Circuits and AMOLED display with self‐aligned a‐IGZO TFTs on polyimide foil

Abstract

Abstract A process to make self‐aligned top‐gate amorphous indium‐gallium‐zinc‐oxide (a‐IGZO) thin‐film transistors (TFTs) on polyimide foil is presented. The source/drain (S/D) region's parasitic resistance reduced during the SiN interlayer deposition step. The sheet resistivity of S/D region after exposure to SiN interlayer deposition decreased to 1.5 kΩ/□. TFTs show field‐effect mobility of 12.0 cm 2 /(V.s), sub‐threshold slope of 0.5 V/decade, and current ratio ( I ON / OFF ) of >10 7 . The threshold voltage shifts of the TFTs were 0.5 V in positive (+1.0 MV/cm) bias direction and 1.5 V in negative (−1.0 MV/cm) bias direction after extended stressing time of 10 4 s. We achieve a stage‐delay of ~19.6 ns at V DD = 20 V measured in a 41‐stage ring oscillator. A top‐emitting quarter‐quarter‐video‐graphics‐array active‐matrix organic light‐emitting diode display with 85 ppi (pixels per inch) resolution has been realized using only five lithographic mask steps. For operation at 6 V supply voltage ( V DD ), the brightness of the display exceeds 150 cd/m 2 .