Thickness Optimization toward High-Performance Bottom-Gated Transparent Tin Dioxide Thin-Film Transistors

Nowadays, transparent amorphous oxide semiconductor (TAOS)-based transparent thin-film transistors (TTFTs) are utilized as the backplane of organic light-emitting diode (OLED) displays. Among many TAOSs examined to date, amorphous (a-)SnO2 is one of the most promising candidates owing to its environmental compatibility, e.g., indium-free. Although several SnO2-based TFTs have been demonstrated so far, the reported characteristics are ambiguous, e.g., extremely high electron mobility (>100 cm2 V–1 s–1) and behaviors far different from those of currently used a-InGaZnO4-based TFTs. Here, we show high-performance bottom-gated a-SnO2-based TTFTs. First, we systematically investigated the electron transport properties and the band gap of SnO2 films with various thicknesses. Then, we optimized the SnO2 thickness by analyzing the operation mechanism of the TTFTs using an electric-field thermopower modulation technique. We found that the optimal SnO2 thickness is 4.2 nm for high-performance TTFTs (highest on-to-off current ratio (∼105) and high mobility (∼20 cm2 V–1 s–1)). The present results would be essential to develop a-SnO2-based TTFTs in commercial applications.