設計與製作具寬頻譜反射之反射式膽固醇液晶顯示器

Abstract

當網路和電腦相關的產業持續成長時，電子資訊顯示產業成為一個廣大的市場。高亮度、高可閱讀性、廣視角、低功率消耗和高色彩飽和度是顯示器的主要考量因素。反射式液晶顯示器使用外在環境光當作光源，不需要使用背光模組。因此，低功率消耗和輕巧是反射式液晶顯示器的主要優點。在許多種類的反射式液晶顯示器當中，雙穩態反射式膽固醇液晶顯示器由於具有低功率消耗、低製造成本和不錯的可閱讀性等優點，近來受到很多的注意。反射式膽固醇液晶顯示器適合低製造成本、高解析度、較長的閱讀時間和較小的功率消耗等應用。 然而，由於膽固醇液晶材料的限制，反射頻譜通常只有窄頻譜的反射，所以此顯示器通常只能呈現單一色彩的影像。單一色彩的影像通常不能滿足使用者的需求。黑白顯示器通常才是使用者所希望看到的。為了解決膽固醇液晶顯示器窄頻譜反射的問題，我們提出一個叫做 “全頻譜反射” 的方法來改善這個問題。這個方法的特性是用膽固醇液晶和下板反射板的兩個反射頻譜疊加在一起來加大整個膽固醇液晶顯示器的反射頻譜。寬頻譜的反射可以呈現白色的影像而不是只有單色的影像。此外，這個方法的暗態是利用膽固醇液晶在圓錐狀態的散射效應和偏光板的濾光作用來產生。因此，黑白反射式膽固醇液晶顯示器可以被實現出來，將來便能藉此製作出彩色的顯示效果。 我們藉由液晶模擬軟體 “DIMOS” 建立一套模擬模型來分析此反射式膽固醇液晶顯示器的特性。我們使用反射綠光、紫外光、紅外光波段膽固醇液晶材料來最佳化此顯示器的光學特性。從模擬的結果得知，使用反射紫外光波段的膽固醇液晶顯示器可以具有寬頻譜的反射而成為黑白的顯示器。 根據模擬的結果，我們使用傳統液晶顯示器的製程來製造膽固醇液晶顯示器的樣品。我們使用四種不同的配向條件和三種不同的膽固醇液晶材料來找出最佳性能的樣品。 最後，我們使用 “ConoScope” 來測量製造的膽固醇液晶顯示器的光學性質，例如：反射頻譜、反射率、對比和視角分佈。從量測的結果得知，使用“全頻譜反射”方法的膽固醇液晶顯示器可以達到寬頻譜反射的特性來實現黑白的顯示器。因此，使用這個方法大大提升膽固醇液晶顯示器的影像品質。使得膽固醇液晶顯示器對使用者具有較佳的可閱讀性。具有低功率消耗、低製造成本、好的影像品質、大的視角分佈等優點的黑白反射式膽固醇液晶顯示器能被實現，並適合於電子書或是電子紙張的應用。

As the Internet and the computer related industries growth continues, the electronic information display is a large market. High brightness, high readability, wide viewing angle, low power consumption and high color saturation are the main concerns. Reflective LCDs utilize ambient light as the light source, thus they do not need backlight modules. Low power consumption and light weight are main advantages of reflective LCDs. Among all reflective LCDs, bistable reflective cholesteric LCDs (Ch-LCDs) have received much attention recently because of their advantages of lower power consumption, low cost, and good readability. This kind of display is ideally applicable for those required low cost, high resolution, and long using time with low power consumption. However, due to the limitation of cholesteric LC materials, the reflective spectrum is narrow band. Therefore, the display is usually monochromic appearance, which often can not satisfy the user’s requirement. Black and white displays are the least desired for viewers. In order to solve the problem of narrow band reflection, a new method “Full Spectrum Reflective Method” is proposed. The characteristic of this method is to use two reflective spectra: one is the spectrum of cholesteric LC, the other is the spectrum of reflector compensating each other to broaden the spectrum of the display. Wide band reflection can display white images instead of monochromic images. Besides, the dark state is created by cholesteric’s scattering effect in focal conic state and polarizer’s filtration effect. Therefore, black and white reflective cholesteric LCD can be demonstrated. Furthermore, the full color mode can be realized. By LCD simulation software “DIMOS”, we established a simulation model used to characterize the features of the reflective Ch-LCDs. We utilized green band, UV band, and infrared band Ch-LC materials to optimize the optical properties of Ch-LCDs. From the simulation results, Ch-LCD with UV band Ch-LC can be wide band reflection, thus, enabling a black and white display. Based on the simulation results, we fabricated Ch-LCD test cells with conventional LCD fabrication process. We utilized four rubbing conditions and three different Ch-LC materials to find out the best performance of test cells. Finally, we used “ConoScope” to measure the optical properties of fabricated Ch-LCDs, such as reflective spectra, reflectance, contrast ratio, and viewing angle. From the measured results, Ch-LCDs with full spectrum reflective method can obtain wide band reflection property to realize black and white displays. Therefore, this method improves the image quality of Ch-LCDs greatly. The displays have better readability. With the advantages of low power consumption, low cost, good image quality, and wide viewing angle, the reflective Ch-LCDs are suitable for electronic books (E-Books) or electronic papers (E-Papers) applications.