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

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 In_0.38Ga_0.32Sn_0.30O_x 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.