Low-Power IGZO TFTs with Improved Positive Bias Stability via Atomic Layer Deposition-Based H2O Treatment

Abstract

In this work, a plasma-free atomic layer deposition (ALD)-based H2O post-treatment method is proposed to precisely modulate hydrogen-related (H-related) traps in indium gallium zinc oxide (IGZO) thin-film transistors (TFTs) by the number of H2O treatment cycles. Under the optimized condition, the scaled device with a channel length of 70 nm exhibits a near-ideal subthreshold swing of 62.9 mV/dec, a low threshold voltage (VTH) of 0.18 V, an acceptable static leakage current, and a high drive current of 3.29 μA/μm at an overdrive voltage and drain voltage of 1 V. In addition, the treated device shows only a 13 mV of VTH shift after 1000 s positive bias stress (PBS), corresponding to a 94% improvement compared with the pristine device. These improvements are attributed to the introduction of two different polarities of hydrogen-related traps after H2O treatment. Furthermore, the influence of H-related traps on bias stability and the mechanisms responsible for VTH shift are systematically clarified. These results establish that an optimized hydrogen incorporation window that maximizes the beneficial effects while balancing severe hydrogen-induced degradation caused by excessive hydrogen incorporation. Consequently, scaled IGZO TFTs with fast switching, low-power operation, high performance, and high reliability can be achieved, providing strong potential for back-end-of-line (BEOL)-compatible electronics and monolithic three-dimensional integrated applications.