中文  |  English

News

News

Electronic Ceramics function and purpose

Hits:1562014-04-17 16:35:37Source: HX MI

Electronic ceramics by function and purpose can be divided into five categories : insulating means porcelain, ceramic capacitors , ferroelectric ceramics , semiconductor ceramic and ionic ceramics. Porcelain insulator device
Short porcelain apparatus having excellent electrical insulation properties, and electronic devices used in the device structure , the substrate and electronic ceramic shell . Absolutely
Porcelain ceramic edge electronic devices including insulators , coil , tube holder, the band switches, capacitors pillar bracket, IC substrate and encapsulation shell. The basic requirements for such a dielectric constant ε of porcelain , low dielectric loss tanδ is small, high insulation resistance ρ , E breakdown strength , good dielectric characteristics and temperature characteristics of the frequency . It also requires high mechanical strength and chemical stability.
In this type of ceramic talc and alumina ceramic porcelain most widely used. Their main phase components were MgSiO3 and Al2O3. Steatite is excellent in electrical insulation and low cost , is a typical high-frequency radio apparatus for ceramic bands . Alumina ceramic is a better kind of high frequency electrical insulation property , high temperature, high strength ceramic device . The electrical and physical properties with increasing Al2O3 content increases . Commonly used are 75% , 95% , high alumina ceramic containing 99% Al2O3 for . In some very high requirements in an integrated circuit , even using Al2O3 content of 99.9% pure corundum , sapphire with a similar nature . High alumina ceramic , porcelain , especially the shortcomings of pure corundum is difficult to manufacture , firing temperature is high, the price expensive.
Another type of device porcelain beryllium oxide (BeO) , represented by high thermal conductivity ceramic . BeO95% beryllium oxide containing ceramic and metal at room temperature thermal conductivity of the same . Beryllium oxide also has good dielectric properties, resistance to changes in temperature resistance and high mechanical strength. The disadvantage is that a lot of raw materials toxic BeO , porcelain firing temperature is high , thus limiting its application. Boron nitride (BN) and aluminum nitride ceramic (AlN) also belongs to the high thermal conductivity ceramic porcelain, though , and its thermal conductivity beryllium oxide ceramic , but non-toxic, processing properties and dielectric properties are good, high-frequency power transistors available and LSI in for cooling and insulation.
Developed a class of SiC -based material, mixed with a small amount of impurities such as hot BeO ceramic . The ceramic insulation performance , thermal conductivity higher than 99% pure beryllium oxide ceramic . Its thermal expansion coefficient of the silicon single crystal may be close to unity and in a wide temperature range , the power dissipation is expected to get larger LSI application .
Low alkali feldspar porcelain used as carbon and metal film resistors matrix is also an important class of porcelain and inexpensive device , but its large dielectric loss , should not be used at high frequencies . Ceramic Capacitors
Ceramic capacitor as the electronic medium . The maximum amount of this type of ceramic , specifications varieties most. The main high-frequency , low-frequency ceramic capacitors ceramic capacitors and semiconductors .
High-frequency ceramic capacitors ceramic capacitors belonging to the class Ⅰ , mainly used in the manufacture of high- frequency circuits ceramic capacitor stability and temperature compensation capacitors. Most of the major components constituting such a ceramic or a rare earth metal titanate salt and titanium -based solid solution ( Table 1 ) .
Electronic Ceramics
Use of different ceramic components can get different dielectric constant and dielectric loss tangent tanδ and dielectric high frequency temperature coefficient αε porcelain capacitors to meet the needs of a variety of temperature compensation . Four tables is only barium titanate ceramic capacitor having high heat stability of the medium , but also an excellent microwave dielectric material.
Low-frequency ceramic capacitors ceramic capacitors are Class Ⅱ , mainly for the manufacture of low-frequency bypass circuit , DC blocking and filtering ceramic capacitors. The main feature is the high dielectric constant ε , loss tangent tanδ and ε is larger and the rate of change with temperature greater . Such ceramics are the most widely used ferroelectric barium titanate (BaTiO3) as a main component , a high ε is obtained by doping ( up to 20,000 at room temperature) and the temperature change rate ε of the ceramic material . With gentle type ferroelectric phase transition lead magnesium niobate (PbMg1/3Nb2/3O3) and other main component of low-temperature low-frequency monolithic capacitors sintered ceramic materials , is an important low-frequency ceramic capacitors .
An insulating layer formed on the inner surface ( grain boundary ) using the semiconductor ceramic capacitor of the semiconductor ceramic grains or the outer surface of the dielectric ceramic capacitors for the electronics . Where the boundary layer ceramic capacitors utilize grain boundary layer dielectric properties and is made of a new class of high-performance, high-reliability capacitors , its small dielectric loss , insulation resistance and high voltage . Semiconductor ceramic capacitors are mainly two types of BaTiO3 and SrTiO3 . In the ceramic BaTiO3, SrTiO3 , or both , solid solution in the crystal phase , a small amount of primary dopant (e.g., Dy2O3 , etc. ) and other additives , in particular after the calcination atmosphere , to give the N-type semiconductor ceramic . Then, the slurry was coated on the surface layer of oxide (e.g., CuO , etc. ) , the oxide by heat treatment of the ceramic grain boundary diffusion , finally among all the semiconductor grains forming an insulating layer . Such as the high dielectric constant ceramic ( up to 105 or more ) , dielectric loss ( less than 1% ) , the volume resistivity is high ( greater than 1011 ohm- cm ) , high- frequency dielectric dispersion ( greater than 1 GHz ) , good moisture resistance , is a high performance , high stability of the capacitor dielectric . Ferroelectric ceramics with ferroelectric transistor -based electronic ceramic crystal phase . The ferroelectric crystal has been found that no less than 1000 , but as a main crystal phase of the ferroelectric ceramics of perovskite or quasi main perovskite ferroelectric crystal or solid solution. Within a certain temperature range exists in the crystal with the applied electric field can change the direction of the spontaneous polarization, which is a ferroelectric crystal . When the temperature exceeds a critical value ─ ─ Curie temperature TC, which dropped to zero polarization , ferroelectric crystal that is lost , and become generally shun transistors ; Meanwhile, crystals occur ferroelectric phase to paraelectric phase phase transition. Ferroelectric polarization electric field and also with the dramatic changes ( Figure 1 ) .
Electronic Ceramics
Important microscopic characteristics of the ferroelectric domain structure having a power , i.e., having a plurality of ferroelectric spontaneous polarization in a specific direction to a small region of domain ─ ─ saturated. The different orientation of domains in separate domain walls ( Figure 2a). In addition a very strong electric field , this field can be a multidomain forced crystal orientation of monodomain ( Figure 2b). This electrical domain with an external electric field is reversed orientation of dynamic processes , including domain wall motion process and the new domain nucleation and growth process. Ferroelectric Ceramics
Multi-function, wide use. Can be made using the piezoelectric characteristic of the piezoelectric device , which is the main application of ferroelectric ceramics , the ferroelectric ceramics therefore often called piezoelectric ceramics . The use of ferroelectric ceramics pyroelectric properties of ( changes in temperature , due to changes in the polarization of the ferroelectric release surface charge effects ) can be made infrared detector , the temperature measurement, temperature control, telemetry , remote sensing as well as areas of biology, medicine , etc. are important applications . A typical pyroelectric lead titanate ceramics (PbTiO3) and so on. Using a transparent ferroelectric ceramics PLZT ( lanthanum-doped lead zirconate titanate ) strong electro-optic effect ( by the applied electric field control of the transparent ferroelectric ceramics domain state to change its optical properties , thus demonstrating electrically controlled birefringence and electric light scattering effects ) , can be made into a laser modulator , optical displays, optical information storage , optical switches, photoelectric sensors, image storage and display, as well as laser or nuclear radiation goggles and other new devices. Semiconductor Ceramics
Measures by semiconductor ceramic grains and a semi- conductive insulating ( or semiconducting ) grain boundaries, thereby rendering the electronic properties of semiconductor ceramic barrier , such as a strong interface .
Ceramic semiconductor oriented methods are mandatory reduction and donor doping method ( also known as valence control method) two . Both methods are formed on a ceramic ion vacancies in the crystal defects , thereby providing a number of conductive electrons in the grains of the ceramic becomes a certain type ( usually N -type ) semiconductor . These grains and the interlayer insulating layer between , or another type (P -type ) semiconductor layer .
Many different types of semiconductor ceramics , including the use of a variety of semiconductor crystal made of porcelain in the very nature of a negative temperature coefficient thermistor ; semiconductor capacitors made by the grain boundary nature , ZnO varistors , BaTiO3 Department of positive temperature coefficient thermistor and a variety of ceramic humidity resistance and gas-sensing resistors made use of surface properties such as ; resistors , CdS/Cu2S solar cells. Table 2 lists typical sensor with a semiconductor ceramic .
CdS/Cu2S Department of Optical Ceramics Unlike in the table above with an insulating layer of semiconductor ceramic nature of the grain boundaries , it is the use of the photovoltaic effect and the P -type N -type CdS Cu2S grain boundary layer between the PN heterojunction . It is made of ceramic with a solar cell as power stations unattended , as an electronic instrument can be coupled to the photovoltaic device . Ion ceramic
Fast ionic conductivity of electronic ceramics. Positive ion having a fast transmission characteristic . Typical representatives are β-Al2O3 ceramic . This ceramic ionic conductivity at 300 ℃ up to 0.1 / ( Europe · cm ) , can be used to produce energy more economical high percentage of solid battery , but also the production of high energy density capacitor slowly discharges. It is the material helps solve the energy problem .