彩膜将消失!吴诗聪团队攻破蓝相液晶壁垒,1500ppi液晶屏明年友达/JNC试产

Original 2017-02-06 小C君 CINNO

美国光学学会本月1日对外宣布，吴诗聪教授团队研发新一代蓝相液晶技术获得成功，使这种先进技术进一步接近量产阶段。据研究团队介绍，该技术可以使电视、电脑屏幕和其他显示器实现更高的解析度，最高可达1500ppi，是目前苹果Retina屏幕的三倍，并且同时可以降低屏幕所需功耗。新液晶针对场序彩色液晶显示器的性能进行了优化，这被认为是非常有前景的下一代显示器技术。

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。

2018年生产蓝相液晶原型

“现在我们已经表明，将蓝相液晶与凸起的电极结构相结合是可行的，下一步是实现工业化生产的样品。“我们的合作伙伴AUO在制造突出电极结构方面具有丰富的经验，并且能够生产这种样品。

吴世聪预测，第一个样品可能在明年实现。因为AUO已经有一个使用凸起的电极结构的样品，剩下就只需要与JNC合作使用新材料来进行生产。

有关吴诗聪教授

来自台湾的吴诗聪（Shin-Tson Wu）教授现任教于中佛州大学，是光电显示领域知名专家，美国国家发明院的首批院士，美国佛罗里达州发明家名人堂首批入选者。吴诗聪教授毕业于台湾大学物理系，并于洛杉矶南加州大学获得电子工程博士学位。他以液晶显示器（LCD）的研究发展荣获国际光学界的多个大奖，包括2014年的斯帖霍夫曼贝勒勋章OSA Esther Hoffman Beller 奖章和2011年的Slottow-Owaki 奖。在于2001年加入中佛州大学任教前，他在位于加州的著名休斯研究实验室（Hughes Research Laboratories）工作了18年。他对液晶显示器的先驱开发研究帮助成形了现在熟知的LCD液晶屏幕技术，被广泛应用在液晶电视，苹果手机和其他智能手机上。他在液晶技术的研究也帮助了自适应镜头（adaptive lenses）的突破使用。

吴教授的研究重点集中在先进液晶显示器，自适应镜头，空间光调制器，生物光子学以及新型光子材料等方面，撰写出版了8部专著，发表过近500篇论文，拥有80多项美国专利。

英文原文：Novel liquid crystal could triple sharpness of today's televisions

Researchers have developed a new technology that could triple the resolution density of displays. The new technology could allow field-sequential color displays where a single subpixel can be quickly switched among red, green or blue. By eliminating the color filters traditionally used to spatially divide one pixelinto red, green or blue subpixels, field-sequential color displays allow the three subpixels to become three independent 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 has developed a new blue-phase liquid crystal that could enable televisions, computer screens and other displays that pack more pixels into the same space while also reducing the power needed to run the device. The new liquid crystal is optimized for field-sequential color liquid crystal displays (LCDs), a promising technology for next-generation displays.

"Today's Apple Retina displays have a resolution density of about 500 pixels per inch," said Shin-Tson Wu, who led the research team at the University of Central Florida's College of Optics and Photonics (CREOL). "With our new technology, a resolution density of 1500 pixels per inch could be achieved on the same sized screen. This is especially attractive for virtual reality headsets or augmented reality technology, which must achieve high resolution in a small screen to look sharp when placed close to our eyes."

Although the first blue-phase LCD prototype was demonstrated by Samsung in 2008, the technology still hasn't moved into production because of problems with high operation voltage and slow capacitor charging time. To tackle these problems, Wu's research team worked with collaborators from liquid crystal manufacturer JNC Petrochemical Corporation in Japan and display manufacturer AU Optronics Corporation in Taiwan.

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

"Field-sequential color displays can be used to achieve the smaller pixels needed to increase resolution density," said Yuge Huang, first author of the paper. "This is important because the resolution density of today's technology is almost at its limit."

How it works

Today's LCD screens contain a thin layer of nematic liquid crystal through which the incoming white LED backlight is modulated. Thin-film transistors deliver the required voltage that controls light transmission in each pixel. The LCD subpixels contain red, green and blue filters that are used in combination to produce different colors to the human eye. The color white is created by combining all three colors.

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

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

The blue-phase liquid crystal also triples the optical efficiency because the light doesn't have to pass through color filters, which limit transmittance to about 30 percent. Another big advantage is that the displayed color is more vivid because it comes directly from red, green and blue LEDs, which eliminates the color crosstalk that occurs with conventional color filters.

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

"We achieved an operational voltage low enough to allow each pixel to be driven by a single transistor while also achieving a response time of less than 1 millisecond," said Haiwei Chen, a doctoral student in Wu's lab. "This delicate balance between operational voltage and response time is key for enabling field sequential color displays."

Making a prototype

"Now that we have shown that combining the blue-phase liquid crystal with the protruded electron structure is feasible, the next step is for industry to combine them into a working prototype," said Wu. "Our partner AU Optronics has extensive experience in manufacturing the protruded electrode structure and is in a good position to produce this prototype."

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