JP4155377B2 - LCD display device - Google Patents

Abstract

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

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to liquid crystal display devices, and more particularly to bistable twisted nematic (BTN) liquid crystal display devices.
[0002]
[Prior art]
The term “twist” as used herein is defined to mean an angle in the plane of the liquid crystal cell through which the liquid crystal director rotates from one surface of the cell to the other. .
[0003]
The BTN effect is shown in EP-A-O 018 180 and D.E. W. Berreman et al., “Journal of Applied Physics”, Vol. 4, page 3032 (1981).
[0004]
A schematic structure of a bistable twisted nematic (BTN) liquid crystal display device is schematically shown in FIG. The device is composed of an upper substrate 1 and a lower substrate 2 and alignment layers 3 and 4 provided on each of these substrates. A layer 5 of cholesteric (twisted nematic) liquid crystal is provided between these substrates. Electrodes (not shown) are provided on the upper substrate 1 and the lower substrate 2 to allow a voltage to be applied to the liquid crystal layer.
[0005]
FIG. 1 (a) to FIG. 1 (d) show the operating principle of a BTN liquid crystal display device. When the rubbing direction of the upper alignment film 3 is anti-parallel to the rubbing direction of the lower alignment film 4, the pitch is substantially twice the cell gap when no voltage is applied to the liquid crystal layer 5. An initial state is adopted in which the cholesteric (twisted nematic) liquid crystal material has a 180 ° twist. When the rubbing directions of the two alignment films are anti-parallel, the 180 ° twist state has a drawback of spreading.
[0006]
In addition to the initial stable 180 ° twist state, there can be two additional metastable states that do not spread, but these states have a slightly unfavorable twist (ie, 0 ° and 360 °). These states are shown in FIG. 1 (c) and FIG. 1 (d), respectively. These metastable states can be generated much faster than the 180 ° twist state, and these two states are used in BTN liquid crystal display devices. When the BTN liquid crystal cell of FIG. 1 (a) is provided between intersecting linear polarizers, the 360 ° twisted state of FIG. 1 (d) appears black, and conversely the optical axis is 45 ° with respect to the polarizer direction. When directed, the 0 ° twisted state of FIG. 1 (c) appears white.
[0007]
The metastable 0 ° and 360 ° twist states shown in FIG. 1 (c) and FIG. 1 (d) use the voltage pulses shown in FIG. 2 (a) and FIG. Are generated from a stable 180 ° twist state. When the liquid crystal is in a 180 ° twist state, the reset pulse 6 is first applied between electrodes (not shown) provided on the upper substrate and the lower substrate. The reset pulse 6 has sufficient amplitude and duration to cause a transition from the 180 ° twist state to the homeotropic state shown in FIG. In the homeotropic state, the liquid crystal molecules in the bulk of the liquid crystal layer 5 (parts away from the immediate vicinity of the alignment films 3 and 4) are aligned perpendicular to the substrates 1 and 2, for example, by the molecules 7. Is done.
[0008]
One of two types of select addressing pulses 8 is then applied to the electrodes to select the desired state of the device. One type of selective addressing pulse 8 switches the liquid crystal from the homeotropic state of FIG. 1 (b) to the 0 ° twist state of FIG. 1 (c). In this state, when the cell is provided between linear polarizers orthogonal to each other with the rubbing orientation of the cell oriented at 45 ° with respect to the transmission axis of the polarizer, the cell appears to have minimal attenuation. Looks white, that is, it looks white.
[0009]
The other type of addressing pulse 8 'switches the homeotropic state of FIG. 1 (b) to the metastable 360 ° twist state of FIG. 1 (d). This is a state where the attenuation is maximum, that is, a black state when the liquid crystal cell is provided between linear polarizers orthogonal to each other.
[0010]
In the above description, the device in which the angle between the alignment directions of the upper and lower alignment films is 180 ° is described, but the BTN is not limited to this. The angle between the alignment directions of the upper and lower alignment films may be other values. When the angle between the alignment directions of the upper and lower alignment films is Φ, the three stable or metastable states are Φ−π, Φ, and Φ + π (ie, Φ−180 °, Φ, and Φ + 180 °). Has a twist.
[0011]
The energy of one stable twist state and two metastable twist states depends 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 exist at different energies, with the stable twist state being the lowest energy state. This state is usually topologically distinct from the two metastable twist states, and this does not correspond to any of the LCD operating states. The energy difference between the three states creates two problems. First, when no voltage is applied to the liquid crystal cell, a stable twist state that is favorable in terms of energy tends to nucleate and change to a metastable operation state during a certain period. Furthermore, when no voltage is applied to the liquid crystal layer 5, even if an undesirable stable twist state does not nucleate, the more energetically preferred of the two metastable states changes slowly to the other. This means that when the device is switched off, the BTNLCD does not maintain the desired display (ie, the BTN LCD is not a true bistable device) and the display must be constantly refreshed to maintain the desired image. It means you have to.
[0012]
[Problems to be solved by the invention]
One particular application for BTN LCDs is low power LCDs, for example portable LCDs. For such devices, it is desirable to have as low a power consumption as possible and to extend the maximum time that the device can be used without recharging. Therefore, having to update the display frequently to prevent unwanted nucleation and changes is undesirable because it increases power consumption. The present invention addresses the problem of having to refresh the image displayed on the BTN LCD.
[0013]
A further example of a bistable twisted nematic (BTN) LCD driven by a passive matrix addressing method is described in T.W. Tanaka et al., “PROC. Asia Display”, page 259 (1995).
[0014]
Two methods for confining the address region within a BTN liquid crystal display are described in D.C. W. Berreman et al., “Journal of Applied Physics”, Vol. 52, no. 4, page 3032 (1981). Both methods described in this document provide a non-address area in the LCD and divide the address area. In order to stabilize the 0 ° twist state in the non-address area, the ratio of the thickness of the non-address area of the LCD to the pitch is lowered. Adjacent address regions can be switched between a 0 ° twist state and a 360 ° twist state, which are separated from each other by non-address regions. One way to reduce the ratio of the thickness to the pitch of the non-address area is to reduce the thickness of the liquid crystal layer in the non-address area. Another method disclosed is to increase the effective pitch of the liquid crystal molecules by increasing the inclination of the director of the liquid crystal molecules at the interface between the liquid crystal layer and the alignment film in the non-address region as compared to the address region. It is.
[0015]
However, isolation by reducing the thickness of the cell in the non-addressed region requires that the entire active region be surrounded by a wall, and this wall height is required to provide effective isolation. Must be at least 2/3 of the thickness. This can be a problem when filling the device with liquid crystal material because air tends to be trapped in the corners of the wall.
[0016]
A further problem arises in obtaining the required uniformity of cell thickness. If spacer balls are used, they can have a diameter of about 1/3 of the cell thickness if they are placed on the wall, but in this case it is difficult to position the spacer balls. Alternatively, spacer balls having a thickness equal to the cell diameter can be used, but this requires great care to ensure that the spacer balls are placed in the active area and not on the wall. Is done. Both of these methods are difficult to implement accurately. As a further option, pillars can be formed on the walls, and the combined height of the walls and pillars is equal to the desired cell thickness. The pillars are provided by repeating the wall forming process, but require a separate mask to provide the pillars rather than the walls. This requires additional process steps and also requires precise positioning of the pillar mask.
[0017]
To perform separation by correcting the pretilt on both substrates, a mask rubbing process is required on both substrates, which means that high accuracy is required when orienting the two substrates.
[0018]
GB 2096342A describes an isolation region that obtains a bistable device by stabilizing the H and V states. These states require parallel orientation. The H state is topologically different from the V (or T) state, and the s = ± 1/2 disclination line separates the H state from the V state. A separation region is built into the device to prevent drift between the two states (ie movement of the disclination line). This separation region is formed by introducing a discontinuous surface (region of different tilt) placed between the active regions on one orientation surface. This separation region has a uniform planar orientation, and the disclination line is fixed to the discontinuous surface of the orientation layer. Switching between states requires removal, movement, and re-fixation of the fixed s = ± 1/2 disclination line.
[0019]
In contrast, BTN is a twisted nematic device in which only one of the three states can be non-twisted. The two operating states (Φ-180 ° and Φ + 180 °) are not topologically different from each other and there is no disclination line between them, but the undesired stable Φ state is topologically different from these. BTN devices require removal and avoidance of undesired conditions throughout operation. The BTN switching mechanism does not include removal, movement, and re-fixation of disclination lines.
[0020]
If BTN is a twisted device with a liquid crystal doped for the required twist (ratio of thickness to pitch), the isolation region is necessarily present if there is no homeotropic alignment on both substrates. Thus, a twisted configuration in which the separation behavior is unclear is obtained. In fact, the separation area configuration applied to BTN, proposed in GB 2096342A, stabilizes the undesired stable state, generates the disclination line, and actually makes the possibility of long-term bistability of BTN. make low. With BTN, the separation region described in the present invention does not fix the disclination, but instead it allows to form a barrier between them in order to separate the two operating states Provide a discontinuous surface. This barrier must be consistent (topologically equivalent) with the two operating states.
[0021]
Hoke et al., “SID 97 Digest”, p. 29, suggests that due to the high speed performance of BTN LCDs, the display should be refreshed frequently enough to prevent nucleation and changes in the 180 ° twist state. . As mentioned above, this method is undesirable because it increases the power consumption of the LCD.
[0022]
EP-A-0 579 247 discloses a technique for selecting the position of a polarizer between which liquid crystal cells are arranged in order to provide maximum contrast in a transmissive BTN LCD.
[0023]
Hoke and Bos, in “SID 98 Digest”, page 854, disclose a BTN LCD in which polymer walls are formed around each pixel to prevent changes in the 180 ° twist state. In this method, a photopolymerizable monomer liquid crystal material is used, which is selectively irradiated using a mask while a voltage is applied to the liquid crystal cell. This method is disadvantageous because it is difficult to obtain a clear wall structure without reducing the area of the active region. Furthermore, the in situ polymerization process can cause ion contamination, resulting in burn-in (ie, difficulty in rewriting pixels from one operating state to another operating state).
[0024]
It can be expected that physical barriers having a height equal to the thickness of the cell are arranged around the individual address areas. However, this has the disadvantage of complicating LCD manufacturing. In particular, it becomes very difficult to fill the panel with a liquid crystal material.
[0025]
[Means for Solving the Problems]
  The liquid crystal display device of the present invention includes first and second substrates, first and second alignment films provided with an alignment direction in an antiparallel state on each of the first and second substrates, and the first and second alignment films, A bistable twisted nematic liquid crystal display device including a BTN liquid crystal material provided between the first and second alignment films, wherein the BTN liquid crystal material is configured to be applied with a voltage. An active liquid crystal region, a second active liquid crystal region, and a separation region provided in a state where no voltage is applied between the first active liquid crystal region and the second active liquid crystal region, Each of the second active liquid crystal regions can be switched between a first liquid crystal state and a second liquid crystal state by application of a voltage, and the separation region is a region that is stable in the third liquid crystal state. Including the first And the second liquid crystal state are a (Φ−π) ° twisted state and a (Φ + π) ° twisted state, respectively, and one alignment condition of the first and second alignment films is the separation region and the first liquid crystal state. And the second active liquid crystal region, wherein the third liquid crystal state isUniform twisted helixIt is.
[0027]
  In addition, the liquid crystal display device of the present invention includes first and second substrates, and first and second alignment films provided with an alignment direction in an antiparallel state on each of the first and second substrates, A bistable twisted nematic liquid crystal display device including a BTN liquid crystal material provided between the first and second alignment films, wherein the BTN liquid crystal material is configured to be applied with a voltage. A first active liquid crystal region, a second active liquid crystal region, and a separation region provided in a state where no voltage is applied between the first active liquid crystal region and the second active liquid crystal region, Each of the first and second active liquid crystal regions can be switched between a first liquid crystal state and a second liquid crystal state by applying a voltage, and the separation region is stably in the third liquid crystal state. Including the area The first and second liquid crystal states are a (Φ−π) ° twist state and a (Φ + π) ° twist state, respectively, and one alignment condition of the first and second alignment films is that the separation region and the Unlike the first and second active liquid crystal regions, the third liquid crystal state is a focal cone structure.
[0030]
  According to an embodiment of the present invention, the first and secondliquid crystalThe states are a 0 ° twist state and a 360 ° twist state, respectively.
[0031]
  According to an embodiment of the present invention, the first and secondliquid crystalThe states are a −90 ° twist state and a 270 ° twist state, respectively.
[0033]
  According to one embodiment of the present invention, the one alignment film is theFirst and secondActivityliquid crystalThe region has a lower pretilt than the separation region.
[0034]
According to an embodiment of the present invention, the one alignment film generates a pretilt of substantially 90 ° in the separation region.
[0035]
According to one embodiment of the present invention, the one alignment film generates a high pretilt randomly oriented in the separation region.
[0036]
  According to one embodiment of the present invention, the one alignment film is theFirst and secondActivityliquid crystalIn the region, a pretilt smaller than 45 ° is generated.
[0037]
  According to one embodiment of the present invention, the one alignment film is theFirst and secondActivityliquid crystalIn the region, a pretilt in the range of 2 ° to 20 ° is generated.
[0038]
According to an embodiment of the present invention, the isolation region includes first and second isolation sub-regions, and the first isolation sub-region is generated according to an alignment condition on the one alignment film, and The two separation subregions are generated by the alignment conditions on the other alignment film.
[0039]
According to an embodiment of the present invention, the first separation subregion is generated by a high pretilt region on the one alignment film, and the second separation subregion is a high pretilt region on the other alignment film. Is generated by
[0040]
According to one embodiment of the invention, the isolation region further comprises a wall extending between the first substrate of the device and the second substrate of the device.
[0041]
According to one embodiment of the invention, the wall extends from the first substrate to the second substrate.
[0042]
According to one embodiment of the invention, the projection of the isolation region onto one of the first and second substrates is at least one of the first and second active regions. Fully envelop the projection to.
[0043]
The present invention provides a bistable twisted nematic liquid crystal display device that includes first and second active liquid crystal layer regions, each active liquid crystal region being between a first liquid crystal state and a second liquid crystal state. It can be switched with. The device further includes an isolation region provided between the first active liquid crystal region and the second active liquid crystal region, wherein the isolation region is a third liquid crystal state different from the first and second liquid crystal states. Is provided with a stable region.
[0044]
The separation region separates the addressable liquid crystal areas from each other so that when the 180 ° twist state is to be nucleated in one active region, it cannot change in the other active region. Furthermore, long-term bistable operation is obtained. Thus, providing an isolation region reduces the rate at which the display degrades, thus reducing the rate at which the display needs to be refreshed and thus reducing the power consumption of the display.
[0045]
Unlike the isolation region proposed by Berreman et al. Above, the stable liquid crystal state in the isolation region of the present invention is not one of the operating states. The stable liquid crystal state in the separation region is a twisted state (twist may exist along, across, or through the separation region), so that the disclination is at the surface of the liquid crystal layer. It becomes fixed (at the point where the orientation changes), resulting in no disclination in the bulk of the liquid crystal. In contrast, when the separation state is an operation state, a clear disclination can be made between the separation state and a different operation state. This is undesirable because disclination in the bulk of the liquid crystal raises the possibility of nucleating undesired states. Thus, the present invention reduces the probability that an undesired state will nucleate.
[0046]
The third liquid crystal state may be a twisted hybrid alignment nematic (HAN) state. Since the twisted HAN state coincides with the operating state at the interface, the disclination exists only on the surface of the liquid crystal layer and does not exist in the bulk liquid crystal layer. This reduces the probability that an undesired state will nucleate, as described above. Alternatively, the third liquid crystal state can be a uniform twisted helix state.
[0047]
The first and second stable liquid crystal states can be a Φ-π twist state and a Φ + π twist state. The first and second stable states can be a 0 ° twist state and a 360 ° twist state, or alternatively can be a −90 ° twist state and a 270 ° twist state. The liquid crystal device may include first and second substrates, first and second alignment layers provided on each of these substrates, and a BTN liquid crystal material provided between the substrates. The alignment direction of one alignment film may be different between the isolation region and the active region. This provides a convenient way to define the separation region. Substrates having alignment films with regions of different alignment conditions (eg, regions of different pretilts) can be used, for example, in UK patent application No. 9911730.1, which is the basis of the priority claim of this application. It can be produced by the method disclosed in US9822762.2.
[0048]
One alignment film may have a lower pretilt in the active region than in the isolation region. One alignment film can produce a pretilt of substantially 90 ° in the separation region. Alternatively, this one alignment film can generate a high pretilt randomly oriented in the separation region, so that the stable state in the separation region is a focal cone state. One alignment film can produce a pretilt less than 45 ° in the active region, which can produce a pretilt in the range of 2 ° to 20 ° in the active region.
[0049]
The isolation region may include first and second isolation sub-regions, and the first isolation sub-region is generated by an alignment condition on one alignment film, and the second isolation sub-region is on the other alignment film. It is generated according to the alignment conditions. By treating both alignment films in the same way, their properties are kept the same. This reduces the bias between alignment films and reduces problems such as image sticking that occur due to ion retention. Furthermore, the pretilt of the two substrates is likely to be approximately equal if the two substrates are exposed to a similar process. Further, by performing the rubbing parallel to the elements on both substrates, the problem of rubbing shadowing by the elements on the substrate is reduced.
[0050]
The first separation subregion can be generated by a high pretilt region on one alignment film, and the second separation subregion can be generated by a high pretilt on the other alignment film.
[0051]
The isolation region may further include 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 the other substrate.
[0052]
In addition to providing separation between the active regions, the use of walls gives the liquid crystal cell greater physical strength. This also improves cell gap uniformity and eliminates the need to supply spacer balls to separate the two substrates away from each other. Since the spacer balls can serve as nucleation sites for undesired steady state, it is preferable to eliminate them. This is because the orientation on the surface of the spacer ball is defined by the conditions under which the device is filled, and certain types of orientation on the surface of the spacer ball can nucleate undesired stable states. Furthermore, the shape of the spacer ball allows the liquid crystal material to flow past the spacer ball when the cell is switched or physically compressed. This flow can cause disclination in the bulk liquid crystal layer that can nucleate undesired stable states. In contrast, the walls, when combined with the wall cross-section, have a well-defined orientation that does not produce disclinations in the bulk liquid crystal layer and thus does not nucleate undesired stable states.
[0053]
Projection of the isolation region onto one substrate may completely surround the projection of at least one active region onto that substrate. This further improves the separation between the two active regions.
[0054]
DETAILED DESCRIPTION OF THE INVENTION
Preferred embodiments of the present invention will now be described by way of example with reference to the accompanying drawings.
[0055]
FIG. 3 is a schematic cross-sectional view of the first embodiment of the present invention. This shows a BTN liquid crystal display device having an upper substrate 1 and a lower substrate 2. This device is a passive address device, in which row electrodes 9 are provided on the upper substrate, and column electrodes 10 are provided on the lower substrate 2 so as to intersect the row electrodes 9. The alignment films 3 and 4 are provided on the upper and lower substrates so as to cover the electrodes, and the alignment direction of the upper alignment film is antiparallel to the alignment direction of the lower alignment film 4.
[0056]
The active region A is defined by the overlap of the row and column electrodes in the liquid crystal region. The liquid crystal in the active region A can be brought into the 0 ° twist state and the 360 ° twist state by applying the voltage pulses shown in FIGS. 2 (a) and 2 (b), respectively.
[0057]
In the present invention, an isolation region I is provided between two active regions A of the device shown in FIG. This isolation region I separates the two active regions from each other and stabilizes the two metastable states in those active regions.
[0058]
The stable liquid crystal state in the isolation region I is neither of the operating states of both active regions A. In the embodiment of FIG. 3, the separation region is composed of a region where the twisted HAN liquid crystal state is stable. In order to obtain a separation region in which the twisted HAN liquid crystal state is stable, the pretilt of the one alignment film on the region corresponding to the separation region is high, preferably greater than 45 °, particularly preferably substantially 90 °. It is. The pretilt of the upper alignment film 3 on the region corresponding to the active region is lower than the pretilt in the separation region, preferably less than 45 °, typically between 2 ° and 20 °. The lower alignment film 4 has a constant pretilt both in the active region and in the separation region, and this pretilt is preferably less than 45 °, typically between 2 ° and 20 °.
[0059]
In the embodiment of FIG. 3, the upper alignment film 3 is provided with a high pretilt region, but conversely, the lower alignment film 4 may have a high pretilt region that defines a twisted HAN region. In this case, the upper alignment film has a constant pretilt, which is preferably less than 45 ° and typically between 2 ° and 20 °.
[0060]
In order for the isolation region I to provide effective isolation between the two active regions A, it is preferable that the active region is completely surrounded by the isolation region. For the case of a device with four active regions, a preferred isolation region is shown in the plan view of FIG.
[0061]
The separation region shown in FIG. 4A includes a high pretilt region having a shape corresponding to the separation region I shown in FIG. And a pretilt region. The other alignment film has a constant low pretilt in both the isolation region and the active region.
[0062]
Another method for generating the separation region I is to change the pretilt on both alignment films. FIG. 4 (b) shows a modified embodiment of the present invention in which the separation region is defined using this method. The separation region I in FIG. 4B can be considered to be composed of a plurality of separation “subregions”. Isolation subregion I₁, I₂And I_ThreeIs defined by the high pretilt region on the upper alignment film and the low pretilt region on the lower alignment film, but the separation subregion I_FourTo I₉Is defined by a high pretilt region on the lower alignment film and a low pretilt region on the upper alignment film. Similarly, in FIG. 4C, the isolation subregion I₁’、 I₂'And I_Three′ Is defined by the high pretilt region on the upper substrate and the low pretilt region on the lower substrate, but the separation subregion I_Four’To I₉'Is defined by a high pretilt region on the lower alignment film and a low pretilt region on the upper alignment film.
[0063]
4 (a) to 4 (c), is the alignment direction of the alignment films 3 and 4 substantially parallel to the boundary of the active region A (which is rectangular in the plan view)? Or vertical.
[0064]
Here, one method for generating a device in the present invention will be described with reference to FIGS. 5 (a) to 5 (f). In this method, the lower alignment film is formed of a polyimide RN-715 (type 0621) from Nissan Chemical Industry. This unrubbed layer of material gives a 90 ° pretilt, but rubbing reduces this pretilt. Depending on the rubbing and processing conditions, the pretilt can be reduced as low as 4 °.
[0065]
An RN-715 polyimide layer 13 dissolved in NMP at a ratio of 1: 3 was spin coated onto a clean glass substrate 11 coated with ITO 12 to form an electrode. The polyimide was spin coated on the substrate at 5 krpm for 30 seconds, after which the polyimide was heated to 90 ° C. for 2 minutes and cured at 250 ° C. for 1 hour.
[0066]
Thereafter, the polyimide layer 13 was coated with a positive photoresist (Photoresist Microposit from Shipley, Europe Limited).^TMS1805 series) layer 14 was spin coated at 4.5 krpm for 40 seconds to form a photoresist layer having a thickness of about 500 nm. The photoresist layer was then soft baked at 95 ° C. for about 2 minutes to evaporate the solvent (FIG. 5B).
[0067]
Photoresist layer 14 was then patterned by irradiating selected portions of the photoresist layer. The irradiation process is 6.9 mW / cm²Exposure to UV light (having a peak wavelength of 365 nm) for 3.5 seconds. This irradiation step was performed through a UV chrome photomask in the hard contact mode of mask alignment. Photoresist layer, then developer Microposit^TMDevelopment was performed for 1 minute using 351 CD31, and the photoresist was removed from the areas exposed to UV light. This was a positive reproduction of the photomask pattern formed in the photoresist (FIG. 5C). The substrate was then thoroughly rinsed in deionized water for 2 minutes to ensure complete removal of the exposed photoresist. The rinsing process is preferable because any remaining photoresist affects the final alignment quality of the alignment film. Hard baking was not performed because it tends to impair final photoresist removal.
[0068]
A low pretilt planar alignment was derived by rubbing the alignment layer three times in the non-masked region of the polyimide layer 13. The rubbing was performed using a rubbing cloth (YA-20-R) on a roller having a diameter of 50 mm rotating at 3 krpm and a forward speed of 20 mm per second at a pushing amount of 0.3 (FIG. 5D). ).
[0069]
The remaining photoresist was then removed by 5 seconds UV flood exposure. This uses a mask aligner without a mask and is 6.9 mW / cm²At a wavelength of 365 nm. Substrate, then developer Microposit^TMIt was immersed in 351 CD31 for 60 seconds. The substrate was then rinsed in deionized water for 2 minutes and dried in a stream of nitrogen gas. The resulting alignment layer included a homeotropic region 15 having a pretilt of substantially 90 ° and a planar region 16 having a pretilt of approximately 10 ° (FIG. 5 (e)).
[0070]
Another method for obtaining the alignment layer patterned pretilt required by the isolation region may be mask irradiation of a suitable optical alignment layer.
[0071]
A second substrate 17 was then created with an ITO layer 18 and a uniformly rubbed RN-715 polyimide unpatterned layer 19. This produced an alignment layer with a uniform low pretilt on top. This was combined with the substrate of FIG. 5 (e) to form a liquid crystal cell having a cell gap of 2 μm as shown in FIG. 5 (f). These substrates were provided so that the alignment direction of the alignment film on the upper substrate was antiparallel to the alignment direction of the alignment film on the lower substrate. Thus, the formed cell was filled with a mixture in which nematic liquid crystal E7 (Merck) was doped with a chiral dopant R1011. When no voltage was applied to the liquid crystal layer, the cell consisted of a region having a 180 ° twisted state separated by a separation region having a twisted HAN state.
[0072]
In the above 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, when the device of the present invention is cooled from an isotropic state, the liquid crystal in the isolation region can assume a uniform twisted helix state and the axis of the helix is found to be parallel to the device substrate. ing. In the uniform twisted helix state, if an electric field is applied to the liquid crystal, it changes to a twisted HAN and remains in the twisted HAN state after the electric field is removed. If the separation region coincides with the gap between adjacent electrodes (eg, as shown in FIG. 13 (a)), the liquid crystal layer in the separation region can be applied even if an electric field is applied to the active region of the liquid crystal layer. It remains in a uniform twisted helix state. It has been found that a separation region in which a uniform twisted helix state is stable provides sufficient separation.
[0073]
A further state suitable as a separation region is the focal cone state. Some liquid crystal materials do not align homeotropically on non-rubbed portions of the alignment layer. Instead, they employ a random planar orientation with a high tilt, and this planar orientation, combined with the orientation on the other substrate, results in a conical liquid crystal state. In this state, the liquid crystal includes a domain that adopts a configuration in which the liquid crystal is twisted, and the twist direction changes randomly between adjacent domains. It has also been found that the conical state provides sufficient separation between adjacent active areas. As an example, when a Merck liquid crystal ZLI-4792 is used with a non-rubbed alignment layer of RN715 (Nissan), a focal cone orientation is observed rather than a homeotropic orientation.
[0074]
All three liquid crystal states described above for the separation region have a twisted structure, with the axis of the twist being directed across, through, or along the separation region.
[0075]
In the device described above, the alignment direction of the alignment films on the upper and lower substrates is perpendicular or parallel to the boundary of the active region. However, the orientation direction is not necessarily perpendicular or parallel to the boundary of the active region. 6 (a) to 6 (c) show an embodiment in which the orientation direction is neither substantially parallel nor substantially perpendicular to the boundary of the active region.
[0076]
As in the case of the device shown in FIGS. 4 (a) to 4 (c), the isolation region of the device of FIGS. 6 (a) to 6 (c) is patterned with an alignment film on one or both of the substrates. Provided.
[0077]
In the device shown in FIG. 6A, the separation region is obtained by providing a high pretilt on one alignment film, and the shape of the higher pretilt region corresponds to the desired shape of the separation region. The region of the alignment film corresponding to the active region has a low pretilt. The other alignment film has a substantially constant low pretilt throughout.
[0078]
6 (b) and 6 (c) show a modification of the embodiment of FIG. 6 (a), where the isolation region is obtained by providing regions of high pretilt in both alignment films. Sub-isolation region I₁And I₂(FIG. 6 (b)), I_Five’、 I₆'And I₇′ (FIG. 6C) is obtained by providing a high pretilt region on the upper alignment film and providing a low pretilt region on the lower alignment film. On the other hand, the separation region I_Three, I_FourAnd I_Five(FIG. 6 (b)), and I₁’、 I₂’、 I_Three'And I_Four′ (FIG. 6C) is obtained by providing a high pretilt region on the lower alignment film and a low pretilt region on the upper alignment film.
[0079]
The present invention is not limited to a BTN liquid crystal display whose operation state is a 0 ° twist state and a 360 ° twist state. 7 (a) to 7 (c) show an embodiment of the present invention when the present invention is applied to a BTN liquid crystal display in which the operating state is a −90 ° twist state and a 270 ° twist state. 7 (a), FIG. 7 (b) and FIG. 7 (c) substantially correspond to the embodiment shown in FIG. 4 (a), FIG. 4 (b) and FIG. 4 (c), respectively. The embodiments of 7 (a), FIG. 7 (b) and FIG. 7 (c) have only two active regions.
[0080]
In the embodiment of FIG. 7A, the isolation region I corresponds to the active region A and the high pretilt region having a shape corresponding to the isolation region I shown in FIG. It is obtained by providing a low pretilt region.
[0081]
In the embodiment of FIGS. 7B and 7C, the isolation region I is formed from a plurality of isolation “sub-regions”. Some of the separation subregions are defined by high pretilt regions on one substrate, and other separation subregions are defined by high pretilt regions on the other substrate. Isolation subregion I₁, I₂(FIG. 7 (b)) and I_Five’To I₇′ (FIG. 7C) is defined by the high pretilt region on the upper alignment film, but the separation subregion I_ThreeTo I_Five(FIG. 7 (b)) and I₁’To I_Four′ (FIG. 7C) is defined by a high pretilt region on the lower alignment film.
[0082]
8 (a) to 8 (c) correspond to FIGS. 7 (a) to 7 (c), but the two metastable operating states are generalized with twist angles Φ-π and Φ + π. Show the case. The isolation region is defined in the same way as the corresponding isolation region of FIGS. 7 (a) to 7 (c) and is therefore not further described.
[0083]
Another embodiment of the present invention is shown in FIGS. 9 (a) and 9 (b). In this embodiment, the isolation region I is not defined only by the region where the twisted HAN state is stable. In this embodiment, the separation region is defined by a combination of a region where the twisted HAN state is stabilized first and a region of the physical wall or barrier. The physical wall extends in the direction between the upper substrate and the lower substrate, thus separating the liquid crystal on one side of the wall from the liquid crystal on the other side of the wall. Preferably, the physical wall extends from the upper substrate toward the lower substrate. This is because this provides a more effective separation between adjacent active regions and also allows these walls to serve as spacers that define the thickness of the liquid crystal layer.
[0084]
If the cross section of the wall has a very small gradient, the thickness at some point along the wall may stabilize the unwanted state that can nucleate adjacent liquid crystal regions, as well as the boundary by the wall There is also the possibility that it may be difficult to switch all the liquid crystals in the attached active region to the desired state. A further disadvantage of having an undesired steady state stabilized along the wall is that light may leak through regions of undesired steady state. For example, when a 360 ° twist state (black state) is addressed, any region of the 0 ° twist state stabilized along the wall appears bright, which reduces the display contrast. Undesired steady state regions stabilized along the walls can be masked out to prevent contrast reduction, but this reduces the aperture ratio of the device. These walls are therefore preferably sharp or have a substantially sharp cross section.
[0085]
In the embodiment of FIG. 9A, the separation region has two physical walls W.₁And W₂, And three twisted HAN isolation subregions I₁, I₂And I_ThreeIt is formed by. These isolation subregions and walls are combined to form an isolation region having the same shape as the isolation region of FIG. In FIG. 9B, three twisted HAN isolation subregions are used again, but four physical walls W '₁To W ’_FourThere is. (The embodiment of FIG. 9 (b) has four physical walls, but instead a wall W '.₁And W ’₂And the wall W ’_ThreeAnd W ’_FourAnd may be continuous. )
The advantage of using a physical wall to define a portion of the isolation region is that the physical wall provides greater physical strength to the liquid crystal cell in addition to providing isolation between adjacent active regions. It is. The physical wall also improves cell uniformity by providing a uniform cell thickness over a large area. The physical wall further eliminates the need to provide spacer balls to space the substrates away from each other. This is desirable. First, spacer balls in the active region have been observed to lower the aperture ratio and second, spacer balls have been observed to function as nucleation sites for undesired stable and / or other operating conditions. is there.
[0086]
In the liquid crystal display device shown in FIGS. 9A and 9B, it can be seen that any part of the liquid crystal region is not completely surrounded by the physical wall. This means that the present invention avoids the difficulties that arise when filling a liquid crystal device having a physical wall that completely surrounds the liquid crystal area.
[0087]
In the embodiment of FIG. 9A, the alignment film on one substrate is patterned so as to form a high pretilt region, and the separation subregion I₁, I₂And I_ThreeIs generated. Physical wall W₁And W₂Are formed on the same substrate as the patterned alignment film and positioned on the patterned alignment film. In contrast, in the embodiment of FIG. 9 (b), the physical wall W '₁To W ’_FourIs first formed on one substrate, and then a patterned alignment film is formed on the wall structure. The advantages of these arrangements depend on the specific material being used. For example, some wall materials require a process that damages the alignment layer, so it is beneficial to position the alignment layer after the wall. Conversely, some other wall material is intended to be positioned after the alignment layer. In addition, some materials can be used to form both the alignment layer and the physical wall.
[0088]
One method of forming the wall is described in P.I. T.A. Kazlas et al. (SID 97 Digest, page 877). This uses a photosensitive resin BCB (benzocyclobutene) developed by Dow Chemical Company. This resin gives a negative image (ie, the area of the resin exposed to UV light remains after processing).
[0089]
It is also possible to form the wall by a method using a positive photoresist. In that case, the exposed areas are removed after development. To form a wall with a height of 2 μm by this method, Microposit^TMA solution of S1828 series positive photoresist dissolved in 5 parts to 1 part of EC solvent in volume (both available from Shipley, Europe) was spin coated onto the substrate in an open spinner for 40 seconds at 4 krpm. (Closed spinners require reduced speed). This resulted in a layer thickness of about 2.1 μm. This layer was soft baked at 95 ° C. for about 2 minutes to evaporate the solvent.
[0090]
This photoresist was then subjected to a wavelength of 365 nm and 6.9 mW / cm²Through a UV chrome photomask in the vacuum contact mode of a Karl Suss mask aligner. The duration of the exposure process was 6 seconds. Photoresist, then developer Microposit^TMDevelopment was performed in 351 CD31 for 1 minute, and the photoresist was removed from the exposed areas in the exposure process. The substrate was then rinsed thoroughly for 2 minutes in deionized water.
[0091]
The substrate was then subjected to strong UV curing for 60 minutes in an Eprom Eraser and then hard baked at 250 ° C. for at least 1 hour. This increased the physical and chemical resistance of the remaining photoresist elements. Some thermal flow of some photoresist occurred during this process, which reduced the wall height to about 2 μm.
[0092]
In order to obtain walls with heights other than 2 μm, the spin conditions of the photoresist, and possibly also the concentration of the photoresist, are changed to give the desired wall thickness.
[0093]
Another embodiment is shown in FIGS. 9 (c) and 9 (d). In these embodiments, the physical wall is provided on one substrate, which is provided with an unpatterned alignment film. The alignment film on the other substrate is patterned to give a high pretilt region and the separation subregion I₁, I₂And I_Three(FIG. 9 (c)), and I₁’、 I₂'And I_Three'(FIG. 9D) is generated. (The embodiment of FIG. 9 (d) has four physical walls, but instead a wall W '.₁And W ’₂And the wall W ’_ThreeAnd W ’_FourAnd may be continuous. )
In FIG. 9A to FIG. 9D, the alignment directions of the alignment films on both the upper and lower substrates are parallel to the direction of the physical wall. But this is not an essential element. FIGS. 10 (a) to 10 (d) show further embodiments of the present invention, which correspond substantially to the embodiments of FIGS. 9 (a) to 9 (d). Here, the alignment direction of the alignment film is parallel to the direction of the twisted HAN region, not the physical wall. (The embodiments of FIGS. 10 (b) and 10 (d) have four physical walls, but instead walls W ′.₁And W ’₂And the wall W ’_ThreeAnd W ’_FourAnd may be continuous. )
11 (a) to 11 (c) show an embodiment that is substantially similar to the embodiment of FIGS. 9 (a), 9 (c), and 9 (d), respectively, but here one substrate. Since the alignment direction of the upper alignment film is orthogonal to the alignment direction of the alignment film on the other substrate, the metastable operation states are −90 ° and 270 ° twist states. In the embodiment of FIG. 11 (a), the high pretilt region and physical wall defining the twisted HAN isolation subregion are provided on the same substrate. Conversely, in FIGS. 11B and 11C, the physical wall is provided on one substrate, and the patterned alignment film having a high pretilt region is provided on the other substrate. Since these embodiments are substantially the same as the embodiments of FIGS. 9 (a), 9 (c) and 9 (d), further description thereof is omitted. (The embodiment of FIG. 11 (c) has four physical walls, but instead a wall W '.₁And W ’₂And the wall W ’_ThreeAnd W ’_FourAnd may be continuous. FIGS. 12 (a) to 12 (c) correspond to FIGS. 11 (a) to 11 (c), respectively, but the two metastable states have twist angles of Φ−π ° and Φ + π °. Regarding the general case of having. (The embodiment of FIG. 12 (c) has four physical walls, but instead a wall W '.₁And W ’₂And the wall W ’_ThreeAnd W ’_FourAnd may be continuous. )
13 (a) and 13 (b) show possible relationships between the row electrodes 9 and the column electrodes 10 and the separation regions in the liquid crystal device according to the present invention.
[0094]
In the device shown in the plan view of FIG. 13A, the separation region I is arranged such that the gap between adjacent row electrodes and the gap between adjacent column electrodes correspond to the separation region. This arrangement maximizes the aperture ratio of the device.
[0095]
FIG. 13 (b) shows another embodiment. Also in this embodiment, the gap between adjacent row electrodes corresponds to the separation region. However, the gap between adjacent column electrodes does not completely correspond to the separation region.
[0096]
In FIG. 13B, the row electrode 9 is provided on the substrate 1 (lower substrate in FIG. 13B), and the column electrode 10 is provided on the substrate 2 (upper substrate in FIG. 13B). It has been. The active region of the liquid crystal region is shifted in the rubbing direction of the substrate on which the row electrode is provided, substantially parallel to the row electrode. Part of the active area of the liquid crystal device (ie, the area that can be switched between operating states) corresponds to the gap between the column electrodes and therefore does not switch, which slightly reduces the aperture ratio of the device . However, it has been found that the portion of the active region that does not switch functions as a good isolation region. Thus, an arrangement of the type shown in FIG. 13 (b) can provide greater separation than the arrangement of FIG. 13 (a) where the internal electrode gap is aligned with the isolation region.
[0097]
In another embodiment (not shown), the gap between adjacent column electrodes corresponds to isolation region I, but the gap between adjacent row electrodes does not completely correspond to isolation region I. The active region of the liquid crystal region is shifted substantially in parallel with the column electrode in the rubbing direction of the substrate on which the column electrode is provided.
[0098]
In another embodiment (not shown), the gap between adjacent row electrodes and the gap between adjacent column electrodes are not completely corresponding to the isolation region I. The active region of the liquid crystal region is shifted substantially in parallel with the column electrode in the rubbing direction of the substrate on which the column electrode is provided, and is substantially parallel to the row electrode in the rubbing of the substrate on which the row electrode is provided. It is also shifted in the direction.
[0099]
FIG. 14 is a schematic diagram showing the orientation of the substrate of a BTN LCD in a further embodiment of the present invention. In this device, the stable operating states are -90 ° and 270 ° twisted states. This device requires that the angle Φ between the orientation directions on the upper and lower substrates is 90 °. In FIG. 14, the separation area is defined by a combination of a physical wall and a separation sub-area. Positioning the physical wall on one substrate and the separation sub-region on the other substrate as shown in FIG. 14 allows the elements provided on each substrate to be parallel to the rubbing direction of the substrate. . This feature is beneficial because it reduces rubbing shadowing by elements provided on these substrates, which helps to keep the pretilt uniform on the substrates.
[0100]
Accordingly, in the embodiment of FIG. 14, the physical wall W is provided on the lower substrate 2 and extends substantially parallel to the rubbing direction of the lower substrate. The separation region is provided on the upper substrate and extends substantially parallel to the rubbing direction of the upper substrate. When the upper substrate is manufactured, the photoresist strip S constituting the photoresist mask (for example, as produced by the method of FIG. 5C) is substantially parallel to the rubbing direction of the upper substrate 1. (Photoresist strip S is of course removed after the step of rubbing the upper substrate and is not incorporated into the final device).
[0101]
The bistable twisted nematic liquid crystal display device comprises first and second active liquid crystal regions that can be switched between a first liquid crystal state and a second liquid crystal state. The isolation region is provided between the two active liquid crystal regions, and prevents an undesired state from nucleating in the active region and changing, or changing the state of one active region to the other active region. prevent. The stable liquid crystal state of the separation region is a state that is neither the first nor the second stable state. For example, a twisted HAN state can be stable in the isolation region.
[0102]
Alternatively, the separation region can be defined by a combination of a separation subregion in which the twisted HAN state is a stable liquid crystal state and a physical wall.
[0103]
Although the present invention has been described with reference to several embodiments, the present invention is not limited to the above-described embodiments. The present invention is not limited to devices having two or four active regions, but can be applied to devices having any number of active regions.
[0104]
In the embodiment described above, the isolation region completely surrounds each active region, so that one active region is completely isolated from the other active region. However, in principle, the separation region may not completely separate the two active regions. This type of isolation region offers some advantages for devices where no isolation region is provided. However, it is desirable for the isolation region to completely surround the active region because it provides improved isolation between the active regions.
[0105]
If the separation region is defined by a combination of a physical wall and a region where the twisted HAN state is stable, the physical wall need not always be perpendicular to the twisted HAN region. Any combination of physical walls and twisted HAN regions that define appropriate separation regions can be used. However, as described above, it is preferable that the active region is not entirely surrounded by the physical wall. This is because if the active region is completely surrounded by the physical wall, it is difficult to fill the active region with a liquid crystal material.
[0106]
【The invention's effect】
Thus, the present invention makes it possible to have the lowest possible power consumption and to extend the maximum time that the device can be used without recharging.
[Brief description of the drawings]
FIG. 1 (a) to FIG. 1 (d) are schematic views of respective BTN LCDs in four liquid crystal states.
FIG. 2 (a) shows voltage pulses required to select a 0 ° twist metastable state in a BTN LCD, and FIG. 2 (b) shows a 360 ° twist metastable state in a BTN LCD. The voltage pulses required to select are shown.
FIG. 3 is a schematic cross-sectional view of the BTN LCD in the first embodiment of the present invention.
4 (a) -4 (c) show possible top views of the LCD of FIG.
FIGS. 5 (a) to 5 (f) illustrate a method of manufacturing the device of FIG.
6 (a) to 6 (c) show further possible top views of the device of FIG. 3 with the orientation direction at an angle with respect to the edge of the active region.
7 (a) to 7 (c) are other plan views of the device of FIG. 3 in which the orientation direction of the upper substrate is perpendicular to the orientation direction of the lower substrate.
8 (a) -8 (c) show other plan views of the device of FIG. 3 in which the orientation direction of the upper substrate is an angle Φ with respect to the orientation direction of the lower substrate.
9 (a) and 9 (b) are plan views of a BTN LCD in another embodiment of the present invention, and FIG. 9 (c) and FIG. 9 (d) illustrate another embodiment of the present invention. The top view of BTN LCD in embodiment of is shown.
FIGS. 10 (a) -10 (d) show plan views of a BTN LCD in a further embodiment of the present invention.
FIGS. 11 (a) -11 (c) show plan views of a BTN LCD in a further embodiment of the present invention.
FIGS. 12 (a) -12 (c) show schematic plan views of a BTN LCD in a further embodiment of the invention.
13 (a) and 13 (b) are partial plan views of the device of FIGS. 12 (a) to 12 (c) showing the position of the electrodes.
FIG. 14 is a partial perspective view of a BTN LCD according to another embodiment of the present invention.
[Explanation of symbols]
1 Upper board
2 Lower board
3 Upper alignment film
4 Lower alignment film
5 Liquid crystal layer
9-row electrode
10 row electrode

Claims (14)

The first and second substrates, the first and second alignment films each having an anti-parallel alignment direction on each of the first and second substrates, and the first and second alignment films. A bistable twisted nematic liquid crystal display device comprising a BTN liquid crystal material provided therebetween,
The BTN liquid crystal material includes a first active liquid crystal region and a second active liquid crystal region configured to be applied with a voltage, and between the first active liquid crystal region and the second active liquid crystal region. A separation region provided in a state where no voltage is applied,
Each of the first and second active liquid crystal regions can be switched between a first liquid crystal state and a second liquid crystal state by application of a voltage, and the separation region is stable in a third liquid crystal state. Including the area
The first and second liquid crystal states are a (Φ−π) ° twist state and a (Φ + π) ° twist state, respectively.
One alignment condition of the first and second alignment films is different between the separation region and the first and second active liquid crystal regions,
A liquid crystal display device, wherein the third liquid crystal state is a uniform twisted helix state. The first and second substrates, the first and second alignment films each having an anti-parallel alignment direction on each of the first and second substrates, and the first and second alignment films. A bistable twisted nematic liquid crystal display device comprising a BTN liquid crystal material provided therebetween,
The BTN liquid crystal material includes a first active liquid crystal region and a second active liquid crystal region configured to be applied with a voltage, and between the first active liquid crystal region and the second active liquid crystal region. A separation region provided in a state where no voltage is applied,
Each of the first and second active liquid crystal regions can be switched between a first liquid crystal state and a second liquid crystal state by application of a voltage, and the separation region is stable in a third liquid crystal state. Including the area
The first and second liquid crystal states are a (Φ−π) ° twist state and a (Φ + π) ° twist state, respectively.
One alignment condition of the first and second alignment films is different between the separation region and the first and second active liquid crystal regions,
A liquid crystal display device, wherein the third liquid crystal state is a focal cone structure. Wherein the first and second liquid crystal state are each a 0 ° twist state and 360 ° twisted state, the liquid crystal display device according to any one of claims 1-2. Wherein the first and second liquid crystal state is a -90 ° twist state and 270 ° twist state, respectively, the liquid crystal display device according to any one of claims 1-2. The one alignment layer, in the above first and second active liquid crystal region, the isolation region having a lower pretilt than liquid crystal display device according to any one of claims 1-2. The liquid crystal display device according to claim 5 , wherein the one alignment film generates a pretilt of substantially 90 ° in the separation region. The one alignment layer, in the separation region, oriented randomly generates a high pretilt liquid crystal display device according to claim 5. The one alignment layer, in the first and second active liquid crystal regions, generates a smaller pretilt than 45 °, the liquid crystal display device according to any one of claims 1-2. The one alignment layer, in the above first and second active liquid crystal region, to produce a pretilt in the range of 20 ° from the 2 °, the liquid crystal display device according to any one of claims 1-2. The isolation region includes first and second isolation subregions, and the first isolation subregion is generated according to an alignment condition on the one alignment film, and the second isolation subregion is the other alignment film. produced by the orientation of the above conditions, the liquid crystal display device according to any one of claims 1-2. Said first isolation sub region, said generated by the high pretilt region on one of the alignment film, the second isolation sub-regions are produced by the high pretilt region on the other orientation film, according to claim 10 LCD device. The isolation region further comprises a liquid crystal display device according to any one of claim 1 to 2 a wall extending between the second substrate of the first substrate and the device of the device. It said wall, said a first substrate and extending to the second substrate, a liquid crystal display device according to any one of claims 1-2. Projection of the isolation region onto one of the first and second substrates completely surrounds projection of at least one of the first and second active liquid crystal regions onto the one substrate; LCD device according to any one of claims 1-2.

Images