Depletion‐Mode a‐IGZO TFTs AM‐OLED Pixel Circuit for V _TH Shift Compensation and Capacitance Deviation Tolerance

ABSTRACT

This paper presents a voltage‐programmed 6T‐2C pixel circuit using amorphous indium gallium zinc oxide thin‐film transistors (a‐IGZO TFTs) for active‐matrix organic light‐emitting diode (AM‐OLED) displays. The circuit adopts a source‐follower programming path to compensate threshold‐voltage (V _TH ) variations even when the driving TFT exhibits depletion‐mode (negative‐V _TH ) behavior. To reduce programming errors caused by fabrication‐induced storage‐capacitance mismatch, the data voltage (V _DATA ) is applied to the common plate of two series‐connected storage capacitors, which suppresses capacitive‐coupling sensitivity to capacitor deviation. Circuit operation is evaluated in HSPICE using measured a‐IGZO TFT transfer characteristics and measured capacitor‐mismatch statistics, and the line‐time settling behavior is verified with an analytical model. A compact 30 μm × 50 μm layout is also demonstrated for feasibility in a 10‐inch UHD (440‐PPI) panel. The proposed circuit compensates for V _TH shifts up to ±2 V and capacitor deviation of ±10%, with maximum OLED current error rates of −10.0% (ΔV _TH  = −2 V) and 7.9% (ΔC = −10%).