Engineering a Subnanometer Interface Tailoring Layer for Precise Hydrogen Incorporation and Defect Passivation for High-End Oxide Thin-Film Transistors

Abstract

Top-gate self-aligned structured oxide thin-film transistors (TFTs) are suitable for the backplanes of high-end displays because of their low parasitic capacitances. The gate insulator (GI) deposition process should be carefully designed to manufacture a highly stable, high-mobility oxide TFT, particularly for a top-gate structure. In this study, a nanometer-thick Al2O3 layer via plasma-enhanced atomic layer deposition (PE-ALD) is deposited on the top-gate bottom-contact structured oxide TFT as the interface tailoring layer, which can also act as the hydrogen barrier to modulate carrier generation from hydrogen incorporation into the active layer of the TFT during the following process such as postannealing. Al-doped InSnZnO (Al/ITZO) with an Al/In/Sn/Zn atomic ratio composition of 1.7:24.3:40:34 was used for high mobility oxide semiconductors, and an Al2O3/Si3N4 bilayer was used for the GI. The degradation issue due to the excellent barrier characteristics of Al2O3 and Si3N4 can be minimized. An oxide TFT fabricated without the interface tailoring layer exhibits conductor-like characteristics owing to the excessive carrier generation by hydrogen incorporation. However, TFTs with additional interface layers exhibit reasonable characteristics and distinct trends in electrical characteristics depending on the thicknesses of the interface layers. The optimized devices exhibit an average turn-on voltage (V-on) of -0.31 V with 33.63 cm(2)/(V s) of high mobility and 0.09 V/dec of subthreshold swing value. The interfaces between the active layer and hydrogen barriers were investigated using a high-resolution transmission electron microscope, contact angle measurement, and secondary ion mass spectroscopy to reveal the origin of the trends in properties between the devices. The top-gate device with a hydrogen barrier using the four-cycle deposition exhibits optimum electrical characteristics of both high mobility and good stability with only a 0.04 V shift of V-on under positive-bias temperature stress (PBTS). We realize a high-end, self-aligned TFT with high mobility [34.7 cm(2)/(V s)] and negligible V-on shift of -0.06 V under PBTS by applying a subnanometer hydrogen barrier.