JPH03194516A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To remedy a defective picture element without changing the brightness of picture element when the insulation of the additive capacitance part is deteriorated by forming the first and second electrodes and third electrode to be laser- welded on the upper surface opposed with a gap formed in any of comb-shaped electrodes in between. CONSTITUTION:The extension 15b of a picture element electrode 15 is formed with plural comb-shaped electrodes 15b1, 15b2 and 15b3, and a part of the electrode 15b1 in contact with the picture element electrode is cut off to form a gap 40. A capacitance is formed with capacitors C1, C2 and C3 between the comb-shaped electrode and a gate bus 18. Even if the insulation of any of the divided additive capacitances, i.e., C2 or C3, is deteriorated, the bridging part 32 of the defective capacitor is laser-cut, the first electrode 41 and the third electrode 43 and the second electrode 42 and the third electrode 43 are electrically connected by laser welding, an additive capacitance C1a is formed between the electrode 15b1 and the gate bus 18, and the additive capacitance after repairing is adjusted approximately to the normal value.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a liquid crystal display element, and more particularly to the configuration of an additional capacitance section connected to a pixel electrode thereof.

"Prior Art" A conventional liquid crystal display element will be explained with reference to FIG. Transparent substrates 4Ii, 11 and 12 such as glass are provided in close opposition to each other, a spacer 13 is interposed at the peripheral edge thereof, and a liquid crystal 14 is sealed between these transparent substrates 11 and 12. A plurality of pixel electrodes I5 are formed on the inner surface of one transparent substrate 11, and in contact with each pixel electrode 15, a T F T'' (thin 11 transistor) is connected as a switching element.
16 is formed, and its TPT I 6 train is connected to the pixel electrode 15. A transparent common electrode 17 is formed on the inner surface of the other transparent substrate 12, facing the plurality of 1iTii elementary electrodes 15.

As shown in FIG. 5, the pixel electrode 15 has substantially square pixel electrodes I5 arranged in close proximity to each other in rows and columns on a transparent substrate 11, and is arranged in close proximity to each row arrangement of pixel electrodes I5 and along this. A gate bus 8 is formed, and a source bus 19 is formed adjacent to and along each column arrangement of pixel electrodes 15.
are formed respectively. A TFT 16 is provided at the intersection of each gate bus 18 and source bus 19, the gate of each TFT 16 is connected to the gate bus 18 at the intersection of both buses, each source is connected to the source bus 19, and Each drain is connected to a pixel electrode 15.

By selecting each of these gate buses 18 and source buses 19 and applying a voltage between them, only the TFT I 6 to which the voltage has been applied becomes conductive, and the TFT 16 that has become conductive becomes conductive.
Charge is accumulated in the pixel-type Fi 15 connected to the drain of the pixel electrode 15, and a voltage is applied only to the portion of the liquid crystal 14 between the pixel electrode 15 and the common electrode 17.
Selective display is performed by making only the portion transparent or blocked. The display can be erased by discharging the charges accumulated in the pixel electrode 5.

6 to 8 show liquid crystal display elements that have already been proposed. A pixel electrode 15 and a source bus 19 are arranged on a transparent substrate 11.
are formed of a transparent conductive film such as ITO, and a semiconductor layer 2 such as amorphous silicon is formed between parallel and adjacent portions of the pixel electrode 15 and the source bus I9.
1 is formed, and a gate insulating film 22 made of silicon nitride or the like is further formed thereon. A gate electrode 23 is formed on the gate insulating film 22 so as to partially overlap the pixel electrode 15 and the source bus 19 with the semiconductor layer 21 interposed therebetween. One end of the gate electrode 23 is connected to the gate bus 18. In this way, the pixel electrode I5 and the source layer L9, which respectively face the gate electrode 23, constitute a torlein electrode Fil 5a and a source electrode 19a, respectively, and these electrodes 15a, 19a, the semiconductor layer 21, and the gate insulating film 22
, the gate electrode 23 constitutes the TFT 16. The gate electrode 23 and the gate lotus 18 are formed at the same time and are made of aluminum, for example. A protective layer 29 is provided to completely cover the gate electrode 23 for protection against the liquid crystal.
is formed.

As shown in FIG. 8, one end of the pixel electrode 5 is extended below the adjacent gate bus 18 to approximately the middle position of the gate bus 18, and an additional capacitance portion 30 is formed between the pixel electrode 5 and the gate bus 18. is formed.

This additional capacitance supplements the capacitance of the pixel electrode section and
This is necessary in order to increase the time constant created by the resistance value of the channel section No. 6.

The additional capacitor section is divided into multiple parts. @Extension part 15b of elementary electrode
is formed of barrel tooth-shaped electrodes 15b115b2 and 15b3, which are stacked in an island shape at an intermediate position in the width direction of the gate bus and connected to the pixel electrode 15 by a bridging piece 32. The capacitance formed between these comb-like electrodes and the gate bus 18 is the capacitor C, , C shown in FIG.
,,C.

In either of the divided additional capacitance parts 3°, pinholes may occur in the gate insulating film 22 between the gate bus 18 and the comb tooth-shaped electrodes, or dust may form during the manufacturing process. If mixed, insulation may deteriorate or a short circuit may occur between both electrodes. Due to such a defect in the additional capacitance section, some pixels in the display element are always turned on (lit) regardless of the video signal to be displayed, degrading the display quality. Therefore, this defective additional capacitance section (
The division part) is deleted. That is, a laser beam is irradiated from the side of the transparent substrate 12 in FIG.
It is focused in μm and separated from the pixel electrode 15 by cutting.

"Problem to be Solved by the Invention" In conventionally proposed liquid crystal display elements, when one divided part of the defective additional capacitor section 30 is laser canted, the capacitance value of the additional capacitor section decreases to the set value of 273. Resulting in.

Therefore, the potential of the pixel electrode relative to the common electrode deviates from the set value, and the brightness of the pixel changes. This is not much of a problem when performing a simple monochrome display, but when performing a high-quality multi-gradation display, the gradations of pixels are shifted, deteriorating the display quality.

An object of the present invention is to make it possible to repair a defective pixel by a method that does not cause a change in the brightness of the pixel when an insulation failure occurs in the additional capacitance section.

"Means for Solving the Problem" A plurality of source buses and a plurality of gate buses are formed on a transparent substrate at equal intervals in directions perpendicular to each other, and the sources that intersect are arranged in correspondence with the positions of their respective intersection points. A thin film transistor connected to the bus and the gate bus is formed in one corner of the mesh surrounded by the source bus and the gate bus, and a pixel electrode connected to the drain electrode of the transistor is formed widely within the mesh. An end of the pixel electrode is extended so as to overlap the lower side of a gate bus to which an adjacent thin film transistor is connected, and a gate insulating film is provided so as to be in contact with the lower surface of the gate bus and cover the pixel electrode and its extension. In the liquid crystal display element in which an additional capacitance portion is formed between the extension portion and the gate bus facing the extension portion, in the present invention, the extension portion of the pixel electrode is formed by a plurality of combs. In one of the comb tooth-like electrodes, a part of the electrode in contact with the pixel electrode is missing to form a gap, and the above-mentioned electrodes facing each other across the gap are The first comb electrode for laser welding is attached to the upper surface of the gap side of the comb tooth electrode and the pixel electrode. Second electrodes are formed respectively, and the first and second electrodes are formed respectively. The gate insulating film is formed to cover the second electrode and fill the gap, and the first electrode is formed on the gate insulating film.
．． A third electrode for laser welding is formed overlapping the second electrode and a portion of the gap portion.

"Embodiment" An embodiment of the present invention will be described with reference to FIGS. 1 to 3. In these figures, parts corresponding to those in FIGS. 4 to 8 are designated by the same reference numerals, and redundant explanation will be omitted. In this embodiment, in the comb tooth-shaped electrode 15bl, a part of the bridging piece 32 that is in contact with the pixel electrode 15 is missing, and the gap portion 4
0 is formed. A first plate made of a high melting point metal (for example, chromium, molybdenum, etc.) for laser welding is provided on each upper surface of the bridging piece 32 where the gap portion 40 is formed and the pixel electrode 15 on opposite sides across the gap portion 40.゜Second electrode 4
1.42 are formed respectively. This high melting point metal may be the same as the well-known high melting point material that is laminated on top of the source bus in order to lower its resistance value, and is patterned in the same process. The first of them.
A gate insulating film 22 is deposited to cover the second electrodes 41 and 42 and to fill the gap portion 40. On the gate insulating film 22, the first. A third electrode 43 for laser welding is formed overlapping the second electrodes 41 and 42 and a portion of the gap portion 40. This third electrode 43 is connected to the gate bus 18
using the same material (e.g. aluminum) as the gate bus 18.
patterned at the same time.

A capacitor CIm is formed between the comb tooth-shaped electrode 15b1 and the gate bus 18. In addition, the first and second electrodes 41
．． 42 and the third electrode 43, each capacitor C1
k and C+C are formed. These three capacitors are connected in series as shown in FIG. If we use the symbols of the capacitors as they are to express the capacitance value of each capacitor, we will get C1C1,C,h C1c For simplicity, we will use C1, and CIc (2) If we use C1, C1, C1c (2), then C, C,, C,, /2 Comb's A capacitor Cz is provided between the toothed electrodes 15b2, 15b3 and the gate bus 18, as in the conventional case.

C3 is formed respectively. FIG. 2 shows one pixel and its surrounding equivalent circuit.

The capacitance values of both capacitors C2 and C1 are set to C for simplicity.

C,=C,=C (4) If the additional capacitance value is expressed as 01, C,=C,+2C(5) becomes.

If the capacitor C3 is short-circuited, the bridging piece 32 of the comb tooth-shaped electrode 15b3 near the pixel electrode 15 is laser-cut as shown by the cut portion 44 in FIG. Also,
The transparent group Fi12 in FIG. 3 or! ■From the side, the third electrode 43
By irradiating a laser beam with a laser weld (a welding machine that uses a laser beam) to the center portions of the first electrode 41 and the second electrode 42 (positions indicated by X marks in FIG. 1A) facing the first electrode 41 and the second electrode 42, As shown in FIG. 3B, the two opposing electrodes are electrically connected by molten metal 45 or 46. As a result, capacitors C1m and C1 (are short-circuited, resulting in a combined capacitance C, -C, , and the additional capacitance becomes c,'=c+c, .) After this repair, the additional capacitor IC ↑
'=C10, , is the additional capacitance value CT of equation (5) at normal time=
It should be set approximately equal to C+ +2C. Therefore (C,'=)C+C,, -C,+2C(=C,) (
6) On the other hand, if capacitor C1m is short-circuited,
It is necessary to set the additional capacitance value Cy"=C+b/2+2C at that time to be approximately equal to the additional capacitance value C7 during normal operation. Therefore, (Ct"=)Ctb/2+2 C=C, +2C(=CT
)(7) From equation (7), c + = c + bi2 (8) From equation (8) and equation (3), it becomes C111-ω (9). Practically speaking, cl, >> C+b/2 (9')
That's fine. (6) From 2, C, 1l-C, l-C(6') If we substitute equation (8) into equation (6'), we get C,,+=C+b/2+CQω.

Let me explain by giving a numerical example to make it easier to understand.
If b=0.5pp, then from equation (9'), C, >>0
．． Must be 25pF, so considering equation 00, C=1. If it is OpF, C,,=0.25+
1.0 = 1.25pF becomes 1.29F, (9')
The equation can be satisfied with a rough approximation. Therefore, C+-=0.5,
The 8 combined capacitance c + is set to C= 1.0, C+a'''1.2 pF as follows from formula (8): C+ = C+b/2=
0.25ρF, but since the capacitance values of each of the above capacitors are proximal, it is better to find C more accurately than equation (3), and cf, Cr', Cr'' (5) respectively.

If calculated from equations (6) and (7), Ct −C++2C=0.21+ 2 X 1 =2.
21pF Q21CT' =C+C1,=1
+1.20=2.20pF O■Ct ” =C+
b/2+2C=0.25+2 =2.25pF 0
41, and it can be seen that the additional capacitances ICT' and C1 after the repair, and the additional capacitance C after the short circuit are almost equal to the normal additional capacitance Icy.

In the explanation up to this point, the comb tooth-shaped electrode 15 of the additional capacitance section 30 has been described.
bl, 15b2, and 15b3 each have a narrow bridging piece 32 on the pixel electrode 15 side and have a constricted shape, but the present invention is not limited to this shape, and any shape may be used.For example, The simplest shape may be a rectangular cane comb-like electrode without constriction. Similarly to the above, the shapes of the first to third @poles may be arbitrary, and the number of comb tooth-shaped electrodes is not limited to three, but may be a plurality.

"Effect of the Invention J According to this invention, even if either of the divided additional capacitors ICt or C1 has an insulation defect, the bridging portion 32 of the defective capacitor is cut by laser cutting, Instead, conduction is made between the first electrode and the third electrode and between the second electrode and the third electrode by laser welding, and the comb tooth-shaped electrode 1
Additional capacity 1c created between 5bl and gate bus 18,
, the additional capacity after repair is 1ffiftl by adding
! can be made almost equal to the normal value.

Further, even if the additional capacitance IC, .

Therefore, in any of the above cases, the brightness of the corresponding pixel is almost the same as that of a normal pixel, and excellent multi-level tone display is possible.

[Brief explanation of drawings]

1A and 1B are a plan view and a sectional view taken along the line B-B showing the main parts of an embodiment of the present invention, respectively. FIG. 2 is an electrical equivalent circuit diagram of the main parts surrounding the pixel electrode 15 in FIG. 3A shows a state in which the comb tooth electrode 15b3 is separated from the pixel electrode 15 by laser cutting when there is an insulation failure between the comb tooth electrode 15b3 and the gate bus 18 in FIG. The plan view, FIG. 3B, is the same as the first one in FIG.
Between the electrode 41 and the third electrode 43 and between the second electrode 42 and the third electrode 43
3A is a sectional view taken along line B-B of FIG. 3A to show the electrical connection between the electrode 43, FIG. 4 is a sectional view of a part of the liquid crystal display element, and FIG. 5 is an equivalent view of the liquid crystal display element. The circuit diagram, Figure 6 is a plan view of the main part of the liquid crystal display element that has already been proposed, and Figure 7 is
The figure is a sectional view along line AA in FIG. 6, and FIG. 8 is a sectional view taken along line BB in FIG.

Claims (1)

[Claims] (1) A plurality of source buses and a plurality of gate buses are formed on a transparent substrate at equal intervals in directions orthogonal to each other, and are connected to the intersecting source buses and gate buses in correspondence with each intersection point position. A thin film transistor is formed in one corner of the mesh surrounded by the source bus and the gate bus, and a pixel electrode connected to the drain electrode of the transistor is formed widely within the mesh, and the edge of the pixel electrode is A gate insulating film is uniformly formed so as to overlap with the lower side of the gate bus to which adjacent thin film transistors are connected, and in contact with the lower surface of the gate bus, covering the pixel electrode and the extension thereof; In a liquid crystal display element in which an additional capacitance section is formed between an extension part and the gate bus facing the extension part, the extension part of the pixel electrode is constituted by a plurality of comb tooth-shaped electrodes, In any one of the tooth-like electrodes, a part of the electrode in contact with the pixel electrode is missing to form a gap, and the gap between the tooth-like electrode of the comb and the pixel electrode facing each other across the gap. First and second electrodes for laser welding are respectively formed on the upper surface of the part side, and the gate insulating film is formed to cover the first and second electrodes and fill the gap part. In the above 1st
A liquid crystal display element, characterized in that a third electrode for laser welding is formed overlapping the second electrode and a part of the gap portion.