Design of Pyroelectric Infrared Detector and Micropower CMOS Integrated Circuitry Towards a Monolithic Gas Sensor

With the emerging trend in miniaturization of complete optical sensor on a silicon platform for gas sensing applications, this paper presents a promising candidate towards monolithic gas sensor with features of 1) a CMOS compatible Aluminum Nitride (AlN)-based pyroelectric infrared detector (PID); 2) customized micropower high-precision CMOS integrated readout circuits. In the PID design, the sensitivity and device integrity are improved with optimized sensing area and modified layer structure. In the readout circuits, to amplify the pico-amperes current from detector, a tunable resistive transimpedance amplifier (TIA) with robust pseudo-resistor in series is proposed to achieve reduced variations against process-voltage-temperature (PVT). A micropower incremental analog-to-digital converter (ADC) is designed to digitize the voltage output from TIA. In addition, to compensate the drifts induced by local temperature change around the detector, an accurate BJT-based temperature sensor is integrated in the circuits as well. Fabricated in an 8-inch wafer, the AlN-based PID with sensing area of 0.29 mm² achieves the detectivity of 6.04× 10⁶ cm√ Hz/W. The readout circuits are implemented in a 40nm-CMOS process, consuming total power of 24.5 μW under 1.2-V supply. Simulation results show that the TIA gain variation is <0.5 dB over PVT corners, the ADC achieves >11-bit resolution over 1 kHz bandwidth, and the temperature error over -20 °C - 80 °C is ±0.65 °C (3σ) without any calibration.