Highly Stable ZnON Thin-Film Transistors With High Field-Effect Mobility Exceeding 50 /Vs

High-performance thin-film transistors (TFTs) based on ZnON channels were fabricated using a dc reactive sputtering method. To improve the photoinduced bias stability, a postannealing process was carried out at a low ambient pressure (~100 mTorr, air ambient) at 250 °C for various annealing times (1-5 h). The transfer characteristics of the postannealed ZnON TFTs exhibited an improved subthreshold swing ranging from 0.60 to 0.42 V/decade. Other transport properties remained similar including a high mobility (μ_sat) of 50 cm²/Vs, a threshold voltage (V_th) of -2.5 V, and an ON-OFF drain current ratio of 10⁸. In addition, photoinduced bias reliability under a gate bias stress (V_G = -20 V) was significantly improved from -10.88 V (1 h) to -2.28 V (5 h). These results can be explained by the enhancement of bonding properties between Zn metal and two different anions (O, N) as stable N-Zn-O states.