Very High-Gain, High-Yield Oxide Thin-Film Amplifiers Enabled by Full Etching Processes

Oxide semiconductors are desirable materials for display driving circuits, wearable electronics, and dynamic random access memory (DRAM), but very limited research has been reported on complementary oxide semiconductor circuits, particularly on their yield. Oxide thin-film transistors (TFTs) and circuits are generally fabricated by the liftoff processes. In this work, we compare oxide TFTs fabricated using the etching process and the liftoff process. The etched TFTs are shown to exhibit significantly better performance in terms of yield, leakage current, breakdown voltage, and uniformity. Furthermore, 80 complementary oxide inverter circuits using n-type indium–gallium–zinc oxide (IGZO) and p-type tin monoxide (SnO) have all worked consistently with a 100% yield. The inverters achieve an open-loop gain of 1264 at a supply voltage of 4.5 V. Even at a supply voltage as low as 1 V, the gain still reaches 56.5. Both the inverter gains and the gain per unit voltage are the highest reported. Finally, such high gains enable demonstration of amplifying two weak human biosignals, electrooculography (EOG) and surface electromyography (sEMG). Even a single-stage amplifier can boost microvolt-level signals to the millivolt range, showing significant potential for applications in flexible electronics and biosensing.