Application of Application of ElectroceramicsElectroceramics

EBB 443-Technical Ceramics

Dr. Sabar D. HutagalungSchool of Materials and Mineral Resources EngineeringUniversiti Sains Malaysia

Capacitors

The multilayer ceramic (MLC) capacitors. The MLCC structure consists of alternate

layers of dielectric and electrode material. Each individual dielectric layer contributes

capacitance to the MLCC as the electrodes terminate in a parallel configuration.

The advances in preparation technology have made it possible to make dielectric layers <1 m thick.

Schematic of a typical multilayer ceramic (MLC) capacitor

Cut-away view of multilayer ceramic capacitor.

Applications of Ferroelectric Thin Films Ferroelectric thin films have attracted attention

for applications in many electronic and electro-optic devices.

Applications of ferroelectric thin films utilize the unique dielectric, piezoelectric, pyroelectric, and electro-optic properties of ferroelectric materials.

Some of the most important electronic applications of ferroelectric thin films include nonvolatile memories, thin films capacitors, pyroelectric sensors, and surface acoustic wave (SAW) substrates.

The electro-optic devices include optical waveguides and optical memories and displays.

Semiconductor memories such as DRAM & SRAM currently dominate the market.

However, the disadvantage of these memories is that they are volatile, i.e. the stored information is lost when the power fails.

The non-volatile memories available at this time include complementary metal oxide semiconductors (CMOS) with battery backup and electrically erasable read only memories (EEPROM's).

These non-volatile memories are very expensive.

Ferroelectric Memories

FeRAM Cross Section

FeRAM

FeRAM is a type of nonvolatile RAM that uses a ferroelectric film as a capacitor for storing data.

FeRAM can achieve high-speed read/write operations comparable to that of DRAM, without losing data when the power is turned off (unlike DRAM).

In addition to nonvolatility and high-speed operation, FeRAM cells offer the advantages of easy embedding into VLSI logic circuits and low power consumption, perhaps their greatest advantage for many applications.

FeRAM-embedded VLSI circuits have been used in smart cards, radio frequency identification (RFID) tags, and as a replacement for BBSRAM (battery

backed-up static RAM), which is used in various devices to protect data from an unexpected power failure, as well as in many other SoC (system on a chip) applications.

FeRAM

A memory cell, where one bit of data is stored, is composed of a cell-selection transistor and a capacitor for 1T1C (one transistor, one capacitor)-type FeRAM.

A major problem encountered when reducing the size of the memory cell is preventing reliability degradation.

The reliability of FeRAM cells is dependent on the materials used (ferroelectric film, electrode, interlayer

dielectric, etc.), fabrication process, device structure, memory cell circuit, and operation sequence.

FeRAM

Schematic drawings of field-effect transistors (FETs) with(a) metal–ferroelectric–insulator–semiconductor (MFIS) and(b) metal–ferroelectric–metal–insulator–semiconductor (MFMIS) gate structures.

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 leakage

current is localized around weak spots in the film; this is important in prolonging the data retention time.

In other words, in an MFIS structure, the effect of the leakage current spreads out to the whole floating gate, and the charge neutrality is completely destroyed in a short time. Thus, an MFIS structure is superior in this regard.

MFMIS structures

In an MFMIS structure, it is possible to optimize the area ratio between the ferroelectric and buffer layer capacitors, so that the induced charges on both capacitors match.

In an MFMIS structure, the floating gate material can be so chosen that a highquality ferroelectric film is formed on the floating gate and that constituent elements in the ferroelectric film do not diffuse into the buffer layer and Si substrate.

Electro-optic Applications

The requirements for using ferroelectric thin films for electro-optic applications include an optically transparent film with a high degree of crystallinity.

The electro-optic thin film devices are of two types; one in which the propagation of light is along the plane of the film (optical waveguides) and the other in which the light passes through the film (optical memory and displays).

Other Ferroelectric Thin Film Applications

Thin Film Capacitors: The high dielectric permittivity of ferroelectric

ceramics such as BaTiO3, PMN and PZT very useful for capacitor applications.

The MLC capacitors have a very high volumetric efficiency (capacitance per unit volume) because of 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 to a small change in temperature. Single crystals of triglycine sulfate (TGS),

LiTaO3, and (Sr,Ba)Nb2O6 are widely used for heat sensing applications.

PbTiO3, (Pb,La)TiO3 and PZT have been widely studied for thin film pyroelectric sensing applications.

Surface Acoustic Wave Substrates : SAW devices are fabricated by depositing

interdigital electrodes on the surface of a piezoelectric substrate.

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.

Schematic representation of the generation, propagation and detection of surface acoustic waves (SAW) on a piezoelectric substrate with interdigital electrode.

Gas Ignitors It consists of two oppositely poled ceramic cylinders attached end to end in order to double the charge available for the spark.

The compressive force has to be applied quickly to avoid the leakage of charge across the surfaces of the piezoelectric ceramic.

The generation of the spark takes place in two stages. The application of a compressive force 'F' on the poled ceramic (under open circuit conditions) leads to a decrease in the length by dLD.

The potential energy developed across the ends must be higher than the breakdown voltage of the gap, for sparking to occur.

A piezoelectric spark generator

Gas Ignitors When the spark gap breakdown

occurs the second stage of energy generation starts.

The electric discharge across the gap results in a change from open circuit conditions to closed circuit conditions with the voltage dropping to a lower level.

The combination of the strains from the open and short circuit conditions produce more energy that can be dissipated in the spark.

Usually PZT ceramic disks are used for this application.

A piezoelectric spark generator

Actuators & Sensors

Schematic description of the geometry and the working principle of the piezoelectric film applied in actuators and sensors.

Actuators & Sensors

An important family of functional materials are ferroelectrics or, more generally, polar materials.

Their piezoelectricity can be used in sensors, actuators, and transducers;

Their pyroelectricity is employed in infrared detectors.

Piezoelectric Microactuator Devices

Schematic draw of optical scanning device with double layered PZT layer (a) and the fabricated device, (b) Mirror plate: 300×300 (µm2, DPZT beam: 800 × 230 µm2).

Schematic drawing of self-actuation cantilever with an integrated piezoresistor.

Micropump using screen-printed PZT actuator on silicon membrane. (Courtesy of Neil White, Univ. of Southampton, 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): Hard magnets

Aplication of Soft Magnetics

In the soft magnetic materials, only a small field is necessary to cause demagnetization and very small energy losses occur per cycle of hysteresis loop.

This is important for applications such as transformers used in touch tone telephones or inductors or magnetic memory cores.

During used a soft ferrites has its magnetic domains rapidly and easily realigned by the changing magnetic field.

Aplication of Hard Magnetics A hard (or permanent) ceramic magnet

achieves its magnetization during manufacture. The magnetic domains are “frozen in” by poling

in an applied magnetic field as the material is cooled through its Tc.

The materials are magnetically very hard and will retain in service the residual flux density, that remains after the strong magnetizing field has been removed.

Hard ferrites are used in loudspeakers, motors.

Aplication of Ferrites

The cubic spinels, also called ferrospinels, are used as soft magnetic materials because of their very low coercive force of 4x10-5 weber/m2 and high saturation magnetization 0.3-0.4 weber/m2.

(1 weber = 1 volt-second = 108 Maxwells) Flux density (induction): 1 Tesla = 104 Gauss = 1

weber/m2. (1 Gauss = 1 Maxwell/cm2). Hexagonal ferrites are hard magnetic materials with

coercive force of 0.2 – 0.4 weber/m2 and large resistance to demagnetization, 2 – 3 J/m3.

Aplication of Garnets

Garnets are especially suited for high frequency microwave applications due to the ability to tailor properties such as magnetization, line width, g-factor, Tc, and temperature stability.

The most common garnet ferrites are based upon 3Y2O3 : 5Fe2O3 or Y3Fe5O12 or YIG.

Tape Recording Before passing over the

record head, a tape passes over the erase head which applies a high amplitude, high frequency magnetic field to the tape to erase any previously recorded signal and to thoroughly randomize the magnetization of the magnetic emulsion.

The gap in the erase head is wider than those in the record head; the tape stays in the field of the head longer to thoroughly erase any previously recorded signal.

Tape Recording High fidelity tape recording requires a high

frequency biasing signal to be applied to the tape head along with the signal to "stir" the magnetization of the tape .

This is because magnetic tapes are very sensitive to their previous magnetic history, a property called hysteresis.

A magnetic "image" of a sound signal can be stored on tape in the form of magnetized iron oxide or chromium dioxide granules in a magnetic emulsion.

The tiny granules are fixed on a polyester film base, but the direction and extent of their magnetization can be changed to record an input signal from a tape head.

Electromagnet

Electromagnets are usually in the form of iron core solenoids.

The ferromagnetic property of the iron core causes the internal magnetic domains of the iron to line up with the smaller driving magnetiv field driving produced by the current in the solenoid.

The solenoid field relationship is

and k is the relative permeability of the iron, shows the magnifying effect of the iron core.

Transformer

A transformer makes use of Faraday’s law and the ferromagnetic properties of an iron core to efficiently raise or lower AC voltages.

It of course cannot increase power so that if the voltage is raised, the current is proportionally lowered and vice versa.

Transformer

Applications of GMR

The largest technological application of GMR is in the data storage industry.

IBM were first to market with hard disks based on GMR technology although today all disk drives make use of this technology.

On-chip GMR sensors are available commercially from Non-Volatile Electronics.

It is expected that the GMR effect will allow disk drive manufacturers to continue increasing density at least until disk capacity reaches 10 Gb per square inch.

At this density, 120 billion bits could be stored on a typical 3.5-inch disk drive, or the equivalent of about a thousand 30-volume encyclopedias.

Applications of GMR

Other applications are as diverse as solid-state compasses, automotive sensors, non-volatile magnetic memory and the detection of landmines.

Applications of GMR

GMR also may spur the replacement of RAM in computers with magnetic RAM (MRAM).

Using GMR, it may be possible to make thin-film MRAM that would be just as fast, dense, and inexpensive.

It would have the additional advantages of being nonvolatile and radiation-resistant.

Data would not be lost if the power failed unexpectedly, and the device would continue to function in the presence of ionizing radiation, making it useful for space 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 Abelmann and J C Lodder, J. Phys. D: Appl. Phys. 38 (2005) 363–370

Application of Superconductors

Power lines. A significant amount of electrical energy is wasted as heat

when electricity is transmitted down cables made of traditional metal conductors.

Superconductors, can conduct electricity with zero resistance and would therefore be more efficient.

Transport. Magnetically levitated trains already exist. Using superconducting magnets, cheaper, faster and more

efficient variants could be produced.Electronics. By harnessing the Josephson effect, extremely fast electronic

switches could be constructed, allowing faster microprocessors to be built.

Microwave DielectricsMicrowave Dielectrics The Microwave materials including of dielectric and

coaxial resonators to meet the demands of microwave applications for high performance, low cost devices in small, 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 and oscillators.

Application: as antenna in microwave and millimeter band.

Advantages of DR: light weight, low cost, small size,

high radiation efficiency, large bandwidth.

High-K dielectric to reduce size

Dielectric Resonator (DR) size is inversely proportional to the frequency:

Larger , lower frequency Larger , smaller size

L

cf2

Photograph of split post dielectric resonators operating at frequencies: 1.4, 3.2 and 33 GHz.

Jerzy Krupka, Journal of the European Ceramic Society 23 (2003) 2607–2610

 

Super-K CCTOSuper-K CCTO