JP3380856B2 - Liquid crystal display - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device having a two-terminal nonlinear element as a switching element for driving a pixel. 2. Description of the Related Art In recent years, liquid crystal display devices have been used in display applications such as personal computers, word processors, office automation terminal displays, and televisions because of their low power consumption, thinness, and light weight. As a result, higher capacity display and higher image quality are required. A conventional liquid crystal display device is a TN (Twist).
ed Nematic) or STN (Super
r Twisted Nematic)
Simple matrix driving by the voltage averaging method has been adopted. However, this method is not suitable for large-capacity display because a sufficient contrast ratio cannot be obtained due to an increase in the number of scanning lines. Therefore, a liquid crystal display device has been developed in which a switching element is provided for each pixel constituting a display screen to perform display by active driving. As the switching element, a thin film transistor or a two-terminal non-linear element is used. However, a liquid crystal display device using a two-terminal non-linear element which has a simple structure and is advantageous in terms of manufacturing cost is expected. Among these switching elements, metal-insulator-metal (Metal-Insulator-
Metal, hereinafter referred to as MIM. ) Structured MIM
The element has been put to practical use. FIG. 8 is a plan view showing one pixel in a liquid crystal display device using a conventional MIM element. FIG. 9 is a cross-sectional view taken along line DD ′ of FIG. One pixel 108 includes a pixel electrode 102 formed on a surface 101 a of a glass substrate 101, a signal wiring 103, and an MIM element 104 indicated by oblique lines. The MIM element 104 includes a lower electrode 10 branched from the signal wiring 103.
3a, an insulating film 105 made of an insulator formed on the lower electrode 103a, and an upper electrode 1 covering the insulating film 105.
06 is a two-terminal non-linear element composed of the element No. 06. Generally, tantalum (Ta), insulating film 1
05 is made of tantalum oxide (TaO _x ), and the upper electrode 106 is made of chromium (Cr), titanium (Ti) or aluminum (Al). A liquid crystal display device is provided by disposing a counter substrate on which a counter electrode is formed on a glass substrate 101 provided with such MIM elements 104 in each pixel, and sealing liquid crystal between the substrates. Is manufactured. [0007] By the way, the MIM
Since the thickness of the insulating film 105 of the element 104 is about 500 to 700 angstroms, the electric breakdown voltage is low, and the dielectric breakdown can be easily caused by static electricity generated during the manufacturing process of the liquid crystal display device. As a result, a pixel in which the upper and lower electrodes of the MIM element 104 are short-circuited and the MIM element 104 no longer functions as a switching element appears as a point defect on a screen, and the yield is deteriorated in manufacturing a liquid crystal display device.
Therefore, as a countermeasure against static electricity, humidity control during the manufacturing process,
Although the worker is grounded and ion showered, the dielectric breakdown of the MIM element cannot be completely prevented. In addition, point defects due to dielectric breakdown of the MIM element are likely to occur at the end of a portion where pixels are arranged. Therefore, for the purpose of protecting the MIM element from dielectric breakdown, a conductive member is formed or a dummy pixel having the MIM element is formed outside a display area where a pixel for performing display is provided. A method for forming a conductive member outside the display area is disclosed in, for example, Japanese Patent Publication No. 4-22499, and a method for forming the dummy pixel outside the display area is described in, for example, JP-A-3-45934, JP-A-5-142578 or JP-A-5-142578. 5-196970. [0009] The conductive member is formed in order to discharge the electrostatic charge generated during the manufacturing process to avoid the accumulation of the charge.
The dummy pixel is formed in order to reduce a potential difference due to dielectric breakdown of the MIM element provided therein. However, although the point defect can be reduced by the above-described method, there is a possibility that the aesthetic appearance of the liquid crystal display device at the time of displaying is impaired. For example, the conductive member is disposed in the immediate vicinity of the display region in which the display pixels are arranged, and the display region and the conductive member are adjacent to each other, and the conductive member does not contribute to display when looking at the lit liquid crystal display device. Since the pattern of the member is inevitably included in the field of view, it is not preferable in terms of aesthetic appearance. On the other hand, even when the dummy pixel is formed, the pattern of the dummy pixel directly enters the field of view when the display pixel which is lit and displayed is viewed, which is similarly undesirably aesthetic. In particular, when there is a dummy pixel at a position near the display pixel array portion which is a display area, the dummy pixel is
Although it is configured to be electrically independent of the display area and not driven, it is more difficult to see because the dummy pixels are charged due to the influence of driving the display pixels in the display area. Normally, the pixel pitch is several hundreds μm (the separation distance between adjacent pixels is several tens of μm). Therefore, covering only the dummy pixels with a cover or the like requires high precision, and in some cases, may cause a problem in the display area. Some parts may be covered, causing problems. There is also a method of using a metal electrode as a pixel electrode of a dummy pixel to block light and avoid lighting. However, there is an aesthetic problem, and it is not easy to confirm the breakage of the dummy element. The present invention has been made to solve such a problem of the prior art, and a dummy pixel for protecting a MIM element of a display pixel from dielectric breakdown caused by static electricity generated during a process is provided. It is an object of the present invention to provide a liquid crystal display device that can be provided without deteriorating aesthetic appearance. According to the present invention, there is provided a liquid crystal display device in which a liquid crystal is provided between a pair of substrates and a non-display region is provided outside a display region. Each of a plurality of display pixels provided in a matrix in a region is used for display in which an insulating film is sandwiched between a pair of electrodes each having one electrode connected to a signal wiring wired from the display region to the non-display region. Each of the dummy pixels provided in the non-display area and at a distance from the end of the display area is connected to an electrode connected to the signal wiring. The two-terminal non-linear element for dummy formed for one dummy pixel is separately driven by the two-terminal non-linear element for dummy in which the insulating film is interposed between a pair of electrodes. By doing The above object is achieved. According to the present invention, a dummy pixel is provided in a non-display area outside the display area and at a distance from an end of the non-display area, and each of the dummy pixels is a display pixel. Each of the dummy two-terminal non-linear elements is driven by a dummy two-terminal non-linear element which is more easily broken down than the terminal non-linear element. Therefore, when static electricity is received, the dummy two-terminal non-linear element has priority over the display two-terminal non-linear element. Dielectric breakdown. Since the outer peripheral portion of the liquid crystal display device is covered up to the vicinity of the seal portion of the liquid crystal cell by the bezel of the liquid crystal cell and the outer cover of the product to be incorporated, the dummy pixels do not directly enter the field of view and the appearance is impaired. There is no. Further, since the pixel electrode of the dummy pixel may be kept transparent, it is easy to confirm the dielectric breakdown of the dummy element by lighting the pixel electrode. If the two-terminal dummy element for dummy has an element area smaller than the element area of the two-terminal non-linear element for display, the breakdown voltage is lowered and the element is destroyed preferentially. At this time, if a plurality of dummy two-terminal nonlinear elements are provided per signal wiring, it is possible to cope with static electricity generation a plurality of times. If a plurality of dummy two-terminal non-linear elements are provided so that the element area is gradually reduced toward the outside of the display area, it is possible to cause dielectric breakdown from a side far from the display area. In a portion where the upper electrode and the lower electrode overlap each other, a step portion of the insulating film covering the side surface of the lower electrode is liable to deteriorate in film quality of the insulating film, and is liable to cause dielectric breakdown due to electric field concentration. Therefore, the dummy two-terminal nonlinear element is also preferentially broken down by making the distance of the step portion longer than that of the two-terminal nonlinear element for display. Embodiments of the present invention will be specifically described below. (First Embodiment) FIG. 3 is a front view showing the appearance of a liquid crystal display device 18 in a first embodiment. FIG. 1 is an enlarged view of a portion C of the element side substrate 1 of the liquid crystal display device 18. FIG. 2 is an enlarged plan view showing a portion C of a counter substrate 12 bonded to the element substrate 1 with a liquid crystal layer interposed therebetween. FIG. 4 is a plan view showing one pixel of the element-side substrate 1, and FIG. 5 is a cross-sectional view taken along line AA 'in FIG. This liquid crystal display device has an element-side substrate 1 and an opposite-side substrate 12 which are disposed opposite to each other with a liquid crystal as a display medium therebetween. As shown in FIG. A non-display area is provided inside the liquid crystal cell in the immediate vicinity, and a display area B is provided inside the non-display area. In the upper and lower non-display areas, a part is C, that is, the dummy MIM elements 11a, 11b, 11c, 11 shown in FIG.
d, 11e respectively having dummy pixels 10a, 10b, 1
0c, 10d, and 10e are formed. In the element-side substrate 1, a plurality of signal wires 3 are formed on the surface 1a of the glass substrate 1 from the display area B to the non-display area. Each of the signal wirings 3 is connected to an element-side terminal 15 which is an external terminal similarly formed on the surface 1 a of the glass substrate 1. Along each of the signal lines 3, a plurality of display pixels 8 are provided in the display region B, and five types of dummy pixels 10a, 10b, 10c, 10d, and 10e are provided in one non-display region.
Is provided. The display pixel 8 includes a pixel electrode 2 provided along each of the signal lines 3 and a counter substrate 1 shown in FIG.
A plurality of opposing electrodes 13 formed in a band shape on the surface 12a of the second electrode 12 oppose each other. The display pixel 8 is driven by the MI connected to the signal line 3 and the pixel electrode 2.
This is performed via the M element 4. On the other hand, the dummy pixel 10 a and the like are configured by a portion where the dummy pixel electrode formed on the element-side substrate 1 and the counter electrode 14 formed on the surface 12 a of the counter-side substrate 12 face each other. This dummy pixel 10a,
Driving of the dummy MIM elements 11a, 11b
b. The MIM element 4 and the dummy MIM elements 11a and 11b have the same structure, but the latter element area is smaller than the former element area, and the latter element area is smaller. Was sequentially reduced from 11e to 11a. As shown in FIGS. 4 and 5, the configuration of the MIM element is such that a lower electrode 3a
An upper electrode 6 is provided on the upper side. The lower electrode 3a includes a portion branched from the signal wiring 3. The upper electrode 6 is connected to the pixel electrode 2 in the display area B, and is connected to the dummy pixel electrode in the non-display area. The counter electrode 13 crosses the signal wiring 3,
For example, it is formed for each row so as to overlap the pixel electrode 2 in a direction orthogonal to the pixel electrode 2, and is connected to the opposing terminal 16 which is an external terminal provided on the opposing substrate 12. In addition, the counter electrode 14
Is connected to a terminal 17 provided separately from the opposite terminal 16. Next, a method of manufacturing the liquid crystal display device having such a configuration will be described. First, the element-side substrate 1 is manufactured as follows. On the surface 1a of the glass substrate 1, which is an element-side substrate,
A first conductor, for example, a tantalum (Ta) thin film to be the lower electrode 3a of the signal wiring 3 and the MIM element 4 is formed by a sputtering method. Next, the first conductor is patterned by a photolithography process to obtain the lower electrode 3a of the MIM element 4 and the signal wiring 3 in the display pixel 8. Further, the insulating film 5 is formed at least on the lower electrode 3a by an anodic oxidation method. Next, a metal thin film, for example, a titanium (Ti) thin film to be the upper electrode 6 of the MIM element 4 is formed by a sputtering method and a photolithography method. Next, in the same manner, the pixel electrode 2 is
(Indium Tin Oxide) is formed by patterning. In the present embodiment, the area of the MIM element 4 in the display pixel 8 is shown in a plan view of FIG.
4 μm (Ta width) × 4 μm (Ti width). The MIM element 4 formed as described above
Are arranged to form a display area B for actually displaying a screen. Simultaneously with the formation of the display pixels 8, dummy MIM elements 11 a, 11 b, 11 c, and 1 are placed in a non-display area outside the display area B.
Dummy pixels 10a, 10b each having 1d, 11e,
10c, 10d, and 10e are formed as follows. That is, the dummy pixels 10a, 10b, 10c, 10
Since d and 10e have the same basic constituent material as the display pixel 8, they were formed simultaneously with the display pixel 8. The formation positions of the dummy pixels 10a and the like are outside the display area B,
In the liquid crystal cell immediately adjacent to the liquid crystal seal portion 9 at a distance from the end of the liquid crystal cell. Also, a dummy MIM element 11a,
11b, 11c, 11d and 11e were formed on the signal wiring 3. The element-side terminals 15 may be formed simultaneously with the formation of the signal wiring 3, or may be formed in a separate step. Thus, the element-side substrate 1 is manufactured. On the other hand, the opposite side substrate 12 is formed by patterning the opposite electrodes 13 and 14 on the surface 12a of the glass substrate 12, which is the opposite side substrate, in the same manner using ITO. Also,
At the same time or in a separate step, the opposing terminal 16 and the terminal 17 are formed. The element-side substrate 1 manufactured as described above
And the opposing substrate 12 are opposed to each other and bonded together.
The liquid crystal display device of the present embodiment is manufactured by enclosing the liquid crystal between the first and second liquid crystals. In the liquid crystal display device having such a configuration, the dummy pixels 10a, 10b, 10c, 10d, and 10e are
5 per signal wiring, outside the display area B,
It was formed in a cell immediately adjacent to the liquid crystal seal portion 9 at a distance from the end of the display area B. Although one dummy pixel is effective for one signal line, the dummy MIM element 1
In order to cope with the absence of the dummy MIM element due to the formation failure such as 1a and the occurrence of static electricity a plurality of times, it is more preferable to dispose a plurality of the MIM elements. The dummy pixels 10a, 10b, 10
c, 10d, and 10e, the element areas of the dummy MIM elements 11a, 11b, 11c, 11d, and 11e are made smaller than the MIM element 4 of the display pixel 8 and sequentially become farther from the end of the display area B. Small, 1
It was made to decrease sequentially from 1e to 11a. For example, the element area of the dummy MIM element 11e is 3.5 μm.
m (Ta width) × 4 μm (Ti width) and the dummy MI
The element area of the M element 11d is 3 μm × 4 μm, the element area of the dummy MIM element 11c is 3 μm × 3 μm, and the element area of the dummy MIM element 11b is 2.5 μm × 2.5.
μm, the element area of the dummy MIM element 11a is 2 μm.
× 2 μm. As described above, the element area of the dummy MIM element is made smaller than that of the MIM element 4 of the display pixel 8 and 1
The reason for decreasing sequentially from 1e to 11a is as follows. That is, the five types of MIs for the dummy are used.
The element area of the M element is the MIM element 4 in the display pixel 8.
Is effective even if the area is the same as the area of the display pixel 8, but is not enough to protect the MIM element 4 of the display pixel 8 because the breakdown voltage is the same. Therefore, the area of the dummy MIM element is smaller than the area of the MIM element 4 in the display pixel 8 as described above. Further, when the size of the dummy MIM element is reduced sequentially, the withstand voltage of the dummy MIM element decreases, and the dummy MIM element is more likely to be preferentially broken down by static electricity in the order of 11a to 11e, which is more preferable. As described above, the dummy MIM element is replaced with the MIM in the display pixel.
Because it is formed without changing the element and any constituent materials,
It does not affect the manufacturing cost of the liquid crystal display device. In particular, in this embodiment, the distance between the end of the display area B and the dummy pixel 10e is 4 mm, and the dummy pixel is formed immediately near the liquid crystal seal portion 9. By doing so, the dummy pixel can be covered with the bezel of the liquid crystal cell and the outer cover of the product to be incorporated, which were difficult at the position where the conventional dummy pixel is formed. Without going directly into the field of view,
Aesthetics were not spoiled. Further, since the dummy pixels do not actually contribute to display and unnecessary lighting must be avoided, an external terminal for connecting the counter electrode 14 shown in FIG. 2, that is, the terminal 17 shown in FIG. Counter electrode 13 provided in display area B
The external terminals for connection with the external terminals, that is, the opposite terminals 16 shown in FIG. As described above, since the external terminal of the opposing electrode 14 of the dummy pixel is made independent, the lighting of the dummy pixel during driving of the liquid crystal display device can be avoided. Further, since the external terminal of the counter electrode 14 is separately provided as the terminal 17, if this terminal 17 is connected to an external power supply, the dummy pixels 10a, 10b, 10c, 1
0d and 10e can be turned on, and the dummy element 11
Confirmation of dielectric breakdown of a, 11b, 11c, 11d, and 11e can be easily performed. In the above embodiment, since the counter electrode 14 does not contribute to display, the counter electrode 14 is formed with a width corresponding to five pixels. However, the counter electrode 14 may be formed for each row similarly to the display pixel 8. In this embodiment, when a point defect in the dummy pixel and the display pixel was examined, in the range of the display area B of 320 × 480 dots, there was no point defect in the display pixel while the dummy pixel had a point defect. Was 15.8%. In addition, 52.6% of those having 5 or less point defects could be obtained. (Second Embodiment) Instead of making the element area of the dummy MIM element smaller than the element area of the MIM element of the display pixel, the distance of the step formed at the overlapping position of the upper electrode and the lower electrode is reduced. It is effective to make the distance longer than the step distance in the MIM element of the display pixel. In an element such as the MIM structure, the insulating film 5 at the stepped portion generated at the overlapping position of the upper electrode 6 and the lower electrode 3a as shown in 7 in FIG. In this case, dielectric breakdown is easily caused by Joule heat caused by concentration of current. Further, the insulating film 5 at the stepped portion is apt to be degraded due to the problem of the film forming technique, so that the insulation is more likely to be broken down. FIG. 6 is a plan view showing an element-side substrate of a liquid crystal display device according to a second embodiment of the present invention, which includes a dummy pixel 10 'having such a dummy MIM element 11'. FIGS. 2 and 3 are front views showing the appearance of the liquid crystal display device according to the second embodiment and plan views of the opposing substrate.
The description is omitted because it is the same as. In this embodiment, the display MIM element in the display area is the same as in the first embodiment, and the dummy MIM element 11 'in the non-display area has a two-part structure as shown in FIG. That is, the element area of each of the two dummy MIM elements 11 ′ is the element area of the display MIM element.
The size of 2 μm × 4 μm is obtained by dividing μm × 4 μm into two. Therefore, the distance between the steps of the dummy MIM element 11 'is twice as long as the distance of the steps of the display MIM element. Therefore, the dummy MIM element 11 'is replaced with the display MIM.
Dielectric breakdown occurs prior to the element. This dummy MI
Even if the dummy pixel 2 ′ is connected to the M element 11 ′ as shown in FIG.
This is effective as protection for the M element. In FIG. 7, 3 'is a lower electrode, and 6' is an upper electrode. Further, in the present embodiment, a plurality of dummy MIM elements 11 'are arranged per signal wiring, as described above, to avoid the absence of the dummy MIM element due to a defective formation, and to prevent static electricity from being discharged a plurality of times. This is so that the occurrence can be dealt with. By doing so, a liquid crystal display device with less point defects can be obtained. In addition,
Even in the case of this embodiment, the dummy MIM element whose dielectric breakdown is preferentially obtained can be obtained only by changing the shape, so that the number of manufacturing steps and the cost do not increase. In the second embodiment, the dummy MIM element is divided into two parts. However, the present invention is not limited to this, and may be divided into three or more parts so as to increase the distance between the steps. As described in detail above, according to the present invention, the dummy provided in the non-display area outside the display area and at a distance from the end of the non-display area. Each of the pixels is individually driven by a dummy two-terminal non-linear element that is more likely to cause dielectric breakdown than a display two-terminal non-linear element. Since the dielectric breakdown occurs preferentially over the two-terminal nonlinear element and the potential difference is reduced, the two-terminal nonlinear element of the display pixel can be protected. Further, since the outer peripheral portion of the liquid crystal display device is covered by the bezel of the liquid crystal cell and the outer cover of the product to be incorporated, the dummy pixels do not directly enter the visual field and the appearance is not impaired. Aesthetic appearance can be maintained. Further, since the pixel electrode of the dummy pixel may be kept transparent, it is easy to confirm the dielectric breakdown of the dummy element by lighting the pixel electrode. Further, by forming a plurality of dummy pixels per signal wiring, it is possible to cope with the absence of dummy pixels due to defective formation and the occurrence of static electricity a plurality of times. Can be provided. At this time, if a plurality of dummy two-terminal non-linear elements are provided so that the element area gradually decreases toward the outside of the display area, it is possible to cause dielectric breakdown from a side far from the display area. Even if the step distance of the two-terminal dummy non-linear element is longer than that of the two-terminal non-linear element of the display pixel, the potential difference is alleviated by preferentially dielectric breakdown due to static electricity. The two-terminal nonlinear element of the pixel can be protected.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view showing an element-side substrate of a liquid crystal display device according to a first embodiment of the present invention. FIG. 2 is a plan view showing a facing substrate of the liquid crystal display device according to the first embodiment of the present invention. FIG. 3 is a front view showing the appearance of the liquid crystal display device according to the first embodiment of the present invention. FIG. 4 illustrates a liquid crystal display device according to a first embodiment of the present invention.
It is a top view showing a pixel. FIG. 5 is a sectional view taken along line AA ′ of FIG. 4; FIG. 6 is a plan view showing an element-side substrate of a liquid crystal display device according to a second embodiment of the present invention. FIG. 7 is a plan view illustrating a dummy pixel of a liquid crystal display device according to a second embodiment of the present invention. FIG. 8 is a plan view showing one pixel in a liquid crystal display device using a conventional MIM element. FIG. 9 is a sectional view taken along line DD ′ of FIG. 8; [Description of Signs] 1 Element side substrate 2, 2 'Pixel electrode 3, 3' Signal wiring 3a, 3'a Lower electrode 4 MIM element 5 Insulating film 6, 6 'Upper electrode 8 Display pixel 9 Liquid crystal seal portions 10a, 10b , 10c, 10d, 10e, 10 '
Dummy pixels 11a, 11b, 11c, 11d, 11e, 11 '
MIM element 12 opposing substrate 13 opposing electrode 14 opposing electrode 15 element side terminal 16 opposing terminal 17 terminal 18 Liquid crystal display B display area

Continuation of front page (72) Inventor Toshiyuki Yoshimizu 22-22, Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (56) References JP-A-5-142578 (JP, A) JP-A-5-196970 (JP) JP-A-3-45934 (JP, A) JP-A-4-225317 (JP, A) JP-A-4-295824 (JP, A) JP-A-6-294968 (JP, A) JP2000 JP-A-187249 (JP, A) JP-A-2000-187251 (JP, A) Patent 3209652 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/1365

Claims (1)

(1) In a liquid crystal display device in which liquid crystal is provided between a pair of substrates and a non-display area is provided outside a display area, the display area is provided in a matrix. Each of the plurality of display pixels is a two-terminal non-linear element for display in which an insulating film is sandwiched between a pair of electrodes, one of which is an electrode connected to a signal wiring wired from the display region to the non-display region. Each of the dummy pixels provided in a portion of the non-display area and at a distance from the end of the display area in the non-display area has a pair of electrodes each having an electrode connected to the signal wiring. The two-terminal non-linear element for the dummy formed for one dummy pixel is separately driven by the two-terminal non-linear element for the dummy with the insulating film interposed therebetween. Liquid crystal display device.