Abstract:
The invention relates to liquid crystal displays used in display sections of electronic apparatus and provides a liquid crystal display in which high anti-pressure characteristics can be achieved with a high aperture ratio maintained. A configuration is provided, which includes a pair of substrates provided opposite to each other, a liquid crystal sealed between the substrates, a plurality of pixel regions provided on the substrates, and protrusion-like structures provided in the pixel regions for regulating the alignment of the liquid crystal and maintaining a cell thickness between the substrates.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a liquid crystal display used in a display section of an electronic apparatus.  
         [0003]     2. Description of the Related Art  
         [0004]     A liquid crystal display has a pair of substrates provided opposite to each other and a liquid crystal layer sandwiched between the substrates. In general, transparent electrodes are formed on each of surfaces of the pair of substrate opposite to each other. The liquid crystal display is enabled for display by applying a voltage between the transparent electrodes to drive the liquid crystal and to thereby control the transmittance of light at each pixel.  
         [0005]     Recently, there are increasing demands and diversifying requirements for liquid crystal displays. In particular, improvement in viewing angle characteristics and display quality is strongly demanded. Multi-domain vertical alignment (MVA) type liquid crystal displays are regarded promising as a technique for achieving improved viewing angle characteristics and display quality.  
         [0006]     In a general active matrix type liquid crystal display, the cell thickness between the substrates is controlled by spherical spacers made of plastic. Spherical spacers are dispersed on one of the substrates at a spacer dispersing step before the substrates are attached. Thereafter, the substrates are attached, and a liquid crystal is injected. Further, pressurization is carried out such that the cell thickness will be maintained at a value close to the diameter of the spherical spacers. However, a liquid crystal display utilizing spherical spacers has a problem in that it is likely to have variation of the cell thickness attributable to variation of the dispersion density of the spherical spacers and leakage of light attributable to damage on alignment films that can occur when the spherical spacers move.  
         [0007]     Recently, as a technique for simplifying manufacturing processes through a reduction of liquid crystal injection time, the one drop filling (ODF) method has been put in use, in which two substrates are attached after dropping a liquid crystal on one of the substrates. When a liquid crystal is injected using the ODF method, it is difficult to distribute spherical spacers uniformly within the plane of a panel because dispersed spherical spacers move when a liquid crystal is dropped. For this reason, spherical spacers cannot be used in a liquid crystal display fabricated using the ODF method.  
         [0008]     Under such circumstances, pillar spacers are used in liquid crystal displays fabricated using the ODF method in particular, the pillar spacers being securely formed on one of substrates using a photolithographic process and contacting the other substrate to maintain a cell thickness after the substrates are attached.  FIG. 9  shows a configuration of an MVA type liquid crystal display according to the related art having pillar spacers, and  FIG. 10  shows a sectional configuration taken along the line X-X in  FIG. 9 . As shown in  FIGS. 9 and 10 , the liquid crystal display has a thin film transistor (TFT) substrate  102  and an opposite substrate  104  which are provided opposite to each other and a liquid crystal  106  sealed between the substrates  102  and  104 . The TFT substrate  102  has a plurality of gate bus lines  112  extending in the horizontal direction in  FIG. 9  on a glass substrate  110 . An insulation film  130  is formed on the gate bus lines  112 . A plurality of drain bus lines  114  extending in the vertical direction in  FIG. 9  are formed such that they intersect the gate bus lines  112  with the insulation film  130  interposed between them. An insulation film  132  is formed on the drain bus lines  114 .  
         [0009]     A TFT  120  is formed in the vicinity of each of intersections between the gate bus lines  112  and the drain bus lines  114 . Transparent pixel electrodes  116  are formed on the insulation film  132  in pixel regions which are surrounded by the gate bus lines  112  and the drain bus lines  114 . Storage capacitor bus lines  118  extending in parallel with the gate bus lines  112  are formed such that they traverse the respective pixel regions substantially in the middle thereof. A storage capacitor electrode (intermediate electrode)  119  is formed in each pixel region above the storage capacitor bus line  118  with the insulation film  130  interposed between them.  
         [0010]     The opposite substrate  104  has a shielding film (BM film)  148  (not shown in  FIG. 9 ) provided on a glass substrate  111  for shielding light-shield regions between adjoining pixel regions and regions (light-shield portions) above the storage capacitor bus lines  118  (storage capacitor electrodes  119 ) in the pixel regions. Color filter (CF) resin layers  140  are formed in the pixel regions on the glass substrate  111 . A common electrode  142  is formed throughout the substrate over the CF resin layers  140 . Linear protrusions  144  extending obliquely relative to edges of the pixel regions are formed on the common electrode  142  as alignment regulating structures for regulating the alignment of the liquid crystal  106 . Pillar spacers  150  are formed in the light-shield regions on the common electrode  142 , one spacer  150  being provided for a few pixels or several tens pixels. The pillar spacers  150  are provided in positions opposite to the intersections between the gate bus lines  112  and the drain bus lines  114 . Pillar spacers  151  are formed in the light-shield portions in the pixel regions, one spacer  151  being provided for a few pixels or several tens pixels. The pillar spacers  151  are provided in positions opposite to the storage capacitor electrodes  119 .  
         [0011]      FIG. 11  shows another configuration of an MVA type liquid crystal display according to the related art. As shown in  FIG. 11 , a pixel electrode  116  formed in a pixel region has a plurality of electrode units  116   a  having a comb-tooth-shaped peripheral section for regulating the alignment of a liquid crystal  106  and connection electrodes  116   b  for electrically connecting the electrode units  116   a . Pillar spacers  151  are formed in light-shield portions in pixel regions in a disposition density of one pixel per a few pixels or several tens pixels. The pillar spacers  151  are provided in positions opposite to the storage capacitor bus lines  118 . Point-like protrusions  145  which are alignment regulating structures are formed on an opposite substrate  104  in positions corresponding to the centers of some of the electrode units  116   a.    
         [0012]     Leakage of light and the like can occur around the pillar spacers  150  and  151  because abnormalities can occur in the alignment of the liquid crystal  106  in such regions in general. Therefore, the pillar spacers  150  and  151  are provided in light-shield regions or the light-shield portion in the pixel regions such that display failures attributable to leakage of light will not be visually perceived.  
         [0013]     The pillar spacers  150  and  151  are provided in a predetermined pattern in the plane of a substrate. A hard liquid crystal display panel having high anti-pressure characteristics can be obtained by increasing the area or number of contacts between the pillar spacers  150  and  151  and the substrate to increase the disposition density of the pillar spacers  150  and  151 .  
         [0014]     An effective way to provide a liquid crystal display with high luminance and less power consumption is to improve utilization of light by increasing the aperture ratio of pixels. In order to improve the aperture ratio of pixels, it is necessary to increase the area of apertures at pixel regions relatively by reducing the area of light-shield regions and light-shield portions of the pixel regions. However, a reduction in the area of the light-shield regions and the light-shield portions of the pixel regions puts a limitation on the size and position of the pillar spacers  150  and  151 . Thus, it is difficult to increase the disposition density of the pillar spacers  150  and  151  by increasing the number of the pillar spacers  150  and  151 . A problem therefore arises in that it is difficult to provide a liquid crystal display having a high aperture ratio with high anti-pressure characteristics.  
         [0015]     In a liquid crystal display fabricated using the ODF method, panel defects associated with liquid crystal injection such as bubbles and variation of the picture frame can occur when there is only a slight change in the amount of liquid crystal dispensed. The generation of such panel defects is attributable to variation of the height of the pillar spacers  150  and  151 , thermal contraction of the liquid crystal  106 , and the characteristics of compressive displacement of the pillar spacers  150  and  151 . In order to increase the margin of the amount of liquid crystal dispensed, it is basically required to use a flexible liquid crystal display panel whose cell thickness can flexibly follow a change in the amount of liquid crystal dispensed in a region under a light load. A flexible liquid crystal display panel can be provided by disposing the pillar spacers  150  and  151  in a low disposition density. However, a simple reduction of the disposition density of the pillar spacers  150  and  151  reduces the anti-pressure characteristics of the liquid crystal display panel, and variation of the cell thickness can be more easily caused by local pressurization from the outside such as a press on the display surface. As thus described, in a liquid crystal display fabricated using the ODF method, the margin of the amount of liquid crystal dispensed and the anti-pressure characteristics of the display are a trade-off in general.  
         [0016]     As a technique which makes it possible to achieve both of a wide margin of the amount of liquid crystal dispensed and high anti-pressure characteristics, there is a liquid crystal display in which pillar spacers having a great height are provided in a low disposition density and pillar spacers having a smaller height are provided in a higher disposal density (see Patent Documents 1 (JP-A-2001-201750) and 2 (JP-A-2003-156750)). In this liquid crystal display, the cell thickness is normally maintained by the pillar spacers having a greater height disposed in a lower density, and the cell thickness is maintained by the pillar spacers having a smaller height disposed in a higher density when a pressure is applied from the outside. Patent Document 1 discloses a method in which plural types of pillar spacers having different heights are formed on the same substrate. Patent Document 2 discloses a method in which pillar spacers of the same height are disposed in different positions with respect to a pixel and in which the pillar spacers are substantially formed as spacers having different heights utilizing steps formed by the thickness of metal wirings on a TFT substrate provided opposite to the spacers.  
         [0017]     However, in a liquid crystal display having a high aperture ratio, since there are limitations on the size and position of pillar spacers as already described, it is difficult to provide pillar spacers having different heights in desired disposal densities as described above. Therefore, a liquid crystal display having a high aperture ratio fabricated using the ODF method has a problem in that it is difficult to achieve a wide margin of the amount of liquid crystal dispensed and high anti-pressure characteristics.  
       SUMMARY OF THE INVENTION  
       [0018]     It is an object of the invention to provide a liquid crystal display which can be provided with high anti-pressure characteristics with a high aperture ratio maintained. It is another object of the invention to provide a liquid crystal display for which a wide margin of the amount of liquid crystal dispensed can be achieved in fabricating the display using the one drop filling method.  
         [0019]     The above-described object is achieved by a liquid crystal display characterized in that it has a pair of substrates provided opposite to each other, a liquid crystal sealed between the pair of substrates, a plurality of pixel regions provided on the substrates, and protrusion-like structures provided in the pixel regions to regulate the alignment of the liquid crystal and to maintain a cell thickness between the pair of substrates.  
         [0020]     The invention makes it possible to provide a liquid crystal display which has high anti-pressure characteristics while maintaining a high aperture ratio. The invention also makes it possible to provide a liquid crystal display for which a wide margin of the amount of liquid crystal dispensed can be achieved in fabricating the display using the one drop filling method. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]      FIG. 1  shows a configuration of a liquid crystal display according to a first embodiment of the invention;  
         [0022]      FIG. 2  shows a schematic sectional configuration of the liquid crystal display according to the first embodiment of the invention;  
         [0023]      FIG. 3  shows disposition of point-like protrusions and protrusion-like structures on an opposite substrate of the liquid crystal display according to the first embodiment of the invention;  
         [0024]      FIG. 4  shows a sectional configuration of the opposite substrate of the liquid crystal display according to the first embodiment of the invention;  
         [0025]      FIGS. 5A  to  5 F show a configuration of the opposite substrate of the liquid crystal display according to the first embodiment of the invention;  
         [0026]      FIG. 6  shows a modification of the configuration of the liquid crystal display according to the first embodiment of the invention;  
         [0027]      FIG. 7  shows a sectional configuration of a liquid crystal display according to a second embodiment of the invention;  
         [0028]      FIG. 8  shows a sectional configuration of a liquid crystal display according to a third embodiment of the invention;  
         [0029]      FIG. 9  shows a configuration of an MVA type liquid crystal display according to the related art;  
         [0030]      FIG. 10  shows a sectional view showing the configuration of the MVA type liquid crystal display according to the related art; and  
         [0031]      FIG. 11  shows another configuration of an MVA type liquid crystal display according to the related art. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     First Embodiment  
       [0032]     A liquid crystal display according to a first embodiment of the invention will now be described with reference to FIGS.  1  to  6 .  FIG. 1  shows a configuration of one pixel of the liquid crystal display according to the present embodiment.  FIG. 2  shows a schematic sectional configuration of the liquid crystal display according to the present embodiment. As shown in  FIGS. 1 and 2 , the liquid crystal display has a TFT substrate  2  and an opposite substrate  4  provided opposite to each other and a liquid crystal  6  sealed between the substrates  2  and  4 . The liquid crystal  6  is aligned substantially perpendicularly to the surfaces of the substrates, and it has negative dielectric constant anisotropy. The liquid crystal display is fabricated through steps of printing and baking alignment films (vertical alignment films) on surfaces of the substrates  2  and  4  opposite to each other, applying a sealing material to a peripheral section of either of the substrates  2  and  4 , attaching the substrates  2  and  4  after dropping the liquid crystal  6 , cutting and chamfering the substrates thereafter, applying polarizers, and so on.  
         [0033]     The TFT substrate  2  has a plurality of gate bus lines  12  extending in the horizontal direction in  FIG. 1  provided on a transparent glass substrate  10 . For example, the gate bus lines  12  are formed by stacking layers of aluminum (Al), neodymium (Nd), and molybdenum (Mo) in the order listed to form a metal film having a thickness of 250 nm on the glass substrate  10  and patterning the film into a predetermined configuration using a photolithographic process. An insulation film  30  constituted by a silicon nitride film (SiN film) having a thickness of, for example, 350 nm is formed on the gate bus lines  12 . A plurality of drain bus lines  14  extending in the vertical direction in  FIG. 1  are formed such that they intersect the gate bus lines  12  with the insulation film  30  interposed between them. For example, the drain bus lines  14  are constituted by a metal film having a thickness of 320 nm provided by stacking layers of Mo, Al and Mo in the order listed. An insulation film  32  constituted by a SiN film having a thickness of, for example, 200 nm is formed on the drain bus lines  14 .  
         [0034]     A TFT  20  is formed in the vicinity of each of intersections between the gate bus lines  12  and the drain bus lines  14 . A drain electrode  21  of a TFT  20  is formed of the same material as that of the drain bus lines  14  and is electrically connected to a drain bus line  14 . A source electrode  22  is provided opposite to the drain electrode  21 . A part of a gate bus line  12  serves as a gate electrode of a TFT  20 . An active semiconductor layer of a TFT  20  is formed of amorphous silicon (a-Si), for example.  
         [0035]     In pixel regions on the insulation film  32  surrounded by the gate bus lines  12  and drain bus lines  14 , pixel electrodes  16  are formed by patterning an ITO film having a thickness of, for example, 40 nm. A pixel electrode  16  is electrically connected to the source electrode  22  of a TFT  20  through a contact hole which is not shown. A pixel electrode  16  has five electrode units  16   a  successively arranged in the extending direction of the drain bus lines  14 , slits  16   c  formed between adjoining electrode units  16   a  and connection electrodes  16   b  for electrically connecting the electrode units  16   a  which are separated by the slits  16   c . An electrode unit  16   a  has a solid portion  16   d  provided in the middle thereof and a comb-tooth-shaped portion  16   e  provided at the periphery of the solid portion  16   d . A comb-tooth-shaped portion  16   e  has a plurality of linear electrodes  16   f  extending from the solid portion  16   d  and spaces  16   g  formed between adjoining linear electrodes  16   f . The linear electrodes  16   f  extend in four different directions in respective regions. Linear electrodes  16   f  at a top right part of an electrode unit  16   a  extend to the right and upward, and linear electrodes  16   f  at a bottom right part of the electrode unit  16   a  extend to the right and downward. Linear electrodes  16   f  at a top left part of the electrode unit  16   a  extend to the left and upward, and linear electrodes  16   f  at a bottom left part of the electrode unit  16   a  extend to the left and downward. Liquid crystal molecules are tilted in parallel with the extending directions of the linear electrodes  16   f  and toward the solid portion  16   d . Thus, the alignment of liquid crystal  6  is divided into four directions at each electrode unit  16   a.    
         [0036]     Storage capacitor bus lines  18  extending in parallel with the gate bus lines  12  are formed such that they traverse respective pixel regions substantially in the middle thereof. The storage capacitor bus lines  18  are formed of the same material as that of the gate bus lines  12 . A storage capacitor electrode  19  is formed in each pixel region above the storage capacitor bus line  18  with the insulation film  30  interposed between them. The storage capacitor electrode  19  is formed of the same material as that of the drain bus line  14 . A storage capacitor electrode  19  is electrically connected to a pixel electrode  16  through a contact hole which is not shown.  
         [0037]     The opposite substrate  4  has a black matrix (BM)  48  (not shown in  FIG. 1 ) provided on a glass substrate  11  for shielding light-shield regions between adjoining pixel regions and regions (light-shield portions) above the storage capacitor bus lines  18  (storage capacitor electrodes  19 ) in the pixel regions. For example, the BM  48  is formed by patterning a low-reflection chromium (Cr) film having a thickness of 160 nm or a black resin film having a thickness of 1.2 μm. A CF resin layer  40  in any of red (R), green (G) and blue (B) is formed in a pixel region on the glass substrate  11 . The CF resin layers  40  are formed by repeating a process of applying and patterning a colored resin having a thickness of, for example, 1.8 μm for each of the colors R, G and B or three times in total. A common electrode  42  constituted by an ITO film having a thickness of, for example, 150 nm is formed throughout the substrate over the CF resin layers  40 .  
         [0038]     Point-like protrusions (alignment regulating protrusions)  45  made of a dielectric material and protrusion-like structures  51  and  52  are formed on the common electrode  42  as alignment regulating structures for regulating the alignment of the liquid crystal  6 .  FIG. 3  shows dispositions of point-like protrusions  45  and protrusion-like structures  51  and  52  in three pixels in R, G and B, respectively, and  FIG. 4  shows a sectional configuration of the opposite substrate  4  taken along the line A-A in  FIG. 3 .  FIG. 5A  shows dispositions and configurations of point-like protrusions  45  and protrusion-like structures  51  and  52  in substantially three pixels.  FIG. 5B  is an enlarged view of the neighborhood of a point-like protrusion  45  and protrusion-like structures  51  and  52 .  FIG. 5C  shows the configuration of the opposite substrate  4  as viewed in an oblique direction.  FIG. 5D  shows a sectional configuration of the opposite substrate  4  taken in the vicinity of a protrusion-like structure  51 .  FIG. 5E  shows a sectional configuration of the opposite substrate  4  taken in the vicinity of a protrusion-like structure  52 .  FIG. 5F  shows a sectional configuration of the opposite substrate  4  taken in the vicinity of a point-like protrusion  45 .  
         [0039]     As shown in FIGS.  3  to  5 F, in each of the pixels on the opposite substrate  4 , five alignment regulating structures (point-like protrusions  45  and protrusion-like structures  51  and  52 ) are provided in total, the structures being arranged linearly. Each of the alignment regulating structures is formed in a position which substantially corresponds to the center of an electrode unit  16   a  on the TFT substrate  2 . In the R and G pixels, one point-like protrusion  45  is provided such that overlaps the light-shield portion shielding the storage capacitor bus line  18  from light, and two point-like protrusions  45  are provided at each of upper and lower apertures in  FIG. 3 . On the contrary, in the B pixel, one protrusion-like structure  51 , three protrusion-like structures  52  and one point-like protrusion  45  are provided. The protrusion-like structure  51  is provided such that it overlaps the light-shield portion shielding the storage capacitor bus line  18  from light. Two protrusion-like structures  52  are provided at the upper aperture in  FIG. 3 . The other protrusion-like structure  52  and the one point-like protrusion  45  are provided at the lower aperture in  FIG. 3 .  
         [0040]     The point-like protrusions  45  are formed by applying a positive photosensitive resist to the common electrode  42  and performing pre-baking, exposing, developing, post-baking steps on the same such that they will have an ultimate height of, for example, about 2.5 μm above the surface of the common electrode  42 . The point-like protrusions  45  have a plan configuration, for example, in the form of a square of 14 μm×14 μm, and they are disposed such that each side of the same will be oblique to an edge of a pixel region. The protrusion-like structures  51  and  52  are formed by applying a negative photosensitive resist to the common electrode  42  and performing pre-baking, exposing, developing, and post-baking steps on the same. The protrusion-like structures  51  and  52  are formed such that they will have an ultimate height h 1  of, for example, about 4.0 μm above the surface of the common electrode  42 .  
         [0041]     A protrusion-like structure  51  is provided in a position associated with a storage capacitor bus line  18  and a storage capacitor electrode  19  on the TFT substrate  2 , and a protrusion-like structure  52  is provided at an aperture of the pixel (see  FIG. 2 ). The height of a region of the TFT substrate  2  where a storage capacitor bus line  18  and a storage capacitor electrode  19  are formed above the glass substrate  10  is greater than that of a pixel aperture region by a height h 2  which is equivalent to the thickness of the metal layers (about 0.5 to 0.6 μm). Therefore, although the protrusion-like structures  51  and  52  are formed with substantially the same height h 1 , the protrusion-like structure  51  contacts the TFT substrate  2  whereas the protrusion-like structure  52  does not contact the TFT substrate  2  when the substrates  2  and  4  are attached. Thus, the protrusion-like structures  51  maintain a first cell thickness (≅h 1 +h 2 ), and the protrusion-like structures  52  maintain a second cell thickness (≅h 1 ) smaller than the first cell thickness when a pressure is applied from the outside. For example, when a heavy load is locally applied to a surface of the panel, the protrusion-like structures  51  are deformed, and the protrusion-like structures  52  come into contact with the TFT substrate  2  before a limit for breakdown of the protrusion-like structures  51  is reached. Since the protrusion-like structures  52  are provided in a high disposition density to support the load by distributing the same, any further change in the cell thickness will not occur. It is therefore possible to prevent the occurrence of cell thickness variation attributable to elastic breakdown of pillar spacers.  
         [0042]     The protrusion-like structures  51  are designed with a low disposition density (e.g., one structure per 18 pixels) based on the characteristics of compressive displacement of acrylic resins such that predetermined displacement will be achieved when they are loaded at the time of manufacture of a panel. The protrusion-like structures  52  are designed with a high disposition density (e.g., three structures per B pixel (or 18 structures per 18 pixels)) such that they can withstand a very heavy localized load such as that applied when a panel is depressed with a finger.  
         [0043]     Although the protrusion-like structures  51  and  52  serve as alignment regulating structures, they may leave slight abnormalities in the alignment of the liquid crystal  6  when compared to the point-like protrusions  45 . It is therefore desirable to form them in pixels of blue which is lowest in transmittance among the three colors R, G and B. When the protrusion-like structures  51  and  52  are formed only in B pixels, display defects attributable to abnormalities of the alignment of the liquid crystal  6  are less visually perceptible compared to those encountered when the protrusion-like structures  51  and  52  are formed also in R and G pixels. When an angle (taper angle) θ 1  defined by side sections of the protrusion-like structures  51  and  52  and the surface of the opposite substrate  4  is made equal to or smaller than 45° by controlling exposing conditions, developing conditions and baking conditions, the possibility of abnormalities in the alignment of the liquid crystal  6  will be lower than that in a case wherein the taper angle θ 1  is greater than 45°. For example, the protrusion-like structures  51  and  52  have a bottom surface (facing the opposite substrate  4 ) in the form of a circle having a diameter of about 20 μm and a top surface (facing the TFT substrate  2 ) having a diameter of about 9 μm. The diameter of the bottom surfaces of the protrusion-like structures  51  and  52  are equal to or smaller than about one-third of the width of an aperture (e.g., 78 μm). Any reduction in the aperture ratio of a pixel can be prevented by keeping the area occupied by a protrusion-like structure  52  (or  51 ) provided at the aperture of the pixel equal to or smaller than about 10% of the area of the aperture.  
         [0044]     According to the present embodiment, since the protrusion-like structures  51  and  52  serving as pillar spacers can be provided also in the apertures of pixels, limitations on positions for disposal of the structures are relaxed, and the protrusion-like structures  51  and  52  which substantially have different heights can be provided in respective desired disposition densities. The disposition of either of the protrusion-like structures  51  and  52  will not affect the disposition of the other. Since this allows an improvement in the characteristics of compressive displacement of the pillar spacers such as elasticity and restorability in response to a change in a cell thickness, a wide margin of the amount of liquid crystal dispensed and high anti-pressure characteristics can be achieved even in a liquid crystal display having a high aperture ratio fabricated using the ODF method. It is therefore possible to provide liquid crystal displays having stable quality with a high yield of manufacture.  
         [0045]      FIG. 6  shows a modification of the configuration of a liquid crystal display according to the present embodiment. As shown in  FIG. 6 , a pixel electrode  16  in the present modification has three electrode units  16   a . A protrusion-like structure  51  is formed on an opposite substrate  4  in each of positions substantially corresponding to the centers of the three electrode units  16   a . Any of the three protrusion-like structures  51  contacts a TFT substrate  2  to maintain a predetermined cell thickness. Thus, only protrusion-like structures  51  having substantially the same height may be formed in a desired disposition density.  
         [0046]     According to the present modification, since the protrusion-like structures  51  serving as pillar spacers can be provided also in apertures of pixels, limitations on positions for disposal of the structures are relaxed, and the structures can be provided in a desired disposition density. It is therefore possible to achieve high anti-pressure characteristics even in a liquid crystal display having a high aperture ratio.  
         [0047]     While the protrusion-like structures  51  and  52  are formed on the CF substrate  4  using an acrylic resin in the present embodiment, the protrusion-like structures  51  and  52  may alternatively be formed on the TFT substrate  2 . The protrusion-like structures  51  and  52  may be formed by stacking parts of the CF resin layers  40  one over another instead of forming the protrusion-like structures  51  and  52  at an independent step.  
       Second Embodiment  
       [0048]     A liquid crystal display according to a second embodiment of the invention will now be described with reference to  FIG. 7 .  FIG. 7  shows a sectional configuration of the liquid crystal display according to the present embodiment. As shown in  FIG. 7 , in the present embodiment, protrusion-like structures  52  and  53  having different heights above a substrate surface are formed on an opposite substrate  4  instead of taking advantage of a difference in the height of a TFT substrate  2 . Point-like protrusions  45  are formed after the formation of the protrusion-like structures  52 , and some of the protrusion-like structures  52  are covered by a resin layer  46  which is formed simultaneously with the point-like protrusions  45  using the same material. A protrusion-like structure  53  greater in height than a protrusion-like structure  52  is formed by the resin layer  46  and a protrusion-like structure  52  which is covered by the resin layer  46 . Thus, there is provided protrusion-like structures  52  which are formed of an acrylic resin and protrusion-like structures  53  which are greater in height than the protrusion-like structures  52 , surface sections of the structures  53  being formed of the same material as that of the point-like protrusions  45 , the remaining sections of the protrusions  53  being formed of the same material as that of the protrusion-like structures  52 . The difference in height between the protrusion-like structures  52  and  53  is in the range from about 0.3 μm to about 0.7 μm.  
         [0049]     According to the present embodiment, since the protrusion-like structures  52  and  53  having different heights can be provided in respective desired disposition densities, a wide margin of the amount of liquid crystal dispensed and high anti-pressure characteristics can be achieved even in a liquid crystal display having a high aperture ratio fabricated using the ODF method. It is therefore possible to provide liquid crystal displays having stable quality with a high yield of manufacture.  
       Third Embodiment  
       [0050]     A liquid crystal display according to a third embodiment of the invention will now be described with reference to  FIG. 8 .  FIG. 8  shows a sectional configuration of the liquid crystal display according to the present embodiment. As shown in  FIG. 8 , in the present embodiment, all protrusion-like structures  52  are covered by a resin layer  46  which is formed simultaneously with point-like protrusions  45  using the same material. Protrusion-like structures  53  and  54  which are substantially different in height are formed by the resin layer  46  and the protrusion-like structures  52  which is covered by the resin layer  46  in the same manner as that in the first embodiment.  
         [0051]     According to the present embodiment, since a taper angle θ 2  of side sections of the protrusion-like structures  53  and  54  is smaller than the taper angle θ 1  shown in  FIG. 2 , a further reduction of abnormalities in the alignment of a liquid crystal  6  can be achieved in comparison to the first embodiment, and display defects will be less visually perceptible.  
         [0052]     The invention is not limited to the above-described embodiments and may be modified in various ways.  
         [0053]     For example, although transmissive liquid crystal displays have been referred to in the above-described embodiments by way of example, the invention is not limited to them and may be applied to other types of liquid crystal displays such as reflective and transflective types.  
         [0054]     Although liquid crystal displays having CF resin layers  40  formed on an opposite substrate  4  have been referred to in the above-described embodiments by way of example, the invention is not limited to them and may be applied to liquid crystal displays having the so-called CF-on-TFT structure in which CF resin layers  40  are formed on a TFT substrate  2 .