Inactivation of low-temperature-induced numerous defects at the electrode/channel interfaces using ultrathin Al₂O₃ layers

The high demand for flexible and stretchable electronics has resulted in new bottlenecks on the process design of amorphous oxide thin-film transistors (TFTs) fabricated at ≥300 °C that involves low-temperature processes to accommodate for the use of polymer substrates. Unlike previous studies aiming to achieve better channel properties, our study focuses on the low-temperature effects of electrical contacts at the source/drain electrodes and oxide channel junction. The decrease in the process temperature causes unfavorable evident changes from an almost ohmic (350 °C) to Schottky (200 °C) junction and shows coincident trends with the degradation of TFT performances. Thus, we here propose a creative process design using ultrathin Al₂O₃ interlayers between the electrode and channel, where they inactivate the role of numerous surface defects existing on the a-IZO channels deposited at low temperatures. The a-IZO TFT with 13 Å Al₂O₃ optimally exhibits a field effect mobility of 17.3 cm²/Vs in the 200 °C low-temperature annealing process, comparable to that of a-IZO TFT annealed at 350 °C. Similarly, the ultrathin Al₂O₃ interlayers led to the reduced specific contact resistance and ohmic junction behavior. From capacitance–voltage analyses, we elucidated that they were attributed to the significantly reduced trapping events of the charges by passivating the interface defects.