Enhancement of Electrical Stability in Oxide Thin-Film Transistors Using Multilayer Channels Grown by Atomic Layer Deposition

The effect of Hf addition on the electrical performance and bias stability of ZnO-based thin-film transistors (TFTs) has been investigated. All channel layers were deposited by atomic layer deposition with various Hf contents. In addition, multilayer oxide channel TFTs consisting of two or three Hf-doped ZnO (HZO) and ZnO layers were developed for the realization of adequate channel mobility and electrical stability. The subthreshold swing and bias stability were improved by the deposition of the thin-HZO layers with amorphous phase as the first and final channel layers. The use of a conductive ZnO layer enhanced the device mobility. The oxide TFTs with a multilayer channel of a-HZO/ZnO/a-HZO exhibited relatively good stability and mobility due to the reduced interface trap density between the channel and dielectric layers, and the suppressed adsorption of negatively charged oxygen on the back channel. The origin of the stability issues and novel channel design are proposed on the basis of the electrical performance of various TFT structures.