Ternary Ga–Sn–O and quaternary In–Ga–Sn–O channel based thin film transistors fabricated by plasma-enhanced atomic layer deposition

Abstract

Amorphous In–Ga–Sn–O (IGTO), as an n-type amorphous oxide semiconductor, has attracted interest owing to its potential applications to the vertical NAND or 3D DRAM channels as well as in high-mobility thin-film transistors (TFTs) for high-resolution displays. In this study, ternary Ga–Sn–O (GTO) and quaternary IGTO films were deposited through plasma-enhanced atomic layer deposition (PEALD) at 200 °C, using dimethyl(N-ethoxy-2,2-dimethylcarboxylicpropanamide)indium, trimethylgallium, and bis(1-dimethylamino-2-methyl-2-propoxide)tin as the In, Ga, and Sn precursors, respectively. First, GTO films were fabricated through PEALD with varying Ga2O3:SnO2 subcycle ratios. The remarkable evolutions of the microstructure and electrical properties of the PEALD GTO films were observed depending on the Ga/Sn cationic ratio. Subsequently, the growth characteristics of the quaternary PEALD IGTO films were examined by introducing In2O3 subcycles, and the In:Ga:Sn cationic composition was precisely engineered by varying the ratios of In2O3, SnO2, and Ga2O3 subcycles in the IGTO deposition process. Composition-controlled IGTO bottom gate staggered-type TFTs were fabricated, and their electrical performance was evaluated depending on the In:Ga:Sn cationic composition of the IGTO channel layer. The optimized TFT with the In0.38Ga0.32Sn0.30Ox film exhibited a high field-effect mobility of 22.5 cm2/V s, turn-on voltage of −4.4 V, and subthreshold swing of 0.26 V/dec.