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 InO_x and GaZnO_y 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 InO_x and GaZnO_y blocks. Here, we evaluate the effect of the thickness of active GaZnO_y and InO_x layers in nanolaminated (InO_x)_n(GaZnO_y)_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 GaZnO_y layer increased, the V_th value shifted positively, and mobility decreased due to the thick GaZnO_y layers to act as effective barriers to out-diffusion of oxygen in the InO_x layers. We also varied the InO_x layer thickness from 4 to 8 nm to improve the mobility of the TFTs. Mobility was shown to increase up to an InO_x layer thickness of 6 nm (with a maximum value of 18 cm² V⁻¹ s⁻¹), but decreased at InO_x layer thicknesses of greater than 6 nm. Additionally, as the InO_x layer increased, the positive bias temperature stress stability degraded. This suggests that the trap site in the interface between the InO_x and GaZnO_y layers increases due to increased crystalline structure, and that nanolaminated (InO_x)_n(GaZnO_y)_m TFTs can effectively control electrical performance.