Single Chip Gas Sensor Array for Air Quality Monitoring

This paper describes the fabrication of a four element gas sensor array for monitoring air pollutants, namely CO, CO2, NO2, and SO2. The four micro-heaters share a single suspended SiO2 diaphragm, utilizing thermal proximity to achieve low power consumption (similar to 10 mW for 300 degrees C). Plasma enhanced chemical vapour deposition SiO2 diaphragm is demonstrated to give higher yield compared with thermally grown SiO2. Sensor array elements are fabricated by customizing each element to sense a specific gas, using different sensing materials. Optimized thin films of ZnO, BaTiO3-CuO doped with 1% Ag, WO3, and V2O5 are used for selective sensing of CO, CO2, NO2, and SO2. Four sensors can be independently controlled to operate at different temperatures to get high selectivity for test gases. The sensor array is packaged on Kovar header, and then characterized for gas sensing. It is demonstrated that the sensors exhibit good sensitivity and selectivity. We report a maximum repeatable response to CO(similar to 78.3% for 4.75 ppm), CO2 (65% for 900 ppm), NO2 (similar to 1948.8% for 0.9 ppm), and SO2 (similar to 77% for 3 ppm) at operating temperatures of 330 degrees C, 298 degrees C, 150 degrees C, and 405 degrees C, respectively.