Feasibility of using sputtered AlOx film as gate insulator for high performance InGaZnO-TFTs

We reported on the electrical and surface characteristics of radio frequency (rf) AlOx film and their applications in InGaZnO-based thin film transistors (TFTs). By optimizing the rf power, AlOx film with the low leakage current density and smooth surface was obtained. The leakage current density for the 180 W AlOx film was observed to be ∼2.0 × 10−9 A/cm2 at electrical field strength of 2 MV/cm. The root mean square (rms) roughness of 180 W AlOx film was about 1.36 nm. InGaZnO-TFTs with different AlOx insulators were fabricated. The InGaZnO-TFT with 180 W AlOx insulator exhibits a field-effect mobility of 6.9 cm2/V s, a threshold voltage of 4.2 V, an on/off ratio of 2.7 × 107, and a much smaller Vth shift of 6.6 V for 20 V bias stress duration of 10,800 s. The improvement of InGaZnO-TFT with 180 W AlOx film is attributed to smooth surface of AlOx film and smaller trap charges. The results indicate that AlOx is a promising candidate insulator for InGaZnO-TFTs.