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

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.