Controlled 2D growth approach via atomic layer deposition for improved stability and performance in flexible SnO thin-film transistors

Abstract

Tin monoxide (SnO) has been extensively studied due to its promising theoretical p-type performance. However, the fabrication of SnO thin films and SnO channel thin-film transistors (TFTs) faces hurdles that are mainly related to the low thermal and air stability of SnO and high number of defect states in the crystalline structure. In this study, our aim was to enhance the 2D structure of (001)-aligned tetragonal SnO by controlling the precursor feeding process and evaluating both the water contact angle and grazing-incidence wide-angle X-ray scattering (GIWAXS). When the lateral grain growth of SnO is fully optimized, structural defects are relieved and the c-axis orientation is improved compared to conventionally deposited SnO. This optimized SnO channel TFT exhibited high on/off ratio (7.38 × 10⁶), moderate field effect mobility (μ_FE, 1.86 cm² V⁻¹ s⁻¹), and low subthreshold swing (0.12 V decade⁻¹). Also, this SnO TFT exhibited record stability in positive/negative bias (temperature) stress tests, with ΔV_th values of +0.47 V and −0.11 V under 10 000 s of the stress conditions with ± 2 MV cm⁻¹ at 60 °C. Finally, we reported highly stable flexible SnO TFT with a ΔV_th of −0.06 V after a 10 000-cycle bending test, which has never been reported before.