Viable Approach of Tuning Oxide Semiconductor Thin Films in Solution-Processed Heterojunction Thin Films Transistors for Both Higher Performances and Stability

Metal-oxide thin-film transistors (TFTs) have garnered much attention because of their advantages such as high transparency, low leakage current, and low processing temperature. However, there is a need to continuously improve their mobility and bias stability for application to next-generation advanced electronics. In this study, the thickness of bilayer semiconductors is finely controlled to enhance the charge transport characteristics and bias stability in solution-processed heterojunction oxide TFTs. The thicknesses of the top and bottom layers in the bilayer are individually adjusted by controlling solution molarity. The introduction of a bilayer channel improved the electrical performance of oxide TFTs via effective charge transport. However, trap-limited conduction becomes dominant in the bilayer with an excessively thick top layer, thereby leading to a significant reduction in mobility and positive bias stability. Meanwhile, although increasing the bottom layer thickness contributes to improved mobility and reliability, it causes a serious negative shift in threshold voltage (V_TH). TFTs with an optimized bilayer structure show high mobility at a V_TH close to 0 V and have particularly excellent positive bias stress stability. This study on bilayer channel thickness will be beneficial for developing advanced transistors with optimized bilayer or multilayer channels.