Trilayer ZnO Thin-Film Transistors With In Situ Al₂ O₃ Passivation

In this letter, we report trilayer ZnO thin-film transistors (TFTs) with in situ Al2O3passivation fabricated using plasma-enhanced atomic layer deposition. The bottom-gate, top-contact TFTs use an Al2O3-ZnO-Al2O3trilayer deposited in one deposition run at 200°C that provides protection for the active layer back surface with no extra passivation step. Compared with Al2O3passivated, nontrilayer ZnO TFTs, these trilayer devices have similar field effect mobility, but more positive turn-on voltage and improved bias stability. Seven-stage trilayer ZnO TFT ring oscillators operated at 3.5 MHz at a supply voltage of 17 V, corresponding to a propagation delay of ~ 27 ns/stage.