场序显示弃用滤光片，新一代蓝相液晶屏比Retina清晰3倍

美国光学学会本月1日对外宣布，新一代蓝相液晶技术研发成功，使这种先进技术进一步接近量产阶段。据这项技术的研究团队介绍，新一代蓝相液晶技术拥有超精细显示能力，像素密度高达1500ppi，是目前苹果Retina屏幕的三倍。

研究人员表示，新一代蓝相液晶技术主要面向虚拟现实头戴设备，目的是能够在近距离上显示足够清晰、细腻的画面。

事实上，三星早在2008年就已经宣布研制成功蓝相液晶屏幕原型，但由于需要较高工作电压和电容充电时间较长等不完善技术因素的影响，此类产品未能推向市场。

而新一代蓝相液晶技术成功解决了上述问题，其颜色驱动速度是普通液晶屏幕的10倍，响应速度低于1ms。同时色彩更加鲜艳。

目前，新一代蓝相液晶技术研发合作方之一的友达光电已经表示在适用于这项技术的电极结构上有所突破，预计将在2018年生产出可装配在原型设备上的屏幕。

中佛罗里达大学光学与光子学院（CREOL）研究团队的吴诗聪教授说，“今天的Apple Retina显示器的像素密度约为每英寸500ppi。“使用我们的新技术，在同样大小的屏幕上可以实现每英寸1500像素的分辨率。这对于需要通过靠近我们的眼睛实现虚拟现实或增强现实的技术特别有吸引力，虚拟现实或增强现实技术必须在小屏幕中实现高分辨率。

尽管第一个蓝相液晶原型在2008年由三星展示，但由于高工作电压和电容充电时间慢等问题，该技术还没有进入生产阶段。为了解决这些问题，吴诗聪教授的研究团队与液晶制造商日本JNC和显示器制造商台湾友达光电公司一起合作。

在来自光学学会（OSA）的期刊Optical Materials Express中，研究人员报道了如何将新液晶与特殊的性能增强电极结构相结合，可以在每像素15V的操作电压下实现74％的透光率，最终可以使场序彩色显示器实用于产品开发。

文章的第一作者Yuge Huang说：“场序彩色显示器可以用来实现较小像素以提高屏幕分辨率。“这很重要，因为当今技术的分辨率几乎达到极限。

蓝相液晶是如何运行的

今天的LCD屏幕是通过向列型液晶调制进入的白色LED背光源。薄膜晶体管提供控制每个像素中的光透射所需的电压。 LCD子像素包含红色，绿色和蓝色的彩色滤光片，它们组合使用以对人眼产生不同的颜色。通过组合所有三种颜色创建白色。

蓝相液晶可以进行切换或控制，比向列型液晶快约10倍。这个亚毫秒响应时间允许每个LED颜色（红色，绿色和蓝色）在不同时间通过液晶发送，并且不需要彩色滤光片。 LED颜色切换如此之快，以使我们的眼睛可以整合红色，绿色和蓝色以形成白色。

“用彩色滤色片时红、绿、蓝光都是同时产生的，”吴诗聪教授说。“然而，对于蓝相液晶，我们可以使用一个子像素来产生所有三种颜色，但在不同的时间，这将空间转换为时间，节省空间的三分之二的配置，其像素密度增加了三倍。

蓝相液晶也使光学效率提升三倍，因为光不必通过彩色滤色片，这将穿透率控制在约30％。另一个大的优点是所显示的颜色会更加鲜艳，因为它直接来自红色，绿色和蓝色LED，这消除了平时与彩色滤色片发生的颜色串扰。

吴诗聪教授的团队与JNC合作，将蓝相液晶的介电常数降低到最小的可接受范围，以减少晶体管充电时间并获得亚毫秒的光学响应时间。然而，每个像素仍然需要高于单个晶体管提供的驱动电压。为了克服这个问题，研究人员设计了一个凸起的电极结构，使得电场能更深入地穿过液晶，以大幅降低驱动每个像素所需的电压，同时保持高光穿透率。

“我们实现了一个足够低的工作电压，允许每个像素由单个晶体管驱动，同时实现小于1毫秒的响应时间，” 吴诗聪实验室的博士生陈海伟（音译）说。“工作电压和响应时间之间的这种微妙平衡是启用现场顺序彩色显示的关键。

液晶显示中黑科技 —蓝相液晶

2016年，韩系面板厂向大陆品牌厂供应曲面OLED显示面板，OPPO/Vivo等中国品牌销量销量出现了数量增长的小跳跃，据行业研究机构预测，OLED技术在手机产品中的渗透终将居于领先地位，那么LCD会被取而代之吗？答案是不会，因为LCD领域的诸多新技术正在蓄势待发。

蓝相液晶做为液晶显示中的黑科技之一，在1888年，F.Reiniter发现液晶时描述样品首先出现的蓝紫色即为苯甲酸胆甾醇酯处于蓝相时具有的颜色。因此可以说在液晶的研究过程中，蓝相液晶(Bluephase liquid crystal, BPLC)是最早被发现的，根据不同分子结构，可将蓝相分为三类：

看到这么复杂的分子结构，就知道蓝相要比我们常用的向列相液晶独特许多，事实也确实如此，蓝相具有克尔效应诱导双折射特性，与向列相液晶展现光学各向异性的过程是完全不同的。

从器件工作原理上看，或许会简单些。Off-State时，蓝相液晶处于各向同性，On-State时，蓝相液晶处于各向异性。

那么表现在产品性能上，蓝相液晶显示具有哪些优良特性呢？

●具有亚毫秒的响应时间，不但使液晶显示有可能实现场序彩色显示模式，还可以大大降低动态伪像，而场序彩色显示模式显示的分辨率和光学效率是常规显示的数倍

●不需要取向层，可大大简化制备工艺过程、提升产品良率和品质

●对液晶盒的厚度不敏感，可应用于大型显示屏制作

看到这里，研发的小伙伴早已心潮澎湃了，但蓝相液晶的缺点也不容小觑

●驱动电压太高。如果采用IPS模式交叉指电极，当BP-LC 的Kerr常数K为约10nm/V2时，驱动电压约为50Vrms

●液晶相温宽过窄，目前大多研究机构及面板厂采用聚合物稳定的方式制作器件，聚合物的寿命、残像等问题也很难攻克

面对黑科技，各研究机构和面板厂又爱又恨，但从未放弃努力，2008年， SID上曾有蓝相液晶显示器件展出，但因材料与器件的问题未完全解决，故相关产品未能面世。

2012年剑桥发表了可达250℃蓝相区间的文章，温宽为世界之最。

目前，关于蓝相液晶的研究的论文和专利数量每年以指数式增长，可见从材料和器件维度，学者和行业内专家坚信这项黑科技终将引领液晶显示走向下一个巅峰。2016年9月22日，在中国平板显示学术论坛上，欧阳钟灿院士指出“液晶仍然处在发展的上升期”。在材料厂商、面板厂、高校及研究机构的共同努力下，诸多黑科技将会为平板显示领域增添更多的惊喜！

摘自：京东方MRI

Researchers have developed a new technology that couldtriple the resolution density of displays. The new technology could allowfield-sequential color displays where a single subpixel can be quickly switchedamong red, green or blue. By eliminating the color filters traditionally usedto spatially divide one pixel into red, green or blue subpixels,field-sequential color displays allow the three subpixels to become threeindependent pixels and thus triples the resolution density.

Credit: Yuge Huang and Ruidong Zhu, CREOL, The College ofOptics and Photonics, University of Central Florida

An international team of researchers hasdeveloped a new blue-phase liquid crystal that could enable televisions,computer screens and other displays that pack more pixels into the same spacewhile also reducing the power needed to run the device. The new liquid crystalis optimized for field-sequential color liquid crystal displays (LCDs), apromising technology for next-generation displays.

"Today's Apple Retina displays havea resolution density of about 500 pixels per inch," said Shin-Tson Wu, wholed the research team at the University of Central Florida's College of Opticsand Photonics (CREOL). "With our new technology, a resolution density of1500 pixels per inch could be achieved on the same sized screen. This isespecially attractive for virtual reality headsets or augmented realitytechnology, which must achieve high resolution in a small screen to look sharpwhen placed close to our eyes."

Although the first blue-phase LCDprototype was demonstrated by Samsung in 2008, the technology still hasn'tmoved into production because of problems with high operation voltage and slowcapacitor charging time. To tackle these problems, Wu's research team worked withcollaborators from liquid crystal manufacturer JNC Petrochemical Corporation inJapan and display manufacturer AU Optronics Corporation in Taiwan.

In the journal Optical MaterialsExpress, from The Optical Society (OSA), the researchers report how combiningthe new liquid crystal with a special performance-enhancing electrode structurecan achieve light transmittance of 74 percent with an operation voltage of 15volts per pixel -- operational levels that could finally make field-sequentialcolor displays practical for product development.

"Field-sequential color displayscan be used to achieve the smaller pixels needed to increase resolutiondensity," said Yuge Huang, first author of the paper. "This isimportant because the resolution density of today's technology is almost at itslimit."

How it works

Today's LCD screens contain a thin layerof nematic liquid crystal through which the incoming white LED backlight ismodulated. Thin-film transistors deliver the required voltage that controlslight transmission in each pixel. The LCD subpixels contain red, green and bluefilters that are used in combination to produce different colors to the humaneye. The color white is created by combining all three colors.

Blue-phase liquid crystal can beswitched, or controlled, about 10 times faster than the nematic type. Thissub-millisecond response time allows each LED color (red, green and blue) to besent through the liquid crystal at different times and eliminates the need forcolor filters. The LED colors are switched so quickly that our eyes canintegrate red, green and blue to form white.

"With color filters, the red, greenand blue light are all generated at the same time," said Wu."However, with blue-phase liquid crystal we can use one subpixel to makeall three colors, but at different times. This converts space into time, aspace-saving configuration of two-thirds, which triples the resolutiondensity."

The blue-phase liquid crystal alsotriples the optical efficiency because the light doesn't have to pass throughcolor filters, which limit transmittance to about 30 percent. Another bigadvantage is that the displayed color is more vivid because it comes directlyfrom red, green and blue LEDs, which eliminates the color crosstalk that occurswith conventional color filters.

Wu's team worked with JNC to reduce theblue-phase liquid crystal's dielectric constant to a minimally acceptable rangeto reduce the transistor charging time and get submillisecond optical responsetime. However, each pixel still needed slightly higher voltage than a singletransistor could provide. To overcome this problem, the researchers implementeda protruded electrode structure that lets the electric field penetrate theliquid crystal more deeply. This lowered the voltage needed to drive each pixelwhile maintaining a high light transmittance.

"We achieved an operational voltagelow enough to allow each pixel to be driven by a single transistor while alsoachieving a response time of less than 1 millisecond," said Haiwei Chen, adoctoral student in Wu's lab. "This delicate balance between operationalvoltage and response time is key for enabling field sequential colordisplays."

Making a prototype

"Now that we have shown thatcombining the blue-phase liquid crystal with the protruded electron structureis feasible, the next step is for industry to combine them into a workingprototype," said Wu. "Our partner AU Optronics has extensiveexperience in manufacturing the protruded electrode structure and is in a goodposition to produce this prototype."

Wu predicts that a working prototypecould be available in the next year. Since AU Optronics already has a prototypethat uses the protruded electrodes, it will only be a matter of working with JNCto get the new material into that prototype.