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

Thin-film transistors (TFTs) featuring ultrathin ($\approx$3 nm) indium gallium oxide (InGaO) channels synthesized by atomic layer deposition (ALD) with systematically varied In:Ga ratios (30%–90% In) were studied. A tradeoff between threshold voltage ($V_{\text {T}}\text {)}$and field-effect mobility ($\mu _{\text {FE}}\text {)}$is observed with varying In content in the channel. As the In-content reaches between 60% and 75%, the device changes from enhancement mode to depletion mode. By adding an O3treatment after source/drain formation, the devices exhibited significant enhancement in subthreshold characteristics and stability. Notably, the 90% In-content TFT evolves from nonideal to excellenton–offcharacteristics, exhibiting a subthreshold slope as low as ~65 mV/dec. Meanwhile,$\mu _{\text {FE}}$increases monotonically with increasing In concentration, reaching a maximum of 47.1 cm2/V$\cdot $s for the device with a 90% In-content channel after O3treatment. The linear correlation between$\mu _{\text {FE}}$and 1/$R_{\text {CH}}$verifies that the enhancements of$\mu _{\text {FE}}$with In-content result dominantly from intrinsic channel conductance. Positive-bias-stress (PBS) stability is dramatically improved after O3treatment. Threshold voltage shifts ($\Delta V_{\text {T}}\text {)}$after stressed at$V_{\text {G}} = V_{\text {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 O3treatment to achieve high-performance and stable oxide TFTs for future low-power electronics.