Effect of dielectric thickness and annealing on threshold voltage instability of low temperature deposited high-k oxides on ZnO TFTs

Abstract

We investigated the effects of hafnium oxide (HfO2) gate dielectric thickness and forming gas annealing on threshold voltage instability in zinc oxide thin film transistors using a variety of gate voltage - drain current testing methodologies. We found that dielectric thickness reduction and annealing significantly decreased the threshold voltage instability and the Vt reduction remained over an extended period of testing. Then, a similar investigation was conducted on zinc oxide thin-film transistors (ZnO TFT) with a thin layer of aluminum oxide (Al2O3) as the dielectric where a significant reduction in ΔVt was also observed.