a-IGZO TFT Pixel Circuit With Double Gate Structure for Compensation of VTH Shift and SS-Induced Low-Gray Dispersion in AMOLED Displays

초록

In this article, we present a voltage-programmed 5T1C pixel circuit based on an amorphous indium-gallium-zinc-oxide (a-IGZO)-only thin-film transistor (TFT) platform for active-matrix organic light-emitting diode (AMOLED) displays. The proposed circuit consists of five TFTs and one storage capacitor (CST), and employs a bottom-gate-biased double-gate driving TFT (DR TFT). A negative bottomgate voltage (V-BG) shifts the DR TFT transfer characteristic toward the positive-threshold-voltage (V-TH) direction, placing the DR TFT in the enhancement-mode operating regime and enabling diode-connected VTH compensation. The VBG sweep is used as a controllable electrostatic perturbation to modulate the DR TFT characteristics and experimentally evaluate robustness against coupled VTH and subthreshold-swing (SS) variations, rather than as a direct compensation signal during pixel operation. Measured transiently programmed OLED currents under VBG modulations of +/- 1.0 and +/- 2.0 V demonstrate suppression of SS-induced low-gray current dispersion. The average LSB error remains below 1 LSB up to 114G and below 5 LSB over the full 8-bit (255G) range. Moreover, the proposed layout achieves a subpixel area of 16 & micro;m & times;36 & micro;m, corresponding to 748 PPI for a 6.3-inch UHD display, supporting high-resolution and low-power a-IGZO-only AMOLED backplanes

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