用于OLED的a-Si TFT有源驱动阵列保护电路的分析

在模拟与仿真的基础上．根据MOS器件的源漏击穿特性．分析了用于a-Si TFT有源驱动阵列的外围保护电路的工作原理;同时根据所采用的有源OLED单元像素驱动电路的特点,确定了电源线、数据线、信号线上的相应保护电路形式。该保护电路可应用于OLED的有源驱动TFT阵列。     

电流模式Poly-Si TFT AM-OLED像素单元的模拟设计

模拟和分析了作为电流模式多晶硅薄膜晶体管(poly-Si TFT)有源矩阵有机发光二极管(AM-LOED)像素单元的poly-Si TFT／OLED耦合对的J-V特性和poly-Si TFT电流镜的I-V特性。使用Mathcad数学计算软件和AIM-SPICE电路模拟工具,分别对OLED和TFT耦合对和TFT电流镜进行了模拟计算。理论上,采用电流模式的poly-Si TFT AM-OLED可以解决器件间的不一致性问题。无论迁移率的不一致还是阈值电压Vth的差异都可以被补偿,从而使灰度的一致性得以改善。因为采用了倒置的OLED结构,可以用N型poly-Si TFT作为电流阱来驱动OLED,所以像素的性能进一步优化。结果表明,poly -Si TFT／OLED耦合对的驱动电压低,在200A／m^2下不超过8V;而TFT电流镜的跟随能力很好,在0．0～2．5μA时饱和电压只有1．5～2．5V。     

用于柔性显示的有机薄膜晶体管像素驱动电路

文中建立一种基于有机半导体TFT器件的模型,并将其应用于基于有机TFT的AMOLED显示背板驱动电路设计,以实现阈值电压补偿功能。首先制备低压有机TFT器件,并利用PSPICE工具对有机TFT器件进行建模;然后详细分析选取模型参数,建立能够准确反映器件电学特性的模型;最后基于模型指导,设计采用有机TFT的7T1C结构的AMOLED像素驱动电路。此外,分析有机TFT器件具有的温度依赖迁移率特性对屏幕亮度均匀性产生的影响。仿真结果表明：AMOLED像素驱动电路可有效实现对TFT器件阈值电压的补偿;且屏幕亮度不一致率低于5%,远低于传统的2T1C像素驱动电路,可大幅降低屏幕亮度的不均匀性。文中建立的有机TFT模型也可为其他基于有机器件的电路设计提供指导。     

卡西欧利用非晶硅开发成功OLED面板

卡西欧计算机日前开发成功了利用非晶硅TFT驱动OLED面板的技术,并试制出2.1英寸、160×128象素的产品。该公司首次开发有机EL面板,并通过自主开发的驱动电路,提高了开口率。OLED面板的驱动一般使用电子迁移率较大的低温多晶硅TFT。不过,低温多晶硅TFT目前因底板尺寸的限制,难以实现超过20英寸以上大尺寸的设计。如果将非晶硅TFT用于OLED面板,那么不仅易于扩大尺寸,而且没有低温多晶硅TFT制造设备的厂商也能够涉足OLED面板业务。目前日本国际显示技术(IDTech)和台湾友达光电等公司正在进行这方面的开发。卡西欧计算机着手开发…     

OLED有源驱动TFT阵列的一种测试方法

提出了一种检测有源驱动OLED TFT阵列的方法,这种电流检测方法是结合TFT的制作工艺进行的.在只增加一块光刻版的情况下,有效地解决了在含有2个TFT的单元像素电路中,检测驱动管困难的难题.这种检测方法能够进行快速的全屏检测,具有精度高,对TFT阵列无损伤的特点.     

OLED有源驱动TFT阵列的一种测试方法

提出了一种检测有源驱动OLED TFT阵列的方法,这种电流检测方法是结合TFT的制作工艺进行的. 在只增加一块光刻版的情况下,有效地解决了在含有2个TFT的单元像素电路中,检测驱动管困难的难题. 这种检测方法能够进行快速的全屏检测,具有精度高,对TFT阵列无损伤的特点.     

2T1C像素电路的AM OLED数字驱动方法研究

为了改善由于像素间TFT特性不同导致的有源矩阵有机发光显示(AM OLED)亮度不均匀现象,研究了基于2T1C像素电路的边寻址边显示(Address While Display,AWD)数字驱动方法,该方法采用等权重的11子场累积式发光方式,并用有序抖动方法实现256灰度级。通过在14cm(5.5in)的AM OLED模组上对该方法的实现和验证,结果表明,数字驱动方法在0~255灰度区间的不均匀性最大为28%,对灰度变化不敏感,而模拟驱动的不均匀性随灰度级的降低显著增大,最大为133%。数字驱动显示图像的均匀性显著优于模拟驱动,且采用基本的2T1C像素电路即可实现,降低了对像素电路和制备成本的要求。     

基于不同TFT技术的AMOLED像素电路仿真分析

非晶硅、非晶氧化铟镓锌、多晶硅薄膜晶体管是可用于设计AMOLED像素驱动电路的3种典型的薄膜晶体管(TFT)技术。文中基于3种TFT的模型,针对大尺寸、高分辨率的AMOLED,分别在典型的电压式驱动和电流式驱动像素电路进行了建模仿真,并对仿真结果做了分析和比较。该研究方法为像素电路的设计提供了一定理论依据。     

多晶硅薄膜的激光晶化技术

1 引言 多晶硅薄膜晶体管(p-Si TFT)在有源LCD和有源OLED中都有重要应用.在有源LCD中,a-SiTFT LCD目前占据绝大部分市场,尤其在大尺寸液晶电视和液晶显示器等方面,p-Si TFT LCD只是在中小尺寸中要求高分辨率的应用领域占据了一部分市场.     

AMOLED用之a—Si与p—Si的比较

本文考查了具有a-Si TFT及LTPS TFT固有性能之OLED底板的性能。LTPS TFT显示了其在AMOLED显示应用巾之令人满意的稳定性,而a—Si AMOLED则表现出在驱动OLED方面具有更好的均匀能力。但是a—Si TFT在长期工作中的稳定性是令人难以接受的,并且尚有使a—SiTFT AMOLED商品化的关键问题需要解决。     

AMOLED驱动管阈值的补偿方法综述

有机电致发光二极管(Organic Light Emitting Diode,OLED)在显示技术中得到越来越广泛的应用,特别是AMOLED已经成为新一代显示技术发展方向,但是一系列影响AMOLED显示质量和寿命的问题需要得到解决。其中,AMOLED的驱动TFT的阈值电压偏移严重影响了AMOLED的性能。该文综述了当前几种典型的AMOLED的像素驱动结构及其驱动TFT阈值电压的补偿方法,并详细介绍其补偿原理。     

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.     

有源矩阵有机电致发光像素电路的研究进展

有源驱动方式的有机发光二极管（AMOLED）较之无源驱动方式易于实现高亮度和高分辨率、功耗更小,更适合大屏幕显示。但传统的两管驱动电路会出现驱动管阈值电压在整个屏幕上分布不均匀,或长时间加偏压后驱动管的阂值电压发生漂移。本文在两管驱动电路的基础上介绍了几种最近提出的补偿电路并描述了它们的改善效果及各自存在的问题。     

Device and circuit level optimization for high performance a-Si:H TFT-based AMOLED displays

Active matrix organic light-emitting diode (AMOLED) displays with amorphous hydrogenated silicon (a-Si:H) thin-film transistor (TFT) backplanes are becoming the state of art in display technology. Though a-Si:H TFTs suffer from an intrinsic device instability, which inturn leads to an instability in pixel brightness, there have been many pixel driving methods that have been introduced to counter this. However, there are issues with these circuits which limit their applicability in terms of speed and resolution. This paper highlights these issues and provides detailed design considerations for the choice of pixel driver circuits in general. In particular, we discuss the circuit and device level optimization of the pixel driver circuit in a-Si:H TFT AMOLED, displays for high gray scale accuracy, subject to constraints of power consumption, and temporal and spatial resolution.     

Functional Pixel Circuits for Elastic AMOLED Displays

While fabrication of active matrix organic LED (AMOLED) displays on plastic substrates continues to face technological challenges, stable electrical operation of thin-film transistor (TFT) pixel circuits under mechanical stress induced by substrate bending remains a critical issue. This paper investigates strain-induced shifts in hydrogenated amorphous silicon TFT characteristics and the compound impact on TFT circuit behavior. Measurements show that the magnitude of the shifts is determined by the direction of current flow in the TFT with respect to the bending stress orientation as well as bias conditions. Physically based compact models are developed that relate device characteristics to material behavior for design and optimization of AMOLED pixel circuits that can maintain immunity to bending stress. In particular, current mirror-based pixel circuits are presented that compensate for the long term threshold voltage shift and instantaneous strain-induced shifts in device characteristics.     

External Compensation of Nonuniform Electrical Characteristics of Thin-Film Transistors and Degradation of OLED Devices in AMOLED Displays

The variation of electrical characteristics of polycrystalline-silicon thin-film transistor (TFT) and degradation of organic light-emitting-diode (OLED) device cause nonuniform intensity of luminance and image sticking in active-matrix OLED (AMOLED) displays. An external compensation method that senses and compensates variations of threshold voltage and mobility of TFTs and degradation of OLED device is proposed. The effect of the external compensation method on AMOLED pixel is experimentally verified by measuring the luminance of OLEDs and the electrical characteristics of TFTs in AMOLED pixels.      

Amorphous silicon thin film transistor circuit integration for organic LED displays on glass and plastic

This paper presents design considerations along with measurement results pertinent to hydrogenated amorphous silicon (a-Si:H) thin film transistor (TFT) drive circuits for active matrix organic light emitting diode (AMOLED) displays. We describe both pixel architectures and TFT circuit topologies that are amenable for vertically integrated, high aperture ratio pixels. Here, the OLED layer is integrated directly above the TFT circuit layer, to provide an active pixel area that is at least 90% of the total pixel area with an aperture ratio that remains virtually independent of scaling. Both voltage-programmed and current-programmed drive circuits are considered. The latter provides compensation for shifts in device characteristics due to metastable shifts in the threshold voltage of the TFT. Various drive circuits on glass and plastic were fabricated and tested. Integration of on-panel gate drivers is also discussed where we present the architecture of an a-Si:H based gate de-multiplexer that is threshold voltage shift invariant. In addition, a programmable current mirror with good linearity and stability is presented. Programmable current sources are an essential requirement in the design of source driver output stages.     

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.     

Accelerated stress testing of a-Si:H pixel circuits for AMOLED displays

Electronics reliability testing is traditionally carried out by accelerating the failure mechanisms using high temperature and high stress, and then predicting the real-life performance with the Arrhenius model. Such methods have also been applied to organic light-emitting diode (OLED) testing to predict lifetimes of tens of thousands of hours. However, testing the active matrix OLED thin-film transistor (TFT) backplane is a unique and complex case where standard accelerated testing cannot be directly applied. This is because the failure mechanism of pixel circuits is governed by multiple material and device effects, which are compounded by the self-compensating nature of the circuits. In this paper, we define and characterize the factors affecting the primary failure mechanism and develop a general method for accelerated stress testing of TFT pixel circuits in a-Si AMOLED displays. The acceleration factors derived are based on high electrical and temperature stress, and can be used to significantly reduce the testing time required to guarantee a 30 000-h display backplane lifespan.     

Amorphous Silicon Display Backplanes on Plastic Substrates

Amorphous silicon (a-Si) thin-film transistor (TFT) backplanes are very promising for active-matrix organic light-emitting diode displays (AMOLEDs) on plastic. The technology benefits from a large manufacturing base, simple fabrication process, and low production cost. The concern lies in the instability of the TFTs threshold voltage (V_T) and its low device mobility. Although V_T-instability can be compensated by means of advanced multi-transistor pixel circuits, the lifetime of the display is still dependent on the TFT process quality and bias conditions. A-Si TFTs with field-effect mobility of 1.1 cm²/Vmiddots and pixel driver circuits have been fabricated on plastic substrates at 150 degC. The circuits are characterized in terms of current drive capability and long-term stability of operation. The results demonstrate sufficient and stable current delivery and the ability of the backplane on plastic to meet AMOLED requirements