Highly improved response and recovery characteristics of Si FET-type gas sensor using pre-bias

By adopting a new pulse pre-bias (V_pre) scheme, the response and recovery characteristics is significantly improved in Si field-effect transistor (FET)-type gas sensor having ZnO film as a sensing layer. A target gas of NO₂, which is one of oxidizing gases, is detected by the FET-type sensor at various V_pres. It is demonstrated that a negative V_pre (-3 V) improves the response by ~2.5 times and a positive V_pre (4 V) reduces the recovery time by ~9 times in 0.5 ppm NO₂ ambience at 180 °C. The mechanism responsible for the pre-bias effect is explained using energy band diagram.