Performance Enhancement for Indium-Free Metal Oxide Thin-Film Transistors with Double-Active-Layers by Magnetron Sputtering at Room Temperature

Abstract

We prepared an indium-free metal oxide thin-film transistor (TFT) using a double-active-layers structure at room temperature. We changed the growth sequence of Al-doped zinc oxide (AZO) and zinc oxide (ZnO) double-active-layers on Si/SiO2 substrates by magnetron sputtering deposition to regulate the field-effect performance of TFTs. According to the analysis of field-effect properties before and after annealing in different atmospheres, the performance of TFT devices with ZnO/AZO/SiO2/Si double-active-layers was obviously better than that with single AZO or ZnO active layer and inverted AZO/ZnO/SiO2/Si double-active-layers in the device structure. The active layer with higher carrier concentration (AZO in this case) was closer to the dielectric layer, which was more favorable for carrier regulation in TFT devices. In addition, the annealed device had a lower on/off ratio (Ion/Ioff), easier-to-reach on-state, and higher mobility. Furthermore, the performance of the devices annealed under vacuum condition was obviously better than that annealed under air atmosphere. The Ion/Ioff could reach 6.8 × 105 and the threshold voltage was only 2.9 V.