Plasma-enhanced atomic-layer deposition of active layers of nanolaminated (InOx)(n)(GaZnOy)(m) for thin-film transistors

Abstract

In this study, we describe the deposition of nanolaminated InOx and GaZnOy layers by a supercycle method in plasma-enhanced atomic-layer deposition (PEALD) to control the electrical and physical properties of oxide semiconductor films. The unique physical and electrical properties of homologous InGaZnO compounds can be varied by changing the thickness of the InOx and GaZnOy blocks. Here, we evaluate the effect of the thickness of active GaZnOy and InOx layers in nanolaminated (InOx)(n)(GaZnOy)(m) on the microstructural, physical, and electrical properties of thin-film transistors (TFTs) using these as-deposited films. From microstructural observations, a multilayer was formed with a sharp interface but no metal-cation mixing by chemical diffusion. As the thickness of the GaZnOy layer increased, the V-th value shifted positively, and mobility decreased due to the thick GaZnOy layers to act as effective barriers to out-diffusion of oxygen in the InOx layers. We also varied the InOx layer thickness from 4 to 8 nm to improve the mobility of the TFTs. Mobility was shown to increase up to an InOx layer thickness of 6 nm (with a maximum value of 18 cm(2) V-1 s(-1)), but decreased at InOx layer thicknesses of greater than 6 nm. Additionally, as the InOx layer increased, the positive bias temperature stress stability degraded. This suggests that the trap site in the interface between the InOx and GaZnOy layers increases due to increased crystalline structure, and that nanolaminated (InOx)(n)(GaZnOy)(m) TFTs can effectively control electrical performance.