Hoon-Ju Chung

A high-endurance low-temperature polysilicon thin-film transistor EEPROM cell

A planar type polysilicon thin-film transistor (poly-Si TFT) EEPROM cell with electron cyclotron resonance (ECR) N/sub 2/O-plasma oxide has been developed with a low temperature (/spl les/400/spl deg/C) process. The poly-Si TFT EEPROM cell has an initial threshold voltage shift of 4 V for programming and erasing voltages of 11 V and -11 V, respectively. Furthermore, the poly-Si TFT EEPROM cell maintains the threshold voltage shift of 4 V after 100 000 program/erase cycles. The excellent high endurance of the fabricated poly-Si TFT EEPROM cell is attributed to the ECR N/sub 2/O-plasma oxide with good charge-to-breakdown (Qbd) characteristics.

Highly Robust Integrated Gate-Driver for In-Cell Touch TFT-LCD Driven in Time Division Driving Method

This paper proposes a gate driver circuit for in-cell touch thin-film transistor (TFT) liquid crystal displays (LCDs) in which display and touch are driven at separate times to avoid cross-talk between display signals and touch signals. In the conventional gate driver circuit, transistors are connected between the gate node of pull-up transistor Q node and the low DC supply voltage V GL to reset the Q node. In the proposed gate driver gate driver circuit, these transistors are instead connected to the Touch Enable signal. During the display operation, the Touch Enable signal voltage is V GL to operate the proposed gate driver circuit in the same way as the conventional circuit. During touch operations, the Touch Enable signal changes to the high DC supply voltage V GH to keep the voltage at the Q node constant without leakage. In simulations and experiments, the proposed gate driver circuit prevented display failures caused by the interval during which the display pauses in the middle of a frame time for touch operation. The fabricated low temperature poly-silicon (LTPS) TFT-LCD has good multi-touch functionality without any ghost touches, and achieved 40-dB SNR and 120 Hz touch report rate.

Novel Digital Driving Method Using Dual Scan for Active Matrix Organic Light-Emitting Diode Displays

A new digital driving method has been developed for low-temperature polycrystalline silicon, transistor-driven, active-matrix organic light-emitting diode (AM-OLED) displays by time-ratio gray-scale expression. This driving method effectively increases the emission ratio and the number of subfields by inserting another subfield set into nondisplay periods in the conventional digital driving method. By employing the proposed modified gravity center coding, this method can be used to effectively compensate for dynamic false contour noise. The operation and performance were verified by current measurement and image simulation. The simulation results using eight test images show that the proposed approach improves the average peak signal-to-noise ratio by 2.61 dB, and the emission ratio by 20.5%, compared with the conventional digital driving method.

Long Life-Time Amorphous-InGaZnO TFT-Based Shift Register Using a Reset Clock Signal

We report a long life-time shift register (SR) made of amorphous-indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs). The life-time of an SR is determined by the stability of the pull-down TFT, which is always under positive bias stress (PBS). To compensate for the nonrecovering characteristic of a-IGZO TFTs, the gate ON time of the pull-down TFT is reduced from 50% to 5% duty ratio by introducing a reset clock signal. By fitting the TFTs PBS-induced threshold voltage shifts to stretched exponentials, the life-time of the SR is estimated to increase from 1.7 to 17.5 years, owing to the reset clock signal with short-term duty.

P-15: AMOLED Pixel Structures Compensating the Hysteresis of Poly-Si TFTs

New voltage programmed pixel circuits for AMOLEDs are proposed and measured. The measurement data indicate that the proposed driving schemes are less sensitive to the hysteresis of low temperature polycrystalline silicon (LTPS) TFTs than the conventional 2T1C pixel structure and can improve the recoverable residual image due to the hysteresis characteristics of LTPS TFTs. In the proposed driving schemes, the black data are inserted in displayed images so that the motion image quality should be improved.

Driving Method Compensating for the Hysteresis of Polycrystalline Silicon Thin-Film Transistors for Active-Matrix Organic Light-Emitting Diode Displays

A new driving method for active-matrix organic light-emitting diode displays is proposed and evaluated. The pixel structure of the proposed driving method is composed of three thin-film transistors (TFTs) and one capacitor. It inserts black data into display images to reset driving TFTs for the purpose of maintaining constant electrical characteristics of driving TFTs. The proposed driving scheme is less sensitive to the hysteresis of low-temperature polycrystalline silicon (LTPS) TFTs than the conventional pixel structure with two TFTs and one capacitor, and this scheme can virtually eliminate the recoverable residual image that occurs owing to the hysteresis characteristics of LTPS TFTs. In the proposed driving scheme, black data are inserted into displayed images so that the motion image quality is improved.

P‐17: Low Power Level Shifter for System‐on‐Panel Applications

A new low power level shifter using low temperature polycrystalline silicon (poly-Si) thin-film transistors (TFTs) for system on panel (SOP) applications is proposed. The proposed level shifter uses a capacitive coupling effect and can reduce power consumption owing to no short circuit current. The proposed level shifter consumed only 28% of the power that is necessary for the conventional one.

Dual-Gate Polycrystalline Silicon Thin-Film Transistors with Intermediate Lightly Doped Region

I have proposed and developed dual-gate polycrystalline silicon thin-film transistors (poly-Si TFTs) with an intermediate lightly doped region (LDR) for the reduction of leakage current. The proposed poly-Si TFTs are easily fabricated and have a symmetric structure less sensitive to misalignment than the conventional LDD poly-Si TFTs. In the proposed TFTs, it is proved that a decrease in leakage current is due to a reduction in lateral electric field at the drain edge and a reduction in on-current is caused by an increase in the resistance of the LDR. The leakage current of the proposed TFTs is significantly reduced and the maximum ON/OFF current ratio is obtained with a 2 µm LDR length and a 2×1013/cm2 LDR implant dose.

Memory-in-Pixel Circuit for Low-Power Liquid Crystal Displays Comprising Oxide Thin-Film Transistors

We propose a new memory-in-pixel (MIP) circuit with only oxide thin-film transistors (Ox-TFTs) for a low-power liquid crystal display with flicker-free feature. The proposed MIP circuit is composed of two new memory circuit units comprising two Ox-TFTs and a capacitor. The proposed memory circuit can modulate the threshold voltage via a simple driving scheme. When the threshold voltage is shifted properly, Ox-TFTs maintain the ON or OFF state by virtue of their extra low leakage current, which enables the MIP operation. By applying the black or white voltage to the pixel directly, flicker can be eliminated. We fabricated the MIP circuit and investigated the circuit performance depending on the capacitance and TFT sizes. Finally, we verified the feasibility of the proposed MIP circuit for low power operation.

A Full p-Type Poly-Si TFT Shift Register for Active Matrix Displays

A new shift register using p-type poly-Si thin-film transistors (TFTs) for active matrix display is proposed. It utilizes only p-type TFTs to simplify the fabrication process, and provides time-shifted output signals with a voltage swing from VSS to VDD without signal-level loss. In the proposed shift register, output is structurally separated from carry and therefore has a high immunity to output signal distortion caused by output load capacitance. We also propose a new light emitting control method using this shift register for high image quality active-matrix organic light emitting diode (AMOLED) displays. The proposed shift register was verified by simulation and measurement.