Cu2O p-type Thin-Film Transistors with Enhanced Switching Characteristics for CMOS Logic Circuit by Controlling Deposition Condition and Annealing in the N2 Atmosphere

Cuprous oxide (Cu2O) p-type thin-film transistors (TFTs) can be practically applied for complementary metal oxide semiconductor (CMOS) logic circuits, but the electrical performances are still insufficient due to high off-current and low field-effect mobility. Here, we have demonstrated Cu2O TFTs with improved field-effect mobility and low off-current through reduction of cupric oxide (CuO) impurities and dissociative Cu defects with the combination of deposition and annealing conditions. Copper oxide was deposited by radio frequency sputtering in mixed gases of argon and oxygen. After that, the deposited copper oxide was annealed at 800 °C in the tube furnace under a N2 atmosphere instead of a high vacuum condition. The fabricated Cu2O thin film had a high crystalline quality, the ratio of dissociative Cu defects decreased from 11.3 to 3.1%, and the electrical performances of the TFT including the fabricated Cu2O thin film exhibited the field-effect mobility of 1.11 ± 0.05 cm2/V·s, the on/off current ratio of 4.68 ± 0.8 × 104, and the subthreshold swing value of 3.91 ± 0.21 V dec–1. The fabricated Cu2O TFT showed a Vth shift of 3.31 V in the transfer curve under negative bias stress. Nitrogen plays a role in promoting Cu2O phase formation while it prevents CuO phase formation during the annealing process. In addition, oxygen added during sputtering increases the ratio of CuO in the copper oxide thin film and works effectively to reduce dissociative Cu defects in the annealing process. To determine the feasibility of the CMOS logic circuit, we also demonstrated the inverter with n-type indium–gallium–zinc oxide (IGZO) TFT and p-type Cu2O TFT, which showed a voltage gain of 14 at VDD = 20 V.