(12) United States Patent
`Harrold et al.
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`US 6,184,951 B1
`Feb. 6, 2001
`
`US006184951B1
`
`(54) LIQUID CRYSTAL DISPLAY WHEREIN
`EACH PIXELS OF FIRST LAYER [5
`OPTICALLY ALIGNED WITH RESPECTIVE
`GROUP OF PIXELS 0F SECOND LAYER
`
`5,243,451 * 9/1993 Kanemoto et a1. .................. .. 349/75
`5,264,952 * 11/1993 Fukutani et a1.
`349/78
`-
`*
`£91??? ett a11-
`8/1994 Yamada et a1. ..
`
`0s 1 a e a. ..
`
`......... ..
`
`252/29901
`
`,
`
`,
`
`5,342,545
`
`
`
`(75) Inventors: Jonathan Harrold, Oxford; Martin David Tillin, Oxfordshire, both of (GB)
`
`’
`
`’
`
`i
`
`
`
`ga::;)\1;2§;1'al'"' g ' """"""""" "
`
`""""" "
`
`
`
`(73) Assignee: Sharp Kabushiki Kaisha, Osaka (JP)
`
`(*) Notice:
`
`Under 35 U.S.C. 154(b), the term of this
`patent shall be extended for 0 days.
`
`FOREIGN PATENT DOCUMENTS
`
`0430591
`0509727
`
`6/1991 (EP) .
`10/1992 (EP) '
`OTHER PUBLICATIONS
`
`(21) Appl, No; 08/622,759
`_
`(22) F1led:
`
`Mar. 27, 1996
`
`Scheffer et al, “Liquid Crystals—Applications and Uses,”
`vol. 1, pp. 269—270, 1990, 10.3.6.4 Substractive Color STN
`Displays_
`
`(30)
`
`Foreign Application Priority Data
`
`* Cited by examiner
`
`Mar. 30, 1995
`7
`Int. Cl- ..................... ..
`
`(GB) ................................................ .. 9506561
`
`GOZF 1/1335
`(52) US. Cl. ............................... .. 349/74; 349/75; 349/78;
`349/86; 349/117
`(58) Field of Search .............................. .. 349/74, 86, 117,
`349/77> 75> 78
`
`(56)
`
`_
`References Clted
`U_S_ PATENT DOCUMENTS
`_
`476107507 * 9/1986 Kfimfimon ct a1~ ~~~~~~~~~~~~~~~~ ~~ 350/335
`4’842’379
`6/1989 Olshl et a1‘ """"" "
`" 349/74
`5,090,794 * 2/1992 Hatano et al.
`359/53
`5,124,818
`6/1992 Conner et a1.
`359/53
`5,150,237 * 9/1992 Iimura et al.
`349/75
`5,194,973 * 3/1993 Isogai et a1. ......................... .. 349/74
`
`ABSTRACT
`
`_
`_
`_
`_
`_
`Primary Exammer—W1ll1arn L. S1kes
`Assistant Examiner_Tarifur
`Chowdhury
`(74) Attorney, Agent, or Firm—Renner, Otto, Boisselle &
`Sklar LLP
`5
`( 7)
`Acolor display includes a ?rst layer of pixels, each of Which
`has an independently controllable light attenuation so as to
`control the display intensity of each display pixel indepen
`dently. A second layer of pixels is provided in Which the
`color of each p1xel can be 1ndependently controlled. Thus,
`each effective display pixel can be controlled, independently
`of the other pixels, With respect to its intensity and chromi
`nance
`'
`
`31 Claims, 13 Drawing Sheets
`
`Patent Owner’s Exhibit 2004
`IPR2015-00021
`Page 1 of 19
`
`

`

`U.S. Patent
`
`Feb. 6, 2001
`
`Sheet 1 0f 13
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`US 6,184,951 B1
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`IPR2015-00021
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`

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`U.S. Patent
`US. Patent
`
`Feb. 6, 2001
`Feb. 6, 2001
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`Sheet 2 0f 13
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`Patent Owner’s Exhibit 2004
`IPR2015-00021
`Page 3 of 19
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`

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`US. Patent
`
`Feb. 6, 2001
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`Page 4 of 19
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`Patent Owner’s Exhibit 2004
`IPR2015-00021
`Page 4 of 19
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`

`

`U.S. Patent
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`Feb. 6, 2001
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`Patent Owner’s Exhibit 2004
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`US. Patent
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`Feb. 6, 2001
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`Patent Owner’s Exhibit 2004
`IPR2015-00021
`Page 6 of 19
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`US 6,184,951 B1
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`U.S. Patent
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`Feb. 6, 2001
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`US 6,184,951 B1
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`Patent Owner’s Exhibit 2004
`IPR2015-00021
`Page 8 of 19
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`

`

`U.S. Patent
`
`Feb. 6, 2001
`
`Sheet 8 0f 13
`
`US 6,184,951 B1
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`Refardance
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`IPR2015-00021
`Page 9 of 19
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`

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`Sheet 9 0f 13
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`Feb. 6, 2001
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`Patent Owner’s Exhibit 2004
`IPR2015-00021
`Page 10 of 19
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`

`

`U.S. Patent
`
`Feb. 6, 2001
`
`Sheet 10 0f 13
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`US 6,184,951 B1
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`Rehardance
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`Patent Owner’s Exhibit 2004
`IPR2015-00021
`Page 11 of 19
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`

`

`U.S. Patent
`
`Feb. 6, 2001
`
`Sheet 11 0f 13
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`US 6,184,951 B1
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`Patent Owner’s Exhibit 2004
`IPR2015-00021
`Page 12 of 19
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`

`

`U.S. Patent
`
`Feb. 6, 2001
`
`Sheet 12 0f 13
`
`US 6,184,951 B1
`
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`Patent Owner’s Exhibit 2004
`IPR2015-00021
`Page 13 of 19
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`

`

`Feb. 6, 2001
`
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`US 6,184,951 B1
`
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`Patent Owner’s Exhibit 2004
`IPR2015-00021
`Page 14 of 19
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`

`

`US 6,184,951 B1
`
`1
`LIQUID CRYSTAL DISPLAY WHEREIN
`EACH PIXELS OF FIRST LAYER IS
`OPTICALLY ALIGNED WITH RESPECTIVE
`GROUP OF PIXELS OF SECOND LAYER
`
`The present invention relates to a display. Such a display
`may, for instance, be used as a high resolution re?ective
`colour display for “personal digital assistant” (PDA) appli
`cations and for high light ef?ciency projection displays.
`A knoWn type of display uses polymer dispersed liquid
`crystals (PDLCs) Which are sWitchable betWeen a clear and
`a light scattering state. No polariser is necessary for such
`displays so that, by placing a 100% absorber beneath them,
`a good approximation to black print-on-paper contrast and
`brightness can be produced. The electro-optic response
`curve of knoWn PDLC materials requires the use of active
`matrix addressing in order to provide an “XY panel”.
`Although it is possible to adapt such displays for pro
`viding a colour display, the resulting display has disadvan
`tages. For instance, by providing cyan, magenta, and yelloW
`colour absorbers under the PDLC, a maximum absorption of
`only 33% is obtained. This results in the maximum black
`level Which can be displayed being a relatively bright grey.
`Using red, green, and blue absorbers under the PDLC gives
`a 66% maximum absorption resulting in an unsatisfactorily
`loW contrast ratio in re?ected light, particularly When back
`scatter from the PDLC is included.
`A further disadvantage of PDLC displays is that the fully
`clear state is oily realised for on-axis vieWing, Whereas it is
`desirable for high contrast to be provided over a substantial
`vieWing angle. This is caused by the anisotropic liquid
`crystal being dispersed in an isotropic polymer. Although
`this problem can be largely overcome by dispersing the
`liquid crystal in a liquid crystal polymer having similar
`anisotropy, the anisotropies of the materials have to be
`matched in planes both perpendicular and parallel to the
`display cell, for instance by initially poling the structure by
`a high electric ?eld. This adds to the cost and complexity of
`manufacturing such displays.
`EP-A-0509727 discloses a liquid crystal display of the
`re?ection type in Which one layer is pixellated and controls
`light attenuation and another layer comprises three electri
`cally controllable colour, unpixellated colour ?lters disposed
`optically in series. Colour images are obtained by time
`division multiplexing such that each ?lter can be activated in
`turn.
`US. Pat. No. 4,842,379 disclosed image recording appa
`ratus utilising a liquid crystal shutter array. The shutter has
`a pixellated layer for controlling light attenuation and an
`electrically controllable, unpixellated birefringent layer for
`controlling colour. The shutter Works in time multiplexed
`mode to enable different colours to be passed in turn.
`The above-described multiplexing systems have the dis
`advantage of needing a liquid crystal device capable of
`being addressed and responding at multiple video-frame
`rate. This is not required in the present invention
`According to the invention, there is provided a display
`comprising a ?rst layer of pixels, each of Which has an
`independently controllable light attenuation, and a second
`layer of pixels, each of Which provides an independently
`controllable colour.
`Preferred embodiments of the invention are de?ned in
`the other appended claims.
`The present invention makes it possible to provide a
`display having a tWo layer pixel structure in Which the ?rst
`layer of display pixels controls the light intensity of each
`image pixel (i.e. the pixel perceived by the vieWer) and the
`
`10
`
`15
`
`25
`
`35
`
`45
`
`55
`
`65
`
`2
`second layer of display pixels controls the chrominance of
`each image pixel. Such a display is capable of providing a
`good range of colours While improving the resolution by a
`factor of three compared With knoWn RGB displays in Which
`three display pixels are required for colouring each image
`pixel. Also, the effective brightness of the display can be
`increased because each display pixel of the second layer can
`be made to display the required colour. Such displays may
`be used as transmissive or re?ective displays and an appro
`priate technologies may be used to embody the tWo layers so
`as to provide pixellated intensity control and pixellated
`chrominance control.
`For chrominance control technologies Which do not
`provide the full required colour palette, tWo or more display
`pixels of the second layer may be allocated to each image
`pixel so as to extend the perceived colour palette by visual
`integration of the colours produced by the tWo display
`pixels. Although this reduces the resolution, nevertheless the
`resolution is still greater than for knoWn RGB displays. Only
`those parts of the display Which are required to display such
`colours need to be controlled in this Way, the remaining parts
`of the display having a single display pixel in the second
`layer corresponding to each image pixel.
`Alternatively, Where loWer resolution is required, the
`display pixels may be made larger. This provides enhanced
`brightness and contrast compared With knoWn displays and
`relaxes manufacturing requirements so as to improve manu
`facturing yield and/or reduce manufacturing cost.
`In order to obtain a desired colour in HLS (hue, lightness,
`saturation) colour space, different components may be pro
`vided in different Ways in re?ective and transmissive
`embodiments of the display. In transmissive embodiments,
`hue is de?ned by the second layer, lightness is de?ned by the
`?rst layer, and saturation is de?ned by controlling an adja
`cent pixel to be White or grey. In re?ective embodiments,
`hue is de?ned by the second layer, lightness is de?ned by
`controlling an adjacent pixel to be black or grey, and
`saturation is de?ned by the ?rst layer.
`The invention Will be further described, by Way of
`example, With reference to the accompanying draWings, in
`Which:
`FIG. 1 is a cross-sectional vieW of a display constituting
`a ?rst embodiment of the invention;
`FIG. 2a is a cross-sectional vieW shoWing part of the
`display of FIG. 1 in more detail;
`FIGS. 2b and 2c are vieWs similar to FIG. 2a but
`respectively illustrating tWo possible modi?cations;
`FIG. 3 shoWs related graphs of retardance against voltage
`and transmission against Wavelength for a J's-cell of the
`display of FIG. 1;
`FIG. 4 is a cross-sectional vieW shoWing part of a display
`constituting a second embodiment of the invention;
`FIG. 5 is a cross-sectional vieW of a display constituting
`a third embodiment of the invention;
`FIG. 6 is a cross-sectional vieW shoWing part of the
`display of FIG. 5 in more detail;
`FIG. 7 shoWs related graphs of retardance against voltage
`and transmission against Wavelength for a J's-cell of the
`display of FIG. 5;
`FIG. 8 is a cross-sectional vieW of a display constituting
`a fourth embodiment of the invention;
`FIG. 9 shoWs related graphs of retardance against voltage
`and transmission against Wavelength for a J's-cell of the
`display of FIG. 8;
`FIG. 10 is a cross-sectional vieW of a display constituting
`a ?fth embodiment of the invention;
`FIG. 11 shoWs related graphs of retardance against
`voltage and transmission against Wavelength for a J's-cell of
`the display of FIG. 10;
`
`Patent Owner’s Exhibit 2004
`IPR2015-00021
`Page 15 of 19
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`

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`US 6,184,951 B1
`
`10
`
`15
`
`25
`
`35
`
`3
`FIG. 12 is a cross-sectional vieW of a display constituting
`a sixth embodiment of the invention; and
`FIG. 13 is a cross-section vieW of a display constituting
`a seventh embodiment of the invention.
`FIG. 1 shoWs a transmissive display in the form of an XY
`panel comprising a rectangular array of picture elements
`Which are independently addressable and controllable in XY
`directions. The display comprises a pixellated variable
`intensity layer 1 formed by a tWisted nematic liquid crystal
`layer With electrodes de?ning the XY pixellation. Avariable
`chrominance layer 2 is similarly pixellated so that the pixels
`of the layers 1 and 2 are optically aligned perpendicular to
`the display surface and are adjacent to each other so as to
`reduce cross-talk betWeen non-aligned pixels. The spacing
`of the layers 1 and 2 is minimised so as to avoid or minimise
`cross-talk. The variable chrominance layer 2 is embodied by
`(a) a voltage-tunable re?ector so that each pixel of layer 2 is
`a voltage-tunable colour-selective re?ector, or (b) an elec
`trochromic cell, or (c) a variable retardation cell. Such cell
`(c) may be an electrically controlled birefringence (ECB)
`cell or a J's-cell. In the folloWing description, the chromi
`nance layer 2 is embodied by a J's-cell.
`The layer 1 is disposed betWeen polarisers 3 and 4 Whose
`polarisations are such that the tWisted nematic liquid crystal
`of the layer 1 has a variable attenuation to light passing
`through the display. Afurther polariser 5 cooperates With the
`layer 2 and the polariser 4 to provide variable retardance to
`light passing through the display so as to control the chromi
`nance or hue transmitted by each pixel of the layer 2. In the
`case Where the layer 2 is a voltage-tunable re?ector, the
`polariser 5 is omitted.
`As is knoWn and, for instance, disclosed in EP-A
`0616240 and GB-A-2286056, n-cells exhibit a retardance
`Which is dependent on the electric ?led applies across the
`cell.
`FIG. 2a is an enlarged vieW of part of the display shoWn
`in FIG. 1 and illustrates tWo pixels of the display. The
`display comprises a ?rst transparent substrate 10 of glass or
`clear plastic Which, in it sloWer surface as shoWn in FIG. 2a,
`carries the polariser 5. The upper surface of the substrate 10
`carries a common transparent electrode 11, for instance of
`indium tin oxide (ITO). The electrode 11 has formed on its
`upper surface an alignment layer 12. The alignment layer 12
`is separated from a further alignment layer 13 by a liquid
`crystal material 14, for instance of the type knoWn as E7
`made by Merck. The alignment layers 12 and 13 have
`parallel alignment directions pointing in the same direction
`so as to form the J's-cell structure illustrated in the draWing.
`The display has a middle plate 15 Which acts as a
`substrate for an active matrix addressing arrangement
`including thin ?lm transistors 16, pixel electrodes 17, and
`conductive connections. The thin ?lm transistor circuitry is
`provided on the upper and loWer surfaces of the plate 15 and
`is interconnected via suitable conductive tracks and connec
`tions to the electrodes 17. The pixel electrodes 17 are made
`of transparent material such as ITO.
`In FIG. 2a, the plate 15 is shoWn as including the
`polariser 4, and a polariser protection layer 6 is provided
`betWeen the polariser 4 and the parts 13, 16, and 17. The
`polariser 4 may be located on the loWer surface of the plate
`15 as shoWn in FIG. 2a, or it may be located on the upper
`surface of the plate 15. In either case, it is disposed optically
`betWeen the layers 1 and 2.
`The plate 15 carries an alignment layer 19 in contact With
`a tWisted nematic liquid crystal 20. A further transparent
`substrate 21 carries a common transparent electrode 22 and
`an alignment layer 23 With the liquid crystal 20 being
`
`45
`
`55
`
`65
`
`4
`disposed betWeen the alignment layers 19 and 23. The
`substrate 21 carries the polariser 3 on its upper surface.
`The polarisers 4 and 5 are aligned such that their pola
`rising directions are substantially at 45° to the pretilt angles
`of the molecules of the liquid crystal 14 at the alignment
`layers 12 and 13 (the alignment directions). The polarising
`directions of the polarisers 4 and 5 may be parallel or
`perpendicular to each other.
`In an alternative arrangement as shoWn in FIG. 2b, the
`polariser protection layer 6 is omitted as it is not required.
`The transistors 16 are located on only one surface of the
`plate 15 and control the aligned electrodes 17 by means of
`conductors Which pass through the plate 15 from one side to
`the other.
`In a further arrangement as shoWn in FIG. 2c, a respec
`tive active matrix addressing system including thin ?lm
`transistors 16, pixel electrodes 17 and conductive connec
`tions is disposed on the inner face of each of the substrates
`10 and 21, Whilst the other electrodes 11 and 22 are located
`on opposite sides of the middle plate 15. This enables the
`internal layer structure de?ned by middle plate 15, other
`electrodes 11 and 22, and alignment layers 13 and 19 to be
`made very thin in order to reduce further, or eliminate,
`cross-talk betWeen the layers 1 and 2.
`In a modi?cation of any of the arrangements of FIGS. 2a
`to 2c, at least one of the thin ?lm transistor (TFT) active
`addressing arrangements is replaced by a thin ?lm diode
`arrangement. In a further modi?cation, the active matrix
`addressing system for the pixels of one or both of the layers
`1 and 2 is replaced by a passive matrix addressing system
`Wherein roW electrodes and column electrodes are provided
`on opposite sides of the layer or the respective layer. The
`arrangement of FIG. 2c may be employed Where at least one
`of the addressing systems is of the active matrix type.
`Adriving circuit 50 is provided for the matrix addressing
`arrangement and electrodes 11 and 22. The display is back
`lit by light source 52. These are only schematically shoWn in
`FIG. 2a.
`In use, the pixel electrodes 17 associated With the liquid
`crystal layer 14 serve to de?ne pixels in the latter, the lateral
`extent of each pixel being de?ned by the pixel electrode 17.
`The voltage across each such pixel enables the optical
`retardance of the respective portion of the liquid crystal 14
`to be varied so that the Wavelength at Which m)»/2 retarda
`tion (Were m is an integer) occurs can be tuned across the
`visible spectrum and beyond. When the polarising directions
`of the polarisers 4 and 5 are mutually perpendicular, this
`results in a transmitted colour Which is voltage-tunable. The
`value of the integer m de?nes the mode of operation of the
`J's-cell. For instance, When the m=2 mode is used to obtain
`a variable colour, the same thickness of cell can be operated
`at a loWer order With appropriate drive voltage to produce
`differently saturated colours.
`The variable intensity layer 1 is operated in the conven
`tional manner but shares the polariser 4 With the chromi
`nance layer 2.
`By appropriately selecting the thickness of the liquid
`crystal layer 14 and the drive voltage range for the pixels of
`the layer 2, the liquid crystal layer 14 is capable of producing
`a range of relatively saturated colours so that the colour of
`each pixel of the display is controllable. The presence of the
`polarisers in the display reduces the overall light throughput
`ef?ciency to less than 50%. HoWever, because there are not
`?xed colour ?lters as are used in conventional displays, for
`instance of the RGB type, there is not further reduction in
`ef?ciency. Thus, the present display can be up to three times
`brighter than the knoWn types of RGB displays With the
`
`Patent Owner’s Exhibit 2004
`IPR2015-00021
`Page 16 of 19
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`US 6,184,951 B1
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`5
`same backlight. The present display can provide the same
`resolution for tWo thirds of the number of display pixels
`required in a conventional RGB display, the display pixels
`being distributed in the tWo layers 1 and 2. Thus, the same
`display resolution can be provided using layers 1 and 2
`having one third of the resolution required for RGB displays.
`Although it is possible to produce a display Which is
`capable of a large colour range, the colours produced by the
`display have ?xed saturation. This is suf?cient for many
`applications of the display, for instance for displaying text
`and many graphics. This is illustrated in FIG. 3 Which shoWs
`tWo related graphs. The upper graph illustrates retardance
`against the drive voltage across the J's-cell With the voltages
`corresponding to the colours of the spectrum being indicated
`by “ROYGBIV”. Retardances corresponding to an integer
`multiple of half a Wavelength of red, green, and blue light
`are indicated on the vertical axis. The loWer graph illustrates
`in continuous lines the transmission of the J's-cell against
`Wavelength for a typical drive voltage corresponding to the
`absorption of the indigo Wavelength region for the m=2
`mode of operation. The dashed line indicates the transmis
`sion characteristic for a different drive voltage correspond
`ing to a different order m of operation of the J's-cell.
`FIG. 3 also illustrates operation of the J's-cell to produce
`a “White colour”. In this case, the retardance of the J's-cell
`approaches Zero so that the effective pass band of the J's-cell
`covers the Whole of the visible spectrum, When polarisers 4
`and 5 are parallel.
`The range of colours Which the display shoWn in FIGS.
`1, 2a, 2b and 2c can provide can be extended by altering the
`effective saturation of the colours produced by the display.
`FIG. 4 shoWs a modi?ed type of display Which differs from
`that shoWn in FIG. 2a in that a ?xed optical retarder 30 is
`provided Within the J's-cell betWeen the polariser 5 and the
`substrate 10. By including such a ?xed retarder having the
`appropriate retardation, the retardation across the J's-cell can
`be reduced to Zero for an appropriate voltage drive level.
`This permits each pixel to produce a good “black” When the
`polarising directions of the polarisers 4 and 5 are mutually
`perpendicular or a good “White” When the polarisation
`directions of the polarisers 4 and 5 are parallel. This provides
`a high brightness high resolution monochrome or “black and
`White” mode of operation. HoWever, by combining a White
`pixel With a ?xed saturation colour pixel, it is possible to
`provide a full colour display. In particular, adjacent colours
`are “integrated” by the vision of the vieWer in the same Way
`that RGB pixels are integrated in knoWn types of displays.
`By operating the display in this mode, a range of colours
`sufficient for displaying photographic or video images is
`provided. By using a suitable display controller, both modes
`of operation may be present in different parts of the display.
`FIG. 5 shoWs a re?ective display Which differs from the
`display shoWn in FIG. 1 in that a polarisation preserving
`re?ector or mirror 32 is located behind the layer 2 and the
`polariser 5, Whereas the polariser 3 is omitted. This is shoWn
`in more detail in FIG. 6. Also, the layer 1 is modi?ed by
`replacing the tWisted nematic liquid crystal 20 With a liquid
`crystal/polymer composite 33, for instance so as to provide
`a PDLC type of structure. The ?xed retarder 30 is optional
`but is shoWn as being present in FIG. 6. The polarisation
`directions of the polarisers 4 and 5 are mutually perpen
`dicular.
`When the PDLC is in its scattering state, it appears
`“paper White” Whereas, When sWitched to its clear state, the
`PDLC alloWs the absorbing J's-cell structure to be visible.
`The variable retardation J's-cell uses high quality polarisers
`so that a good black can be produced at every pixel. The
`
`10
`
`15
`
`25
`
`35
`
`45
`
`55
`
`65
`
`6
`presence of the ?xed retarder 30 alloWs the J's-cell to be
`capable of Zero retardance so as to produce a good black.
`The use of the polarisation preserving re?ector 32 alloWs the
`polariser 5 to be omitted, Which reduces the display contrast
`but increases the display brightness compared With the
`presence of the crossed polarisers 4 and 5. As described
`above for the transmissive display, the appropriate selection
`of the operating order of the variable retarder cell operating
`mode alloWs a range of ?xed saturation colours to be
`produced Which includes black, White, red, green, blue, and
`yelloW as illustrated in FIG. 7, Which corresponds to FIG. 3.
`It is thus possible to provide a high brightness re?ective
`display Which can effectively simulate black and a number
`of coloured pens on White paper. Such an arrangement
`makes full use of the resolution of the display pixels and
`permits excellent quality text and graphics to be displayed.
`As shoWn in FIG. 7 and as in the case of the transmissive
`display described hereinbefore, the display is capable of
`producing a good range of ?xed saturation colours. By
`combining “grey scale” partially-sWitched scattering of the
`PDLC, the underlying colour transmitted by the liquid
`crystal in layer 2 can be partially mixed With the incoming
`“White” light so that the saturation of the colours produced
`by the liquid crystals in layer 2 can be reduced. Again, as
`described for the transmissive display, by sacri?cing spatial
`resolution in order to mix or integrate the colours of adjacent
`pixels, a full colour display capable of displaying photo
`graphic or bit-map images may be provided. Thus, colour
`quality can be sacri?ced for spatial resolution and vice versa
`in accordance With the images being displayed over all or
`part of the display.
`FIGS. 8 and 9 correspond to FIGS. 5 and 7, respectively,
`and illustrate an alternative re?ective mode in Which the
`polariser 5 is omitted. This mode of operation gives higher
`brightness colours but poorer contrast than the mode of
`operation illustrated in FIGS. 5 to 7.
`FIGS. 10 and 11 correspond to FIGS. 8 and 9,
`respectively, but shoW a modi?ed form of re?ective display.
`In particular, the display of FIG. 10 differs from that shoWn
`in FIG. 8 in that all of the polarisers are omitted and the
`PDLC in the layer 1 is replaced by untWisted guest-host
`liquid crystals (GHLC). In GHLC, a dichroic dye guest is
`added to the liquid crystal host and the orientation of the
`liquid crystal determines the orientation of the guest dye
`molecules. In the unselected state, the GHLC acts as a
`polariser for the chrominance layer 2. This gives operation
`equivalent to the parallel polariser con?guration using a
`polarisation preserving re?ector as illustrated in FIG. 8.
`In the selected state, the GHLC does not polarise the
`incoming light and a high brightness (White) re?ected light
`display is provided. BetWeen these tWo states, a continuous
`grey scale is available from the GHLC, thus giving a
`variable saturation to the underlying J's-cell hue.
`This display has the advantage that a high brightness
`White can be achieved. In order to ensure a good black state
`and a high brightness select state, the GHLC should contain
`a dye With order parameter above 0.6 and preferably above
`0.8. Using a GHLC With alignment of the liquid crystal
`director parallel to the substrate gives the best polarisation of
`incident light, Whereas using a GHLC With a tilted homeo
`tropic alignment and negative dielectric anisotropy liquid
`crystal gives the brightest display at the expense of polari
`sation ef?ciency and hence at the expense of darkness of the
`black state (display contrast).
`In order to increase on-axis brightness of the display at
`the expense of off-axis vieWing angle, Brightness Enhancing
`?lm (BEF) of the type manufactured by 3M Company, or a
`
`Patent Owner’s Exhibit 2004
`IPR2015-00021
`Page 17 of 19
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`

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`US 6,184,951 B1
`
`7
`similar optical element, may be used With any of the
`embodiments described hereinbefore. BEF is particularly
`effective in the display using PDLC shoWn in FIG. 8, Where
`it re?ects a signi?cant portion of the high-angle forWard
`scattered light. This also reduces the off-axis haZe effect as
`described hereinbefore.
`FIG. 12 shoWs an alternative embodiment Wherein each
`piXel of the variable intensity layer 1 is optically aligned
`With a group of, in this case three, piXels of the variable
`chrominance layer 2 in the illustrated piXel roW and,
`possibly, With one or more piXels in an adjacent roW or roWs
`(not shoWn).
`FIG. 13 shoWs a further alternative embodiment Where
`each piXel of the variable chrominance layer 2 is optically
`aligned With a group of, in this case tWo, piXels of the
`variable intensity layer 1 in the illustrated piXel roW and,
`possibly, With one or more piXels in an adjacent roW or roWs
`(not shoWn).
`What is claimed is:
`1. A display comprising a ?rst layer of piXels, each of
`Which has an independently controllable light attenuation,
`and a second layer of pixels, each of Which provides an
`independently controllable color, Wherein each of the piXels
`of the ?rst layer is optically aligned With a respective group
`of piXels of the second layer.
`2. A display as claimed in claim 1, Wherein each of the
`piXels of the second layer is controllable to produce any
`selected one of a plurality of hues.
`3. A display as claimed in claim 1, Wherein the piXels of
`the second layer comprise a plurality of sets, each of Which
`comprises at least tWo piXels, there being provided means
`for controlling the piXels of each of the plurality of sets to
`produce at least tWo different colors for integration by an
`observer to perceive a further different color.
`4. A display as claimed in claim 1, Wherein each of the
`piXels of the second layer has a variable optical retardation.
`5. A display as claimed in claim 4, Wherein the piXels of
`the second layer are de?ned in a liquid crystal layer.
`6. A display as claimed in claim 5, Wherein the liquid
`crystal layer forms a part of a J's-cell or an electrically
`controlled birefringence cell.
`7. Adisplay as claimed in claim 4, Wherein a ?Xed optical
`retarder is provided in series With the second layer.
`8. A display as claimed in claim 1, Wherein the piXels of
`the ?rst layer are de?ned in a liquid crystal layer.
`9. A display as claimed in claim 1, further comprising a
`transparent plate betWeen the ?rst layer and the second layer,
`Wherein the transparent plate acts as a substrate for an
`addressing system including respective transparent elec
`trodes for the piXels of the ?rst layer and the second layer.
`10. A display as claimed in claim 1, further comprising:
`a transparent plate betWeen the ?rst layer and the second
`layer, the transparent plate acting as a substrate for
`respective transparent electrodes for the ?rst layer and
`the second layer;
`a ?rst substrate disposed on the opposite side of th