Congwei Liao

Design of Integrated Amorphous-Silicon Thin-Film Transistor Gate Driver

A thorough study on the gate driver integrated with hydrogenated amorphous-silicon thin-film transistors (a-Si:H TFTs) for active-matrix flat-panel display (AM-FPD) is carried out in this work. The single stage circuit of the a-Si:H gate driver consists of input, pull-up, pull-down, and low-level holding units. The operation principle of the driver is described in detail. The subtle static and dynamic characteristics of the a-Si:H TFT based circuit are analyzed systematically for the first time. The long term reliability issue is also addressed. Design equations for determining the device sizes of the circuit are derived. The TFT-LCD panels integrated with the designed gate driver are fabricated to verify the design efficiency.

Implementation of an a-Si:H TFT Gate Driver Using a Five-Transistor Integrated Approach

An integrated five-transistor/one-capacitor approach for realizing a a-Si:H thin-film transistor (TFT) gate driver operating in multiphase-clock mode is proposed and investigated. The driver needs only one large-size TFT and one small-size storage capacitor. The performance and function of the proposed driver are verified experimentally. The dependence of the performance on the device size is studied in detail. Stability of the fabricated drivers is tested using a flexible measurement scheme. Measured results show that the fabricated gate driver can work stably even though the low-level-holding TFTs have a threshold-voltage shift of 19 V.

A Compact Bi-Direction Scannable a-Si:H TFT Gate Driver

An integrated a-Si:H thin-film transistors (TFTs) gate driver on array with both forward and backward scanning function is proposed. The single stage of the gate driver only consists of seven TFTs. The bi-direction scannable function is just realized by controlling the turning-on sequence of two input TFTs. Both scanning modes use the same driving TFT for pulling-up and pulling-down the output voltage and the same circuit unit for holding the low level. The proposed gate driver is fabricated in the 4.5 G TFT production line, and the measurements with the fabricated drivers verify the feasibility of the proposed driver.

Integrated a-Si:H Gate Driver With Low-Level Holding TFTs Biased Under Bipolar Pulses

A hydrogenated amorphous silicon (a-Si:H) thin-film transistor (TFT) gate driver on array with low-level holding TFTs (LLH TFTs) biased under bipolar pulse is investigated. It is shown that the bipolar bias at low frequency significantly alleviates the threshold voltage shift of the LLH TFTs. As a result, the lifetime of the proposed gate driver is demonstrated to be several times of that under the conventional unipolar pulse bias. In addition, the improvement in the lifetime becomes more significant at the higher work temperature. The liquid crystal display television panels (32-in, 1366 × RGB × 768) with the proposed a-Si:H gate drivers integrated on array are manufactured, and the feasibility of the proposed driving scheme is well verified.

An a-IGZO TFT pixel circuit for AMOLED with simultaneous V T compensation

In this paper, a four a-IGZO TFTs based pixel circuit with simultaneous VT compensation function for AMOLED is proposed. The proposed circuit can not only simplify the peripheral circuits of the panel, but also compensate for both positive and negative VT shift with a charging VT-generation method. Simulation results show that the current changes only by 18.9% and 3.9% when ΔVT is -3 V and 2 V, respectively. Furthermore, by applying the grouping driving scheme, the OLED lighting time can be largely increased which manifests superiority when applied to high resolution or high frame rate displays.

Threshold Voltage Shift Effect of a-Si:H TFTs Under Bipolar Pulse Bias

Threshold voltage shift (ΔVTH) effect of hydrogenated amorphous silicon thin-film transistors under bipolar pulse bias stress (BPBS) is investigated. The dependence of the ΔVTH effect on the signal pulsewidth, stress temperature, and negative pulse voltage magnitude of the BPBS is systematically measured, and explained by the charge trapping and detrapping theory. Results show that the BPBS leads to a noticeably suppressed ΔVTH, compared with the conventional unipolar pulse bias stress. It is suggested that the BPBS with proper negative pulse voltage magnitude and low pulse frequency is an effective way of suppressing ΔVTH, especially when the thin-film transistors work relatively at high temperature.

A new four-transistor poly-si pixel circuit for AMOLED

This paper presents a new poly-Si thin film transistor (TFT) pixel circuit for active-matrix organic light-emitting diode (AMOLED) displays. The pixel circuit has a simple four-transistor configuration and is controlled by two adjacent gate scan pulses, allowing a small circuit area and simple driving scheme. Simulation results show that this pixel circuit can provide the OLED with a current non-uniformity of less than 3% under ±0.5V threshold voltage (VTH) variation.

One Gate Diode-Connected Dual-Gate a-IGZO TFT Driven Pixel Circuit for Active Matrix Organic Light-Emitting Diode Displays

A dual-gate (DG) amorphous indium-gallium- zinc-oxide thin-film transistor (TFT)-driven pixel circuit for active-matrix organic light-emitting diode displays is presented. One gate of the DGs serves as a primary gate (PG) and the other as an auxiliary gate (AG). The threshold voltage (V_TH) of the DG TFT under the PG operation is modulated by the AG bias voltage. The VTH variation (ΔV_TH) is compensated with the AG and the drain diode-connected structure. The validity of the presented pixel circuit is experimentally verified. The measured current error rates are less than 3.2% at a ΔV_TH of TFT = ±0.5 V and a ΔV_TH of OLED = 0.5 V with the emission current ranging from 7 nA to 1.13 μA.

An IGZO TFT based in-cell capacitance touch sensor

An in-cell active matrix capacitive touch sensor using IGZO TFT is proposed in this paper. The sensor does not need touch deformation, complicated detection mechanisms or extra components. In the sensor, touching events are identified as capacitive coupling between internal detection electrodes and touch objects. Then the coupling can be converted to voltage signal and amplified. TFT sizes are decreased for the high mobility and good uniformity of IGZO, which result in a significantly improved accuracy. A capacitance with the order of 1 fF caused by the coupling could be detected and converted to an adequate output voltage signal.

A fast integrated a-Si gate driver

A fast integrated gate driver with amorphous silicon thin film transistor (a-Si:H TFT) is proposed in this paper. To improve the circuit speed, a new input scheme is designed to provide a full scale pre-charge voltage. So the loss of pre-charge voltage, a challenge in the conventional designs, is avoided. Simulations show that the proposed gate driver has a much improved driving speed in comparison with the conventional ones. The improvement is more effective in the case of the higher VTH and lower supply voltage. The proposed gate driver is suitable for high performance display applications.