Development of transparent oxide thin films for flexible devices

In this work, the electrical conductivity of Ga-doped ZnO (GZO) films was discussed with varying sputtering powers for transparent electrodes. The dependence of the optical bandgap, Eopt, of the GZO films on sputtering power density was expressed by the Burstein-Moss shift model correlated with the carrier concentration in the GZO films. The lowest electrical resistivity of the GZO films was obtained to be 3×10-4 ohm-cm with carrier concentration of 9.2×1020 cm-3 and Hall mobility of 22 cm2 /Vs. Amorphous InGaZnO (a-IGZO) was developed by radio frequency magnetron sputtering as the active channel layer under different gas flow rates at room temperature. It is revealed that oxygen flow rate played an important role in controlling the conductance in the a-IGZO channel layer. The characteristics of the bottom-gate aIGZO thin film transistors exhibited the saturation field effect mobility of 15.5 cm2 /Vs with an on/off current ratio of 105 . The improvement of transistors performance from depletion to enhancement mode is attributed to depressing the carrier concentration to realize normally-off device characteristics.