Effect of charge storage engineering on the NO2 gas sensing properties of a WO3 FET-type gas sensor with a horizontal floating-gate

In this paper, we investigate the effects of charge storage engineering (CSE) on the NO2 gas sensing properties such as response, recovery, and sensitivity of a FET-type gas sensor with a horizontal floating-gate (FG) having tungsten trioxide (WO3) as a sensing layer. When the FET transducer is set at an erase state (Delta V-th = -2 V), the holes injected into the FG by Fowler-Nordheim (F-N) tunneling increase the electron concentration at the WO3-passivation layer interface. Accordingly, an oxidizing gas, NO2, can take more electrons from WO3, which increases the change in the FG voltage (Delta V-FG) by a factor of 2.4. Also, the recovery speed of the sensor in the erase state can be improved by applying pre-bias (V-pre) which is larger than the read bias (V-read). As the carriers in the WO3 film that can interact with NO2 increase by the excess holes stored in the FG by the erase operation, the sensitivity of the sensor also increases 3.2 times. The effects of CSE on various sensing performances are explained using energy band diagrams.