Sensitivity Improvement of P+Si/Au Thermopile-Based Gas Flow Sensor by Optimizing Heat-Sink and Thermal-Insulation Configuration

This paper reports a front-sided microfabricated high-sensitive p+Si/Au thermopile-based gas flow sensor for high-yield and low-cost volume production. Herein, the suspended p+Si beams, under the dielectric membrane and used to construct the p+Si/Au thermopile-based flow sensor, are only fabricated from one side of single crystal silicon wafer, without double-sided alignment exposure, cavity-SOI process, and wafer-bonding needed. The fabricated gas flow sensor with tiny-size of $0.5\text{mm}\times 0.7\text{mm}$ is achieved. Compared to the most of previously reported p+Si/metal thermopile-based flow sensor, by embedding the cold junction of p+Si beam into the silicon substrate and optimizing the thermal insulation of the suspended membrane from the silicon substrate, the fabricated flow sensor achieves higher sensitivity of 0.337mV/(SLM)/mW (Output without any amplification) for nitrogen gas flow and quick response time of 1.5ms.