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 degrees 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 degrees 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-kappa multilayer/multicomponent dielectric. Close-to-zero turn-on voltage, field-effect mobility approximate to 5 cm(2) 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.