液晶物理學及其應用液晶物理學及其應用林啟湟中山大學物理系11.Introduction to Liquid Crystals(LCs)1.Introduction to Liquid Crystals(LCs)2.Optical Properties of Liquid Crystals2.Optical Properties of Liquid Crystals3.Survey of LCDs:3.Survey of LCDs:4.Jones Calculus:Matrix Representation of Polarization4.Jones Calculus:Matrix Representation of Polarization5.Optical Transmission of LC cells5.Optical Transmission of LC cells6.Brightness Enhancement of LCDs6.Brightness Enhancement of LCDs7.Aligments of Liquid Crystals7.Aligments of Liquid Crystals8.TFT-LCDs,color filters,and Cell Assembly8.TFT-LCDs,color filters,and Cell Assembly9.Fast response LCs9.Fast response LCs10.Wide-Viewing Angle10.Wide-Viewing Angle11.Backlighting11.Backlighting12 Color Vision12 Color Vision課程大綱課程大綱2Chapter 1Chapter 1Introduction to Liquid Crystals(LCs)Introduction to Liquid Crystals(LCs)3 DISPLAY ISSUESDISPLAY ISSUESViewabilityViewabilityWide-angleContrastBrightnessReflectivity(sunlight readable)Power ConsumptionPower ConsumptionCost of Drive ElectronicsCost of Drive ElectronicsSize and WeightSize and WeightAddressing TimeAddressing Time (Video rate not always required)Color/Black-on-WhiteColor/Black-on-WhiteManufacturability and ReliabilityManufacturability and Reliability4 MARKETSConsumerConsumerTV,movie,etcTransportationTransportationAviation Automotive,Passenger entertainmentBusiness ApplicationBusiness ApplicationVideoconferencingAutomated TellerPagersIndustrial ApplicationsIndustrial ApplicationsProcess controlAnalytical EquipmentMedical Technology Medical Technology Computer Application Computer Application Viewer ApplicationViewer ApplicationElectronic booksElectronic newspaperDocument viewers5History of the Taiwan FPD IndustryEmbryo Period(19761986):Embryo Period(19761986):TN-LCD and STN-LCMTN-LCD and STN-LCM-1976:TN-LCD assembly technology transferred from Hughes-1980:STN-LCD back-end assembly factories set up by Japanese companies-Export-oriented module assemblyIncubation Period(19871997):Incubation Period(19871997):STN-LCD,small and medium-size TFT-LCDSTN-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 support enticed overseas brain-drain Thriving Period(1998):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,Market incentives,government support,superior human resources,international collaboration,plentiful capitalinternational collaboration,plentiful capitalDrivingDrivingForcesForces62004年我國大型年我國大型TFT產值比較產值比較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)。
72004年我國中小型年我國中小型TFT產值比較產值比較 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%，排名第三89我國我國20042005年平面顯示產業產值分佈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 10我國大型TFT廠商營利表現比較 11韓國大型TFT廠商營利表現比較 12Aim to make Taiwan the worlds largest supplier of TFT-LCD Aim to make Taiwan the worlds largest supplier of TFT-LCD panels.panels.Build Taiwan into the worlds most important center for color Build Taiwan into the worlds most important center for color imaging device R&D and manufacturing.imaging device R&D and manufacturing.Attain production value of at least NT$1.37 trillion for the color Attain production value of at least NT$1.37 trillion for the color imaging industry in 2006.imaging industry in 2006.Reach at least NT$350 billion in private-sector investment over the Reach at least NT$350 billion in private-sector investment over the next five years.next five years.13 LCD LCD結構圖結構圖Or 3M DEBF1415 Basic ConceptBasic Concept 液晶簡介16 物質的相變物質的相變17何謂液晶何謂液晶?對於一般常見的物質由結晶狀的固體結晶狀的固體(Crystalline Solid)相變為各向同各向同性的液體性的液體(Isotropic Liquid)，通常是經由單一過程的相變單一過程的相變。
但有很多有機很多有機物物由結晶固體到各向同性液體間卻需要經過多個步驟的相變多個步驟的相變因此必定存在一個或多個介於結晶固體與各向同性液體間的中間相中間相(Mesophases)由於這些中間相的分子次序是介於結晶固體與各向同性液體間，所以這些 相 的 力 學、光 學 性 質 和 對 稱 性 也 介 於 結 晶固體與液體之間到目前為止，已被發現的這些中間相中間相大致可被區分成兩大類別:Disordered Crystal Mesophases:一般稱之為塑性晶體塑性晶體(Plastic Crystals)其分子形狀常為圓球狀圓球狀(Globular)，故易形成分子位置有次序性，但方向無次序性的相因其分子位置仍保留三維晶格排列，故不具流動性1)18Ordered Fluid Mesophases:通常稱為液態晶體液態晶體(Liquid Crystals)簡稱液晶由於此相常由長條狀長條狀(Rod-like)或圓盤狀圓盤狀(Dise-like)的分子所組成故易形成一分子重心位置無次序性，但方向有次序性的相由於此相分子重心位置不受限於晶格位置無序，故具有一定程度的流動性2)由上述可知，這些中間相的分子形狀分子形狀是決定其物性的重要因素。
在此我們僅對本課程相關的液晶作更進一步地介紹結晶固體溶解結晶固體溶解:晶格位子晶格位子,方向方向 在此我們僅對本課程相關的液晶作更進一步地介紹19中間相中間相(Mesophases)Disordered Crystal Mesophases塑性晶體 Ordered Fluid Mesophases 液態晶體液態晶體 圓球狀 長條狀、圓盤狀 位置有序，方向無序 位置無序，方向有序 晶格排列，不具流動性 位置無序，有流動性 結晶狀的固體(Crystalline Solid)各向同性的液體(Isotropic Liquid)20液晶的分類 1)Thermotropic(熱致液晶)2)Lyotropic(溶致液晶)因溫度溫度的改變而產生相變 因溶於溶劑中濃度比例濃度比例的改變而產生相變 a)長條狀 b)圓盤狀 1.Nematics(向列相)2.Cholesterics(膽固醇相)3.Smectics(近晶相)1.Columnar 2.Nematic 以產生相變產生相變之原因來區分LCDs:Thermotropic(熱致液晶)分子形狀分子形狀排列方式排列方式21:LCDs22液晶以分子形狀分類液晶以分子形狀分類23Types of Low Molecular Weight Liquid Crystal MaterialsLyotropic Liquid Crystals(Lyotropic Liquid Crystals(溶致液晶溶致液晶)form liquid crystal phases over certain concentrationranges when mixed with a solvent24Thermotropic Liquid CrystalThermotropic Liquid Crystal(熱致液晶熱致液晶)-)-(Used for LCDs)(Used for LCDs)molecules consisting for a rigid core and flexible tail(s)-form liquid crystal phase over certain temperature ranges254.分子排分子排列之有序列之有序性性溶液26Melting of a SolidDirector axis27Nematic 液晶液晶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)Director n 與 n 的狀態是不可區分的長條狀之Nematic相液晶的分子排列nLCD用液晶用液晶28Cholesteric 液晶液晶 將Chiral溶解在Nematic相液晶中，原來的Nematic液晶結構會出現螺旋畸變我們將這種螺旋的Nematic相稱為Cholesteric相Cholesteric 相液晶的分子排列Lnnnnxyzq qo o 0 0 表液晶分子為右旋排列，q qo o 01013 ohm-cm(TFT)37高度幾何異向性高度幾何異向性(長條狀長條狀或或圓盤狀圓盤狀)分子形狀分子排列秩序性秩序性物理性質非均向性非均向性介電係數介電係數磁導率磁導率折射率折射率黏滯係數黏滯係數 由於液晶分子之形狀具有高度幾何異向性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不同而有所差異。
液晶之非均向性液晶之非均向性(Anisotropic)38Dielectric constant 之非均向性EPEDoElectric displacement:/oeo100010001 )1(即)(1o)(1o/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永久偶極矩及誘導偶極矩性質誘導偶極矩性質而定/39外加電場對外加電場對 nematic 相的影響相的影響 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/DEn E n221488D dEEn E.0 /則 n E 能 量 最 低 液 晶 分 子電 場 方 向.0 /則 n/E 能 量 最 低 液 晶 分 子電 場 方 向40液晶之介電異向性液晶之介電異向性液晶之介電常數值液晶之介電常數值 越大產生的越大產生的induce dipole越大越大介電異向性介電異向性決定決定LCLC之轉動之轉動41(=|-)0(=|-)+-+-|EEE|nE|nEn 42 介電係數與溫度之關係介電係數與溫度之關係5CB之介電係數與溫度之關係曲線。
43 The Order Parameter*Solid=0 S=1Isotropic phase orientation is random=1/3 S=044連續彈性體理論連續彈性體理論 通常在液晶中之導軸n是隨位置而變化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11Splay,KBend,K33Twist,K22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彈性常數K33K11K2245 Creating Deformation with a Field and Surface46液晶形變自由能密度液晶形變自由能密度總自由能總自由能F=Fd +Fs +Fext液晶連續體理論液晶連續體理論fd=彈性自由能彈性自由能介面作用自由能介面作用自由能外場作用自由能外場作用自由能外場作用自由能密度外場作用自由能密度2)(21Enfe2)(21Hnfm)(81)(81BHDEfop電能電能磁能磁能光能光能求總自由能求總自由能F之最小值可得到外場下之最小值可得到外場下LC之排列狀態之排列狀態47Free energy density:Torque density Nematic(K11=K33=K10-11 N)and d=10 mFor steel:shear modules=108 N/m2212dfKx22dddfKdd211222510224/10NKNmdmDeformation Torque48Rotation viscosity 1(轉動粘滯係數轉動粘滯係數)1LC分子分子 1 代表液晶分子轉動的難易度 1越小越小LC反應越快反應越快Response time 正比於正比於“LC黏度黏度“和和“cell gap平方平方”0之之LC其粘滯係數較小其粘滯係數較小 49 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?Nomenclature Parameter ()Elastic ConstantKii S2Birefringencen SDielectric Anisotropy SMagnetic Anisotropy SViscosity Anisotropyh Sproportional to各物理參數與秩序參數各物理參數與秩序參數S之相關性之相關性因故溫度上升時，其臨界電壓Vth 應下降。
SSSKV2th1 ;0.2 5cTST50Thermal PropertiesThermal PropertiesPhase Transition:lIsotropic-Nematic:Weakly first order(latent heat of transition)(heat of transition)N-I=1 kcal/mole(heat of transition)ice-water=1.4 kcal/molelNematic-Smectic:First or second orderlNematic-Smectic C:First order lSmectic A Smectic C:Second OrderTemp51Techniques for Identifying Liquid Crystal PhaseTechniques for Identifying Liquid Crystal Phase1.1.Polarizing Microscope and Heating StagePolarizing Microscope and Heating Stage1.Change in appearances with temperature2.2.Differential Scanning Calorimetry(DSC)Differential Scanning Calorimetry(DSC)1.Monitor energy required for phase transiton3.3.X-ray CrystallographyX-ray CrystallographyStructure of phase determined by x-ray scattering pattern52Polarizing Microscopy and Heating StagePolarizing Microscopy and Heating StageSample PreparationSample PreparationlSmall amount of sample placed on a microscopic slide with cover sliplSubstrate surface may be treated to control alignmentlSubstrates may be mechanically sheered to control alignmentObservationObservationlMicroscope equipped with crossed polarizerslSample placed in heating stage on microscope stage lAppearance changes with temperature(texture,color)lOften difficult to distinguish different smectic phase 53Nematic SchlierenNematic Schlieren texture textureCholestericsCholestericsUniform Nematic Uniform Nematic texturetexture54Differential Scanning Calorimetry(DSC)Monitor the amount of energy required to heat the samplePhase transition requires energy Plot of energy input vs temperature show phase transition as peakOn-set Transition temp55Cholesterics under external field2/2d1xyz220;=81 F2If we consider a pure twistncos(),nsin(),n01.cholesteric2ddFFE nwhereKdivnzzFKqz(1)0 /E(2)0 E helical axishelical axisuntwisting21(2Kn231)(2onqK n2)n56Electric field effect to the planar texture57Field Untwisting of a Cholesteric HelixField-Induced Dielectric Instabilities of CholestericsField-Induced Dielectric Instabilities of Cholesterics1222 2024400622 241.1 2 82t hKEPPEPEPK058Planar textureFocal-conic textureFingerprint texture59演讲完毕，谢谢观看！。