IVI LLC EXHIBIT 2010
`XILINX V. IVI LLC
`IPR Case 2013-00029
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`US. Patent
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`Nov. 8, 2011
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`Sheet 1 0111
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`US 8,054,535 I32
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`US. Patent
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`Nov. 8, 2011
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`US 8,054,535 32
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`US. Patent
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`Nov. 8, 2011
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`US. Patent
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`Nov. 8, 2011
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`US. Patent
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`Nov. 8, 2011
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`US. Patent
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`Nov. 8, 2011
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`Sheet 10 ofl]
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`US 8,054,535 32
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`US. Patent
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`Nov. 8, 2011
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`Sheet 11 0111
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`1
`ELEC TRO PI-IORETIC.‘ DISPLAY DEV ICE
`
`2
`SUMMARY OF THE INVENTION
`
`US 8,054,535 B2
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`The present invention relates to an electrophoretic display
`device.
`
`lilectrophoretic display devices typically comprise a pair
`of opposed substrates provided with transparent electrode
`patterns on their inner surfaces. Sandwiched between the
`substrates is a non—conductive liquid in which is dispersed
`highly scattering or absorbing micropartielcs. The micropar-
`ticles beComc electrically charged. and can be reversibly
`attracted to the top or lower surface of the display by appli-
`cation o f a suitable electrical field across the electrode struc-
`tures. The optical contrast
`is achieved by contrasting of
`colours of the microparticles with dye doped liquids or by
`contrasting colours of oppositely charged dual
`tuicropar—
`ticles. suspended in a transparent liquid. A problem with such
`displays is that they lack threshold. i.e. the particles begin to
`move at a low voltage. and move faster as a higher voltage is
`applied. This makes the technology unsuitable for passive
`tuatrix addressing which require a relatively sharp threshold
`to reduce crosstalk.
`
`Conventional electrophoretic displays also are typically
`slow to switch. making them unsuitable for applications
`requiring t'ast switching. such as video displays.
`In US 200510094087. which is owned by the present
`assignee and the contents of which are hereby incorporated
`by reference in their entirely. a bistable electrophoretic liquid
`crystal display is described. which allows switching with
`threshold and video rate. This uses overlapping transparent
`row-colunm electrodes on separate substrates which enable
`matrix addreSsing.
`Conventional etectrophoretic displays are configured with
`the opposing electrodes being arranged vertically with one
`being an upper electrode and one being a lower electrode with
`respect to the display surface of the display device. In such
`displays. with vertical particle motion between the elec—
`trodes. the pixel is defined by the area of transparent elec—
`trodes. via which all electric field is applied to the pixel.
`‘l‘ransparent electrodes attenuate transmitted light. which
`limits the peak brightness of the display. The transparent
`electrodes also have high resistivity. which can limit the size
`of a simple passively addressed display. The brightness of
`electrophoretic displays can be improved by the use of in—
`plane electrodes. for example provided by two strip elec-
`trodes on the same substrate. between which the pigments
`move horizontally under an applied electric lield. In such
`construction the liquid medium is transparent. without a dye.
`and provides a good stability o f the mixture with suspended
`pigments. US 20030275933 describes such an electro—
`phoretic device. which has a substrate with in—plane elec—
`trodes and an opposite substrate which is li'ee of electrodes.
`Simple passive matrix addressing is dillicult to achieve for a
`device o f this construction.
`
`U .8. Pat. No. 4.648.056 describes alt electrophoretic dis-
`play in which one substrate has single pixel transparent dis-
`play electrodes and the opposite substrate has strip collecting
`electrodes. Under an applied voltage the pigments cover the
`whole pixel area with transparent single display electrodes
`and the dev ice is in art 01’1" state. Applying a suitable different
`voltage causes collection of the pigments on the strip collect-
`ing electrodes on the opposite side in such a manner that the
`spacing between the strip electrodes is transparent. The light
`passes through the pixel. and accordingly this determines the
`device‘s ON state.
`
`The transparent conductive layer of the display pixels
`reduces transmittance of the display and the resistivity limits
`passive matrix addressing of large area displays.
`
`Aspects ol‘the invention are specified in the independent
`claims. Preferred features are specified in the dependent
`claims.
`The invention provides an electrophoretic display device
`which is multi-stable and which has a threshold voltage. A
`bistable device is the simplest example of a nutlti—stable
`device. Ilte principles described in the present specification
`can be applied to both bistable and multi-stable display
`devices.
`
`1U
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`The device may be driven by a simple passive matrix
`scheme. The metal electrodes maybe in the forth of fine wires
`which provide adequate conductivity for large areas displays
`and which occupy little area. providing high light transitiit—
`tance. The liquid crystal with suspended pigments allows
`mnlti-stable switching with threshold. which gives a possi-
`bility o i‘ passive matrix addressing.
`111 one embodiment the display is suitable for operation in
`a transmissive tnode. with transparent colour pigments. This
`gives a possibility o f building a full colour display. by stack-
`ing 2 or 3 display layers with suitable transparent colour
`pigments.
`
`BRII-fil" I)l-:‘.S(.‘RII"I‘ION Ol" 'l‘l-ll'i DRAWINGS
`
`The invention will now be further described. by way of
`example only. with reference to the following drawings in
`which:
`
`FIG. 1 shows a plan view and a schematic sectional view
`through a device in accordzmce with a first embodiment of the
`invention:
`FIG. 2 shows plan views of part ol’a lirst substrate ol‘the
`device ofl'ICi. l:
`FIG. 3 shows schematic sectional views of a device in
`
`accordance with the embodiment of FIG. I. in dit'lerent opti—
`cal states:
`FIG. 4 shovvs photographs of a test device in accordance
`with the embodiment of FIG. 1:
`
`FIG. 5 shows graphs ot'transtnittance t‘or dillbrettt optical
`states o l‘ devices in accordance with the embodiment o l‘ FIG.
`1:
`
`FIGS. 6 and 7 are schematic sectional views of devices in
`accordance with second and third embodiments of the inven—
`tion‘.
`FIG. 8 shows schematic sectional and plan views of a
`device in accordance with a fourth embodiment ol‘the inven-
`lion;
`FIG. 9 is a schematic sectional view ofthe device ofl-‘IG.
`8 in a dark state and in a light state:
`FIG. 10 shows schematic plan views ofthe device of FIG.
`
`9:
`
`F IGS. 11-13 show views of a device in accordemce with a
`sixth embodiment of the invention;
`
`FIG. I4 shows photonticrogmplts of the dark state attd the
`light state ofthe device ofI'lCi. 13:
`FIG. 15 is a graph ot'contrast ratio (CR) against applied
`voltage for the device of FIG. 13:
`FIG. 16 illustrates a device in accordance with a seventh
`embodiment o t' the invention: and
`FIG. 17 is a schematic sectional view through a device in
`accordance with a further embodiment ol‘ the invention.
`
`DETA] 1. ED DESCRIPTION
`
`As used in the present specification and in the appended
`claims. the term ”mtllti-stablc" or ”multi-stability" refers to
`
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`US 8,054,535 B2
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`tlte property o fa cell ofan electrophoretic display to be stable
`itt arty o f‘ntany optical states. With mult i-stability. the charged
`particles will remain wherever they are. even somewhere in
`between the two electrodes. in the absence ot'an electric field
`between the electrodes causing further migration.
`Consequently. a pixel may retail] 3 state in which sortie ol‘
`the charged particles are in view and some are not. giving the
`pixel a color somewhere between that when all or none o f tlte
`particles are in view.
`‘lhus. multi-stability allows the cells or pixels oftlte elec-
`trophoretic display to take on arty ol'a number ot‘inlcrmediate
`shades or colors thus allowing the image to be displayed in
`grayscale. The principles described in the present specifica—
`tion can be applied to both bistable and multi—stable display
`dcv ices.
`[n the following description. for purposes of explanation.
`numerous specific details are set forth in order to provide a
`thorough understanding of the present systems and methods.
`It will be apparent. however. to one skilled in the art that the
`present systetns and methods may be practiced without these
`specific details. Reference in the specilication to “an embodi-
`ment." “an example“ or similar language means that a par-
`ticular feature. structure. or characteristic described in con—
`ttection with the embodintettt or example is included itt at
`least
`that one embodiment. but not necessarily in other
`embodiments. The various instzmces ot' the phrase “in one -
`embodiment" or similar Phrases in various places in the speci-
`fication are not necessarily all referring to the same embodi-
`ment.
`
`The principles disclosed herein will now be discussed with
`respect to illustrative systems and methods.
`The ntultistable electrophorctic display device I of HG. 1
`comprises a first substrate 2 and a second substrate 3. The
`substrates 2.3 are spaced apart from each other and enclose a
`layer of an electrophoretic medium 4 cotnprising a liquid
`crystal material 13 having finely divided pigment particles 5
`dispersed in it.
`First electrodes 6a and second electrodes 6b are provided
`on an inner surface of' the first substrate 2 for applying an
`electric held across at
`least some of the electrophoretic
`medium 4. The second substrate 3 does not carry an electrode.
`so that its light transmissivity is high. As best shown itt FIG.
`2. the first electrodes 60 are interdigitated with the second
`electrodes 6b on the [irst substrate 2. Although first and sec-
`ond electrodes are shown by way of illustration. it will be
`understood that the invention is not limited to two electrodes
`per pixel. Three or more electrodes may optionally be used.
`The display 1 in this example is made up o l‘ several seg-
`ments 9 each o l‘which carries a set o Iii nterdigitatcd electrodes
`6o.6b that dcfittca pixel. The electrodes 6 in this example (30
`inn spaces) were formed with 10 ttIlt width metal litres on the
`first substrate 2 formed from a plastics tnaterial. The second
`substrate 3 was a bare plastics sheet. spaced from the first
`substrate 2 by spacers It}. In this example the spacers ID
`comprised 10 um spacer beads: however other types ofspacer
`known in the art could be used. for example threads or wires.
`or mou lded. embossed or cast features such as pillars or posts.
`The electrophoretic medium 4 comprised a nematic liquid
`crystal mixture (le-GGSI Merck) with suspended trans-
`parent blue pigments llostaperm Blue 132(i-I) with sine 87
`ttm (Clariant) and 2% of 10 um spacer beads. The pigment
`particles acquire a negative charge in the LC.
`‘l'he substrates were provided with a ligament layers. In this
`example the substrates were treated with a chrome complex
`solution: however other types of surlaee treatments can be
`used for providing appropriate interaction ot‘ liquid crystal
`molecules and pigment particles with the surface. Alignment
`layers or structures known in the art may be used. for example
`gratings. microstructures. evaporated silicon monoxide or a
`surface active agent such as lecithin. Writing to the light state
`
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`(FIG. 4b) was done using 60 V pulses (100 ms) attd writing to
`the dark state (FIG. 4a) was achieved using —60 V" pulses
`(60-80 ms).
`The electrodes 6 occupy substantially less than the entire
`field of v iew o l‘ the display and can be ttsed to el'l‘ect switching
`between a first optical state (FIG. 3a} and a second optical
`state (FIG. 3b). In the first (dark) optical state. most incident
`light that passes through the first substrate 2 is absorbed by the
`pigment particles 5. [n the second (light) optical state. most
`incident
`light
`that passes through the first substrate 2
`impinges on the second substrate 3 and does not impinge on
`a pigment particle 5.
`A fringing electric field will cover the space between the
`two in-plane electrodes 6o.6b. Consequently the molecules'
`dipole. which provides charging of the pigment particles. will
`also be oriented along the fringe field lines. Switching is via
`in-plane electric fields which move the particles in and out of
`the main field ol'view. Accordingly the pigment particles will
`be forced to migrate in this direction due to their interaction
`with the oriented l.(‘ molecules. A suitable voltage pulse
`provides movement of pigment particles 5 towards the line
`electrode 6a (FIG. 3b} where the pigment particles are col—
`lected. or in the space between line electrodes fiafih (FIG. 3a)
`At new field the pigments will be locked in the area between
`electrodes. due to interaction of the l.(' with the pigment
`particles 5. providing a stable network of I..Clpigment par-
`ticles. Because ol‘this the device enables bistable switching
`without stacking of the pigment particles 5 on flat. broad
`electrodes.
`To spread the pigments 5 between electrodes 60.61). the
`electrical pulse should have a length andj'or amplitude which
`is not enough to produce full migration of'pigments between
`electrodes. Such switching can be controlled by variation in
`pulse length or voltage. which is linked w itlt electromigmtion
`distance by the following equation:
`
`[—09:331."
`
`where t is the drilling time between electrodes. U is applied
`voltage. d is the spacing between electrodes. and tl is the
`electrophoretic mobility.
`13y dispersing the pigment particles 5 in a liquid crystal
`medium. in this example a nematic liquid crystal. the display
`is made bistable and has a threshold voltage. Switching is via
`ill-plane electric fields which move the panieles ill and out ol‘
`the main field of view. For improved threshold voltage char—
`acteristics and switching speed. it is preferred that the liquid
`crystal material have a dielectric anisotropy which is greater
`than about +2 or leSs than about —2.
`
`Experimental mixtures have been made for use as the elec-
`tropltoretic medium 4 using transparent coloured pigment
`particles 5 (C lariant) and 10 tttn spacer beads 10. Formula—
`tions were:
`I. M[.(76681 nematic [.(‘ (Merck) +3% ] lostaperm pigment
`Blue BZCi-l) (negative charge):
`2. MCI.6681+3% Ilostaperm pigment Pink [3.02 (positive
`charge):
`3. MLC6681+3% Novaperm pigment Yellow 4G (negative
`charge).
`A full colour transmissive display ‘zut be realised by stack-
`ittg such ('MY cells with transparent pigments.
`FIG. 5 shows the transmittance spectral measurement of
`switched states of the pixel. provided in two in‘plane cells.
`One device was tilled with liquid crystal Ml.('6681. contain-
`ittg transparent pigment llostaperm Blue BEG-D (FIG. 5a)
`and the other was tilled with MI.(‘6881 containing lIos-
`taperm Pink li02 (_l"l(i. 5b).
`Use of oppositely charged pigments 5a. 5b with different
`colours allows switching between two colours in the display
`cell. as illustrated in the embodiments shown in FIG. 6 and
`FIG. 7
`
`

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`US 8,054,535 B2
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`6
`
`Turning now to FIGS. 8—10. another embodiment of the
`invention is illustrated schematically. The [irst electrode 6a is
`in the form of an elongate wire or line metal line on an inner
`surface ol‘ the lirst substrate 2. The second electrode 6b is in
`the form o I‘ an elongate wire or line metal line on an opposing
`ituter surface ot‘the second substrate 3. The second electrode
`6!) defines an outline of a two—dimensional shape.
`in this
`example a rectangle. The device enables bistable switching
`without stacking ol‘ the pigment particles 5 on flat. broad
`electrodes. A fringing electric field between the two elec-
`trodes 6am; will cover space within the rectangular area of
`the second electrode 6!). Consequently the dipole which pro-
`vides charging ot'the pigment particles will also be oriented
`along the fringe lield lilies. Accordingly the pigment particles
`will be Forced to migrate in this direction due to their inter-
`action with the oriented I.C molecules. A suitable voltage
`pulse provides movement of pigment particles 5 towards the
`top line electrode 6a (FIGS. 95.1025) where the pigment par-
`ticles are collected. Consequently the area boundary defined
`by the second electrode 6!: will be transparent.
`In this
`example. the area defined by the second electrode 6b is rect-
`angular in shape; however it will be understood that the area
`could be of any desired shape. In the light state shown in
`FIGS. 9!) mid 1015. most of the light that traverses the first
`substrate 2 will not encounter an electrode. thereby improv-
`ing light transmissivity compared to prior art displays in _
`which a transparent electrode is needed to attract particles to
`its surface. Although this aspect of the invention is illustrated
`with respect to areas bottrrded by an unbroken second elec—
`trode 6!). it will be understood that this is not essential to the
`working of the invention. A break (12) ill the second electrode
`6!) (for example as illustrated in FIG. 10¢) is acceptable
`providing that the resulting fringe field is sufficient to cause
`substantially all of the defined area to receive pigment par-
`ticles 5 when the display is driven to the dark state.
`Application ora voltage pulse with opposite polarity pro-
`vides movement towards the rectangular area bounded by the
`second electrode 6b. where the pigment particles are spread
`out (FIGS. 9a.10a). By tuning the voltage pulse length and
`amplitude. the pigments can be stopped in the area betwetm
`the top and bottom substrates along the fringe [ield Ii nes. Due
`to the strong interaction with I.(‘ molecules. this state will be
`stable at zero lield.
`The device shown in FIGS. 11—13. the switching mecha—
`nism is essentially the same as in the device ofFIGS. 8—10.
`The diITerences are that this device has a plurality of parallel
`first electrodes 6a opposite a single second electrode 6!)
`which defines the boundary of a rectangle that
`is opposite
`each o I‘ the first electrodes. In this example. each electrode 6
`has a width ot'about 5 pm. In the dark state (FIGS. 12a and
`13a) the pigment particles 5 are spread out over the entire area
`bounded by the second electrode 6b.
`FIG. 14:: is a photomicrograph ol‘the dark state (I-‘IGS. 12a
`and 130) and FIG. 14!) is a photomicrograph ot'the light state
`(FIGS. 12b and 135}. The movement ol'pigment particles 5 is
`between the first (top) substrate 2 and the second (lower)
`substrate 3. with a cell gap o I‘ about 10 pm. Smaller cell gaps
`can decrease the amplitude and pulse length required.
`Particle mobility [it] was calculated as follows:
`i.
`(12:: t:
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`FIG. 15 shows contrast ratio versus applied voltage for the
`device ot‘ I-‘IGS. 11-13 with 10 ten wide electrodes and a
`spacing of 20 tlm. ‘I'he electrophoretic medium comprised
`ML(‘—6681 LC and R700 ('I'iOZ) pigment particles. The dis—
`play was driven with unipolar pulses 30 85 50 ritsr‘SOV: 30 ms
`()I-‘Ii-state. 50 ms [)N-state. The curve shows quite good
`threshold characteristics. which indicates the possibility of
`passive tuatrix addressing.
`In the embodiment shown in FIG. 16. a combination o I' line
`metal lines as first (Y) electrodes 6a and line metal lines
`dclining square electrodes as second (617) electrodes is used.
`The display is matrix addressable. with each pixel 8 being
`defined by the area surrounded by a square portion of the
`X-electrodc and overlapped by a line Y—electrode. When a
`suitable threshold voltage is applied between an X-electrode
`and a Y—electrode. the pixel 8 is bistably switched to an ON—
`state or an OFF-state and will reina in in that state until driven
`to the other state by a suitable pulse ot'oppositc polarity. The
`electrodes 6 occupy less than 30% ot'the Iield of view ol‘tlte
`display and can switch substantially the remaining lield o I'
`view between the ()N-state and the OFF-state. The metal
`electrodes 6 may be very line; they preferably occupy less
`titan 20%. notably from 1—20%. of the field of view of the
`display.
`The device oI‘IilG. IT uses in-plane electrodes similar to
`the de (ice of FIG. 3. but includes a third substrate 7. and
`additional electrodes 6:".60’ on another surl‘ace ol‘ the second
`substrate 3. The electrodes are not
`limited to the second
`substrate and could also be located on the first and third
`substrates. By providing two layers 411.4!) o l‘ electroplioretic
`medium. any o 1‘ four diITercnt colours or optical states may be
`selected for a given pixel. The [irst electrophoretic medium 4a
`has dispersed pigment particles 55:25!) ol'opposite charge. and
`the second electmphoretic medium 4!) has different dispersed
`pigment particles 5c,5d of opposite charge to each other.
`Use o l‘ magenta and cyan transparent pigment particles in
`the first display layer. and yellow and black pigments in the
`second stacked layer. permits realisation ot'a full colour dis—
`play. The fill] colour display cart also be built by stacking of
`layers with single ( 'MY transparent colour pigment particles.
`It will be understood that other combinations ot'C‘MYK could
`
`be used in the two layers in addition to the (‘Mt’YK combi-
`nation specilically described herein lor purposes of illustra-
`tion. A further example is a combination of blackhnagenta
`(KM) in the first layer and cyant’yellow (CY) in the second
`layer.
`In the experiments we used a wide range ol‘liquid crystals.
`including:
`MLC‘668L
`MI_.(‘643(1-000.
`MIFGGSO.
`MI.{_‘6204-000. MI.(‘6639.
`l'i'r‘. ZI.[4788-t)00. MBA-03-
`4518. ZI._.I 14792 (from Merck). As opaque pigments we used
`white TiOI pigments R700. 11900 (Dupont). WPIOS. red
`RP IOS. yellow YPl OS and black I3]J IDS. We used transparent
`pigments blue llostaperm pigment Blue liZG-I). magenta
`I-Iostaperm pigment Pink E02. yellow Novopenn pigment
`Yellow 4G ( li'om Clariant). The cells are assembled by using
`plastic and glass substrates with specified metallic electrodes.
`We have observed bistability and voltage threshold switch~
`ing in devices according to the present invention. which 0 tier
`the potential for l‘ull colour passive matrix addressed displays
`as well as ”electronic paper‘ applications.
`The articles ‘a‘ and ‘an‘ are used herein to denote “at least
`one‘ unless the context otherwise requires.
`
`til—2“ tnn=2xltt 'sem
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`This experimental display was not optimised but achieved
`a contrast ratio close to 4.
`
`What is claimed is:
`
`I. A multi-stablc electrophoretic display device having a
`plurality ol‘ pixels and comprising a Iirst substrate and a
`second substrate. the substrates being spaced apart from each
`' other and enclosing a layer of an electrophoretic medium
`comprising a liquid crystal material having pigment particles
`dispersed therein: attd
`
`

`

`7
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`8
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`US 8,054,535 B2
`
`opposing electrode littes corresponding to eaclt of said
`pixels and for selectively applying an electric field
`across at least sortie of the electrophoretic rttedium in
`each pixel area: wherein said opposing electrode lilies
`for eaclt pixel are coplanar on said first substrate:
`wherein the electrode litres effect switching between a first
`optical state irt which said pigment particles are col—
`lected around otte of two electrode lines for a pixel such
`that most light incident on that pixel does ttol impinge on
`a pigtttettt particle. arid a second optical state in which
`said pigment particles are held in a space between said
`two electrode lirtes for that pixel such that most light
`incident on that pixel impinges on pigment particles.
`2. A device according to claim I. wherein said electrode
`lilies comprise [irst arid second inlcrdigitated electrodes pro-
`vided on the first substrate.
`3. A device according to claim 1. wherein said liquid crys
`tal material has two different types ol‘pigment particles dis-
`persed therein. one type of which acquires a positive charge
`and the other type ol‘ which acquires a negative charge.
`4. A device according to claim I. wherein said electrode
`lines are tirade of metal.
`5. A device according to claim 1. further comprising a third
`substrate spaced apart front the second substrate. and a layer
`of a second elcctrophoretic medium enclosed between the
`second substrate and the third substrate: and electrodes for
`applying an electric field across at least soittc of the second
`electrophoretic medium: the second electrophoretic medium
`comprising a liquid crystal material having pigment particles
`dispersed therein.
`6. A device according to claim 5. wherein the pigment
`particles in one ofthe layers are ofa different composition to
`the pigment particles in the other layer.
`1’. A device according to claim 5. wherein each ofthe layers
`has two different types ol'pigment pan icles dispersed therein.
`one type ofwlticlt acquires a positive charg‘ arid the other
`type 0 f which acquires a negative charge.
`8. A device according to claim 1. wherein the electrode
`litres ltave a width ol‘abont 10 um or less.
`9. A device according to claim I. wherein the electrode
`lines have a width irt the range from about 1 run to about (i run.
`It}. A device according to claim I. wherein the electrode
`lines have a width in the range from about 3 tun to about 5 run.
`11 . A device according to claim 1. wherein when the de “ice
`is in the first optical state. most light which is transmitted
`tltrotlgh the first substrate impinges on the second substrate.
`12. A device according to claim I. wherein the pigment
`particles reflect or scatter light. the elcctrophorctic medium
`further includes a dissolved dye. attd wherein when the device
`is in the first optical state most light incident on a pixel is
`absorbed by the dye.
`13. A device accordittg to claim I. wherein the pigment
`particles selectively absorb light in a specified waveband and
`substantially transmit light outside the specified waveband.
`14. A multimstable electrophoretic display device having a
`plurality of pixels and comprising a first stlbstrate and a
`second substrate. the substrates being spaced apart from each
`other arid enclosing a layer of an electrophoretic medium
`comprising a liquid crystal material having pigment particles
`dispersed therein: and
`electrode lines for formation of pixels and applying an
`electric field across at least some of the electrophoretic
`medium in the pixel area:
`wherein the electrode lilies cll'ect switching between a first
`optical state in which most light incident on a pixel does
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`not impinge on a pigment particle. aItd a second optical
`state in which most light incident on a pixel impinges on
`pigment particles; and
`wherein the electrode lines effect switching to at least one
`intermediate optical state in which the pigment particles
`occttpy more ofthe pixel area than when the device is irt
`the first optical state. bttt the pigment particles occupy
`less of the pixel area than when the device is in the
`second optical slate. providing caclt pixel with grayscale
`capability.
`IS. A niult i-stable electrophoretic display device compris-
`ing a first substrate and a second substrate. the substrates
`being spaced apart from each other and enclosing a layer ofan
`electropltoretic medium comprising a liquid crystal material
`having liltcly divided pigment particles dispersed therein: and
`irt—plane metallic electrodes on an inner surface of the first
`substrate driven with different voltage signals liar apply-
`ing an electric field across at least sortie of the electro-
`phoretic medium: wherein
`the electrodes occupy substantially less than the entire field
`ofv iew o l‘thc display and can be used to effect switching
`between a first optical state in which most incident light
`on a pixel does rtot impinge on a pigment particle. and a
`second optical state 111 which ntost incident light on a
`pi xcl impinges on pigment particles.
`16. A device according to claim 15. wherein said electrodes
`comprise first attd second interdigitated metallic electrodes
`provided on the first substrate.
`1 7. A device according to claim 1 5. wherein the electrodes
`occupy less than 30% of the field of view of the display and
`can switch substantially the remaining field of view not occu-
`pied by the electrodes between the first optical state and the
`second optical state.
`18. A device according to claim 1 5. wherein the electrodes
`occupy front 1-20% of the field of view ofthe display.
`19. A multi-stahle electrophoretic display device compris-
`ittg a first substrate and a second substrate. the substrates
`being spaced apart from each other and enclosing a layer ofart
`electrophoretic medium comprising a liquid crystal material
`having pigment particles dispersed therein: and
`electrodes for applying an electric field across at least some
`of the electropltoretic medium: wherein said electrodes
`comprise an elongate first metal wire on an inner surface
`of the first substrate and an opposed second metal wire
`on art inner surface of the second substrate. the second
`wire defining an outline of a two-dimensional shape
`which occupies a greater area than an opposed portion of
`the at least one first wire: wherein
`
`the electrodes effect switching between a first optical state
`in which most incident light on a pixel does riot impinge
`on a pigment particle. artd a second optical state in which
`rrrost incident light tilt a pixel impinges on pigment par-
`ticles.
`20. A device according to claim 19. wherein the second
`wire defines the otttlinc of a substantially rectangular shape.
`21.:X device according to claim 19. wherein the electrodes
`occupy less than 30% of the field of view of the display and
`can switch substantially the remaining field ol‘ view not occu-
`pied by the electrodes between the first optical slate and the
`second optical state.
`22. A device according to claim 21. wherein the electrodes
`occupy liom l-20% of the field of view of the display.
`
`