Ferroelectric ceramics:properties,processing and applications
اسلاید 1: FERROELECTRIC CERAMICS: properties, processing and applicationsIgnacio Martin-Fabiani, Dai Peng, Fang Yeyu and Sohaib AfzalTuesday, 17 October 2006
اسلاید 2: IntroductionA ferroelectric ceramic mixes the smartness of a ferroelectric material and the tailoring possibilities of ceramics. Since both kind of materials exhibit many interesting properties, the mixture should be good…
اسلاید 3: Ferroelectrics: 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 domains.
اسلاید 4: Ferroelectrics: hysteresis loopSaturation and remanent polarizationCoercive fieldPossibility to reverse the polarizationSmart material: it keeps information (remanent poalrization)
اسلاید 5: Ferroelectrics: phase transitionFerroelectricity is a phase transition (Curie point)Ferroelectric phase has always lower symmetryExample: BaTiO3 (cubic changes into tetragonal)
اسلاید 6: Ferroelectrics: summaryPresent spontanous polarizationPolarization can be inversedFerroelectric domainsHysteresis loopFerroelectricity is a phase transitionPiezoelectric and pyroelectric effect
اسلاید 7: Ceramics is a wide term… The term ceramics covers all inorganic non-metallic materials whose formation is due to the action of heat.So you could think something like this…
اسلاید 8: …but we are dealing with ADVANCED ceramics!We can control, modify and optimize its properties by tailoring the material!
اسلاید 9: Properties of ceramicsMechanical: poor toughness (under study)Electrical: semiconductors, superconductors, piezoelectrics, pyroelectrics, ferroelectrics (BaTiO3, PZT…)High resistance to abrasion Excellent hot strengthChemical inertnessWe can tailor properties for specific applications
اسلاید 10: Why are ferroelectric ceramics so important?FERROELECTRICSHigh permittivitiesSpontaneus polarizationElectric conducticity can be controlledPiezoelectric and pyroelectric effectOptical anisotropy, electrooptic an photorefractive deffectCERAMICSBroad range of chemical compositionControl of grain size, porosity…Possibility of varying its shape and size.High resistance to abrasionExcellent hot strengthChemical inertnessAll this properties lead to a lot of potential applications!
اسلاید 11: 2.Processing of Ferroelectric ceramics
اسلاید 12: 1. General Procedure of Processing Raw MaterialsMixingSinteringCalciningMillingCharacter -izationPoling Binder Burnout
اسلاید 13: 1. raw materials Weighing the raw materials according to the stoichiometric formula of the ferroelectric ceramic desired .
اسلاید 14: 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 it is done by precipitating the precursors in the same container.
اسلاید 15: 3.Calcination The solid phase reaction takes place between the constituents giving the ferroelectric phase during the calcination step
اسلاید 16: 4. Milling The lumps are ground by milling after calcining.
اسلاید 17: 5. binder burnout After shaping, the green bodies are heated very slowly to between 500-600° C in order to remove any binder present.
اسلاید 18: 6.SinteringAfter the binder burnout is over, the samples are taken to a higher temperature for sintering to take place.
اسلاید 19: 7.Polingit does not show any piezoelectricity when the ferroelectric ceramic is cooled after sintering . Piezoelectric behavior 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.
اسلاید 20: 8.Characterization On the application of the 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
اسلاید 21: Two special important methods widely uses in the labs .Metal Organic Decomposition (MOD) (2)hot-pressed solid-state sintering method
اسلاید 22: 1. MODMOD: Metal Organic Decomposition
اسلاید 23: Desired 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 furnace at 470 ℃for 30 minutes to remove the residual organics and promote chemical reaction
اسلاید 24: Ferroelectric BST-thick film ceramic on an alumina substrate
اسلاید 25: 2. hot-pressed solid-state sintering method SEM micrograph of a cross section of PLZT transparent ferroelectric ceramics.
اسلاید 26: hot-pressed solid-state sintering methodPbO, La2O3, ZnO, Nb2O5, ZrO2, and TiO2 with purity of 99.4–99.8% 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 were pressed under 80 kg/pressure into a cylindrical bar of 60 mm in diameter and 60 mm in height.
اسلاید 27: 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 for 1⁄2 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.
اسلاید 28: hot-pressed solid-state sintering method The temperature and pressure were kept for 6 h before the pressure was released. Subsequently, the temperature was continuously increased to 1250 °C in 1⁄2 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.
اسلاید 29: Applications of Ferroelectric Ceramics ( general overview )
اسلاید 30: 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 worldwide
اسلاید 31: 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.
اسلاید 32: multilayer ceramic (MLC)The volumetric efficiency can be further enhanced .consists of alternate layers of dielectric and electrode material.
اسلاید 33: 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 endurance
اسلاید 34: Overview of FRAM
اسلاید 35: Advantages over EEPROMTransaction Time - 30,000 times faster than EEROM
اسلاید 36: Energy Consumption 200 times lower power consumption compare to EEPROM 1 FRAM Cycle is just Reading 1 EEPROM Cycle consists of erasing , writing and reading
اسلاید 37: Endurance 100,000 times higher endurance over EEPROM and the energy consumption is at 64Byte every write cycle
اسلاید 38: 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 .
اسلاید 39: Other Ferroelectric Thin Film Applications Pyroelectric Detectors :Pyroelectric detectors are current sources with an output proportional to the rate of change of its temperature
اسلاید 40: Surface Acoustic Wave Substrates An elastic wave generated at the input interdigital transducer (IDT) travels along the surface 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
اسلاید 41: Most Common Commercial Ferroelectric Ceramic
اسلاید 42: Lead Zirconate Titanate (PZT)Chemical formula Pb Zrx 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.
اسلاید 43: Lead Zirconate Titanate (PZT)generates a voltage when some mechanical stress is applied … piezoelectric effect useful for sensor and actuator applicationDoping Acceptor doping internal friction losses piezoelectric constant Donor doping internal friction losses piezoelectric constant
اسلاید 44: Lead Zirconate Titanate (PZT)Poling High Temperature High VoltageRepeat to achieve high piezoelectric constant
اسلاید 45: PZT Thin FilmsUsed in number of devicesThickness of 90nmlow crystallization temperature good surface morphology high remnant polarization
اسلاید 46: Application of PZTAcoustic Device for underwater Application
اسلاید 47: Acoustic Device for underwater Application Ultrasonic Sensors Commercial sound waves generating devices use PZT thin films Bulky ferroelectric ceramic sensors
اسلاید 48: 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 sputtering [4] MOCVD [5] ECR [6] laser ablation [7] and sol-gel [8]
اسلاید 49: Fabrication0.25µm oxide layer0.3µm Pt. electrodePZT thin film deposition for 2 hours at 350˚C Annealing at 650˚C for 20 minutesCooled to room temperature
اسلاید 50: FabricationSEM patterns of deposited PZT thin film PZT thin film annealed at 850˚C for 5 minutes
اسلاید 51: FabricationLithography used to form a window in silicone substrate Oxide layer is removed 100µm diaphragm was created by etchingSuccessive layers of Pt, PZT and Pt deposited poling under an electric field of 10kV per cm at a temperature of 130˚C
اسلاید 52: Results Improved ferroelectric property Improved accuracyEconomical sensor Very small and light weightCan be used for application underwater
اسلاید 53: ResultsSenstivity
اسلاید 54: Applications Ultra Sonic CleanersSODARSONARMedical DiagnosticsPrinter Heads Gas LightersMicro PositionersActuatorsAnnunciatorsSensorsCapacitorsFRAMCeramic resonatorsMemory devices in thin film form
اسلاید 55: References of all material and diagrams are given in report
اسلاید 56: Thankyou for your kind attention !!
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