Improved Performance of Amorphous InGaZnO Thin-Film Transistor With Ta2O5 Gate Dielectric by Using La Incorporation

In this paper, a comparative study of amorphous InGaZnO thin-film transistors with Ta2O5 and TaLaO gate dielectrics has been conducted. It is found that the electrical characteristics of thin-film transistors, including saturation carrier mobility, subthreshold swing, hysteresis, and on-off current ratio, can be effectively improved by the incorporation of La in Ta2O5 gate dielectric, which is ascribed to the fact that La incorporation can enlarge the bandgap of Ta oxide and its conduction-band offset with InGaZnO and also reduce the trap densities in the gate dielectric and at the InGaZnO/gate-dielectric interface. As a result, the sample with higher La concentration in the gate dielectric presents superior electrical characteristics, e. g., a high carrier mobility of 30.9 cm(2)/V . s, a small subthreshold swing of 0.17 V/dec, and slight hysteresis. Moreover, low-frequency noise measurement and X-ray photoelectron spectrum further support that the improvements in electrical properties are due to reduced trap densities induced by the incorporation of La in the Ta2O5 gate dielectric.