In2O3-based thin-film transistors with a (400) polar surface for CO2 gas detection at 150 °C

Abstract

Because of increasing demand for CO₂ detection, CO₂ sensors capable of low-temperature operation are desired. However, conventional oxide semiconductor sensors still require high operating temperatures. In this study, we fabricated a CO₂ sensor that can operate at 150 °C. The sensor is based on an open-channel-type thin-film transistor (TFT) structure with an In₂O₃(4 0 0) polar plane as a channel. Because the In₂O₃(4 0 0) surface is polar, many OH groups are adsorbed onto the as-prepared surface. When CO₂ gas is introduced, CO₂ molecules react with the OH groups and the TFT characteristics change. As a result, CO₂ can be detected with a sensitivity 2.9 times greater than that under an inert N₂ atmosphere despite the operating temperature of only 150 °C. In a TFT with nonpolar In₂O₃(2 2 2) planes, the sensitivity remains at 1.3 times. We therefore believe that TFTs fabricated with the polar surface of an oxide semiconductor are useful for gas-sensing applications.