GB2343260A

GB2343260A - Wall-shaped spacers for improvements in liquid crystal displays

Info

Publication number: GB2343260A
Application number: GB9925273A
Authority: GB
Inventors: Kazuhiko Tamai; Hideki Uchida; Mitsuhiro Shigeta
Original assignee: UK Secretary of State for Defence; Sharp Corp
Current assignee: UK Secretary of State for Defence; Sharp Corp
Priority date: 1998-10-30
Filing date: 1999-10-27
Publication date: 2000-05-03
Anticipated expiration: 2019-10-27
Also published as: JP2000137232A; GB2343260B; GB9925273D0

Abstract

Wall-shaped spacers of uniform height are fabricated upon a plurality of electrodes on one of two facing substrates of an LCD. The spacers are formed to be parallel to the electrodes on the opposing substrate when the complete LCD is assembled.

Description

LIQUID CRYSTAL DISPLAY ELEMENT AND METHOD OF MANUFACTURING SAME The present invention relates to a liquid crystal display element realizing excellent shock stability and good display quality, and a method of manufacturing the same.

A conventionally known liquid crystal display element is a liquid crystal display element which is formed by assembling a pair of substrates together so that the respective surfaces thereof provided with electrodes face each other and by filling a space between the substrates with a liquid crystal. In such a liquid crystal display element, when the distance between the opposing substrates (cell thickness) is varied due to deformation of the substrates caused by external pressure, etc., a variation of the threshold voltage, an electrode short circuit between the opposing substrates, disorderly alignment of liquid crystal molecules, etc. occur. Therefore, a good display can not be provided. In order to realize a good display, there has been a known method in which spacers are provided between a pair of substrates to maintain a uniform distance between the substrates. Conventionally, either a method (1) of dispersing spherical particles, or a method (2) of forming organic or inorganic pillars has been usually employed. More specifically, known examples of the method (1) include a dry process of spreading spherical fine particles made of an organic resin, for example, divinylbenzenebase polymer, on the substrate by dispersing the particles in an atmosphere of nitrogen; and a process of mixing the spherical fine particles into a solution such as an alcohol solution and spraying the mixture on the substrate- However, the method (1) suffers from the following problems. The first problem is that it is difficult to spread the fine particles uniformly on the substrate because of their aggregation properties and thus difficult to realize a uniform cell thickness. The second problem is that it is difficult to control the positions of the fine particles, and the fine particles spread on pixel regions may cause alignment defects and lower the display quality. Further, the third problem is that it is difficult to secure sufficient strength against external pressure because the substrates are supported by point contacts with the spherical fine particles as the spacers.

Meanwhile, the method (2) is more specifically a method of forming an organic or inorganic film in a predetermined thickness, forming a resist film on the organic or inorganic film, and then forming pillars as the spacers by mask exposure. It is also possible to use a photosensitive organic resin such as photosensitive polyimide or a photosensitive acrylic resin, instead of the resist film. Thus, the method (2) can selectively form the pillars outside of the pixels. Moreover, the method (2) has the advantage of forming the contact surface between the substrate and pillars in an arbitrary pattern, and realizes superior uniformity of the cell thickness, strength against external pressure, and display quality compared to the method (1).

In resent years, a ferroelectric liquid crystal has been noted as a liquid crystal material. The ferroelectric liquid crystal has excellent properties such as high-speed response achieved by its spontaneous polarization, but suffers from the following problem.

Since the regularity of the alignment of molecules has a structure close to the crystal, when the regularity of the molecular alignment is disordered by external pressure, the molecular alignment can hardly return to the original state, i. e., the ferroelectric liquid crystal is weak against shock. In order to overcome this problem of the ferroelectric liquid crystal, it is necessary to realize a substrate structure having excellent shock stability. As a method of manufacturing such a liquid crystal display element, it has been considered that the method (2) is better than the method (1).

A conventional liquid crystal display element has, for example, the structure shown in Fig. 6 (a). In this structure, electrodes 103 and 104 in the shape of stripes, insulating layers 105 and 106, and alignment control layers 107 and 108 are formed respectively on a pair of substrates 101 and 102, at least one of which has light transmittance, wall-shaped spacers 109 of uniform height are provided on the alignment control layer 107 so as to extend parallel to a longitudinal direction of the electrodes 103, the spacers 109 and the alignment control layer 108 are bonded to each other to assemble the pair of substrates 101 and 102 together, and a liquid crystal is sealed between the space of the substrates 101 and 102 to form a liquid crystal layer 110.

By the way, the above conventional structure suffers from the following problems.

Fig. 6 (b) is a cross section of Fig. 6 (a) cut across a line connecting arrows Y and Y'. As described above, the spacers 109 are formed so as to extend parallel to a longitudinal direction of the electrodes 103 on the substrate 101. Therefore, areas for the formation of the spacers 109 are free from the influence of the difference in level caused by the film thickness of the electrodes 103, and the upper ends of the spacers 109 are flat. However, when assembling the substrate 101 and the opposite substrate 102 together, the electrodes 104 cross the upper ends of the spacers 109. Thus, recessions 111 formed due to the film thickness of the electrodes 104 are present at positions facing the upper ends of the spacers 109.

Consequently, the upper ends of the spacers 109 are not bonded entirely to the substrate 102 without forming a space therebetween.

An improvement of shock stability of the liquid crystal display element can be usually realized by supporting a pair of substrates with wall-shaped spacers of uniform height so as to limit a variation in the cell thickness. However, in order to further improve the shock stability, it is necessary to separate the liquid crystal by the wall-shaped spacers to prevent a flow of the liquid crystal. When the liquid crystal is separated, even if the cell thickness is varied by application of pressure and the alignment of the liquid crystal is disordered, the disorderly area is limited within a region separated by the spacers, and the disorderly alignment does not spread to areas separated by adjacent spacers.

However, in the above-mentioned conventional structure, since the recessions 111 are formed, the upper ends of the spacers 109 are not bonded to the alignment control layer 108 due to the recessions 111, and the liquid crystal moves in a direction perpendicular to a longitudinal direction of the spacers 109 and a direction along the substrate surface through the recessions 111. Therefore, the disorderly alignment caused by the application of pressure is transferred through the recessions 111, and spreads gradually to adjacent areas separated by the spacers 109. Moreover, when filling the liquid crystal, the liquid crystal does not easily fill the recessions 111, and filling defects may occur.

Examples of a method for making the areas of the substrate 102 which come into contact with the upper ends of the spacers 109 flat by eliminating portions like the recessions 111 which cause a difference in level include a method of forming buried members 112 between adjacent electrodes 104 as shown in Fig. 7; and a method of forming a flattening film 113 covering the electrodes 104 as shown in Fig. 8. However, these methods cause the process to be complicated and the cost to be increased.

An object of the present invention is to provide a liquid crystal display element which has a uniform cell thickness and sufficient shock stability and can realize good display quality which is free of unevenness, and also to provide a method of manufacturing the same.

According to the present invention, there is provided a liquid crystal display element including: a pair of substrates, at least one of which has light transmittance, provided with a plurality of electrodes extending in respective directions which mutually cross; a liquid crystal layer sandwiched between the substrates, which are placed so that the respective surfaces thereof provided with the electrodes face each other; and wall-shaped spacers of uniform height, provided on at least one of the substrates, which are bonded to the opposite substrate directly or through a film, the spacers being provided so as to extend parallel to a longitudinal direction of the electrodes provided on the opposite substrate to which the spacers are bonded, or of metal lines provided adjacent to the electrodes.

According to this structure, the pair of substrates are assembled together with the wall-shaped spacers of uniform height which maintain a uniform distance therebetween. Besides, the spacers are provided on the substrate provided with the electrodes so that the spacers extend perpendicularly to a longitudinal direction of the electrodes and parallel to a longitudinal direction of the electrodes provided on the opposite substrate. More specifically, on the substrate whereon the spacers are provided, the spacers extend perpendicularly to a longitudinal direction of the electrodes or of metal lines and along the substrate surface.

Consequently a structure (see Fig. 2) in which the spacers cross bumps and recessions caused by the thickness of the electrodes or metal lines is obtained, thereby reducing the influence of the difference in level caused by the bumps and recessions, on the spacers. As a result, the upper ends of the spacers become almost flat. Besides, even if the difference in level is not completely eliminated by the spacers, since the space formed at the recession is reduced significantly, the contact area between the spacer and the substrate is increased, thereby improving the shock stability of the liquid crystal display element.

Specifically, since the upper ends of the spacers are bonded to the flat areas on the opposite substrate directly or through a film, it is possible to bond the upper ends of the spacers to the opposite substrate without a space therebetween. It is thus possible to provide a liquid crystal display element having excellent shock stability and a uniform cell thickness, without filling defects.

In general, the thickness of the electrode is usually between 0.02 and 0.5 ym, the height of the spacer is equal to the cell thickness ranging from 1 to 8 zm, and the thickness of each of the insulating film and alignment film is between 0.02 and 0.4 ym. Since the thickness of each of the insulating film and alignment film is less than the thickness of the spacer, the spacers reduce the influence of the difference in level caused by the electrodes to a greater extent and become flat more easily. On the other hand, when the thickness of the insulating film or alignment film is increased for a flattening purpose, problems, such as deterioration of the alignment and a lowering of voltage applied to the liquid crystal, occur.

Meanwhile, the areas of the opposite substrate which are in contact with the upper ends of the spacers are not areas lying between the electrodes or areas having a difference in level caused by the metal lines on the opposite substrate, but are flat because the spacers are provided so as to extend parallel to a longitudinal direction of the electrode or of the metal lines on the opposite substrate. Therefore, the flat upper ends of the spacers are bonded to the flat opposite substrate without a space therebetween.

Consequently, the buried members and the flattening film which are used by the above-described prior arts to fill the space are not necessary, and the abovementioned object can be achieved by a simple process without increasing the cost.

In the liquid crystal display element, it is preferred that the spacers are bonded directly or through a film to the opposite substrate at positions between adjacent electrodes thereof. With this structure, since the spacers are formed in areas outside of the pixel regions, it is possible to prevent a lowering of the aperture ratio and of display quality which will occur when the spacers are formed within the pixels.

Moreover, it is preferred that the spacers are bonded to the opposite substrate at positions thereof in which are provided the metal lines. With this structure, the spacers are positioned, directly or through a film, on the metal lines on the opposite substrate. The metal lines produce the effect of reducing the resistance of the electrodes, but cause a lowering of the aperture ratio because of the light shielding properties of the metal. Besides, if the spacers have optical isotropic properties, they do not transmit light under a crossed Nicols state, and lower the aperture ratio. Therefore, by forming the spacer and the metal line at the same position in the direction of the cell thickness, it is possible to realize a high aperture ratio because the lowering of the aperture ratio caused by the spacer and metal line is minimized. Furthermore, since the spacer is formed so as to extend parallel to a longitudinal direction of the metal line, the flat upper end of the spacer is in contact with the flat metal line directly or through a film. Therefore, the spacer is free from the influence of a difference in level caused by the thickness of the metal line, and space which allows movement of the liquid crystal is not present on the upper end of the spacer.

It is thus possible to prevent a lowering of the display quality. Moreover, since the flat upper ends of the spacers are in contact with the flat metal lines directly or through a film, it is possible to provide a liquid crystal display element with excellent shock stability.

Further, it is preferred that the liquid crystal forming the liquid crystal layer is a ferroelectric liquid crystal. Since the ferroelectric liquid crystal has spontaneous polarization and achieves a high-speed response by its memory ability, it is possible to provide, for example, a liquid crystal display element capable of displaying a large capacity, high-definition image. Moreover, since the molecular alignment of the ferroelectric liquid crystal is close to the crystal compared with a nematic liquid crystal, if the regularity of the molecular alignment is once disordered by an external pressure, it cannot easily return to the original state, i. e., the ferroelectric liquid crystal has a weak resistance against shock.

However, if the above-mentioned spacer structure is employed, since a sufficient substrate strength is realized, such a drawback is overcome.

Hence, since the ferroelectric liquid crystal is sandwiched between the substrates having excellent shock stability, a demerit of the ferroelectric liquid crystal, i. e., weak resistance against external pressure, is cancelled. It is thus possible to provide a liquid crystal display element exhibiting excellent properties of the ferroelectric liquid crystal.

Additionally, it is preferred that the liquid crystal forming the liquid crystal layer shows a smectic phase, and the spacers are provided so as to extend parallel to a normal direction of a smectic layer of the liquid crystal. When an external pressure is applied to the liquid crystal display element sandwiching a ferroelectric liquid crystal between the substrates, the disorderly alignment caused by the external pressure spreads in a layer direction of the smectic layer but does not spread in a normal direction of the layer. Therefore, in order to improve the shock stability, it is necessary to prevent movement of the liquid crystal in a direction parallel to a layer direction of the smectic layer. Hence, as described above, when the spacers are provided so as to extend parallel to a normal direction of the smectic layer, the movement of the liquid crystal in a direction parallel to a layer direction of the smectic layer is prevented by the spacers. It is thus possible to provide a ferroelectric liquid crystal display element with further improved shock stability.

According to the present invention, there is provided a method of manufacturing a liquid crystal display element formed by sealing a liquid crystal between a pair of substrates, at least one of which has light transmittance, including the steps of: (1) providing electrodes on the pair of substrates; (2) providing on one of the substrates wall-shaped spacers of uniform height so that the wall-shaped spacers extend parallel to a longitudinal direction of the electrodes provided on the opposite substrate, or of metal lines provided adjacent to the electrodes; and (3) bonding the spacers to the opposite substrate directly or through a film to assemble the substrates together.

According to this method, first, the electrodes are formed on the substrates in the step (1). Prior to or after the step (1), it is possible to form color filters, light shielding layers, metal lines, etc., on the substrates, if necessary. Thereafter, in the step (2), the spacers are formed so as to extend perpendicularly to a longitudinal direction of the electrodes and parallel to a longitudinal direction of the electrodes on the opposite substrate. In other words, on the substrate whereon the spacers are formed, since the spacers cross areas having a difference in level due to the electrodes or metal lines, the influence of the difference in level is reduced, and the upper ends of the spacers become almost flat.

Besides, in the areas of the opposite substrate which come into contact with the upper ends of the spacers, since the spacers are provided so as to extend parallel to a longitudinal direction of the electrodes or metal lines on the opposite substrate, they are free from the influence of the difference in level caused by the electrodes on the opposite substrate, and flat.

Therefore, the flat upper ends of the spacers are bonded to the flat opposite substrate, without forming a space therebetween. It is thus possible to provide a liquid crystal display element of improved shock stability.

Incidentally, the spacers may be formed before or after the formation of the insulating films or alignment films, or the upper ends of the spacers may be bonded to the opposite substrate directly or through a film.

In the step (2) of the above manufacturing method, it is preferred that the spacers are located at positions between adjacent electrodes on the opposite substrate to which the spacers are bonded in the step (3). With this arrangement, since the spacers are formed in areas outside of the pixel regions, it is possible to prevent a lowering of the aperture ratio and of display quality which will occur when the spacers are formed within the pixels.

Moreover, in the step (2), it is preferred that the spacers are located at opposite positions of the opposite substrate to which the spacers are bonded in the step (3), in which are provided the metal lines.

With this arrangement, the spacers and metal lines are formed at the same positions in the direction of the cell thickness. It is therefore possible to minimize a lowering of the aperture ratio due to the spacers and metal lines.

Furthermore, in the step (2), it is preferred that the spacers are provided so as to extend parallel to a normal direction of the smectic layer of the liquid crystal, which shows a smectic phase. With this arrangement, since the movement of the liquid crystal in a layer direction of the smectic layer is prevented by the spacers, disorderly alignment which is caused in an area by external pressure does not spread to adjacent areas separated by the spacers. It is therefore possible to provide a liquid crystal display element with further improved shock stability.

The invention will be further described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 (a) is a cross section showing a schematic structure of a liquid crystal display element according to one embodiment of the present invention, and Fig. l (b) is a cross section of Fig. l (a) cut across a line connecting arrows X and X' ; Fig. 2 is a perspective view showing a schematic structure of one of electrode substrates of the liquid crystal display element; Fig. 3 is a cross section of the structure shown in Fig. 2; Fig. 4 is a cross section showing a schematic structure of a liquid crystal display element according to another embodiment of the present invention; Fig. 5 (a) and Fig. 5 (b) are plan views showing two different structures and arrangements of electrodes and metal lines of the liquid crystal display element of Fig. 4; Fig. 6 (a) is a cross section showing a schematic structure of a liquid crystal display element fabricated by a conventional manufacturing process, and Fig. 6 (b) is a cross section of Fig. 6 (a) cut across a line connecting arrows Y and Y' ; Fig. 7 is a cross section showing a schematic structure of another liquid crystal display element fabricated by the conventional manufacturing process; and Fig. 8 is a cross section showing a schematic structure of still another liquid crystal display element fabricated by the conventional manufacturing process.

[FIRST EMBODIMENT] The following description will explain one embodiment of the present invention with reference to Figs. 1 through 3.

Fig. l (a) shows a schematic structure of a liquid crystal display element according to one embodiment of the present invention, and Fig. l (b) is a cross section of Fig. 1 (a) cut across a line connecting arrows X and X'. Besides, Figs. 2 and 3 show the shape of a spacer.

This liquid crystal display element is formed by assembling a pair of electrode substrates 10 and 20 together so as to face each other and by sealing a liquid crystal therebetween to form a liquid crystal layer 31. The electrode substrate 10 includes an insulating substrate 11, a plurality of electrodes 12 formed parallel to each other in the shape of stripes, an insulating film 13 formed to cover the insulating substrate 11 and electrodes 12, an alignment control layer 14 formed to cover the insulating film 13, and spacers 15 provided on the alignment control layer 14.

Meanwhile, the electrode substrate 20 includes an insulating substrate 21, a plurality of electrodes 22 formed parallel to each other in the shape of stripes, an insulating film 23 formed to cover the insulating substrate 21 and electrodes 22, and an alignment control layer 24 formed to cover the insulating film 23.

The spacers 15 extend parallel to a longitudinal direction of the electrodes 22 and parallel to a normal direction of the smectic layer of the liquid crystal.

Moreover, the electrode substrates 10 and 20 are assembled together by bonding the upper ends of the spacers 15 provided on the insulating substrate 11 to the alignment control layer 24 formed on the insulating substrate 21.

At lest one of the insulating substrates 11 and 21 is made of a transparent material such as glass and plastic. Besides, as the electrodes 12 and 22, transparent electrodes formed of ITO (indium tin oxide) are usually used, but it is possible to use electrodes formed of other metal.

As a liquid crystal for use in this embodiment, a ferroelectric liquid crystal composition is used. The ferroelectric liquid crystal has excellent properties such as high-speed response and a memory ability, thereby enabling a display of a large-capacity, highdefinition image. Besides, it is possible to use a liquid crystal such as an antiferroelectric liquid crystal if it shows a smectic phase, other than the ferroelectric liquid crystal.

The liquid crystal display element having the above-described structure is manufactured by the following process.

First, an ITO film with a thickness of around 200 nm is formed on the surface of the insulating substrate 11 by sputtering, and patterned to form the electrodes 12 in the shape of stripes using photolithography.

Additionally, SiO2 is applied onto them by spincoating to form the insulating film 13 of uniform surface.

Incidentally, the insulating film 13 can be sometimes omitted.

Next, an alignment film PSI-A-2101 available from Chisso Corporation is applied in a thickness of 50 nm by spincoating, and baked at about 200 C for 1 hour to form the alignment control layer 14. Thereafter, a negative photosensitive acrylic resin V-259 available from Nippon Steel Chemical Co., Ltd. is applied onto the alignment control layer 14 by spincoating so that the thickness thereof after sintering is 1.5 ym.

Further, ultraviolet rays are irradiated after applying a photomask to positions between adjacent electrodes 22, where the spacers 15 are to be provided, in a direction perpendicular to a longitudinal direction of the electrodes 12 and a direction along the substrate surface, i. e., parallel to a longitudinal direction of the electrodes 22 so as to remove the unexposed portions, and then sintering is performed at about 180 C for 1 hour to form the spacers 15 as shown in Fig. 2.

The electrode substrate 10 can be formed by the above-mentioned process. On the other hand, the electrode substrate 20 is formed by forming the electrodes 22, insulating film 23 and alignment control layer 24 sequentially on the insulating substrate 21 by the same process as above.

Next, the alignment control layers 14 and 24 are rubbed along a longitudinal direction of the spacers 15, and the electrode substrates 10 and 20 are placed so that the rubbing directions of the alignment control layers 14 and 24 are aligned with each other. Then, a pressure of 0.9 kg/cm2 is applied at about 180 C for 1 hour to bond the spacers 15 and the alignment control layer 24. Moreover, the space between the electrode substrates 10 and 20 is filled with a liquid crystal to complete the liquid crystal display element.

It was confirmed that the liquid crystal display element fabricated by the above-mentioned process did not show disorderly alignment even when a pressure of 20 kg/cm2 was applied and had excellent shock stability.

Additionally, this liquid crystal display element secured a uniform cell thickness with flatness within 0. 03 ym, and had no filling defects.

As the material of the spacers 15, it is possible to use organic resins, such as non-photosensitive polyimide and acrylic resins, and metals such as Cr, Mo, and Al, other than the negative photosensitive organic resin. When a photosensitive organic resin is used, since a photoresist is not necessary, there are advantages that the spacers 15 are formed more easily and at lower cost. Moreover, although the spacers 15 can be formed in any areas on the substrate, in order to prevent a lowering of the display quality, it is desired to form the spacers 15 in areas outside of the pixel display areas.

Incidentally, the liquid crystal display element of the above-described structure is fabricated by the process in which the spacers 15 are formed on the alignment control layer 14. However, it is also possible to form the spacers 15 prior to or after the formation of the insulating film 13, and assemble the electrode substrates 10 and 20 together by bonding the alignment films 14 and 24 to each other. In this case, the spacers 15 are bonded to the electrode substrate 20 indirectly through the insulating film 13 and alignment control layer 14.

Besides, it is not necessarily to provide the insulating films 13 and 23. The insulating films 13 and 23 can be omitted if a leakage current is not produced between the electrode substrates 10 and 20.

As described above, the liquid crystal display element of the first embodiment includes a pair of electrode substrates 10 and 20, and one of the electrode substrates, 10, includes the electrodes 12 formed on the insulating substrate 11 and the spacers 15 formed on the electrodes 12 so as to extend parallel to a longitudinal direction of the electrodes 22 on the other electrode substrate 20 after the formation of the electrodes 12.

Thus, the spacers 15 are formed so as to extend perpendicularly to a longitudinal direction of the electrodes 12, i. e., to cross the difference in level caused by the electrodes 12. Hence, the influence of the difference in level caused by the electrodes 12 is reduced, and the upper ends of the spacers 15 become flat as shown in Fig. 2.

Figs. 3 and Table 1 show a level difference D2 produced at the upper end of the spacer 15 with a thickness of D, formed on the electrode 12 having a thickness of D3. Table 1 shows the level difference D2 when the thickness D1 is 1.00 ym, 1.25 ym, 1.50 Hm, or 1.75 Fm, for the electrode thickness D3 of 0.20 ym, 0.30 ym, and 0.50 ym, respectively. Note that there is not practical problem if the level difference D2 is approximately 0.3 Am or less.

[Table 1]

D1 ( m) D2 ( m) D3 ( m) 0.20 0.30 0.50 1.00 0.10 0.17 0.28 1.25 0.08 0.15 0.28 1.50 0.08 0.13 0.20 1.75 0.08 0.12 0.20 In Figs. 2 and 3, for the sake of simplification, the insulating film 13 and alignment control layer 14 are not shown.

According to the prior art, the level difference between adjacent electrode almost remain (see Fig.

6 (b)). On the other hand, according to the liquid crystal display element of this embodiment, it is possible to reduce the influence of the level difference caused by the electrodes by forming the spacers 15 to extend parallel to a longitudinal direction of the electrodes 22 on the electrode substrate 20. Moreover, by changing the material of the spacers to a material which can easily form a flat surface (absorb the level difference D2), it is possible to make the upper ends of the spacers 15 substantially completely flat.

Furthermore, positions on the electrode substrate 10 where the upper ends of the spacers 15 come into contact with the electrode substrate 20 are located between adjacent electrodes 22 and these positions are flat without a level difference. Thus, since the flat upper ends of the spacers 15 are in contact with the flat areas on the electrode substrate 20, a structure having almost no space between the upper ends of the spacers 15 and the electrode substrate 20 is achieved.

In this structure, since the liquid crystal does not move across a longitudinal direction of the spacers 15 through such a space, disorderly alignment does not spread, thereby providing a liquid crystal display element with excellent shock stability. In addition, since the spacers 15 are formed so as to extend parallel to a normal direction of the smectic layer of the liquid crystal, the movement of the liquid crystal in a layer direction of the smectic layer is prevented by the spacers.

In this embodiment, an example in which the electrodes form a striped pattern is illustrated.

However, the present invention can employ various electrode patterns as described later (see Figs. 5 (a) and 5b)).

[Second Embodiment] The following description will explain another embodiment of the present invention with reference to Figs. 4 and 5. The same constituent elements as those of the first embodiment will be designated by the same codes and the explanation thereof will be omitted.

As illustrated in Fig. 4, a liquid crystal display element according to this embodiment is provided with electrode substrates 30 and 40 which additionally include metal lines 16 and 26 in the electrode substrates 10 and 20, respectively, of the first embodiment. Specifically, in the first embodiment, the metal lines 16 and 26 are provided in the form of stripes prior to the formation of the electrodes 12 and 22 of the first embodiment. The metal lines 16 and 26 are made of metal material, such as copper, aluminum, titanium, chrome, and tantalum, by a liftoff method, an etching method, or other method, so as to lower the wiring resistance of the electrodes 12 and 22.

Thereafter, the electrodes 12 and 22 are formed so as to partly overlap and be parallel to the metal lines 16 and 26.

Moreover, the spacers 15 are formed on the substrate 11 so as to extend parallel to a longitudinal direction of the electrodes 22 and metal lines 26. The positions at which the spacers 15 are formed are such positions on the substrate 21 corresponding to the following areas. Specifically, the position at which the spacer 15a is to be formed is an area A on the electrode 22 where the electrode 22 overlaps the metal line 26, the position at which the spacer 15b is to be formed is an area C which is located between adjacent electrodes 22 and on the metal line 26, and the position at which the spacer 15c is to be formed is an area D which is on the metal line 26 and partly overlaps the electrode 22.

Thus, the spacers 15a to 15c are formed on the electrode substrate 30 so as to extend perpendicularly to a longitudinal direction of the electrodes 12 and metal lines 16 and along the substrate surface so that they cross the electrodes 12 and metal lines 16.

Therefore, like the first embodiment, the influence of the difference in level due to the electrodes 12 and metal lines 16 is reduced, and the upper ends of the spacers 15 become flat.

Further, the areas A and C in which the upper ends of the spacers 15a and 15b are in contact with the electrode substrate 40 do not have a difference in level due to the electrodes 22 and metal lines 26, and are flat. Hence, since the flat upper ends of the spacers 15a and 15b are in contact with the flat areas on the electrode substrate 40, it is possible to realize a structure in which there is almost no space between the upper ends of the spacers 15a and 15b and the electrode substrate 40.

Besides, the area D is composed of an area E on the metal line 26 which overlaps the electrode 22 and an area F on the metal line 26 which does not overlap the electrode 22. The areas E and F are not present on the same plane because of the thicknesses of the electrode 22 and metal line 26, and thus there is a difference in level between the areas E and F.

Accordingly, the upper end of the spacer 15c is in contact with the electrode substrate 40 only in the area E, and there is a space between the upper end of the spacer 15c and the electrode substrate 40 in the area F. However, since there is no space between the upper end of the spacer 15c and the electrode substrate 40 in the area E, the space produced in the area F does not extend perpendicularly to a longitudinal direction of the spacer 15c and along the direction of the substrate surface, i. e., the space does not spread over the entire width of the upper end of the spacer 15c.

In this structure, since the liquid crystal does not move across the spacer 15c, disorderly alignment does not spread, thereby providing a liquid crystal display element with excellent shock stability.

For the same reasons, even in a structure where the upper end of the spacer 15b is in contact with the electrode substrate 40 in both the area B where the electrodes 22 and metal lines 26 are not formed and the area C, disorderly alignment does not spread, thereby providing a liquid crystal display element with excellent shock stability.

Hence, the spacers 15a to 15c can be formed at any positions on the metal lines 26 on the electrode substrate 40 if the spacers 15a to 15c extend parallel to a longitudinal direction of the electrodes 22 and metal lines 26.

It was confirmed that, even when a pressure of 20 kg/cm2 was applied to a liquid crystal display element fabricated in the above-mentioned process, the alignment was not disordered and the liquid crystal display element had excellent shock stability.

Moreover, the liquid crystal display element secured a uniform cell thickness within 0. 03 ym, and had no filling defects.

In this embodiment, although the metal lines 16 and 26 are formed prior to the formation of the electrodes 12 and 22, they can be formed after the formation of the electrodes 12 and 22. Besides, the metal lines 16 and 26 may be formed adjacent to the electrodes 12 and 22 without overlapping the electrodes 12 and 22, or formed over or under the electrodes 12 and 22 to partly or entirely overlap the electrodes 12 and 22.

In this embodiment the longitudinal direction of the electrodes 12 and 22 or the metal lines 16 and 26 is a direction of the long sides of the electrodes 12 and 22 or the metal lines 16 and 26 if the electrodes 12 and 22 or the metal lines 16 and 26 are provided in the shape of stripes.

On the other hand, in the electrode structures shown in Figs. 5 (a) and 5 (b), the definition of the longitudinal direction differs. In the electrode structure shown in Fig. 5 (a), the electrodes 12 and 22 are formed independently for each pixel or a group of a plurality of pixels, and connected to each other with the metal lines 16 and 26 in the form of straight lines. In this structure, the direction of the long sides of the metal lines 16 and 26 is the longitudinal direction. In contrast, in the electrode structure shown in Fig. 5 (b), the electrodes 12 and 22 are formed independently for each pixel or a group of a plurality of pixels, and adjacent two electrodes 12 (22) are connected to each other with a short metal line 16 (26). In this structure, the direction in which the electrodes 12 or 22 are electrically connected to each other with the metal line 16 or 26 is the longitudinal direction.

[First Comparative Example] Here, a liquid crystal display element fabricated by a conventional process is illustrated as a comparative example and compared with the liquid crystal display elements of the first and second embodiments.

As shown in Figs. 6 (a) and 6 (b), a conventional liquid crystal display element includes spacers 109 provided on a substrate 101, at positions between adjacent electrodes 103, so as to extend parallel to a longitudinal direction of the electrodes 103.

Since the spacer 109 is formed in a flat area between adjacent electrodes 103, it is free from the influence of the difference in level between the area and the electrodes 103. Thus, the upper ends of the spacers 109 are flat.

However, when bonding the spacers 109 to a substrate 102, the spacers 109 cross electrodes 104.

Therefore, on the upper end of the spacer 109, a space (recession 111) due to the difference in level between an area where an adjacent electrode 104 is present and an area where no electrode 104 is present is produced.

In the above-described first embodiment, since the spacers 15 are formed to cross the electrodes 12, the influence of the difference in level due to the electrodes 12 is reduced, and the flat upper ends of the spacers 15 and the alignment control layer 24 on the electrode substrate 20 are bonded substantially perfectly to each other without a space therebetween.

On the other hand, in this comparative example, although the upper ends of the spacers 109 are flat, when the spacers 109 are bonded to the substrate 102, the above-mentioned space is present in areas where the substrate 102 is in contact with the upper ends of the spacers 109. This is the difference between the first embodiment and the first comparative example.

When a pressure of 5 kg/cm2 is applied to a liquid crystal display element fabricated in the abovementioned conventional process, the alignment was disordered and the disorderly alignment spread through the above-mentioned space from an area separated by the spacer 109 to adjacent areas. Thus, it was found that the liquid crystal display element of this comparative example had lower shock stability compared with the liquid crystal display element of the first embodiment.

[Second Comparative Example] A liquid crystal display element according to another comparative example has basically the same structure as the liquid crystal display element of the first comparative example, but is characterized by a rubbing treatment applied to alignment control layers 107 and 108 in a direction perpendicular to a longitudinal direction of the spacers 109. More specifically, the spacers 15 are formed so as to extend parallel to a normal direction of the smectic layer of the liquid crystal in the above-described first embodiment, while the spacers 109 are formed so as to extend perpendicularly to a normal direction of the smectic layer in this second comparative example. This is the difference between the second comparative example and the first embodiment.

When a pressure was applied to a liquid crystal display element fabricated in the above-mentioned conventional process, a disorderly alignment occurred in a direction perpendicular to a normal direction of the smectic layer. Since the spacers 109 were formed to extend perpendicularly to a normal direction of the smectic layer, the spread of disorderly alignment could not be stopped by the spacers 109, and the disorderly alignment spread over a wide range. It was found by comparing the liquid crystal display element fabricated such a conventional process with the liquid crystal display element of the first embodiment that the liquid crystal display element of the first embodiment had superior shock stability.

Claims

CLAIMS: 1. A liquid crystal display element comprising: a pair of substrates, at least one of which has light transmittance, provided with a plurality of electrodes extending in respective directions which mutually cross; a liquid crystal layer sandwiched between said substrates, which are placed so that the respective surfaces thereof provided with said electrodes face each other; and wall-shaped spacers of uniform height, provided on at least one of said substrates, which are bonded to the opposite substrate directly or through a film, wherein said spacers are provided extending parallel to a longitudinal direction of said electrodes provided on said opposite substrate to which said spacers are bonded, or of metal lines provided adjacent to said electrodes.
2. The liquid crystal display element as set forth in claim 1, wherein said spacers are bonded to said opposite substrate at positions between adjacent electrodes thereof.
3. The liquid crystal display element as set forth in either claim 1 or claim 2, wherein said spacers are bonded to said opposite substrate at positions thereof in which are provided said metal lines.
4. The liquid crystal display element as set forth in claim 3, wherein said electrodes and said metal lines partly overlap at positions where said spacers are bonded to said opposite substrate.
5. The liquid crystal display element as set forth in any one of claim 1 through claim 4, wherein a liquid crystal forming said liquid crystal layer is a ferroelectric liquid crystal.
6. The liquid crystal display element as set forth in any one of claim 1 through claim 5, wherein a liquid crystal forming said liquid crystal layer shows a smectic phase, and said spacers are provided extending parallel to a normal direction of a smectic layer of said liquid crystal.
7. The liquid crystal display element as set forth in any one of claim 1 through claim 6, wherein said spacers are made of a photosensitive organic resin.
8. The liquid crystal display element as set forth in any one of claim 1 through claim 6, wherein said spacers are made of a nonphotosensitive organic resin.
9. The liquid crystal display element as set forth in any one of claim 1 through claim 6, wherein said spacers are made of a metal.
10. A method of manufacturing a liquid crystal display element formed by sealing a liquid crystal between a pair of substrates, at least one of which has light transmittance, comprising the steps of: (1) providing electrodes on said pair of substrates; (2) providing on one of the substrates wallshaped spacers of uniform height, so as to extend parallel to a longitudinal direction of the electrodes provided on the opposite substrate, or of metal lines provided adjacent to the electrodes; and (3) bonding the spacers to the opposite substrate directly or through a film to assemble the substrates together.
11. The method of manufacturing a liquid crystal display element as set forth in claim 10, wherein, in said step (2), the spacers are located at positions between adjacent electrodes of the opposite substrate to which the spacers are bonded in said step (3).
12. The method of manufacturing a liquid crystal display element as set forth in either claim 10 or claim 11, wherein, in said step (2), the spacers are located at opposite positions of the opposite substrate to which the spacers are bonded in said step (3), in which are provided the metal lines.
13. The method of manufacturing a liquid crystal display element as set forth in claim 12, wherein, in said step (2), the spacers are located at positions where the electrodes and the metal lines partly overlap.
14. The method of manufacturing a liquid crystal display element as set forth in any one of claim 10 through claim 13, wherein, in said step (2), the spacers are provided so as to extend parallel to a normal direction of a smectic layer of the liquid crystal, which shows a smectic phase.
15. The method of manufacturing a liquid crystal display element as set forth in any one of claim 10 through claim 14, wherein said spacers are made of a photosensitive organic resin.
16. The method of manufacturing a liquid crystal display element as set forth in any one of claim 10 through claim 14, wherein said spacers are made of a nonphotosensitive organic resin.
17. The method of manufacturing a liquid crystal display element as set forth in any one of claim 10 through claim 14, wherein said spacers are made of a metal.