Electronic ceramic refers to ceramic that can be used as electronic or magnetic in the electronic industry.Electronic ceramics are ceramics with new functions through precise control of surface, grain boundary and size structure.In energy, household appliances, automobiles and other aspects can be widely used.
Widely used in the production of electronic functional components, mostly composed of oxide sintered body materials.The manufacturing process of electronic ceramics is similar to that of traditional ceramics.
Electronic ceramics or electronic industrial ceramics, it in the chemical composition, microstructure and mechanical and electrical properties, and the general electric power ceramics with the essential difference.Is the difference between the electronics industry for electronic ceramics have put forward a series of special technical requirements, which formed one of the most important is must has high mechanical strength, resistance to high temperature and high humidity, radiation resistance, dielectric constant changes in a very wide scope, dielectric loss tangent Angle is small, the temperature coefficient of capacitance can be adjusted (or capacitance change rate can be adjusted).High electrical strength and insulation resistance, and excellent aging performance.
classification
Electronic ceramics can be divided into five categories according to their functions and USES: insulator ceramics, capacitor ceramics, ferroelectric ceramics, semiconductor ceramics and ionic ceramics.
Insulating porcelain
Referred to as device porcelain, it has excellent electrical insulation performance and is used as electronic ceramics for structural parts, substrates and shells of electronic equipment and devices.A perfect
The porcelain parts of the edge device include various insulators, coil skeletons, electron tube bases, band switches, capacitor supports, integrated circuit substrates and packaging shells, etc.The basic requirements for this kind of porcelain are low dielectric constant, low dielectric loss tan delta, high dielectric resistivity rho, high breakdown strength E, good dielectric temperature characteristic and frequency characteristic.In addition, it requires high mechanical strength and chemical stability.
Talc and alumina are the most widely used ceramics of this kind.Their main crystalline phase compositions are MgSiO3 and Al2O3 respectively.Talc porcelain is a typical high frequency device porcelain used in radio frequency band because of its excellent electrical insulation and low cost.Alumina porcelain is a kind of high frequency, high temperature and high strength equipment porcelain with better electrical insulation.Its electrical and physical properties increase with the content of alumina.High-alumina porcelain with 75%, 95% and 99% alumina is commonly used.In some demanding integrated circuits, pure corundum porcelain containing 99.9% alumina is even used, whose properties are similar to those of sapphire single crystal.
There is also a kind of high thermal conductivity porcelain represented by beryllium oxide (BeO).The thermal conductivity of bea 95% is the same as that of metal at room temperature.Beryllium oxide also has good dielectric properties, temperature resistance and high mechanical strength.The disadvantage is that the toxicity of BeO material is very high and the firing temperature of porcelain material is high, so its application is limited.Boron nitride (BN) porcelain and aluminum nitride (AlN) porcelain also belong to high thermal conductivity porcelain. Although their thermal conductivity is not as good as beryllium oxide porcelain, it is non-toxic and has good processing and dielectric properties. They can be used for heat dissipation and insulation in high-frequency high-power transistors and large-scale integrated circuits.
Electronic ceramics
Microeconomic characteristics of ferroelectrics are electric domain structure, namely the ferroelectric has many small areas of spontaneous polarization along a specific direction to the saturated ─ ─ electrical domain.These domains with different orientations are separated by domain walls.Under the action of strong external electric field, this kind of multi-domain crystal can be forced to orientate to single domain by electric field.The dynamic process in which the domain orientation is reversed with the external electric field includes the movement of the domain wall and the nucleation and growth of new domains.
Semiconductor ceramics
Electronic ceramics with semi-conductive grain and insulative (or semi-conductive) grain boundaries, which exhibit strong interface barrier and other semiconductor properties.
There are two main methods to semiconductor ceramics: forced reduction method and donor doping method (also called valence control method).In both cases, defects such as ion vacancies are formed in the crystal of the ceramic, providing a large number of electrically conductive electrons and making the grains of the ceramic a type (usually n-type) semiconductor.The interlayer between these grains is an insulating layer or another type (P type) of semiconductor layer.
There are many kinds of semiconductor ceramics, including negative temperature coefficient thermistors made by using the properties of the grains themselves.Semiconductor capacitor made of grain boundary property, ZnO varistor, BaTiO3 series positive temperature coefficient thermistor, CdS/Cu2S solar cell;And the use of surface properties of various ceramic type wet - sensitive resistors and gas - sensitive resistors.
CdS/Cu2S photoelectric ceramics are different from the semiconductor ceramics listed in the above table, which use the properties of insulating grain boundary layer. What it USES is the photovoltaic effect of PN heterojunction between n-type CdS and p-type Cu2S grain boundary layer.The ceramic solar cell can be used as power source of unattended station or photoelectric coupler of electronic instrument.
Application prospect of electrical insulating ceramics
For electrical insulating ceramics have good thermal conductivity and electrical conductivity, low dielectric constant and low dielectric loss, high mechanical strength, chemical stability is good wait for a characteristic, is widely used in metal molten bath, molten salt container, packaging materials, integrated substrate, electrolytic cell lining, reinforced metal matrix composites, active armor materials, heat sink, and high temperature furnace heater.In the electronic and power industries, insulating ceramics, such as insulators, insulating bushing, resistance matrix, coil frame, power tube base of electron tube and integrated circuit substrate of power equipment, are mainly used for the installation, protection, support, insulation, connection and isolation of electrical components.
Application prospect of dielectric ceramics
Dielectric ceramics are widely used in the manufacturing of IC substrates due to their high strength, low dielectric loss, heat resistance and stability.For example, beryllium oxide, aluminum oxide, aluminum nitride and silicon carbide can be widely used as ceramic materials for integrated circuit substrates.Although the thermal conductivity of silicon carbide is better than alumina, and the high-performance substrate made by hot pressing method can still meet the practical requirements at about 200 degrees Celsius. However, due to the complex hot pressing sintering process and toxic additives, its development is also limited.Although the other electrical properties of aluminum nitride are roughly the same as those of alumina ceramics, its thermal conductivity is about 10 times that of alumina ceramics, so it is very likely to become the next generation of high-quality substrate materials for vlsi.
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