61.1: Invited paper: ZnO thin film transistors and circuits on flexible polymeric substrates by low-temperature PEALD

We report using a novel, weak oxidant, plasma-enhanced atomic layer deposition (PEALD) process at 200 °C to fabricate stable, high mobility ZnO thin film transistors (TFTs) and fast circuits on glass and polyimide substrates. Weak oxidant PEALD provides a simple, fast deposition process that results in uniform, conformal semiconductor and dielectric layers and enhancement-mode MOSFETs from uncompensated films. Highly conformal PEALD Al₂O₃ layers provide a high yield dielectric on rough plastic substrates for both PEALD ZnO TFTs and cross-overs. Our PEALD ZnO TFTs have field-effect mobility of >20 cm²/V·s on polyimide substrates with excellent bias stress stability. TFTs biased continuously for 40,000s showed <50 mV threshold voltage shift. We also report fast PEALD ZnO circuits on polyimide substrates with propagation delay <20 ns/stage for V_DD = 18 V.