Rational design of oxide heterostructure InGaZnO/TiO2 for high-performance thin-film transistors

Abstract

In this study, hetero-structured and self-passivated oxide thin film transistors (TFTs) were fabricated, wherein the channel comprised a N2O plasma (a-IGZO:N2O) treated a-IGZO front layer and TiO2 ultra-thin back layer. A high field-effect mobility (μFE) of 40.5 cm2/Vs and small sub-threshold swing (SS) of 250 mV/decade upon a SiO2/Si substrate were achieved using a rational design. Moreover, small threshold voltage shifts (ΔVth) of 0.5 (−0.7) and 0.8 (−0.9) V under gate bias and light illumination stress tests were obtained. Using Si3N4/HfO2 gate dielectrics, μFE and SS were enhanced to 53.6 cm2/Vs and 75 mV/decade, respectively. Experimental observations indicate that the electrons transfer from TiO2 to a-IGZO:N2O layer resulted in the accumulation of free carriers near a-IGZO:N2O/TiO2 interfaces. Additionally, an appropriate N2O treatment reduced the oxygen-related defects and bulk/interface trap density, while controlling the carrier density in the bilayer a-IGZO:N2O/TiO2 TFTs. Furthermore, the ultra-thin TiO2 layer acted as a surface passivation layer that reduced the leakage current and protected the channel from ambient influences. The proposed high-performance hetero-structured a-IGZO:N2O/TiO2 TFTs with superior stability are expected to provide a new and effective approach to obtaining high-performance metal oxide TFTs for application in thin film electronics.