A comparative study of amorphous InGaZnO thin-film transistors with HfOxNy and HfO2 gate dielectrics
High-κ HfOxNy and HfO2 films are applied to amorphous InGaZnO (a-IGZO) devices as gate dielectric using radio-frequency reactive sputtering. The electrical characteristics and reliability of a-IGZO metal–insulator–semiconductor (MIS) capacitors and thin-film transistors (TFTs) are then investigated. Experimental results indicate that the nitrogen incorporation into HfO2 can effectively improve the interface quality and enhance the reliability of the devices. Electrical properties with an interface-state density of 5.2 × 1011 eV−1 cm−2, capacitance equivalent thickness of 1.65 nm, gate leakage current density of 3.4 × 10−5 A cm−2 at Vfb +1 V, equivalent permittivity of 23.6 and hysteresis voltage of 110 mV are obtained for an Al/HfOxNy/a-IGZO MIS capacitor. Superior performance of HfOxNy/a-IGZO TFTs has also been achieved with a low threshold voltage of 0.33 V, a high saturation mobility of 12.1 cm2 V−1 s−1 and a large on–off current ratio up to 7 × 107 (W/L = 500/20 µm) at 3 V.