometimes
including frequency, stability). Variations in the excitation
may alter the transducer’s transfer function.
For example:
Max current through a thermistor: 50 A in air, 200 A
in water.
Dynamic characteristics
Transfer function describes only the static operation
condition of a sensor. When an input stimulus varies, a
sensor response generally does not follow with input perfectly.
Dynamic characteristic: time depend characteristic. Note:
the difference between static errors and dynamic errors.
NTHU ESS5841
F. G. Tseng
The Principles and Applications of Micro Transducers
Spring/2001, 1-1, p14
Warm-up time: the time between applying to the sensor
power or excitation signal and the moment when the
sensor can operate within its specified accuracy.
Frequency response: how fast the sensor can react to a
change in the input stimulus, in Hz or rad/sec. As in
the following figure. A commonly used frequency
limited is –3 dB, at which the output signals drop by
about 30%. The frequency response limit, fu, is
often called upper cutoff frequency.
Speed response: related to frequency, defined as input
stimulus/unit time.
Time constant: τ=RC. C: electrical capacitance, or
thermal capacity, etc., R: electrical resistance, or
thermal resistance, etc.
For example: first order system:
S  S m (1  e  t /  ) , Sm: steady-state output.
When t=τ, S/Sm=0.6321
For t= τ: 63%
t=2τ: 86.5%
t=3τ: 95%
Lower cutoff frequency: The lowest frequency of stimulus
the sensor can process. It shows how slowly
changing stimuli the sensor can process. As shown
on the above figure on the right side. For first order
system:
S  S m (1  e  t /  u )e  t /  L
The relationship between cut off frequency fc and time
constant:
NTHU ESS5841
F. G. Tseng
The Principles and Applications of Micro Transducers
Spring/2001, 1-1, p15
fc 
0.159

Phase shift: How the output signal lags behind in
representing the stimulus change, angular
degrees or rads. Phase lag reduces the phase
margin of the system and may result in the
overall instability.
Resonant (natural) frequency: the frequency point at
which sensor resonates. For the second order
system, first order system would not resonant.
Operation should be below 60% of this
frequency. (however, some sensors operate in
this region: glass breakage detectors, gyroscope,
etc…)
Damping: Progressive reduction or suppression of the
oscillation in the sensor having higher than the first
order response.
s 2  2 z n s   n2  0,
z

n
(z, damping
NTHU ESS5841
F. G. Tseng
The Principles and Applications of Micro Transducers
Spring/2001, 1-1, p16
factor)
damping factor=F/A=A/B=B/C…
Environmental Factors
Storage conditions: non-operation environmental limits to
which a sensor may be subjected during a specified
period without permanently altering its performance
under normal operating conditions.
Need to be considered: temperature, humidity,
maximum pressure, presence of some gases or
contamination fumes, etc.
Short and long term stabilities (drift):
short term stability: in minutes, hours or days, is
bi-directional, and can be described as ultra-low
frequency noise.
Long term stability: related to aging of the sensor
materials, irreversible process, unidirectional, in
months or years. Aging greatly depends on
NTHU ESS5841
F. G. Tseng
The Principles and Applications of Micro Transducers
Spring/2001, 1-1, p17
environmental storage and operating conditions.
Pre-age process can improve long term stability, by
cycling the extreme conditions on the sensors.
Environmental stability: temperature of air and surrounding
components, humidity, vibration, ionizing radiation,
electromagnetic fields, gravitational forces, etc.
Protection is desired such as protective box, electrical
shielding, thermal isolation, or a thermostat.
Temperature factors: Many sensors change with temperature
and transfers function shift significantly. Temperature
also affect dynamic characteristics, when sensor
employing viscous damping.
Self heating error: when an excitation signal is absorbed by
the sensor and changes its temperature and affect its
accuracy.
Sensor's
temperature
increase
above
surroundings may be found from the formula:
its
V2
T  
(vc   ) R
: sensor's mass density, v: volume of the sensor, c:
specific heat, : coefficient of thermal
conductivity. R: sensor resistance, V operation
voltage.
So increase  (well thermal couple, increase contact
area, applying thermally conductive grease or
adhesive), high R, and decrease V are desirable.
NTHU ESS5841
F. G. Tseng
The Principles and Applications of Micro Transducers
Spring/2001, 1-1, p18
Reliability
The ability of a sensor to perform a required function
under stated conditions for a stated period. Reliability
is not a characteristic of drift of noise stability, but it
specifies the possibility of a failure under normal
operation conditions.
MTBF (mean time between failure): indirect, hard to
apply to everyday use.
Accelerated life qualification: using real world stresses
and compressing test time, which can identify
first failure mode.
Environment tests for reliability:
1. High temperature/high humidity
2. Mechanical shocks
3. Extreme Storage conditions
4. Thermal shock or temperature cycle (TC)
5. Sea conditions
Application Characteristics
Design, price, Weight and overall dimensions.
NTHU ESS5841
F. G. Tseng
The Principles and Applications of Micro Transducers
Spring/2001, 1-1, p19
 Actuator characteristics
Repeatability:
How repeatable the behavior of an actuator is.
R  Yi ( X )  Yk ( X )
i, k different cycles
worse case:
Rm  Ymax ( X )  Ymin ( X )
Result from: internal relaxations, friction, structure
instability…
Linearity:
The linearity of its output as a function of its input and is
expressed as a percent of its full-scale output. Refer to a
NTHU ESS5841
F. G. Tseng
The Principles and Applications of Micro Transducers
Spring/2001, 1-1, p20
best fit straight line, or a line drawn between the minimum
and maximum output. (the base line is Yr(X))
L  Y ( X )  Yr ( X ) max
Precision (精確度):
How exactly and reproducibly a desired actuation is executed.
Note: precision does not imply accuracy and accuracy
without precision is not meaningful.
Accuracy (正確度):
A measure of how closely the output of the actuator
approximates a desired calibrated scale.
 a (%)  100(Ya  Yt ) / Yt
Yt: true value, Ya: actuated value
For expressed as full scale output (FSO):
 FSO (%)  100(Ya  Yt ) / YFSO
Note:
 FSO   a
Resolution (解析度):
The smallest increment in the value of the input that results
in a detectable actuation.
NTHU ESS5841
F. G. Tseng
The Principles and Applications of Micro Transducers
Spring/2001, 1-1, p21
Rmax (%)  100( min ) /( max   min )
δmax: Maximum displacement increment, δmin: Minimum
displacement increment
Sensitivity (靈敏度):
The ratio of the actuator output (Y) to an incremental
change in its input (X).
S  Y / X
Sensitivity may vary as a function of temperature and other
environmental parameters, and may not be linear over the
output range.
NTHU ESS5841
F. G. Tseng
The Principles and Applications of Micro Transducers
Spring/2001, 1-1, p22
Smallest Inducible Output (sIO):
The smallest change in the actuator output that can be
induced and detected. (letter d in figure)
sIO is determined by the actuation mechanism and the noise
at the actuator output.
Piezoelectric actuators: small, from thermal vibration
TiNi shape memory alloy, magnetic actuators: large, from
bistable situation.
Electrostatic actuators: small.
Threshold:
Starting from zero input, the smallest initial increment in the
input that results in a detectable actuator output. (letter a in
the figure). Due to actuator non-linearity, different from
sIO.
Conformance (一致性):
The closeness of the experimental actuator output to a
theoretical curve or curves obtained using least-squares, or
other fits. Expressed in %FSO (full scale output)
Hysteresis (遲滯):
The difference in the actuator output Y when Y is reached
from two opposite directions, i.e., from Y- and Y+.
Caused by a lag in the action of their deformable parts.
(magnetic actuators: alignment of magnetic moments)
NTHU ESS5841
F. G. Tseng
The Principles and Applications of Micro Transducers
Spring/2001, 1-1, p23
Note: hysteresis is different from backlash (b in figure).
Instability and Drift:
Change in actuator output (with zero input) with time,
temperature and any other parameter.
Load-bearing Capability Stiffness:
Actuator's behavior when connected to a load. (note the
equilibrium position on the curve)
Span:
The full scale operation rage of the actuator output.
Speed:
v  dY / dt
for over a cycle
v  Y /( on   off )
NTHU ESS5841
F. G. Tseng
The Principles and Applications of Micro Transducers
Spring/2001, 1-1, p24
Step-Response:
For a second order system, consider the system response :
critical, under, over damped. For a over damped system:
Power Efficiency:
Conservation of energy:
Pin  Ps  Pout  Pw
Pin : input power, Ps : power drawn from power source, Pout :
power output, Pw: internal power consumption (waste)
Power efficiency:
 p  Pout /( Pin  Pw  Pout )
P~F*S/t, however, in most of mechanical actuators, F has a
nonlinear relationship to S, better to use power to express the
ability of energy transformation. Power efficiency for
NTHU ESS5841
F. G. Tseng
The Principles and Applications of Micro Transducers
Spring/2001, 1-1, p25
biological actuators (i.e., muscle), ranges from 0.25 to 0.5.
Noise:
Results from: manifestations of mechanical or electrical
fluctuations occurring in the actuators.
Determined by: actuation mechanism, fabrication methods
(grain size and boundary situation.)
Scaling:
Using a scalability measure to evaluate the size reduction
effect—better yield , performance or not.
Sc  (d / dV )
Overall Performance:
1. the worst case approach
2. the root-mean-square approach
NTHU ESS5841
F. G. Tseng
The Principles and Applications of Micro Transducers
Spring/2001, 1-1, p26
 Statistical analysis
Under noisy conditions, the sensors and data acquisition
systems are tested and analyzed by statistical methods.
Distortions may be systematic: nonlinearity, hysteresis, dead
band, miscalibration, etc, or random to have noise
characteristics.
Descriptive statistics: classifies data- performance
histograms that correspond to frequency
distribution, computation of sample means,
medians, modes, variance, means absolute
deviations, and ranges.
Inferential statistics: relies on a limited number of data to
make decision about an overall performance of
the device.
Mean value:
n
S 
S
i 1
i
n
Mean absolute deviation
n
M . A.D. 
 (S
i 1
i
n
Sample standard deviation
S)
NTHU ESS5841
F. G. Tseng
The Principles and Applications of Micro Transducers
Spring/2001, 1-1, p27
n
v
2
(
S

S
)
 i
i 1
n 1
Gaussian (Normal) Distribution:
Distribution: the frequency of occurrence
f (s) 
1 
e
2
( s  s )2
2 2
,
ss

: Standard normal value
Standard deviation: 
68% of values falls within 
95% of values falls within 2
99.7% of values falls within 3
NTHU ESS5841
F. G. Tseng
The Principles and Applications of Micro Transducers
Spring/2001, 1-1, p28
NTHU ESS5841
F. G. Tseng
The Principles and Applications of Micro Transducers
Spring/2001, 1-1, p29
 MEMS Fabrication fundamentals:
Lithography, PVD, CVD, Wet etching, Dry etching, Bulk
micromachining, surface micromachining, LIGA/Deep UV
lithography, packaging and wafer bonding…
Will be considered a common knowledge in this course and will not
be elaborated. Those who are not familiar with the aforementioned
topics please refer to Introduction to MEMS, MEMS design,
MEMS Fabrication Lab class notes, or related references.
 MEMS literatures:
Journals:
JMEMS: Journal of Microelectromechanical Systems, IEEE/ASME joint
publication (ISSN 1057-7157), quarterly from March 1992.
JMM: Journal of Micromechanics and Microengineering, American Institute
of Physics (ISSN 0960-1317), quarterly from March 1991.
S&A: Sensors and Actuators A, Elsevier Sequoia (ISSN 0924-4274), 5 Vol.
Per year, 3 issues per volume.
S&M: Sensors and Materials, Scientific Publishing Division of MY, Japan
(ISSN 0914-4935). 6 issues per volume.
B&B: Biosensors and Bioelectronics, Elsevier Science (ISSN 0956-5663), 12
issues per year from 1986
BM: Biomedical Microdevices-BioMEMS and Biomedical Nanotechnology,
Kluwer Academic Publishers (ISSN: 1387-2176), 2 issues per year from
1999.
MST: Micro system Technology, Germany.
Conferences:
MEMS##: IEEE Micro Electro Mechanical Systems
1987 and annual form 1989, held in February (Abstract due in Sep.)
ASME IMECE: ASME winter annual meeting
Annual (MEMS symposium from 1990), in Nov/Dec (Abstract due in Feb.)
Trans##: International Conference on Solid-State Sensors and actuators
(Transducers “xx) biennial from 1981, in June (Abstract due in Dec.)
HH##: IEEE Solid-State Sensor and Actuator Workshop, biennial from 1984,
NTHU ESS5841
F. G. Tseng
The Principles and Applications of Micro Transducers
Spring/2001, 1-1, p30
in June (Abstract due in Jan.)
SPIE##: International Society for Optical Engineering, conference for
MEMS or Optical MEMS, annual
EURO sensor
Actuator'##, Europe conference
Harmst'##, follow transducer
Reference:
1. Micromachined Transducers source book, Gregory T.A. Kovacs, McGraw Hill,
1998, chapter 1.
2. Microactuators, Electrical, Magnetic, Thermal, Optical, Mechanical, Chemical
and Smart Structures, Massood Tabib-Azar, Kluwer Academic Publishers, 1998,
chapter 1.
3. AIP Handbooks of Modern Sensors, Jacob Fraden, American Institute of Physics,
New York, 1993, chapter 2.