Low-frequency noise in high performance and stability of Li-doped ZnO thin-film transistors

In this work, thin film transistors (TFTs) based on the ZnO-doped with different concentrations of Li were fabricated by radio frequency sputtering. Using the optimal Li doping concentration of 1% and rationally designed passivation layer (PVL), a TFT with high mobility of 28.5 cm2/Vs, low SS of 0.28 V decade−1, high Ion/Ioff of 107 and small Vth of 0.8 V were obtained. Moreover, the 1% Li-doped ZnO TFT with Al2O3 PVL exhibits the best stability with the small Vth shifts of 1.1 (− 1.2) V and 1.6 (− 1.8) V under gate bias and light illumination test. Low-frequency noise and x-ray photo-electron spectroscopy band structure analysis suggests that the enhanced properties and stability are mostly due to the Li doping concentration. Because the Li doping not only increased the carrier concentration, but also reduced the oxygen vacancy defects and interface trap density. In addition, the high quality Al2O3 PVL reduced the photo-adsorption/desorption behavior, and protected the channel from environmental influences. Overall, the reliable and high performance Li-doped ZnO TFTs have a great potential in flat-panel display application.