Nanothick TiO2 Channel Thin Film Transistors for UV and Gas Sensing

Abstract

Nanothick TiO2 channel-thin film transistors (TFTs) are examined as UV and gas sensors. The TiO2 thin films were deposited by atomic layer deposition on thermally oxidized n+ Si substrates with deposition thicknesses from 17 to 42 nm, where the channel length and width were fixed at 60 μm and 1 mm, respectively. The titanium drain and source electrodes were fabricated on the TiO2 channel and the n+ Si substrate was used as the gate electrode. The nanothick TiO2-channel TFT exhibits an extremely high drain current modulation of ∼20 μA in the atmosphere with a UV exposure of 1.6 × 10−5 W cm−2 and a wavelength of 278 nm. This corresponds to a UV sensitivity of 2 × 103 A W−1. The strong drain current modulation by the UV light is explained not only with the direct absorption of the UV photons in the channel but also with the surface interactions with gas molecules in the atmosphere. In the course of the mechanism study about the UV sensing, we confirm the strong modulation of the drain current with various ambience of air, dry air, N2, and vacuum, suggesting a possibility as the gas sensor in the dark. The operation mechanism of the nanothick TiO2 TFT is discussed in this paper.