采用简化多晶硅TFT工艺的有源矩阵OLED显示器件

我们提出并开发了一种先进的6步光掩模工艺,可用于制备有源矩阵有机发光二极管(AMOLED)中p型沟道多晶硅薄膜晶体管(TFT)面板。通过去除电源线(Vdd)和触排(bank)光处理工艺,将8步掩模简化至6步。通过6步光掩模工艺制备的p型沟道TFT,场效应迁移率可达80cm2/Vsec,亚阈值(sub-threshold)电压波动降至0.3V/dec,阈值电压约为-2V。利用6步光掩模工艺成功地获得了采用电压驱动方式的7英寸WVGA(720×480)AMOLED面板。     

柔性AMOLED的技术现状与进展

目前已经有商业化的AMOLED产品应用在MP3、手机上,而采用柔性基板的AMOLED也正在研制中,但真正实现商业化还面临诸多技术难题,如柔性衬底处理技术,柔性基板的TFT制备方法,有机薄膜蒸镀和薄膜封装等。具体分析了相关问题的处理方法和技术现状。指出使用塑胶衬底,开展有机氧化物TFT制备的发展思路。提示我国在有机薄膜蒸镀和薄膜封装领域有较大的潜在机会。     

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.     

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 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.     

3.5‐Inch QCIF AMOLED Panels with Ultra‐low‐Temperature Polycrystalline Silicon Thin Film Transistor on Plastic Substrate

In this paper, we describe the fabrication of 3.5‐inch QCIF active matrix organic light emitting display (AMOLED) panels driven by thin film transistors, which are produced by an ultra‐low‐temperature polycrystalline silicon process on plastic substrates. The over all processing scheme and technical details are discussed from the viewpoint of mechanical stability and display performance. New ideas, such as a new triple‐layered metal gate structure to lower leakage current and organic layers for electrical passivation and stress reduction are highlighted. The operation of a 3.5‐inch QCIF AMOLED is also demonstrated.     

移动可视设备制造商就新显示技术对移动可视设备影响的展望

新的显示技术是否会替代AMLCD技术而成为移动可视设备中的霸主呢?来自一线设备制造商的答案最具有权威性和可信度。     

An active‐matrix organic light‐emitting‐diode pixel circuit for the compensation of I × R voltage drop in power line

Abstract— A new voltage‐driving active‐matrix organic light‐emitting diode (AMOLED) pixel circuit is proposed to improve the display image‐quality of AMOLED displays. Because OLEDs are current‐driven devices, the I × R voltage drop in the power lines is evitable. Accordingly, the I × R voltage‐drop compensation scheme should be included in the pixel‐driving method when a voltage‐compensation method is used. The proposed pixel was designed for the compensation of an I × R voltage drop in the power lines as well as for the compensation of the threshold‐voltage non‐uniformity of low‐temperature polycrystalline‐silicon thin‐film transistors (LTPS TFTs). In order to verify the compensation ability of the proposed pixel, SPICE simulation was performed and compared with those of other conventional pixels. When the Vss voltage varies from 0 to 1 V, the drain current of the proposed pixel decreased by under 1% while that of conventional Vth compensation methods without Vss compensation decreased by over 60%. 2.2‐in. QCIF⁺ full‐color AMOLED displays, which employ the proposed pixel, have been also developed. It was verified by comparison of the display image quality with a conventional panel that our proposed panel successfully overcame the voltage‐drop problems in the power lines.     

Investigation of the hysteresis phenomenon of an a‐Si:H TFT at an elevated temperature for AMOLED displays

Abstract— The temperature dependence of the hysteresis of an a‐Si:H TFT has been investigated. An a‐Si:H TFT pixel driving scheme has been proposed and investigated. This scheme can eliminate changes in the organic light‐emitting diode (OLED) current caused by hysteresis of an a‐Si:H TFT. The VTH of the a‐Si:H TFT was changed according to the gate‐voltage sweep direction because of the hysteresis of the a‐Si:H TFT. The variation of VTH for a a‐Si:H TFT decreased from 0.41 to 0.17 V at an elevated temperature of 60°C because the sub‐threshold slope (s‐slope) of the a‐Si:H TFT, in the reverse voltage sweep direction, increased more than in the forward voltage sweep direction due to a greater increase in the initial electron trapped charges than the hole charges. Although the OLED current variation caused by hysteresis decreased (～14%) as the temperature increased, the error in the OLED current needed to be improved in order to drive the pixel circuit of AMOLED displays. The proposed pixel circuit can apply the reset voltage (?10 V) before the data voltage for the present frame that was written to fix the sweep direction of the data voltage. The variation in the OLED current caused by hysteresis of the a‐Si:H TFT was eliminated by the fixed voltage sweep direction in the proposed pixel circuit regardless of operating temperature.     

An LTPS active‐matrix process with PECVD doped N+ drain/source areas

Abstract— A low‐temperature polysilicon active‐matrix process without the need for ion implantation to dope drain and source areas of TFTs has been developed. A doped silicon layer is deposited by PECVD and structured prior to the deposition of the intrinsic silicon for the channel. The dopant is diffused and activated during the excimer‐laser crystallization step. N‐channel test TFTs with different geometries were realized. The TFT properties (mobility, on/off ratio, saturation, etc.) are suitable to realize AMLCDs and AMOLED displays and to integrate driver electronics on the displays. In addition to simple TFTs, a full‐color 4‐in. quarter‐VGA AMLCD was realized. The complete display (including photolithographic masks, active‐matrix backplane, and color‐filter/black‐matrix frontplane), and an addressing system were developed and manufactured at the Chair of Display Technology, University of Stuttgart, Germany. The substitution of ion doping by PECVD deposition overcomes a major limitation for panel sizes in poly‐Si technology and avoids large investment costs for ion‐implantation equipment.