FERROELECTRIC CERAMICS properties, processing and applications

1、FERROELECTRIC CERAMICS:properties, processing and applicationsIgnacio Martin-Fabiani, Dai Peng, Fang Yeyu and Sohaib AfzalTuesday, 17 October 2006IntroductionA ferroelectric ceramic mixes the smartness of a ferroelectric material and the tailoring possibilities of ceramics. Since both kind of materi

2、als exhibit many interesting properties, the mixture should be goodFerroelectrics: ferroelectric domainsFerroelectric domains are generated by coupling between dipole moments of atoms.When subjected to electric field, the domains pointing towards its direction start to grow over its neighbouring dom

3、ains.Ferroelectrics: hysteresis loopSaturation and remanent polarizationCoercive fieldPossibility to reverse the polarizationSmart material: it keeps information (remanent poalrization)Ferroelectrics: phase transitionFerroelectricity is a phase transition (Curie point)Ferroelectric phase has always

4、lower symmetryExample: BaTiO3 (cubic changes into tetragonal)Ferroelectrics: summaryPresent spontanous polarizationPolarization can be inversedFerroelectric domainsHysteresis loopFerroelectricity is a phase transitionPiezoelectric and pyroelectric effectCeramics is a wide term The term ceramics cove

5、rs all inorganic non-metallic materials whose formation is due to the action of heat.So you could think something like this but we are dealing with ADVANCED ceramics!We can control, modify and optimize its properties by tailoring the material!Properties of ceramicsMechanical: poor toughness (under s

6、tudy)Electrical: semiconductors, superconductors, piezoelectrics, pyroelectrics, ferroelectrics (BaTiO3, PZT)High resistance to abrasion Excellent hot strengthChemical inertnessWe can tailor properties for specific applicationsWhy are ferroelectric ceramics so important?FERROELECTRICSHigh permittivi

7、tiesSpontaneus polarizationElectric conducticity can be controlledPiezoelectric and pyroelectric effectOptical anisotropy, electrooptic an photorefractive deffectCERAMICSBroad range of chemical compositionControl of grain size, porosityPossibility of varying its shape and size.High resistance to abr

8、asionExcellent hot strengthChemical inertnessAll this properties lead to a lot of potential applications!2.Processing of Ferroelectric ceramics1. General Procedure of Processing Raw MaterialsMixingSinteringCalciningMillingCharacter -izationPoling Binder Burnout1. raw materials Weighing the raw mater

9、ials according to the stoichiometric formula of the ferroelectric ceramic desired .2. Mixing Mixing the powders either mechanically or chemically Mechanical mixing is usually done by either ball milling or attrition milling for a short time. Chemical mixing on the other hand is more homogeneous as i

10、t is done by precipitating the precursors in the same container. The solid phase reaction takes place between the constituents giving the ferroelectric phase during the calcination step 4. Milling The lumps are ground by milling after calcining.5. binder burnout After shaping, the green bodies are h

11、eated very slowly to between 500-600 C in order to remove any binder present. After the binder burnout is over, the samples are taken to a higher temperature for sintering to take place. it does not show any piezoelectricity when the ferroelectric ceramic is cooled after sintering . Piezoelectric be

12、havior can be induced in a ferroelectric ceramic by a process called poling .In this process a direct current (dc) electric field with a strength larger than the coercive field strength is applied to the ferroelectric ceramic at a high temperature, but below the Curie point. On the application of th

13、e external dc field the spontaneous polarization within each grain gets orientated towards the direction of the applied field. This leads to a net polarization in the poling direction Two special important methods widely uses in the labs .Metal Organic Decomposition (MOD) (2)hot-pressed solid-state

14、sintering method1. MODMOD: Metal Organic DecompositionDesired thickness of the film is achieved spin-coat the solution on a bulk Si wafer at 4000 rpm, 20 seconds . the film is baked on hot plate at 150 for 10 minutes to remove the solvent . then the film is given a pyrolysis heat treatment in a furn

15、ace at 470 for 30 minutes to remove the residual organics and promote chemical reaction Ferroelectric BST-thick film ceramic on analumina substrate2. hot-pressed solid-state sintering method SEM micrograph of a cross section of PLZT transparent ferroelectric ceramics. hot-pressed solid-state sinteri

16、ng methodPbO, La2O3, ZnO, Nb2O5, ZrO2, and TiO2 with purity of 99.499.8% and micrometer particle size were used as starting materials. The stoichiometric mixture was ballmilled in a plastic container with zirconia grinding media in alcohol solution, then dried and ground. The ground mixture powders

17、were pressed under 80 kg/pressure into a cylindrical bar of 60 mm in diameter and 60 mm in height.hot-pressed solid-state sintering method During a sintering process, an oxygen flow of 3 L/min was passed through the oven. The sintering temperature was elevated to 950 C at a rate of 200 C/h and kept

18、for 12 h, then pressure was gradually applied to the sample until 480 kg/ while the oven temperature was increased to 1200 C at the same time. hot-pressed solid-state sintering method The temperature and pressure were kept for 6 h before the pressure was released. Subsequently, the temperature was c

19、ontinuously increased to 1250 C in 12 h and kept for 10 h. After sintering, the oven was cooled down to 950 C at a rate of 140 C/h and then cooled naturally until room temperature. The sintered specimen was cut and polished to obtain the required size for different measurements.Applications of Ferro

20、electric Ceramics ( general overview )backgroundFerroelectric ceramics are used in a very broad range of functional ceramics and form the materials base for the majority of electronic applications. These electronic applicators account for more than 60% of the total high technology ceramics market wo

21、rldwide Capacitors Basic principle C is the capacitance, is the permittivity of free space, is the relative dielectric permittivity, t is the distance between the electrodes, A is the area of the electrodes. multilayer ceramic (MLC)The volumetric efficiency can be further enhanced .consists of alter

22、nate layers of dielectric and electrode material. Ferroelectric Memories FRAM (Ferroelectric Random Access Memory) is a non-volatile memory combining both ROM and RAM advantages in addition to non-volatility features. It has higher speed in write mode, lower power consumption and higher enduranceOve

23、rview of FRAM Advantages over EEPROMTransaction Time - 30,000 times faster than EEROM Energy Consumption 200 times lower power consumption compare to EEPROM 1 FRAM Cycle is just Reading 1 EEPROM Cycle consists of erasing , writing and readingEndurance 100,000 times higher endurance over EEPROM and t

24、he energy consumption is at 64Byte every write cycle Electro-optic Applications Ferroelectric Thin Film Waveguides. An optical waveguide controls the propagation of light in a transparent material (ferroelectric thin film) along a certain path Ferroelectric Thin Film Optical Memory Displays . Other

25、Ferroelectric Thin Film Applications Pyroelectric Detectors :Pyroelectric detectors are current sources with an output proportional to the rate of change of its temperature Surface Acoustic Wave Substrates An elastic wave generated at the input interdigital transducer (IDT) travels along the surface

26、 of the piezoelectric substrate and it is detected by the output interdigital transducer. These devices are mainly used for delay lines and filters in television and microwave communication applications Most Common Commercial Ferroelectric CeramicLead Zirconate Titanate (PZT)Chemical formula Pb Zrx

27、Ti1-x O3 “Perovskite” ABO3 A and B are different in size A cation is at centre B cation is at the corner O atom are at centre of unit cell faces. Lead Zirconate Titanate (PZT)generates a voltage when some mechanical stress is applied piezoelectric effect useful for sensor and actuator applicationDop

28、ing Acceptor doping internal friction losses piezoelectric constant Donor doping internal friction losses piezoelectric constantLead Zirconate Titanate (PZT)Poling High Temperature High VoltageRepeat to achieve high piezoelectric constantPZT Thin FilmsUsed in number of devicesThickness of 90nmlow cr

29、ystallization temperature good surface morphology high remnant polarization Application of PZTAcoustic Device for underwater Application Acoustic Device for underwater Application Ultrasonic Sensors Commercial sound waves generating devices use PZT thin films Bulky ferroelectric ceramic sensors Acoustic Device for underwater ApplicationHence Thin films are used Low fabrication cost Film deposition techniques Electron beam evaporation 1 Rf diode sputtering 2 Ion beam deposition 3 RF planar magnetron s