Indium-free Zn-Sn-Al-O based thin-film transistors fabricated by plasma-enhanced atomic layer deposition

Abstract

The escalating demands of advanced display technologies, particularly in virtual and augmented reality applications, necessitate the development of sustainable alternatives to conventional indium-based amorphous oxide semiconductors. This study presents the fabrication and characterization of indium-free zinc-tin-aluminum oxide (ZTAO) thin-film transistors (TFTs) using plasma-enhanced atomic layer deposition (PEALD). Through precise control of PEALD supercycles, we systematically modulate the composition of ZTAO films while maintaining an amorphous structure. The optimized ZTAO (15:15:1) composition demonstrates superior electrical characteristics with a Hall mobility of 13.9 cm² V⁻¹ s⁻¹. Capitalizing on these optimized ZTAO films, we fabricate staggered bottom-gate TFTs and assess their electrical performances. The ZTAO (15:15:1) TFTs emerged as the optimal configuration, demonstrating excellent performance with a lower threshold voltage (−1.46 ± 0.34 V), high current on/off ratio ((1.13 ± 0.53) × 10⁶), remarkable field-effect mobility (10.92 ± 0.14 cm² V⁻¹ s⁻¹), and minimal subthreshold swing (0.48 ± 0.01 V dec⁻¹). Enhancement of the performance is further achieved through post-annealing treatment at 250 °C in air, which also confirms the robust bias stability of devices (threshold voltage shift: 0.76 V and −1.17 V for positive and negative bias stress of 2000 s, respectively). These findings demonstrate the potential of PEALD-based ZTAO as a sustainable and high-performance alternative for next-generation display technologies.