電漿束配向技術於光學補償彎曲式液晶顯示器之研究

國

立

交

通

大

學

顯示科技研究所

碩士論文

電漿束配向技術於光學補償彎曲式液晶顯

示器之研究

Investigation on Plasma Beam Alignment Technique

for OCB Mode Liquid Crystal Display

研 究 生: 周鴻杰

指導教授: 陳皇銘 博士

電漿束配向技術於光學補償彎曲式液晶顯

示器之研究

Investigation on Plasma Beam Alignment Technique

for OCB Mode Liquid Crystal Display

研 究 生: 周鴻杰 Student: Hong-Chieh Chou

指導教授: 陳皇銘 Advisor: Dr. Huang-Ming P. Chen

國立交通大學 電機資訊學院

顯示科技研究所

碩士論文

A Thesis

Submitted to Display Institute

College of Electrical Engineering and Computer Science

National Chiao-Tung University

in Partial Fulfillment of the Requirements

for the Degree of

Master

in

Display Institute

June 2007

中華民國九十六年六月

電漿束配向技術於光學補償彎曲式液晶顯

示器之研究

碩士研究生: 周鴻杰

指導教授: 陳皇銘

國立交通大學 顯示科技研究所

中文摘要

陽極層電漿源早期為俄羅斯使用於太空衛星推進器，近幾年此原理才開始被 應用於液晶配向技術。此電漿束產生方式為利用直流電漿系統產生一電漿源，利 用其正電極所產生的正偏壓強電場，使得電漿中的離子群被推動並對配向膜產生 表面處理，藉以提升配向膜品質。傳統的定向刷磨方式所造成的塵屑污染、靜電 殘留、刷痕產生等問題，對於大型化高解析度液晶顯示器面臨許多的瓶頸。電漿 束配向法屬於非接觸式配向法，沒有上述定向刷磨的缺點，為目前最有潛力取代 傳統刷磨之一。 光學補償彎曲式液晶顯示器具有廣視角以及快速的反應速度之特性，對於色 序型顯示器有著良好的應用。然而一般的配向法仍以定向刷磨為主，對於非接觸 之配向則較少琢磨。因此，本論文主要在探討經由電漿束配向後其光學補償彎曲 式液晶盒之光電特性、液晶之預傾角與配向膜之表面形貌，並與傳統之刷磨法作 為比較。

Investigation on Plasma Beam Alignment Technique

for OCB Mode Liquid Crystal Display

Student: Hong-Chieh Chou Advisor: Dr. Huang-Ming P. Chen

Display Institute

National Chiao Tung University

Abstract

ALT (Anode Layer thruster), originally used for the satellite propulsion in Russia, was modified to be the plasma source for the application of LC alignment technique. The ALT source consists of outer and inner cathode and anode. Permanent magnet is necessary to generate magnet pole at outer cathode. The plasma flux is generated by cross electric field (E) and magnetic field (H) immediately. In contrast to current rubbing manufacturing process, the plasma alignment has fewer problems of electrostatic charge and debris and is the potential candidate to replace conventional rubbing process for the next generation large display.

The OCB (Optically Compensated Bend) mode LC is known for its fast response time and wide viewing angle. Rubbing process is still the main method for preparation of OCB. In addition, the electro-optical characteristics, pretilt angle of OCB cells and surface morphology of alignment layer after plasma treatment were investigated. The influence of OCB cells between these two alignments was also be discussed. Fast response time (3.3ms) was revealed and has the potential for OCB mode LCD to replace conventional rubbing process.

誌 謝

首先誠摯感謝指導教授陳皇銘博士的幫助，迷惘中將我拉進液晶顯示器這塊 領域。在這段期間中，不論是計畫的撰寫、實驗的設計與討論對於我的指導令我 受益匪淺。 此外由衷地感謝實驗室大家的幫助，讓我可以在有限的時間內順利完成此論 文。感謝淇文、宜揚、書豪、世民、佑儒、耿睿、佳恬、耀慶、昆展、威慶、俊 民、彣綺、文孚、怡帆、謹瑋、祥志、蓮馨，不論是實驗上的討論或是彼此互相 的加油鼓勵，讓我深刻體驗到這裡的溫暖。感謝老夥伴以及所辦助理們，正宇、 龍材、偉誠、鈳銳、義淵、子民、雅惠，你們的雪中送炭，我感激於心。 感謝我最摯愛的爸媽，因為您們的支持與鼓勵，使得我屢屢有著堅持下去的 動力，也謝謝伯父一家人的關懷，讓我感受到許多溫暖與助力，我亦銘記於心。 最後將此論文呈現給我最摯愛的雙親，因為有您們才有現在的我。

Contents

Chapter 1

Introduction

1.1 Display Technology………. ………...….1

1.2 Liquid Crystal Displays……….………...1

1.2.1 The fundamental concept of Liquid Crystal Displays...…...3

1.2.2 Optically Compensated Bend (OCB) Mode………....……….5

1.3 Alignment Process……….……….7

1.4 Motivation and objective………..……….…..10

1.5 Organization of this thesis………...…………10

Chapter 2

Principle

2.1 Introduction……….…….12

2.2 Discharge Characteristics....……..………..12

2.2.1 Plasma...12

2.2.2 Glow Discharge...13

2.3 Anode Layer Thruster (ALT) Source..………17

2.3.1 History and Background...17

2.3.2 Application for LC Alignment...19

2.4 Alignment Mechanism………..………....21

Fabrication and Measurement Instruments

3.1 Introduction………..23

3.2 Fabrication Process……...………...……24

3.2.1 Flow Chart……..……….24

3.2.2 Cell Fabrication……….………...…...25

3.3 Measurement Instruments...………27

3.3.1 Electro-optical Measurement System..………...…...27

3.3.2 Cell Gap Measurement System………...………...29

3.3.3 Pretilt Angle Measurement System…….………...32

3.3.4. Atomic Force Microscopy (AFM)………..33

Chapter 4

Experimental Results and Discussions

4.1 Introduction……….…….35

4.2 V-T Characteristics……...………..………..35

4.2.1 Plasma Alignment Treatment...………...…...35

4.2.2 Hybrid Cell………...37

4.3 AFM Analysis...…..………39

4.4 Pretilt Agnle Dependence...………...…...44

4.5 POM Characteristics.………...…………....45

4.6 Response Time…..………...……….47

Chapter 5

Conclusions

5.1 Conclusions.………...………...49

5.2 Future Work………...50

Figure caption

Fig. 1-1 The structure of liquid crystal display………..………....2 Fig. 1-2 (a) Sketch of Trnasmissive (left) and Reflective (Right) LCD………..…..3 Fig. 1-2 (b) Sketch of Transflective LCD……….………...…4 Fig. 1-3 Setup and basic principle of the OCB switching mode in the off (left) and

on (right) state………..6 Fig. 1-5 The flow effect accelerates the relaxation motion in the center of the Pi cell………..7

Fig. 1-6 History of the development of photo-alignment………...…….11 Fig. 2-1 Space and laboratory plasmas classified by their electron temperature and charged particle density……….13 Fig. 2-2 Voltage-Current (V-I) characteristic for a discharge…………..….…….14 Fig. 2-3 Voltage distribution in a dc glow discharge process….……….…16 Fig. 2-4 Cross-sectional schematic drawing of the linear ion source………….…18 Fig. 2-5 Schematic diagram of ALT plasma system………....19 Fig. 2-6 ALT Plasma beam with race-trap sharp……...……….…20 Fig. 3-1 The fabrication flow chart of the OCB cell………....………...24 Fig. 3-2 The schematic diagram of electro-optical measurement system……….28 Fig. 3-3 Two reflecting surfaces separated by a layer causing a light interference. The dotted line indicates the first internal reflection………..…29 Fig. 3-4 The reflection as a function of wavelength using a air gap of 5.0µm…...31 Fig. 3-5 Pretilt angle measurement system (Autronic DMS 101 TBA)……..……32 Fig. 3-6 Schematic diagram of crystal rotation method………..……32 Fig. 3-7 Concept of AFM and the optical lever………33 Fig. 4-1 V-T characteristics as different exposure time (20sec, 35sec and 50sec) compare with the rubbing method………....36

Fig. 4-2 V-T characteristics as different exposure time (5sec, 20sec, 35sec, 50sec and 50sec) with hybrid OCB cells……….38 Fig. 4-3 V-T characteristics as 50sec plasma exposure time compare with hybrid cell………....39 Fig. 4-4 Dependence of thickness of polyimide as function of exposure time...40 Fig. 4-5 Surface morphology of polyimide (a) original surface (b) 20sec plasma treatment (c) 65sec plasma treatment (d) 3D before plasma (e) 3D after plasma 65sec……….43 Fig. 4-6 Surface roughness as function of exposure time.………...43 Fig. 4-7 Pretilt angle dependence as function of exposure time……….44 Fig. 4-8 Dark state for OCB cell as function of plasma exposure time after driving 10v (a) plasma 5sec (b) plasma 20sec (c) plasma 50sec (d) plasma 65sec (e) hybrid cell……….…….……….46 Fig. 4-9 Response time dependence as function of plasma exposure time………48 Fig. 4-10 Comparison between pure plasma and hybrid cells………...48

List of tables

Table 3-1 The parameters of the ALT plasma alignment..……….26

Table 3-2 The procedure of the ALT plasma alignment………...………..27

Table 4-1 List of transition voltage of OCB cells……….………....37