SiC as dielectric material for high temperature applications

A capacitor using SiC as the dielectric material has been developed for high temperature, high power, high density aircraft and aerospace applications. The conventional capacitor consists of a large number of metallized films, such as polysulfone, that are arranged in parallel and enclosed in a sealed metal case. However, problems with electrical failure, thermal failure, and dielectric flaws were experienced by Air Force suppliers for both the capacitor component and subsystems. The high breakdown electrical field, high thermal conductivity, and high temperature operational resistance of SiC compared to the same properties of the conventional ceramic and polymer dielectrics make it a better choice for high temperature, high power filter capacitors. The quality of the SiC films, bulk single crystal SiC, and polycrystalline diamond films were evaluated. The electrical parameters, such as the capacitance, dissipation factor (DF), equivalent series resistance (ESR) and dielectric withstand voltage, were also measured. The electric parameters were investigated under thermal cycling conditions in the temperature range of 40°C to 200°C. The values of equivalent series resistance of bulk single crystal SiC were significantly lower than the sputtered SiC films. The high ESR can be reduced by removing the substrate and improving the packaging. The results indicate that the quality of the SIC film needs to be improved to satisfy the requirements of high power filter capacitors, and that SiC has much potential to become a reliable, high temperature dielectric