藍相液晶顯示器之三維電極結構模擬設計

Abstract

現今人們大多是藉由視覺作為接收資訊的媒介，因此在資訊的提供上，顯示器扮演相當重要的角色。其中液晶顯示器 (LCD) 是目前廣受大眾使用的顯示器。在LCD面板技術發展純熟的世代，人們更進一步發展高幀頻顯示器提升其響應時間，儘管傳統LCD有著許多優點，但其反應時間較慢，畫面可能出現動態模糊、殘影等。而近幾年發展出的藍相液晶顯示器 (BPLCD) 則能滿足對響應時間的要求，除此之外，其優點還包括高對比度、廣視角、製程簡單，因此是目前廣受業界及學術界研究的重要題材之一。其中也包含一些缺點，如操作電壓高、穿透率低，所以需要利用克爾常數高的藍向液晶分子或是凸起物等新型電極結構來解決。 本研究提出單邊三維電極結構，目的是減少二維結構在y方向的穿透率無效區(dead-zone)，提升藍相液晶顯示器的穿透率表現。以IPS結構原理為基礎，首先以平面形電極作為基礎結構，再設計三種凸起物電極結構來降低操作電壓或提升光穿透率。本論文以2009年吳詩聰教授的研究團隊所提出的梯形結構做為第一種凸起物電極，但因為梯形頂端的電場為垂直分量，無法使藍相液晶分子產生雙折射性，導致梯形頂端會形成穿透率無效區，因此我們為了提升穿透率參考同樣為吳詩聰教授在2010年提出的三角形電極結構，利用三角形頂部的尖角降低電極上方的穿透率無效區，增加顯示器整體的穿透率，但此結構的邊界斜率比梯形低，能提供的水平電場強度不如梯形，造成操作電壓值也會跟著提高。於是我們再提出於梯形頂端加上一層與本體電極電性相反的平面形電極，使梯形頂端的電場產生水平分量，降低穿透率無效區，藉此達到高穿透率、低操作電壓的特性。 本研究藉由改變不同的電極寬度、電極間距，個別分析四種電極形狀在二維結構及三維結構之電壓-穿透率 (V-T) 特性，最後將兩者進行比較。由模擬結果中發現，不論是哪種形狀中，二維結構的最佳穿透率及操作電壓表現都比三維結構來的好，我們發現這是因為三維電極結構中存在著中央穿透率無效區，由於這個中央穿透率無效區的影響，縱使三維電極結構能改善y方向的穿透率，但仍無法超越傳統二維結構。但我們發現當電極寬度越寬，或是電極間距越窄時，能夠有效降低中央穿透率無效區的比例，使得三維結構在寬度較寬或是間距較窄的電極尺寸下，確實能夠擁有比二維結構優良的穿透率表現。並且在三維結構中優化後的梯形搭配頂部平面電極的穿透率65.16%及操作電壓(14.3 V)，我們設計此新型電極結構使其在三維電極結構中更加往高穿透率、低操作電壓的藍相液晶顯示器邁進。

Nowadays, most people receive information by vision, therefore the display plays an important interface to provide these information. One of widely used display is liquid crystal display (LCD). In the LCD panel technology development of generation, people further develop high frame rate display to enhance its response time. Although the traditional LCD has many advantages, but the response time is too long, the image may appear motion blur, defect and so on. In resent years, people developed blue-phase liquid crystal display (BPLCD) which has fast response time. In addition, its advantages include high contrast, wide viewing angle, simple process, so it is widely accepted by the industry and academia. But BPLCD also contains some shortcomings, such as high operating voltage, low transmittance, so we need to introduce high Kerr constant of BPLCs or new electrode structure like protrusion to solve these problems. We propose a single-sided three-dimensional electrode structure to reduce the y-direction dead zone of the two-dimensional structure then enhance the transmittance of BPLCDs. Based on the IPS structure, the planar electrode is used as the fundamental structure, and design three kinds of protrusion electrode structures to reduce the operating voltage and enhance the transmittance. The first protrusion electrode is trapezoid structure proposed by the group of Professor Shin-Tson Wu in 2009. But the electric field on the top of trapezoid is vertical field that can not make blue phase liquid crystal molecules produce birefringence, resulting in dead zone on the top of trapezoid. So we further refers to triangle electrode structure also proposed by the group of Professor Shin-Tson Wu in 2010. The sharp corners at the top of the triangle can reduce the dead zone, increasing the overall transmittance of the display. But its slope of the boundary is lower than that of the trapezoid so the horizontal field intensity would not strong as trapezoid, the operation voltage would be increased. So we propose adding a flat electrode on the top of trapezoid electrode with the opposite polarity of the body electrode, in order to produce a horizontal field, reducing the dead zone, thereby achieving high transmittance and low operating voltage characteristics. Changing the electrode width and the electrode spacing, then analyze the voltage-transmittance (V-T) characteristics of two-dimensional structure and the three-dimensional structure, compare two of them finally. We found that the optimal transmittance and operating voltage of two-dimensional structure are better than those of three-dimensional structure in any shape of electrode due to the center dead zone in three-dimensional electrode structure that degrades its transmittance. However, when the electrode width wider, or the electrode spacing is narrower, it is possible to effectively reduce the proportion of the center dead zone so that the transmittance of three-dimensional structure would be higher than two-dimensional structure. After optimizing, the transmittance and operating voltage of the 3D Trapezoid with top flat electrode structure are 65.16% and 14.3 V better than 3D Triangle electrode which are 64.87% and 17 V, respectively. This new electrode structure would allow for higher transmittance and low operating voltage for BPLCDs applications.