CN1129806C - 铁电液晶显示器 - Google Patents

铁电液晶显示器 Download PDF

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CN1129806C
CN1129806C CN96112048.7A CN96112048A CN1129806C CN 1129806 C CN1129806 C CN 1129806C CN 96112048 A CN96112048 A CN 96112048A CN 1129806 C CN1129806 C CN 1129806C
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J·芬夫施林
M·沙德特
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    • G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
    • G09G3/36—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using liquid crystals
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    • G02F1/1347—Arrangement of liquid crystal layers or cells in which the final condition of one light beam is achieved by the addition of the effects of two or more layers or cells
    • G02F1/13471—Arrangement of liquid crystal layers or cells in which the final condition of one light beam is achieved by the addition of the effects of two or more layers or cells in which all the liquid crystal cells or layers remain transparent, e.g. FLC, ECB, DAP, HAN, TN, STN, SBE-LC cells
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    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/137—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering
    • G02F1/139—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering based on orientation effects in which the liquid crystal remains transparent
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    • G—PHYSICS
    • G02—OPTICS
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Abstract

一种铁电液晶显示器包括在两个起偏振器之间设成一个在另一个后面的两个液晶盒。一个液晶盒具有线电极，另一个具有象素电极。通过用与线电极同步的图象信息致动象素电极，所述的液晶盒的取向及折射率选定为使得当控制电压反向时透光度并没有实质改变，并且两个显示器被致动使得转换角决不超过±22.5°，并且电压的极性周期地反向使平均来说没有直流电压流过所述的液晶盒。

Description

铁电液晶显示器
本发明涉及铁电液晶显示器。
铁电液晶显示器，特别是DHF型(即变形螺旋铁电型)是对普通TN型(扭转向列型)，或STN型(超扭转向列型)显示器的引人注意的替换方案，特别在例如在低温操作时，要求大的视角，灰色调或短的转换时间的情况下更是如此。
在例如EP-A-309774中公开了铁电液晶显示器的操作。如果在“对称”模式下工作，它们具有最大的透光度必须的±45°的大转换角的缺点。具有大转换角的混合物难以制造且一般比具有小转换角的混合物制造更慢。它们还倾向在达到最大转换角以前卷紧成螺旋线。迄今为止还没有具有最佳的转换角，也就是在对称模式中的最佳亮度的LC材料。另一方面，如果它们以“非对称模式操作，一个缺点是不能用单个图象的交替的极性。例如，如果显示器必须长时间保持黑暗，必须在这段时间内始终加上一负电压。这导致在液晶中及在边界表面处产生空间电荷。这种空间电荷改变了电光学特征，其可以导致重影以及类似的严重干扰效应，这可使显示器无法使用。
本发明的目的是提供一种不具有以前已知的这类显示器缺点的铁电液晶显示器。
本发明的目的通过下面的措施达到，按照本发明提供了一种铁电液晶显示器，包括在两个起偏振器之间设成一个在另一个后面的两个液晶盒，一个液晶盒具有线电极，另一个具有象素电极，通过用与线电极同步的图象信息致动象素电极，所述的液晶盒的取向及折射率选定为使得当控制电压反向时透光度并没有实质改变，并且两个显示器被致动使得转换角决不超过+22.5°，并且电压的极性周期地反向使平均来说没有直流电压流过所述的液晶盒。
下面参照附图详细说明本发明的最佳实施例。附图中，
图1是普通的变形螺旋铁电液晶盒的剖面图；
图2是本发明的变形螺旋铁电液晶盒的透视图；
图3示出另一装置的取向及双折射性能；
图4显示图2的液晶盒装置的取向及双折射性能。
如图1所示，普通的变形螺旋铁电液晶盒包括两块装有透明电极10及取向层11的玻璃板12，它们间隔约2μm。其间设置一液晶层13。液晶具有带螺旋结构的铁电“Sc*”相。螺旋的轴14与板平行，而螺距比可见光的波长短。如果没有加上电压，螺旋是不变形的，并且平均折射率指向螺旋线的轴。如果在两电极之间加上电压，平均折射率(也就是折射率椭圆的长轴或主轴)在玻璃板的平面中转动，加正电压朝着一方向，加负电压朝相反方向。如果电压逐渐增加，角度在最大转换角qmax处变为饱和，这是铁电液晶的特征。在该饱和状态螺旋线卷紧。如果电压降低，螺旋线还原。但是这一过程会花费一些时间，因此在变形螺旋铁电液晶盒中通常可避免螺旋线的卷紧。但这意味着可用的最大转动角必须选为小于qmax.
如果变形螺旋铁电液晶盒放在交叉的起偏振器之间，由于折射率的转动引起透光度的改变。已表明45°的转动对于从最大亮度切换到黑暗是必须的。在黑暗状态，光轴与一个起偏振器平行，而在光亮状态，光轴从上述位置转过45°。如上面已经说明，一个变形螺旋铁电显示器可在两个模式下工作，就在施加0V的电压时，在主光轴和一个起偏振器之间的角度q(0)而言，它们是不同的，如下：
在对称模式，施加电压U＝0V相应于角度q＝0，也就是黑暗。在正和负电压U的情况下透光度增加，当q＝±45°时达到最大。因此对于等值的正负电压得到同样的透光度。这使得可以交替地用正负电压记录同样的图象，因此平均来说液晶盒中不产生直流电压成分，因此不会发生重影。在非对称模式中，U＝0V相应于转动角度为22.5°，也就是50％的透光度。一个极性(例如正性)的电压增加q，相应地增加透光度，而另一极性使该两个量减少。对于从光亮到黑暗的完全转换，q值的调节范围只需要为±22.5°。
本发明结合了两个工作模式的优点而没有上述的缺点。本发明的最重要优点是铁电液晶显示器可以“非对称”模式致动，而不产生重影且在变形螺旋铁电液晶盒情况下无需大转换角，这一点至今为至还是行不通的。
图2示出本发明的一个实施例，其中直接相互紧跟的两个变形螺旋铁电液晶盒210，211设置在相交的起偏振器21，28之间。液晶盒210以已知的方式包括一设在两衬底之间的液晶层23，两衬底一个具有线电极22，另一个具有表面电极24。液晶盒以恒定的振幅一次转换一行。液晶盒211包括一设在两衬底之间的液晶层26，该两衬底包括象素电极25，27，并且该液晶盒用与液晶盒210同步的图象信息致动。图2中省略了取向层，与液晶显示器的电连接，或液晶盒211的任何有源矩阵元件。
按照本发明，液晶盒210及211具有的结构及被致动的方式可避免干扰直流电压成分。这一点可通过从一图象到另一图象改变施加电压的极性来达到。本发明的重要特点是在两个相位中透光度(灰度值)是同样的。
图4图解地示出了对三个灰色阶段，也就是行35的亮态，行36的灰态，行37的暗态，两个液晶盒201和211的取向及双折射性能，图中两栏31及32是对于第一相位，而后两栏33和34是对于相对致动的第二相位。在栏31中，起偏振器21(图2)在直角位置，也就是与主轴平行地偏振，而检偏振器24与其交叉。
两个液晶盒的双折射是同样的，近似等于波长的一半，也就是Δn.d＝γ/2，Δn＝na-n0
式中：na，。表示变形螺旋铁电结构的异常的及正常的折射率，
      d＝液晶盒的厚度，及
      
图4中阴影部分示出在电光学应用中主光轴的旋转范围；负电压(例如栏31)使主轴往左转，但是正电压(例如栏33)使主轴往右转。施加电压为0V时，在第一液晶盒210的情况下(栏31和栏33)主光轴从垂直位置顺时针转22.5°，在第二液晶盒211的情况下(栏32和34)反时针转67.5°。总之，这两个液晶盒，也就是例如取向层的两个摩擦方向相对转了90°。
图4直接示出两相位中的透光度是同样的。在行35，第一相，线性的偏振光不受第一液晶盒210(第31栏)影响，因为它平行于光轴偏振。第二液晶盒211(第32栏)起γ/2板的作用，也就是它使偏振方向转过90°，使得光能穿过检偏振器24而没有散射。在第二相，第一液晶盒210(第33栏)起γ/2板的作用，第二液晶盒211(第34栏)不影响偏振。因此，在两个相位，光无散射地传送。在另一最小透光度的极端情况下(第37行)，在第一相(第31和32栏)和第二相(第33和34栏)两液晶盒的双折射平衡掉，也就是在交叉的起偏振器之间透光度最小。
在一般情况下，也就是灰态(第36行)的情形下将｜U2｜≤｜U1｜的电压U2加到第二液晶盒211上。在第一相，到达第二液晶盒211的光在直角位置偏振，而第一液晶盒210，如前所述，对偏振无影响。第二液晶盒211的光轴相对于检偏振器转过α＜45°的角，该角度由电压U2控制。这导致透光度与sin2(2α)成正比。在第二相，第一液晶盒210使偏振作用转过90°(第33栏)，随后在到达第二液晶盒211时成水平。由于在第二相(第34栏)加上电压-U2，光轴相对检偏振器转动45°-α，因而透光度与cos2[2(45°-α)]成正比。用“ cos”是因为入射光平行检偏振器偏振。但是这就与sin2(2α)成正比，也就是与第一相一样。
因为α可根据信号电压U2取0-45°之间的任意值，所以透光度Sin2(2α)取0至1之间的任意值。
交叉的起偏振器或两个液晶盒的确切定位并非决定性的。如图4所示，由于双折射正好抵销，对交叉的起偏振器的任何方向，暗态的透光度(行37)是最小的。在亮态(行35)情形下，颜色略取决于起偏振器的位置，因此确切定位可用于使颜色最佳化。
图3示出两个液晶盒及起偏振器另一种可能的互换排列。与图4不同，两液晶盒仅相互转过45°。结果，在第一相，在暗态(行47，栏41和42)加入相位移代替如图4所示的相互补偿。但是如果起偏振器是平行取向的，并与所产生的主轴成直角，则透光度是最小的。
本专业的熟练技术人员可以明白，还可以有具有类似的效果的其它结构，特别当使用具有Δn.d＝γ或Δn.d＝3γ/2的较厚的双折射液晶盒时。
虽然变形螺旋铁电液晶盒是特别优选的，但本发明的应用并不限于这种液晶盒。在SSF液晶显示器的情形下，周期改变偏振作用也是有利的，在这些显示器中也可以作为避免重影及转换延迟的措施。

Claims (2)

1.一种铁电液晶显示器，包括在两个起偏振器之间设成一个在另一个后面的两个液晶盒，一个液晶盒具有线电极，另一个具有象素电极，通过用图象信息同步致动线电极与象素电极，所述的液晶盒的取向及折射率选定为使得当控制电压反向时透光度并没有实质改变，并且两个液晶盒被致动使得转换角决不超过±22.5°，并且电压的极性周期地反向使平均来说在所述的液晶盒上没有直流电压。
2.按照权利要求1所述的液晶显示器，其中所述的两个液晶盒是变形螺旋铁电液晶盒。
CN96112048.7A 1995-11-07 1996-11-06 铁电液晶显示器 Expired - Fee Related CN1129806C (zh)

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US5457551A (en) * 1993-10-08 1995-10-10 Planar Systems, Inc. Frame response compensated, video rate addressable liquid crystal passive matrix display system
US5477354A (en) * 1994-11-21 1995-12-19 Rockwell International Corporation Ferroelectric liquid crystal phase-only modulator with one ferroelectric liquid crystal spatial light modulator's smectic layers orthogonal to another's

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SG60021A1 (en) 1999-02-22
JPH09281527A (ja) 1997-10-31
US5818548A (en) 1998-10-06
EP0773467A1 (de) 1997-05-14
DE59610807D1 (de) 2003-12-11
EP0773467B1 (de) 2003-11-05
CN1159004A (zh) 1997-09-10
HK1011090A1 (en) 1999-07-02

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