Structural, Optical, and Electrical Properties of InOx Thin Films Deposited by Plasma-Enhanced Atomic Layer Deposition for Flexible Device Applications

Indium oxide (InOx) thin films have attractive carrier transport properties for oxide semiconductors because of the large isotropic 5 s orbital overlap. In this study, InOx films were deposited by plasma-enhanced atomic layer deposition (PEALD). We evaluated the effects of the ALD process conditions such as the process temperature, plasma power, and plasma duration time on the microstructure, physical, chemical, and electrical properties of the as-deposited InOx films. The InOx film deposited at an even growth temperature of 100 °C exhibited a polycrystalline structure without impurities. As the growth temperature increased, the (222) orientation became favorable and the surface morphology of the as-deposited films improved. In addition, staggered-bottom gate structure thin-film transistors (TFTs) were fabricated to examine the feasibility of the ALD-processed InOx film as a channel material for TFTs. As the growth temperature increased from 100 to 250 °C, the mobility increased from 3.4 to 12.6 cm2/V s and the hysteresis value decreased from 1.85 to 0.94 V due to increasing carrier concentrations and decreasing defect states, respectively. Finally, a flexible device was fabricated on a polyethylene naphthalate substrate; the device parameters of Vth and μsat were determined to be 2.21 V and 16.6 cm2/V s, respectively. These results demonstrate the potential for fabricating flexible TFT applications using PEALD.