Improved Performance of Amorphous InGaZnO Thin-Film Transistor With 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 cm²/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.