High-performance annealing-free InGaZnOx thin film transistors by thermal ALD

Abstract

We report indium–gallium–zinc oxide (IGZO) thin-film transistors (TFTs) fabricated entirely by thermal atomic layer deposition (TALD) within a low thermal budget (≤300 °C) and without post-deposition annealing. A targeted O3 overdose step integrated into the Ga2O3 sub-cycles of the IGZO TALD super-cycle raises the local oxygen chemical potential and helps suppress inter-sub-cycle redox reactions and vacancy formation. Structural and chemical analyses confirm smooth, fully amorphous Al2O3/IGZO stacks with abrupt interfaces and reduced oxygen-vacancy signatures, while cation states remain stable. Standard TFTs fabricated from these layer stacks exhibit excellent device performance, including near-ideal subthreshold swing (SS) values of 66.4–70 mV/dec, operation windows within 3 V, field-effect mobilities ranging between μFE = 23.6–25.6 cm2/Vs, threshold voltages (VTH) close to 0 V, and negligible hysteresis. Under positive-bias temperature stress, ΔVTH remains small across 25–85 °C, indicating good device reliability. A holistic comparison with prior ALD-based oxide TFTs shows that the combination of low temperature processing, near-ideal SS, and small drift under stress places our devices on the favorable end of performance–stability trade-off. The O3 overdose concept presented here provides a generalizable lever for oxygen vacancy control in the TALD of multi-cation oxides and is naturally compatible with BEOL and monolithic 3D integration.