Dielectric layers operating temperatures

The common gases used for CVD synthesis of SiO are silane and oxygen, dichlo-rosilane (SiCl H ) and nitrous oxide (N O), or tetraethylorthosilicate (SiCOCjHj) ). SijN has high electrical resistance and dielectric strength and is suitable as a passivating layer and storage capacitor in dynamic random access memory. The Si source for SijN can be SiH, SiCl or SiCl H, the nitride source being NHj or N +Hj. The common precursor for the CVD of SijN in the semiconductor industry is SiCljHj -i-NHj and the deposition is operated at a temperature between 750 and 900 °C and a pressure of 25-115 Pa [5]. 

Many of the design features of the dielectric are governed by the necessity to operate the cable at a temperature suitable for the Nb3Sn superconductor (6 to 8 K). Extruded pol3rmer is not a viable mode of insulation application since the very large thermal contraction associated with extruded polyethylene would almost certainly lead to early mechanical failure of this dielectric. Instead, the choice was made to lap many layers of plastic tape and impregnate the butt-gaps with supercritical helium. The major dielectric, mechanical, and thermal specifications for the dielectric tapes are summarized in Table I. 

In static operations, the lifetime is mainly limited by the humidity, which penetrates through the external insulation layer and leads to a leakage current increase. A larger leakage current can lead to an electrical breakdown. Due to the dielectric and mechanical losses, the piezoelectric actuator warms up under continuous excitation. Losses are mainly non-linear and depend on the excitation frequency, the voltage amplitude and the humidity. To avoid a depoling effect of the ceramic, the temperature in the actuator should be monitored to ensure that it stays well below the ceramics Curie temperature. So a typical range of temperatures is —40°C to 80 °C. 

Polyimide resin-based laminates are the workhorse of electronics that must withstand high temperatures in operation or in assembly or repair. Common applications include down-the-hole well-drilling equipment, avionics, missiles, supercomputers, and PCBs with very high layer count. The principle advantage of polyimide is its ability to withstand high temperatures. It has approximately the same dielectric constant as epoxy resin systems. It is more difficult to work with in fabrication, is more costly than FR-4 systems, and absorbs more moisture. 

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