Metal Oxide-Based Monolithic Gas Sensing Microsystem With 11.1 mW Power Consumption

The smart gas sensing market in long-term applications has driven increasing demand for low-power monolithic microsystems. Metal oxide gas sensors offer advantages such as compact size, low cost, and long lifetime. However, their monolithic integration remains challenging due to high heating power requirements and CMOS process compatibility issues. This work proposes a monolithic gas sensing microsystem, composed of a SnO₂-based gas sensor and an on-chip CMOS circuit. To reduce heating power, the geometric parameters of the cantilever-based micro-hotplate are optimized through thermal simulation. In addition, the SnO₂ sensing film is deposited by sputtering and lift-off process to enable precise patterning, allowing for reduced beam dimension and improved thermal efficiency. A post-CMOS process is developed to ensure CMOS process compatibility and enable mass production. Experimental results indicate that the relative change in amplifier gain caused by the post-CMOS process is within 0.6%. Through optimization of geometric parameters and fabrication process, the microsystem achieves a sensitive and repeatable response to H₂ at sub-10 ppm levels with total power consumption of 11.1 mW, demonstrating its potential for long-term operation in smart gas monitoring.