Some Applications of Ferroelectric Ceramics

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Some Applications of Ferroelectric Ceramics

• 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. Medical Ultrasound Applications
2. Gas Ignitors
3. Displacement Transducers
4. Accelerometers
5. Piezoelectric Transformers
6. Impact Printer Head
7. Precision X-Y Stage

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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 (gt 50 of the ceramic
capacitor market) The Volume Efficiency greatly
enhanced by Multilayer Ceramic Capacitors
(MLC) Tape Casting Technique
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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
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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)
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Ferroelectric Thin Film Memories
Ferroelectric Random Access Memories
(FRAMs) Storing data using the reversible
polarization mechanism of ferroelectrics Polariza
tion 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
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Ferroelectric Thin Film for Electro-Optics
Ferroelectric Thin Film for Optical Memories and
Displays ? Replacing PLZT bulk ceramics ? Advantag
es 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
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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, La-PT, 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
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Piezoelectric Ceramic Applications
Medical Ultrasound Applications ? Piezoelectric
ceramics Active and Passive Transducers ? Passiv
e 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
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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
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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
• ?
• Force F on ceramic causes change of dL (under
  open circuit)
• Discharge through gap causes closed circuit

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Piezoelectric Ceramic Applications

• Displacement Transducers
• ?
• Bimorph Configuration
• ?
• Two long poled piezoelectric ceramic specimens
  bond together
• ?
• Force F on the cantilever beam results in induced
  electric field

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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
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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
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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
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Piezoelectric Ceramic Applications
Impact Printer Head ? Dot-matrix printer driven
by piezoelectric ceramic actuators
Precision XY stage ? Piezoelectric Actuators
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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)