Development of a Stable High-Temperature Diamond Thermistor Using Enhanced Supporting Designs

Diamond is an excellent material for a high-temperature thermistor given its superior material properties. Despite its long history of the development, diamond thermistor is not widely used for commercial sensors because it is difficult to maintain optimum conditions for the diamond thermistor to operate at high temperature ranges in a compact size. In this paper, we demonstrate methods to improve the practicality and the feasibility of the diamond thermistor, focusing on the supporting components. The diamond thermistor design, where the diamond is sandwiched between contact pads, is tested up to 700 °C and being characterized by the Steinhart-Hart equations. For temperatures higher than 700 °C, the design of the thermistor is improved by encasing it in a metal sheath tube that protects and seals the diamond thermistor. Our supporting components provide oxygen free environment and a sturdy structure for the sensor components in a compact size. The encased diamond thermistor operates up to 880 °C and shows stable performance in a cycling test between 880 °C and the room temperature. An additional long-term stability test is performed at various temperatures for 10-hour durations. The tests show that the metal sheath tube design enables the diamond thermistor to be used as a practical temperature sensor at high-temperature ranges.