Improved Performance of Amorphous InGaZnO Thin-Film Transistor by Hf Incorporation in La2O3 Gate Dielectric

The effects of Hf incorporation in La
₂
O
₃
gate dielectric on the electrical characteristics of amorphous InGaZnO thin-film transistor are studied. With an appropriate dose of Hf, the device performance can be significantly improved, resulting in high saturation mobility of 30.5 cm
²
V
^-1
s
^-1
, small subthreshold slope of 0.15 V/dec, and negligible hysteresis (0.05 V). These improvements are attributed to suppressed crystallization and enhanced moisture resistance of the gate dielectric (supported by transmission electron microscopy and atomic force microscopy respectively), both induced by the Hf incorporation. However, excessive Hf incorporation leads to device degradation, likely due to more oxygen vacancies generated in the gate dielectric as shown by X-ray photoelectron spectroscopy.