Enhancing Oxygen Sensing Precision Through Gate-Controlled TiO2 Field Effect Transistors Under Ultraviolet Excitation

We report on the fabrication and characterization of a novel oxygen sensor based on a TiO 2 thin film field effect transistor (FET) deposited on a silicon substrate with an oxide layer by magnetron sputtering. TiO 2 is a n -type semiconductor with a wide band gap, which allows the formation of oxygen vacancies or adsorbed oxygen species on its surface under ambient conditions. These oxygen-related defects act as electron traps that modulate the electrical conductivity of the TiO 2 film. Under ultraviolet (UV) irradiation, at 310 nm wavelength, the photogenerated carriers in the TiO 2 film are captured by the oxygen defects, resulting in a decrease of the film resistance that depends on the oxygen concentration. We demonstrate that the sensitivity and resolution of the oxygen sensor can be enhanced by applying a positive gate voltage to the FET device. The photocurrent variation per unit of oxygen concentration (Δ I photo /ΔCPO) increases from 1.08 at VG =0 V to 2.5 at VG= 20 V in the range of 5%–20% oxygen concentration. The gate voltage also extends the controllable range of oxygen defects and photocurrent. Our study provides a new insight into the design and optimization of gas sensors based on TiO 2 thin film FETs.