JP2012168347A - Liquid crystal display element and method for manufacturing liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase flexibility between substrates and to suppress degradation in image quality due to birefringence or the like, by forming a step-like part in a sealing part on a substrate where pixel electrodes are formed, the step-like part in a different level from the pixel electrode surface, so as to increase the thickness of a sealing.SOLUTION: A liquid crystal display element 20 comprises a semiconductor substrate 21 having a display area on the surface thereof, where a plurality of pixel electrodes 2 having light-reflecting property is formed in a matrix, and a transparent substrate 4 having light-transmitting property on which a transparent electrode 5 having light-transmitting property and conductivity is formed on one surface thereof. The two substrates are disposed as spaced apart from each other with the pixel electrodes 2 and the transparent electrode 5 opposing to each other, and laminated to form a gap (A) called as a cell gap by an annular sealing part 23 enclosing the display area via alignment layers 9, 10. The gap (A) is filled with a liquid crystal 8. The semiconductor substrate 21 is formed in such a manner that the thickness of an annular adhesion area where the sealing part 23 is formed is smaller by a value represented by # in the figure than the thickness of other display areas where pixel electrodes and the like are formed, and thus, a step-like part 22 is formed.

Description

  The present invention relates to a liquid crystal display element and a method for manufacturing the liquid crystal display element, and more particularly to a reflective liquid crystal display element and a method for manufacturing the liquid crystal display element.

Projection-type liquid crystal display devices such as projectors and projection televisions are widely used as displays capable of displaying images on a large screen with high definition. The liquid crystal display element used in the projection type liquid crystal display device generally includes a transmission type in which light incident from one of the liquid crystal display elements is transmitted through the liquid crystal display element and emitted to the other, and one of the liquid crystal display elements. There is a reflection type in which the light incident from is reflected by the liquid crystal display element and emitted to the incident side.
Although transmissive liquid crystal display elements tend to be inferior in aperture ratio compared to reflective liquid crystal display elements, there is a merit that the optical system combined at the time of projection can be simplified because the light incident and exit surfaces are different. .

  On the other hand, the reflective liquid crystal display element is more advantageous than the transmissive liquid crystal display element in realizing high resolution without reducing the aperture ratio. In the reflective liquid crystal display element, a MOS transistor corresponding to each pixel is generally arranged on a silicon-based semiconductor substrate, a metal wiring is provided on the upper layer, and a reflective electrode pixel is formed thereon.

  FIG. 4 is a schematic cross-sectional view of an example of a conventional reflective liquid crystal display element. As shown in FIG. 4, a conventional reflective liquid crystal display element 1 includes a semiconductor substrate 3 in which a plurality of pixel electrodes 2 having light reflectivity are formed in a predetermined range on a surface, and a surface (in FIG. A transparent substrate 4 having a light transmitting property on a transparent electrode 5 having a light transmitting property (corresponding to the lower surface of the substrate 4) has a gap A so that the pixel electrode 2 and the transparent electrode 5 face each other. A liquid crystal 8 is filled in the gap A, which is disposed between the seal portion 7, the transparent substrate, and the semiconductor substrate. The seal portion 7 is formed so as to finally surround a predetermined range of the surface of the semiconductor substrate 3.

  In addition, an alignment film 9 is formed on the semiconductor substrate 3 so as to cover at least a predetermined range of the surface thereof. In addition, an alignment film 10 is formed on the transparent substrate 4 to cover the transparent electrode 5 in a range corresponding to at least the predetermined range on the surface. An antireflection film 11 is formed on the back surface of the transparent substrate 4 (corresponding to the upper surface of the transparent substrate 4 in FIG. 4). In the reflective liquid crystal display element 1, the predetermined range is a display area for displaying an image. The length of the gap A is called a cell gap.

  In addition, since the light which injects into this liquid crystal display element 1 is not perfect parallel light, it will be irradiated to element parts other than a display area as it is. In particular, the light that hits the seal portion 7 has a random polarization direction, so that it shines brightly even in a non-driven state, resulting in a very poor image quality. For this reason, the reflective liquid crystal display element 1 has an aperture corresponding to the display area, and an aperture mask 12 that is a black plate that does not reflect light is placed above the antireflection film 11, thereby reducing the image quality. The structure is such that light does not enter the region.

  Here, in general, the liquid crystal often dislikes impurities entering from the outside. For this reason, the reflective liquid crystal display element 1 is bonded between the semiconductor substrate 3 and the transparent substrate 4 via the seal portion 7, and the semiconductor substrate Since the liquid crystal 8 is sealed in the space between the transparent substrate 4 and the transparent substrate 4, the sealing portion 7 is particularly required to have a high barrier property. Moisture is considered as an impurity that enters the liquid crystal cell in a normal environment, and the seal portion 7 has high moisture resistance for preventing moisture from entering.

  Although the moisture resistance of the seal portion 7 itself is very high, it is difficult to completely suppress moisture entering from the interface with the substrate to be bonded, and some moisture exists as impurities. There is a good correlation between the amount of entering water and the seal portion 7, and in particular, the material and width of the seal portion 7 are important factors that determine moisture resistance.

  As shown in Patent Document 1, it is desirable that the application region of the seal portion 7 be on the same surface as the pixel. The main purpose of this is to stably obtain various characteristics determined by the cell gap and to reduce the unevenness of the screen luminance due to the in-plane gap thickness unevenness. The semiconductor substrate 3 has a structure in which a transistor is formed as a base, and a polysilicon film and an oxide film and wiring, or a metal film serving as a surface electrode are formed in multiple layers on the upper layer. As a basic flattening method, a level difference caused by a difference in circuit density and process between the pixel region and the peripheral circuit region is made uniform by performing surface polishing during the wiring process.

Japanese Patent No. 3513410

  By the way, normally, when high moisture resistance is required for the seal portion 7 itself, it is necessary to closely contact the interface between the seal portion 7, the transparent electrode 5, and the semiconductor substrate 3. The hardness of is likely to be high. However, if the adhesive is bonded too firmly, birefringence occurs in the transparent substrate 4 due to shrinkage of the adhesive itself or stress due to the difference in thermal expansion coefficient between the transparent electrode 5 and the semiconductor substrate 3 to be bonded, resulting in display quality. Will be lowered. On the other hand, if a flexible material, for example, a material containing a large amount of rubber material or the like is used to reduce the stress in the seal portion 7, in many cases, the adhesive strength is insufficient, and the intrusion of moisture from the above-mentioned interface. It will be easy.

  The width of the seal portion 7 is also a very large factor that determines moisture resistance. Basically, the diffusion of moisture tends to be inversely proportional to the square of the width of the seal portion 7, and it is very significant how much width can be secured. Further, when considering the stress applied by the seal portion 7, when the seal thickness is thin and the width is widened, the two substrates 3 and 4 have a reduced degree of freedom, and birefringence is likely to occur.

  In recent years, liquid crystal display elements are highly demanded for cost reduction, and it is necessary to lower the unit cost per chip by increasing the pixel density and increasing the number of arrangements per wafer by downsizing the pixels. From such a point of view, the seal width cannot be widened and efforts have been made to secure the moisture resistance and reliability expected by the performance improvement of the seal portion 7 and the application position management of the seal portion 7. However, considering the current performance of the seal portion 7 and the moisture resistance obtained thereby, it has been difficult to make significant improvements, and it is particularly difficult to achieve it while satisfying all of the conventional required performance.

  Further, the performance required for recent liquid crystal display elements includes high-speed response, high contrast, and reduction of disclination amount, all of which are directed toward narrowing the cell gap of the liquid crystal display element. However, as described above, the seal portion 7 having high moisture resistance tends to have a high hardness, and when the thickness of the seal portion 7 is reduced to narrow the cell gap, the degree of freedom between the substrates 3 and 4 is relatively increased. However, it is easy to cause deterioration in image quality due to birefringence, and it is difficult to easily improve the material of the seal portion 7.

  The present invention has been made in view of the above points, and the degree of freedom between the substrates is increased by increasing the seal thickness by providing a step different from the pixel electrode surface in the seal portion on the substrate on which the pixel electrode is formed. An object of the present invention is to provide a liquid crystal display element and a method for manufacturing the liquid crystal display element that can suppress degradation of image quality due to the above.

  In order to achieve the above object, the liquid crystal display element of the present invention has a display area on which a plurality of pixel electrodes are formed on the surface, and an annular adhesion area surrounding the display area with respect to the surface of the display area. Formed on one surface is a semiconductor substrate formed with a step that is lower by a predetermined height, and a transparent electrode with light transmission and conductivity that is placed opposite to each other with a predetermined gap (A) between a plurality of pixel electrodes A transparent substrate having a light transmitting property, a bonding area of the semiconductor substrate, a seal portion to be bonded between a region corresponding to the bonding area of the transparent substrate with a predetermined gap, and a predetermined gap filled And a liquid crystal.

  In order to achieve the above object, the liquid crystal display element of the present invention has a predetermined height of the level difference of 0.5 when the average thickness of the liquid crystal layer in the gap in which the liquid crystal is sealed is 1.5 μm or less. It is characterized by being set to 5 μm or more.

  In order to achieve the above object, a method of manufacturing a liquid crystal display element according to the present invention includes a display region in which a plurality of pixel electrodes are arranged on the surface of a semiconductor substrate, and a surface of the display region so as to surround the display region. Forming an annular adhesive region having a step difference by a predetermined height, forming a transparent electrode on one surface of a transparent substrate having light transmissivity, and bonding a semiconductor substrate A seal portion is formed between the region and the region corresponding to the bonding region of the transparent substrate, with the sealing material and the display region of the semiconductor substrate and the transparent electrode of the transparent substrate facing each other with a predetermined gap therebetween And a liquid crystal filling step of filling a predetermined gap with liquid crystal.

  In order to achieve the above object, in the method of manufacturing a liquid crystal display element of the present invention, the region forming step has a predetermined height of the step, and the average thickness of the liquid crystal layer in the gap in which the liquid crystal is sealed is 1. When it is 5 μm or less, it is characterized by being formed to be 0.5 μm or more.

  According to the present invention, the degree of freedom between the two substrates to be bonded is increased by providing a step different from the pixel electrode surface in the seal portion on the substrate on which the pixel electrode is formed and increasing the seal thickness, and due to birefringence or the like. Degradation of image quality can be suppressed.

It is typical sectional drawing of one Embodiment of the liquid crystal display element of this invention. 1 is a schematic plan view of an embodiment of a liquid crystal display element of the present invention. It is element sectional drawing of each process of one Embodiment of the manufacturing method of the liquid crystal display element of this invention. It is typical sectional drawing of an example of the conventional liquid crystal display element.

  Next, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic sectional view of an embodiment of a liquid crystal display element according to the present invention, and FIG. 2 is a schematic plan view of an embodiment of a liquid crystal display element according to the present invention. In both drawings, the same components are denoted by the same reference numerals.

  As shown in FIG. 1, the liquid crystal display element 20 of the present embodiment is a reflective liquid crystal display element, and has a display region on the surface of which a plurality of pixel electrodes 2 having light reflectivity are formed in a matrix. And a transparent substrate 4 having a light transmission property in which a transparent electrode 5 having light transparency and conductivity is formed on one surface, and a transparent antireflection film 11 is formed on the other surface, is a pixel electrode. 2 and the transparent electrode 5 are disposed so as to be opposed to each other so as to face each other, and are bonded to each other with a gap A called a cell gap by an annular seal portion 23 surrounding the display area via the alignment films 9 and 10. The gap A has a structure in which the liquid crystal 8 is filled.

  The semiconductor substrate 21 is formed so that the thickness of the annular bonding region where the seal portion 23 is formed is thinner than the thickness of the display region where the other pixel electrodes are formed by the length indicated by #. A step 22 is formed. The semiconductor substrate 21 on which the pixel electrode 2 and the alignment film 9 are formed constitutes a pixel electrode substrate. Further, as shown in FIG. 2, a display area of a predetermined range D in which a plurality of pixel electrodes 2 are arranged in a matrix is formed on the semiconductor substrate 21, and further, the display area is shown in FIG. An alignment film 9 is formed.

  Further, a drive circuit section 24 is formed around the display area of the predetermined range D, and further includes a part of the drive circuit section 24, and an annular seal section 23 so as to surround the display area of the predetermined range D and the alignment film 9. Is formed. Further, adjacent to the drive circuit unit 24, a pad arrangement region 25 for wire bonding that electrically connects the liquid crystal display element 20 and the outside, which is not shown in FIG. 1, is formed. The alignment film 10 shown in FIG. 1 is formed so as to cover the transparent electrode 5 in a range corresponding to the predetermined range D shown in FIG. The transparent substrate 11 on which the transparent electrode 5 and the antireflection film 11 are formed, the alignment film 10 and the pixel electrode substrate can be formed using a known method for manufacturing a liquid crystal display element.

  Next, the seal part 23 which forms the main part of the present invention will be described. The height of the seal portion 23 is required to be substantially parallel to the pixel surface. The reason is that, as described in Patent Document 1 described above, various characteristics determined by the cell gap can be stably obtained, and unevenness of screen luminance due to in-plane gap thickness unevenness can be reduced. It is necessary. Therefore, it is necessary to flatten the seal portion 23 once using the technique described in Patent Document 1 and to align it with the same height as the pixel surface.

  A step 22 is created through the steps of photolithography, etching, and resist removal, which are generally used in the semiconductor manufacturing process, for the seal portion 23 having the same height as the pixel surface. An element is formed using the pixel electrode substrate thus prepared. In the present embodiment, when the average thickness of the liquid crystal layer in the gap A in which the liquid crystal 8 is sealed is 1.5 μm or less, the step 22 formed in the adhesion region of the seal portion 23 on the semiconductor substrate 21 is shown in FIG. The difference (height) from the plane of the region where the pixel electrode 5 is indicated by # is set to 0.5 μm or more. This is based on the result of calculating the required dimensions roughly in consideration of the refractive index of the general liquid crystal 8 and the incident / exit angle of the optical system.

  As described above, according to the liquid crystal display element 20 of the present embodiment, the thickness of the seal portion 23 is increased as compared with the conventional structure by providing the step 22 with the bonding region of the seal portion 23 on the semiconductor substrate 21. Therefore, when the pixel electrode substrate including the semiconductor substrate 21 and the transparent electrode substrate including the transparent substrate 4 are bonded together by the seal portion 23, the degree of freedom between the substrates is increased, and deterioration in image quality due to birefringence or the like is suppressed. It is possible. As a result, according to the liquid crystal display element 20 of the present embodiment, the image quality can be improved without greatly changing the conventional element structure and without increasing the cost due to the deterioration of productivity and the reduction in the number of pixel electrode substrates. Deterioration can be suppressed.

  As with the conventional liquid crystal display element 1, the liquid crystal display element 40 of the present embodiment also has a structure in which the aperture mask 12 is placed above the antireflection film 11 so that light does not enter a region that causes a reduction in image quality. It is also possible to take

  Next, the manufacturing method of the liquid crystal display element 20 of this Embodiment is demonstrated with the element sectional drawing of each process of FIG.

  First, as shown in FIG. 3A, a plurality of pixel electrodes 2 are formed in a matrix in a predetermined range D on the semiconductor substrate 21 by a known method. Subsequently, as shown in FIG. 3B, the entire surface of the semiconductor substrate 21 on which the pixel electrode 2 is formed is covered with a resist film 31, and then a normal photolithography technique is used as shown in FIG. , The region corresponding to the display region of the resist film 31 is masked by the exposure mask 32, and the portion of the resist film 31 that is not masked by the exposure mask 32 is irradiated with the exposure light. Subsequently, as shown in FIG. 3D, the exposure mask 32 is removed and then developed to leave a portion of the resist film 31 that is not irradiated with the exposure light.

  Next, as shown by an arrow 33 in FIG. 3E, known etching is performed using the resist film 31 as a mask, and a portion not covered with the resist film 31 (that is, a portion where the seal portion 23 is formed) is predetermined. Remove the depth of. Subsequently, as shown in FIG. 3 (f), the resist film 31 is removed by a known method using a chlorine-based gas or the like, so that a portion of the adhesion region of the semiconductor substrate 21 not covered with the resist film 31 is obtained. A step 22 is formed on the substrate. The surface of the step 22 is formed to be parallel to the surface of the pixel electrode 2. Further, when the average thickness of the liquid crystal layer in the gap A in which the liquid crystal 8 to be described later is enclosed is 1.5 μm or less, the difference between the surface of the step 22 and the plane of the pixel electrode 2 is 0.5 μm or more. Is formed.

  Next, as shown in FIG. 3 (g), a light transmissive and electrically conductive transparent electrode 5 is formed on one surface, and a transparent antireflection film 11 is formed on the other surface. A transparent substrate 4 having properties is prepared. The transparent electrode 5 and the antireflection film 11 can be easily formed on both surfaces of the transparent substrate using a known liquid crystal display device manufacturing method.

  Subsequently, as shown in FIG. 3H, the counter electrode substrate in which the predetermined region D on the surface of the transparent electrode 5 is coated with the alignment film 10 and the alignment region 9 in which the pixel electrode 2 is formed are coated with the alignment film 9. The pixel electrode substrate is arranged so that the alignment film 9 and the alignment film 10 face each other.

  Subsequently, as shown in FIG. 3 (i), a sealing material 34 in which a spacer ball having a predetermined diameter corresponding to the cell gap A (see FIG. 1) is mixed with the ultraviolet curable resin is disposed on the step 22 of the semiconductor substrate 31. Apply in a ring shape. The sealing material 34 is a material having high hardness that can easily improve moisture resistance.

  Then, as shown in FIG. 3 (j), the transparent substrate 4 (counter electrode substrate) including the transparent electrode 5, the antireflection film 11 and the alignment film 10 is placed in a state where the alignment film 10 and the alignment film 9 face each other. The sealing material 34 is cured by irradiation with ultraviolet (UV) light 35 while applying a predetermined pressure in the approaching direction to form the seal portion 23, and the bonding region between the semiconductor substrate 21 and the counter electrode substrate is bonded. Paste the area corresponding to the area. At this time, the seal part 23 can set the distance of the cell gap A according to the diameter of the spacer.

  The shape of the sealing material 34 applied at this time leaves a space for completely injecting liquid crystal later when the periphery of the plurality of pixel electrodes 2 in the display region (corresponding to the predetermined region D in FIG. 2) is completely covered. Two types of cases are conceivable. When completely covering, before superimposing the pixel electrode substrate and the counter electrode substrate, an amount of liquid crystal corresponding to the volume of the space formed between the pixel electrode substrate and the counter electrode substrate is placed on one of the substrates. It is necessary to supply in advance.

  Further, an ordinary sealing material uses 3000 mJ in terms of 365 nm as an energy necessary for curing the sealing material, and cures the sealing material by UV light irradiation for about 30 seconds using a 100 mW UV light source.

  After the sealing material 34 is cured by UV light irradiation as described above to form the seal portion 23, it is introduced into a generally used liquid crystal injection apparatus, and a gap for injecting the previous liquid crystal using a vacuum injection method. Then, the liquid crystal is injected into a gap surrounded by the alignment film 9, the alignment film 10, and the seal portion 23. After injecting the liquid crystal, a sealing material is again applied to the gap between the seal portions 23 into which the liquid crystal has been injected, and is cured and completely sealed. Thereafter, the liquid crystal and other foreign matters adhering to the periphery are removed.

  After that, an FPC (Flexible Printed Circuit) for connecting to the external drive substrate is attached, and the liquid crystal display element and the FPC are electrically connected by wire bonding or the like, as shown in FIGS. 1 and 2 of the present embodiment. A liquid crystal display element 20 similar to the above is completed.

  Note that the present invention is not limited to the above embodiment, and for example, the present invention can be applied to a transmissive liquid crystal display element. Further, the present invention is not limited to the above embodiment, and it goes without saying that various modifications can be made without departing from the gist of the present invention. In the above embodiment, the average thickness of the gap A is 1.5 μm or less, and the difference between the surface of the step 22 and the plane of the pixel electrode 2 is 0.5 μm, but a range of about 0.2 μm before and after is allowed. .

2 pixel electrode 4 transparent substrate 5 transparent electrode 8 liquid crystal 9, 10 alignment film 11 antireflection film 20 liquid crystal display element 21 semiconductor substrate 22 step 23 seal part 24 drive circuit part A gap

Claims (4)

A semiconductor substrate having a display region having a plurality of pixel electrodes formed on the surface, and an annular adhesive region surrounding the display region formed at a step which is lower than the surface of the display region by a predetermined height; ,
A transparent substrate having a light transmitting property, wherein a transparent electrode having a light transmitting property and a conductive property disposed on a surface of the plurality of pixel electrodes with a predetermined gap therebetween is formed;
A seal portion for bonding between the adhesion region of the semiconductor substrate and a region corresponding to the adhesion region of the transparent substrate with the predetermined gap;
A liquid crystal display element comprising: a liquid crystal filled in the predetermined gap.   The predetermined height of the step is set to 0.5 μm or more when an average thickness of a liquid crystal layer in the gap in which the liquid crystal is sealed is 1.5 μm or less. 1. A liquid crystal display element according to 1. An area for forming a display area in which a plurality of pixel electrodes are arranged on the surface of a semiconductor substrate, and an annular adhesion area having a step that is lower than the surface of the display area by a predetermined height so as to surround the display area Forming process;
A transparent electrode forming step of forming a transparent electrode on one surface of a transparent substrate having light permeability;
A gap between the bonding region of the semiconductor substrate and a region corresponding to the bonding region of the transparent substrate has a predetermined gap between the display region of the semiconductor substrate and the transparent electrode of the transparent substrate. Then, a seal part forming step for bonding in a state of facing each other,
And a liquid crystal filling step of filling the predetermined gap with liquid crystal.   In the region forming step, the predetermined height of the step is formed to be 0.5 μm or more when the average thickness of the liquid crystal layer in the gap in which the liquid crystal is sealed is 1.5 μm or less. A method for producing a liquid crystal display element according to claim 3.

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