CA2315494A1 - Liquid crystal display with nonspecular reflectors - Google Patents
Liquid crystal display with nonspecular reflectors Download PDFInfo
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- CA2315494A1 CA2315494A1 CA002315494A CA2315494A CA2315494A1 CA 2315494 A1 CA2315494 A1 CA 2315494A1 CA 002315494 A CA002315494 A CA 002315494A CA 2315494 A CA2315494 A CA 2315494A CA 2315494 A1 CA2315494 A1 CA 2315494A1
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- liquid crystal
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—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
- G02F1/01—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
- 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
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
- G02F1/1333—Constructional arrangements; Manufacturing methods
- G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
- G02F1/133553—Reflecting elements
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—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
- G02F1/29—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 position or the direction of light beams, i.e. deflection
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—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
- G02F1/01—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
- 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
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
- G02F1/1333—Constructional arrangements; Manufacturing methods
- G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
- G02F1/133504—Diffusing, scattering, diffracting elements
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—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
- G02F1/01—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
- 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
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
- G02F1/1333—Constructional arrangements; Manufacturing methods
- G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
- G02F1/133528—Polarisers
- G02F1/133531—Polarisers characterised by the arrangement of polariser or analyser axes
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—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
- G02F1/01—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
- 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
- G02F1/1396—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 the liquid crystal being selectively controlled between a twisted state and a non-twisted state, e.g. TN-LC cell
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F2202/00—Materials and properties
- G02F2202/40—Materials having a particular birefringence, retardation
Abstract
The present invention deals with liquid crystal displays where the incident light and reflected light going through the display are not specularly related. The incident light can be at a range of angles to the display while the reflected. light, i.e. the viewing direction is at or nearly normal to the display. For such nonspecular liquid crystal displays, the polarizer angles, the input/output directors of the liquid crystal cell, and the liquid crystal cell retardation have to be specially optimized to obtain the best viewing effects.
Conventional liquid crystal display modes do not work optimally in this nonspecular situation. We also disclose the new image-mode and shadow-mode nonspecular liquid crystal displays. Such displays have very bright background and are free from viewing glare common in most liquid crystal displays. The present invention applies to all twist angle, e.g. the 90° TN, the 120° and 150°
HTN, the 180°, 240° and 270° STN displays.
Conventional liquid crystal display modes do not work optimally in this nonspecular situation. We also disclose the new image-mode and shadow-mode nonspecular liquid crystal displays. Such displays have very bright background and are free from viewing glare common in most liquid crystal displays. The present invention applies to all twist angle, e.g. the 90° TN, the 120° and 150°
HTN, the 180°, 240° and 270° STN displays.
Description
LIUTJID CRYSTAL DISPLAY WITH
NOIyISPECULAR REFLECTORS
The pre~;ent invention relates to a new type of liquid crystal display whE:r_e the input and output light beams do not follow the usual specula.r relationship.
Liquid crystal displays are usually manufactured with a structure as showr.~ in Fig. 1. It comprises an input polarizes l, a li<~uid crystal cell 2 , an output polarizes 3 and a reflective diffuser 4. T:!-ie liquid crystal cell is commonly made of two pieces cf: glass 5,6, alignment layers .,8, conductive electrodE~ films 9,10 and the liquid crystal material 11 which possesses a twisting alignment in conformance with the alignment layers 7 and 8.
In this common reflective (or sometimes known as transflective) liquid crystal display, the light 12 enters the d-splay from one direction at some azimuthal angle B relative to the surface normal 13 of the display.
The corresponding polar angle of t:he incident light is relative to some x--axis on the surface of the display.
Thus the angles specifying the light propagation direction is given by ( B, c~ ) . 'This light is scattered and reflected by the dif::=us ive ref ~ectcr and goes through the liquid c:rys tal cell once more and is seen by the observer 14. This light intensity is strongest at the reflection angle ( B, ~-rr ) . Tr~is is ca 1 led specular reflection or glare reflection. There is light obser~,rable at angles other than (FJ,~+n) as shown because of scattering, but its intensity drops off rapidly as the angle deviates from B. The situation is depicted in Fig. 2. By the same scattering rn~_chanism, at any viewing direction (B,~+n),, there is contribution of light incident from (B,~), and light from incident angles near (B,~).
However,, a majority of the light is from the (B,~) direction.
In designing and optimizing such common liquid crystal displays, the alignment direction of the top and bottom glass plates and t:he placement o_E the input and output polarizEars are c:ru.cial. If one sakes the example of a 90° twisted nemat_i.c liquid crystal display, the most common configuration is shown in Fig. 3. The input polarizes PiL and 'the input director nLn are aligned at right angles. The output polarizes Pout is also perpendicular to the output liquid crystal director n°ut as shown . This i:the so-cal:~ed o-mode operation for the TN display. The .1i_ght enters the liquid crystal display from the 12 c.)'cloc~: direction 15 and the viewer looks at the display .'rom the 6 0'clecJc direction ?6. This is in contras t to the e--.node operation where Pia and nin are parallel , and P°u= anal n°ut are also parallel. The viewing angle polar plot fcr the o-mode TN display is shown in Figs. 4 and 5. F~a. 4 is the polar plot for V=0 and Fig.
is the polar plot cf transm_ttanc:e for 2.5V. They show clearly 'the optima__ viewing direction which is at the 6 O'clock position. The darkest part of the polar plot in Fig. 5 indicates th.e light should exit the display at an azimutha:l angle B of 30° and a polar angle ~ of 270°.
This optimization of the viewing angle of the liquid crystal display is well-known and has been discussed in the literature. Fo r_ example, the books by Blinov et al (Electrooptic Effects in Liquid Crystal Materials Springer-Verlag, 1994) and Bahadur (Liquid Crystals Applications and Uses, World Scientific, Singapore, 1990) have discussions on the viewing angle of liquid crystal displays.. In these discussions, the light is assumed to traverse the liquid crystal cell at an oblique angle once. The viewing angle diagram plots the contrast of the display at the working voltages for light going through 'the liquid crystal cell at an angle of (8,~) where B is the angle between the light beam and the surface normal of the liquid crystGl cell (the azimuthal angle) anal ~ is the angla between the projection of the light beam cn the liquid cr~;stal cell surface and the i G+
reference x-axis (the polar anglEa). The input director of the liquid crystal is alsc; measured referenced to this x-axis. Fcr the case of the 90' twist TN display, as shown in Fic. 3, the x-axis is usually taken to be at 45°
to the :input director .
In the traditional optimization of the liquid crystal display,, it is generally assumed that light enters at a certain angle. Many plots of the transmission-voltage curves have been shown in the )_iterature for various combinations of t.h:e light viFa~~ing angl a characterized by (~,8). Implicit in such curves, with only one value of 6 specified, it is assumed that :Light enters and exits the cell at the same azimuthal angle. The possibility of light entering and exiting the liquid crystal cell at differer.~t azimutha.l angles is never considered in the numerical and experimental optimization procedures. The present invention ;shows that for the case of nonspecular reflection, it is important to perform the simultaneous optimization of all important LCD parameters by considering light entering and exiting the LCD at different angles.
Fig. shown the transmission-voli_age curves for liquid crystal displays operating in the so-called second minimum . This second m~nimurn corresponds to a i retardaticn valuE.=_, the product of the cell thickness and the birEafringenc~s of the 1 iquid crystal (dc~n) , of 1. 075 ~m and a liquid crystal twist angle of 90°. Curve 17 is when the viewing angle and the light entrance angle are 0° (normal to the cell). Curve 18 corresponds to light entering at B=30°, ~=90° and the display is viewed at B=30°, ~=270°. Tr,is is the so-called 6 O'clock viewing condition. Curve 19 corresponds to conditions exactly opposite' to curve 7_8, i.e. light entering at 8=30°, ~=270°
and the display is; viewed at B=30°, ~=9.0°. In the 6 O'clock position, the liquid crys=al cell turns off at a lower voltage and the change in transmission as a function of voltage (the transmission-voltage or T-V
curve 18) is sharper. This leads to a much better multiplexing capability for this display. Fig. 7 and 8 are similar plots for the cases of 120° and 180° twist displays.
In this present invention, we recognize the fact that it is possible to manufacture LCDs where the input light angle and the outFut light angle are greatly different (non-specular reflection). Such a possibility of having non-specular light. reflection was pointed out in US
patent No. 5,659,40f3 of M. Wenyon. One way of obtaining this sii~uat_on _i_s tc use the so-called holographic reflector fi;_ms ( s<=e, for Flxamp ~ e, ~Z. Wenyon et al, "White Holographic: Reflector for LCDs", SID Symp. Dig.
J.997). There are additionally many types of structured scattering surfaces that can achieve such non-specular reflections. However, such prior LCDs do not optimize the reflection.
It is accordingly an object of the invention to seek to mitigate this disadvantage.
According to the invention there is provided a liquid cryst al display, characterised by the incident light direction and the direction of light exiting the display after reflection being dif:Eerent: directions which are non-specular.
Using the invention it is possible to provide that the incident and reflected light beaams to be at different angles. The transmission-voltage curves should be calculated using different values of input and output angles.
A liquid crystal display embodyj_ng the invention thus has a7_1 of its critical parameters simultaneously optimized allowing for the input light angle and the viewing angle to be different from each other, thus yielding retardation values of the display that are significantly d_if~erent from conventional liquid crystal displays. The polarizes angles, the input/output directors and/e:r t:he liquid crystal cell retardation may thus be eptimizec'_ for non-specu~_ar operation.
Another significant aspect of the present invention is the recognition ef the fact that most cf the nenspecular reflectors are monochromatic. That is, even with white light input, the reflected light will have a color, e.g.
green. Hence the optimization of the nonspecular LCD
does not: ha~~e to take int;~ account color dispersion effects. One can assume a menoc:hromatic light 3s the input. Of course, this invention does not preclude the situation where th.e nonspecslar reflector can be wide bared or c_an reflect. white light as well.
It is therefore possible using the invention to provide a set or sets of operating conditi~~ns for LCDs that are made wi~~h non-spec:ular scattering reflectors.
Such non-s~ecular_ LCDs are classified into two broad categories: t~.e _=mage mode (i-mode) and the shadow mode (s-mede). In bo-~:~ the i-mode and the s-mode, the light.
comes into the LCD from tile 12 O' clock direction T.,aith ~=90°, and with B cf typically about 30-45°. The reflected light E=_.;~its the :GCD at near normal incidence, which .is the convenient directi~~n for viewing an LCD.
In the i-mode, t:he polarizer directions and the input director of thE:l liquid crystal cell are placed in the same manner as an. ordinary liauid crystal display viewed at 6 O'clock. 3:n this way, lights enters the LCD from the 12 0'c_Lock direct:~.on, and viewed at near normal. Using the 90° TN LCD as an example, the resultant T-V curve will correspond t:o multiplying i:he T-V curves 17 and 19 in Fig. 6. As a comparison, in the conventional specular LCD, with light incident from the 12 O'clock direction and vis=wed at th~a 6 O'clock direction, the overall T-V
curve would corr~sspond to multiplying curves 18 and 1°.
In the s-made, t:he entire pclarizer-1 iquid crystal cell-analyzer assemb_L,~~ is rotated 180° while the nonspecul ar reflector is not changed. In this ~aay, light still enters from (30-~5°, 90°) and is viewed at (0°,0°).
However, the overall T-V cur_Tre would be represented by the product of curves 17 and 18 in Fig. 6. The most impcrl_ant obser-Tation is that the s-mode turns cn much earlier at a Tll~.iCI1 lower VC'ltagE: t}'lan the 1-mcde device.
MGreCVer, the OVcrall trc?lSilliSSlCn-Voltage Curve iS much steeper in the case of the ..-mode than the i-mode.
Steeper T-V curve means that mere data can be shown on the display with less cress talk. Both the nonspecular i-mode and s-mode are different from the specular L,CD in terms of the T-V curve.
While Fig. 6 i_?lustrates thE: idea of the present invention using 1=:~e °0° TN LCD, the same idea applies to all twist angles. For example, Figs. 7 and 8 show the transmi ssion-volt=age curves for the case of 120° twist and 180° twist displays. It can be seen that there is a large difference between 6 O'clock light,incidence and 12 O'clock light incidence as well. Thus for non-specula.r reflection displays, the arrangement of the polarizers and th~~ directions of the viewing angle and light incident angle are critical in obtaining a good contrast display.
The fact that the taking into acccunt of the angle of incidence in opti:-nizing both ~=he s-mode ar_d i-mode display is illustz-ated by F_.g. 9. In this ~'lg~:re, ae y~l~~t ~.::' transmiwtanc;= ,~f ~~0° twi s ~-~ lav t ~~lJp as a function of i_he d/~n value of the liquid crystal.
Here d star_ds f,:~i the t::ic~lness of the liquid crystal cell and ~n t:: he birefringence of the liquid crys is tat material . he r: ~_re four curvE:s with 1 fight incident angles ranging from 0 to 60. :It can clearly be seen that the pcsit ion of the first minimum (actually the first peak with100 ~ normalized transmittance) shifts to lower values the light incidence angle increases . The as difference between the 0 case and. 60 case is as much as 50 o decmease d.,~r..
in The polarizer placement is also important in optimizing the i-mode and s-mode displays. Again, using the 120°
twist display as. an example, Fig. 9 shows the transmittance as a function of c3~ln for the polarizer arrangement shown in Fig. 10. It can be seen that the peak of the first minimum has shifted to a lower din value as the light incident angle is increased to 60°.
However, if the po_'_arizer arrangement is changed to the one shown in Fig. 11, then the peak shifts to a larcrer value of dOn as the ~-i ght incident angle is increased, as shown in F icr. 12 .
In Fig. 13, the need for optimization of the non-specular display is shown, taking into account both the angle of incidence and angle of reflection. In Fig. 1~, i1 we plot the changE: i n transmittar._ce as a function of dlln for 0° and 60° ar.c.l a of ir_ci deuce . We al so plot the product cf ~_he two curves svnce _Light will traverse the liquid crystal cell at these -~-,No directions. This represents the nc;n-specu 1 ar reflection ,case of light incident. at 60° degree to the display and viewed at near normal angle. It c-an be seen that the shifts in the peak of the f:first min~.m.um is not as drastic, but nonetheless is still. signi fic:art.
For a better unde~i~stand~ng of the present invention, embodiments will no~,r be described by way of exampl e, with reference to the accompanying dravaings, in which:-Fig. 1 shows the components of a typical known liquid crystal display;
Fig. 2 shows the scattering of light by a common diffusive reflector used in transt:lective LCD;
Fig. 3 shows the common alignment of polarizers and liquid crystal directors for a 90° TN LCD, for optimal viewing at the o (:)'clock position;
-=g. ~ shows the po~' ar plot .__ the OV transmittance cf a 0 ° _'~1 ° "' ~C,~ =a,_th pciir_:~e-. arc:~.i avid c r " r~TStd~ ~l.r°C tOr as shown in Fig. ;;
Fi g. 5 shows the polar plot cf tr.e 2 . S i;- transmittance of °0° TN :GCD :,rlth poles=izers ~;nd liquid cr-~stal directors as shown. in Fig. :3;
Fig. 6 shows the t:~_ansmission-vo7_tage curves for the 90°
TN LCD for light entering ti.e display at various angles of incidence. Curve A is when the viewer is at -30° ( 6 O'clock) , curve l3 is when the viewer at 0° (normal to the cell), and curve f corresponds tc the viewer at +30° (12 O'clock);
Fig. 7 shows the tr.~insmission-voltage curves for the 120°
TN LCD f:or light er_tering the display a,t various angles of incidence. Curve A is when the viewer is at -30° (6 O'clock) , curve B is when the viewer at 0° (normal to the cell), and curve C corresponds to the viewer at +30° (12 O'clock);
Fig. 8 shows the transmission-voltage curves far the 180°
TN LCD for light en~ering the displalT at various angles ef incidence. Curve A is when the viewer is at -30° (6 0' clock) ,, curve B i;s wizen the viewer at 0° ( normal to the ce 1 1 ) , and cur-re C~ corresponds to the v, .ewer at -~20° ( 1?
O'clock);
Fig. ° shcws tran.~:mittance of the 120° t,~ist LCD as a functicn cf din fc= various light angles of incidence;
Fig. 10 shows a :regular polarizes arrangement;
Fig. 11 shows an in~Terted polarizes arrangement;
Fig. 12 shows transmittance of the 120° twist LCD as a function of dpn for varicus light angles of incidence;
Fig. 13 shows tr3rl~iiltlttance of t.~e 120° twist LCD as a function of dJn fo_r the cases o = 0° and 60° angles of incidence for the regular polarizes arrangement in Fig.
12;
Fig. 14 shows alignment of the polarizers and the licruid crystal directors f:or the first preferred embodiment;
Fig. 15 shcws alignment of the pclarizers and the liquid crystal directors fcr the second preferred embodiment;
Fig. 16 shows alignment of the pclarizers and the liquid crystal d.irectcrs fcr the third preferred embodiment;
Fv ~ ' ; s.!nows al ig:r~rnf~nt of the pcl~~r,~zer~ and -he i~_cu,-d !=r;TSta- '1~_~:=Ct~?~ i:Jz.' ~..le i~ll'"~."1 ~L'=ferr-(~.TII~OCi-iILlenL;
dnC1 i4 F-a. 18 shows l.iql..~id crystay cii,pla,. structure for the fifth' prs=erred E-.:nbod.iment .
In t:le :Lust embc~dl.ment of tl~e neTrr liquid crystal display according to the F;z-esent invention, the alignment of the polarizers and thE: liquid cr_rstal directors are as shown in Fig. 14. The polarizers are at or near 90° to each other, and are disposed symmetric~illy with respect to the input and output ~irectors of the liquid crystal cell.
In this embcdiment, the input polarizes P_a is on the same side as the input director n1a rE=_lative to the y-axis .
The twist angle of the liquid crystal, which corresponds to the angle between nLZ and n°ut, can be any angle from 60° to 270°. In particular, it can be 90° TN, or a 120°
IiTN, or a 180°-240° STN display. The values of the thickness d times the birefringence On of the liquid crystal cell can beg any of the values listed in Table III
below. For each twist angle, the ddn value can correspond to the first minimum or second minimum according to the design o. LCL~s. This embodiment corresponds ~o a o O~clock v-_ewing of the LCD. In this arrangement, light enters the display from the ~=°0°
direction at an cbl._:.que anal a and viewed at near normal direction. '~his is al:._o the i-mode display.
~.Tn the second eribcd~~men- o~= the ne~N ~-iquid cr-rsta 1 i5 display according too the invention, the alignment of~the polarizE~rs and t=he liquid cr.yst.l directors are as shown in F~~. ~, he polarizers are at cr near 90° to each ot:~er, a.nd are dls~:csed s;~mmetric~:lly with respect to the input and output directors of the liquid crystal cell.
In this embodiment, the input pc~larizer P:n is on the opposite side as t:he input director nyn relative to the y-axis . The twisl~ angle of the liquid crystal, which corresponds to the angle bet-,~een n_a and nut, can be any angle from 60° tc> 270°. In :parti~~ular, it can be a 90°
TN, cr a 120° HTN, o.r a 180°-2=0° Si'N display. The values of the t=hickness d times the birefringence On of the liquid crystal cell can be any of the values listed in Table III below. For each twist angle, the din value can correspond to the first minimum or second minimum according to the design of LCDs. This embodiment corresponds to a o O'clock viewing of the LCD. In this arrangement, light enters the display from the ~=9p°
direction. at an oblique angle and viewed at near normal directian. This i.s also the i-mod= display.
In the third embodiment of the new liquid crystal display according to the invention, the alignment of the polarizer:~ and the i=.QU_d cr-rs ~al directors are as shown in r ig. to . The z:~o 1 arizers are at cr near 90° to each other, and are d.i;s~csed s=rnmletric:aliy with respect to the input and output directors of the 1?cuid crystal cell.
In this embodiment, the irpu~ pcl arizer P:~ is on the same side as th« i nput director n.~ _=el ative tc the y-axis .
The tTNis t angle cf the l i quid cr~Ts tal, which corresponds to the angle be cT,,teen n;u and n°uL, car_ be any angle from 60° t.c ?70°. In particular, it can be a 90° TN, or a 120°
HTN, o:r a 180°-240° STN displalr. The values of the thickness d times the birefringence ~n of the liquid crystal cell can be any of the va:Lues listed in Table III
below. For each twist angle, the dOn value can correspond to the first minimum or second minimum according to the design cf LC~Ds. This embodiment corresponds to a 7_:? O'clock viewing of the LCD. In this' arrangement, light. enters the display from the ~=90°
direction at an oblique angle anc3 viewed at near normal direction. This ..s also the s-mode display.
In the fourth end:odiment of the new liquid crystal display according t:o the invention, the alignment of the polarizers and the ~=quid crystal directors are as shown in Fig. 17. The polarizers are at or near 90° to each other , and are disposed sl,~mmetr i ca.lly w, th respect to the input and output :i__rectors of th~= liquid crjrstal cell.
T:n this embodimenl_, the input pol arizer a _a is on the opposite s ide as t: he input di rec:tor n;n relative to the y-axis . The t;ai;;~_ angle cf the liquid crystal, which corresponds to thc= angle be tween nir and n°ut, can be any angle from 60° to 270°. In particul ar, it can be a 90°
TN, or a 120° HTN, or a 180°-240° STN display. The values of the thickness d times the birefringence ~n of the liquid crystal cell can be any of the values listed in Table III below. For each twist angle, the din value can correspond to th.e first mi.niirum or second minimum according to the design of LC:Ds. This embodiment corresponds to a f O'clock viewing of the LCD. In this arrangement, light enters the display from the ~-90°
direction at an oblique angle and viewed at near normal direction. This i.s also the s-mode display.
In the fifth embodiment of this new liquid crystal display, the rear polarizer can be absent. The normal version of this display has been discussed by Yu et al, "A New T:LV-LCD Mode Ref lective LCD with Large Cell Gap and Low 0 eratin Volta a P g g , pp 155-158, Int'1 Display Research Conference, Toronto, 1997. In th.e embodiment discussed here, the ncnspecular reflector 24 can be placed inside the liquid crystal cell as shown in Fig. 18. In this preferred embodiment, only an input polarizer 17 is needed. The iiqu~_d cr-~sLCli dysNla-r consists of the usual glass su3~str at's ld and 1?, ~:~e liquid cr_TStal alignment layers 21 and 2.~, the patterned conductive transparent a 1 ectrodes 20 ai;d 2 ~? , and the licuid crys tat 25 . The ncnspecul ar refl ec;:or 2~ may or may not have a protective coating bet,,~een itsel f and the patterned electrode 23 .
The twist angle a:nd the pol arizer angles are optimized for oblique incident light and near normal viewing.
Since the nenspefcu.~_ar reflec for ~:4 is inside the liquid crystal cell, them= is no shadow effect. Both the shadow mode and image mode can be seen simultaneously.
Depending on the polarizer arrangement as described in the previ ous preaerred embodiments , the display can be either :in the s-mode or the i-mode . For the s-mode operation the threshold is significantly lowered and the T-V curve s ign if _ic ant l y s harper than the i-mode operation.
i9 TABLE I
F,_rst possibl a c,scrletr~ of various LCD modes . Al l angles a_~e measured rela,_i,re to thc~ x-a=rt's which is hcyizontal t0 the Vi ewing C'~...~I=-=:Ct'iCn p0 ~:ltiZlCj ~rCm 1 eft t0 right .
TWIST INPUT' OUTPLT INPUT OUTPUT
ANGLE DIRECTOR DIRECTOR fOLARIZER POLARIZER
ANGLE - ANGLE ANGLE ANGLE
90 45 _ 135 Q5 _45 120 30 -_ 150 45 -45 ..
150 ~ 15 165 45 -45 180 i 0 _ 180 45 _45 I
240 I -30 210 45 _45 TABLE II
Second pcssible gec_:metrJ of vari ous LCD modes . A11 angles are measured relative to the x-axis which is horizontal to the viewing direction pointing from left to right.
TWIST INPUT OUTPUT INPUT OUTPUT
ANGLE DIRECTJF; DIRECTOR POLARIZER POLARIZER
ANGLE ANGLE ANGLE
_ ANGLE
90 ~ j 135 -45 45 120 I 30 I 150 -45 ~ 45 150 ~ 15 165 I -45 45 180 I 0 _ 180 -45 45 240 _30 ~ 210 I - -45 4 TABLE III
Optimal. retarda :~cn vaiues cf the ~Tar i cus operating ccr_~iti.ons ci the rcr=-specuyar dispialj.
TTwIST FIR~;T SECOND SECOND
ANGLE' ~ FIRST MINIMUM_ MINIMUM
MINI1~IU_N tam) AT 60 MINIMUM INCIDENCE
Wm) AT m t60 ~
INCIDENCE
~ L~ ) u ) 90 0.5 _ 1.075 0 0.4 95 .
120 0.6 0.52 1.24 1.2 150 0.64 _ 1.28 1.25 0.58 180 0.63 _ 1.27 1 ~ 25 0.67.
0 0.66 - 0.56 1.38 .
1.25
NOIyISPECULAR REFLECTORS
The pre~;ent invention relates to a new type of liquid crystal display whE:r_e the input and output light beams do not follow the usual specula.r relationship.
Liquid crystal displays are usually manufactured with a structure as showr.~ in Fig. 1. It comprises an input polarizes l, a li<~uid crystal cell 2 , an output polarizes 3 and a reflective diffuser 4. T:!-ie liquid crystal cell is commonly made of two pieces cf: glass 5,6, alignment layers .,8, conductive electrodE~ films 9,10 and the liquid crystal material 11 which possesses a twisting alignment in conformance with the alignment layers 7 and 8.
In this common reflective (or sometimes known as transflective) liquid crystal display, the light 12 enters the d-splay from one direction at some azimuthal angle B relative to the surface normal 13 of the display.
The corresponding polar angle of t:he incident light is relative to some x--axis on the surface of the display.
Thus the angles specifying the light propagation direction is given by ( B, c~ ) . 'This light is scattered and reflected by the dif::=us ive ref ~ectcr and goes through the liquid c:rys tal cell once more and is seen by the observer 14. This light intensity is strongest at the reflection angle ( B, ~-rr ) . Tr~is is ca 1 led specular reflection or glare reflection. There is light obser~,rable at angles other than (FJ,~+n) as shown because of scattering, but its intensity drops off rapidly as the angle deviates from B. The situation is depicted in Fig. 2. By the same scattering rn~_chanism, at any viewing direction (B,~+n),, there is contribution of light incident from (B,~), and light from incident angles near (B,~).
However,, a majority of the light is from the (B,~) direction.
In designing and optimizing such common liquid crystal displays, the alignment direction of the top and bottom glass plates and t:he placement o_E the input and output polarizEars are c:ru.cial. If one sakes the example of a 90° twisted nemat_i.c liquid crystal display, the most common configuration is shown in Fig. 3. The input polarizes PiL and 'the input director nLn are aligned at right angles. The output polarizes Pout is also perpendicular to the output liquid crystal director n°ut as shown . This i:the so-cal:~ed o-mode operation for the TN display. The .1i_ght enters the liquid crystal display from the 12 c.)'cloc~: direction 15 and the viewer looks at the display .'rom the 6 0'clecJc direction ?6. This is in contras t to the e--.node operation where Pia and nin are parallel , and P°u= anal n°ut are also parallel. The viewing angle polar plot fcr the o-mode TN display is shown in Figs. 4 and 5. F~a. 4 is the polar plot for V=0 and Fig.
is the polar plot cf transm_ttanc:e for 2.5V. They show clearly 'the optima__ viewing direction which is at the 6 O'clock position. The darkest part of the polar plot in Fig. 5 indicates th.e light should exit the display at an azimutha:l angle B of 30° and a polar angle ~ of 270°.
This optimization of the viewing angle of the liquid crystal display is well-known and has been discussed in the literature. Fo r_ example, the books by Blinov et al (Electrooptic Effects in Liquid Crystal Materials Springer-Verlag, 1994) and Bahadur (Liquid Crystals Applications and Uses, World Scientific, Singapore, 1990) have discussions on the viewing angle of liquid crystal displays.. In these discussions, the light is assumed to traverse the liquid crystal cell at an oblique angle once. The viewing angle diagram plots the contrast of the display at the working voltages for light going through 'the liquid crystal cell at an angle of (8,~) where B is the angle between the light beam and the surface normal of the liquid crystGl cell (the azimuthal angle) anal ~ is the angla between the projection of the light beam cn the liquid cr~;stal cell surface and the i G+
reference x-axis (the polar anglEa). The input director of the liquid crystal is alsc; measured referenced to this x-axis. Fcr the case of the 90' twist TN display, as shown in Fic. 3, the x-axis is usually taken to be at 45°
to the :input director .
In the traditional optimization of the liquid crystal display,, it is generally assumed that light enters at a certain angle. Many plots of the transmission-voltage curves have been shown in the )_iterature for various combinations of t.h:e light viFa~~ing angl a characterized by (~,8). Implicit in such curves, with only one value of 6 specified, it is assumed that :Light enters and exits the cell at the same azimuthal angle. The possibility of light entering and exiting the liquid crystal cell at differer.~t azimutha.l angles is never considered in the numerical and experimental optimization procedures. The present invention ;shows that for the case of nonspecular reflection, it is important to perform the simultaneous optimization of all important LCD parameters by considering light entering and exiting the LCD at different angles.
Fig. shown the transmission-voli_age curves for liquid crystal displays operating in the so-called second minimum . This second m~nimurn corresponds to a i retardaticn valuE.=_, the product of the cell thickness and the birEafringenc~s of the 1 iquid crystal (dc~n) , of 1. 075 ~m and a liquid crystal twist angle of 90°. Curve 17 is when the viewing angle and the light entrance angle are 0° (normal to the cell). Curve 18 corresponds to light entering at B=30°, ~=90° and the display is viewed at B=30°, ~=270°. Tr,is is the so-called 6 O'clock viewing condition. Curve 19 corresponds to conditions exactly opposite' to curve 7_8, i.e. light entering at 8=30°, ~=270°
and the display is; viewed at B=30°, ~=9.0°. In the 6 O'clock position, the liquid crys=al cell turns off at a lower voltage and the change in transmission as a function of voltage (the transmission-voltage or T-V
curve 18) is sharper. This leads to a much better multiplexing capability for this display. Fig. 7 and 8 are similar plots for the cases of 120° and 180° twist displays.
In this present invention, we recognize the fact that it is possible to manufacture LCDs where the input light angle and the outFut light angle are greatly different (non-specular reflection). Such a possibility of having non-specular light. reflection was pointed out in US
patent No. 5,659,40f3 of M. Wenyon. One way of obtaining this sii~uat_on _i_s tc use the so-called holographic reflector fi;_ms ( s<=e, for Flxamp ~ e, ~Z. Wenyon et al, "White Holographic: Reflector for LCDs", SID Symp. Dig.
J.997). There are additionally many types of structured scattering surfaces that can achieve such non-specular reflections. However, such prior LCDs do not optimize the reflection.
It is accordingly an object of the invention to seek to mitigate this disadvantage.
According to the invention there is provided a liquid cryst al display, characterised by the incident light direction and the direction of light exiting the display after reflection being dif:Eerent: directions which are non-specular.
Using the invention it is possible to provide that the incident and reflected light beaams to be at different angles. The transmission-voltage curves should be calculated using different values of input and output angles.
A liquid crystal display embodyj_ng the invention thus has a7_1 of its critical parameters simultaneously optimized allowing for the input light angle and the viewing angle to be different from each other, thus yielding retardation values of the display that are significantly d_if~erent from conventional liquid crystal displays. The polarizes angles, the input/output directors and/e:r t:he liquid crystal cell retardation may thus be eptimizec'_ for non-specu~_ar operation.
Another significant aspect of the present invention is the recognition ef the fact that most cf the nenspecular reflectors are monochromatic. That is, even with white light input, the reflected light will have a color, e.g.
green. Hence the optimization of the nonspecular LCD
does not: ha~~e to take int;~ account color dispersion effects. One can assume a menoc:hromatic light 3s the input. Of course, this invention does not preclude the situation where th.e nonspecslar reflector can be wide bared or c_an reflect. white light as well.
It is therefore possible using the invention to provide a set or sets of operating conditi~~ns for LCDs that are made wi~~h non-spec:ular scattering reflectors.
Such non-s~ecular_ LCDs are classified into two broad categories: t~.e _=mage mode (i-mode) and the shadow mode (s-mede). In bo-~:~ the i-mode and the s-mode, the light.
comes into the LCD from tile 12 O' clock direction T.,aith ~=90°, and with B cf typically about 30-45°. The reflected light E=_.;~its the :GCD at near normal incidence, which .is the convenient directi~~n for viewing an LCD.
In the i-mode, t:he polarizer directions and the input director of thE:l liquid crystal cell are placed in the same manner as an. ordinary liauid crystal display viewed at 6 O'clock. 3:n this way, lights enters the LCD from the 12 0'c_Lock direct:~.on, and viewed at near normal. Using the 90° TN LCD as an example, the resultant T-V curve will correspond t:o multiplying i:he T-V curves 17 and 19 in Fig. 6. As a comparison, in the conventional specular LCD, with light incident from the 12 O'clock direction and vis=wed at th~a 6 O'clock direction, the overall T-V
curve would corr~sspond to multiplying curves 18 and 1°.
In the s-made, t:he entire pclarizer-1 iquid crystal cell-analyzer assemb_L,~~ is rotated 180° while the nonspecul ar reflector is not changed. In this ~aay, light still enters from (30-~5°, 90°) and is viewed at (0°,0°).
However, the overall T-V cur_Tre would be represented by the product of curves 17 and 18 in Fig. 6. The most impcrl_ant obser-Tation is that the s-mode turns cn much earlier at a Tll~.iCI1 lower VC'ltagE: t}'lan the 1-mcde device.
MGreCVer, the OVcrall trc?lSilliSSlCn-Voltage Curve iS much steeper in the case of the ..-mode than the i-mode.
Steeper T-V curve means that mere data can be shown on the display with less cress talk. Both the nonspecular i-mode and s-mode are different from the specular L,CD in terms of the T-V curve.
While Fig. 6 i_?lustrates thE: idea of the present invention using 1=:~e °0° TN LCD, the same idea applies to all twist angles. For example, Figs. 7 and 8 show the transmi ssion-volt=age curves for the case of 120° twist and 180° twist displays. It can be seen that there is a large difference between 6 O'clock light,incidence and 12 O'clock light incidence as well. Thus for non-specula.r reflection displays, the arrangement of the polarizers and th~~ directions of the viewing angle and light incident angle are critical in obtaining a good contrast display.
The fact that the taking into acccunt of the angle of incidence in opti:-nizing both ~=he s-mode ar_d i-mode display is illustz-ated by F_.g. 9. In this ~'lg~:re, ae y~l~~t ~.::' transmiwtanc;= ,~f ~~0° twi s ~-~ lav t ~~lJp as a function of i_he d/~n value of the liquid crystal.
Here d star_ds f,:~i the t::ic~lness of the liquid crystal cell and ~n t:: he birefringence of the liquid crys is tat material . he r: ~_re four curvE:s with 1 fight incident angles ranging from 0 to 60. :It can clearly be seen that the pcsit ion of the first minimum (actually the first peak with100 ~ normalized transmittance) shifts to lower values the light incidence angle increases . The as difference between the 0 case and. 60 case is as much as 50 o decmease d.,~r..
in The polarizer placement is also important in optimizing the i-mode and s-mode displays. Again, using the 120°
twist display as. an example, Fig. 9 shows the transmittance as a function of c3~ln for the polarizer arrangement shown in Fig. 10. It can be seen that the peak of the first minimum has shifted to a lower din value as the light incident angle is increased to 60°.
However, if the po_'_arizer arrangement is changed to the one shown in Fig. 11, then the peak shifts to a larcrer value of dOn as the ~-i ght incident angle is increased, as shown in F icr. 12 .
In Fig. 13, the need for optimization of the non-specular display is shown, taking into account both the angle of incidence and angle of reflection. In Fig. 1~, i1 we plot the changE: i n transmittar._ce as a function of dlln for 0° and 60° ar.c.l a of ir_ci deuce . We al so plot the product cf ~_he two curves svnce _Light will traverse the liquid crystal cell at these -~-,No directions. This represents the nc;n-specu 1 ar reflection ,case of light incident. at 60° degree to the display and viewed at near normal angle. It c-an be seen that the shifts in the peak of the f:first min~.m.um is not as drastic, but nonetheless is still. signi fic:art.
For a better unde~i~stand~ng of the present invention, embodiments will no~,r be described by way of exampl e, with reference to the accompanying dravaings, in which:-Fig. 1 shows the components of a typical known liquid crystal display;
Fig. 2 shows the scattering of light by a common diffusive reflector used in transt:lective LCD;
Fig. 3 shows the common alignment of polarizers and liquid crystal directors for a 90° TN LCD, for optimal viewing at the o (:)'clock position;
-=g. ~ shows the po~' ar plot .__ the OV transmittance cf a 0 ° _'~1 ° "' ~C,~ =a,_th pciir_:~e-. arc:~.i avid c r " r~TStd~ ~l.r°C tOr as shown in Fig. ;;
Fi g. 5 shows the polar plot cf tr.e 2 . S i;- transmittance of °0° TN :GCD :,rlth poles=izers ~;nd liquid cr-~stal directors as shown. in Fig. :3;
Fig. 6 shows the t:~_ansmission-vo7_tage curves for the 90°
TN LCD for light entering ti.e display at various angles of incidence. Curve A is when the viewer is at -30° ( 6 O'clock) , curve l3 is when the viewer at 0° (normal to the cell), and curve f corresponds tc the viewer at +30° (12 O'clock);
Fig. 7 shows the tr.~insmission-voltage curves for the 120°
TN LCD f:or light er_tering the display a,t various angles of incidence. Curve A is when the viewer is at -30° (6 O'clock) , curve B is when the viewer at 0° (normal to the cell), and curve C corresponds to the viewer at +30° (12 O'clock);
Fig. 8 shows the transmission-voltage curves far the 180°
TN LCD for light en~ering the displalT at various angles ef incidence. Curve A is when the viewer is at -30° (6 0' clock) ,, curve B i;s wizen the viewer at 0° ( normal to the ce 1 1 ) , and cur-re C~ corresponds to the v, .ewer at -~20° ( 1?
O'clock);
Fig. ° shcws tran.~:mittance of the 120° t,~ist LCD as a functicn cf din fc= various light angles of incidence;
Fig. 10 shows a :regular polarizes arrangement;
Fig. 11 shows an in~Terted polarizes arrangement;
Fig. 12 shows transmittance of the 120° twist LCD as a function of dpn for varicus light angles of incidence;
Fig. 13 shows tr3rl~iiltlttance of t.~e 120° twist LCD as a function of dJn fo_r the cases o = 0° and 60° angles of incidence for the regular polarizes arrangement in Fig.
12;
Fig. 14 shows alignment of the polarizers and the licruid crystal directors f:or the first preferred embodiment;
Fig. 15 shcws alignment of the pclarizers and the liquid crystal directors fcr the second preferred embodiment;
Fig. 16 shows alignment of the pclarizers and the liquid crystal d.irectcrs fcr the third preferred embodiment;
Fv ~ ' ; s.!nows al ig:r~rnf~nt of the pcl~~r,~zer~ and -he i~_cu,-d !=r;TSta- '1~_~:=Ct~?~ i:Jz.' ~..le i~ll'"~."1 ~L'=ferr-(~.TII~OCi-iILlenL;
dnC1 i4 F-a. 18 shows l.iql..~id crystay cii,pla,. structure for the fifth' prs=erred E-.:nbod.iment .
In t:le :Lust embc~dl.ment of tl~e neTrr liquid crystal display according to the F;z-esent invention, the alignment of the polarizers and thE: liquid cr_rstal directors are as shown in Fig. 14. The polarizers are at or near 90° to each other, and are disposed symmetric~illy with respect to the input and output ~irectors of the liquid crystal cell.
In this embcdiment, the input polarizes P_a is on the same side as the input director n1a rE=_lative to the y-axis .
The twist angle of the liquid crystal, which corresponds to the angle between nLZ and n°ut, can be any angle from 60° to 270°. In particular, it can be 90° TN, or a 120°
IiTN, or a 180°-240° STN display. The values of the thickness d times the birefringence On of the liquid crystal cell can beg any of the values listed in Table III
below. For each twist angle, the ddn value can correspond to the first minimum or second minimum according to the design o. LCL~s. This embodiment corresponds ~o a o O~clock v-_ewing of the LCD. In this arrangement, light enters the display from the ~=°0°
direction at an cbl._:.que anal a and viewed at near normal direction. '~his is al:._o the i-mode display.
~.Tn the second eribcd~~men- o~= the ne~N ~-iquid cr-rsta 1 i5 display according too the invention, the alignment of~the polarizE~rs and t=he liquid cr.yst.l directors are as shown in F~~. ~, he polarizers are at cr near 90° to each ot:~er, a.nd are dls~:csed s;~mmetric~:lly with respect to the input and output directors of the liquid crystal cell.
In this embodiment, the input pc~larizer P:n is on the opposite side as t:he input director nyn relative to the y-axis . The twisl~ angle of the liquid crystal, which corresponds to the angle bet-,~een n_a and nut, can be any angle from 60° tc> 270°. In :parti~~ular, it can be a 90°
TN, cr a 120° HTN, o.r a 180°-2=0° Si'N display. The values of the t=hickness d times the birefringence On of the liquid crystal cell can be any of the values listed in Table III below. For each twist angle, the din value can correspond to the first minimum or second minimum according to the design of LCDs. This embodiment corresponds to a o O'clock viewing of the LCD. In this arrangement, light enters the display from the ~=9p°
direction. at an oblique angle and viewed at near normal directian. This i.s also the i-mod= display.
In the third embodiment of the new liquid crystal display according to the invention, the alignment of the polarizer:~ and the i=.QU_d cr-rs ~al directors are as shown in r ig. to . The z:~o 1 arizers are at cr near 90° to each other, and are d.i;s~csed s=rnmletric:aliy with respect to the input and output directors of the 1?cuid crystal cell.
In this embodiment, the irpu~ pcl arizer P:~ is on the same side as th« i nput director n.~ _=el ative tc the y-axis .
The tTNis t angle cf the l i quid cr~Ts tal, which corresponds to the angle be cT,,teen n;u and n°uL, car_ be any angle from 60° t.c ?70°. In particular, it can be a 90° TN, or a 120°
HTN, o:r a 180°-240° STN displalr. The values of the thickness d times the birefringence ~n of the liquid crystal cell can be any of the va:Lues listed in Table III
below. For each twist angle, the dOn value can correspond to the first minimum or second minimum according to the design cf LC~Ds. This embodiment corresponds to a 7_:? O'clock viewing of the LCD. In this' arrangement, light. enters the display from the ~=90°
direction at an oblique angle anc3 viewed at near normal direction. This ..s also the s-mode display.
In the fourth end:odiment of the new liquid crystal display according t:o the invention, the alignment of the polarizers and the ~=quid crystal directors are as shown in Fig. 17. The polarizers are at or near 90° to each other , and are disposed sl,~mmetr i ca.lly w, th respect to the input and output :i__rectors of th~= liquid crjrstal cell.
T:n this embodimenl_, the input pol arizer a _a is on the opposite s ide as t: he input di rec:tor n;n relative to the y-axis . The t;ai;;~_ angle cf the liquid crystal, which corresponds to thc= angle be tween nir and n°ut, can be any angle from 60° to 270°. In particul ar, it can be a 90°
TN, or a 120° HTN, or a 180°-240° STN display. The values of the thickness d times the birefringence ~n of the liquid crystal cell can be any of the values listed in Table III below. For each twist angle, the din value can correspond to th.e first mi.niirum or second minimum according to the design of LC:Ds. This embodiment corresponds to a f O'clock viewing of the LCD. In this arrangement, light enters the display from the ~-90°
direction at an oblique angle and viewed at near normal direction. This i.s also the s-mode display.
In the fifth embodiment of this new liquid crystal display, the rear polarizer can be absent. The normal version of this display has been discussed by Yu et al, "A New T:LV-LCD Mode Ref lective LCD with Large Cell Gap and Low 0 eratin Volta a P g g , pp 155-158, Int'1 Display Research Conference, Toronto, 1997. In th.e embodiment discussed here, the ncnspecular reflector 24 can be placed inside the liquid crystal cell as shown in Fig. 18. In this preferred embodiment, only an input polarizer 17 is needed. The iiqu~_d cr-~sLCli dysNla-r consists of the usual glass su3~str at's ld and 1?, ~:~e liquid cr_TStal alignment layers 21 and 2.~, the patterned conductive transparent a 1 ectrodes 20 ai;d 2 ~? , and the licuid crys tat 25 . The ncnspecul ar refl ec;:or 2~ may or may not have a protective coating bet,,~een itsel f and the patterned electrode 23 .
The twist angle a:nd the pol arizer angles are optimized for oblique incident light and near normal viewing.
Since the nenspefcu.~_ar reflec for ~:4 is inside the liquid crystal cell, them= is no shadow effect. Both the shadow mode and image mode can be seen simultaneously.
Depending on the polarizer arrangement as described in the previ ous preaerred embodiments , the display can be either :in the s-mode or the i-mode . For the s-mode operation the threshold is significantly lowered and the T-V curve s ign if _ic ant l y s harper than the i-mode operation.
i9 TABLE I
F,_rst possibl a c,scrletr~ of various LCD modes . Al l angles a_~e measured rela,_i,re to thc~ x-a=rt's which is hcyizontal t0 the Vi ewing C'~...~I=-=:Ct'iCn p0 ~:ltiZlCj ~rCm 1 eft t0 right .
TWIST INPUT' OUTPLT INPUT OUTPUT
ANGLE DIRECTOR DIRECTOR fOLARIZER POLARIZER
ANGLE - ANGLE ANGLE ANGLE
90 45 _ 135 Q5 _45 120 30 -_ 150 45 -45 ..
150 ~ 15 165 45 -45 180 i 0 _ 180 45 _45 I
240 I -30 210 45 _45 TABLE II
Second pcssible gec_:metrJ of vari ous LCD modes . A11 angles are measured relative to the x-axis which is horizontal to the viewing direction pointing from left to right.
TWIST INPUT OUTPUT INPUT OUTPUT
ANGLE DIRECTJF; DIRECTOR POLARIZER POLARIZER
ANGLE ANGLE ANGLE
_ ANGLE
90 ~ j 135 -45 45 120 I 30 I 150 -45 ~ 45 150 ~ 15 165 I -45 45 180 I 0 _ 180 -45 45 240 _30 ~ 210 I - -45 4 TABLE III
Optimal. retarda :~cn vaiues cf the ~Tar i cus operating ccr_~iti.ons ci the rcr=-specuyar dispialj.
TTwIST FIR~;T SECOND SECOND
ANGLE' ~ FIRST MINIMUM_ MINIMUM
MINI1~IU_N tam) AT 60 MINIMUM INCIDENCE
Wm) AT m t60 ~
INCIDENCE
~ L~ ) u ) 90 0.5 _ 1.075 0 0.4 95 .
120 0.6 0.52 1.24 1.2 150 0.64 _ 1.28 1.25 0.58 180 0.63 _ 1.27 1 ~ 25 0.67.
0 0.66 - 0.56 1.38 .
1.25
Claims (30)
1. A liquid crystal display, comprising:
(i) an incident light direction;
(ii) a direction of light exiting the display after reflection; and (iii) said directions being different and non-specular.
(i) an incident light direction;
(ii) a direction of light exiting the display after reflection; and (iii) said directions being different and non-specular.
2. A liquid crystal display as defined in Claim 1, whereas incident angle(s) of light beams and reflected angle(s) of light beams are different from one another.
3. A liquid crystal display as defined in Claim 2, wherein that transmission-voltage curves therefor are calculated using said different values of input and output angles.
4. A liquid crystal display, as defined in Claim 1, wherein said display comprises a non-specular scattering reflector.
5. A liquid crystal display as defined in Claim 1 wherein said display comprises an input polarizer, a liquid crystal cell, and a non-specular reflector at the rear of the display.
6. A liquid crystal display as defined in Claim 2, wherein said display comprises an input polarizer, a liquid crystal display and a non-specular reflector at the rear of the display, and wherein said display is characterised by light entering the display at an angle .theta. to the surface normal of the display, and by being viewed at an angle .theta.'to the surface normal of the display, where .theta.' is significantly different from .theta..
7. A liquid crystal display as defined in Claim 6, whereby said angle .theta. is between 30°-60°.
8. A liquid crystal display as defined in Claim 6, wherein said angle H is between 0°-10°.
9. A liquid crystal display as defined in Claim 4, wherein said non-specular reflector is a holographic reflector.
10. A liquid crystal display as defined in Claim 5, wherein the said display comprises a rear polarizer.
11. A liquid crystal display as defined in Claim 5, wherein said display comprises a rear polarizer, and wherein there is a retardation film placed between said liquid crystal cell and said rear polarizer.
12. A liquid crystal display as defined in Claim 5, wherein said display comprises a twist angle of 90°~10°, a thickness times birefringence product of 0.5~0.1 ,µm, and wherein polarizer(s) and liquid crystal director(s) are arranged to provide an image mode (i-mode) operation.
13. A liquid crystal display as defined in Claim 5, wherein said display comprises a twist angle of 90°~10°, a thickness times birefringence product of 1.075~0.1µm, wherein polarizer (s) and liquid crystal director(s) are arranged to provide an image mode (i-mode) operation.
14. A liquid crystal display as defined in Claim 5, wherein said display comprises a twist angle of 120°~10°, a thickness times birefringence product of 0.6~0.1 µm, wherein polarizer(s) and liquid crystal director (s) are arranged to provide an image mode (i-mode) operation.
15. A liquid crystal display as defined in Claim 5, wherein said display comprises a twist angle of 120°~10°, a thickness times birefringence product of 1.24~0.1 µm, wherein polarizer(s) and liquid crystal director (s) are arranged to provide an image mode (i-mode) operation.
16. A liquid crystal display as defined in Claim 5, wherein said display comprises a twist angle of 180°~10°, a thickness birefringence product of 0.62~0.1 µm, wherein polarizer(s) and liquid crystal director(s) are arranged to provide an image mode (i-mode) operation.
17. A liquid crystal display as defined in Claim 5, wherein said display comprises a twist angle of 180°~10°, thickness times birefringence product of 1.25~0.1 µm, wherein polarizer(s) and liquid crystal director(s) are arranged to provide an image mode (i-mode) operation.
18. A liquid crystal display as defined in Claim 5, wherein said display comprises a twist angle of 240°~10°, a thickness times birefringence product of 0.65~0.1 µm, wherein polarizer(s) and liquid crystal director(s) being arranged to provide an image mode (i-mode) operation.
19. A liquid crystal display as defined in Claim 5, wherein said display comprises a twist angle of 240°~10°, a thickness times birefringence product of 1.3~0.1 µm, wherein polarizer(s) and liquid crystal directors) are arranged to provide an image mode (i-mode) operation.
20. A liquid crystal display as defined in Claim 5, wherein said display comprises a twist angle of 90°~240°, by polarizer(s) and liquid crystal director(s) are arranged to provide an image mode (i-mode) operation.
21. A liquid crystal display as defined in Claim 5, wherein said display comprises twist angle of 90°~10°, a thickness times birefringence product of 1.075~0.1 µm, wherein polarizer(s) and liquid crystal director(s) are arranged to provide a shadow mode (s-mode) operation.
22. A liquid crystal display as defined in Claim 5, wherein said display comprises a twist angle of 120°~10°, a thickness times birefringence product of 0.6~0.1 µm, wherein polarizer(s) and liquid crystal director(s) are arranged to provide a shadow mode (s-mode) operation.
23. A liquid crystal display as defined in Claim 5, wherein said display comprises a twist angle of 120°~10°, a thickness times birefringence product of 1.24~0.1 µm, wherein polarizer(s) and liquid crystal directors) being arranged to provide a shadow mode (s-mode) operation.
24. A liquid crystal display as defined in Claim 5, wherein said display comprises a twist angle of 180°~10°, a thickness times birefringence product of 0.62~0.1 µm, wherein polarizer(s) and liquid crystal director(s) are arranged to provide a shadow mode (s-mode) operation.
25. A liquid crystal display as defined in Claim 5, wherein said display comprises a twist angle of 180°~10°, a thickness times birefringence product of 1.25~0.1 ,µm, wherein polarizer(s) and liquid crystal director(s) are arranged to provide a shadow mode (s-mode) operation.
26. A liquid crystal display as defined in Claim 5, wherein said display comprises a twist angle of 240°~10°, a thickness times birefringence product of 0.65~0.1 µm, wherein polarizer(s) and liquid crystal director(s) are arranged to provide a shadow mode (s-mode) operation.
27. A liquid crystal display as defined in Claim 5, wherein said display comprises a twist angle of 240°~10°, a thickness times birefringence product of 1.3~0.1 µm, wherein polarizer(s) and liquid crystal director(s) are arranged to provide a shadow mode (s-mode) operation.
28. A liquid crystal display as defined in Claim 5, wherein said display comprise, a twist angle of 90°~240°, wherein polarizer(s) and liquid crystal directors) are arranged to provide an shadow mode (s-mode) operation.
29. A liquid crystal display as defined in Claim 5, wherein said display comprises a polarizes and liquid crystal alignment as shown in Table I, and by retardation values as shown in Table III.
30. A liquid crystal display as defined in Claim 5, wherein said display comprises a polarizer and liquid crystal alignment as shown in Table II, and by retardation values as shown in Table III.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GBGB9919094.4A GB9919094D0 (en) | 1999-08-12 | 1999-08-12 | Liquid crystal display with nonspecular reflectors |
| GB9919094.4 | 1999-08-12 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2315494A1 true CA2315494A1 (en) | 2001-02-12 |
Family
ID=10859065
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002315494A Abandoned CA2315494A1 (en) | 1999-08-12 | 2000-08-11 | Liquid crystal display with nonspecular reflectors |
Country Status (12)
| Country | Link |
|---|---|
| US (1) | US6532051B1 (en) |
| EP (1) | EP1081532A3 (en) |
| JP (1) | JP2001108985A (en) |
| KR (1) | KR20010021287A (en) |
| CN (1) | CN1160685C (en) |
| BR (1) | BR0006757A (en) |
| CA (1) | CA2315494A1 (en) |
| GB (1) | GB9919094D0 (en) |
| IL (1) | IL137801A0 (en) |
| MX (1) | MXPA00007847A (en) |
| SG (1) | SG97914A1 (en) |
| TW (1) | TW581889B (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7015990B2 (en) * | 2000-04-24 | 2006-03-21 | Nitto Denko Corporation | Liquid crystal display including O-type and E-type polarizer |
| JP2003215591A (en) * | 2002-01-25 | 2003-07-30 | Alps Electric Co Ltd | Transflective liquid crystal display device |
| JP5824249B2 (en) | 2010-06-11 | 2015-11-25 | 東友ファインケム株式会社Ｄｏｎｇｗｏｏ Ｆｉｎｅ−Ｃｈｅｍ Ｃｏ．， Ｌｔｄ． | Cleaning liquid composition |
| KR20130048070A (en) * | 2011-11-01 | 2013-05-09 | 삼성디스플레이 주식회사 | Display apparatus |
Family Cites Families (20)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5555113A (en) * | 1990-03-23 | 1996-09-10 | U.S. Philips Corporation | Liquid crystal display device with twist angle φ of 70° to 90°and alignment to polarization direction angle between φ/2+30°and φ/2+60° |
| EP0470817A3 (en) * | 1990-08-09 | 1992-11-25 | Seiko Epson Corporation | Liquid crystal electro-optical device |
| JPH06289382A (en) * | 1993-03-30 | 1994-10-18 | Hitachi Ltd | Liquid crystal display device |
| US5907378A (en) * | 1993-12-15 | 1999-05-25 | Ois Optical Imaging Systems, Inc. | Normally white twisted nematic liquid crystal display including retardation films for improving viewing characteristics |
| US5753937A (en) * | 1994-05-31 | 1998-05-19 | Casio Computer Co., Ltd. | Color liquid crystal display device having a semitransparent layer on the inner surface of one of the substrates |
| US5694189A (en) * | 1994-07-29 | 1997-12-02 | Kabushiki Kaisha Toshiba | Reflection type liquid crystal display having inclined pixel electrodes |
| US5737047A (en) * | 1995-03-27 | 1998-04-07 | Casio Computer Co., Ltd. | Color liquid crystal display device with optical axes of retardation polarization plates set in an opposite direction of twist direction of LC molecules |
| US5659408A (en) * | 1995-05-24 | 1997-08-19 | Polaroid Corporation | Reflective image-providing display viewed with holographically diffused ambient light |
| US5933207A (en) * | 1995-10-23 | 1999-08-03 | Hughes Electronics Corporation | Reflective-type liquid crystal displays using mixed-mode twist nematic cells |
| JPH09138396A (en) * | 1995-11-14 | 1997-05-27 | Toppan Printing Co Ltd | Reflection type liquid crystal display device |
| JPH09292504A (en) * | 1996-02-27 | 1997-11-11 | Sharp Corp | Reflection plate and its manufacture as well as reflection type liquid crystal display device formed by using this reflection plate |
| JP3412426B2 (en) * | 1996-11-15 | 2003-06-03 | 凸版印刷株式会社 | Holographic reflector and reflective liquid crystal display using the same |
| JP3291432B2 (en) * | 1996-06-11 | 2002-06-10 | シャープ株式会社 | Liquid crystal display device and terminal device using the same |
| US5714247A (en) * | 1996-06-14 | 1998-02-03 | Industrial Technology Research Institute | Reflective surface for LCD and method for forming it |
| JP3722920B2 (en) * | 1996-08-27 | 2005-11-30 | 株式会社リコー | Plastic film liquid crystal display element |
| US6025894A (en) * | 1996-09-04 | 2000-02-15 | Casio Computer Co., Ltd. | Scatter control member for organic electroluminescent light source for passing light with or without scattering depending upon an incident angle |
| US6141070A (en) * | 1997-06-13 | 2000-10-31 | Citizen Watch Co., Ltd. | Normally black liquid crystal display with twisted compensator and . .DELTAnd of 1500-1800 nm |
| US5940155A (en) * | 1997-09-04 | 1999-08-17 | International Business Machines Corporation | Liquid crystal displays containing tilted optical axis compensation films having a negative birefringence |
| JP3376308B2 (en) * | 1998-03-16 | 2003-02-10 | 株式会社東芝 | Reflector and liquid crystal display |
| US6181394B1 (en) * | 1999-01-22 | 2001-01-30 | White Electronic Designs, Corp. | Super bright low reflection liquid crystal display |
-
1999
- 1999-08-12 GB GBGB9919094.4A patent/GB9919094D0/en not_active Ceased
-
2000
- 2000-08-10 IL IL13780100A patent/IL137801A0/en unknown
- 2000-08-11 CA CA002315494A patent/CA2315494A1/en not_active Abandoned
- 2000-08-11 MX MXPA00007847A patent/MXPA00007847A/en unknown
- 2000-08-11 JP JP2000244754A patent/JP2001108985A/en active Pending
- 2000-08-11 SG SG200004426A patent/SG97914A1/en unknown
- 2000-08-11 BR BR0006757-1A patent/BR0006757A/en not_active Application Discontinuation
- 2000-08-11 US US09/637,983 patent/US6532051B1/en not_active Expired - Fee Related
- 2000-08-11 EP EP00306904A patent/EP1081532A3/en not_active Ceased
- 2000-08-12 KR KR1020000046780A patent/KR20010021287A/en not_active Application Discontinuation
- 2000-08-14 CN CNB001212885A patent/CN1160685C/en not_active Expired - Fee Related
- 2000-10-09 TW TW089121068A patent/TW581889B/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| CN1160685C (en) | 2004-08-04 |
| SG97914A1 (en) | 2003-08-20 |
| TW581889B (en) | 2004-04-01 |
| IL137801A0 (en) | 2001-10-31 |
| JP2001108985A (en) | 2001-04-20 |
| GB9919094D0 (en) | 1999-10-13 |
| CN1284705A (en) | 2001-02-21 |
| EP1081532A2 (en) | 2001-03-07 |
| KR20010021287A (en) | 2001-03-15 |
| US6532051B1 (en) | 2003-03-11 |
| MXPA00007847A (en) | 2004-11-10 |
| BR0006757A (en) | 2002-12-31 |
| EP1081532A3 (en) | 2004-01-02 |
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Legal Events
| Date | Code | Title | Description |
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| FZDE | Discontinued |