A Sustainable Approach to Flexible Electronics with Zinc-Tin Oxide Thin-Film Transistors

Zinc-tin oxide (ZTO) is widely invoked as a promising indium and gallium-free alternative for amorphous oxide semiconductor based thin-film transistors (TFTs). The main bottleneck of this semiconductor material compared to mainstream indium-gallium-zinc oxide (IGZO) is centered in the larger processing temperatures required to achieve acceptable performance (>300 °C), not compatible with low-cost flexible substrates. This work reports for the first time flexible amorphous-ZTO TFTs processed at a maximum temperature of 180 °C. Different aspects are explored to obtain performance levels comparable to IGZO devices at these low processing temperatures, such as hydrogen incorporation during ZTO sputtering and integration with a high-κ multilayer/multicomponent dielectric. Close-to-zero turn-on voltage, field-effect mobility ≈5 cm² V^-1 s^-1, and subthreshold slope of 0.26 V dec^-1 are obtained. Stability under negative-bias-illumination stress is dramatically improved with hydrogen incorporation in ZTO and device performance is insensitive to bending under a radius of curvature of 15 mm. Inverters using the ZTO TFTs enable rail-to-rail operation with supply voltage V _DD as low as 5 V, while a differential amplifier with positive feedback loop provides a gain of 17 dB and unity gain frequency of 40 kHz, limited by the large gate-to-source and gate-to-drain overlaps used herein.