High-Speed Shift Register with Dual-Gated Thin-Film Transistors for a 31-Inch 4K AMOLED Display

Abstract

In this work, a promising dual-gated thin film transistor (TFT) structure has been proposed and introduced in the shift register (SR)-integrated circuits to reduce the rising time. The threshold voltage can be simultaneously changed by the top gate and the bottom gate in the proposed dual-gated TFTs. When the SR circuits start to export the scan signals in the displays, the driving currents in the SR circuits are increased by switching the working station of driving TFTs from the enhancement characterization to the depletion characterization. Subsequently, the detailed smart spice simulation has been used to study the function of the proposed SR circuits. In the next step, the proposed SR circuits have been fabricated in a G4.5 active-matrix organic light-emitting diode manufacture factory. The simulated and experimental results indicate that the shift register pulses with the full swing amplitude can be obtained in the SR circuits. Moreover, in contrast to the conventional SR circuits employing with the single-gated TFTs, it has been found that the rising time of the output signals can be reduced from 3.75 μs to 1.23 μs in the proposed SR circuits with the dual-gated TFTs, thus exhibiting the significant improvement of the driving force in the proposed SR circuits. Finally, we demonstrated a 31-inch 4K AMOLED display with the proposed SR circuits.

A Simple Scan Driver Circuit Suitable for Depletion-Mode Metal-Oxide Thin-Film Transistors in Active-Matrix Displays

“…However, n-type MOx TFTs often have depletion mode characteristics, i.e., the threshold voltage (V TH ) is lower than 0 V. So, if a peripheral driving circuit of the AM display such as the scan driver is composed only of MOx TFT, the TFT does not turn off when the gatesource voltage (V GS ) is 0 V due to the depletion mode characteristics, causing the circuit to malfunction and increasing the power consumption. To cope with the depletion mode characteristics, the peripheral driving circuit requires additional techniques such as STT structure and negative voltage clock, resulting in a more complex circuit structure and a larger area [9][10][11][12][13][14]. Therefore, MOx TFT-based scan driver circuits have not been utilized for high-resolution-e.g., over 600 ppi-mobile displays with narrow bezels.…”

“…In this paper, we report a simple scan driver circuit composed of only ten TFTs and two capacitors, which can be integrated into a small bezel area of a high-resolution mobile display even with MOx TFTs, in contrast with the previous circuit [9][10][11][12][13][14]. We tried to devise an Electronics 2024, 13, 2254 2 of 10 optimal solution that minimizes the area increase and provides an improved device margin considering the practical operation conditions of the high-resolution mobile displays.…”