1、Chapter 2 LCD顯示原理,液晶以分子排列分類,Nematic liquid crystal線狀液晶,LCD用液晶之主流,排列特點:分子傾向指著某個特定方向,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,介電異向性決定LC之轉動,Induced Dipole,0,LC birefringence n定義,n|,n,n= n|- n,LC,LC,n會改變入射光的偏振進而讓LCD產生顯示的效果,E,E,E,液晶配向之方法,配向過程: 配向膜印刷 rubbing process 玻璃對組注入LC,Inject LC,Panel assembly,Attach S
2、pacers,Apply Sealant,Rubbing,Cell Process,Apply PI Film,Seal,Homogenous alignment (ECB),Homeotropic alignment,Twisted alignment (Twisted nematic),Hybrid alignment,配向過程: 配向膜印刷 rubbing process 玻璃對組注入LC,常見液晶配向排列模式,Alignment film,晶體光學,光入射液晶之可能現象和效應,吸收(absorption)和穿透(transmission) 折射(refraction)和反射 雙折射效應
3、(birefringence effect) 旋光效應(polarization rotation effect) 散射(scattering) 繞射(diffraction) 色散(dispersion),Polarized Wave,Linear Polarization,Circular Polarization Left-hand/Right-hand,Elliptical Polarization,Polarization of Optical Waves,相位延遲與偏振狀態之關係, = 0 或 時, 電場為線偏極化, 偏振方向與x軸之夾角 = /2 且 時, 電場為圓偏極化(正號為
4、左圓;負號為右圓偏振)若 時, 電場為橢圓偏極化且主軸在x或y軸上 (3)其餘狀況為橢圓偏振,0,/2,-/2,-,/4,3/4,-/4,-3/4,E=Ex(z,t)+Ey(z,t),為相位差,=0,Time increases,線偏振,圓偏振 =/2,Ex,Ey,Ey,Ex,Ey,Ex,Ex,Ey,Ex,Ey,Ey,Ex,Ey,Ex,Ex,Ey,(Assume Eox=Eoy),圖示相位延遲與偏振狀態之關係,雙折射晶體種類,光在一晶體內傳播時若看到兩種折射率則此晶體為雙折射晶體(例如液晶) 光在雙折射晶體內的折射率值跟光的入射角度和偏振有關 單光軸晶體nx=ny nz 雙光軸晶體nx ny
5、nz,k,正單光軸晶體之折射率橢圓球,nx,ny,nz,neff,no,正單光軸晶體 nx=nynz,Birefringence n=neff-no0,1. 顯示器用液晶為正單光軸液晶 2. 棒狀液晶為正單光軸,光入射時單光軸晶體之雙折射特性,短軸 no=nx=ny,光入射晶體時: 晶體之兩個折射率值分別為k垂直平面和折射率橢圓球產生之橢圓截面之長短軸,橢圓截面,長軸,k,負單光軸晶體(negative uniaxial)之折射率橢圓球,nx,ny,nz,neff,no,負單光軸晶體 nx=nynz,Birefringence n=neff-no0,1.負單光軸晶體用於顯示器之光學補償膜 2.
6、盤狀液晶(discotic LC) 為負單光軸,光入射時單光軸晶體之雙折射特性,短軸 no=nx=ny,長軸,橢圓截面之,光在x方向傳播時折射率為ny和nz 光在y方向傳播時折射率為nx和nz光在z方向傳播時只一種折射率nx(=ny)晶體只在一個方向(z方向)得到單一折射率(即n=0)所以稱單光軸晶體z軸為光軸,光入射時單光軸晶體之雙折射特性,單光軸晶體nx=ny nz,光入射時雙光軸晶體之雙折射特性,雙光軸 nx ny nz,雙光軸晶體用於顯示器之光學補償膜(補償視角),nx,ny,nz,雙光軸晶體折射率橢球,光在晶體之x方向傳播時看到之折射率為ny和nz 光在晶體之y方向傳播時看到之折射率
7、為nx和nz光在晶體之z方向傳播時看到之折射率為nx和ny 雙光軸晶體有兩方向無論光之偏振為何光只看到一種折射率所以稱之為雙光軸,單光軸晶體的分類,Positive A-plate,Negative A-plate,Positive C-plate,Negative C-plate,A-plate:光軸平行film材表面,C-plate:光軸垂直film材表面稱,A-plate, C-plate用於LCD之補償膜,Color dispersion(色散),ne,no,Refractive index,Refractive index depend on ,Refractive Index of
8、 a typical nematic LC,n=n-n n=constant t1/2S =density S= degree of order,Tc,光在雙折射晶體內之偏振變化,Phase Retardation,d,光電場分量1,光電場分量2,光電場在晶體內可分成兩分量,光在各方同向之介質中,各方同向介質內無相位差,線偏振光,相位延遲=,0,0,0,0,光在各方同向之介質中向位差值維持一定所以偏振不變,光在雙折射晶體內之偏振變化,雙折射晶體內有nd,線偏振光,相位延遲=,/2,/4,3/4,5/4,3/2,7/4,2,光在雙折射晶體內隨相位延遲量的不同而有不同的偏振形狀,/4 plate
9、and /2 plate,/2,Crossed wave plates,Slow axis,Slow axis,/4 plate,/4 plate,+,Slow axis,=,/2 plate,Slow axis,Slow axis,/4 plate,/4 plate,+,=,isotropic,光在雙折射晶體內之偏振變化,Special case:,/4波板,nd=/4相位延遲量= /2,45o,光軸,/2波板,光軸,nd=/2相位延遲量= ,2,線偏振光之偏振和/4波板光軸夾45o 入射,出射光為圓偏振 線偏振光之偏振和/2波板光軸夾入射,出射光之偏振轉2,園偏振,偏光板有吸收軸跟穿透軸,
10、兩軸永遠相互垂直 非偏振光通過偏光板變成線偏振光,此線偏振光之偏振平行穿透軸 非偏振光通過偏光板後光強度剩原來之一半,Polarizer的作用,LCD基本介紹LCD架構,Cell gap,CF glass,Array glass,Side view of a LCD panel,Transmissive type LCD-TN LCD,Ex. TN Mode,外加電壓,改變液晶的排列方式,造成光極化態的改變,再搭配Polarizer或補償膜,完成亮暗顯示的效果,V-T Curve,NW NB,LC為一光閥:控制通過光的強弱(本身不發光),electrode,Demo,TN operation
11、principal,Normally Black,NB:上下偏光板穿透軸平行,Normally White,NW:上下偏光板穿透軸垂直,一般TN均為Normally white,TN之光電曲線,NW在暗狀態下有self-compensation effect對比高 NB在暗狀態下液晶對光有作用所以有色散現對比低,等效Dn =0,LC,LC,Optics of TN LC,Calculate LC Directors profile Calculate transmittance:Jones Matrices 3. Calculate viewing angleExtended Jones Ma
12、trices,Rubbing direction 與配向之關係,Rubbing direction,LC分子沿著rubbing方向排列,LC,配向膜,TN LCD之製作方法,Rubbing process,Assembly,Rubbing direction on panel,TN LCD之製作方法,Structure of a TN LCD,Rubbing direction,Rubbing direction,大部分之TN LCD為左旋設計,TFT,CF,LC rotation trace,Pretilt angle,90o,Transmittance of a TN-LCD,TN之穿透率
13、(T)和1. LC之nd和twist angle , 2. 入射光偏振和第一層LC之夾角相關,其中,From Jones matrix calculation,Transmittance of LCD,Transmittance for ECB type,考慮通過低一片偏光板之光強會少一半,ECB type,ECB,LC,ECB (Electrically Controlled Birefringence),analyzer,polarizer,=45o,analyzer,polarizer,nd = 0,E,Transmittance of TN (Twisted Nematic) LCD,
14、=0.866,TN, =90o,named for NB,T有極大值,且其值和無關,m=1,m=2,nd在1st minimum (or 2nd., 3rd. minimum 時T和無關),TN之nd選在 1st minimum 附近(m=1) 當=0o, Mauguin limit nd 時,旋光效應,NW,V=0,As V increases,i.e. u1,=90o, =0o,1st minimum and polarization rotation effect,(NW),TN之e-mode和o-mode,入射光偏振和第一層LC分子平行,e-mode,入射光偏振和第一層LC分子垂直,o
15、-mode,對比的定義,CR,對比高,對比低,NW,黑畫面電壓,白畫面電壓,視角的定義,CR10,No Gray-Scale Inversion,Color Dispersion (uv0.004),顯示器座標定義,Normal,= 0,:,Viewing Angle,:,Viewing Direction,=0,=180,=270,=90,=0,=180,=270,=90,Normal,= 0,:,Viewing Angle,:,Viewing Direction,上,下,左,右,Iso-Contrast Contour,TN-LCD的視角限制,Bright state,Dark state
16、,LC residual phase LC optical anisotropy 視角不足,TN-LCD的視角限制,Upper,Lower,Glass substrate,Side View,LC director,Glass substrate,Grey Scale Inversion,GSI angle,Gray Scale Inversion(GSI)的定義,n=0,Gray Scale Inversion(GSI)原理,LC (液晶分子),光,Gray Scale Inversion(GSI)原理,V1,V1V2,V2,V1 V2,V1 V2,Gary scale inversion,
17、灰階反轉,灰階反轉(Gray Scale Inversion),CIE (Commission Internationale de lEclairage ) x-y色座標,顏色用座標來表示 越靠近邊界顏色越飽和 白色座標?,GSI,Color dispersion,視角的定義,NTSC Ratio(色域)的定義,National Television System Committee,EBU: European Broadcasting Union,NTSC ratio = 100 %,NTSC,RGB,color gamut,Color saturation index,High NTSC
18、ratio,Low NTSC ratio,NTSC ratio 色彩飽和度,Equivalent Circuit of a Pixel,Capacitor,LC layer,LCD Module Structure,Module,Polarizer,Back Light + PCB,Polarizer,Definition of Resolution,1-pixel including R,G,B 3-sub-pixel,1-G-sub-pixel,CF頻譜,Backlight頻譜,LCD顯色原理,= output,x,R,G,B,C,M,Y,W,RGB混色關係,Aperture Ratio
19、of a Pixel,Effective area = Aperture Ratio,Some terminology of display resolution,Data Display,Video Display,Passive Matrix LCD (PM-LCD) vs. Active Matrix LCD (AM-LCD),PM-LCD: TN/STN1.無開關元件2.沒有操作的畫素會受其他 畫素寫入電壓的影響3.中低解析度, 低單價產品,AM-LCD: 1.以TFT作為畫素(pixel)開關及儲 存電容2.適合高解析度,TFT的作用,因TFT元件的動作類似一個開關(Switch)，液晶元件的作用類似一個電容，藉Switch的ON/OFF對電容儲存的電壓值進行更新/保持。 SW ON時信號寫入(加入、記錄)在液晶電容上，在以外時間 SW OFF，可防止信號從液晶電容洩漏。 在必要時可將保持電容與液晶電容並聯，以改善其保持特性.,TFT為一三端子元件。 在LCD的應用上可將其視為一開關。,TFT的作用,Structure of a Pixel,儲存電容(Cst),L,W,TFT-LCD的操作原理,TFT-LCD的訊號傳輸說明,
