Amorphous InGaZnO x (a-IGZO) thin-film transistors (TFTs) are currently used in flat-panel displays due to their beneficial properties. However, the mobility of ∼10 cm2/(V s) for the a-IGZO TFTs used in commercial organic light-emitting diode TVs is not satisfactory for high-resolution display applications such as virtual and augmented reality applications. In general, the electrical properties of amorphous oxide semiconductors are strongly dependent on their chemical composition; the indium (In)-rich IGZO achieves a high mobility of 50 cm2/(V s). However, the In-rich IGZO TFTs possess another issue of negative threshold voltage owing to intrinsically high carrier density. Therefore, the development of an effective way of carrier density suppression in In-rich IGZO will be a key strategy to the realization of practical high-mobility a-IGZO TFTs. In this study, we report that In-rich IGZO TFTs with vertically stacked InO x , ZnO x , and GaO x atomic layers exhibit excellent performances such as saturation mobilities of ∼74 cm2/(V s), threshold voltage of −1.3 V, on/off ratio of 8.9 × 108, subthreshold swing of 0.26 V/decade, and hysteresis of 0.2 V, while keeping a reasonable carrier density of ∼1017 cm–3. We found that the vertical dimension control of IGZO active layers is critical to TFT performance parameters such as mobility and threshold voltage. This study illustrates the potential advantages of atomic layer deposition processes for fabricating ultrahigh-mobility oxide TFTs.

Indium oxide (In 2 O 3 ) thin films were deposited via thermal atomic layer deposition (ALD) to exploit their potential as semiconductors in thin-film transistors (TFTs), using a new liquid t y p e i n d i u m c o m p l e x p r e c u r s o r ( I n -(CH 3 ) 3 [CH 3 OCH 2 CH 2 NHtBu]). In 2 O 3 films were deposited successfully at lower temperatures and exhibited a satisfactory growth rate (∼0.35 Å per cycle). In addition, we investigated the effect of deposition temperature from 100 to 250 °C on the microstructure and chemical and physical properties of In 2 O 3 films. Interestingly, the In 2 O 3 film had a clear rhombohedral structure at deposition temperatures from 100 to 150 °C. For the 200 and 250 °C deposition temperatures, the phase of In 2 O 3 transformed to a cubic structure. The crystalline structure of the In 2 O 3 film was extremely sensitive to deposition temperatures, giving rise to a wide range of tunable physical and electrical properties. Based on a comparison of comprehensive structural transmission electron microscopy analysis, density functional theory calculations, and systematic experimental measurements, we explored the possibility of TFTs with an ALD-processed In 2 O 3 layer as a semiconductor.

Atomic layer deposition (ALD) is a promising deposition method to precisely control the thickness and metal composition of oxide semiconductors, making them attractive materials for use in thin-film transistors because of their high mobility and stability. However, multicomponent deposition using ALD is difficult to control without understanding the growth mechanisms of the precursors and reactants. Thus, the adsorption and surface reactivity of various precursors must be investigated. In this study, InGaO (IGO) semiconductors were deposited by plasma-enhanced atomic layer deposition (PEALD) using two sets of In and Ga precursors. The first set of precursors consisted of In­(CH3)3[CH3OCH2CH2NHtBu] (TMION) and Ga­(CH3)3­[CH3­OCH2­CH2­NHtBu]) (TMGON), denoted as TM-IGO; the other set of precursors was (CH3)2In­(CH2)3N­(CH3)2 (DADI) and (CH3)3Ga (TMGa), denoted as DT-IGO. We varied the number of InO subcycles between 3 and 19 to control the chemical composition of the ALD-processed films. The indium compositions of TM-IGO and DT-IGO thin films increased as the InO subcycles increased. However, the indium/gallium metal ratios of TM-IGO and DT-IGO were quite different, despite having the same InO subcycles. The steric hindrance of the precursors and different densities of the adsorption sites contributed to the different TM-IGO and DT-IGO metal ratios. The electrical properties of the precursors, such as Hall characteristics and device parameters of the thin-film transistors, were also different, even though the same deposition process was used. These differences might have resulted from the growth behavior, anion/cation ratios, and binding states of the IGO thin films.

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