All-sapphire-based high-temperature pressure sensor system with in situ temperature compensation: innovative cavity design, fabrication, and APSC-FFT algorithm.

Targeting the environment of gas-cooled reactors (800 °C, 1 Mpa), we propose an all-sapphire composite-cavity sensor system for pressure measurement with in-situ temperature compensation. The sensor based on a fully sapphire-based dual-cavity structure and white-light interferometry principle. Decoupling two cavities' information enables the simultaneous measurement. The high hardness and excellent thermal stability of sapphire ensure the high-temperature resilience. The novel central platform structure of the pressure-sensitive diaphragm enhances the spectrum contrast and measurement accuracy while maintaining high sensitivity. An optimized MEMS wet etching process guarantees superior diaphragm surface roughness and etching rate, and high-temperature wafer-level bonding ensures hermeticity. Furthermore, the adaptive peak-shift correction FFT algorithm is proposed for demodulation, achieving a sub-nanometer theoretical resolution. Experimental results under 0-1.2 MPa and 28-800 °C demonstrate that the system exhibits systematic error better than 0.13% F.S (temperature) and 0.18% F.S (pressure). The stability is better than 0.04% F.S. (temperature) and 0.12% F.S (pressure). The sensing chip remains stable performance after prolonged annealing at 1500 °C followed by cooling. It demonstrates the sensor is suitable for pressure monitoring in 800 °C and the potential of the chip for applications in extreme temperature, such as exceeding 1300 °C in aero-engines.