Sapphire Fabry–Perot Pressure Sensor at High Temperature

There is a need for pressure sensor technology that can operate for longer times at very high temperatures. We propose a sapphire pressure sensor designed to operate at high temperature. A Fabry-Perot (FP) sensing cavity created by directly bonding two sapphire wafers through reactive-ion etching functions as a single sapphire structure for pressure measurement at high temperatures. Applying white-light interferometry and diaphragm deflection theory, the fabricated device is experimentally tested by measuring the pressure over a range of 0.1 to 2.1 MPa at 25-1000 °C. The FP sensing cavity length depends on the pressure and the temperature simultaneously. The FP sensing cavity length varies linearly with pressure at 25 °C, and the linearity is preserved with different sensitivity at high temperatures. The structure of the sensor body, enveloping the cavity inside, varies via the coefficient of thermal expansion of sapphire like a single sapphire wafer, and the FP sensing cavity is tightly sealed without any air leakage at high temperature.