Investigation of Bottom Gate Connection in Double-Gate a-IGZO TFTs for Optimizing Compensation Performance of AMOLED Displays

Abstract

This study fabricated double-gate (DG) amorphous indium-gallium–zinc oxide (a-IGZO) thin-film transistors (TFTs) and consequently assessed their characteristics in both bottom gate-top gate connection (BTC) and bottom gate-source connection (BSC) modes to improve the performance of active-matrix organic light-emitting diode (AMOLED) displays. The BTC mode exhibited a subthreshold swing (SS) of 84.4 mV/dec, demonstrating superior switching performance, whereas the BSC mode showed a relatively lower characteristic at 199.9 mV/dec. It is well known that low SS is beneficial for TFT switches. However, this article demonstrates that a TFT with low SS is disadvantageous for threshold voltage compensation in pixel circuits. To investigate the effect of the electrical characteristics of DG a-IGZO TFTs on the compensation quality of OLED displays, simulations were conducted via the application of each BG connection mode to the driving TFT ( ${T}_{\text {DR}}$ ) within a circuit comprising four nMOS TFTs and two capacitors. The compensation performance was evaluated based on the variations in ${V}_{\text {TH}}$ . In the BTC mode, when the ${V}_{\text {TH}}$ variation ( $\Delta {V}_{\text {TH}}$ ) of ${T}_{\text {DR}}$ was −0.5 V, the pixel current variation (PCV) was 133.6%. By contrast, in the BSC mode, the PCV was significantly lower 18.6%, demonstrating superior compensation quality.