Fabrication of ZnO thin film transistors by atomic force microscopy nanolithogrophy through zinc thin films

Abstract

Zinc oxide (ZnO) thin film transistors were fabricated by local anodic oxidation (LAO) of polycrystalline zinc film using an atomic force microscope (AFM). Nanometer-thin zinc film can be locally transformed into $p$-type zinc oxide by an anodic oxidation technique using an AFM at room temperature. With this fabrication process, we have fabricated a backgate, Schottky-barrier-contact type thin film ZnO transistor. This fabrication requires no semiconductor material to produce transistors, only conventional metal film. The fabrication creates active area and source/drain contacts through simple AFM oxidation, with no requirement for additional semiconductor thin film deposition and photolithography. A representative LAO thin film transistor fabricated in this study exhibited a field-effect mobility of $23.6\text{ }{\text{cm}}^{2}/\text{V}\text{ }\text{s}$, a peak transconductance of $15.8\text{ }\ensuremath{\mu}\text{S}$, and an ${I}_{\text{on}}/{I}_{\text{off}}$ ratio of ${10}^{6}$. To the best of our knowledge, the mobility value attained for this LAO thin film transistor is higher than that of any previously reported amorphous-silicon-based thin film transistors. Its peak transconductance and ${I}_{\text{on}}/{I}_{\text{off}}$ ratio are also enhanced compared with a backgate field-effect transistor with the same amorphous silicon channel as utilized in conventional thin film transistors.