Thermal breakdown, electrical properties

Surface layers of silicon oxide are important in semiconductor device fabrication as interlayer dielectrics for capacitors, isolation of conducting layers, or as masking materials. However, anodic oxides, due to their relatively poor electrical properties, breakdown voltage, and leakage current, have not yet found much use in device technology, and cannot compete with thermal oxides obtained at high temperatures of 700 to 900 °C. 

Banford et al. studied the radiation effects on electrical properties of low-density polyethylene (LDPE) at 5 K with the use of a 60Co gamma source and a thermal nuclear reactor [86]. They reported that both the electrical conductivity and the dielectric breakdown strength of LDPE at 5 K were not significantly affected by radiation absorbed doses up to 10s Gy, but an erratic pulse activity under high applied fields was observed in the sample irradiated at 106 Gy. 

Electrical properties comprising dielectric constant, dielectric loss, breakdown strength and leakage current, and Thermal properties such as response to heat treatment cycles and thermogravimetric analysis (TGA), out gassing, etc. 

The formation of radical intermediates influences not only the chemical state of irradiated polymers, but it brings also about physical characteristics solubility, fusion enthalpy, heat capacity, crystallinity, mechanical features, electrical properties permittivity, dielectric loss, breakdown tension, thermal conductivity. The new formed structures may be unlike in comparison with initial material, because intermolecular bridges, new organic functions appeared on macromolecular backbones, general molecular order or free volumes attain other values. 

As a result of these properties, silicone fluids find application for example as heat transfer media, hydraulic fluids, brake fluids, lubricants and vacuum pump oils. One of their earliest uses was as dielectrics the dielectric constant changes very little with temperature and is also essentially independent of frequency over the range 10 -10 Hz. On thermal breakdown organic polymers have the disadvantage that they commonly produce carbon, which conducts electricity. Organosiloxanes are more robust and also tend to decompose or oxidize to products which are themselves insulators, such as silica or volatiles of low molecular weight. 

Silicon carbide has favorable properties such as a wide bandgap, high thermal conductivity, high breakdown electric field strength, and high thermal stabihty. It... 

Applications. For use as a gaseous dielectric, other specific properties are needed in addition to high breakdown strength, and a compromise must be made between electrical and mechanical requirements. Desirable properties include low toxicity, thermal stabiUty toward materials of constmction. 

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