Control of Surface Potential in WO 3 Gas Sensors Using UV Light

We introduce the first control of surface potential (SP) in MOX gas sensors using UV light (367 nm). The control is based on sigma-delta modulation implementing a sliding mode control on the surface potential of the sensor. Measurements are presented using a sensor made of WO 3 nanowires under mild heating at 125 oC. Without control, the sensor shows no response to ethanol. Under control, the detection limit is beyond 2 ppm with a response time below 5 minutes. For NO 2 , the response time is reduced by a factor of 10. By operating the sensor at constant SP it is possible to improve both dynamics and sensitivity. This new methodology applies generally to a wide range of gas sensitive materials and transducing elements.