KR20010020872A - A liquid crystal display device - Google Patents

Abstract

PURPOSE: An LCD is provided to extend the max time for use with low power consumption by forming active liquid crystal areas each area of which can be switched between first and second liquid crystal states and forming a separation area containing a area having a stable third liquid crystal state. CONSTITUTION: The active area A is regulated by the overlapped row and column electrodes in the liquid crystal area, and when voltage pulses are applied, the liquid crystals in the active area A can be controlled to a 0°C twist state and 360°C twist state. A separation area I is formed between two active areas A to separate them and to stabilize the two metastable states in each active area. The separation area is formed as a stable twisted HAN liquid crystal state, and in order to obtain a stable separation area, the pretilt angle of one alignment film in the area corresponding to the separation area is controlled preferably to about 45°C or larger, and more preferably to 90°C. The active area A is preferably completely surrounded by the separation area I in order to effectively separate the active areas A by the separation area I.

Description

Liquid crystal display device {A LIQUID CRYSTAL DISPLAY DEVICE}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to liquid crystal display devices, and more particularly to bistable twisted nematic (BTN) liquid crystal display devices.

As used herein, the term "twist" is defined as meaning the angle in the plane of the liquid crystal cell in which the liquid crystal director rotates from one surface of the liquid crystal cell to the other.

The BTN effect is described in EP-A-0 018 180 and in D. W. Berreman et al., "Journal of Applied Physics" Vol 52, No. 4 p3032 (1981).

The general structure of a bistable twisted nematic (BTN) liquid crystal display device is shown schematically in FIG. The device consists of upper and lower substrates 1, 2 and alignment layers 3, 4 arranged on their respective substrates. A layer 5 of cholesteric (twisted nematic) liquid crystal is arranged between the substrates. Electrodes (not shown) are provided on the upper and lower substrates 1 and 2 so that voltage can be applied across the liquid crystal layer.

1A to 1D show the operating principle of the BTN liquid crystal display device. A cholesteric (twisted nematic) liquid crystal material having a pitch nearly twice as large as the cell gap when the rubbing direction of the upper alignment film 3 is anti-parallel with the rubbing direction of the lower alignment film 4. Adopts an initial state with a twist of 180 ° when no voltage is applied across the liquid crystal layer 5. When the rubbing directions of the two alignment films are antiparallel, a twist state of 180 ° has a disadvantage of being splayed.

In addition to the initial stable 180 ° twist state, there may be two additional metastable states, 0 ° and 360 °, in which there is no splay but the degree of twist is not very good. These states are shown in Figs. 1C and 1D, respectively. These metastable states can be created much faster than 180 ° twisted states and are two states used in BTN liquid crystal display devices. If the BTN liquid crystal cell of FIG. 1 (a) is placed between crossed linear polarizers, the 360 ° twist state of FIG. 1 (d) appears black, and FIG. 1 when its optical axis is oriented at 45 ° with respect to the polarizer directions. The 0 ° twisted state in (c) looks white.

The metastable 0 ° and 360 ° twist states shown in FIGS. 1 (c) and (d) are stable 180 ° in FIG. 1 (a) using the voltage pulses shown in FIGS. 2 (a) and (b). Generated from twisted state. When the liquid crystal is in a 180 ° twisted state, a reset pulse 6 is applied across the electrodes (not shown) initially disposed on the upper and lower substrates. The reset pulse 6 has an amplitude and period sufficient to cause a transition from the 180 ° twisted state to the homeotropic state shown in Fig. 1 (b). In the homeotropic state, the liquid crystal molecules in the bulk of the liquid crystal layer 5 (away from the adjacent positions of the alignment films 3, 4) are, for example, substrates 1, as illustrated by the molecule 7. , 2) perpendicular to the 2).

One of two kinds of optional addressing pulses 8 is applied to the electrodes to select the desired state of the device. One type of selective addressing pulse 8 causes the liquid crystal to switch from the homeotropic state of FIG. 1 (b) to the metastable 0 ° twisted state of FIG. 1 (c). In this state, the cell appears to attenuate to a minimum when the cell is placed between the orthogonal linear polarizers with the rubbing direction of the cell oriented at 45 ° with respect to the light transmission axis of the polarizers. That looks white.

Another type of addressing pulse 8 'causes the homeotropic state of FIG. 1 (b) to switch to the metastable 360 ° twist state of FIG. 1 (d). This is the maximum attenuation, ie the black state, when the liquid crystal cell is placed between the orthogonal linear polarizers.

While the foregoing is directed to devices in which the angle between the alignment directions of the upper and lower alignment films is 180 °, BTN is not limited to this. The angle between the alignment directions of the upper and lower alignment layers can take different values, and when the angle between the alignment directions of the upper and lower alignment layers is Φ, the three stable or metastable states are Φ-π, Φ, and Will have twists of Φ + π (ie, Φ−180 °, Φ, and Φ + 180 °).

The energies of the stable twist state and the two metastable twist states depend on the ratio between the cell gap of the liquid crystal cell and the pitch of the liquid crystal molecules. In general, all three states have different energies, with the stable twist state being the lowest energy state. This state is usually phased distinct from the two metastable twist states and does not correspond to one of the operating states of the LCD. This energy difference between the three states presents two problems. First, the energeticly stable stable twist state is likely to nucleate over a predetermined period of time when no voltage is applied to the liquid crystal cell and grow into a metastable operating state. Moreover, even if the unwanted stable twist state is not nucleated, the more energetic advantage of the two metastable states will slowly grow to another when no voltage is applied across the liquid crystal layer 5. This means that the BTN LCD does not retain the desired display when the device is switched off, and that the BTN LCD is not a true bistable device, and must constantly refresh the display to maintain the desired image.

One particular application of BTN LCDs is low power LCDs such as portable LCDs. In order to increase the maximum time that a device can be used without recharging, it is desirable for such a device to have as low power consumption as possible. Therefore, it is undesirable to frequently update the display to prevent nucleation and growth of unwanted states. Because this increases the power consumption. The present invention seeks to address the problem of refreshing the image displayed on a BTN LCD.

Another example of a bistable twisted nematic (BTN) LCD driven by a passive matrix addressing method is disclosed in "PROC. Asia Display" p259 (1995) by T. Tanaka et al.

Two methods of defining the area addressed in a BTN liquid crystal display are described in D. W. Berreman et al., "Journal of Applied Physics" Vol 52, No. 4 p3032 (1981). Both methods described in this document provide unaddressed areas in the LCD to separate the addressed areas. The ratio of thickness to pitch of the unaddressed area of the LCD is reduced to stabilize the 0 ° twist state in the unaddressed area. Adjacent addressed areas can be switched between 0 ° and 360 ° twisted states and are separated from each other by unaddressed areas. One way to reduce the thickness to pitch ratio of unaddressed regions is to reduce the thickness of the liquid crystal layer of the non-addressed regions. Another disclosed method is to increase the effective pitch of liquid crystal molecules by increasing the tilt of the director of the liquid crystal molecules at an interface between the liquid crystal layer and the alignment films in an unaddressed region as compared to the addressed region.

However, in the case of separation by reduction of cell thickness in unaddressed areas, the entire active area needs to be surrounded by a wall, and the wall height must be at least two thirds of the cell thickness to provide effective separation. do. This can cause problems when filling the device with liquid crystal material because air is likely to trap in the corners of the walls.

Another problem arises in obtaining the required uniformity in the thickness of the cell. If spacer balls are used, they may have a diameter of ˜1 / 3 of the cell thickness when placed on the walls, but in this case it is difficult to place the spacer balls. Alternatively, spacer balls having a thickness equal to the cell thickness may be used, but in this case, great care is required so that the spacer balls are not disposed on the walls but in the active regions. Both of these methods are difficult to perform correctly. Another alternative is to manufacture a pillar on the walls and to make the combined height of the walls and pillars equal to the desired cell thickness. Fillers are provided by repeating the wall manufacturing process, but using a different mask to provide fillers that are not walls. This requires additional processing steps and also requires precise alignment of the mask for the filler.

Providing separation by changing the pre-tilt on both substrates requires a rubbing process masked on both substrates, which means that high precision is required when aligning the two substrates.

GB 2096342 A describes an isolation region for obtaining bistable devices by stabilizing H and V states. These states require parallel alignment. The H state is topologically distinct from the V (or T) state and a s = ± 1/2 disclination line separates the H state from the V state. An isolation area is integrated into the device to prevent movement between the two states. Separation is formed by introducing surface discontinuities (regions of different tilt) disposed between active regions on one of the alignment surfaces. The separation region has a uniform planar alignment and the disclination line is pinned at the surface discontinuity of the alignment layer. Switching between states requires the separation, movement and re-pinning of the fixed s = ± 1/2 disclination line.

In contrast, a BTN is a twisted nematic device in which only one of the three states may not be twisted. Since the two operating states (Φ-180 ° and Φ + 180 °) are not phased apart from each other, there is no disclination line between them, and the undesirable stable Φ state is phased apart from them. BTN devices require the elimination and avoidance of undesirable states throughout their operation. The switching mechanism of the BTN does not involve detachment, movement and reassembly of the disclination line.

Since BTN is a twisted device whose liquid crystal is doped for the necessary twist (thickness to pitch ratio), without homeotropic alignment on both substrates, the isolation region will inevitably be a twisted configuration where the separation action is not apparent. In fact, the proposed configuration in GB 2096342 A for the isolation region applied to BTN will actually stabilize the unwanted steady state, creating disclination lines and actually reducing the possibility of long-term bistable stability of BTN. In BTN, the isolation regions described within the present invention do not fix the disclination, but instead provide a surface discontinuity that allows the formation of a barrier between those operating states to separate the two operating states, which barriers The two operating states must be conformal (phase-wise).

Hoke et al. "SID 97 Digest", p29, suggest that for the high speed performance of BTN LCDs the display should be refreshed frequently enough to prevent nucleation and growth in the 180 ° twisted state. As mentioned above, this method is undesirable because it increases the power consumption of the LCD.

EP-A-0 579 247 discloses a technique for selecting the position of polarizers between which liquid crystal cells are disposed in order to provide maximum contrast in a transmissive BTN LCD.

Hoke and Bos, at "SID 98 Digest", p854, disclose a BTN LCD in which polymer walls are formed around each pixel to prevent growth in a 180 ° twist state. In this method, a photopolymerizable monomer liquid crystal material is used, which is selectively exposed to radiation using a mask while voltage is applied to the liquid crystal cell. This method is disadvantageous because it is difficult to obtain well-defined wall structures without reducing the area of the active region. Moreover, the original polymerization process can cause ion contamination, resulting in image sticking (i.e., difficulty in rewriting pixels from one operating state to another).

It may be foreseen to place a physical barrier having a height equal to the cell thickness around the individual addressed regions. However, this has the disadvantage of complicating the manufacture of LCDs. In particular, it becomes very difficult to fill a panel with a liquid crystal material.

The present invention provides a first and second active liquid crystal layer regions, each of the active liquid crystal layer regions being switchable between a first liquid crystal state and a second liquid crystal state; And an isolation region provided between the first active liquid crystal layer region and the second active liquid crystal layer region, the separation region including a region in which a third liquid crystal state different from the first and second liquid crystal states is stabilized. A bistable twisted nematic liquid crystal display device is provided.

The isolation region separates the addressable liquid crystal regions from each other, so if one 180 ° twisted state is nucleated in one of the active regions, it will not be able to grow to the other active region. Moreover, long term bi-stability of operating states is obtained. Therefore, by providing the separation area, the rate at which the display is degraded is reduced, and thus the rate at which the display should be refreshed will be reduced, and thus the power consumption of the display will be reduced.

In contrast to the separation regions proposed by Berreman et al., The stable liquid crystal state in the separation region of the present invention is not one of the operating states. Since the stable liquid crystal state in the separation region is a twisted state (twist can be made along or across or through the separation region), the disclinations will be fixed to the surface of the liquid crystal layer (at the point where the alignment changes). Therefore, there will be no disclination in the bulk of the liquid crystal. In contrast, if the disconnected state is an operating state, there will be a clear discrepancy between the detached state and the distinctive operating state, but this is not desirable. This is because declining in the bulk liquid crystal increases the likelihood of nucleation of an unwanted state. Thus, the present invention reduces the possibility of nucleation in an unwanted state.

The third liquid crystal state may be a twisted hybrid aligned nematic (HAN) state. Since the twisted-HAN state depends on the operating state at its interface, the disclinations exist only on the surfaces of the liquid crystal layer and not in the bulk of the liquid crystal layer. This reduces the likelihood of unwanted state nucleation as described above. Alternatively, the third liquid crystal state may be a uniform twisted helix state.

The first and second stable liquid crystal states may be a φ-π twisted state and a φ + π twisted state. The first and second stable states may be a 0 ° twisted state and a 360 ° twisted state, or alternatively, may be a -90 ° state and a 270 ° twisted state.

The liquid crystal device includes first and second substrates; First and second alignment layers disposed on the respective substrates; And a BTN liquid crystal material disposed between the substrates, and an alignment direction of one of the alignment layers may be different between the isolation region and the active regions. This provides a convenient way of defining the separation area. Substrates having alignment films having regions of different alignment conditions, such as regions of different pretilt, can be produced, for example, by the method disclosed in the pending UK patent application 9822762.2 with the present application.

One alignment film may have a lower pretilt in the active regions than in the isolation region. This one alignment film can produce substantially 90 ° pretilt in the separation region. Alternatively, this one alignment film can produce a high pretilt that is randomly oriented in the separation region, so that the stable state in the separation region becomes a focal conic state. This one alignment film may generate less than 45 ° pretilt in the active regions, and may generate pretilt in the range of 2-20 ° in the active region.

The separation region includes first and second separation sub-regions, wherein the first separation sub-region is generated by alignment conditions on one alignment film, and the second separation sub-region is generated by alignment conditions on another alignment film. can do. By carrying out similar processing on both alignment films, their properties are kept similar. This reduces the biasing between the alignment films, thus reducing problems such as image flicker due to ion retention. In addition, the possibility of making the pretilts of the two substrates almost the same if a similar process is performed for the two substrates. Moreover, by performing parallel rubbing on the features on both substrates, the problem of shadowing of the rub by the features on the substrates is reduced.

The first separation subregion may be created by a high pretilt region on one alignment layer and the second separation subregion may be created by a high pretilt region on another alignment layer.

The isolation region may further comprise a wall extending between the first substrate of the device and the second substrate of the device. This wall may extend from the first substrate to another substrate.

In addition to providing separation between the active regions, the use of a wall will provide greater physical strength to the liquid crystal cell. In addition, the uniformity of the cell gaps will be improved, and furthermore, the need to provide spacer balls to separate the substrates from each other will be eliminated. Removal of the spacer balls is desirable, since these spacer balls act as nucleation sites for unwanted stable states. This is because the alignment on the surface of the spacer balls is defined by the conditions under which the filling of the device is made, and any type of alignment on the surface of the spacer balls can nucleate an undesired stable state. In addition, the shape of the spacer balls allows the liquid crystal material to flow past the spacer balls when the cell is switched or physically pressed, and this flow can lead to disclination in the bulk of the liquid crystal layer, which is an undesired steady state. Can nucleate. In contrast, the wall has a well-defined alignment, which, in combination with the wall profile, does not produce disclinations in the bulk liquid crystal layer and thus does not nucleate an unwanted stable state.

Projecting the isolation region onto one of the substrates can completely surround the projection of at least one of the active regions onto the one of the substrates. This further improves the separation between the two active regions.

1A to 1D are schematic diagrams of BTN LCDs in four liquid crystal states.

FIG. 2A shows the voltage pulses required to select a 0 ° twist state in a BTN LCD.

FIG. 2B is a diagram showing voltage pulses required for selecting a 360 ° twist state in a BTN LCD.

3 is a schematic sectional view of a BTN LCD according to a first embodiment of the present invention;

4A-4C are possible top views of the LCD of FIG.

5A-5F illustrate a method of manufacturing the device of FIG. 3.

6A-6C are yet other possible top views of the device of FIG. 3, wherein the alignment directions are at an angle to the edge of the active regions.

7A-7C are yet another plan views of the device of FIG. 3, where the alignment direction of the upper substrate is perpendicular to the alignment direction of the lower substrate.

8A-8C show yet another plan view of the device of FIG. 3, wherein the alignment direction of the upper substrate is at an angle of Φ relative to the alignment direction of the lower substrate.

9A and 9B are plan views of a BTN LCD according to another embodiment of the present invention.

9C and 9D are plan views of a BTN LCD according to another embodiment of the present invention.

10A and 10B are plan views of a BTN LCD according to another embodiment of the present invention.

10C and 10D are plan views of a BTN LCD according to another embodiment of the present invention.

11A-11C are plan views of BTN LCDs according to other embodiments of the present invention.

12A-12C are schematic plan views of a BTN LCD according to another embodiment of the present invention.

13A and 13B are partial plan views of the device of FIGS. 12A-12C showing the location of the electrodes.

14 is a partial perspective view of a BTN LCD according to another embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

1, 2: substrate

3, 4: alignment membrane

9: row electrode

10: column electrode

A: active area

I: separation area

3 is a schematic cross-sectional view of the first embodiment of the present invention. This shows a BTN liquid crystal display device having upper and lower substrates 1, 2. This device is a manually addressed device, the row electrode 9 is disposed on the upper substrate, and the column electrode 10 crossed with the row electrode 9 is disposed on the lower substrate 2. The alignment films 3 and 4 are disposed on the upper and lower substrates 1 and 2 through the electrodes, and the alignment direction of the upper alignment film is not parallel to the alignment direction of the lower alignment film 4.

The active region A is defined in the liquid crystal region by the overlap of the row and column electrodes. By applying the voltage pulse of FIG. 2 (a) or FIG. 2 (b), the liquid crystal of the active region A can be placed in a 0 ° twisted state or a 360 ° twisted state.

In the present invention, an isolation region I is provided between two active regions A of the device shown in FIG. 3. The isolation region I separates the two active regions from each other and stabilizes two metastable states in the active region.

The stable liquid crystal state of the isolation region I is not one of the operating states of the active regions A and A. FIG. In the embodiment of Fig. 3, the isolation region is composed of a twisted-HAN liquid crystal state as a stable region. In order for the twisted-HAN state to obtain a stable separation region, the pretilt of the region of one alignment film corresponding to the separation region is high, preferably 45 ° or more, and more preferably substantially 90 °. The pretilt for the region of the upper alignment film 3 corresponding to the active region is lower than the pretilt in the isolation region, and may typically be between 2 ° and 20 °. The lower alignment film 4 has a constant pretilt in both the active region and the isolation region, which will preferably be less than 45 ° and typically between 2 ° and 20 °.

In the embodiment of FIG. 3, the upper alignment film 3 is provided with a high pretilt area, but alternatively the lower alignment film 4 may have a high pretilt area defining a twist-HAN region. In this case, the upper alignment film will preferably have a constant pretilt of less than 45 ° and typically between 2 ° and 20 °.

In order for the isolation region I to provide effective separation between the active regions A and A, the active region is preferably completely surrounded by the isolation region. A preferred isolation region in the case of a device having four active regions is shown in the top view of Fig. 4A.

The isolation region shown in FIG. 4A provides a high pretilt region having a shape corresponding to the isolation region I shown in FIG. 4A for one of the upper and lower alignment films, and a low pretilt region corresponding to the active region. By providing it. The other of the alignment films will have a constant low pretilt in both the isolation and active regions.

An alternative way to create the separation region I is to change the pretilt for all alignment films. 4B shows a modified embodiment of the invention in which the isolation region is thus defined. The isolation region I in FIG. 4B will be considered to consist of a plurality of separation “sub-regions”. Separation sub-regions (I) ₁ , I ₂ and I ₃ are defined as regions of high pretilt for the upper alignment layer and regions of low pretilt for the lower alignment layer, while separation sub-regions (I) ₄ to I ₉ is defined as the region of high pretilt for the lower alignment film and the region of low pretilt for the upper alignment film. Similarly, in FIG. 4C, the separating sub-regions I ₁ , I ₂ ′ and I ₃ ′ are defined as the high pretilt region on the upper substrate and the low pretilt region on the lower substrate, while the separating sub region I ₄ 'to I ₉ ' are defined as the high pretilt region on the lower alignment layer and the low pretilt region on the upper alignment layer.

4A to 4C, the alignment direction of the alignment films 3 and 4 is substantially parallel or perpendicular to the boundary of the active region A (perpendicular to the plane).

From now on, one method of creating a device according to the invention will be described with reference to FIGS. 5A-5F. In this method, the lower alignment membrane is made of polyimide RN-715 (type 0621) from Nissan Chemical Corporation. The non-rubbing layer of this material provides 90 ° pretilt, while rubbing reduces the pretilt. Depending on the rubbing and processing conditions, the pretilt can be reduced by as low as 4 °.

The layer 13 of RN-715 decomposed in a 1: 3 ratio to NMP is rotated on a clean glass substrate 11 coated with ITO 12 to form an electrode. The polyimide is spun on the substrate at 5 krpm for 30 seconds, then heated to 90 ° C. for 2 minutes and then cured to 250 ° for 1 hour.

The polyimide layer 13 was then coated with a layer of positive photo-resist (Shipley, Photo-resist Microposit ^™ S1805 series from Europe) at 4.5 kpm for 40 seconds to obtain a photo-resist layer having a thickness of about 500 nm. to provide. The photo-resist layer is then provided with soft bake for about 2 minutes at 95 ° C. to evacuate the solvent (see FIG. 5B).

Photo-resist layer 14 is then patterned by irradiating an optional portion of the photo-resist layer. The irradiation step includes exposure for 3.5 seconds to UV light (with a peak wavelength of 365 nm) at an intensity of 6.9 mW / cm 2. This irradiation step is carried out via a UV-chrome photomask in hard contact mode with mask alignment. The photo-resist is then developed for one minute using developer Microposit ^™ 351 CD31 to remove the photo-resist from the area exposed to UV light. This leaves a positive reproduction of the photo mask pattern formed in the photo-resist (see FIG. 5C). The substrate is then thoroughly rinsed with non-ionized water for 2 minutes to completely remove the exposed photo-resist. This rinsing step is preferred because any remaining photo-resist affects the fine alignment quality of the alignment film. Hard bake is not performed because it tends to damage the final removal of the photo-resist.

The low pretilt planar alignment is achieved by aligning layer 3 with a rubbing cloth (YA-20-R) and a forward speed of 20 mm / s on a 50 nm diameter roller rotating at 3 kpm with a piling strain of 0.3. By rubbing it is introduced into the unmasked area of the polyimide layer 13 (see FIG. 5D).

The remaining photo-resist is then removed by five second UV filled exposures. This is done with an intensity of 6.9 mW / cm 2 at a wavelength of 365 nm using a mask aligner without a mask. The substrate is then immersed in the developer Microposit ^™ 351 CD31 for 60 seconds. The substrate is then rinsed with non-ionized water for 2 minutes and dried with a stream of nitrogen gas. The final alignment layer comprises coplanar regions 15 with substantially 90 ° pretilt and planar regions 16 with about 10 ° pretilt (see FIG. 5E).

An alternative method for obtaining the patterned pretilt of the alignment layer required for the isolation region may be masked illumination of a suitable photo-alignment layer.

The second substrate 17 is then prepared with an ITO layer 18 of RN-715 polyimide and a uniformly rubbed non-patterning layer 19. This will create an alignment layer with low pretilt that is uniform on the alignment film. This is combined with the substrate of FIG. 5E to form a liquid crystal cell having a 2 μm cell gap, as shown in FIG. 5F. The substrate is arranged so that the alignment direction of the alignment film on the upper substrate is not parallel to the alignment direction of the alignment film on the lower substrate. The cell thus formed is filled with a doping mixture of nematic liquid crystals E7 (Merck) and Chiral dopant R1011. When no voltage is applied across the liquid crystal layer, the cell consists of a region with a 180 ° twist state, separated by a separation region with a twisted-HAN state.

In this embodiment, the stable state in the isolation region is a twisted-HAN state. However, the present invention is not limited to devices in which the stable state in the isolation region is a twisted-HAN state. For example, it has been found that when the device of the present invention is cooled from an anisotropic state, the liquid crystal in the isolation region can adopt a twisted helix state uniformly along the axis of the helix parallel to the substrate of the device. If the electric field is uniformly applied to the liquid crystal in the twisted helix state, it will change to twisted-HAN and remain in the twisted-HAN state even after the electric field is removed. If the isolation region coincides with the gap between adjacent electrodes (e.g., shown in Figure 13A), the liquid crystal layer in the isolation region will remain uniformly twisted helix even when an electric field is applied across the active region of the liquid crystal layer. . Separation regions that are stable in a uniformly twisted helix state have been found to provide satisfactory separation.

Another state suitable for the isolation region is the focal cone state. Some liquid crystal materials do not align in the same direction on the non-rubbed portion of the alignment layer. Instead they employ a random planar alignment with a high tilt resulting in a focal cone liquid crystal state in combination with the alignment on other substrates. In this state, the liquid crystal includes domains that adopt a twisted configuration along the twist direction in which the liquid crystal randomly changes between adjacent domains. The focal cone state has also been found to provide satisfactory separation between adjacent active regions. As an example, Merk's liquid crystal ZLI-4792, when used as a non-rubbed alignment layer of RN715 (Nissan), focus cone alignment is more observed than co-directional alignment.

All three liquid crystal states for the aforementioned separation regions have a twisted structure along the twist axis directed across, along or along the separation region.

In the above-described device, the alignment direction of the alignment film on the upper and lower substrates will be perpendicular or horizontal to the boundary of the active area. However, the alignment direction need not be perpendicular or horizontal to the boundary of the active area. 6A-6C illustrate embodiments in which the alignment direction is not substantially horizontal or perpendicular to the boundary of the active region.

In conjunction with the devices shown in FIGS. 4A-4C, the isolation regions of the devices of FIGS. 6A-6C may be provided by patterning alignment films on one substrate or all substrates.

In the device shown in FIG. 6A, the isolation region is obtained by providing a high pretilt region on one of the alignment films, depending on the shape of the higher pretilt region corresponding to the predetermined shape of the isolation region. The region of the alignment film corresponding to the active region has low pretilt. The other of the alignment membranes is substantially constant over its entire area and has low pretilt.

6B and 6C show a modification of the embodiment of FIG. 6A obtained by providing all the alignment films in the region of the pretilt having a high separation region. Sub separation regions (I) ₁ and I ₂ (FIG. 6B) and I ₅ ′, I ₆ ′, and I ₇ ′ (FIG. 6C) show high pretilt regions on the upper alignment layer and low pretilt regions on the lower alignment layer. While isolation regions I ₃ , I ₄ and I ₅ (FIG. 6B) and I ₁ ′, I ₂ ′, I ₃ ′, and I ₄ ′ (FIG. 6C) are obtained by providing a high pretilt on the lower alignment layer. By providing a low pretilt region on the region and the upper alignment layer.

The present invention is not limited to the BTN liquid crystal display device in which the operating state is 0 ° twisted state and 360 ° twisted state. 7A to 7C show an embodiment of the present invention to which the present invention is applied to a BTN liquid crystal display device in which the operating state is -90 ° twisted state and 270 ° twisted state. 7A, 7B, and 7C generally correspond to the embodiments shown in FIGS. 4A, 4B, and 4C, respectively, except that the embodiment of FIGS. 7A-7C has only two active regions.

In the embodiment of FIG. 7A, the isolation region I provides one of the upper and lower alignment films to the high pretilt region having a shape corresponding to the isolation region I shown in FIG. 7A, and the active region A It is obtained by providing a low pretilt area corresponding to.

In the embodiment of FIGS. 7B and 7C, isolation region I is formed from a plurality of isolation “sub-regions”. Some of the isolation subregions are defined as high pretilt regions on one of the substrates and another is defined as high pretilt regions on the other substrate. Separation subregions I ₁ , I ₂ (FIG. 7B) and I ₅ ′ to I ₇ ′ (FIG. 7C) are defined as regions of high pretilt on the upper alignment layer, while separation sub-regions I to ₃ . I ₆ (FIG. 7B) and I ₁ ′ to I ₄ ′ (FIG. 7C) are defined as regions of high pretilt on the lower alignment layer.

8A-8C correspond to FIGS. 7A-7C, but show the general case where two metastable operating states have twist angles Φ−π and Φ + π. The isolation region is defined in the same manner as the corresponding isolation region in FIGS. 7A-7C and will not be further described.

Another embodiment of the present invention is shown in FIGS. 9A and 9B. In this embodiment, the isolation region I is not defined only by the region in which the twisted-HAN state is stable. In this embodiment, the separation region is defined by the combination of the region where the first twisted-HAN state is stable and the second physical wall or boundary. The physical wall extends in the direction between the upper substrate and the lower substrate, thus separating the liquid crystal on the other side of the month from the liquid crystal on the other side of the month. Preferably, the physical wall extends from the upper substrate to the lower substrate because it provides more effective separation between adjacent active regions and also allows the wall to function as a spacer that defines the thickness of the liquid crystal layer.

If the cross-sectional profile of the wall has a very small gradient, at some point along it the thickness may stabilize the undesired possible state of nucleation into the adjacent liquid crystal region, There is a possibility that it will be difficult to switch all liquid crystals in the active region bounded by the wall to the desired state. An additional disadvantage of stabilizing along the wall and having an undesired steady state is that light can leak through the region of the undesired steady state. For example, when the 360 ° twist state (black state) is reached, any areas of the stabilized 0 ° twist state along the month will appear bright, which will reduce the contrast of the display. will be. The regions of unwanted steady state stabilized along the wall may be masked out to suppress the reduction of contrast but this may reduce the aperture ratio of the device. Therefore, the walls have a clear or substantially clear cross-sectional profile.

In the embodiment of FIG. 9A, the separation region is formed by two physical walls W ₁ , W ₂ and three twisted-HAN separation sub-regions I ₁ , I ₂ , I ₃ . These separation sub-regions and the wall combine to form a separation region having the same shape as the separation region of Fig. 4A. In Fig. 9B, the three twisted-HAN separation subregions are reused, but at (W ' ₁ ) There are four physical months up to W ' _4. (The above embodiment of FIG. 9B has four physical months, but optionally the months W' ₁ and W ' ₂ are continuous, and the months W' ₃ to ₃ ). It is possible for (W ' ₄ ) to be contiguous.) The advantage of using a physical wall to define a portion of the isolation region is that larger physical for the liquid crystal cell, besides providing separation between adjacent active regions. To provide strength, and they provide uniform cell thickness over large areas Improves the uniformity of the existing cells, which also eliminates the need to provide spacer balls to separate the substrates from each other, firstly the spacer balls in the active region reduce the aperture ratio, and secondly the spacers This is desirable because the ball has been observed to act as a nucleation site for undesired steady state and / or other operating states.

In the liquid crystal display device shown in FIGS. 9A and 9B, it will be seen that no part of the liquid crystal region is completely surrounded by physical walls. This means that the present invention can avoid the difficulty of creating a liquid crystal device having a physical wall that completely surrounds the liquid crystal region.

In the embodiment of FIG. 9A, an alignment film on one substrate is patterned to form regions of high pre-tilt to create separation subregions I ₁ , I ₂ , I ₃ . It is done. Then, the physical walls W ₁ , W ₂ are formed of the patterned alignment film on the same substrate and disposed on the patterned alignment film. In contrast, in the embodiment of Fig. 9 (b), the physical walls W ' ₁ to W' ₄ are first formed on one of the substrates, and then the patterned alignment film is formed on the wall structure. The benefit of this alignment depends on the specific material used. For example, certain monthly materials require processes that damage the alignment layer and it is therefore advantageous to place the alignment layer above the moon. In contrast, other wall materials are intended to be placed on the alignment layer. Moreover, any material may be used to form both the alignment layer and the physical layer.

One way of forming the wall is blood. tea. Kazlas et al. (SID 97 Digest, p877). This provides a photo-definable resin BCB (benzocyclobutene)-negative image developed by Dow Chemical Company (i.e. of resins exposed to UV light after processing). Area remains).

The wall can also be made by using positive photoresist, in which the exposed area is removed after development. To make the height of the month having the 2㎛ In this way, the first part (part) to a volume of EC for the solvent (which both may be obtained from a break-free (Shipley) in Europe), the dissolution of 5 parts Micro opposite ^TM A solution of (Microposit ^™ ) S1828 series positive photoresist is spin coated onto the substrate for 40 seconds at an open bowl spinner at a speed of 4 krpm. (In a closed bowl spinner, a slower speed is needed.) This forms a layer approximately 2.1 μm thick. The layer is then soft baked at 95 ° C. for about 2 minutes to evaporate the solvent.

The photoresist was then UV with an intensity of 6.9 μs / cm 2 and a wavelength of 365 nm through a UV-chrome photomask in a vacuum contact mode of Karl Suss mask aligner. Are exposed to light. The time of the exposure step is 6 seconds. The photoresist is then developed for one minute in a development device microposite ^™ 351 CD31 to remove the photoresist from the area exposed in the exposing step. The substrate is then washed thoroughly for 2 minutes in de-ionised water.

The substrate is then hard baked at 250 ° C. for at least 1 hour after 60 minutes Deep UV cure in an Eprom Eraser. This increases physical and chemical resistance among remaining photoresist properties. During this step, a thermal flow of photoresist is produced, which reduces the height of the wall to about 2 μm.

In order to obtain a wall having a height different from 2 μm, the spinning conditions of the photoresist and possibly the concentration of the photoresist should be varied to give the desired wall thickness.

Another embodiment is shown in FIGS. 9C and 9D. In this embodiment, a physical wall is disposed on one of the substrates, which substrate is provided with an unpatterned alignment film. Alignment films on other substrates may be of high pretilt to produce separation sub-regions I ₁ , I ₂ , I ₃ (FIG. 9C) and (I ′ ₁ , I ' ₂ , I' ₃ ) (FIG. 9D). Patterned to provide an area. (The above embodiment of FIG. 9D has four physical months, but it is possible for the months W ' ₁ and W' ₂ to be continuous, and the months W ' ₃ to W' ₄ are continuous.)

9A-9D the alignment direction of the alignment film for both the upper and lower substrates is parallel to the direction of the physical wall. However, this is not an essential characteristic. 10a to 10d show a further embodiment of the invention-embodiments generally correspond to the embodiment of FIGS. 9a to 9d, except that the alignment direction of the alignment film is parallel to the direction of the twist-HAN region rather than the physical wall. -Is shown. (The above embodiment of FIGS. 10B and 10D has four physical months, but it is possible for the months W ' ₁ and W' ₂ to be continuous, and the months W ' ₃ to W' ₄ may be continuous.)

11A-11C are generally except that the alignment direction of the alignment film on one substrate is orthogonal to the alignment direction of the alignment film on another substrate, such as the metastable operating states of -90 ° and 270 ° twisted states. 9A, 9C and 9D, respectively. In the embodiment of FIG. 11A, a high pretilt region defining a twist-HAN isolation sub-region and a physical wall is provided on the same substrate. In contrast, in FIGS. 11B and 11C, a physical wall is provided on one substrate and the patterned alignment film having a high pretilt area is provided on another substrate. Since these embodiments are generally similar to those of FIGS. 9A, 9C, and 9D, they will not be described further. (The above embodiment of FIG. 11C has four physical months, but it is possible for the months W ' ₁ and W' ₂ to be continuous, and the months W ' ₃ to W' ₄ are continuous.)

12A-12C correspond to FIGS. 11A-11C, respectively, but in relation to the general case where two metastable states have twist angles of Φ−π ° and Φ + π °. [The embodiment of FIG. 12C has four physical months, but it is possible for the months W ' ₁ and W' ₂ to be contiguous, and the months W ' ₃ to W' ₄ are contiguous.]

13A and 13B show possible relationships between row and column electrodes 9, 10 and isolation regions in the liquid crystal device according to the invention.

In the device shown in the plan view of FIG. 13A, the isolation regions I are arranged such that the gap between adjacent row electrodes and the gap between adjacent column electrodes coincide with the isolation region. This arrangement maximizes the aperture ratio of the device.

13B illustrates another embodiment. In this embodiment, the gap between adjacent row electrodes again coincides with the isolation region. However, the gap between adjacent column electrodes does not completely coincide with the isolation region.

In FIG. 13B, the row electrode 9 is located above the substrate 1. (The lower substrate in FIG. 13B) And the column electrode 10 is located on the substrate 2 (the upper substrate in FIG. 13B). The active region of the liquid crystal region is displaced substantially in parallel with the row electrode in the rubbing direction of the substrate on which the row electrode is disposed. A portion of the active region of the liquid crystal device-ie the switchable region between the operating states-coincides with the gap between the column electrodes and as a result can not be switched, which slightly reduces the aperture ratio of the device. However, this portion of the unswitched active region has been shown to act as a good isolation region. The type of arrangement shown in FIG. 13B provides greater separation than the arrangement of FIG. 13A in which inter-electrodes gaps are registered as isolation regions.

In another embodiment (not shown), the gap between adjacent column electrodes coincides with the isolation region I while the gap between adjacent row electrodes does not completely coincide with the isolation region I. The active region of the liquid crystal region is displaced substantially parallel to the column electrode in the rubbing direction of the substrate on which the column electrode is disposed.

In another embodiment (not shown), the gap between adjacent row electrodes and the gap between adjacent column electrodes do not all coincide with the isolation region I completely. The active region of the liquid crystal region is displaced substantially parallel to the column electrode in the rubbing direction of the substrate on which the column electrode is disposed, and also substantially displaced substantially parallel to the row electrode in the rubbing direction of the substrate on which the row electrode is disposed. .

14 is a schematic diagram illustrating the orientation of a substrate of a BTN LCD in accordance with a further embodiment of the present invention. In this device, stable operating states are -90 ° and 270 ° twisted states. This device requires that the angle φ between the alignment directions for the upper and lower substrates is 90 °. In FIG. 14, separation regions are defined by a combination of physical walls and separation sub-regions. As shown in FIG. 14, placing the physical wall on one substrate and the separating sub-region on another substrate causes the features provided on each substrate to be parallel to the rubbing direction of the substrate. This feature is advantageous because the features provided on the substrate reduce shadowing of the rub, which helps to maintain a uniform pretilt with respect to the substrate.

Thus, in the embodiment of FIG. 14 the physical wall W is disposed above the lower substrate 2 and extends generally parallel to the rubbing direction of the lower substrate. The separation region is provided on the upper substrate and extends parallel to the rubbing direction of the upper substrate. When the upper substrate is manufactured, the strip S of the photoresist constituting the photoresist mask is generally in the rubbing direction of the upper substrate 1 (as produced, for example, by the method of FIG. 5C). Extends parallel to (The strip S of photoresist is of course removed after the step of rubbing the upper substrate and is not included in the final device.)

Although the present invention has been described with reference to certain specific embodiments, the present invention is not limited to the above-described embodiments. The present invention is not limited to a device having two or four active regions, but can be applied to a device having any number of active regions.

In the above-described embodiment, the isolation regions completely surround each of the active regions and as a result separate one active region completely from the other active region. In general, however, it is possible that the isolation region does not completely separate the two active regions. This type of isolation region provides certain advantages for devices that do not provide isolation regions, but it is desirable that the isolation regions completely surround the active regions because they provide improved separation between the active regions.

Where the separation region is defined by a combination of physical months and regions in which the twist-HAN state is stabilized, the physical wall does not always need to be perpendicular to the twist-HAN region. Any combination of twisted-HAN regions that define the physical wall and appropriate isolation regions can be used. However, as described above, since it is difficult to fill the active region with the liquid crystal material, it is preferable that the active region is not completely surrounded by the physical wall.

The bistable twisted nematic liquid crystal display device of the present invention provides a separation region (I) between the first and second active liquid crystal regions (A), thereby preventing the unwanted state from nucleating and growing into the active region, It is also possible to prevent a state in one active region from growing into another active region.

Claims (18)

In a bistable twisted nematic liquid crystal display device, First and second active liquid crystal regions, each of the active liquid crystal regions being switchable between a first liquid crystal state and a second liquid crystal state; And A separation region provided between the first active liquid crystal region and the second active liquid crystal region, wherein the separation region includes a region where the third liquid crystal state is stable Liquid crystal display device comprising a. The liquid crystal display device as claimed in claim 1, wherein the third stable liquid crystal state is a twisted-HAN state. 2. A liquid crystal display device as claimed in claim 1, wherein the third stable liquid crystal state is a uniform twisted helix state. 2. A liquid crystal display device as claimed in claim 1, wherein said third stable liquid crystal state is of focal conic texture. The liquid crystal display device according to claim 1, wherein the first and second stable states are a (Φ-π) ˚ twisted state and a (Φ + π) ˚ twisted state. 6. The liquid crystal display device as claimed in claim 5, wherein the first and second stable states are a 0 degree twisted state and a 360 degree twisted state. 6. The liquid crystal display device as claimed in claim 5, wherein the first and second stable states are a -90 ° twisted state and a 270 ° twisted state. The liquid crystal device of claim 1, wherein First and second substrates; First and second alignment layers disposed on the respective substrates; And BTN liquid crystal material disposed between the substrates Including, And an alignment condition of one of the alignment layers is different between the separation region and the active liquid crystal regions. 9. A liquid crystal display device as claimed in claim 8, wherein said one alignment film has a lower pre-tilt in said active regions than in said isolation region. 10. A liquid crystal display device as claimed in claim 9, wherein said one alignment film produces substantially 90 [deg.] Of pretilt in said separation region. 10. The liquid crystal display device as claimed in claim 9, wherein the one alignment film generates a high pretilt randomly directed in the separation region. 9. A liquid crystal display device as claimed in claim 8, wherein said one alignment film produces less than 45 [deg.] Pretilt in said active regions. The liquid crystal display device of claim 8, wherein the one alignment layer generates a pretilt in a range of 2 to 20 ° in the active regions. 9. The method of claim 8 wherein the separation region comprises first and second separation sub-regions, wherein the first separation sub-region is created by alignment conditions on one alignment layer, and the second separation sub- And the region is created by alignment conditions on another alignment film. 15. The method of claim 14, wherein the first separation sub-region is generated by a high pretilt region on the one alignment layer and the second separation sub-region is generated by a high pretilt region on the other alignment layer. A liquid crystal display device characterized by the above-mentioned. The liquid crystal display device of claim 1, wherein the isolation region further comprises a wall extending between the first substrate of the device and the second substrate of the device. 17. The liquid crystal display device as claimed in claim 16, wherein the wall extends from the first substrate to the other substrate. 9. The method of claim 8, wherein projecting the separation region onto one of the substrates comprises: projecting at least one of the first and second active regions onto the one of the substrates. A liquid crystal display device which completely encloses the projected thing.