Analysis of Hump Characteristics in Thin-Film Transistors With ZnO Channels Deposited by Sputtering at Various Oxygen Partial Pressures

The electrical properties of thin-film transistors (TFTs) with ZnO channels which were deposited by radio-frequency magnetron sputtering at various oxygen partial pressures [p( O₂)] are investigated. A negative shift of the turn-on voltage with a “hump” was observed, and donorlike traps were generated at intermediate energy levels from the conduction band when the ZnO channel was deposited at p(O₂) below a critical pressure. Thermal desorption spectroscopy study revealed that the donorlike traps were generated when the ZnO film changed from O- to Zn-rich condition. The Zn-related native defects would be a possible origin of the donorlike traps generated at intermediate energy levels in the ZnO TFTs.