Exploration of Chemical Composition of In-Ga-Zn-O System via PEALD Technique for Optimal Physical and Electrical Properties

In-Ga-Zn-O (IGZO) material has been researched due to its favorable electrical characteristics for application in thin-film transistor (TFT) applications such as low off current and relatively high mobility. However, most recently, as the developing and expanding application fields, conventional IGZO is a challenging aspect because higher mobility and excellent step-coverage are required to be applied to high-resolution displays and 3D NAND. In this regard, atomic layer deposition (ALD) is suggested as a novel deposition method for tackling issues. Here, this work systematically synthesizes IGZO films with various compositions by the supercycle technique of plasma-enhanced ALD (PEALD) to determine the optimum metal cation composition range of the IGZO system for high-mobility TFTs. The trends in the metal composition dependent electrical properties of ALD processed IGZO films are comparable to the previously reported results, while the structural properties are exclusive. Since both microstructure and carrier concentration affect to device characteristics complexly, the optimal In-Ga-Zn region is newly demonstrated via PEALD (X-In: 0.56-0.63, X-Ga: 0.13-0.17, X-Zn: 0.17-0.34). In this region, the device exhibits a remarkably high mu(FE) of 41.4-43.7 cm(2) V-1 s(-1), a low subthreshold swing (SS) of 0.24-0.25 V decade(-1), an initial threshold voltage (V-th) of -0.9 to -1.0 V, and a slight V-th shift (0.01 V) under the positive bias temperature stability (PBTS).