一种针对AMOLED器件劣化的电学补偿技术

AMOLED显示屏经过长时间的使用,不可避免地会有OLED器件劣化的问题。同一显示屏内不同位置的像素器件的劣化程度不同,造成显示屏整体亮度下降和显示残像。使用越久、亮度越高的像素,器件劣化就越严重。本文提出一种电学补偿技术,用以改善OLED器件劣化造成的亮度下降和显示残像。采用电学侦测的方法获得各个像素的OLED器件的VTH,将其存储于闪存芯片内,显示时通过查找表找到对应的OLED发光效率,计算得出各个像素的补偿后灰阶值,实现实时补偿的效果。本技术可以使劣化越严重的像素,获得越大的像素电流,从而弥补由于劣化造成的发光效率下降,最终得到理想的像素亮度。使用该方法可以补偿由于OLED劣化造成的亮度下降和显示残像,残像指标JND小于3.1。     

Electrical Compensation of OLED Luminance Degradation

This letter presents a stable compensation scheme for active-matrix organic light-emitting-diode (AMOLED) displays based on the observed strong interdependence between the luminance degradation of organic light-emitting diodes (OLEDs) and its current drop under bias stress. This feedback-based compensation provides 30% improvement in luminance stability under 1600 h of accelerative stress. To employ this scheme in AMOLED displays, a new pixel circuit is presented that provides on-pixel electrical access to the OLED current without compromising the aperture ratio.     

A novel 3-TFT voltage driving method of compensating VTH shift for a-Si:H TFT and OLED degradation for AMOLED

This work demonstrates the feasibility of a novel pixel circuit by using three a-Si:H TFTs. The proposed circuit can stabilize the OLED current and provide an additional driving current to ameliorate the brightness degradation of the AMOLED. Measurement results indicate that the current degradation of the proposed circuit, caused by V_TH variations, is less than 5% over more than 50,000 s at 60 °C, whereas that of a conventional 2T1C pixel circuit is larger than 34%. Furthermore, to ameliorate the decrease in luminance owing to the OLED degradation, the OLED current can be increased by 10% by analyzing the current degradation and modulating the detected voltage appropriately.     

A new pixel circuit for active matrix organic light emitting diodes

We propose a new thin-film-transistor (TFT) pixel circuit for active-matrix organic light-emitting diode (AMOLED) composed of four TFTs and two capacitors. The simulation results, based on the device performances measured for an OLED and a poly-Si TFT, indicate that the proposed circuit has high immunity to the variation of poly-Si TFT characteristics     

AMOLED Pixel Circuit With Electronic Compensation of Luminance Degradation

A new voltage-programmed pixel circuit using hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) for active-matrix organic light-emitting diodes (AMOLEDs) is presented. In addition to compensating for the shift in threshold voltage of TFTs, the circuit is capable of compensating for OLED luminance degradation by employing the shift in OLED voltage as a feedback of OLED degradation     

A Novel Voltage-Feedback Pixel Circuit for AMOLED Displays

This study presents a novel voltage-modulated pixel circuit for active-matrix organic light-emitting diode (AMOLED) consisting of five n-type thin-film transistors (TFTs), one additional control signal, and one storage capacitor. The proposed circuit, which can be implemented in all-n-type and all-p-type low temperature poly-silicon (LTPS) TFT technologies, successfully compensates for threshold voltage deviation of TFTs and facilitates correction of OLED degradation using a voltage feedback method. Simulation and experimental results for all-n-type TFTs indicate that the proposed pixel circuit reduced the nonuniformity brightness problem effectively by compensating for threshold voltage variation in TFTs and reduced the degradation of emission efficiency in OLEDs.     

A new current scaling pixel circuit for AMOLED

A new active-matrix organic light-emitting diode (AMOLED) pixel design, composed of four polycrystalline silicon thin-film transistor (poly-Si TFT) and one capacitor, is proposed by employing a novel current scaling scheme. The simulation results, based on the measured characteristics of an OLED and poly-Si TFTs, show that the proposed pixel design would scale down the data current more effectively, so as to guarantee a lower charging time compared with the conventional current mirror structure, as well as successfully compensate the variation of the electrical characteristics of the poly-Si TFTs, such as the threshold voltage and mobility.     

Comparison of Pentacene and Amorphous Silicon AMOLED Display Driver Circuits

Organic light-emitting diode (OLED) displays offer distinct advantages over liquid crystal displays for portable electronics applications, including light weight, high brightness, low power consumption, wide viewing angle, and low processing costs. They also are attractive candidates for highly flexible substrates. In active-matrix OLED (AMOLED) displays, a small transistor circuit is used to drive each OLED device. This paper compares the simulated performance of two state-of-the-art AMOLED drivers with a proposed 5 thin-film-transistor (TFT) voltage programmed driver circuit which combines the advantages of the first two configurations. A competitive evaluation is also done between amorphous silicon (alpha-Si) and organic TFTs (OTFTs,) using comparable empirical device models for alpha-Si) and pentacene OTFTs. The 5-TFT circuit is found to match the speed of the 2-TFT while achieving a stability closer to the 4-TFT circuits and demonstrating a better speed-stability tradeoff.     

多晶硅薄膜阳极微腔有机发光器件及其简化制备流程的研究

介绍了溶液法金属诱导晶化的p型掺杂多晶硅薄膜(p -poly-Si)的制备,并研究了它的电学特性和光学特性.由于p -MIC poly-Si薄膜具有比较好的电学特性,且在红光区域具有比较高的反射率与透射率和很小的吸收率,因此我们将它用作红光OLED的阳极.结果显示该器件的最大发光效率为5.88cd/A,比用ITO作阳极制备的OLED效率提高了57%.这是由于此薄膜对可见光比较高的反射率和阴极铝对可见光的很高反射性能,使之形成了一定Q值的微腔效应所至.这样,可以实现发光强度较高、单色饱和性较好的单色显示器件.本研究的意义还在于,由于此MOLED的p型掺杂MIC多晶硅阳极是与其共面型驱动TFT有源层、源/漏两极同层材料制备,即是TFT漏极的延伸;这样,不仅形成了高性能的AMOLED单色显示,而且也大大简化了AMOLED工艺流程,从而形成了简化流程的4-mask AMOLED基板制备工艺.     

A new a-Si:H TFT pixel circuit compensating the threshold voltage shift of a-Si:H TFT and OLED for active matrix OLED

We propose a new hydrogenated amorphous silicon thin-film transistor (a-Si:H TFT) pixel circuit for an active matrix organic light-emitting diode (AMOLED) employing a voltage programming. The proposed a-Si:H TFT pixel circuit, which consists of five switching TFTs, one driving TFT, and one capacitor, successfully minimizes a decrease of OLED current caused by threshold voltage degradation of a-Si:H TFT and OLED. Our experimental results, based on the bias-temperature stress, exhibit that the output current for OLED is decreased by 7% in the proposed pixel, while it is decreased by 28% in the conventional 2-TFT pixel.     

基于低温多晶硅薄膜晶体管的AMOLED交流像素电路

This work presents a new voltage programmed pixel circuit for an active-matrix organic light-emitting diode(AMOLED) display.The proposed pixel circuit consists of six low temperature polycrystalline silicon thinfilm transistors(LTPS TFTs),one storage capacitor,and one OLED,and is verified by simulation work using HSPICE software.Besides effectively compensating for the threshold voltage variation of the driving TFT and OLED,the proposed pixel circuit offers an AC driving mode for the OLED,which can suppress the degradation of the OLED.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.     

具有顶部发光结构的AMOLED交流驱动电路

A new voltage programmed pixel circuit with top emission design for active-matrix organic lightemitting diode(AMOLED) displays is presented and verified by HSPICE simulations.The proposed pixel circuit consists of five poly-Si TFTs,and can effectively compensate for the threshold voltage variation of the driving TFT.Meanwhile,the proposed pixel circuit offers an AC driving mode for the OLED by the two adjacent pulse voltage sources,which can suppress the degradation of the OLED.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.     

Single-Technology-Based Statistical Calibration for High-Performance Active-Matrix Organic LED Displays

Active-matrix organic light-emitting-diode (AMOLED) displays based on amorphous hydrogenated silicon (a-Si:H) thin-film transistors (TFTs) are the state of the art in display technology, owing to the feasilibility of low-cost fabrication and accessability to well-established TFT-LCD fabrication. While the a-Si:H TFT offers excellent matching of device properties over large areas, it suffers from a gate-bias-dependent threshold voltage shift in time, leading to grayscale inaccuracies. In order to counter this problem, many compensation circuits have been designed. The purpose of the compensation circuit is to estimate the threshold voltage shift in driver TFTs and apply a correction so as to maintain a constant brightness. However, all of the compensation circuits designed to date suffer from low spatial and temporal resolution and reliability issues or high cost due to the use of custom-made CMOS technology. In this paper, we focus on building AMOLED display systems solely based on a-Si:H TFT technology along with the use of off-the-shelf CMOS components to lower costs. Furthermore, we achieve high spatial and temporal resolution and high yield with the use of a two-TFT voltage programmed pixel circuit along with a statistical based external calibration circuit.     

Real-time external sensing and compensation method for organic light emitting diode displays

A real-time external sensing and compensation method for active matrix organic light emitting diode displays is proposed. The proposed method senses and compensates for the variation of electrical characteristics of poly-Si thin-film transistors (TFTs) during display time. Experimental results show that the proposed method successfully senses the electrical characteristics of TFTs in real-time and compensates for the non-uniform emission current error.     

High-speed low-power voltage-programmed driving scheme for AMOLED displays

A new voltage-programmed driving scheme named the mixed parallel addressing scheme is presented for AMOLED displays, in which one compensation interval can be divided into the first compensation frame and the consequent N-1 post-compensation frames without periods of initialization and threshold voltage detection. The proposed driving scheme has the advantages of both high speed and low driving power due to the mixture of the pipeline technology and the threshold voltage one-time detection technology. Corresponding to the proposed driving scheme, we also propose a new voltage-programmed compensation pixel circuit, which consists of five TFTs and two capacitors(5T2C). In-Zn-O thin-film transistors(IZO TFTs) are used to build the proposed 5T2C pixel circuit. It is shown that the non-uniformity of the proposed pixel circuit is considerably reduced compared with that of the conventional 2T1C pixel circuit. The number of frames(N) preserved in the proposed driving scheme are measured and can be up to 35 with the variation of the OLED current remaining in an acceptable range. Moreover, the proposed voltage-programmed driving scheme can be more valuable for an AMOLED display with high resolution, and may also be applied to other compensation pixel circuits.     

一种支持OLED亮度补偿的电流型PWM像素驱动电路

OLED(organic light-emitting diode,OLED)微显示器长时间工作在高对比度、高亮度的状态下,OLED像素衰退不一致,发光亮度衰退也不一致,会产生残影现象。因此,提出了一种改进的电流型PWM像素驱动电路,保持了对OLED像素衰退补偿效果,同时可以读出OLED阳极电压,计算得到OLED衰退信息,以便于对OLED亮度衰退进行有效的补偿。文章中分析了改进的电流型PWM驱动电路结构,及其对OLED衰退补偿和亮度补偿的原理。通过模拟仿真,得到几个影响OLED衰退补偿效果的关键参数。当OLED像素衰退电阻R_oled小于40 MΩ时,该电流型PWM驱动电路电流衰退度与传统2T1C驱动电路相比,只为其衰退度的50%。     

一种基于低温多晶硅薄膜晶体管的交流AMOLED像素补偿电路

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 tran- sistor （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 New Poly-Si TFT Current-Mirror Pixel for Active Matrix Organic Light Emitting Diode

A new poly-Si thin-film-transistor (TFT) current-mirror-active-matrix-organic-light-emitting-diode (AMOLED) pixel, which successfully compensates for the variation of the threshold voltage as well as mobility in the excimer laser annealed poly-Si TFT pixel, is designed and fabricated. The OLED current$(I_ OLED)$of the proposed pixel does not depend on the operating temperature. When the temperature of pixel is increased from 27$^circhboxC$to 60$^circhboxC$, the$I_ OLED$of the new pixel circuit composed of four TFTs and one capacitor increases only about 1.5%, while that of a conventional pixel composed of two TFTs and one capacitor increases about 37%. At room temperature, nonuniformity of the$I_ OLED$in the proposed circuit was also considerably suppressed at around 9%. We have successfully fabricated a 1.2-in AMOLED panel$(hbox96 times hbox96 times hboxred green blue)$to evaluate the performance of the proposed pixel. A troublesome residual image caused by the hysteresis phenomenon of the poly-Si TFT was almost eliminated in the proposed AMOLED panel as a result of current programming.     

一种有机发光二极管的电路仿真宏模型

文章介绍了一种有机发光二极管的电路仿真宏模型及其元件参数数值的提取方法。该电路仿真宏模型不但表征了有机发光二极管的全固态多层结构,而且表征有机发光二极管发光的物理过程。同时还提出了采用交流阻抗法提取该有机发光二极管电路仿真宏模型的元件参数的方法。该有机发光二极管的电路仿真宏模型可用于有源二极管显示器的背板电路设计过程中,背板电路与有机发光二极管器件的联合电路功能仿真,从而实现更准确的背板电路性能评估。     

Low-Power Low-Cost Voltage-Programmed a-Si:H AMOLED Display for Portable Devices

This paper presents a driving scheme to achieve highly stable low-power amorphous silicon (a-Si:H) active-matrix organic light-emitting diode (AMOLED) displays. Although the conventional 2-thin-film transistor (TFT) a-Si:H AMOLED display has demonstrated interesting features, including simplicity, it is prone to growing nonuniformity due to the temporal instability of the a-Si:H material. Several compensating techniques have been proposed to control the nonuniformity, but they tend to compromise the key attributes of the simple 2-TFT display such as low power consumption, high yield, high aperture ratio, low implementation cost, and fast programming. For mobile applications which have tight constrains on power consumption, cost, and escalating resolution requirements, we propose a new driving and addressing scheme that not only improves the backplane stability, but also compensates for the OLED luminance degradation while maintaining the attractive features of the simple 2-TFT pixel circuit. The overhead in power consumption and implementation cost is reduced by over 90% compared to existing compensation driving schemes.