An Enhanced Voltage Programming Pixel Circuit for Compensating GB-Induced Variations in Poly-Si TFTs for AMOLED Displays

The variation and reliability issues of display backplane pose major challenges for poly silicon (poly-Si) active matrix organic light-emitting diode (AMOLED) displays. Adjacent poly-Si thin-film transistors (TFTs) exhibit different threshold voltages and mobilities due to random distribution of grain boundaries (GBs). Furthermore, the threshold voltage and mobility of TFTs have noticeable shift in time because of electrical stress. In this study, we propose an improved voltage programming pixel circuit for compensating the shift of threshold voltage and mobility in driver TFTs (DTFTs) as well as compensating the supply voltage degradation. HSPICE simulation results demonstrate that the drive current for OLED has a deviation of less than ±2% for a mobility variation of ±40% and a maximum deviation of 30 nA when the threshold voltage varies from 0.3 to -0.3 V. Moreover, if the supply voltage degrades from 10 to 8.5 V, the drive current shift is less than 15%.