High-performance ZnO thin-film transistors on gate dielectrics grown by atomic layer deposition

We fabricated high-performance ZnO thin-film transistors on gate dielectrics of HfO₂, HfSiO_x, and Al₂O₃, grown by atomic layer deposition (ALD). Devices on HfO₂ had a mobility of 12.2 cm²/V s with a threshold voltage of 2.6 V and subthreshold slope of 0.5 V/decade. Device performance on Al₂O₃ depended on synthesis temperature. For 100 nm thick Al₂O₃, synthesized at 200 °C, ZnO devices had a mobility of 17.6 cm²/V s with a threshold voltage of 6 V and less than ∼0.1 nA gate leakage at 20 V. The overall trends were that devices on Hf oxides had a lower threshold voltage, while the gate leakage current density was lower on Al₂O₃. Device characteristics for all ALD dielectrics exhibited negligibly small hysteresis, suggesting a low defect density at the interface of ZnO with the gate dielectric.