Complementary Oxide–Semiconductor-Based Circuits With n-Channel ZnO and p-Channel SnO Thin-Film Transistors

Fully oxide thin-film transistor (TFT)-based complementary metal-oxide-semiconductor (CMOS) ring oscillators are reported, for the first time, using large-area-compatible sputtering processes. The p-channel tin monoxide (SnO) and n-channel zinc oxide (ZnO) TFTs used in the CMOS inverter have inverted-staggered bottom-gate structures. The SnO TFT exhibits a threshold voltage (Vth) of 3.5 V, field-effect mobility of 0.33 cm²/V-s, subthreshold swing of 2.5 V/decade, and ON/OFF current ratio of ~10³. The corresponding values for the ZnO TFT are 6.22 V, 3.5 cm²/V-s, 350 mV/decade, and >10⁶. The achieved voltage gain of the CMOS inverters is ~17 at a supplied voltage (VDD) of 10 V when the geometric aspect ratio is 5. An oscillation frequency of 2 kHz is obtained from a five-stage oxide-based CMOS voltage control oscillator at (VDD) of 14 V.