Classifications

• • 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
  • G02F1/1391—Bistable or multi-stable liquid crystal cells
• • 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
  • G02F1/133388—Constructional arrangements; Manufacturing methods with constructional differences between the display region and the peripheral region
• • 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
  • G02F1/1337—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers
  • G02F1/13378—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers by treatment of the surface, e.g. embossing, rubbing or light irradiation
  • G02F1/133784—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers by treatment of the surface, e.g. embossing, rubbing or light irradiation by rubbing

Definitions

• the present invention relates to the field of liquid crystal displays.
• the present invention relates to nematic liquid crystal bistable displays.
• the present invention is particularly applicable to bistable nematic liquid crystal displays having an anchoring fracture of which two stable textures differ by a twist of about 180 °.
• the object of the present invention is to improve the performance of bistable display devices.
• the object of the invention is to improve, by the use of new means, the state switching at the edges of
• liquid crystal displays use a nematic type liquid crystal. They consist of two glass substrates on which
• a conductive electrode and an alignment layer are deposited. Between the two substrates a layer of liquid crystal is injected. The thickness of the cell is kept constant using balls distributed throughout the cell, whose diameter is equal to the desired thickness (typically 2 to 6 microns).
• nematic displays twisted nematic (TN), supertordus (STN), electrically controlled birefringence (ECB), vertically aligned nematic (VAN), etc.
• TN twisted nematic
• STN supertordus
• EOB electrically controlled birefringence
• VAN vertically aligned nematic
• these displays can be addressed directly (very low resolution), in multiplex mode (medium resolution) or in active mode (high resolution).
• the BINEM ® bistable display (documents [1], [2] and [3]) is shown schematically in Figure 1. It uses two textures, one uniform or slightly twisted U (shown on the left of Figure 1 ) in which the molecules are substantially parallel to each other and the other T (illustrated on the right of Figure 1) which differs from the first by a twist of about +/- 180 °.
• the liquid crystal layer 30 is placed between two substrates 10, 20, respectively the master blade 20, which comprises an alignment layer 24 making a strong anchoring of the liquid crystal and a "pretilt” or pre-inclination with respect to the surface of the substrate, of a conventional value around 5 °, and the slave blade 10, which comprises an alignment layer 14 providing a weak anchorage of the liquid crystal and a "pretilt” ⁇ very low ( ⁇ "1 ° [4] ).
• the two pretilts are in the same direction, that is to say that the liquid crystal molecules remain inclined at the same sign of inclination over the entire thickness of the cell.
• Transparent electrodes 12, 22 deposited on the two blades or substrates 10, 20 make it possible to apply an electric field perpendicular to the substrates.
• the U and T textures are optically different, and a BiNem cell placed between crossed or parallel polarizers allows modulation of light in black (blocking state) and white (on state).
• the nematic is chiralised with a spontaneous pitch po, chosen close to four times the thickness d of the cell, to equalize the energies of the two aforementioned textures.
• the ratio between cell thickness d and po spontaneous pitch, d / po, is therefore about 0.25 +/- 0.1. Without a field, these are the states of minimum energy: the cell is bistable.
• the texture U is obtained by elastic coupling, aided by the possible inclination of the weak anchorage.
• switching of a screen element
• BiNem does this for the liquid crystal molecules to go through the homeotropic state H (anchoring break), then to evolve towards one of the two bistable U or T textures, or a combination of the two textures, at the cutoff of the electric field.
• the hydrodynamic coupling [5] between the slave blade 10 and the master blade 20 is related to the viscosity of the liquid crystal.
• the return to equilibrium of the molecules anchored on the master blade 20 creates a flow near it.
• the viscosity causes this flow to diffuse throughout the thickness of the cell in less than a microsecond. If the flow is strong enough near the slave blade 10, it inclines the molecules in the direction that induces the texture T. The molecules turn in opposite directions on the two blades 10, 20.
• the return to the equilibrium of the molecules close to the slave blade 10 is a second motor of the flow, it reinforces it and helps the homogeneous passage of the pixel in texture T.
• the elastic coupling between the two blades 10, 20 gives a very slight inclination of the molecules near the slave blade 10, in the texture H under field, even if the applied field tends to orient them perpendicularly to the blades 10, 20. Indeed the steep anchoring of the master blade 20 maintains inclined adjacent molecules.
• the inclination near the master blade 20 is transmitted by the elasticity of orientation of the liquid crystal to the slave blade 10. On it the force of the anchoring and a possible inclination thereof amplifies the inclination of molecules [6].
• the hydrodynamic coupling is insufficient to fight against the residual inclination of the molecules near the slave blade 10, the molecules near the two blades 10, 20 return to equilibrium by rotating in the same direction : the texture U is obtained. These two rotations are simultaneous they induce flows in the opposite direction which are opposed. The total flow is zero. There is therefore no overall displacement of the liquid crystal during the passage of the texture H to the texture U.
• the switching U or T pixel is therefore directly a function of the intensity of the hydrodynamic flow in the vicinity of the master blade 20.
• an electric field pulse flank of steep descent for example a niche type signal.
• a slow descent-side electric field pulse generating a very small hydrodynamic flow is necessary, for example a gentle slope descent or in successive trays [7], [8].
• Another important parameter for switching a BiNem cell is the value of the pretilt ⁇ .
• Document [4] indicates that it must be very weak ("1 °). It must also remain between two values ⁇ l and ⁇ 2 so that the two switches to U and to T can be made: if ⁇ ⁇ l switching to U becomes difficult and impossible, if ⁇ > ⁇ 2 T switching becomes difficult and impossible .
• This important sensitivity to the pretilt value is specific to the operation of a BiNem cell, the classical modes such as TN and STN, for example, using strong anchors, do not have this behavior.
• the 3 addressing modes developed for standard liquid crystal can be used for the BiNem display.
• the most common addressing mode for the BiNem display is multiplex addressing, it is simple because it has no active element and allows, thanks to the bistability of the display, to address a lot of lines.
• the BiNem display is a matrix screen formed of nxm screen elements called pixels, made at the intersection of perpendicular conductive strips respectively deposited on the master and slave substrates 10 (see FIG. 3). The area between two adjacent conductive strips carried by the same substrate is called interpixel space. Outside the display zone or active zone delimited by all the addressed pixels, these conductive strips are transformed into tracks which make the connection to the control circuits called drivers located for example on flexible connection elements welded to the screen.
• FIG. 4 A schematic diagram of the design of known electrodes formed on the two glass substrates 10, 20 of a conventional display according to the state of the art is illustrated in FIG. 4.
• the conductive electrodes are made with a transparent conductor called ITO (mixed oxide of Indium and tin). But when the display is reflective, the electrodes located opposite to the observer do not have the transparency constraint, they can be made with an opaque conductive material, for example aluminum.
• a thin electrode layer is deposited on the two glass substrates 10, 20 and then etched in the desired conformation for the electrodes.
• Figure 4a illustrates the mask for engraving the so-called upper blade 20, in our example the columns.
• Figure 4b illustrates the mask for engraving the electrodes on the so-called lower blade 10, in our example the lines.
• FIGS. 4a and 4b refer to 50, 52 the column and line electrode strips for addressing the useful area and 54, 56 to the tracks connecting the aforementioned bands to the drivers.
• FIG. 5a illustrates the mask of the upper plate 20, in our example the columns
• FIG. 5b the mask of the lower blade 10, in our example the lines.
• the actual dimensions of the display may vary over a wide range.
• the display has an active area of 160 ⁇ 160 square pixels of size 350 ⁇ m ⁇ 350 ⁇ m, ie an active area of 56 ⁇ 56 mm, with a interpixel space of 10 ⁇ m. Due to the very small size of the pixels, the ITO structure is not visible to scale.
• An enlargement of an edge of the active zone, referenced VI in FIG. 5, is given in FIG. 6.
• FIG. 6a illustrates the mask of the upper blade 20, in our example the columns
• FIG. 6b the mask of the lower blade. 10, in our example the lines.
• the two areas illustrated in Figures 6a and 6b are superimposed during assembly and sealing of the cell.
• the zone outside the active zone is called the non-active zone.
• Figure 7 illustrates these switching faults.
• the entire cell first receives an electrical signal by multiplexing
• the "periphery effect" is a U or T switching problem located on the edges of the active zone, over a distance of a few millimeters.
• the edges of the active zone correspond to the location where the junction between the substrate zone on which PITO (rough) has been deposited for the formation of electrodes and that where the glass of the substrate is free of ITO.
• the material used to make the weak anchoring layer 14, which completely covers the substrate 10, including electrodes 12, may be for example that described in document [9]. Once deposited, it is relatively soft compared to the polyimide type layers conventionally used for strong anchoring layers.
• the brushing roller 70 whose contact surface with the substrate is about ten millimeters, arrives at the glass junction (non-active zone) - ITO (edge of active zone), it first presses the material 14 deposited on the smooth glass 10.
• the disturbed area is a few millimeters in the direction of brushing.
• the bristles of the roll 75 the direction of rotation of the roll, 76 the direction of movement of the roll, 77 the area of crushing of the roll, 78 the beginning of the active zone represented by a ITO layer 12 and 79 the disturbed area.
• the roll 70 arrives at the ITO-glass interface, the reasoning is the same except that the material "driven out” by the poor adhesion on the glass makes a turn on the roll 70 before to be redeposited on the layer of ITO 12.
• the roller 70 moving about 1 mm / turn, a few millimeters of the active area will also be disturbed.
• the disturbed zone 60 corresponds to the edges of the active zone which extend perpendicular to the brushing direction 40 (a few millimeters on each edge).
• This very important sensitivity to the conditions of brushing, related to the narrow window ⁇ for the value of the pretilt ⁇ on the weak anchoring layer 14, is specific to the switching mode of the bistable display anchor break, it does not does not exist for standard liquid crystal displays of type TN or STN, for example.
• the present invention proposes a liquid crystal display device comprising two substrates provided with respective electrodes, and located on either side of a layer of liquid crystal molecules, the electrodes provided on at least one of the two substrates being covered with an anchoring layer defining a weak zenith anchorage allowing an anchoring break and switching between two textures of liquid crystal molecules whose torsion differs from the order of +/- 180 °, by hydrodynamic coupling between the two substrates, characterized in that it comprises on at least one of the two substrates patterns which have a thickness at least substantially identical to that of the electrodes and which have adhesion characteristics with respect to said anchoring layer, substantially identical to those of the electrodes, these patterns not contributing to the addressing of the display, and located in the non-active area thereof, adjacent to a active zone at least on both sides of an active zone perpendicular to the direction of brushing and the direction of the hydrodynamic flow, which is parallel to the direction of brushing.
• the above-mentioned units consist of the same material used to constitute the electrodes of the display.
• the switching between the two textures at the edge of the active zone is performed under the same conditions as the switching between the two textures in the center of the active area of the display.
• said patterns which do not contribute to the addressing of the display, in the non-active area are electrically isolated.
• FIG. 1 previously described schematically represents the switching principle of a BiNem type display
• FIG. 2 previously described schematically represents a hydrodynamic flow during a sudden electric field interruption in a BiNem type device
• FIG. 3 previously described represents the basic diagram of the operation of a conventional matrix screen
• FIGS. 4a and 4b previously described represent the schematic diagram of the drawing of the known electrodes intended to be formed respectively on the two substrates,
• FIGS. 5a and 5b previously described represent examples of masks for the formation of these electrodes
• FIGS. 6a and 6b previously described represent enlarged views of an edge of the masks illustrated in FIGS. 5a and 5b,
• FIG. 7 previously described represents the photograph of the active zone of a BiNem display according to the state of the art, more specifically FIG. 7a shows the whole of the display in a first switched state in T (black), while Figure 7b shows the same display in a second U-switched state (white),
• FIG. 8 previously described schematically represents the disturbance of the anchoring properties at the edge of the active zone caused by the brushing on a weak anchoring layer of a BiNem device
• FIG. 9 schematically represents the principle underlying the invention of adding patterns in the non-active zone adjacent to an active zone
• FIG. 10 represents a plan view of "neutral" patterns (here of the ITO) according to the present invention positioned on the two sides of an active zone perpendicular to the brushing direction, respectively for the two blades of a display in Figures 10a and 10b,
• FIG. 11 represents a variant of such "neutral" patterns (here of the ITO) according to the present invention positioned all around a non-active zone which adjoins an active zone, respectively for the two blades of a display in Figures 11a and 1b1,
• FIG. 12 represents another variant of "neutral" patterns (here of the ITO) according to the invention broken up into small individual blocks, respectively for the two blades of a display in FIGS. 12a and 12b
• FIG. 13 represents an enlarged view of an edge of the active zone of a display blade according to the present invention and more precisely illustrates a dense paving of "neutral” grounds (here of the ITO) in a non active adjacent to the active area
• FIG. 14 respectively represent in FIGS. 14a and 14b two series of patterns (here of the ITO) "neutral" strictly superimposable once the two blades are facing each other for sealing the cell, and
• FIG. 15 represents a photograph of the active zone of a BiNem display according to the present invention, FIG. 15a showing the active zone of the display after it has received an electrical signal intended to switch all the pixels. in state T (off state or black), while FIG. 15b represents the same active zone of the display after it has received an electrical signal intended to switch it to the U state (on state or White).
• the means for suppressing the disruptive effect of brushing at the edge of the active zone consists in adding patterns 120, the thickness and adhesion characteristics of which are in relation to the layer 14 of low zenith anchoring energy, are substantially equivalent to those of the electrodes 12, 22 of the display, in the non-active zone which adjoins the active zone, as illustrated in FIG. thickness of blocks 120 does not differ by more than 10% from that of electrodes
• the upper surface of the blocks 120 is at least substantially coplanar with the upper surface of the electrodes 12, 22.
• the material of the low anchoring alignment layer 14 is thus homogeneously deposited, with good adhesion to all the patterns 12 (forming the electrodes in the active zone 64) and 120 (located in the non-active zone 62).
• the scrubbing roller 70 passes from the non-active area 62 to the active area 64 and vice versa, the material 14 is not "driven out" of the non-active portion 64 to the active portion 62 and the brushing parameter defining the pretilt is not disturbed.
• patterns 120 are not electrically connected. They are not intended to address a liquid crystal area. They are intended to ensure the continuity of the brushing parameters at the edge of active zone 64. These patterns 120 added according to the invention are called patterns
• the "neutral" patterns according to the invention may consist of the same material as that constituting the conductive electrode of the display.
• This material may be, for example, TITO, generally used as a transparent electrode in liquid crystal displays.
• neutral units according to the invention are preferably deposited on the two substrates of the display, so as to ensure a good homogeneity of the thickness of the cell.
• neutral patterns 120 may be provided on a single substrate, it is then preferably the substrate 10 which carries the anchoring layer 14 defining a low zenith anchoring energy.
• FIG. 10 A first variant illustrated in FIG. 10 consists in positioning the "neutral patterns" 120 according to the invention on both sides of an active zone 64 perpendicular to the brushing direction 40.
• FIG. 10a illustrates ITO 120 patterns on the said blade. upper 20, in our example the columns
• Figure 10b illustrates ITO patterns 120 on the lower blade 10, in our example lines.
• FIG. 11 illustrates the positioning of "neutral" motuses of ITO 120 according to the invention all around the nonactive zone 62 which adjoins an active zone. 64.
• FIG. 1a illustrates the ITO patterns 120 on the upper blade 20, in our example the columns
• FIG. 11b illustrates ITO patterns 120 on the lower blade 10, in our example the lines.
• a third variant consists of splitting the "neutral" ITO patterns 120, for example into small rectangular blocks or of any other appropriate form, rather than using continuous blocks.
• the aforementioned pavers may have identical shapes to each other or to various shapes.
• FIG. 12a illustrates ITO patterns 120 on the upper blade 20, in our example the columns
• FIG. 12b illustrates ITO patterns 120 on the lower blade 10, in our example the lines.
• a fourth variant consists in carrying out a paving as dense as possible of "neutral" ITO patterns 120 in the non-active zone 62 adjoining an active zone 64 as illustrated in FIG. 13.
• a fifth variant consists in producing on each strip strictly superposable patterns 120 once the two blades 10, 20 facing each other. sealing of the cell.
• FIG. 14 represents an enlargement of an edge of the active area of a 160x160 pixel display as described above, incorporating the fourth and fifth variants of the invention.
• FIG. 14a illustrates ITO patterns 120 on the upper blade 20, in our example the columns
• FIG. 14b illustrates ITO patterns 120 on the lower blade 10, in our example the lines.
• FIG. 15 shows the active zone 64 of a 160x160 display according to the invention, incorporating variants 4 and 5 of the invention. Switching is carried out under the same conditions as those described in the paragraph entitled
• edge effect firstly the entire display is switched to T (black figure 15a). Then the entire display is switched to U
• the "neutral" ITO patterns 120 are preferably shaped to conform to the contour of the electrodes 12 formed in the active zone 64. In other words, the gap between The "neutral" ITOs 120 and the active electrodes 12 are reduced to the minimum width to provide the required electrical insulation between these electrically conductive pads.
• the distance (referenced d1 in FIG. 9) separating the neutral ITO units 120 and the adjacent active electrodes 12 is between 1 and 500 ⁇ m, very preferably between 5 and 50 ⁇ m. Moreover, in the context of the present invention, preferably the distance separating the neutral ITO units 120 from each other is also between 1 and 500 ⁇ m, very preferably between 5 and 50 ⁇ m.
• the present description of the invention relates to a bypass liquid crystal display device with multiplexed or direct passive addressing.
• the invention can also be applied to a liquid crystal display device bistable active addressing using transistors deposited on glass to control the switching of the pixels, as described for example in document [8].
• the two textures that differ by about 180 ° are not necessarily one uniform or slightly twisted (ie a twist close to 0 °) and the other close to the half turn (ie a twist close to 180 °). Indeed, in the context of the present invention, it is possible to provide different twists for these two textures, for example 45 ° and 225 °, the important thing being that the twists between the two textures differ by an angle of about 180 ° C. °.

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• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Devices For Indicating Variable Information By Combining Individual Elements (AREA)
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