TIN OXIDE GAS SENSOR FABRICATED USING CMOS MICRO-HOTPLATES AND INSITU PROCESSING

We report the first monolithic tin oxide (SnO2) gas sensor realized by commercial CMOS foundry fabrication (MOSIS) and post-fabrication processing techniques. The device is composed of a sensing film that is sputter-deposited on a silicon micromachined hotplate. The fabrication technique requires no masking and utilizes in-situ process control and monitoring of film resistivity during film growth. Micro-hotplate temperature is controlled from ambient to 500-degrees-C with a thermal efficiency of 8-degrees-C / mW and thermal response time of 0.6 ms. Gas sensor responses of pure SnO2 filMS to H-2 and O2 with an operating temperature of 350-degrees-C are reported. The fabrication methodology allows integration of an array of gas sensors of various films with separate temperature control for each element in the array, and circuits for a low-cost CMOS-based gas sensor system.