Low-Temperature Solution-Processed n-Channel SnO₂ Thin-Film Transistors and High-Gain Zero-V_GS-Load Inverter

Low-cost inorganic solution processing for oxide semiconductor thin-film transistors (TFTs) is crucial for developing next-generation cost-effective, ubiquitous, and flexible electronics, and the development of low-temperature solution-processed high-performance oxide-TFTs is highly demanded. We developed a simple oxidation promotion step using sodium hydroxide (NaOH) for the low-temperature solution processing of n-channel stannic oxide (SnO2)-TFTs. The presented SnO2-TFTs were fabricated using a low-cost inorganic salt (SnCl2) solution at a maximum process temperature of 200 °C under an ambient atmosphere; they exhibited good TFT characteristics with a reasonably high saturation mobility of ∼6.7 cm2 V–1 s–1, a small s-value of ∼210 mV dec–1, and a high on/off-current ratio of ∼108. We found that the NaOH solution dipping step effectively assisted in enhancing the oxidation of Sn ions and enabled the fabrication of a device-quality SnO2 channel at low temperatures. We also fabricated enhancement/depletion-mode TFTs and developed a solution-processed SnO2-TFT-based zero-VGS-load inverter exhibiting a full-swing characteristic with a high voltage gain of ∼198, a narrow transition width of ∼0.88 V, and a static power dissipation of ∼0.12 μW.