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

Abstract

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 (VGS) value for pull‐down units. The results showed all the VOUT voltage waveforms were maintained at VGH voltage despite depletion‐mode operation. The proposed circuit could also obtain stable VOUT 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 × 1080) display panel. The results showed that the AC‐driven method could achieve improved VOUT 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.

P‐2: Narrow Bezel Gate Driver Generating Positive Pulse for AMOLED Display Using LTPO Technology with Depletion Mode Oxide TFTs

“…Thus, study of integrated gate drivers on array (GOAs) is essential to reduce the bezel area. Also, it is difficult to apply LTPO technology to GOAs because oxide TFTs can be easily working in depletion mode with negative threshold voltage (VTH), which induces malfunction of GOAs due to large leakage current path [4]. Gate drivers with oxide TFTs have complicated and bulky structures to prevent the leakage current path of depletion mode oxide TFTs [4][5].…”

P‐37: Adaptive Frequency Driving Scan Driver with NOR Logic Gate Based on a‐InGaZnO TFTs

“…On the other hand, amorphous indium gallium zinc oxide (a-InGaZnO) TFT possess advantages including visible transparency, low processing temperature, good uniformity, comparable mobility, and extremely low off-current, which make it very favorable for display backplane [4][5][6][7]. In addition, a-InGaZnO TFTs exhibit high on-off ratio over 10 9 comparing that amorphous silicon (a-Si) TFT and LTPS TFT have usually 10 6 and 10 7 , respectively, that can provide advantage on low refresh rate operation [7,8]. However, despite all the merits of a-InGaZnO TFTs, high operation voltage (>15 V) can induce high power consumption, which can be big obstacle to battery-powered portable electronics.…”

“…In spite of these advantages, LTPS TFTs have critical limits on high off-state current, high process cost, and uniformity issues about grainboundary [2,3]. On the other hand, amorphous indium gallium zinc oxide (a-InGaZnO) TFT possess advantages including visible transparency, low processing temperature, good uniformity, comparable mobility, and extremely low off-current, which make it very favorable for display backplane [4][5][6][7]. In addition, a-InGaZnO TFTs exhibit high on-off ratio over 10 9 comparing that amorphous silicon (a-Si) TFT and LTPS TFT have usually 10 6 and 10 7 , respectively, that can provide advantage on low refresh rate operation [7,8].…”

P‐36: Highly Reliable a‐IGZO TFT Gate Driver Circuit to Prevent Leakage Path in Depletion Mode Operation

“…The oxide TFT can present a negative threshold voltage (Vth) in the initial state. In this case, TFT can be turned on even when the gate-source voltage becomes zero bias condition [3], [4]. Therefore, depletion mode operation can cause serious operation failures in the gate driver circuit, such as output degradation and abnormal power consumption.…”