Oxide TFT with multilayer gate insulator for backplane of AMOLED device

Abstract— An indium gallium zinc oxide (IGZO) film with an amorphous phase was deposited and had a very flat morphology with a RMS value of 0.35 nm. IGZO TFTs were fabricated on a glass substrate by conventional photolithography and wet-etching processes. IGZO TFTs demonstrated a high mobility of 124 cm2/V-sec, a high on/off ratio of over 108, a desirable threshold voltage of 0.7 V, and a sub-threshold swing of 0.43 V/decade. High mobility partially resulted from the fringing-electric-field effect that leads to an additional current flow beyond the device edges. Therefore, considering our device geometry, the actual mobility was about 100 cm2/V-sec, and had a very low dependence on the variation of W/L (channel width and length) and thickness of the active layer. IGZO TFTs were also fabricated on a flexible metal substrate for a conformable display application. TFT devices showed an actual mobility of 72 cm2/V-sec, a high on/off ratio of ∼107, and a sub-threshold swing of 0.36 V/decade. There was no significant difference before, during, or after bending. Moreover, an IGZO TFT array was fabricated and a top-emitting OLED device was successfully driven by it. Therefore, the oxide TFT could be a promising candidate as a backplane for OLED devices.