Suppression of Interfacial Disorders in Solution-Processed Metal Oxide Thin-Film Transistors by Mg Doping

The fabrication of high-performance metal oxide thin-film transistors (TFTs) using a low-temperature solution process may facilitate the realization of ultraflexible and wearable electronic devices. However, the development of highly stable oxide gate dielectrics at a low temperature has been a challenging issue since a considerable amount of residual impurities and defective bonding states is present in low-temperature-processed gate dielectrics causing a large counterclockwise hysteresis and a significant instability. Here, we report a new approach to effectively remove the residual impurities and suppress the relevant dipole disorder in a low-temperature-processed (180 °C) AlO_x gate dielectric layer by magnesium (Mg) doping. Mg is well known as a promising material for suppression of oxygen vacancy defects and improvement of operational stability due to a high oxygen vacancy formation energy (E_vo = 9.8 eV) and a low standard reduction potential (E =-2.38 V). Therefore, with an adequate control of Mg concentration in metal oxide (MO) films, oxygen-related defects could be easily suppressed without additional treatments and then stable metal-oxygen-metal (M-O-M) network formation could be achieved, causing excellent operational stability. By optimal Mg doping (10%) in the InO_x channel layer, Mg:InO_x TFTs exhibited negligible clockwise hysteresis and a field-effect mobility of >4 cm² V^-1 s^-1. Furthermore, the electric characteristics of the low-temperature-processed AlO_x gate dielectric with high impurities were improved by Mg diffusion originating in Mg doping, resulting in stable threshold voltage shift in the bias stability test.