Effects of Composition and Ozone Treatment on the Electrical Performance and Stability of ALD Indium Gallium Oxide TFTs

Thin-film transistors (TFTs) featuring ultrathin (≈ 3 nm) indium gallium oxide (InGaO) channels synthesized by atomic layer deposition (ALD) with systematically varied In:Ga ratios (30%–90% In) were studied. A tradeoff between threshold voltage (V_T) and field-effect mobility (µ_FE) is observed with varying In content in the channel. As the In-content reaches between 60% and 75%, the device changes from enhancement mode to depletion mode. By adding an O₃ treatment after source/drain formation, the devices exhibited significant enhancement in subthreshold characteristics and stability. Notably, the 90% In-content TFT evolves from nonideal to excellent ON–OFF characteristics, exhibiting a subthreshold slope as low as ~65 mV/dec. Meanwhile, µ_FE increases monotonically with increasing In concentration, reaching a maximum of 47.1 cm²/V · s for the device with a 90% In-content channel after O₃ treatment. The linear correlation between µ_FE and 1/ R_CH verifies that the enhancements of µ_FE with In-content result dominantly from intrinsic channel conductance. Positive-bias-stress (PBS) stability is dramatically improved after O₃ treatment. Threshold voltage shifts (ΔV_T) after stressed at V_G = V_T+3 V for 3600 s are 9 and 64 mV for channels with 60% and 75% In-content, respectively. These findings underscore the potential of combining compositional engineering and O₃ treatment to achieve high-performance and stable oxide TFTs for future low-power electronics.