Effects of thermal annealing time and molar ratio of channel layers on solution-processed ZnO/SnO2 thin-film transistors

Abstract

In solution-processed zinc tin oxide (ZTO) dual-active-layer (DAL) thin-film transistors (TFTs), a thermal limitation exists whereby the ZTO channel layer requires a high annealing temperature—above 470 °C—to achieve stable performance. This disadvantage has been overcome by applying ZnO/SnO2 channel structures and additional annealing methods. However, these methods are expensive due to equipment requirements. Therefore, we aimed at lowering the annealing temperature of solution-processed ZnO/SnO2 TFTs by varying the molar ratio and annealing conditions of the channel layers. The optimized TFTs were fabricated at an annealing temperature of 350 °C without employing additional annealing methods. The fabricated TFTs showed superior and more stable performance as compared to ZTO TFTs annealed at 350 °C. The electrical characteristics of the fabricated ZnO/SnO2 TFTs included a saturation mobility (µsat) of 3.04 cm2/V·s, an on-off-current ratio (ION/OFF) of 1.41 × 106, a threshold voltage (Vth) of 3.04 V, and a subthreshold swing (SS) of 1.49 V/dec. Based on X-ray photoelectron spectroscopy results, compared with the ZTO DAL channel layer, the ZnO/SnO2 channel layer showed an increased ratio of metal-oxygen bonds and a decreased ratio of metal-hydroxyl bonds in O 1s deconvolution peaks.