Polycrystalline Diamond Pressure Sensor using Spin Coat Seeding Method

Abstract

Pressure sensors using polycrystalline diamond can operate at a high temperature. However, the sensors usually have a very low Gauge Factor (G.F.), less than 100 and the special process is required to improve the sensitivity. In order to obtain a high G.F. without the special fabrication process, the combination of scratch and spin coat seeding methods have been introduced. By using the proposed method, it was possible to grow the diamond film uniformly on a SiO₂ substrate and the adhesion force of the film to the substrate increased up to 900 N/cm² at the maximum value. Boron doped diamond films were deposited on a Si diaphragm using the developed method in a fabrication process of a pressure sensor. Although the sensor demonstrated a good linearity in the pressure response, the G.F. was only 29 because of the poor surface conduction. To improve the surface conduction, the oxygen termination of the surface and relaxation of hydrogen defect by annealing were introduced respectively. As a result, the G.F. was improved up to 168. Oxidization by hot mixed acid also improved the G.F. to 285. The sensor treated by this oxidization showed the better uniformity in the temperature characteristic.