A study on the electrical characteristics of InGaZnO thin-film transistor with HfLaO gate dielectric annealed in different gases

•The effects of dielectric-annealing gas on a-IGZO TFT are studied.•The N2-annealed sample has a high saturation carrier mobility of 35.1 cm2/V s.•The O2-annealed sample shows poorer performance compared to the N2-annealed one.•The NH3-annealed sample displays the lowest threshold voltage (1.95 V).

The effects of dielectric-annealing gas (O2, N2 and NH3) on the electrical characteristics of amorphous InGaZnO thin-film transistor with HfLaO gate dielectric are studied in-depth, and improvements in device performance by the dielectric annealing are observed for each gas. Among the samples, the N2-annealed sample has a high saturation carrier mobility of 35.1 cm2/V s, the lowest subthreshold swing of 0.206 V/dec and a negligible hysteresis. On the contrary, the O2-annealed sample shows poorer performance (e.g. saturation carrier mobility of 15.7 cm2/V s, larger threshold voltage, larger subthreshold swing of 0.231 V/dec and larger hysteresis), which is due to the decrease of electron concentration in InGaZnO associated with the filling of oxygen vacancies by oxygen atoms. Furthermore, the NH3-annealed sample displays the lowest threshold voltage (1.95 V), which is attributed to the increased gate-oxide capacitance and introduced positive oxide charges. This sample also reveals a change in the dominant trap type due to the over-reduction of acceptor-like border and interface traps, as demonstrated by a hysteresis phenomenon in the opposite direction. Lastly, the low-frequency noise of the samples has also been studied to support the analysis based on their electrical characteristics.