Chia-Che Hung

Lifetime Amelioration for an AMOLED Pixel Circuit by Using a Novel AC Driving Scheme

This paper describes how a reversed-bias voltage affects organic light-emitting diodes (OLEDs) with green emitting Alq3:C545T (40 nm). The luminance efficiency and the active area of the test OLED devices are 8-11 cd/A and 2.5 mm × 2.5 mm, respectively. The OLED lifetime under an ac driving scheme can be apparently improved, in contrast with that under a dc driving scheme. Experimental results indicate that adjusting the duty ratio of the ac driving scheme can ameliorate the brightness uniformity; meanwhile, the normalized luminance of a 20% duty ratio after a 3600-s stress is 94.3%, and that of dc stress is 76.4%. Therefore, a novel pixel circuit with three p-type thin-film transistors (TFTs) for an active-matrix OLED application is proposed to ameliorate the brightness uniformity. Variations of the threshold voltage of the driving TFT are compensated for, and the performance and lifetime of the OLED are improved by using an ac driving method. Simulation results indicate that the output current is almost constant over the data range. Furthermore, the current error rate of the proposed pixel circuit is less than 6.5%.

New LTPS Pixel Circuit With AC Driving Method to Reduce OLED Degradation for 3D AMOLED Displays

This work presents a new low-temperature polysilicon (LTPS) thin-film transistor pixel circuit with a novel driving scheme that is based on the simultaneous emission and reverse-biased methods. During high-speed 3D operation at 240 Hz, the proposed circuit can successfully compensate for the TFT threshold voltage variation and improve the IR drop in the power line. Simulation and experimental results confirm the stability of the OLED current and the amelioration of the OLED lifetime. Furthermore, over the entire range of data voltages, the nonuniformity of OLED current is less than 5%.

P-39: A Highly Stable a-Si:H TFT Gate Driver Circuit with Reducing Clock Duty Ratio

This paper presents a new a-Si:H gate driver circuit for large panel applications. Consisting of 12 TFTs and three capacitors, the proposed circuit is fabricated for measurement. The threshold voltage shift of TFTs is significantly reduced by reducing clock duty ratio. Experimental results indicate that the gate driver circuit operates stably under long-term and high temperature testing.

Novel a-Si:H AMOLED Pixel Circuit to Ameliorate OLED Luminance Degradation by External Detection

This letter presents a novel hydrogenated amorphous silicon (a-Si:H) active-matrix organic light-emitting diode (OLED) pixel circuit that compensates for the threshold voltage shift of TFT using an internal compensated structure and reduces luminance decay by external detection method, based on the interdependence between the luminance degradation of OLED and the decrease in current under constant voltage bias stress. Experimental results demonstrate that the luminance of the OLED device with the proposed external detection method is more stable than that with the conventional 2T1C pixel circuit.

To suppress photoexcited current of hydrogenated polysilicon TFTs with low temperature oxidation of polychannel

In this letter, a short time low temperature oxidation of poly-Si channel has been studied to suppress the photoexcited current of the hydrogenated poly-Si TFTs. The effect of the treatment, which contains different-time oxidation and different-time post-hydrogenation, on the dark-current and photocurrent of poly-Si TFTs under off state were investigated in detail. An optimal combination of both technologies has been proposed according to the investigation. The poly-Si TFTs treated with the optimal process can be operated well under a high illumination environment.

P‐50: Power Consumption Ameliorated for Integrated Gate Driver Circuit with Low Frequency Clock

This paper presents a novel low power consumption gate driver circuit with 12 TFTs and one capacitor which is made by hydrogenated amorphous silicon technology. The pull-down structure can not only prevent the floating of gate lines, but also suppress the threshold voltage shift of a-Si:H TFTs. According to the measurement results, the proposed gate driver circuit can be operated stably more than 10 days at high temperature (T = 100 °C). Furthermore, the power consumption of the proposed gate driver circuit can be reduced 52.6% compared to the previously proposed gate driver circuit.

Reducing OLED Degradation Using Self-Compensated Circuit for AMOLED Displays

In this letter, the electric characteristics of the fabricated organic light-emitting diode (OLED) devices are analyzed after a bias stress. Experimental results demonstrate that when a constant voltage is applied to the OLED device, the OLED threshold voltage gradually increases, resulting in the driving current to decay. Therefore, a novel voltage driving scheme for active-matrix OLEDs using low-temperature polysilicon thin-film transistors (poly-Si TFTs) is proposed. This circuit uses three TFTs to increase the aperture ratio of panels and the driving current of the OLED device to ameliorate the luminance drop that is caused by OLED degradation. Simulation results indicate that the proposed pixel circuit has high immunity to VTH variations of the poly-Si TFTs and provides an extra compensation current against OLED degradation.

P-52: A New Current Programming Pixel Circuit for Compensating Luminance Degradation of AMOLED

A new pixel circuit using low-temperature polycrystalline-silicon (LTPS) thin-film transistors for Active Matrix Organic Light Emitting Diodes (AMOLEDs) is presented. The proposed current programming circuit without charging time problem at low gray level compensates for the threshold voltage variation of TFT as well as OLED luminance decay. The simulation results demonstrate driving current of this circuit is independent of the variation of TFT and maintain luminance for long term operation.

P-51: A Novel Analog Buffer Circuit using Low Temperature Poly-Si TFT

A novel source follower circuit employing low temperature polycrystalline silicon (LTPS) thin film transistors (TFT) is proposed as an analog buffer for integrated data driver circuit. Instead of capacitive bootstrapping for self-compensation of the characteristic of TFTs, a new compensation method is applied so that the error programming of gate voltage of driving TFT can be effectively eliminated. The feasibility of proposed circuit is exhibited through the simulation results.

Transflective LCDs With Two TFTs and Single Data Line

A simplified single-cell-gap transflective liquid crystal display with two thin-film-transistors and only one data line is proposed. The simulated voltage-dependent transmittance (VT) and reflectance (VR) curves overlap reasonably well, which enables a single gamma curve driving. The need of only one data line improves the aperture ratio, reduces the fabrication cost, and stabilizes the manufacturing process.