High‐performance, coplanar amorphous InGaZnO thin‐film transistors by spray pyrolysis on polyimide substrate for low‐cost manufacturing of foldable active‐matrix organic light emitting diode display

Abstract

We report a method for low-cost deposition of bubble-free, high-quality amorphous InGaZnO (a-IGZO) on polyimide (PI) substrate for foldable activematrix organic light emitting diode (AMOLED) display by spray pyrolysis. The coplanar thin-film transistor (TFT) with spray-pyrolyzed (SP) a-IGZO on PI substrate exhibits threshold voltage (VTH) of À0.8 V, saturation mobility of 40.95 cm2 V À1 s À1 , and subthreshold swing of 0.18 V per decade with on/off drain current ratio of $108. The high mobility TFT could be achieved using high substrate temperature (350 C) and low contact resistance by NF3 plasma on the SP a-IGZO. The TFT shows a ΔVTH of À0.4 V when it is bent on a cylinder of 1-mm radius. The TFT shows the ΔVTH of +0.05 V for positive bias temperature stress at +20 V at 60 C for 1 h. The ring oscillator made of a-IGZO TFTs exhibits an oscillation frequency of 2.38 MHz at VDD of 10 V with a propagation delay of 9.13 ns per stage. Therefore, the a-IGZO TFT by spray pyrolysis could be used for low-cost, high-performance, and flexible display TFT backplane.