A High-Sensitivity Thermal-Based Integrated Sensor System With a Low-Noise Chopper-Stabilized CCIA Using Customized CMOS-MEMS Process

This article presents a high-sensitivity complementary metal oxide semiconductor (CMOS)-microelectromechanical system (MEMS) thermal-based integrated sensor system for flow rate sensing, which integrates thermopile detectors and a low-noise capacitively coupled instrumentation amplifier (CCIA) interface circuit. To enhance sensor performance, we propose a custom post-CMOS fabrication process that utilizes the metal-2 layer as a hard mask, enabling self-alignment patterning and suspended film thinning. This fabrication method improves both sensitivity and power efficiency. The thermal detector is designed using high Seebeck-coefficient materials (n+ / p+ polysilicon) within the CMOS fabrication process, incorporating a series connection of 32 pairs of thermocouples to further enhance sensitivity. To optimize integration and minimize chip size, a hybrid ASIC amplification circuit is incorporated for system-level analysis. The CCIA circuit employs chopper modulation to effectively suppress dc offset and flicker noise, while a high-gain two-stage operational amplifier (op-amp) ensures precise closed-loop gain control. Experimental results demonstrate that the proposed system achieves an ultrahigh sensitivity of 3.42 mV/(m/s)/mW, a detection limit of 2.49 mm/s, and a rapid response time of 3 ms. These results highlight the potential of the proposed sensor system for high-precision, portable flow sensing applications.