Introduction to Electroceramics EBB 443 Seramik Teknikal
Ceramic Materials • Ceramic materials can now be broadly considered to be all inorganic non-metallic materials. • However, it is more useful to classify them as polycrystalline non-metallic materials. • The inherent physical properties of ceramics has made them desirable for use in wide range of industries, with their first applications in the electronics sector.
What are electroceramics? • The term Electroceramic is used to describe ceramic materials that have been specially formulated for specific electrical, magnetic, or optical properties. • Their properties can be tailored to operation as insulators, ferroelectric materials, highly conductive ceramics, electrodes as well as sensors and actuators. • The performance of electroceramic materials and devices depends on the • complex interplay between processing, • chemistry, • structure at many levels and • device physics.
What are electroceramics? • The applications of ceramics in the electronics industry can be divided into two groups: • the use of materials for interconnection and packaging of semiconductor circuits, and • the use of ceramics in circuit components which perform a function in their own right, such as capacitors and sensors. • The former application forms a large market and has been well reviewed elsewhere. • The latter is particularly interesting because the materials which are used for a very wide range of applications are in many cases closely related in crystal structure.
Common Applications for Electroceramics • Insulator • Resistor • High dielectric constant capacitors • Piezoelectric sonar transducers • Ultrasonic transducers • Radio & communication filters • Medical diagnostic transducers • Ultrasonic motors • Electro-optic light valves • Thin-film capacitors • Ferroelectric thin-film memories
Bulk Ceramic Thermistors Bulk Ceramic Varistors (VDR-voltage dependent resistors)
Cellular Telephone • Portable communication devices such as cordless, portable, and car telephone have become popular worlwide. • Do you know what kind of dielectric and ferroelectriccomponents are used in a cellular phone?
Chip Monolithic ceramic capacitors Microwave Oscillators Microwave Filters Ceramic Resonators High Frequency SAW Filter Ceramic Filters Piezoelectric Receivers Piezoelectric Speakers Cellular Telephone
Johanson Dielectrics Capacitor Products: Ceramic SMT and Leaded High Voltage and High Temperature, Dual and Multi Capacitor Arrays, Low Inductance, X2Y, Switchmode.
Q = CV Q: charge (Coulomb) C: capacitance (Farad) V: potential difference (Volt) d: separation/thickness (meter) o: permitivity of vacuum = 8.854x10-12 C2/m2 or F/m r: dielectric constant
Multilayer Ceramic Capacitor • The demands for miniaturization largely preclude an increase in the face area A. • One exception is the multilayer ceramic capacitor (MLCC), in which case: • where N is the number of stacked plates. • Ideally, the dielectric should have a low electrical conductivity so that the leakage current is not too large.
Multilayer Ceramic Capacitor Cut-away view of multilayer ceramic capacitor.
Surface-Mount Ceramic Capacitors Military electronics
Surface-Mount Capacitors • Ceramic surface-mount capacitors are used in every type of electronic equipment including computers, telecommunication, automotive electronics, military electronics, medical electronics and consumer electronics. • High voltage and high temperature ceramic capacitorsare serve military, aerospace, oil service, oil exploration and other markets including medical imaging, power generation, and high voltage power supply.
Temperature Sensitive Resistor • There are numerous uses for resistors with high valuea of the temperature coefficient of resistance (TCR) and they may be negative (NTC) or positive (PTC).
Circuit to be protected Source VDR Voltage-dependent Resistors (Varistors) • There are a number of situations in which it is valuable to have a resistor which offers a high resistance at low voltagesanda low resistance at high voltages. • Such a devices can be used to protect a circuit from high-voltage transients by providing a path across the power suply that • takes only a small current under normal conditions but takes large current if the voltage rises abnormally, • thus preventing high-voltage pulses from reaching the circuit. • Schematic use of a VDR to protect a circuit against transients,
Schematic representation of varistor-capacitor device construction and its equivalent circuit.
High-K Dielectric Materials • The discovery of materials with unusually high-dielectric constants (r > 2000-100000), and their ferroelectric nature, led to an explosion in ceramic use. • The first employed in high-k capacitors is BaTiO3 based, and later developed into • piezoelectric transducers, • positive temperature coefficient (PTC) devices, and • electro-optic light valves. • Recent developments in the field of ferroelectric ceramics is their use in • medical ultrasonic composites, • high displacement piezoelectric actuators, and • photoresistors.
Piezoelectric • Piezoelectricity was discovered in 1880 by J & P Curie during studies into the effect of pressure on the generation of electrical charge by crystals (such as quartz). • Described as the generation of electricity as a result of mechanical pressure, or • "electrical polarisation produced by mechanical strain in crystals belonging to certain classes". • The phenomenon can be attributed to a lack of centre of symmetry in the crystallographic unit cell - or the unit cell is described as non-centrosymmetric.
Piezoelectric • For Piezoelectricity - • the effect is linear and reversible, • the magnitude of the polarisation is dependant on the magnitude of the stress, • the sign of the charge produced is dependant on the type of stress (tensile or compressive).
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.)
Ferroelectric ceramics • This kind of material has perovskite structure, with general formula ABO3, in which • A is a large divalent metal ion such as Pb2+ or Ba2+, • B is a small tetravalent metal ion, such as Ti4+ or Zr4+, octahedrally coordinating with oxygen. • Ferroelectricity occurs due to the displacement of positive ions B4+ and negative ions O2- in opposite directions.
Ferroelectric Ceramics • This displacement causes spontaneous polarisation which is the origin of many other properties such as • extremely high dielectric constant, • hysteresis loop (non-linear dependence of polarisation with applied field), • piezoelectricity (the ability to change the dimension with applied field and to produce the current with applied mechanical stress).
Ferroelectric ceramics: PZT (PbZrTiO3) structure • Ferroelectric ceramics are widely used in modern technology with various applications (sensors, actuators, generators, transducers to very recent IC for RAM). • They can be used for DRAM (dynamic random access memory), and high remanent polarisation and low coercive field for being used as NVRAM (non-volatile random access memory).
Examples of piezoelectric microsensors on silicon: (a) microphone and (b) accelerometer. (OPA N.V., Taylor and Francis Ltd.)
Microwave 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. • ApplicationsPatch antennasResonators/inductorsSubstrates C-band resonator-mobile Filters
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
EM Spectrum Mobile phones operate in two main frequency ranges: • In US - the older systems ~850 MHz & the newer ~1900 MHz. • In European - near 900 MHz & 1800 MHz (GSM).
Magnetic Ceramics • There are various types of magnetic material classified by their magnetic susceptibilities: diamagnetic, paramagnetic and ferromagnetic. • Diamagnetic, have very small negative susceptibilities (about 10-6). • Example: inert gases, hydrogen, many metals, most non-metals and many organic compounds. • Paramagnetics are those materials in which the atoms have a permanent magnetic moment arising from spinning and orbiting electrons. • The susceptibilities are therefore positive but again small (in range 10-3 – 10-6).
Magnetic Ceramics- cont. • Ferromagneticmaterials are spontaneously magnetized below the Curie point. • The spontaneous magnetization is not apparent in materials which have not been exposed to an external field because of the formation of small volumes (domains) of materials each having its own direction of magnetization. • Spontaneous magnetization is due to the alignment of uncompensated electron spin by the strong quantum mechanical exchange forces.
Giant Magnetoresistance (GMR) • The GMR is the change in electrical resistance of some materials in response to an applied magnetic field. • GMR effect was discovered in 1988 by two European scientists working independently: • Peter Gruenberg of the KFA research institute in Julich, Germany, and • Albert Fert of the University of Paris-Sud . • They saw very large resistance changes - 6 percent and 50 percent, respectively - in materials comprised of alternating very thin layers of various metallic elements. • These experiments were performed at low temperatures and in the presence of very high magnetic fields.
Intrinsic Magnetoresistance • SrRuO3 • Tl2Mn2O7 • CrO2 • La0.7(Ca1-ySry)0.3MnO3 • Fe3O4 • CaCu3Mn4O12 (CCMO)
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. • Other applications are as diverse as solid-state compasses, automotive sensors, non-volatile magnetic memory and the detection of landmines.
Applications of GMR • Read sensors that employ the GMR effect available for detecting the fields from tiny regions of magnetization. • These tiny sensors can be made in such a way that a very small magnetic field causes a detectable change in their resistivity; such changes in the resistivity produce electrical signals corresponding to the data on the disk. • 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.