A novel gate driver circuit for depletion-mode a-IGZO TFTs

In this paper, a novel gate driver circuit, which can achieve high reliability for depletion mode in a-InGaZnO thin-film transistors (TFTs), was proposed. To prevent the leakage current paths for Q node effectively, the new driving method was proposed by adopting the negative gate-to-source voltage (V-GS) value for pull-down units. The results showed all the V-OUT voltage waveforms were maintained at VGH voltage despite depletion-mode operation. The proposed circuit could also obtain stable V-OUT voltage when the threshold voltage for all TFTs was changed from -6.5 to +11.5 V. Therefore, the circuit can achieve high reliability regardless of threshold voltage value for a-IGZO TFTs. In addition, the output characteristics and total power consumption were shown for the alternating current (AC)-driven and direct current (DC)-driven methods based on 120-Hz full-HD graphics (1920 x 1080) display panel. The results showed that the AC-driven method could achieve improved V-OUT characteristics compared with DC-driven method since the leakage current path for Q node can be completely eliminated. Although power consumption of the AC-driven method can be slightly increased compared with the DC-driven method for enhancement mode, consumption can be lower when the operation has depletion-mode characteristics by preventing a leakage current path for pull-down units. Consequently, the proposed gate driver circuit can overcome the problems caused by the characteristics of a-IGZO TFTs.