液晶显示器视角相关性能的研究进展(特邀)

Research Progress on Viewing Angle-related Performance of Liquid Crystal Display(Invited)

液晶显示器(Liquid Crystal Display,LCD)是重要的显示技术,被广泛地应用于电视、电脑显示器、手机显示屏等领域,覆盖了大中小尺寸几乎所有的需求范围。LCD具有市场规模大、性价比高、寿命长等优点,但也存在一些瓶颈问题,突出表现在视角相关问题,例如倾斜视角下的对比度下降、灰阶偏移、色彩偏移等。此外,随着应用场景的具体化,市场上逐渐涌现出一些特殊的视角需求,例如窄视角、指定视角、视角可控等需求。针对以上问题,研究人员进行了大量的优化和改进,目前LCD的视角相关性能已经得到了明显提升。本文综述了部分有代表性的研究工作,首先,介绍了LCD的基本结构、显示原理、以及常见的显示模式;然后,介绍了与视角相关的性能参数,总结了能够改善视角相关问题的技术方法;最后,归纳了几种特殊的视角控制技术并进行了展望。

At present,Liquid Crystal Display(LCD) has become an important display technology,especially in the large-size display field. Since the liquid crystal is optically anisotropic materials,LCD has inherent viewing angle-related problems,which is increasingly becoming a bottleneck restricting its further development. In this case,LCD needs to constantly innovate to cope with the fierce competition with other display technologies and the increasing performance demands from consumers. In recent years,some technologies that can improve the LCD’s viewing angle problem have been proposed. In order to make the researchers quickly find out the relevant technical progress,we summarize some research on improving the viewing angle-related performance in recent years. This overview can be divided into the following three parts:LCD structure and display mode,the research progress of viewing angle-related performance,and special viewing angle control technology. 1) LCD structure and display mode. The basic structure and display principle of LCD are first introduced,and four common display modes,including twisted nematic,vertical alignment,in-plane switching,and fringe-field switching,are described in the order in which they were proposed. We then describe the spatial positions of the electrode structures and the initial liquid crystal orientation in the four display modes. Besides,the specific display principles of the different display modes are explained in detail. Then,the advantages and disadvantages of the different display modes and their suitable applicable fields are briefly introduced. As we know,the viewing angle problems of different display modes are different, and thus the corresponding improvement measures are also different.2)Research progress of viewing angle-related performance. Among the many display performances,some performances have the dependence on viewing angle. Here,we introduce the properties related to viewing angle,such as brightness,contrast,grayscale,color,and color gamut. Representative improvement methods are pointed out at these performances,and the advantages and disadvantages of different methods are analyzed. In terms of brightness,several methods that can improve the brightness at the full viewing angle are introduced,such as high brightness backlight,narrow electrode technology,and field sequential color technology. We introduce the wide viewing angle compensation film,regional dimming technology,dual-cell display technology,and surface anti-reflection structure to improve the contrast. In terms of the grayscale and color performance,we introduce the use of light scattering films,single-domain and multidomain electrode structures,and optimized driving methods to reduce the gamma shift and color difference.In addition,the methods to improve the color gamut of LCD are pointed out,such as high color gamut backlights and broadband optical filters. Each of the above methods has an important reference value for improving the viewing angle-related performance of LCD,but each approach focuses on a different viewing angle problem,and each method has its advantages and disadvantages. Therefore,researchers need to choose the appropriate methods to solve their specific problems. 3) Special viewing angle control technology. In some special application fields,the wide viewing angle technology is no longer applicable,such as business mobile phones,bank automated teller machines,ciphers,and aviation display that require privacy protection. In order to address the needs of the above fields,several special viewing angle control technologies are introduced,including narrow viewing angle,specified viewing angle,and viewing angle controllable technologies. In the aspect of narrow viewing angle technology,two commonly used methods of shading privacy film and viewing angle compensation film are introduced. In terms of the more special non-face-to-view display field,the specified viewing angle display technology based on the viewing angle deflection film is introduced. Besides,several viewing angle controllable technologies are introduced,such as dual-pixel structure,dual-cell device structure,electrode bias method. These methods can make LCD exhibit the viewing angle performance different from the common LCD with wide viewing angle,and they have the application value for some application fields with special viewing angle requirements. In different practical situations,relevant researchers should select out the appropriate technical solutions according to the actual needs,so as to solve the specific viewing angle problems in the design and manufacturing processes.Due to the limited space of this overview,the research on the various viewing angle performances cannot be summed up in all. And thus,only some representative research works are reviewed. It should be noted that,in addition to the viewing angle-related performance introduced in this overview,LCD needs to be continuously optimized in terms of flexible display,reducing the motion picture response time,and reducing the power consumption,etc. Driven by market competition,consumers pay more attention to the comprehensive performances of display technology,thus we should not sacrifice other performances just to improve one performance of LCD. In fact,how to realize the“multi-parameter linkage optimization”has become an important task to improve the comprehensive performance of LCD,which also poses a greater challenge to future research works. At present,LCD is still a relatively important display technology. From the perspective of development trends,the overall display performance of LCD based on the Mini LED backlight and regional dimming is excellent. It has the advantages of a million-level dynamic contrast ratio,more than 2 000 nits peak brightness,and ultra-high color gamut. Therefore,Mini LED LCD is an important display technology in the future,the methods mentioned in the paper are also effective in improving the viewing angle-related performance of LCD.