ZnO thin film, device, and circuit fabrication using low-temperature PECVD processes

We report undoped ZnO films deposited at low temperature (200°C) using plasma-enhanced chemical vapor deposition (PECVD). ZnO thin-film transistors (TFTs) fabricated using ZnO and Al ₂O ₃ deposited in situ by PECVD with moderate gate leakage show a field-effect mobility of 10 cm ²/V s, threshold voltage of 7.5 V, subthreshold slope <1 V/dec, and current on/off ratios >10 ⁴. Inverter circuits fabricated using these ZnO TFTs show peak gain magnitude (dV _out/dV _in) ~5. These devices appear to be strongly limited by interface states and reducing the gate leakage results in TFTs with lower mobility. For example, ZnO TFTs fabricated with low-leakage Al ₂O ₃ have mobility near 0.05 cm ²/V s, and five-stage ring-oscillator integrated circuits fabricated using these TFTs have a 1.2 kHz oscillation frequency at 60 V, likely limited by interface states.