电子行业-液晶物理学及其应用(PPT 59页).ppt

1、1,液晶物理學及其應用,林啟湟 中山大學物理系,2,1.Introduction to Liquid Crystals (LCs) 2.Optical Properties of Liquid Crystals 3.Survey of LCDs: 4.Jones Calculus: Matrix Representation of Polarization 5.Optical Transmission of LC cells 6.Brightness Enhancement of LCDs 7.Aligments of Liquid Crystals 8.TFT-LCDs,color filt

2、ers, and Cell Assembly 9.Fast response LCs 10.Wide-Viewing Angle 11.Backlighting 12 Color Vision,課程大綱,3,Chapter 1 Introduction to Liquid Crystals (LCs),4,DISPLAY ISSUES Viewability Wide-angle Contrast Brightness Reflectivity(sunlight readable) Power Consumption Cost of Drive Electronics Size and Wei

3、ght Addressing Time (Video rate not always required) Color/Black-on-White Manufacturability and Reliability,5,MARKETS,Consumer TV, movie, etc Transportation Aviation Automotive , Passenger entertainment Business Application Videoconferencing Automated Teller Pagers Industrial Applications Process co

4、ntrol Analytical Equipment Medical Technology Computer Application Viewer Application Electronic books Electronic newspaper Document viewers,6,History of the Taiwan FPD Industry,Embryo Period (19761986): TN-LCD and STN-LCM -1976: TN-LCD assembly technology transferred from Hughes -1980: STN-LCD back

5、-end assembly factories set up by Japanese companies -Export-oriented module assembly Incubation Period (19871997): STN-LCD, small and medium-size TFT-LCD -1987: ERSO/ITRI started to R&D in TFT-LCD technologies -1992: First -TFT LCD pilot line set up in ERSO for experimental production -Governmental

6、 support enticed overseas brain-drain Thriving Period (1998 ): -Mass production tech. transferred from Japan, venture capital -New technologies, such as LTPS-TFT LCDs, OLED and LCOS, probed.,Market incentives, government support, superior human resources, international collaboration, plentiful capit

7、al,Driving Forces,7,2004年我國大型TFT產值比較 2004年全球大型TFT產值約346億美元，而我國產值較前一年成長67%，估計佔全球比重約38%，僅次於韓國45%；另外，日本約佔17%，排名第三(圖一)。,8,2004年我國中小型TFT產值比較 2004年全球中小型TFT產值約102億美元，而我國產值較前一年成長140%，估計佔全球比重約12%，次於日本78%，而韓國約佔10%，排名第三。,9,10,我國20042005年平面顯示產業產值分佈,表一 我國2004年平面顯示產業產值分佈,11,我國大型TFT廠商營利表現比較,12,韓國大型TFT廠商營利表現比較,Aim

8、to make Taiwan the worlds largest supplier of TFT-LCD panels. Build Taiwan into the worlds most important center for color imaging device R&D and manufacturing. Attain production value of at least NT$1.37 trillion for the color imaging industry in 2006. Reach at least NT$350 billion in private-secto

9、r investment over the next five years.,Prospect of Taiwan FPD Industry,14,LCD結構圖,Or 3M DEBF,15,Basic Concept 液晶簡介,17,物質的相變,18,何謂液晶?,19,20,中間相 (Mesophases),結晶狀的固體 (Crystalline Solid),各向同性的液體 (Isotropic Liquid),21,液晶的分類,1) Thermotropic (熱致液晶),2) Lyotropic (溶致液晶),因溫度的改變而產生相變,因溶於溶劑中濃度比例的改變而產生相變,以產生相變之原因

10、來區分,LCDs:Thermotropic (熱致液晶),分子形狀,排列方式,22,:LCDs,23,液晶以分子形狀分類,24,Types of Low Molecular Weight Liquid Crystal Materials,Lyotropic Liquid Crystals (溶致液晶) form liquid crystal phases over certain concentration ranges when mixed with a solvent,25,Thermotropic Liquid Crystal(熱致液晶)- (Used for LCDs) molecul

11、es consisting for a rigid core and flexible tail(s) )-form liquid crystal phase over certain temperature ranges,26,4. 分子排列之有序性,溶液,27,Melting of a Solid,Director axis,28,Nematic 液晶,Nematic 液晶特性:,(a) 分子的重心位置沒有次序性。 (b) 分子的排列方向存在一定程度的次序性，分子傾向平行於某個共同的方向去排列，如圖所示，我們定義這個方向為Director (Director Axis)以 n 表示。 (c

12、) Director n 與 n 的狀態是不可區分的。,LCD用液晶,29,Cholesteric 液晶,反射波長波長=np之入射光,30,The Chiral Nematic,31,Chirality,H-C-C-C-C-C,C N,H,H,H,H,H,H,H,H,H,H,non-chiral,H-C-C-C-C-C,C N,H,H,H,CH3,H,H,H,H,H,H,chiral (RH),Chiral center,Chiral structure,RH chiral and LH chiral,32,Application of cholesteric LC,Color reflect

13、ive display 亮度加強膜 Smart windows in building Broadband circular polarizer 缺點 : Narrow bandwidth (LC之n0.3),33,Smectic 液晶,由結構上的差異Smectic液晶又可被細分成Smectic A、B、C.等共十餘種。但結構上看，所有的Smectics相都具有層狀結構，層與層之間的距離是一定的，層間距可以用X-ray繞射方法來量測。由此可見Smectics的之次序性比Nematics高。對於任何俱備此兩種相的材料 而言，其Smectic相的溫度範圍總比Nematic相為低。,34,35,(c

14、) Smectic C* (SmC*)-Ferroelectric LCs,與Smectic C相似其分子導軸之方向與層面法線方向有一夾角。但相鄰之液晶層的分子導軸會沿著層面法線作緩慢之螺旋轉動，如圖所示。此結構之形成通常可由Smectic C之液晶再加入 chiral agent所形成。故又名為chiral smectic C。,36,37,Some Characteristics of Liquid Crystal Phase,-Long-Range Molecular Order -Fluid Viscosities -Optical Anisotropy (Birefringence)

15、 n=n/-n(or ne-n0) -Dielectric Anisotropy = -Optical Activity -Electrical Resistivity 1013 ohm-cm(TFT),38,由於液晶分子之形狀具有高度幾何異向性長條狀或圓盤狀，導致其分子之排列方向具有秩序性，此一異於各向同性(isotropic)液體的特性亦表現在電性、磁性、光學及力學等各方面。當量測其介電係數(dielectric constant)、磁導率(magnetic susceptibility)、折射率(refractive index)及黏滯係數(viscosity)等時，將因液晶分子排列方向

16、不同而有所差異。,液晶之非均向性(Anisotropic),39,Dielectric constant 之非均向性,Electric displacement :,即,故 與 分別代表外加電場 E 之方向垂直與平行於液晶導軸時之dielectric constant 。而 為液晶之重要參數，其值可 正 可 負。端視液晶分子之永久偶極矩及誘導偶極矩性質而定。,40,外加電場對 nematic 相的影響,對一 nematic 相液晶外加一電場 E，其相應的電位移 D 為 此時電場對系統之能量貢獻(每 cm3)可寫,41,液晶之介電異向性,液晶之介電常數值越大產生的induce dipole越大,

17、介電異向性決定LC之轉動,42,(=|-) 0, (=|-) 0,LC靠Induce dipole 與電場的作用發生旋轉 力矩=E= 1/2oE2sin2 反向電場不影響液晶之旋轉方向,液晶分子外加電場下之旋轉,+,+,+,-,-,-,+,-,|,| ,+,-,+,-,|,| ,-,-,+,+,|,|,E,E,43,介電係數與溫度之關係,5CB之介電係數與溫度之關係曲線。,44,The Order Parameter,*Solid =0 S=1 Isotropic phase orientation is random =1/3 S=0,45,連續彈性體理論,通常在液晶中之導軸n是隨位置而變化

18、的。此變化在微觀尺度上十分微小，而液晶無論是受到表面配向或外加力場之作用而導致液晶分子排列方式的任何形變，均可以如下之三種基本形變來探討其物理現象。,其中: K11、K22、K33分別為Splay、Twist、Bend形變之彈性係數(elastic constant),液晶之連續彈性體理論，僅對彈性能量考量及假設所有秩序參數S為常數。此假設於方向或位置秩序有缺陷(defect)之區域即不成立。,彈性常數K33K11K22,46,Creating Deformation with a Field and Surface,47,液晶形變自由能密度,總自由能F = Fd + Fs + Fext,液晶

19、連續體理論,fd=,彈性自由能,介面作用自由能,外場作用自由能,外場作用自由能密度,電能,磁能,光能,求總自由能F之最小值可得到外場下LC之排列狀態,48,Free energy density : Torque density Nematic (K11=K33=K10-11 N) and d=10 m For steel : shear modules=108 N/m2,Deformation Torque,49,Rotation viscosity 1(轉動粘滯係數),1,LC分子,1 代表液晶分子轉動的難易度 1越小LC反應越快,Response time 正比於 “LC黏度“和“cel

20、l gap平方” 0之LC其粘滯係數較小,50,許多影響LCD性能之物理參數與秩序參數S間有著密切之相關性，如下所示:,Example: 當TN cell之溫度上升時，其臨界電壓Vth 如何變化?,各物理參數與秩序參數S之相關性,因,故溫度上升時，其臨界電壓Vth 應下降。,51,Thermal Properties,Phase Transition : Isotropic-Nematic:Weakly first order (latent heat of transition ) (heat of transition)N-I= 1 kcal/mole (heat of transitio

21、n) ice-water=1.4 kcal/mole Nematic-Smectic: First or second order Nematic-Smectic C : First order Smectic A Smectic C : Second Order,Temp,52,Techniques for Identifying Liquid Crystal Phase,Polarizing Microscope and Heating Stage Change in appearances with temperature Differential Scanning Calorimetr

22、y (DSC) Monitor energy required for phase transiton X-ray Crystallography Structure of phase determined by x-ray scattering pattern,53,Polarizing Microscopy and Heating Stage,Sample Preparation Small amount of sample placed on a microscopic slide with cover slip Substrate surface may be treated to control alignment Substrates may be mechanically sheered to c