Effects of IGZO film thickness on H₂S gas sensing performance: Response, excessive recovery, low-frequency noise, and signal-to-noise ratio

In this work, we investigate the effects of IGZO film thickness on the H₂S gas sensing performance, such as response, excess recovery, low-frequency noise (LFN), and signal-to-noise ratio (SNR) in the resistor- and FET-type gas sensors. A transition of the dominant sensing area from the surface to the bulk of the IGZO film is observed with increasing film thickness. Also, excessive recovery is observed and its detailed mechanism is analyzed for the first time. The resistor-type gas sensor with thicker IGZO film has a smaller 1/f noise due to the decreased trap density and impurity scattering, which guarantees the largest SNR and the lowest limit of detection (LOD). In the case of the FET-type gas sensor, the thicker film with high porosity allows H₂S gas to diffuse more easily into the IGZO-O/N/O interface and increases the response. Also, the LFN characteristics of the FET-type gas sensor have no dependence on the IGZO film thickness. Thus, the SNR of the FET-type gas sensor is the largest when the IGZO film thickness is 60 nm.