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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)
