Effect of a pre-bias on the adsorption and desorption of oxidizing gases in FET-type sensor

Abstract

An efficient pre-bias method is proposed in the reading operation of a Field-Effect-Transistor(FET)-type gas sensor which utilizes flatband voltage change of the sensing material formed between the control-gate (CG) and floating-gate (FG) of the FET. The proposed method improves greatly recovery speed and shortens recovery time by more than 10 times at 180°C, which can reduce the power consumed by heater. Since the polarity of the pre-bias affects response, sensing and recovery speeds, it is possible to identify the redox characteristics of the detected gas. To verify experimentally the pre-bias effect, we apply pulses for the pre-biasing and reading to the sensor with a sensing material of 200-nm-thick SnOx layer to detect NO2 gas as an example. The mechanism is explained theoretically by energy band theory. The pre-biasing method is expected to open a new biasing scheme which improves significantly sensing characteristics, gas identification, and power dissipation.