Fabrication of Passive Components for High Temperature Instrumentation

Thin-film resistors and capacitors have been fabricated for use in geothermal well-logging tools. The resistors can operate from 25°C-500°C with a temperature coefficient below 100 ppm/°C; capacitors can operate from 25°C-350°C with a similar temperature coefficient. Chemical vapor deposition (CVD) is used to fabricate both resistors and capacitors. The processing is compatible with most microcircuit processes; and resistors, capacitors, interconnecting metallization, and possivation are all produced by CVD and can be integrated on a single substrate. Resistor material is tungsten-silicon, capacitor electrodes and metallization are tungsten, and dielectric material is silicon nitride. Photolithography is used to delineate component geometry.