GB2382415A

GB2382415A - Vertically aligned liquid crystal device

Info

Publication number: GB2382415A
Application number: GB0127876A
Authority: GB
Inventors: Harry Garth Walton; Paul Antony Gass
Original assignee: Sharp Corp
Current assignee: Sharp Corp
Priority date: 2001-11-21
Filing date: 2001-11-21
Publication date: 2003-05-28
Also published as: GB0127876D0

Abstract

A vertically aligned liquid crystal display 20 comprises at least two domains of differing alignments, one domain 13 being smaller in area than the other domain 14. The first domain 13 corresponds to the display portion of the device and has a pre-tilt angle of 90{ while the second domain 14 corresponds to the non display portion of the device and has a pretilt angle of less than 90 {. The alignment layers that produce these alignments may be produced by photopolymerisation. In one method both liquid crystal and a polymerisable material are disposed between two substrates, liquid crystal in the first domain is put into a high voltage state, and the polymerisable material polymerised by irradiation.

Description

A LIQUID CRYSTAL DISPLAY DEVICE AND A METHOD OF MANUFACTURE THEREOF The present invention relates to a liquid crystal display device, in particular to a liquid crystal display device in which liquid crystal molecules adjacent the substrates of the device are oriented perpendicular, or nearly perpendicular, to the substrates. Such a device is known as a vertically aligned, or pseudo-vertically aligned, respectively, liquid crystal display device or"VAN LCD". The invention also relates to the manufacture of such a liquid crystal display device.

A liquid crystal display device of this general type is disclosed in European Patent application No. 0 433 999. The structure and operation of such a liquid crystal display device is illustrated in Figures l (a) to l (c).

Figure l (a) is a schematic cross-sectional view of such a liquid crystal display device.

The device consists of a lower substrate 1 and an upper substrate l'that are opposed to one another and are spaced apart from one another. The substrates 1, 1'are transparent, and are normally of glass, quartz, or plastic. The upper substrate I'and the lower substrate 1 are spaced a few microns (typically 1-10 microns) apart. The upper face of the lower substrate 1 is generally parallel to the lower face of the upper substrate 1', and a uniform spacing is achieved by providing spacers (such as, for example, spacer balls) between the upper substrate and the lower substrate. The spacers have been omitted from Figure l (a) for clarity. The upper surface of the lower surface I is coated with a thin layer 2 of a transparent electrically conductive material such as indium tin oxide (ITO). A similar thin transparent, electrically conductive layer 2'is disposed on the lower surface of the upper substrate 1'.

An alignment layer 4 is disposed on the lower substrate 1, over the transparent electrically conductive layer 2. An alignment layer 4'is also disposed on the upper substrate 1', over the transparent electrically conductive layer 2'. The alignment layers 4,4', as is well known in the art, induce alignment in liquid crystal molecules that are adjacent the alignment layers. In the device of Figure l (a), the lower alignment layer 4

induces a pre-tilt angle 0] in the adjacent liquid crystal molecules, and the upper alignment layer 4'induces a pre-tilt angle 82 in the adjacent liquid crystal molecules.

For convenience of description, the statement that an alignment layer induces a pre-tilt angle 8 in adjacent liquid crystal molecules will be abbreviated to"the alignment layer has a pre-tilt angle 0".

A layer 3 of liquid crystal material is disposed between the upper and lower substrates.

In some liquid crystal display devices the upper and lower alignment films 4, 4'each have a pre-tilt of substantially 90 . The liquid crystal molecules 6 in this case are oriented substantially perpendicular to the upper and lower substrates, and this is generally referred to as"vertical alignment". In other devices the alignment films 4,4' have a pre-tilt angle that is near to, but is less than, 90 . In this case the liquid crystal molecules 6 are not perpendicular to the upper and lower substrates, but are inclined by

a few degrees from the perpendicular direction. This is referred to as"pseudo-vertical alignment", and is illustrated in Figure l (a).

The liquid crystal display device further comprises means 5 for, in conjunction with the transparent conductive layers 2,2', applying a voltage across the liquid crystal layer 3.

In many liquid crystal display devices one of the conductive layers is normally patterned so as to define a plurality of distinct pixel electrodes that may be independently addressed so as to display a desired image. In such a device, the means for applying a voltage across the liquid crystal layer may include an array of thin film transistors, one transistor for each pixel electrode, together with the required electrodes for switching the transistors.

The effect of applying a voltage across the liquid crystal layer 3 is shown in Figure 1 (b).

The liquid crystal material used in a vertical or pseudo-vertical aligned liquid crystal display device is a nematic liquid crystal having a negative dielectric anisotropy. In the presence of an applied electric field, each of the liquid crystal molecules 6 tends to align itself so that its long axis is perpendicular to the applied field. The applied field will, ignoring edge effects, be perpendicular to the upper and lower electrodes, so that the

effect of applying the field is to cause the liquid crystal molecules to align themselves substantially parallel to the substrates. The orientation of the liquid crystal molecules adjacent the upper and lower alignment films, 2,2'are fixed by the alignment layers, so that the orientation of these molecules does not change significantly when the electric field is applied. It is therefore only liquid crystal molecules away from the substrates that are able to change their alignment upon application of an electric field.

Furthermore, since the liquid crystal molecules adjacent the upper and lower substrates cannot vary their alignment, the liquid crystal molecules in the centre of the liquid crystal layer do not become exactly parallel to the substrates, but are slightly tilted in their original tilt direction.

Hereinafter, liquid crystal molecules that are away from the substrates and whose orientation can therefore change are referred to as being"in the bulk of the liquid crystal layer".

The optical properties of the liquid crystal layer change when the voltage is applied across the liquid crystal layer to change the alignment as shown in Figure 1 (b). If the liquid crystal device is placed between a pair of linear polarisers, the optical transmission through the composite device will vary as the voltage across the liquid crystal layer is changed so as to vary the alignment of the liquid crystal molecules.

A practical liquid crystal display device may incorporate other components such as, for example, colour filters (not shown) to enable a full-colour image to be displayed. Other layers such as passive optical films may also be provided. The liquid crystal device may also be embodied as a reflective device, rather than as a transmissive device as shown in Figures l (a) and 1 (b). In a reflective device only one of the substrates is required to be transparent, and only one polariser is required.

In the VAN LCD of Figure l (a) the magnitude of the pre-tilt angle O ; of the lower alignment film 4 is preferably equal to the magnitude of the pre-tilt angle 82 of the upper alignment film 4'. However, the direction of the pre-tilt is not the same for the two alignment films. As shown schematically in Figure l (c) the direction of pre-tilt 8

of the lower alignment film 4 is opposite to the direction of pre-tilt 7 of the upper alignment layer 4'-that is, the two alignment directions vary by 1800. It should be noted that a pre-tilt direction is not defined for exact perpendicular alignment (i. e. when the pre-tilt angle 0 = 90 ).

Twisted vertically or pseudo-vertically aligned nematic liquid crystal display devices are known, and these are generally known as a TVAN LCD. In a TVAN LCD the alignment direction 7 of the alignment layer on one substrate is not at 180 to the alignment direction of the other alignment layer, but is at another angle. This induces twist into the alignment of the liquid crystal molecules. Chiral molecules may also be included in the liquid crystal layer 3 to cause twist of the liquid crystal alignment. The detailed optical properties of a TVAN LCD differ from those of a VAN LCD, but both types of device operate in a generally similar fashion and will be considered as equivalent for the purposes of this application.

One problem with existing liquid crystal display devices is that their optical properties vary when the angle from which the device is viewed varies. This dependence on the viewing angle occurs because, as shown in Figure l (b), the liquid crystal molecules 6 are tilted in a common direction throughout the bulk of the liquid crystal layer. The effect of the liquid crystal molecules on light travelling in the direction X shown in Figure 1 (b) will not be the same as their effect on light travelling in direction Y shown in Figure 1 (b). Display properties, such as the contrast of a displayed image, therefore vary depending on the direction in which the display is viewed. This means that a conventional display device of the type shown in Figure 1 (b) provides good display qualities only when viewed in a narrow angular range.

One known approach of improving the angular range in which a liquid crystal display can be viewed is to divide each pixel of the display into a number of regions or domains of different liquid crystal orientation. Such LCD devices are commonly known as "multi-domain displays", or domain-divided displays. An example of such a device is shown in Figures 2 (a) to 2 (c).

The general structure of the liquid crystal display device 12 shown in Figure 2 (a) to 2 (c) is generally similar to that of the LCD 11 shown in Figures 1 (a) to 1 (c). However, in the device of Figure 2 (a) the liquid crystal layer 3 contains two liquid crystal domains 9, 10. The direction of the pre-tilt of the upper alignment film in the first domain 9 is opposite to the direction of the pre-tilt of the upper alignment film in the second domain 10, and the direction of the pre-tilt of the lower alignment film in the first domain 9 is opposite to the direction of the pre-tilt of the lower alignment film in the second domain 10. In both domains, the direction of the pre-tilt of the upper alignment film is opposite to the direction of the pre-tilt of the lower alignment film. When no field is applied across the liquid crystal layer, therefore, the tilt of the liquid crystal molecules in the first domain 9 is in the opposite direction to the tilt of the liquid crystal molecules in the second domain 10.

When an electric field is applied across the LCD, the molecules in the bulk of the liquid crystal layer tilt in opposite directions in the two domains, as a result of the different surface alignment conditions in the two domains. This is shown in Figure 2 (b). It will be seen that light passing through the device along the path X makes a similar angle to the liquid crystal molecules as does light passing through the liquid crystal device along the path Y. Thus, the optical characteristics of the display device when viewed in the direction X will be generally similar to the properties when it is viewed in the direction Y. The cross-sectional area of the domains are made small enough that the individual domains are not well resolved by the human eye, so that the effect of the opposite tilt directions in the two domains is to reduce the variation in the optical properties with the viewing angle.

As indicated in Figure 2 (c), for each of the alignment films 4, 4'in the device the pretilt direction in the domain 9 is opposite to the pre-tilt direction in the domain 10. In Figure 2 (c) the solid arrow indicates the pre-tilt direction of the upper alignment film 4', and the broken arrows indicate the pre-tilt directions of the lower alignment layer 4.

Fabrication of a domain-divided VAN LCD of the type shown generally in Figures 2 (a) to 2 (c) requires the production of an alignment film having a pre-tilt direction that is not

constant over the area of the alignment layer. In the case of the device shown in Figures 2 (a) to 2 (c), each alignment film 4, 4'has two regions, with the tilt direction in one region being 1800 different to the pre-tilt direction in the other region. An alignment layer having regions of differing pre-tilt is generally produced by providing the alignment layer with a uniform pre-tilt angle and pre-tilt direction over its entire area, masking a portion of the alignment layer, and treating the un-masked portion so as to vary the pre-tilt angle and/or the pre-tilt direction.

US Patent No. 5 757 454 describes a method of producing a multi-domain TVAN LCD in which the alignment layers of the device undergo a rubbing treatment to induce domains of different pre-tilt direction. US Patent No. 5 909 265 describes a method of forming an alignment layer that produces two separate liquid crystal domains by a process that involves selective irradiation of an alignment layer with ultra violet light.

The irradiation influences the pre-tilt of the alignment layer, so that the pre-tilt of an irradiated portion of the alignment layer will be different from the pre-tilt of an area of the alignment layer that was not irradiated. These documents both relate to pseudovertically aligned LCDs.

A method in which the pre-tilt angle and/or the pre-tilt direction of an alignment layer is changed using exposure to light, normally to ultra-violet light, is generally known as a "photo alignment" method. It has been generally found that a photo-alignment method has advantages over a rubbing method, since it provides greater control over the formation of regions of different pre-tilt conditions on a single alignment layer.

Furthermore, a photo-alignment method does not have the problems of generation of dust and generation of static electricity which can accompany a rubbing process. US-A- 4 974 941, EP-A-0 525 477 and EP-A-O 632 311 describe examples of such photo alignment methods.

As is shown in Figures 1 (b) and 2 (b), the direction of tilt of the molecules in the bulk of the liquid crystal layer of a pseudo-vertically aligned LCD is dependent upon the direction of the pre-tilt of the alignment layers. (Other factors such as the presence of chiral dopants in the liquid crystal layer may possibly have an additional effect upon the

direction of the tilt of the molecules in the bulk of the liquid crystal layer). In a vertically aligned (0 = 90 ) device, however, no pre-tilt direction is defined by the alignment layers. The alignment layers thus have no influence on the direction in which molecules in the bulk of the liquid crystal layer tilt when a voltage is applied across the liquid crystal layer. It is found that the liquid crystal molecules of a vertically aligned LCD tilt in essentially random directions when a voltage is applied, and so form an uncontrolled number of liquid crystal domains, with the liquid crystal orientation in each domain being arbitrary. Dislocations or other defects form at boundaries between adjacent liquid crystal domains, and these can adversely affect the display properties of the device. It is therefore desirable to control the formation of domains in a vertically aligned LCD.

Methods of controlling the formation of domains in a VAN LCD have been described in US Patent Nos. 5 136 407 and 5 686 179. These methods involve forming holes in the pixel electrodes of the LCD. The presence of holes in the pixel electrodes causes a distortion of the lines of electric field which are generated when a voltage is applied across the liquid crystal layer. The resultant spatial variations of the electric field within the liquid crystal layer influences the direction in which liquid crystal molecules tilt when a voltage is applied across the liquid crystal layer. Thus, it is in principle possible to control the formation of domains in the liquid crystal layer by making an appropriate choice of the size and positioning of the holes in the electrodes. This prior art technique has the disadvantage that fringing fields are difficult to predict and model, so it is difficult to design devices that rely on fringing fields to control the formation of liquid crystal domains. Furthermore fringing fields may vary from one pixel to another over the area of an LCD panel, and this reduces the reliability of the technique.

US Patent No. 6 040 885 describes a vertically aligned LCD in which three liquid crystal domains exist in a pixel region. The liquid crystal molecules in two of the domains adopt a tilted orientation when a voltage is applied across the liquid crystal layer, and the third domain shows a substantially vertically alignment regardless of the applied voltage across the liquid crystal layer.

A first aspect of the present invention provides a liquid crystal display device comprising: a first substrate; a second substrate opposed to the first substrate; and a liquid crystal layer disposed between the first substrate and the second substrate; wherein the liquid crystal layer comprises, in the absence of an applied voltage, a first domain in which the liquid crystal molecules are aligned substantially perpendicular to the first and second substrates and a second domain in which the liquid crystal molecules are inclined with respect to the first and second substrates; and wherein the area of the second domain is smaller than the area of the first domain.

The liquid crystal alignment at either one of the first and second substrates will affect the orientation of the liquid crystal molecules throughout the volume between it and the other of the first and second substrates. It is accordingly possible to characterise each domain of the liquid crystal layer by an area which may be, for example, the area of the domain adjacent to one or other of the first and second substrates.

The liquid crystal molecules in the second, minority, domain of the liquid crystal layer bias the liquid crystal-molecules in the first, majority, domain of the liquid crystal layer into, when a voltage is applied across the liquid crystal layer, adopting an orientation that is tilted in the same direction as the tilted orientation in the second domain. Thus, even though the majority of the liquid crystal layer has a substantially vertical (0 = 90 ) alignment, the formation of random domains when a voltage is applied is prevented.

A conventional photo-alignment treatment will lead to non-uniformity of the alignment film. In the invention, however, the majority domain has a substantially vertical (6 = 90 ) alignment, and this may be produced by an alignment film without the need to treat the alignment film using a rubbing or photo-alignment treatment. Thus, the majority domain will not suffer from the non-uniformity present in conventional devices.

The first liquid crystal domain may be adjacent to the second liquid crystal domain.

The first liquid crystal domain may correspond to a display portion of the device. The second liquid crystal domain may correspond to a non-display portion of the device.

An alignment layer may be disposed on the first substrate, a region of the alignment layer corresponding to the first domain may have a pre-tilt angle of substantially 90 and a region of the alignment layer corresponding the second domain may have a pre- tilt angle of less than 90 .

The liquid crystal layer may further comprise a third liquid crystal domain in which the liquid crystal molecules are inclined with respect to the first and second substrates; and the area of the third domain may be smaller than the area of the first domain.

The third domain, like the second domain, biases the liquid crystal molecules in the first, majority, domain of the liquid crystal layer. When a voltage is applied across the liquid crystal layer, the liquid crystal molecules in the first, majority, domain are biased into adopting an orientation that is tilted in the same direction as the tilted orientation in the third domain.

The second and third liquid crystal domains may be disposed on opposite sides of the first liquid domain. The direction of inclination of liquid crystal molecules in the second liquid crystal domain may be opposite to the direction of inclination of liquid crystal molecules in the third liquid crystal domain. The area of the third domain may be approximately equal to the area of the first domain.

The liquid crystal layer may comprise a nematic liquid crystal material having negative d-electric anisotropy.

The liquid crystal layer may comprise a liquid crystal material and a polymeric material.

The polymeric material may be a photo-polymerised material.

The second liquid crystal domain may comprise a first region having a first liquid crystal alignment direction and a second region having a second liquid crystal alignment direction different from the first liquid crystal alignment direction.

The device may be a pixellated device and each pixel may comprise a first liquid crystal domain and one or more second liquid crystal domains.

A second aspect of the present invention provides a method of manufacturing a liquid crystal display device as defined above, the method comprising the steps of : (a) disposing a liquid crystal material and a polymerisable material between the first substrate and the second substrate; (b) putting the liquid crystal material in the first domain of the liquid crystal layer into a high voltage state; and (c) polymerising the polymerisable material in at least the first domain of the liquid crystal layer.

Step (a) may comprise introducing a liquid crystal material and a photo-polymerisable material between the first substrate and the second substrate, and step (c) may comprise irradiating at least the first domain. Step (c) may comprise irradiating at least the first domain of the liquid crystal display device with ultra-violet radiation.

Step (b) may comprise applying an electric field between the first substrate and the second substrate.

Preferred embodiments of the present invention will now be described by illustrative example with reference to the accompanying figures in which: Figure l (a) is a schematic sectional view of a conventional VAN LCD in the absence of an applied voltage across the liquid crystal layer; Figure 1 (b) is a schematic cross-sectional view of the LCD of Figure 1 (a) when a voltage is applied across the liquid crystal layer;

Figure l (c) illustrates the pre-tilt directions of the device of Figure l (a) ; Figure 2 (a) is a schematic sectional view through a conventional domain-divided VAN LCD when no voltage is applied across the liquid crystal layer;

Figure 2 (b) is a schematic sectional view through the LCD of Figure 2 (a) when a voltage is applied across the liquid crystal layer; Figure 2 (c) illustrates the pre-tilt directions of the LCD of Figure 2 (a); Figure 3 (a) is a schematic sectional view of a LCD according to a first embodiment of the present invention when no voltage is applied across the liquid crystal layer; Figure 3 (b) is a schematic sectional view of the LCD of Figure 3 (a) when a voltage is applied across the liquid crystal layer; Figure 4 (a) is a schematic sectional view of an LCD according to a second embodiment of the present invention when no voltage is applied across the liquid crystal layer; Figure 4 (b) is a schematic sectional view of the LCD of Figure 4 (a) when a voltage is applied across the liquid crystal layer; Figure 5 (a) is a schematic plan view of an LCD according to a third embodiment of the present invention when no voltage is applied across the liquid crystal layer; Figure 5 (b) is a schematic plan view of the LCD of Figure 5 (a) when a voltage sufficient to switch the liquid crystal is applied across the liquid crystal layer; Figure 5 (c) is a schematic plan view of a conventional LCD when a voltage sufficient to switch the liquid crystal is applied across the liquid crystal layer;

Figure 6 (a) is a schematic plan view of an LCD according to a fourth embodiment of the present invention when no voltage is applied across the liquid crystal layer; Figure 6 (b) is a schematic plan view of the LCD of Figure 6 (a) 20ms after a voltage sufficient to switch the liquid crystal has been applied across the liquid crystal layer; Figure 6 (c) is a schematic plan view of an LCD according to a fourth embodiment of the present invention 20ms after a voltage sufficient to switch the liquid crystal has been applied across the liquid crystal layer; Figures 7 (a), 7 (b) and 7 (c) are schematic plan views of LCDs according to further embodiments of the present invention; Figure 8 is a schematic plan view of an LCD according to a further embodiment of the present invention; and Figures 9 (a), 9 (b) and 9 (c) are schematic plan views of LCDs according to further embodiments of the present invention.

Like reference numerals denote like components throughout the drawings.

Figure 3 (a) and Figure 3 (b) are sectional views through a liquid crystal display device according to the first embodiment of the present invention. Figure 3 (a) shows the LCD when no voltage is applied across the liquid crystal layer, and Figure 3 (b) shows the device when a voltage is applied across the liquid crystal layer.

The LCD 20 of Figures 3 (a) and 3 (b) comprises first and second substrates 1, l'that are opposed to one another. For convenience of description the substrates will hereinafter be referred to as "upper" and "lower" substrates, in accordance with the orientation shown in Figure 3 (a), but the invention is not limited to this specific orientation. The substrates 1, l'are transparent, and may be of, for example, glass, quartz, or plastic.

The upper substrate 1'and the lower substrate 1 are spaced a few microns (typically 1-

10 microns) apart. The upper face of the lower substrate 1 is generally parallel to the lower face of the upper substrate 1', and a uniform spacing is achieved by providing spacers (such as, for example, spacer balls) between the upper substrate and the lower substrate. The spacers have been omitted from Figure 3 (a) for clarity. A transparent electrically conductive layer 2, 2' is disposed on each substrate, and this is formed from, for example, ITO. One or both of the transparent electrically conductive layers 2,2' may be patterned to define pixels that may be independently addressed in order to allow a desired image to be displayed. Alternatively, the upper and lower conductive layers may both be patterned into linearly-extending electrodes to provide a passivelyaddressed LCD. Drive means 5 for applying a voltage between the upper conductive layer (or a selected part thereof) and the lower conductive layer (or a selected part thereof) are provided, and any suitable drive means may be used.

A layer 3 of a nematic liquid crystal having a negative dielectric anisotropy is disposed between the upper substrate 1'and the lower substrate 1.

In use, the liquid crystal device 20 of Figure 3 (a) is disposed between a pair of linear polarisers, as for a prior art device. The optical transmission through the composite device is varied by changing the voltage applied across the liquid crystal layer so as to vary the alignment of the liquid crystal molecules.

The alignment layers 4, 4'induce high pre-tilt alignment in adjacent liquid crystal molecules. Examples of suitable alignment materials are JALS 2026 and JALS 943, both available from Japan Synthetic Rubber Co. Ltd. These materials, when deposited on a suitable substrate and baked at elevated temperature following the manufacturer's instructions, produce 900 pre-tilt in negative dielectric anisotropy liquid crystal materials such as, for example, MJ97174 available from Merck KGaA. As is well known, rubbing such an alignment layer, or irradiating such an alignment layer with ultra violet light, will reduce the pre-tilt angle of the alignment layer.

The liquid crystal display device 20 of Figure 3 (a) contains two liquid crystal domains 13,14. Each domain extends from one substrate 1 to the other substrate 1'. The

domain 13 occupies a greater area of the liquid crystal layer, when the device is seen in plan view, than does the domain 14 and so is known as the majority domain, whereas the other domain 14 is known as the minority domain. In particular, the area of the majority domain 13 at the upper or lower substrate is greater than at the area, again at the upper or lower substrate, of the minority domain 14.

The portion of the lower alignment layer 4 that corresponds to the majority domain 13 has not been treated in any way to reduce its pre-tilt, and so retains a pre-tilt off = 900.

The portion of the upper alignment layer 4'that corresponds to the majority domain 13 has also not been treated to reduce its pre-tilt, and so also retains a pre-tilt ouf 0 = 90'.

As a result, the liquid crystal molecules in the majority domain 13 adopt a perpendicular (vertical) alignment (apart from liquid crystal molecules near to the boundary 22 between the majority domain 13 and the minority domain, as will be described below).

The portion of the lower alignment film 4 that corresponds to the minority domain 14 has been treated, for example by rubbing or irradiation, to reduce its pre-tilt below 90 .

The portion of the upper alignment layer 4'that corresponds to the minority domain 14 has also been treated to reduce its pre-tilt angle below 90 . In the absence of an applied field, therefore, the liquid crystal molecules in the minority domain 14 adopt a pseudovertical alignment and so are tilted with respect to the normal direction to the upper and lower substrates as shown in Figure 3 (a).

The molecules of the liquid crystal material 3 are not independent of one another, but interact with one another via elastic forces. This means that liquid crystal molecules in the majority domain 13 that are near to the boundary with the minority domain 14 will nevertheless show a small tilt. For example, the molecule 15 in the majority domain 13 adopts a tilted orientation by virtue of its proximity to molecules (such as the molecule 16) in the minority domain 14. As indicated in Figure 3 (a) therefore, molecules in the majority domain 13 that are near to the domain boundary 22 will adopt a tilted orientation, rather than an exact vertical orientation. It should be noted that this applies only to liquid crystal molecules in the bulk of the liquid crystal layer. The orientation of liquid crystal molecules adjacent the alignment layers 4,14 will be determined by the

pre-tilt of the alignment layers, and these molecules will therefore retain a vertical orientation.

The effect of the minority domain 14 is therefore to bias the majority domain 13 towards a tilted alignment. Although most of the majority domain adopts a vertical alignment, as shown in Figure 3 (a), liquid crystal molecules in the majority domain 13 that are (a) in the bulk of the liquid crystal layer and (b) near the boundary 22 with the minority domain 14 will adopt a tilted orientation, owing to the influence of molecules in the minority domain 14. As a result, when a voltage is applied across the liquid crystal layer 3 a uniform tilted alignment is obtained across the entire liquid crystal layer as shown in Figure 3 (b). In more detail, as the electric field across the liquid crystal layer is increased and it becomes energetically favourable for the liquid crystal molecules to adopt an orientation that is substantially perpendicular to the applied field, liquid crystal molecules in the majority domain, near the boundary 22 with the minority domain 14, are already biased into a particular tilt direction owing to the tilted alignment present in the minority domain 14. The tilted alignment of the minority domain 14 thus grows into the entire liquid crystal layer, so that a uniform tilted alignment is obtained over the entire liquid crystal layer (except that molecules in the majority domain that are adjacent the upper or lower alignment film 4, 4'retain a vertical orientation). Thus, the present invention prevents the formation of random domains in the vertically aligned domain 13. The required size of the minority domain will depend on the liquid crystal parameters and on the required switching time.

The present invention requires the pre-tilt of the alignment layers 4, 4'to be reduced below 90 only for the portion of the upper alignment layer and the portion of the lower alignment layer that correspond to the minority domain 14 having the pseudo-vertical alignment. The portions of the alignment layers 4, 4'that correspond to the majority domain 13 having the vertical alignment retain their 90 pre-tilt and do not require any treatment. Photo-alignment or rubbing processes intended to reduce the pre-tilt of an alignment layer can be difficult to control reliably over the entire area of a substrate. As a result, in a conventional device which requires an alignment layer having a pre-tilt of less than 900 over the entire area of the device, such as the devices shown in Figures

l (a) and 2 (a), it can be difficult to obtain an alignment layer having a uniform pre-tilt angle. In practice, the alignment layers of the devices shown in Figures l (a) and 2 (a) are likely to show considerable variations in the pre-tilt angle over the surface area of the alignment layer. Furthermore, the pre-tilt angle may vary over the lifetime of a device. Such variations in pre-tilt lead to variations in the optical properties of a display device over its area and/or over its lifetime.

In the present invention, however, the areas of the liquid crystal device which require a pre-tilt below 90 , and hence require treatment of the alignment layer to obtain the reduced pre-tilt angle, constitute only a small proportion of the area of the device. The majority of the area of both the upper and lower alignment layers are required to have a pre-tilt of 90 , and so does not require treatment by a rubbing of photo-alignment process. Only the areas of the alignment layers that correspond to the minority domain need to be treated to reduce their pre-tilt. Thus, any variations in the pre-tilt that occur during the treatment of the alignment layers, or over time, are confined to the minority domain 14 of the device. The effect of any such variations has a far less significant impact on the optical properties of the device than it would for a conventional device in which a rubbing or photo alignment process must be applied to the entire area of the device.

Where the present invention is applied to a pixelated liquid crystal display device, it is preferred that each pixel of the device is provided with a majority domain having vertical alignment and one or more minority domains each having a tilted (pseudovertical) alignment.

In a particularly preferred embodiment of the invention, the majority domain 13 corresponds to a display portion of the device, and the minority domain 14 of pseudovertical alignment is at least partially placed in a non-display portion of the display device. This further reduces the impact of any variations in the pre-tilt angle of the portions of the alignment layers corresponding to the minority domain, whether over the area of the minority domain or over the life time of the device. In particular, where the present invention is applied to a pixelated device it is preferable if the pseudo-vertically

aligned domain 14 is disposed at least partially in an inter-pixel gap where one or both of the transparent electrodes is/are absent. This ensures that the entire active pixel area corresponds to regions of the alignment films that contain only liquid crystal molecules having a vertical alignment. Any variations in the pre-tilt of the region of the alignment film that corresponds to the pseudo-vertically aligned domain will have no effect on the display properties of the device, since this domain is in an inter-pixel gap which is a non-display portion of the device.

For ease of manufacture, the pre-tilt angle of the portions of the alignment layers corresponding to the minority domain 14 preferably lie in the pre-tilt ranges 0 < 0 < 10 or 800 < e < 90 since pre-tilt angles within these ranges are easy to achieve in practice.

A pre-tilt angle within the range 0 < 0 < 10 has the further advantage of being very stable. In principle, however, the pre-tilt angle of the portions of the alignment layers corresponding to the minority domain 14 may lie anywhere in the range 0 < 0 < 900.

The pre-tilt angle of the portion of the upper alignment layer 4'corresponding to the minority domain may differ from the pre-tilt angle of the portion of the lower alignment layer 4 corresponding to the minority domain 14. In principle, only one of the alignment layers 4, 4' needs to be provided with regions of different pre-tilt, and the other alignment layer may have a pre-tilt of substantially 90 over its entire area.

Figure 4 (a) illustrates a second embodiment of the invention. This embodiment is generally similar to the embodiment of Figure 3 (a), and only the differences between the embodiments will be described.

In the embodiment of Figure 4 (a), the liquid crystal layer comprises three domains 17, 18 and 19. The first domain 19 is a majority domain 19 of vertical alignment, and this is disposed between a second domain 17 and a third domain 18. The second and third domains 17,18 are each minority domains 17,18, and have a smaller area, at the substrates, then the majority domain. Each of the minority domains 17,18 has a pseudo-vertical alignment, but the tilt direction in the minority domain 17 is opposite to the tilt direction in the other minority domain 18. In principle, the pre-tilt angles of the

two minority domains 17,18 may have different magnitudes from one another, and/or the areas of the two minority domains may not be equal to one another. It may however, be preferable if the magnitudes of the pre-tilt angles of the two minority domains 17,18 are approximately equal to one another, and if the areas of the two minority domains (at the upper or lower substrate) are approximately equal to one another, since in this case the area of the majority domain 19 in which the alignment is influenced by one minority domain 17 should be approximately equal to the area of the majority domain in which the alignment is influenced by the other minority domain 18.

In the device of Figure 4 (a), liquid crystal molecules in the majority domain 19 that are (a) in the bulk of the liquid crystal layer and (b) near the boundary 22 with the first minority domain 17 are biased towards the tilted alignment of the first minority domain 17. Similarly, liquid crystal molecules in the majority domain 19 that are (a) in the bulk of the liquid crystal layer and (b) near the boundary 23 with the second minority domain 18 are likewise biased towards the tilted alignment of the second minority domain 18.

When an electric field is applied across the liquid crystal layer 3, therefore, the part of the majority domain 19 closer to the first minority domain 17 adopts a tilted alignment that is tilted in the same direction as the tilted alignment in the first minority domain 17.

The part of the majority domain 19 that is closer to the second majority domain, however, adopts a tilted alignment that is tilted in the direction of the tilt alignment in the second minority domain 18. As a result, the liquid crystal layer adopts a domaindivided alignment, as shown in Figure 4 (b). The present invention is therefore able to produce a domain-divided LCD of the type shown in Figure 2 (b).

Where the embodiment of Figures 4 (a) and 4 (b) is applied to a pixelated device, it is preferable that each pixel is provided with a majority domain and two minority domains.

As with the embodiment of Figures 3 (a) and 3 (b), it is preferable if one or both of the minority domains 17,18 are located at least partially in non-display portions of the device. In the case a pixelated device, one or both of the minority domains 17,18 are preferably located at least partially in inter-pixel gaps.

A device according to the embodiment of Figures 4 (a) and 4 (b) may be fabricated in a similar way to a device according to the embodiment of Figures 3 (a) and 3 (b). In one suitable method, the upper and lower substrates are each provided with an alignment layer that has a pre-tilt of 90 over its entire area. A first portion of the upper alignment film, that will correspond to one of the minority domains when the device is assembled, is then treated to reduce the pre-tilt of that portion of the alignment film, and also to define a pre-tilt direction for that portion of the alignment film. A second portion of the upper alignment film, that will correspond to the other one of the minority domains when the device is assembled, is then treated to reduce the pre-tilt of the second portion of the alignment film, and also to define a pre-tilt direction for the second portion of the alignment film that is different to the pre-tilt direction of the first portion of the alignment film. For example, the first and second portions of the alignment film may undergo a rubbing treatment, with the first portion being rubbed in a different direction to the second portion.

The regions of different pre-tilt direction may alternatively be defined using an irradiation process. For example, for alignment by irradiation with UV radiation the pre-tilt may be defined by suitable combination of the UV exposure energy, the angle at which UV radiation is incident on the alignment layer, and the polarisation directions of the UV radiation. It is possible to produce areas having different pre-tilt directions from one another by a series ofUV irradiation steps through a photomask.

Where the two minority domains are disposed at opposite sides of the majority domain, as in Figures 4 (a) and 4 (b) it will generally be preferable for the pre-tilt directions of the two portions of the alignment layer that correspond to the minority domains to be opposite (that is, at 180 to one another). This will provide the widest possible viewing angle range for the LCD.

If it is desired to provide the alignment layer of the lower substrate with regions of different pre-tilt, it may be treated in a similar way. The LCD is then assembled in any conventional manner.

Figures 5 (a) and 5 (b) are schematic plan views of a LCD according to a further embodiment of the present invention. In this case, the device comprises a striped- shaped majority domain 13, and two stripe-shaped minority domains 14. The majority domain 13 is disposed between the two minority domains 14. In the embodiment shown in Figures 5 (a) and 5 (b) the majority domains 13 and the minority domains 14 all have a substantially uniform width, and the long axis each domain is generally parallel to one edge of the LCD. In principle, one or more of the domains 13,14 could have a width that varied along the domain. Furthermore, the domains could in principle be arranged with their axis at an angle to the sides of the LCD.

The embodiment shown in Figures 5 (a) and 5 (b) contains two minority domains and one majority domain, but this embodiment is not limited to this specific number of minority domains and majority domains in an LCD.

This embodiment was manufactured using ITO-coated glass substrates that were spin- coated with a layer of the polyimide JALS 2026 (manufactured by Japan Synthetic Rubber Co. Limited). The polyimide layers were dried on a hotplate at 80 C, and were then cured in an atmosphere of nitrogen gas at 180 C for 10 minutes.

The polyimide layers were then subjected to a two stage irradiation process using a 200WHg/Xe high pressure arc lamp. The substrates were masked using a mask that had stripe-shaped opaque areas alternating with strip-shaped transparent areas. A suitably patterned chrome photo-mask is a suitable mask for this process.

Initially, the polyimide layer on one substrate was exposed through the photo-mask at normal incidence to polarised UV radiation having a total energy of2J/cm2. The alignment layer was then exposed to unpolarised UV radiation at 45 incidence and having a total energy of2. 5J/cm2. The result of these two exposures was to produce a pre-tilt direction in the irradiated areas of the alignment layer that was substantially perpendicular to the polarisation direction of the first UV irradiation step. The areas of

the polyimide layer that were not exposed retained a substantially 900 pre-tilt angle. In the irradiated areas the pre-tilt angle was reduced to approximately 10 or below.

The same two-stage UV irradiation process was then applied to the polyimide layer on the second substrate.

The two substrates were then assembled to form a LCD cell. They were assembled so that an un-irradiated area of the polyimide layer of the lower substrate was opposite an un-irradiated area of the polyimide layer of the upper substrate, and so that an irradiated area of the polyimide layer on the lower substrate was opposite an irradiated area of the polyimide layer of the upper substrate. The substrates were assembled so that the alignment direction of an irradiated region of the polyimide layer on the lower substrate was anti-parallel to the alignment direction of an irradiated region of the polyimide layer of the upper substrate.

The spacing of the gap between the upper and lower substrates was controlled, using glass spacer beads, to be 5um. The cell was filled with liquid crystal MJ97174, a liquid crystal material having negative di-electric anisotropy (available from Merck KGaA).

The liquid crystal material was introduced at a temperature at which it was in its isotropic phase, and the LCD was then cooled to room temperature.

The resulting alignment of the liquid crystal molecules, when no voltage was applied across the liquid crystal layer, was substantially perpendicular to the substrates in an area of the liquid crystal layer corresponding to un-irradiated regions of the polyimide layers. This region of the liquid crystal layer forms the majority domain 13 shown in Figures 5 (a) and 5 (b), and has a substantially vertical alignment. The liquid crystal alignment in the regions of the liquid crystal layer that correspond to the irradiated regions of the polyimide layers was tilted by an angle in the range from 00 to approximately 10 relative to the substrates. These regions of the liquid crystal layer form the minority domains 14. (In principle, a photo-alignment process could produce a parallel liquid crystal alignment in the minority domains. However, the invention

requires at least one minority domain of tilted alignment to determine the sense of the tilt of the liquid crystal molecules in the majority, non-photo-aligned domains.) Figure 5 (a) shows the appearance of the LCD of this embodiment when disposed between crossed linear polarisers and illuminated by unpolarised light. As can be seen, substantially no light is transmitted through the majority domains 13 in which the liquid crystal molecules are perpendicular to substrates. The majority domains are thus in their"dark"or"off'state.

Figure 5 (b) shows the effect of applying an electric field across the liquid crystal layer.

When a sufficient electric field is applied, the liquid crystal molecules in the majority domains 13 re-orient themselves so as to be substantially perpendicular to the applied electric field, and these domains therefore transmit light (Figure 5 (b) again shows the LCD as it appears when disposed between crossed linear polarisers). It can be seen that the majority domains have a uniform brightness, and are free from random defect lines.

This occurs because the minority domains 14 of tilted alignment induce uniform switching in the adjacent majority domains 13 of vertical alignment.

Figure 5 (c) shows the effect of switching a conventional LCD which does not contain the minority domains 14 of tilted alignment of the invention. As can be seen, random domains and defect lines form when an electric field is applied across the liquid crystal layer, so that the brightness of the pixel is not uniform over the pixel.

In a further embodiment of the invention, three LCDs were manufactured in a similar way to that described above for the embodiment of Figures 5 (a) and 5 (b). Each pixel of the LCDs of this embodiment comprised a stripe-shaped majority domain 13 and two stripe-minority domains 14, one disposed along each long side edge of the majority domain 13. The majority domains 13 and the minority domains 14 had uniform widths

in all three LCDs. However, the width Wmaj of the majority domains 13 was lOum in one LCD, 50m in a second LCD and 100flm in a third LCD. In each LCD, the width of the minority domains was less than the width of the majority domain.

The uniformity of switching of the majority, non-photo aligned domains was measured for the different domain widths for the three LCD cells. Images of each LCD cell were acquired at specific delay times after an electric field was applied across the liquid crystal layer to induce switching. In a LCD intended for video rate operation, it is necessary to achieve uniform switching of the liquid crystal layer within 20ms after the electric field is applied.

It was found that, in order to obtain uniform switching of the majority, non-photo aligned domains within 20ms, the width of the non-photo aligned domains Wmaj should be 50pro or less. In the LCD in which Wmaj = 100m, the majority domains had not completely switched within 20ms of the electric field being applied. 20ms after the electric field had been applied the majority domains in this LCD contained some random domains and defect lines because the switching of the liquid crystal layer had not been completed. Both the LCD with waj = lOum and the LCD with wma, = cm switched completely within 20ms after the electric field was applied across the liquid crystal layer.

Thus, where a LCD according to Figures 5 (a) and 5 (b) is intended for a video rate operation, so that uniform switching of the majority, non-photo aligned domains 13 is required within 20ms (or another desired, pre-determined time) of applying an electric field, the maximum width of the non-photo aligned domains 13 should be chosen so that switching can be completed with 20ms (or within any other desired pre-determined time). If the majority domains are too wide, they will not completely switch within 20ms (or other desired pre-determined time) after the field is applied.

It should be noted that the exact maximum width that is acceptable for the majority, non-photo aligned domains will vary depending on the specific parameters of the LCD, and may not always be 501im. However, it will generally be the case that there will be a maximum width for the majority non-photo aligned domains that cannot be exceeded if uniform switching of the liquid crystal within 20ms (or another pre-determined time) after a field has been applied is desired.

Figures 6 (a) and 6 (b) illustrate a further LCD of the present invention. This was produced in generally the same matter as described with reference to Figures 5 (a) and 5 (b) above, except that in this embodiment the majority domain 13 is in the form of a rectangle, in this embodiment in the form of a square. In this embodiment the majority domain 13 is a square having a width of 100Jlm. A minority domain 14 surrounds the majority domain 13.

Figure 6 (a) is a schematic plan view of the LCD, as seen when disposed between crossed linear polarisers and illuminated by unpolarised light. It will be seen that the

majority domain 13 transmits substantially no light and so is in its "dark" or "off'state. i Figure 6 (b) shows the LCD, again as seen when disposed between crossed linear polarisers 20ms after an electric field has been applied across the liquid crystal layer. It will be seen that although some switching has occurred, the alignment of the liquid crystal molecules in the centre of the majority domain 13 is not uniform and contains random defect lines. This is because the width of the majority domain 13 is too large for uniform switching to occur over the entire area of the majority domain in 20ms.

However, if the electric field is applied for longer periods, the majority domain 13 will adopt a uniform alignment over its entire area.

In order to provide fast switching, and so allow larger majority domains to be used in a LCD that requires video rate switching, in a further embodiment of the invention a photo-reactive monomer is added to the liquid crystal material of the LCD. The photoreactive monomer is irradiated once the majority domains have switched following application of an electric field across the liquid crystal layer. In this further embodiment of the invention, a LCD was manufactured in generally the manner described above with reference to Figure 6 (a) and 6 (b). However, the liquid crystal layer contained 99.6% by weight of the liquid crystal material MJ 97174,0. 38% by weight of the photo reactive monomer SK-13 (available from Kanto Chemical Co, Inc.) and 0.02% by weight of the photo-initiator Irgacure 651 (available from CIBA Speciality Chemicals PLC).

Initially, the LCD was filled with the liquid crystal material at a temperature in which it is in its isotropic phase, and the cell was then cooled to room temperature.

Next, an electric field was applied across the liquid crystal layer to switch the liquid crystal material in the majority domain into a high voltage state of the type shown in Figure l (b). (This state is not an exact perpendicular alignment, owing to the pre-tilt of the alignment layers.) Once switching was complete, and a uniform liquid crystal alignment had been developed in the majority domain 13, the liquid crystal layer was irradiated to cause the polymerisation of the photo-reactive monomer. In this embodiment this was done by irradiating the liquid crystal material with near UV radiation using a Vilber Lourmat Bio-Link IN Cross Linker. The electric field continued to be applied across the liquid crystal layer during this irradiation step. The UV exposure caused the photo-reactive monomer in the liquid crystal material to polymerise and form a network. Owing to the low concentration of the monomer in the liquid crystal material, the polymer network does not substantially change the liquid crystal alignment that exists in the majority, non-photo aligned domains when the electric field is removed. Thus, the"dark"state of the majority domains is not significantly affected. However, the polymer network was sufficient to increase the switching uniformity of the majority domain when the electric field is subsequently applied. Figure 6 (c) shows the LCD of this embodiment 20ms after an electric field has been applied across the liquid crystal layer. It will be seen that the majority domain 13 has completely switched, and that a uniform liquid crystal alignment exists substantially over the entire area of the majority domain. By comparing the results in figures 6 (b) and figures 6 (c) it can clearly be seen that the embodiment of Figure 6 (c) provides more uniform fast switching of liquid crystal material.

Although this embodiment has been described with reference to UV-induced polymerisation it is not, in principle, limited to UV-induced or even photo-induced polymerisation.

In the above-described embodiment the entire area of the liquid crystal layer is irradiated so that the polymer network is provided throughout the liquid crystal layer.

In principle, the polymer network needs to be provided only in the majority domain, and need not be provided in the remainder of the LCD. In manufacture, however, it may be easier to form a polymer network over the whole area of an LCD panel than to restrict the polymer network only to the majority domain. In the case of generating the polymer network by photo-induced polymerisation, for example, it may be easier to irradiate the whole area of an LCD panel than to mask the panel during the irradiation step so as to irradiate only the majority domain.

As noted above, where the invention is applied to a pixellated device, each pixel preferably is provided with a majority domain and one or more minority domains.

Figures 7 (a)-9 (c) illustrate possible arrangements of the majority domain 13 and the minority domain (s) 14 in a pixel.

In Figure 8 (a) a pixel is provided with one majority domain 13 and two minority domains 14. The minority domains have the form of thin strips, and are provided along opposite edges of the pixels. The arrow heads shown in Figures 7 (a) to 9 (c) illustrate the average tilt alignment direction of the LC molecules through the bulk of the LC layer in the minority domains 14 (in distinction to the arrows in Figures 1 (a) to 4 (b) which indicate the pre-tilt direction of the alignment layers). It will be seen that the average tilt alignment direction of one minority domain 14 in the embodiment of Figure 7 (a) is at approximately at 180 to the average tilt alignment direction of the other minority domain 14. Thus, a cross-section along the line AA in Figure 7 (a) would correspond generally to the device shown in Figure 4 (a).

In the embodiment of Figure 7 (b), a pixel is provided with one majority domain 13, and with four minority domains 14. Each minority domain has the form of a narrow stripe, and is arranged along one edge of the pixel. The average tilt alignment direction of the minority domain 14 along one side of the pixel is at approximately 180 to the average tilt alignment direction of the minority domain along the opposite side of the pixel. The average tilt alignment direction of the minority domain 14 along one side of the pixel is

at approximately 90 to the average tilt alignment directions of the minority domains along the adjacent sides of the pixel. The comer regions 24 are not included in the minority domains in the embodiment shown in Figure 7 (b), but the comer regions 24 could alternatively be included in the minority domains.

In the embodiment of Figure 7 (c) a pixel is again provided with one majority domain of vertical alignment and four minority domains of tilted alignment. Each photo-aligned domain has the form of a narrow strip, and is arranged one side of the pixel. The average tilt alignment direction in one minority domain 14 is at approximately 180 to the average tilt alignment direction of the minority domains along the opposite edge of the pixel. The average tilt alignment direction of the minority domain 14 along one side of the pixel is at approximately 90 to the average tilt alignment directions of the minority domains along the adjacent sides of the pixel. In this embodiment, however, the average tilt alignment direction of each minority domain is approximately parallel to the edge of the pixel along which the domain is located. In contrast, in the embodiment of Figure 7 (b) the average tilt alignment direction of each minority domain 14 is at approximately 90 to the edge of the pixel along which the minority domain extends.

In the embodiment shown in Figure 7 (c) the comer regions 24 of the pixel are again not included in the minority domains. In principle, however, the comer regions 24 could be included in the minority domains 14.

In the embodiments of Figures 7 (a) to 7 (c), the minority domains of tilted alignment 14 are provided only at the edges of the pixel. These embodiments are suitable for a small pixel, or for a pixel in a LCD which does not require a video rate switching. It is preferable for the minority domains of tilted alignment to be provided within the area of the black mask that surrounds the pixel, and this may conveniently be done when the minority domains 14 are disposed only at the edges of the pixels.

Figure 8 is a schematic plan view showing a further embodiment of the arrangement of the minority domains of tilted alignment. This generally corresponds to the embodiment of Figure 7 (c), except that the pixel is not square as in Figure 7 (a) but is

rectangular with a substantially 3: 1 aspect ratio. Such pixels are commonly used in colour LCDs as one part of a RGB three-colour triad. The pixel is provided with two minority domains 14, disposed on opposite sides of the majority domain 13. The minority domains 14 are in the form of narrow strips, extending along opposite sides of the pixel. The minority domains 14 are provided along the edges of the pixel which have the smallest separation, to ensure that the switching time of the pixel will be small.

If the minority domains were disposed along the short edges of the pixel, not along the long edges of the pixel as shown in Figure 8, then the separation between the minority domains would be approximately three times as great, and the time required to switch the liquid crystal material of the majority domain 13 so that it had a uniform liquid crystal alignment would be correspondingly greater.

As for the embodiments of Figures 7 (a) to 7 (c), the minority domains 14 are preferably disposed and dimensioned such that they will be contained within the area of the black mask of the pixel.

Figures 9 (a) to 9 (c) show embodiments that are suitable for use with a larger pixel that requires video rate switching. In order to ensure that uniform switching of the majority domain 13 can be achieved within the 20ms required for video rate switching, minority photo-aligned domains 14 are provided both at the edges of the pixel and within the interior of the pixel.

In the embodiment of Figure 9 (a) a pixel is provided with 16 minority domains 14, arranged in a 4 x 4 grid. The arrow heads indicate the average tilt alignment direction of each minority domain 14, and it will be seen that the average tilt alignment direction varies by 900 between adjacent minority domains in a row or column, and varies by approximately 1800 between domains that are adjacent to one another along a diagonal of the pixel.

The embodiment of Figure 9 (b) is generally similar to that of Figure 9 (a), except that the average tilt alignment directions of the minority domains 14 in Figure 9 (b) are parallel to edges of the pixel. In the embodiment of Figure 9 (a), the average tilt

alignment directions of the minority domains 14 are generally parallel to the diagonals of the pixel and are at approximately 45 to the edges of the pixels.

Figure 9 (c) shows a further embodiment in which minority domains 14 are provided within the interior of a pixel as well as along its boundaries. In this embodiment, minority domains 14 are again provided in a regular grid, in these embodiments a 4 x 4 grid. However, some of the domains 14 are"composite"minority domains, since they include regions of two or more different average tilt alignment directions. For example, the minority domain 14a, which is disposed along one side of the pixel, consists of two regions 14a (l) and 14a (2). The average tilt alignment direction in the region 14a (l) is at approximately 90 to the average tilt alignment direction in the region 14a (2). (For clarity, the arrowheads are shown as extended beyond the photo-aligned domains in Figure 9 (c). ) The average tilt alignment directions of the two regions of the domain 14a are each at approximately 45 to the adjacent edge of the pixel.

The minority domain 14b located in the interior of the pixel is also a composite domain, and includes four regions 14b (l) to 14b (4), each having a different average tilt alignment direction. Each region of the minority domain has an average tilt alignment direction that is at approximately 90 to the average tilt alignment direction of a region that is laterally or vertically adjacent, and has an average tilt alignment direction that is at approximately 180 to the average tilt alignment direction of a region that is diagonally adjacent.

In the minority domain 14b the average tilt alignment directions of the regions 14b (l) to 14b (4) are directed out of the minority domain 14 (b). That is, the average tilt alignment direction of each region 14b (l) etc is directed towards an edge of the region that is adjacent to the majority domain 13, and not towards an edge that is adjacent to another of the regions 14b (2) etc.

The average tilt alignment directions of the regions of the minority domain 14a disposed on one side of the pixel are also directed out of the minority domain 14a. The average tilt alignment direction of each region 14a (1), 14a (2) is directed towards an edge of the

region that is adjacent to the majority domain 13, not towards the other region of the minority domain or towards the boundary side of the pixel.

The minority domains 14c in each comer of the pixel are not composite minority domains, but contain just a single photo-aligned region. The average tilt alignment direction of the minority domain 14c is again directed towards an edge of the minority domain that is adjacent to the minority domain 13, rather than towards the edge of the pixel.

The photo aligned domains of the LCD of Figure 9 (c) may be produced by patterning an alignment layer to produce two or four adjacent regions having different alignment directions.

The invention has been described above with reference to transmissive LCDs. The invention is not limited to transmissive LCDs, however, and may be applied to a reflective LCD. When the invention is applied to a reflective LCD, one of the substrates, and the conductive layer disposed thereon, are not required to be transparent.

The invention has been described above with reference to LCDs in which the liquid crystal layer has zero twist. The invention may, however, be applied to a TVAN LCD.

For example, the liquid crystal layer 3 may contain a chiral dopant.

The present invention may be applied to both an active matrix LCD and a passivelyaddressed LCD. The invention is not restricted to LCDs that are electrically addressed, and it may be applied to a plasma-addressed LCD of the general type disclosed in US patent No 5 077 553.

As is known in the art, a LCD of the invention may incorporate other components such as, for example, colour filters (not shown) to enable a full-colour image to be displayed.

Other layers such as passive optical films may also be provided.

Claims

CLAIMS:

1. A liquid crystal display device comprising: a first substrate; a second substrate opposed to the first substrate; and a liquid crystal layer disposed between the first substrate and the second substrate; wherein the liquid crystal layer comprises, in the absence of an applied voltage, a first domain in which the liquid crystal molecules are aligned substantially perpendicular to the first and second substrates and a second domain in which the liquid crystal molecules are inclined with respect to the first and second substrates; and wherein the area of the second domain is smaller than the area of the first domain.

2. A liquid crystal display device as claimed in claim 1 wherein the first liquid crystal domain is adjacent to the second liquid crystal domain.

3. A liquid crystal display device as claimed in claim 1 or 2 wherein the first liquid crystal domain corresponds to a display portion of the device.

4. A liquid crystal display device as claimed in claim 1,2 or 3 wherein the second liquid crystal domain corresponds to a non-display portion of the device.

5. A liquid crystal display device as claimed in claim 1,2, 3 or 4 wherein an alignment layer is disposed on the first substrate, a region of the alignment layer corresponding to the first domain having a pre-tilt angle of substantially 90 and a region of the alignment layer corresponding the second domain having a pre-tilt angle of less than 90 .

6. A liquid crystal display device as claimed in any preceding claim wherein the liquid crystal layer further comprises a third liquid crystal domain in which the liquid crystal molecules are inclined with respect to the first and second substrates; and wherein the area of the third domain is smaller than the area of the first domain.

7. A liquid crystal display device as claimed in claim 6 wherein, the second and third liquid crystal domains are disposed on opposite sides of the first liquid domain.

8. A liquid crystal display device as claimed in claim 6 or 7 wherein the direction of inclination of liquid crystal molecules in the second liquid crystal domain is opposite to the direction of inclination of liquid crystal molecules in the third liquid crystal domain.

9. A liquid crystal display device as claimed in claim 6,7 or 8 wherein the area of the third domain is approximately equal to the area of the second domain.

10. A liquid crystal display device as claimed in any preceding claims wherein the liquid crystal layer comprises a nematic liquid crystal material having negative dielectric anisotropy.

11. A liquid crystal display device as claimed in any preceding claims wherein the liquid crystal layer comprises a liquid crystal material and a polymeric material.

12. A liquid crystal display device as claimed in claim 11 wherein the polymeric material is a photo-polymerised material.

13. A liquid crystal display device as claimed in any preceding claim wherein the second liquid crystal domain comprises a first region having a first liquid crystal alignment direction and a second region having a second liquid crystal alignment direction different from the first liquid crystal alignment direction.

14. A liquid crystal display device as claimed in any preceding claim wherein the device is a pixellated device and each pixel comprises a first liquid crystal domain and one or more second liquid crystal domains.

15. A liquid crystal display device substantially as described herein with reference to Figures 3 (a) and 3 (b), or to Figures 4 (a) and 4 (b), or to Figures 5 (a) and 5 (b), or to

Figures 6 (a) and 6 (b), or to Figure 6 (c), or to Figure 7 (a), or to Figure 7 (b), or to Figure 7 (c), or to Figure 8, or to Figure 9 (a), or to Figure 9 (b), or to Figure 9 (c) of the accompanying drawings.

16. A method of manufacturing a liquid crystal display device as defined in any preceding claim, the method comprising the steps of; a) disposing a liquid crystal material and a polymerisable material between the first substrate and the second substrate; b) putting the liquid crystal material in the first domain of the liquid crystal layer into a high voltage state; and c) polymerising the polymerisable material in at least the first domain of the liquid crystal layer.

17. A method as claimed in claim 16 wherein step (a) comprises introducing a liquid crystal material and a photo-polymerisable material between the first substrate and the second substrate, and wherein step (c) comprises irradiating at least the first domain.

18. A method as claimed in claim 17 wherein step (c) comprises irradiating at least the first domain of the liquid crystal display device with ultra-violet radiation.

19. A method as claimed in claim 16,17 or 18 wherein step (b) comprises applying an electric field between the first substrate and the second substrate.