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

Abstract

We report on the fabrication and characterization of a novel oxygen sensor based on a TiO2 thin film field effect transistor (FET) deposited on a silicon substrate with an oxide layer by magnetron sputtering. TiO2 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 TiO2 film. Under ultraviolet (UV) irradiation, at 310 nm wavelength, the photogenerated carriers in the TiO2 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 (ΔIphoto/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 TiO2 thin film FETs.