Towards environmentally stable solution-processed oxide thin-film transistors: A rare-metal-free oxide-based semiconductor/insulator heterostructure and chemically stable multi-stacking

For practical solution-processed oxide thin-film transistors (TFTs) with cost efficiency, high performance, and long-term environmental reliability, we suggested a novel sol-gel processed rare-metal-free oxide-based semiconductor/insulator [ZnSnO (ZTO)/Al₂O₃] heterostructure channel and chemically stable sol-gel multi-stacking method. In the rare-metal-free ZTO/Al₂O₃ heterostructure, an In- and Ga-free ZTO semiconductor with high chemical durability is employed as an effective electron transport layer. An earth-abundant Al₂O₃ insulator is employed as both an ambient gas molecule barrier in the ZTO back-channel region and a tunneling-induced electron transport layer beneath the source/drain electrodes. In order to minimize inevitable chemical attack coming from acidic and basic precursor solutions during the sol-gel based heterostructure construction, chemically stable sol-gel ZTO/Al₂O₃ heterostructure stacking was successfully demonstrated with a chemically durable Sn-modulated ZTO semiconductor and weakly corrosive pH-engineered Al₂O₃ precursor solution. The proposed rare-metal-free ZTO/Al₂O₃ heterostructure and chemically stable stacking realized sol-gel processed oxide TFT with excellent stability under humidity, temperature, bias voltage, and light exposure. We believe that our novel ZTO/Al₂O₃ heterostructure and chemically stable sol-gel stacking method will provide an interesting route for the fabrication of practical solution-based oxide TFTs with cost efficiency, high performance, and long-term reliability, instead of conventional rare-metal based oxide materials and channel structures with high environmental instability.