OLED Degradation Research Articles

A 6T1C pixel circuit compensating for TFT electrical characteristics variations, voltage drop, and OLED degradation

A voltage-programmed pixel circuit based on low-temperature poly-silicon (LTPS) thin-film transistors (TFTs) is presented for active-matrix organic light-emitting diode (AMOLED) displays. The circuit consists of six p-type transistors and one capacitor (6T1C). During the extraction stage, the circuit extracts the driving TFT’s threshold voltage and the power supply voltage. During the data input stage, the circuit generates a charging voltage, which is associated with the driving TFT’s mobility and the OLED’s threshold voltage. Consequently, the pixel circuit, using only one capacitor, compensates not only for the TFT’s electrical characteristics variations, i.e., the threshold voltage variation and mobility variation, but also for the power supply voltage drop and the OLED degradation. The circuit simulation results reveal that the OLED current error rates (CERs) are lower than 5.09% when the threshold voltage varies by ±0.5V, lower than 3.61% when the mobility varies by ±30%, and lower than 9.16% when the voltage drop varies by −0.5V in the data voltage range.

An Active-Matrix Organic Light-Emitting Diode Pixel Circuit Featuring Mobility Compensation for Portable Applications.

A 6T1C pixel circuit based on low-temperature polycrystalline oxide (LTPO) technology for portable active-matrix organic light-emitting diode (AMOLED) display applications is proposed in this paper. For superior high-end portable applications including 4K high resolution and high PPI (pixels per inch), the proposed pixel circuit employs a single storage capacitor and signal sharing switch-control design and provides low-voltage driving and immunity to the IR-drop issue and OLED degradation. Furthermore, the threshold voltage and mobility-compensating capabilities are improved by both compensation mechanisms, which are based on a negative feedback system, and mobility-related compensation parameters. Simulation results reveal that threshold voltage variations of ±0.33 V in the driving thin-film transistors can be well sensed and compensated while the maximum OLED current shift is 4.25%. The maximum variation in OLED currents within all gray levels is only 1.05% with mobility variations of ±30%. As a result, the proposed 6T1C pixel circuit is a good candidate for portable AMOLED display usage.

P‐121: Evidence for the formation of localized charge traps during OLED degradation

In this study we investigate the details of the degradation processes occurring in a specific TADF OLED stack. The devices are stressed with constant current. In order to gain understanding in the underlying degradation mechanisms, a series of experimental techniques are performed during stressing interruption. To complement the measurements, electrical device simulations are used to model the OLEDs and identify the degradation causes. Specifically, it is found that the generation of trap states at an interface causes a variation of the charge injection and accumulation inside the device.

New Low-Voltage Driving Compensating Pixel Circuit Based on High-Mobility Amorphous Indium-Zinc-Tin-Oxide Thin-Film Transistors for High-Resolution Portable Active-Matrix OLED Displays

In recent years, active-matrix organic light-emitting diodes (AMOLEDs) has been the most popular display for portable application. To satisfy the requirement for the application of the portable display, the design of the compensating pixel circuit with the low-voltage driving and low-power consumption will be requested. In addition to the circuit with the design of the low-voltage driving, high-mobility thin-film transistors as driving device will be also necessary in order to supply larger driving current at low-voltage driving. Therefore, the study presents a new low-voltage driving AMOLED pixel circuit with high-mobility amorphous indium–zinc–tin–oxide (a-IZTO) thin-film transistors (TFTs) as driving device for portable displays with high resolution. The proposed pixel circuit can simultaneously compensate for the threshold voltage variation of driving TFT (ΔVTH_TFT), OLED degradation (ΔVTH_OLED), and the I-R drop of a power line (ΔVDD). By using AIM-Spice for simulation based on fabricated a-IZTO TFTs with mobility of 70 cm2V−1S−1 as driving devices, we discovered that the error rates of the driving current were all lower than 5.71% for all input data when ΔVTH_TFT = ±1 V, ΔVDD = 0.5 V, and ΔVTH_OLED = 0.5 V were all considered simultaneously. We revealed that the proposed 5T2C pixel circuit containing a high-mobility a-IZTO TFT as a driving device was suitable for high-resolution portable displays.

An Aging Current Model for OLED Degradation

An Aging Current Model for OLED Degradation

An Aging Current Model for OLED Degradation

An Aging Current Model for OLED Degradation

P‐1.1: A New Compensation Pixel Circuit with LTPO TFTs

This work presents a new pixel circuit using low‐temperature polycrystalline‐oxide thin‐film transistors (LTPO TFT) for active‐matrix organic light‐emitting diode (AMOLED) displays. The proposed circuit can compensate for the threshold voltage (Vth) variations of driving TFT. Moreover, the degradation of OLED can be reduced to a certain degree. The simulation results demonstrate that the current of OLED is independent of the Vth shifting and changes as the OLED threshold voltage. That means this LTPO circuit can improve the stability of displays.

High Resolution a-IGZO TFT Pixel Circuit for Compensating Threshold Voltage Shifts and OLED Degradations

In this paper, we propose a novel voltage programmed pixel circuit based on amorphous-indium-gallium-zinc-oxide thin-film transistors (a-IGZO TFTs) for active-matrix organic light-emitting displays. Through the extensive simulation work based on a-IGZO TFT and OLED models, we confirm that the proposed pixel circuit can compensate for threshold voltage variations of TFTs and OLED degradation over wide dynamic range (~104) of OLED current as well as achieve a high pixel aperture ratio with the suppressed OLED current error rate below 9%.

3‐3: Influence of Vacuum Chamber Impurities on OLED Degradation

We evaluated the influence of impurities in the vacuum chamber used for device fabrication on the lifetime of OLEDs and found a correlation between lifetime and the device fabrication time. Our results suggest that impurities including previously deposited materials and plasticizers from the chamber components impact lifetime and reproducibility.

A LTPS-TFT pixel circuit for active matrix organic light emitting diode based on improved current mirror

In this paper, a voltage-driving and current compensation method for active matrix organic light emitting diode (AMOLED) displays is proposed. An improved current mirror is introduced into the pixel circuit to overcome the channel length modulation effect of TFTs. The SPICE simulation results show that the proposed pixel circuit not only effectively compensates for non-idealities related with deviations of μ and VT in TFTs, the OLED degradation, but also offers a less setting time and guarantees a good liner relationship between VDATA and IOLED.

7-3: AMOLED Pixel Structure Using the Close Loop Negative Feedback Method for High Resolution Displays

A new 5T2C pixel circuit is proposed in this study to compensate TFT Vth variation, power line IR-drop, and OLED degradation in LTPS PMOS process and it also has The Close Loop Negative Feedback Method (CL-NFM) to compensate the gate voltage distortion of the driving TFT during the emission phase. The simulation showed that the emission current error are 4.85%, 9.02% and 39.25% separated for high, middle and low grey level compared between the current value in 1ms and 16ms, which is 12.51%, 38.14% and 97.8% for the conventional pixel structure, respectively.

P‐19: A New Pixel Circuit to Compensate Panel Non‐uniformity and OLED Degradation on Large IGZO AMOLED Panel

AbstractA new 4T2C pixel circuit is proposed in this study to compensate TFT process variations, Vth, mobility, power line IR‐drop, and OLED degradation in IGZO‐TFT process. Compensation performances show only from ±0.8% to ±1.74% panel non‐uniformity in average.

A new poly-Si TFT compensation pixel circuit employing AC driving mode for AMOLED displays

This paper presents a new poly-Si pixel circuit employing AC driving mode for active matrix organic light-emitting diode (AMOLED) displays. The proposed pixel circuit, which consists of one driving thin-film transistor (TFT), three switching TFTs, and one storage capacitor, can effectively compensate for the threshold voltage variation in poly-Si and the OLED degradation. As there is no light emission, except for during the emitting period, and a small number of devices used in the proposed pixel circuit, a high contrast ratio and a high pixel aperture ratio can be easily achieved. Simulation results by SMART-SPICE software show that the non-uniformity of the OLED current for the proposed pixel circuit is significantly decreased (< 10%) with an average value of 2.63%, while that of the conventional 2T1C is 103%. Thus the brightness uniformity of AMOLED displays can be improved by using the proposed pixel circuit.

A Novel Voltage-Programmed Pixel Circuit Utilizing $V_{T}$-Dependent Charge-Transfer to Improve Stability of AMOLED Display

A novel voltage-programmed pixel circuit using hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) for active-matrix organic light-emitting diode (AMOLED) displays is proposed. The threshold voltage shift (ΔVT) of the drive TFT caused by electrical stress is compensated by an incremental gate-to-source voltage (ΔVGS) generated by utilizing the ΔVT-dependent charge transfer from the drive TFT to a TFT-based metal-insulator-semiconductor (MIS) capacitor. A second MIS capacitor is used to inject positive charge to the gate of the drive TFT to improve the OLED drive current. The non-ideality of the ΔVT-compensation, TFT overlap capacitance, programming speed, and OLED degradation are discussed. The effectiveness of the proposed pixel circuit is verified by simulation results.

High-Speed Voltage-Programmed Pixel Circuit for AMOLED Displays Employing Threshold Voltage One-Time Detection Method

This letter presents a high-speed, voltage-programmed pixel circuit for active-matrix organic light-emitting diode displays employing threshold voltage one-time detection method. The proposed pixel circuit that consists of one driving thin-film transistor (TFT), four switching TFTs, two capacitors, and four control signal lines can effectively compensate for the threshold voltage shift of the driving TFT and the OLED degradation. The threshold voltage of one-time detection method is realized by an ingenious application of capacitor coupling effect, and it is well-verified by comparing it with the conventional driving scheme. In this method, data is directly renewed without the periods of initialization and threshold voltage detection from the second-frame beginning. Moreover, this method can also be applied to other compensation pixel circuits.

An AC Driving Pixel Circuit Compensating for TFTs Threshold-Voltage Shift and OLED Degradation for AMOLED

This paper presents an ac driving pixel circuit for active-matrix organic light-emitting diode (AMOLED) displays, which is composed of one driving thin-film transistor (TFT), three switching TFTs and one capacitor. The proposed pixel circuit can not only make OLED work at the ac driving mode, but also effectively compensate for the threshold-voltage shift of the driving TFT and the degradation of OLED. Simulation results show that the nonuniformity of the proposed pixel circuit is significantly reduced (<; 10%) with an average value of 4.2% compared with that of the conventional 2T1C pixel circuit, and thus, the brightness uniformity of AMOLED displays can be enhanced. Moreover, a high contrast ratio can be achieved by the proposed pixel circuit due to no light emitting except for the emission period, as well as a relatively high aperture ratio due to a small number of components.

A new compensation pixel circuit with all-p-type TFTs for AMOLED displays

This paper presents a new pixel circuit with all-p-type TFTs for AMOLED displays. The proposed pixel circuit can effectively compensate for the threshold-voltage shift of the driving TFT, the degradation of OLED and the parasitic resistance of the power supply line. And thus, the brightness uniformity of AMOLED displays can be enhanced. It is shown that the nonuniformity of the OLED current with an average value of 7.3% can be achieved by the proposed pixel circuit, while that of the conventional 2T1C pixel circuit is 73%. Moreover, a high contrast ratio can be also obtained by the proposed pixel circuit since there is no light emitting except for the emission period.

48.2: A Novel Current‐Mode Driving Technique for Real‐Time Image Compensation in AMOLED Displays

AbstractA new compensation method using current‐mode driving is introduced to solve image degradation in AMOLED displays. The proposed method can, in real time, compensate for degraded OLEDs without additional sensing lines. Moreover, there is no acceleration of OLED degradation because the method does not require an extra‐large compensation current. The conventional drawbacks associated with current‐mode driving, such as the driving speed and the channel‐to‐channel current variation, are solved with this novel technique.

A New Voltage-Programmed Pixel Circuit for Enhancing the Uniformity of AMOLED Displays

This letter presents a new voltage-programmed pixel circuit for the active-matrix organic light-emitting diode (AMOLED) displays, which consists of one driving thin-film transistor (TFT), four switching TFTs, two capacitors, and three control signal lines. The proposed pixel circuit can effectively compensate for the threshold-voltage shift of the driving TFT and the OLED degradation, which is verified by the simulation work using SMART-SPICE software. It is shown that the average nonuniformity of the OLED current for the proposed pixel circuit is 5.7% compared with 85.7% for the conventional 2T1C pixel circuit, and thus, the brightness uniformity of AMOLED displays can be enhanced. Moreover, a high contrast ratio can be achieved by the proposed pixel circuit since the OLED does not emit any light except for the emission period.

P‐22: Realizing a New Pixel Circuit Design for Alleviating OLED Degradation in a 2.4 Inch AMOLED Panel

AbstractThis study proposes the pixel circuit of degradation alleviation realized in a 2.4 inch AMOLED panel. The panel is fabricated with the designs of panel supply signal and layout regulation. The OLED degradation measurements made possible by the newly‐fabricated panel are recorded and show good performance.