All-oxide thin-film transistors with channels of mixed InOx-ZnOy formed by plasma-enhanced atomic layer deposition process

To make high mobility oxide thin-film transistors (TFTs) for transparent large displays, the authors fabricated all-oxide TFTs having amorphous mixed-oxide channels of indium oxide (InOx) and zinc oxide (ZnOy). Liquid precursors of 3-(dimethyl amino)propyl-dimethyl indium (C₇H₁₈InN) and diethyl zinc [(C₂H₅)₂Zn] and oxygen plasma were used to form mixed-oxide channels by plasma-enhanced atomic layer deposition (ALD). The authors varied the cycle ratio of InOx and ZnOy to deduce the optimal ratio of InOx:ZnOy for high performance TFTs. X-ray photoelectron spectroscopy analyses were performed to reveal the decrease in the oxygen-deficient state as the fraction of InOx increases. At a deposition cycle ratio of InOx:ZnOy = 2:1, the TFT demonstrated the best performance of field effect mobility of 30.3 cm²/V s, subthreshold of 0.14 V/decade, and I_on/I_off ratio of 3.1 × 10⁹. By adjusting the relative cycles of different oxides in an ALD process, one may obtain the desired mixed-oxide channel TFT properties, which is not readily possible in the sputtering process. By varying the compositions of the oxide channel layer, the latitude of device fabrication could be widening, thereby enabling performance customization.