Effects of channel layer thickness and time on the electrical characteristics of ZnO: (Li, N) TFT

The preparation and electrical properties of ZnO: (Li,N) thin film transistors were studied in this work. The Li–N dual doped ZnO films, as the active layers with thickness varied from 20 to 60 nm, were deposited on SiO2/n-type Si substrates by radio frequency magnetron sputtering. The transistor with 30-nm-thick ZnO: (Li,N) film shows the best performance with a field effect mobility of 33.6 cm2/V.s, a threshold voltage of −6 V and an on/off current ratio of 1.08 × 108. And the time-dependent instability of the device was studied. The mobility increases to 41.5 cm2/V after 120 days, and then decreases to 31.2 cm2/V after 180 days, accompanied by a negative shift of threshold voltage and a decrease of on/off ratio as day increases. The main cause of the instability may be the adsorption of humidity from ambient air.