Abstract:
The invention concerns a liquid crystal display comprising two substrates ( 10, 20 ) provided with respective electrodes ( 12, 22 ), and located on either side of a layer of liquid crystal molecules ( 30 ), the electrodes arranged on one at least of the two substrates ( 10, 20 ) being coated with an anchoring layer ( 14, 24 ) defining a slight zenithal anchoring enabling the anchor to be ruptured and two textures of liquid crystal molecules whose difference in twisting is of the order of +/−180° to be switched, by hydrodynamic coupling between both substrates. The invention is characterized in that it comprises on at least one of the two substrates ( 10, 20 ) patterns ( 120 ) which have at least one thickness at least substantially identical to that of the electrodes ( 12, 22 ) and which have adhesion properties relative to said anchoring layer ( 14,24 ) substantially identical to those of the electrodes ( 12, 22 ), said patterns ( 120 ) not participating in addressing the display, and located in the non-active zone thereof ( 62 ), adjacent an active zone ( 64 ) at least on both sides of an active zone ( 64 ) perpendicular to the brushing direction ( 40 ) and to the direction of the hydrodynamic flux, which is parallel to the brushing di-reaction.

Description:
TECHNICAL DOMAIN 
       [0001]    This present invention concerns the area of liquid crystal displays. 
         [0002]    More precisely, this present invention concerns bistable displays with nematic liquid crystals. This present invention applies in particular to bistable displays with nematic liquid crystals, and with a shear break condition in which two stable textures differ by a twist of about 180°. 
       OBJECTIVE OF THE INVENTION 
       [0003]    The objective of this present invention is to improve the performance of bistable display devices. In particular the invention has as its objective to improve the switching of state at the edges of the display area of the display, called the “active zone”, by the use of new techniques. 
       Previous Designs 
     Conventional LCD Displays 
       [0004]    The most commonly-used liquid crystal displays employ a liquid crystal of the nematic type. These are composed of two glass substrates on which a conducting electrode, and then an alignment layer, are deposited. Between the two substrates, a liquid crystal layer is injected. The thickness of the cell is held constant by means of balls distributed over all of the cell, whose diameter is equal to the desired thickness (typically 2 to 6 μm). 
         [0005]    Most of the liquid-crystal-based devices proposed and created at present are monostable. In the absence of an electric field, a single texture is created in the device. This corresponds to an absolute minimum of the total energy of the cell. In an electric field, this texture is deformed continuously, and its optical properties vary as a function of the voltage applied. On switching off the field, the nematic again returns to the monostable texture only. Among these systems, the professional engineer will recognise the most widespread operating modes of the nematic displays, namely twisted nematics (TN), super-twisted nematics (STN), electrically controlled birefringence (ECB), vertically aligned nematics (VAN), etc. As far as addressing is concerned, these displays can be addressed directly (very low resolution), in multiplex mode (medium resolution) or in active mode (high resolution). 
       State of the BiNem Technology 
       [0006]    A new generation of nematic displays, known as “bistables”, has appeared over the last few years. These operate by switching between two stable states in the absence of an electric field. The external electric field is applied only for the time necessary to cause the texture of the liquid crystal to switch from one state to the other. In the absence of an electrical control signal, the display remains in the state it has reached. By its operating principle, this type of display consumes energy in proportion to the number of image changes. Thus, when their frequency reduces, the power necessary to operate the display tends toward zero. 
       Principle of Operation 
       [0007]    The BINEM® bistable display (documents [1], [2] and [3]) is presented schematically in  FIG. 1 . It uses two textures, one being a uniform or slightly twisted one U (illustrated on the left of  FIG. 1 ), in which the molecules are more or less parallel to each other, and the other T (illustrated on the right of  FIG. 1 ) which differs from the first in having a twist of about ± 1800 . The liquid crystal layer  30  is placed between 2 substrates  10 ,  20 , namely the master plate  20 , which includes an alignment layer  24  that provides strong anchoring of the liquid crystal, and a “pre-tilt” layer, pre-tilted in relation to the surface of the substrate, with a conventional value of around 5°, and a slave plate  10 , which includes an alignment layer  14  that provides a weak anchoring of the liquid crystal and a very weak “pre-tilt” φ (where φ&lt;&lt;1° [4]). The two pre-tilts are in the same direction, meaning that the liquid crystal molecules remain tilted with the same tilt sign over the whole thickness of the cell. Transparent electrodes  12 ,  22  deposited on the two plates or substrates  10 ,  20  are used to apply an electric field perpendicular to the substrates. 
         [0008]    The textures U and T are optically different, and a BiNem cell placed between crossed or parallel polarisers allows a modulation of the light between black (off state) and white (on state). 
         [0009]    The nematic is chiralised with a spontaneous pitch p 0 , chosen close to four times the thickness d of the cell, in order to equalise the energies of the two aforementioned textures. The ratio between the thickness d of the cell and the spontaneous pitch p 0 , namely d/p 0 , is therefore about equal to 0.25±0.1. Without a field, these are the minimum energy states, and the cell is bistable. 
         [0010]    In a strong electric field, an almost homeotropic texture, labelled H and illustrated in the centre of  FIG. 1 , is created. On the slave surface  10 , the molecules are normal to the plate in the vicinity of its surface, and the anchoring is said to be “broken”. On switching off the electric field, the cell migrates toward one or other of the bistable textures U or T (see  FIG. 1 ). When the control signals employed induce a strong flow of the liquid crystal in the vicinity of the master plate  20 , the hydrodynamic coupling between the master plate  20  and the slave plate  10  brings about the T texture. Otherwise, the U texture is obtained by elastic coupling, assisted by any tilt of the weak anchoring. 
         [0011]    In what follows, the “switching” of a BiNem screen element refers to the liquid crystal molecules passing from the homeotropic state H (shear break), and then migrating toward one of the two bistable textures U or T, or a combination of the two textures, on switching off the electric field. 
         [0012]    The hydrodynamic coupling  5  between slave plate  10  and master plate  20  is associated with the viscosity of the liquid crystal. On switching off the field, the return to equilibrium of the molecules anchored to the master plate  20  creates a flow close to the latter. The viscosity causes this flow to diffuse throughout the thickness of the cell in less than one microsecond. If the flow is strong enough close to the slave plate  10 , it tilts the molecules in the direction which induces the T texture. The molecules rotate in the opposite direction on the two plates  10 ,  20 . The return to equilibrium of the molecules close to the slave plate  10  is a second engine of the flow process, in that it reinforces the latter, and assists with the homogeneous passage of the pixel to the T texture. Thus the passage from the H texture in the field to the T texture is achieved due to a flow and therefore a movement of the liquid crystal in the direction in which the anchoring of the molecules on the master plate  20  is tilted (see  FIG. 2 ). This direction is parallel to the rubbing direction, which is referenced as  40  in  FIG. 2 . 
         [0013]    The elastic coupling between the two plates  10 ,  20  results in a very slight tilt of the molecules close to the slave plate  10 , in the H texture in a field, even if the applied field tends to orient them perpendicularly to the plates  10 ,  20 . In fact, the strong anchoring tilt of the master plate  20  maintains the tilt of the adjacent molecules. The tilt close to the master plate  20  is transmitted by the orientation elasticity of the liquid crystal up to the slave plate  10 . On the latter, the force of the anchoring, and any tilt of the latter, amplifies the tilt of the molecules [6]. When the hydrodynamic coupling is insufficient, on switching off the field, to resist the residual tilt of the molecules close to the slave plate  10 , then the molecules close to the two plates  10 ,  20  return to equilibrium by rotating in the same direction, when the U texture is obtained. These two rotations are simultaneous. They induce flows in the opposite direction, which oppose each other. The total flow is zero. There is therefore no overall movement of the liquid crystal during the passage from the H texture to the U texture. 
         [0014]    The switching to U or to T of the pixel is therefore directly a function of the intensity or magnitude of the hydrodynamic flow in the vicinity of the master plate  20 . In order to obtain a large hydrodynamic flow that brings about the T texture, it is necessary to apply a pulse of an electric field with a steep trailing edge, such as a signal of the slotted or square-wave type. In order to obtain the U texture, a pulse of an electric field with a slow trailing edge, generating a very weak hydrodynamic flow, is necessary, achieved, for example, by a gradual fall-off or one in successive steps [7], [8]. 
         [0015]    Another important parameter for the switching of a BiNem cell is the value of the pre-tilt φ. Document [4] indicates that it must be very weak (much less than 1°). It must also remain between two values φ 1  and φ 2  so that the two switching actions to U and to T can take place. If φ&lt;φ 1 , then switching to U becomes difficult and then impossible, and if φ&gt;φ 2 , then switching to T becomes difficult and then impossible. The range of values of φ in which window ΔΦ=φ 2 −φ 1 , at which the two switching actions can take place is reduced, is typically of the order of 0.50. This high sensitivity to the value of the pre-tilt is specific to the operation of a BiNem cell. The conventional methods, such as TN and STN, for example, which employ strong anchoring, do not exhibit this behaviour. 
       Addressing 
       [0016]    The 3 addressing modes developed for the standard liquid crystals can be employed for the BiNem display. The most common addressing mode for the BiNem display is multiplex addressing. This is simple, since it includes no active element and, due to the bistable nature of the display, it can be used to address up to a large number of lines. In this mode, the BiNem display is a matrix screen formed of n×m picture elements called pixels, created at the intersection of perpendicular conducting strips deposited respectively on the master  20  and slave  10  substrates (see  FIG. 3 ). The zone located between two adjacent conducting strips carried by a given substrate is called the interpixel space. Outside the display area or active zone formed by all of the addressed pixels, these conducting strips convert into tracks which make the connection to the control circuits, called drivers, located, for example, on flexible connection elements welded to the screen. In  FIG. 3 ,  42  refers to the column electrodes placed on a first substrate, the top substrate  20  for example, and  44  refers to the line electrodes placed on the second substrate, on the bottom slave substrate  10  for example. To display the pixel at coordinates N, M, a column signal is applied to column M and a line signal to line N. 
         [0017]    A diagrammatic representation of the design of known electrodes formed on the two glass substrates  10 ,  20  of a conventional display conforming to previous designs is illustrated in  FIG. 4 . In general, the conducting electrodes are created with a transparent conductor called ITO (an Indium Tin Oxide mixture). However, when the display is reflective, the electrodes located on the opposite side to the observer do not have the transparency constraint, and can be created with an opaque conducting material such as aluminium. A thin electrode layer is deposited on the two glass substrates  10 , and then etched according to the design sought for the electrodes.  FIG. 4   a  illustrates the mask used to etch the so-called upper plate  20 , the columns in our example.  FIG. 4   b  illustrates the mask used to etch the electrodes on the so-called bottom plate  10 , the lines in our example. In  FIGS. 4   a  and  4   b ,  50 ,  52  refer to the strips of column and line electrodes used or addressing the used zone, and  54 ,  56  refer to the tracks used for the connection of the aforementioned strips to the drivers. 
         [0018]    In what follows, we choose to use an ITO electrode, but this example is in no way limiting in respect of the material of which the electrode is composed. An example of a mask representing the structure of the transparent electrodes in ITO of a multiplex BiNem screen according to previous design is provided in  FIG. 5 .  FIG. 5   a  illustrates the mask of the top plate  20 , which in our example are the columns, and  FIG. 5   b  the mask of the bottom plate  10 , which in our example are the lines. 
         [0019]    The actual dimensions of the display can vary over a wide range. In the example of  FIG. 5 , the display has an active zone of 160×160 square pixels measuring 350 μm×350 μm making an active zone of 56 mm×56 mm, with an interpixel space of 10 μm. Due to the very small size of the pixels, the structure of the ITO is not visible at this scale. An enlargement of one edge of the active zone, referenced VI in  FIG. 5 , is provided in  FIG. 6 .  FIG. 6   a  illustrates the mask of the top plate  20 , which in our example are the columns, and  FIG. 6   b  the mask of the bottom plate  10 , which in our example are the lines. The two zones illustrated in  FIGS. 6   a  and  6   b  are superimposed during the assembly and sealing of the cell. 
         [0020]    The zone outside the active zone is called the non-active zone. 
       Limitations of the BiNem Displays Created According to Previous Design: “the Periphery Effect” 
       [0021]    When one addresses a BiNem screen created according to previous design, with the design of the ITO described in the preceding paragraph, it is sometimes observed that there are problems switching to the U texture at the edges of the active zone.  FIG. 7  illustrates these switching faults. The active zone of a BiNem display created according to the mask of  FIG. 5  is represented in  FIG. 7 . When the display is mounted in transmissive mode, the T texture corresponds to the off or black state, while the U texture corresponds to the on or white state. All of the cell first receives an electrical signal by multiplexing (as described in document [7]) designed to switch the T pixels that is to the off or black state ( FIG. 7   a ). And then all of the cell receives an electrical signal by multiplexing (as described in document [7]) designed to switch the U pixels that is to the on or white state ( FIG. 7   b ). In  FIG. 7   b , one observes at the edges of the active zone some areas that remain black, meaning zones where the U-switching does not occur, and these zones remain in the T texture (the off or black state). These zones are known as disturbed states. They are referenced  60  in  FIG. 7   b . In  FIGS. 7   a  and  7   b ,  40  refers to the rubbing direction and that of the hydrodynamic flow. 
         [0022]    The U switching has not been effected for these pixels located in the disturbed zones  60 . The disturbed zones  60  in  FIG. 7  thus demonstrate a difference of behaviour at the switching level in relation to the remainder of the cell. Other BiNem cells, created in slightly different conditions, show the same fault but for the T switching. 
         [0023]    This type of fault, corresponding to a failure to switch to one of the textures at the edge of the active zone, is called “the periphery effect”. 
       The Origin of the Periphery Effect 
       [0024]    The analyses conducted by the inventors tend to explain this “periphery effect” as follows: 
         [0025]    The “periphery effect” is a U or T switching problem located at the edges of the active zone, over a distance of a few millimetres. 
         [0026]    The edges of the active zone correspond to the location of the junction between the zone of the substrate on which ITO (rough) has been deposited for the formation of electrodes, and that where the glass of the substrate is lacking in ITO. The material used to create the weak anchoring layer  14 , which totally covers the substrate  10 , electrodes  12  included, can be that described in document [9] for example. Once deposited, it is relatively soft in relation to the layers of the polyimide type conventionally used for the strong anchoring layers. When the rubbing roller  70 , whose contact area with the substrate is about ten or so millimetres, arrives at the junction of the glass (non-active zone) and the ITO (edge of the active zone), it first rests on the material  14  deposited on the smooth glass  10 . The adhesion of this material  14  to the smooth glass  10  is not as strong as to the ITO  12 , and the roller  70  moves, “chases” part of the deposited material  14  from the glass  10  to the ITO layer  12  marking the start of the active zone (this movement of material  14 , by the roller  70  is shown as  72  in  FIG. 8 ), creating a disturbance of the rubbing action locally at this location, and therefore of the anchoring properties of the material. Since the switching of the BiNem is very sensitive to the value of the pre-tilt on the weak anchoring layer  14  (window Δφ), then U or T switching can be rendered difficult or even impossible in the disturbed zone. With the roller moving by about 1 mm per revolution, the disturbed zone is a few millimetres in the direction of the rubbing action. 
         [0027]    In  FIG. 8 ,  74  refers to the hairs of the roller,  75  is the direction of rotation of the roller,  76  is the direction of movement of the roller,  77  is the crushing area of the roller,  78  is the start of the active zone created by an ITO layer  12 , and  79  is the disturbed zone. 
         [0028]    When the roller  70  arrives at the ITO—glass interface on the other side of the cell, the reasoning is the same except that the material “chased” by the poor adhesion to the glass does a turn on the roller  70  before being re-deposited on the ITO layer  12 . With the roller  70  moving by about 1 mm per rotation, a few millimetres of the active zone will also be disturbed. 
         [0029]    In  FIG. 7 , it can be seen that the disturbed zone  60  corresponds closely to the edges of the active zone which lies perpendicularly to the rubbing direction  40  (a few millimetres at each edge). 
         [0030]    This very high sensitivity to the rubbing conditions, which is associated with the narrow window, Δφ for the pre-tilt value φ on the weak anchoring layer  14 , is specific to the switching mode of the bistable display at the shear break. This does not exist for standard liquid crystal displays of the TN or STN type for example. 
       DESCRIPTION OF THE INVENTION 
       [0031]    In order to overcome the drawbacks inherent in the previous designs, such as the “the periphery effect”, this present invention proposes a liquid crystal display device with two substrates, respectively equipped with electrodes and located on either side of a layer of liquid crystal molecules, with the electrodes provided on at least one of the two substrates being covered with an anchoring layer that determines a weak zenithal anchoring that allows a shear break to occur, and switching between two textures of liquid crystal molecules whose twist differs by some ±180°, by hydrodynamic coupling between the two substrates, characterised by the fact that it includes patterns, on at least one of the two substrates, which have a thickness that is at least approximately the same as that of the electrodes, and which has adhesion characteristics, in relation to the said anchoring layer, that is more or less identical to that of the electrodes, with these patterns not contributing to the addressing of the display, and located in the non-active zone of the latter, alongside a zone that is active at least on the two sides of an active zone perpendicular to the rubbing direction and to the direction of the hydrodynamic flow, which is parallel to the rubbing direction. 
         [0032]    According to another advantageous characteristic of this present invention, the aforementioned patterns are composed of the same material as that uses to make up the electrodes of the display. 
         [0033]    Thus due to this present invention, the switching between the two textures at the edge of the active zone takes place in the same conditions as the switching between the two textures at the centre of the active zone of the display. 
         [0034]    According to one advantageous characteristic of this present invention, the said patterns which do not contribute to the addressing of the display, in the non-active zone, are isolated electrically. 
     
    
     
       DETAILED DESCRIPTION OF THE INVENTION 
         [0035]    Other characteristics objectives and advantages of this present invention will appear on reading the detailed description that follows, and with reference to the appended drawings, which are provided by way of non-limiting examples and in which: 
           [0036]      FIG. 1 , described previously, schematically represents the switching principle of a display of the BiNem type, 
           [0037]      FIG. 2 , described previously, schematically represents a hydrodynamic flow  20  during a sudden cut-off of the electric field in a device of the BiNem type, 
           [0038]      FIG. 3 , described previously, is a diagrammatic representation of the operation of a conventional matrix screen, 
           [0039]      FIGS. 4   a  and  4   b , described previously, are a diagrammatic representation of the design of the known electrodes intended to be formed on the two substrates respectively, 
           [0040]      FIGS. 5   a  and  5   b , described previously, show examples of masks for the formation of these electrodes, 
           [0041]      FIGS. 6   a  and  6   b , described previously, represent enlarged views of one edge of the masks illustrated in  FIGS. 5   a  and  5   b,    
           [0042]      FIG. 7 , described previously, is a photograph of the active zone of a BiNem display according to previous design. More precisely,  FIG. 7   a  represents the whole of the display in a first, T-switched state (black), while  FIG. 7   b  represents the same display in a second, U-switched state (white), 
           [0043]      FIG. 8 , described previously, schematically represents the disturbance of the anchoring properties at the edge of the active zone brought about by the rubbing on a weak anchoring layer of a BiNem device, 
           [0044]      FIG. 9  schematically represents the principle at the foundation of the invention, which consists of adding patterns to the non-active zone alongside an active zone, 
           [0045]      FIG. 10  is a plan view of “neutral” patterns (here they are ITO) in accordance with this present invention, positioned on the two sides of an active zone perpendicular to the rubbing direction, for the two plates of the display in  FIGS. 10   a  and  10   b  respectively, 
           [0046]      FIG. 11  represents a variant of such “neutral” patterns (here they are ITO) in accordance with this present invention, positioned all around the edges of a non-active zone which lies alongside an active zone, for the two plates of the display in  FIGS. 11   a  and  11   b  respectively, 
           [0047]      FIG. 12  represents another variant of “neutral” patterns (here they are ITO) according to the invention broken up into small individual tiles, for the two plates of the display in  FIGS. 12   a  and  12   b  respectively, 
           [0048]      FIG. 13  is an enlarged view of one edge of the active zone of a display plate according to this present invention, and more precisely illustrates a dense tiling of “neutral” patterns (here they are ITO) in a non-active zone alongside the active zone, 
           [0049]      FIG. 14  represents, in  FIGS. 14   a  and  14   b  respectively, two series of “neutral” patterns (here they are ITO) which are strictly superimposable once the two plates are facing each other for the sealing of the cell, and 
           [0050]      FIG. 15  is a photograph of the active zone of a BiNem display according to this present invention, with  FIG. 15   a  representing the active zone of the display, after which the latter has received an electrical signal intended to switch all of the pixels to the T state (off or black state), while 
           [0051]      FIG. 15   b  represents the same active zone of the display after the latter has received an electrical signal intended to switch it to the U state (On or white state). 
       
    
    
       [0052]    The invention will now be explained in greater detail, with reference to  FIGS. 9  et seq. 
         [0053]    This present invention applies to bistable nematic displays of the BiNem type whose general technology is now known to the professional engineer, and whose general principles have been described above. 
         [0054]    In the case of a bistable liquid crystal display according to the invention, the means used to eliminate the disturbing effect of the rubbing at the edge of the active zone consists of adding patterns  120  whose thickness and adhesion characteristics in relation to the low-energy of zenithal anchoring layer  14 , are more or less equivalent to those of the electrodes  12 ,  22  of the display, in the non-active zone which lies alongside the active zone, such as that illustrated in  FIG. 9 . Typically the thickness of the blocks  120  do not differ by more than 10% of that of the electrodes  12 ,  22 . Thus the top surface of the blocks  120  is at least approximately coplanar with the top surface of the electrodes  12 ,  22 . 
         [0055]    In  FIG. 9 ,  120  refers to a pattern according to the invention which is not connected electrically and placed in a non-active zone  62 , on the outside the active zone  64  of the display. 
         [0056]    The material of the weak anchoring alignment layer  14  is thus deposited in a homogeneous manner, with a good adhesion over all of the patterns,  12  (forming the electrodes in the active zone  64 ) and  120  located in the non-active zone  62 . When the rubbing roller  70  passes from the non-active zone  62  to the active zone  64  and vice versa, the material  14  is not “chased” from the non-active part  64  to the active part  62 , and the rubbing parameter forming the pre-tilt is not disturbed. 
         [0057]    These patterns  120 , added in the context of this present invention, are not connected electrically. They have no vocation to address a liquid crystal zone. They are intended to ensure the continuity of the rubbing parameters at the edge of the active zone  64 . These added patterns  120  of the invention are called “neutral” patterns. 
         [0058]    In a non-limiting manner, the “neutral” patterns according to the invention can be composed of the same material as that constituting the conducting electrode of the display. This material can be ITO for example, generally used as the transparent electrode in liquid crystal displays. 
         [0059]    The “neutral” patterns according to the invention are preferably deposited on the two substrates of the display, so as to ensure good homogeneity of the cell thickness. Where appropriate however, such neutral patterns  120  can be provided on a single substrate, and this is preferably the substrate  10  that carries the anchoring layer  14  forming a weak zenithal anchoring energy. 
         [0060]    Several variants are possible at the level of the “neutral” patterns  120  which we will choose for the remainder, composed of ITO by way of an example. 
         [0061]    A first variant, illustrated in  FIG. 10 , consists of positioning the “neutral patterns”  120  of the invention on the two sides of an active zone  64  perpendicular to the rubbing direction  40 .  FIG. 10   a  illustrates ITO patterns  120  on the so-called upper plate  20 , which in our example are the columns, and  FIG. 10   b  illustrates ITO patterns  120  on the bottom plate  10 , which in our example are the lines. 
         [0062]    The “periphery effect”, which essentially appears on these two sides, is thus eliminated. However this design is tributary to the rubbing direction  40  of the display. 
         [0063]    In order to render the design independent of the rubbing direction  40 , a second variant ( FIG. 11 ) proposes to position “neutral ITO patterns”  120  according to the invention all around the edges of the non-active zone  62  lying alongside an active zone  64 .  FIG. 11   a  illustrates ITO patterns  120  on the top plate  20 , which in our example are the columns, and  FIG. 11   b  illustrates ITO patterns  120  on the bottom plate  10 , which in our example are the lines. 
         [0064]    In order to avoid short-circuits and field effects, a third variant consists of dividing the ITO “neutral” patterns  120  into small rectangular tiles, for example, or any other appropriate form, rather than using continuous blocks, like that illustrated in  FIG. 12 . The aforementioned tiles can have shapes that are identical to each other or be of diverse shape.  FIG. 12   a  illustrates ITO patterns  120  on the top plate  20 , which in our example are the columns, and  FIG. 12   b  illustrates ITO patterns  120  on the bottom plate  10 , which in our example are the lines. 
         [0065]    A fourth variant consists of creating a tiling of “neutral” ITO patterns  120  that is as dense as possible in the non-active zone  62  alongside an active zone  64  as illustrated in  FIG. 13 . 
         [0066]    A fifth variant consists of creating, on each plate, patterns  120  that are strictly superimposable once the two plates  10 ,  20  are opposite to each other for the sealing of the cell.  FIG. 14  shows an enlargement of one edge of the active zone of a 160×160 pixel display as described above, integrating the fourth and fifth variants of the invention. 
         [0067]      FIG. 14   a  illustrates ITO patterns  120  on the top plate  20 , which in our example are the columns, and  FIG. 14   b  illustrates ITO patterns  120  on the bottom plate  10 , which in our example are the lines. 
         [0068]    Naturally, all of the combinations of the different variants described above are possible. 
         [0069]      FIG. 15  shows the active zone  64  of a 160×160 display according to the invention, which integrates variants  4  and  5  of the invention. The switching takes place in the same conditions as those described in the paragraph entitled “Limitations presented by the BiNem created according to previous design: the periphery effect”. To begin with, all of the display is T-switched (black in  FIG. 15   a ). Then all of the display is U-switched (white in  FIG. 15   b ). It can be seen from  FIG. 15   b , by comparing it with  FIG. 7   b , that the “periphery effect” has disappeared, and all of the active zone  64  has switched to the U state (white). 
         [0070]    As can be seen in  FIGS. 13 and 14 , the “neutral” ITO patterns  120  are preferably shaped to fit the contour of the electrodes  12  formed in the active zone  64 . In other words, the interval separating the “neutral” ITO patterns  120  and the active electrodes  12  is reduced to the minimum width to ensure the electrical isolation required between these electrically conducting areas. 
         [0071]    Preferably, in the context of this present invention, the distance (referenced d 1  in  FIG. 9 ) separating the “neutral” ITO patterns  120  and the adjacent active electrodes actives  12  is between 1 and 500 μm, and most preferably between 5 and 50 μm. 
         [0072]    Moreover, in the context of this present invention, the distance separating the neutral ITO patterns  120  from each other, is also preferably between 1 and 500 μm, and most preferably between 5 and 50 μm. 
         [0073]    Naturally, this present invention is not limited to the particular methods of implementation that have been described above, but also extends to any variant that conforms to its spirit. 
         [0074]    For example, this present description of the invention concerns a bistable liquid crystal display device with multiplex passive or direct addressing. But the invention can also be applied to a bistable liquid crystal display device with active addressing using transistors deposited on glass to control the switching of the pixels, as described in document [8] for example. 
         [0075]    In the context of this present invention, the two textures, which differ by about 180°, are not necessarily one uniform or slightly twisted (with a twist close to 0°) and the other close to a half turn (with a twist close to 180°). In fact, in the context of this present invention, it is possible to have different twists for these two textures, such as 45° and 225° for example, the important thing being that the twists between the two textures different by an angle of about 180°. 
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