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Transcript
Some Applications of Ferroelectric Ceramics
1.
2.
Capacitors
Ferroelectric Thin Films
2.1 Ferroelectric Memories
2.2 Electro-Optic Applications
2.2.1 Thin Film Waveguides
2.2.2 Thin Film Optical Memories and Displays
2.2.3 Thin Film Capacitors
2.2.4 Pyroelectric Detectors
2.2.5 Surface Acoustic Wave Substrates
Some Applications of Piezoelectric Ceramics
1.
2.
3.
4.
5.
6.
7.
Medical Ultrasound Applications
Gas Ignitors
Displacement Transducers
Accelerometers
Piezoelectric Transformers
Impact Printer Head
Precision X-Y Stage
Capacitors
A parallel plate capacitor made of a dielectric material sandwiched
between two electrodes
C = eoerA/d
C is the capacitance , er the relative dielectric permittivity
A the area of the electrode, d the thickness of the dielectric
High volume efficiency arises from large relative dielectric
permittivity, large area, and small thickness
BaTiO3 very high er  small disk capacitor
(> 50 % of the ceramic capacitor market)
The Volume Efficiency greatly enhanced by
Multilayer Ceramic Capacitors (MLC)
Tape Casting Technique
Ferroelectric Thin Film
Applications for electronic and electro-optic devices
Materials of Interest
BT, PT, PZT, PMN Perovskite
Bi4Ti3012, (Pb, Ba)Nb2O6
Applications
Electronic
non-volatile memories, thin-film capacitors, pyroelectric
sensors, surface acoustic wave (SAW) substrates
Electro-optic
optical waveguide and optical memories and displays
Ferroelectric Thin Film Memories
Current Dominating Market is based on Semiconductor Memories
Dynamic Random Access Memories (DRAMs)
Static Random Access Memories (SRAMs)

Disadvantages : Volatile (lost of information when out of power)

Solutions are with Non-Volatile Memories
Complementary Metal Oxide Semiconductor (CMOS) (with back-up battery)
Electrically Erasable Read Only Memories (EEPROMs)

Disadvantages : Very Expensive

Possible Solution with Non-Volatile Ferroelectric Memories
Ferroelectric Random Access Memories (FRAMs)
High Speed (30 ns cycle time for read/erase/rewrite)
High Density (4 mm2 cell size)
Ferroelectric Thin Film Memories
Ferroelectric Random Access Memories (FRAMs)
Storing data using the reversible polarization mechanism of ferroelectrics
“Polarization Switching”

Non-Volatile Memories
Hysteresis Properties : Remnant Polarization after Field Removed

Thin Film Fabrications with PVD, CVD, LPE, EGM, MBE, Laser, or Sol-Gel

Several Critical Processing Parameters
Ec, Pr, Hysteresis Characteristics
Small Film Thickness is better to minimize switching field
(200-300 nm thick films require ~ 5 V potential for switching)
Interface with substrate to minimize non-ferroelectric phases
Inert electrode with PZT film at high temperature
Minimize “fatigue” problem from which FRAMs lose memory with time
(Fatigue resistance of 1012 cycles is required)
Extensive On-Going Research
Ferroelectric Thin Film for Electro-Optics
Ferroelectric Thin Film for Optical Memories and Displays

Replacing PLZT bulk ceramics

Advantages of thin films
Simplification of the display devices
Lower operating voltage

Require large electro-optic coefficients
Strong photosensitivities for the film PZT and PLZT
Ferroelectric Thin Film for Electronics
Thin Film Capacitors

Large volume efficiency

BT and PMN are mostly choice of materials
Ferroelectric Thin Film for Electronics
Ferroelectric Thin Film for
Pyroelectric Detectors

Heat sensing applications

Advantages of thin films
Low cost fabrication, as compared with
single crystals
Convenient geometry for device design

Materials of Interest
TGS, LiTaO3, (Sr, Ba)Nb2O6, PT, LaPT, and PZT
Thin Film for Surface
Acoustic Wave (SAW)
Substrates

Interdigital electrodes as SAW
detector functionality

LiNbO3, LiTaO3, PZT

Delay lines and filter
applications in television and
microwave communication
Piezoelectric Ceramic Applications
Medical Ultrasound Applications

Piezoelectric ceramics : Active and Passive Transducers

Passive : Sound receiver
Active : Sound transmitter

Pulse Echo Mode : Both active and passive functions
sound waves penetrate the medium with faint echo

Ultrasound imaging is done without the cutting/surgery
Resolution better than X-rays (which can done in bones)
Lower power levels

Pulse Echo method employed

Frequency span between 1.5-30 MHz
Piezoelectric Ceramic Applications
Applications in large frequency span

Operating Frequency depends on samples and organs to be diagnosed

2-5 MHz: Abdominal, Obstetrical, Cardiological applications
5-7.5 MHz : Pediatric and peripheral vascular applications
10-30 MHz : Intravascular, intracardiac, eye-imaging applications

Resolution at a certain frequency is calculated from c = 
Human body, c ~ 1500 m/s  Resolution varies 1-50 mm
( when frequency ~ 1.5-30 MHz)

Impedance Z issue
Matching layer at the interface

Soft PZT ceramics are widely used for medical imaging
Piezoelectric Ceramic Applications
Gas Ignitors

Voltage generator consists of two oppositely pole ceramic cylinders and attached
end to end to double the charge available for the spark

Two Stages Process for Spark Generation

1. Force F on ceramic causes change of dL (under open circuit)
2. Discharge through gap causes closed circuit
Piezoelectric Ceramic Applications
Displacement Transducers

Bimorph Configuration

Two long poled piezoelectric ceramic specimens bond together

1. Force F on the cantilever beam results in induced electric field
Piezoelectric Ceramic Applications
Displacement Transducers

Bimorph Configuration

Two long poled piezoelectric ceramic specimens bond together

2. Electric Field E on the cantilever beam results in induced bending
Piezoelectric Ceramic Applications
Accelerometers

Device that gives an electrical output proportional to acceleration

Shear mode utilized

Poled along axis, but another new electrodes in inner and outer parts of the tube
Piezoelectric Ceramic Applications
Piezoelectric Transformer

Low-to-High Voltage Transformer with piezoeletric plates

Electrode configurations vary, samples are poled separately in different direction

A length mode is excited in the large area by AC field
Piezoelectric Ceramic Applications
Impact Printer Head

Dot-matrix printer driven by piezoelectric ceramic actuators
Precision XY stage

Piezoelectric Actuators
Piezoelectric Ceramic Applications
Other Examples of Applications of Piezoelectric Ceramics
Actuators
Precision motion control, autofocusing cameras ink-jet printer, positioning
VCR head, micromachining metals, valves
Ultrasonic Motors
Compact and high efficiency motors
Delay Lines and Wave Filters
Delay Line : in TV and other household appliances
Wave Filters : resonant behavior of piezoelectric ceramics/quartz
Sonic Energy Generation
High-Fi Tweeter made from circular bimorph
Others: Generators ( solid-state batteries), Sonic and Ultrasonic
Transducers (buzzers, microphones, speakers, echo-sounders,
atomizers, welding equipment, cleaning process), Sensors
(pressure sensors, knock sensors)