Capacitors The multilayer ceramic (MLC) capacitors. The MLCC structure consists of alternate layers ofdielectric and electrode material. Each individual dielectric layer contributescapacitance to the MLCC as the electrodesterminate in a parallel configuration. The advances in preparation technology havemade it possible to make dielectric layers <1 µmthick.
Schematic of a typical multilayerceramic (MLC) capacitorCut-away view of multilayerceramic capacitor.
Applications of Ferroelectric ThinFilms Ferroelectric thin films have attracted attention forapplications in many electronic and electro-opticdevices. Applications of ferroelectric thin films utilize theunique dielectric, piezoelectric, pyroelectric, andelectro-optic properties of ferroelectric materials. Some of the most important electronic applications offerroelectric thin films include nonvolatile memories,thin films capacitors, pyroelectric sensors, andsurface acoustic wave (SAW) substrates. The electro-optic devices include optical waveguidesand optical memories and displays.
Semiconductor memories such as DRAM & SRAMcurrently dominate the market. However, the disadvantage of these memories is thatthey are volatile, i.e. the stored information is lost whenthe power fails. The non-volatile memories available at this time includecomplementary metal oxide semiconductors (CMOS)with battery backup and electrically erasable read onlymemories (EEPROMs). These non-volatile memories are very expensive.Ferroelectric Memories
FeRAM FeRAM is a type of nonvolatile RAM that uses aferroelectric film as a capacitor for storing data. FeRAM can achieve high-speed read/writeoperations comparable to that of DRAM, withoutlosing data when the power is turned off (unlikeDRAM). In addition to nonvolatility and high-speed operation,FeRAM cells offer the advantages of easyembedding into VLSI logic circuits and low powerconsumption, perhaps their greatest advantage formany applications.
FeRAM-embedded VLSI circuits have beenused in smart cards, radio frequency identification (RFID) tags, and as a replacement for BBSRAM (batterybacked-up static RAM), which is used in variousdevices to protect data from an unexpectedpower failure, as well as in many other SoC(system on a chip) applications.FeRAM
A memory cell, where one bit of data is stored, iscomposed of a cell-selection transistor and a capacitorfor 1T1C (one transistor, one capacitor)-type FeRAM. A major problem encountered when reducing the size ofthe memory cell is preventing reliability degradation. The reliability of FeRAM cells is dependent on the materials used (ferroelectric film, electrode, interlayerdielectric, etc.), fabrication process, device structure, memory cell circuit, and operation sequence.FeRAM
MFIS structures The MFIS structure is simple and small in area. Thus, it is suitable for high-density integration. In an MFIS structure, the effect of the leakagecurrent is localized around weak spots in the film;this is important in prolonging the data retentiontime. In other words, in an MFIS structure, the effect ofthe leakage current spreads out to the whole floatinggate, and the charge neutrality is completelydestroyed in a short time. Thus, an MFIS structure issuperior in this regard.
MFMIS structures In an MFMIS structure, it is possible to optimize thearea ratio between the ferroelectric and buffer layercapacitors, so that the induced charges on bothcapacitors match. In an MFMIS structure, the floating gate materialcan be so chosen that a highquality ferroelectric filmis formed on the floating gate and that constituentelements in the ferroelectric film do not diffuse intothe buffer layer and Si substrate.
Electro-optic Applications The requirements for using ferroelectricthin films for electro-optic applicationsinclude an optically transparent film with ahigh degree of crystallinity. The electro-optic thin film devices are oftwo types; one in which the propagation oflight is along the plane of the film (opticalwaveguides) and the other in which thelight passes through the film (opticalmemory and displays).
Other Ferroelectric Thin FilmApplicationsThin Film Capacitors: The high dielectric permittivity of ferroelectricceramics such as BaTiO3, PMN and PZT very usefulfor capacitor applications. The MLC capacitors have a very high volumetricefficiency (capacitance per unit volume) becauseof the combined capacitance of thin ceramic tapes(~ 10-20 m m) stacked one on top of the other.
Pyroelectric Detectors : Pyroelectricity is the polarization produced due toa small change in temperature. Single crystals of triglycine sulfate (TGS), LiTaO3,and (Sr,Ba)Nb2O6are widely used for heat sensingapplications. PbTiO3, (Pb,La)TiO3and PZT have been widelystudied for thin film pyroelectric sensingapplications.
Surface Acoustic Wave Substrates : SAW devices are fabricated by depositinginterdigital electrodes on the surface of apiezoelectric substrate. An elastic wave generated at the input interdigitaltransducer (IDT) travels along the surface of thepiezoelectric substrate and it is detected by theoutput interdigital transducer. These devices are mainly used for delay lines andfilters in television and microwavecommunication applications.
Schematic representation of the generation,propagation and detection of surface acousticwaves (SAW) on a piezoelectric substrate withinterdigital electrode.
Gas Ignitors It consists of two oppositelypoled ceramic cylindersattached end to end in order todouble the charge available forthe spark. The compressive force has tobe applied quickly to avoid theleakage of charge across thesurfaces of the piezoelectricceramic. The generation of the sparktakes place in two stages. Theapplication of a compressiveforce F on the poled ceramic(under open circuit conditions)leads to a decrease in thelength by dLD. The potential energy developedacross the ends must be higherthan the breakdown voltage ofthe gap, for sparking to occur.A piezoelectric spark generator
Gas Ignitors When the spark gap breakdownoccurs the second stage ofenergy generation starts. The electric discharge across thegap results in a change fromopen circuit conditions to closedcircuit conditions with the voltagedropping to a lower level. The combination of the strainsfrom the open and short circuitconditions produce more energythat can be dissipated in thespark. Usually PZT ceramic disks areused for this application.A piezoelectric spark generator
Actuators & SensorsSchematic description of the geometry and the working principleof the piezoelectric film applied in actuators and sensors.
Actuators & Sensors An important family of functional materialsare ferroelectrics or, more generally, polarmaterials. Their piezoelectricity can be used in sensors,actuators, and transducers; Their pyroelectricity is employed in infrareddetectors.
Piezoelectric Microactuator DevicesSchematic draw of optical scanning device withdouble layered PZT layer (a) and thefabricated device, (b) Mirror plate: 300×300(µm2, DPZT beam: 800 × 230 µm2).Schematic drawing of self-actuationcantilever with an integratedpiezoresistor.Micropump using screen-printed PZTactuator on silicon membrane.(Courtesy of Neil White, Univ. ofSouthampton, UK.)
Aplication of Magnetic Ceramics Entertainment electronic (Radio, TV) Computer Microwave applications (Radar,communication, heating) Recording Tape Permanent motor
Aplication of Magnetic Ceramics Spinel (cubic ferrites): Soft magnets Garnet (rare earth ferrites): Microwave devices Magnetoplumbite (hexagonal ferrites): Hardmagnets
Aplication of Soft Magnetics In the soft magnetic materials, only a small field isnecessary to cause demagnetization and very smallenergy losses occur per cycle of hysteresis loop. This is important for applications such astransformers used in touch tone telephones orinductors or magnetic memory cores. During used a soft ferrites has its magnetic domainsrapidly and easily realigned by the changingmagnetic field.
Aplication of Hard Magnetics A hard (or permanent) ceramic magnet achieves itsmagnetization during manufacture. The magnetic domains are “frozen in” by poling inan applied magnetic field as the material is cooledthrough its Tc. The materials are magnetically very hard and willretain in service the residual flux density, thatremains after the strong magnetizing field has beenremoved. Hard ferrites are used in loudspeakers, motors.
Aplication of Ferrites The cubic spinels, also called ferrospinels, areused as soft magnetic materials because of theirvery low coercive force of 4x10-5weber/m2and highsaturation magnetization 0.3-0.4 weber/m2.(1 weber = 1 volt-second = 108Maxwells) Flux density (induction): 1 Tesla = 104Gauss = 1weber/m2. (1 Gauss = 1 Maxwell/cm2). Hexagonal ferrites are hard magnetic materials withcoercive force of 0.2 – 0.4 weber/m2and largeresistance to demagnetization, 2 – 3 J/m3.
Aplication of Garnets Garnets are especially suited for high frequencymicrowave applications due to the ability to tailorproperties such as magnetization, line width, g-factor, Tc, and temperature stability. The most common garnet ferrites are based upon3Y2O3: 5Fe2O3or Y3Fe5O12or YIG.
Tape Recording Before passing over the record head,a tape passes over the erase headwhich applies a high amplitude, highfrequency magnetic field to the tapeto erase any previously recordedsignal and to thoroughly randomizethe magnetization of the magneticemulsion. The gap in the erase head is widerthan those in the record head; thetape stays in the field of the headlonger to thoroughly erase anypreviously recorded signal.
Tape Recording High fidelity tape recording requires a high frequencybiasing signal to be applied to the tape head along withthe signal to "stir" the magnetization of the tape . This is because magnetic tapes are very sensitive to theirprevious magnetic history, a property called hysteresis. A magnetic "image" of a sound signal can be stored ontape in the form of magnetized iron oxide or chromiumdioxide granules in a magnetic emulsion. The tiny granules are fixed on a polyester film base, butthe direction and extent of their magnetization can bechanged to record an input signal from a tape head.
Electromagnet Electromagnets are usually in the form of iron coresolenoids. The ferromagnetic property of the iron core causesthe internal magnetic domains of the iron to line upwith the smaller driving magnetiv field drivingproduced by the current in the solenoid. The solenoid field relationship isand k is the relative permeability of the iron, showsthe magnifying effect of the iron core.
Transformer A transformer makes use of Faraday’s law and theferromagnetic properties of an iron core to efficientlyraise or lower AC voltages. It of course cannot increase power so that if the voltageis raised, the current is proportionally lowered and viceversa.
Applications of GMR The largest technological application of GMR is in the datastorage industry. IBM were first to market with hard disks based on GMRtechnology although today all disk drives make use of thistechnology. On-chip GMR sensors are available commercially fromNon-Volatile Electronics. It is expected that the GMR effect will allow disk drivemanufacturers to continue increasing density at least untildisk capacity reaches 10 Gb per square inch. At this density, 120 billion bits could be stored on a typical3.5-inch disk drive, or the equivalent of about a thousand30-volume encyclopedias.
Applications of GMR Other applications are as diverse as solid-statecompasses, automotive sensors, non-volatilemagnetic memory and the detection of landmines.
Applications of GMR GMR also may spur the replacement of RAM incomputers with magnetic RAM (MRAM). Using GMR, it may be possible to make thin-filmMRAM that would be just as fast, dense, andinexpensive. It would have the additional advantages of beingnonvolatile and radiation-resistant. Data would not be lost if the power failed unexpectedly,and the device would continue to function in thepresence of ionizing radiation, making it useful forspace and defense applications.
Applications of GMR Reading and writing with a magnetoresistive probe. C B Craus, T Onoue, K Ramstock,W G M A Geerts, M H Siekman, L Abelmannand J C Lodder, J. Phys. D: Appl. Phys. 38 (2005) 363–370
Application of SuperconductorsPower lines. A significant amount of electrical energy is wasted as heatwhen electricity is transmitted down cables made of traditionalmetal conductors. Superconductors, can conduct electricity with zero resistanceand would therefore be more efficient.Transport. Magnetically levitated trains already exist. Using superconducting magnets, cheaper, faster and moreefficient variants could be produced.Electronics. By harnessing the Josephson effect, extremely fast electronicswitches could be constructed, allowing faster microprocessorsto be built.
Microwave DielectricsMicrowave Dielectrics The Microwave materials including of dielectric andcoaxial resonators to meet the demands of microwaveapplications for high performance, low cost devices insmall, medium and large quantities. Applications Patch antennas Resonators /inductors Substrates C-band resonator-mobile Filters
Dielectric Resonator (DR) Used in shielded microwave circuits,such as cavity resonator, filters andoscillators. Application: as antenna in microwaveand millimeter band. Advantages of DR: light weight, low cost, small size, highradiation efficiency, large bandwidth.
High-K dielectric to reduce size Dielectric Resonator (DR)size is inversely proportionalto the frequency: Larger ε, lower frequency Larger ε, smaller sizeεLcf2=
Photograph of split post dielectric resonatorsoperating at frequencies: 1.4, 3.2 and 33 GHz.Jerzy Krupka, Journal of the European Ceramic Society 23 (2003) 2607–2610