EP1784685A1

EP1784685A1 - Liquid crystal display comprising improved switching means at the display periphery

Info

Publication number: EP1784685A1
Application number: EP05796022A
Authority: EP
Inventors: Zaccharia Zenati; Jacques Angele; Nicolas Bollenbach; Sylvain Lallemant; Bertrand Pecout
Original assignee: Nemoptic SA
Current assignee: France Brevets SAS
Priority date: 2004-08-17
Filing date: 2005-08-10
Publication date: 2007-05-16
Also published as: FR2874447A1; WO2006021675A1; US20090033853A1; JP2008510195A; WO2006021675A9; FR2874447B1

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 direction.

Description

LIQUID CRYSTAL DISPLAY DEVICE COMPRISING IMPROVED MEANS OF CO MMUTATION AT THE PERIPHERY OF THE DISPLAY

TECHNICAL AREA

The present invention relates to the field of liquid crystal displays.

More specifically, 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 °.

PURPOSE OF THE INVENTION

The object of the present invention is to improve the performance of bistable display devices. In particular, the object of the invention is to improve, by the use of new means, the state switching at the edges of

15 the display area of the display called "active zone". STATE OF THE ART Classic LCD Displays

The most widely used 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).

Most liquid crystal devices proposed and realized for this purpose

25 days are monostable. In the absence of an electric field, only one texture is produced in the device. It corresponds to an absolute minimum of the total energy of the cell. Under an electric field, this texture is continuously deformed and its optical properties vary according to the applied voltage. At the cutting of the field, the nematic returns again in the single monostable texture. The man

Those of the art will recognize among these systems the most prevalent modes of operation of nematic displays: twisted nematic (TN), supertordus (STN), electrically controlled birefringence (ECB), vertically aligned nematic (VAN), etc. At the addressing level, these displays can be addressed directly (very low resolution), in multiplex mode (medium resolution) or in active mode (high resolution).

State of BiNem technology

A new generation of nematic displays, known as "bistable", has appeared for a few years: they function 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 switch the texture of the liquid crystal from one state to another. In the absence of an electrical control signal, the display remains in the state obtained. By principle Func ⁺ ioning, this type of display consumes an energy proportional to the number of image changes. Thus, when their frequency decreases, the power required for the operation of the display tends to zero. Principle of operation

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" ψ very low (ψ "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.

Under a strong electric field an almost homeotropic texture called H and

• illustrated in the middle of Figure 1 is obtained. On the slave surface 10, the molecules are normal to the plate in the vicinity of its surface, the anchoring is said

"Broken": at the cutoff of the electric field, the cell evolves towards one or the other of the bistable textures U and T (see Figure 1). When the control signals used induce a strong flow of the liquid crystal in the vicinity of the master blade 20, the hydrodynamic coupling between the master blade 20 and the slave blade

In the opposite case, the texture U is obtained by elastic coupling, aided by the possible inclination of the weak anchorage. In the following will be designated by "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. At the end of the field, 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. Thus the passage of the texture H under field to the texture T is obtained thanks to a flow so a displacement of the liquid crystal in the direction in which the anchoring of the molecules is inclined to the master blade 20 (see FIG. 2). This direction is parallel to the brushing direction which is referenced 40 in FIG.

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]. When, at the end of the field, 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. To obtain a significant hydrodynamic flow inducing the texture T, it is necessary to apply an electric field pulse flank of steep descent, for example a niche type signal. To obtain the texture U, 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 ψ. Document [4] indicates that it must be very weak ("1 °). It must also remain between two values ψl and ψ2 so that the two switches to U and to T can be made: if ψ <ψl switching to U becomes difficult and impossible, if ψ> ψ2 T switching becomes difficult and impossible . The interval of values of ψ or window Δψ = ψ2-ψl for which the two commutations can be performed is reduced, typically of the order of 0.5 °. 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. addressing 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. In this mode, 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. In FIG. 3 reference is made to the column electrodes placed on a first substrate, for example the upper substrate, and reference is made to the row electrodes placed on the second substrate, for example the lower slave substrate. coordinate pixel N, M, a column signal is applied to the column M and a line signal to the line N.

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. Generally, 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. the the

In what follows, an ITO electrode is chosen, but this example is in no way limiting as to the material of which the electrode is made. An example of a mask representing the structure of the ITO transparent electrodes of a multiplexed BiNem screen according to the state of the art is given in FIG. 5. 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.

In the example of FIG. 5, the display has an active area of 160 × 160 square pixels of size 350 μm × 350 μm, ie an active area of 56 × 56 mm, with a interpixel space of 10 μm. 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.

LIMITATIONS PRESENTED BY BINEM REALIZED DISPLAYS

ACCORDING TO THE STATE OF THE ART: "PERIPHERAL EFFECT" When addressing a BiNem screen made according to the state of the art with the drawing of ITO described in the previous paragraph, it is sometimes found, in the edges of the active zone, switching problems to the U texture.

Figure 7 illustrates these switching faults. The active area of a display

BiNem made according to the mask of FIG. 5 is represented in FIG. 7. When the display is mounted in transmissive mode, the texture T corresponds to the non-conducting state or black, while the texture U corresponds to the on state. or white.

The entire cell first receives an electrical signal by multiplexing

(as described in document [7]) for switching T-pixels in black

(Figure 7a). Then the whole of the cell receives an electrical signal by multiplexing (as described in document [7]) intended to switch the pixels in

U is in the off state in white (Figure 7b). In FIG. 7b, on the edges of the active zone, there are black spots, ie zones where U-switching has not occurred and these areas have remained in texture T (state no passing or black). These areas are called disturbed areas. They are referenced 60 in FIG. 7b. In FIGS. 7a and 7b, reference is made to the direction of brushing and the hydrodynamic flow.

U-switching has not been performed for these pixels located on the disturbed areas 60. The disturbed areas 60 of Figure 7 thus show a difference in behavior at the switching level with respect to the rest of the cell. Other BiNem cells, made under slightly different conditions, show the same defect but for switching in T.

This type of fault, corresponding to a non-switching to one of the textures at the edge of the active zone, is called a "peripheral effect". ORIGIN OF THE "PERIPHERAL EFFECT"

The analyzes conducted by the inventors tend to explain this "periphery effect" as follows.

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. When 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 adhesion of this material 14 to the smooth glass 10 is not as strong as on PITO 12, and the roller 70 moves, "flush", a portion of the material 14 deposited, the glass 10 to the ITO layer 12 marking the beginning of the active zone (this displacement of material 14, by the roller 70, is shown schematically 72 in FIG. 8), locally creating at this point a disturbance of the brushing and therefore the properties anchoring the material. Since the switching of the BiNem is very sensitive to the value of the pretilt on the weak anchor layer 14 (window Δψ), switching in U or T can be made difficult or impossible in the disturbed zone. The the

roller moving about 1mm / turn, the disturbed area is a few millimeters in the direction of brushing.

In FIG. 8, 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.

When on the other side of the cell 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.

It can be seen in FIG. 7 that 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 Δψ for the value of the pretilt ψ 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. DESCRIPTION OF THE INVENTION

In order to overcome the disadvantages inherent in the state of the art such as "peripheral effect", 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.

According to another advantageous characteristic of the present invention, the above-mentioned units consist of the same material used to constitute the electrodes of the display.

Thus, thanks to the present invention, 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. According to an advantageous characteristic of the present invention, said patterns which do not contribute to the addressing of the display, in the non-active area, are electrically isolated. DETAILED DESCRIPTION OF THE INVENTION

Other features and advantages of the present invention will appear on reading the detailed description which follows, and with reference to the accompanying drawings, given by way of non-limiting examples and in which: 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).

We will now explain in more detail the invention with reference to Figures 9 and following. The present invention applies to BiNem bistable nematic displays whose general technology is now known to those skilled in the art and whose general principles have been recalled previously.

In the case of a bistable liquid crystal display according to the invention, 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

Thus, the upper surface of the blocks 120 is at least substantially coplanar with the upper surface of the electrodes 12, 22.

In this figure 9, there is referenced 120 a pattern according to the invention not electrically connected and disposed in a non-active area 62, on the outside of the active area 64 of the display.

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). When 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.

These patterns 120, added in the context of the present invention, 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

"Neutral".

Without limitation, 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.

The "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. However, if appropriate, such 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.

Several variants are possible at the level of the "neutral" patterns 120, which we will choose for the rest consisting of ITO as an example.

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.

The "periphery effect", which appears essentially on these two sides, is thus removed. But this design is dependent on the brushing direction 40 of the display. In order to make the drawing independent of the brushing direction 40, a second variant (FIG. 11) provides for 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.

In order to avoid short-circuits and field effects, 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. As illustrated in FIG. 12. 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. Of course, all combinations between the different variants described above are possible

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

"Limitations presented by BiNem displays made according to the state of the art:" edge effect ": firstly the entire display is switched to T (black figure 15a). Then the entire display is switched to U

(white figure 15b). It can be seen in FIG. 15b, comparing it with FIG. 7b, that the "periphery effect" has disappeared, the whole of the active zone 64 has switched to the U (white) state.

As seen in FIGS. 13 and 14, 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.

Preferably, in the context of the present invention, the distance (referenced d1 in FIG. 9) separating the neutral ITO units 120 and the adjacent active electrodes 12 is between 1 and 500 μm, very preferably between 5 and 50 μm. . 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 μm, very preferably between 5 and 50 μm.

Naturally, the present invention is not limited to the particular embodiments which have just been described, but extends to any variant within its spirit.

For example, the present description of the invention relates to a bypass liquid crystal display device with multiplexed or direct passive addressing. But 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].

In the context of the present invention, 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. °.

Documents cited Doc [1]: FR-A-2 740 893

Doc [2]: FR-A-2,740,894

Doc [3]: US-A-6,327,017

Doc [4]: P. Martinot Lagarde et al, SPIE vol. 5003 (2003), p25-34

Doc [5]: M. Giocondo, I. Lelidis, I. Dozov, G. Durand, Eur. Phys. J. AP 5, 227 (1999).

Doc [6]:: I. Dozov, Ph. Martinot-Lagarde, Phys. Rev. E., 58, 7442 (1998).

Doc [7]: FR-A-2,835,644

Doc [8]: FR-A-2,847,704

Doc [9]: FR-A-2,840,694

Claims

1. A liquid crystal display device 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 provided on at least one of the two substrates (10, 20) being covered with an anchoring layer (14, 24) 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 (10, 20) patterns (120) which have a thickness at least substantially identical to that of the electrodes (12, 22) and which have adhesion characteristics with respect to said anchoring layer (14, 24), substantially identical to those of the electrodes (12, 22). ), these patterns (120) not contributing to the addressing of the display , and located in the non-active area (62) thereof, adjoining an active area (64) at least on both sides of an active area (64) perpendicular to the brushing direction (40) and to the direction hydrodynamic flow, which is parallel to the brushing direction.

2. Device according to claim 1, characterized in that the patterns (120) are made of the same material used to form the electrodes (12, 22) of the display,

3. Device according to one of claims 1 or 2, characterized in that the patterns (120) are provided on a substrate (10) having an anchoring layer (14) which defines a low zenith anchoring energy.

4. Device according to one of claims 1 to 3, characterized in that the units (120) are provided on the two substrates (10, 20).

5. Device according to at least one of claims 1 to 4, characterized in that it comprises, on at least one of the substrates (10, 20), means for anchoring the liquid crystal molecules, which allow anchoring breaking when applying a suitable electric field between electrodes (12, 22) respectively provided on the substrates (10, 20).

6. Device according to one of claims 1 to 5, characterized in that it comprises means defining two stable states for the liquid crystal molecules in the absence of electric field.

7. Device according to one of claims 1 to 6, charac ^f érisé in that it uses two textures of liquid crystal molecules, one uniform or slightly twisted in which the molecules are at least substantially parallel to each other, and the other which differs from the first by a twist of about 180 °.

8. Device according to one of claims 1 to 7, characterized in that the ratio between the thickness d of the cell and the spontaneous pitch po liquid crystal molecules, is approximately equal to 0.25 +/- 0 1.

9. Device according to one of claims 1 to 8, characterized in that the patterns (120) which do not contribute to the addressing of the display are electrically isolated.

10. Device according to one of claims 1 to 9, characterized in that patterns (120) which do not contribute to the addressing of the display are placed around the periphery of an active area (64).

11. Device according to one of claims 1 to 10, characterized in that the patterns (120) which do not contribute to the addressing of the display are formed of solid patterns.

12. Device according to one of claims 1 to 11, characterized in that the patterns (120) which do not contribute to the addressing of the display are fragmented.

13. Device according to claim 12, characterized in that the distance separating the units (120) between them is between 1 and 500 microns, very preferably between 5 and 50 microns.

14. Device according to one of claims 1 to 13, characterized in that the patterns (120) which do not contribute to the addressing of the display are formed of paved patterns.

15. Device according to one of claims 1 to 14, characterized in that the patterns (120) which do not contribute to the addressing of the display are formed at least in part of paving patterns of almost identical geometry between them.

16. Device according to one of claims 1 to 14, characterized in that the patterns (120) which do not contribute to the addressing of the display are formed at least in part of pavers patterns of various shapes.

17. Device according to one of claims 1 to 16, characterized in that the patterns (120) which do not contribute to the addressing of the display are formed of very dense paving patterns.

18. Device according to one of claims 1 to 17, characterized in that the patterns (120) which do not contribute to the addressing of the display are shaped to fit the contour of the electrodes (12) formed in the area active (64).

19. Device according to one of claims 1 to 18, characterized in that the interval (dl) separating the patterns (120) which do not contribute to the addressing of the display and the active electrodes (12) is reduced to the minimum width to provide the required electrical insulation between these electrically conductive pads. 20. Device according to one of claims 1 to 19, characterized in that each of the two substrates (10,

20) respectively comprises patterns (120) which do not contribute to the addressing of the display, exactly superimposable.

21. Device according to one of claims 1 to 20, characterized in that the patterns (120) which do not contribute to the addressing of the display are made of ITO.

22. Device according to one of claims 1 to 21, characterized in that it comprises passive multiplex addressing means.

23. Device according to one of claims 1 to 21, characterized in that it comprises direct passive addressing means.

24. Device according to one of claims 1 to 21, characterized in that it comprises active addressing means.

25. Device according to one of claims 1 to 24, characterized in that the distance (dl) separating the units (120) and the adjacent active electrodes (12) is between 2 and 500 μm, very preferably between 5 and 5 μm. and 50 μm.

26. Device according to one of claims 1 to 25, characterized in that the upper surface of the patterns (120) is at least substantially coplanar with the upper surface of the electrodes (12, 22).