Oxide TFT with multilayer gate insulator for backplane of AMOLED device

Abstract

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 cm 2 /V‐sec, a high on/off ratio of over 10 8 , 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 cm 2 /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 cm 2 /V‐sec, a high on/off ratio of ∼10 7 , 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.