JP2714650B2 - Liquid crystal display device - 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 configuration of an additional capacitance unit connected to a pixel electrode.

[Prior Art] A conventional liquid crystal display device will be described with reference to FIG. Transparent substrates 11 and 12 such as glass are provided so as to face each other, and a spacer 13 is interposed at the periphery thereof, and a liquid crystal 14 is sealed between the transparent substrates 11 and 12. A plurality of pixel electrodes 15 are formed on the inner surface of one of the transparent substrates 11, and a TFT is provided as a switching element in contact with each of the pixel electrodes 15.
A (thin film transistor) 16 is formed, and the drain of the TFT 16 is connected to the pixel electrode 15. A transparent common electrode 17 is formed on the inner surface of the other transparent substrate 12 so as to face the plurality of pixel electrodes 15.

As shown in FIG. 5, the pixel electrodes 15 are arranged such that substantially square pixel electrodes 15 are arranged in rows and columns on the transparent substrate 11. A gate bus 18 is formed, and a source bus 19 is formed adjacent to and along each column array of the pixel electrodes 15. Each of these gate bus 18 and source bus
A TFT 16 is provided at the intersection of 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 the pixel electrode 15. .

One of each of the gate bus 18 and the source bus 19 is selected, a voltage is applied between them, and the TF to which the voltage is applied is applied.
Only T16 conducts, accumulates electric charge in the pixel electrode 15 connected to the drain of the TFT 16 that conducts, and applies a voltage only to the portion of the liquid crystal 14 between the pixel electrode 15 and the common electrode 17,
Thus, selective display is performed by making only the pixel electrode 15 light transparent or light shielded. This pixel electrode
The display can be erased by discharging the electric charge accumulated in 15.

6 to 8 show a liquid crystal display element that has already been proposed. The pixel electrode 15 and the source bus 19 are formed on the transparent substrate 11.
The pixel electrode 15 is formed of a transparent conductive film such as ITO.
A semiconductor layer 21 such as amorphous silicon is formed so as to extend between portions of the source bus 19 that are parallel and adjacent to each other, and a gate insulating film 22 such as silicon nitride is formed thereon. On this gate insulating film 22, the semiconductor layer 21
, A gate electrode 23 is formed so as to partially overlap the pixel electrode 15 and the source bus 19 respectively. One end of the gate electrode 23 is connected to the gate bus 18. In this way, the pixel electrode 15 and the source bus 19 respectively facing the gate electrode 23 constitute a drain electrode 15a and a source electrode 19a, respectively, and these electrodes 15a and 19a, the semiconductor layer 21, the gate insulating film 22, and the gate electrode 23 The TFT 16 is configured. The gate electrode 23 and the gate bus 18 are formed simultaneously and are made of, for example, aluminum. A protective layer 29 is formed on gate electrode 23 so as to cover the entire surface for protection against liquid crystal.

As shown in FIG. 8, one end of the pixel electrode 15 is extended below the adjacent gate bus 18 to a substantially intermediate position of the gate bus 18, and an additional capacitance portion 30 is provided between the pixel bus 15 and the gate bus 18. It is formed. This additional capacitance is required to compensate for the capacitance of the pixel electrode portion and increase the time constant formed by the resistance value of the TFT 16 channel portion.

The additional capacity unit is divided into a plurality. Pixel electrode extension 15b
Are formed in an island shape by being superimposed at an intermediate position in the width direction of the gate bus, and are configured by comb tooth-shaped electrodes 15b1, 15b2, and 15b3 connected to the pixel electrodes 15 by bridging pieces 32. Capacitances formed between the comb-shaped electrodes of these combs and the gate bus 18 are the capacitors C ₁ , C ₂ and C _{3 shown} in FIG. If a pinhole occurs in the gate insulating film 22 between the gate bus 18 and the interdigital electrode of the comb or dust enters during the manufacturing process in any of the divided additional capacitance units 30, During this time, a decrease in insulation or a short circuit may occur. Due to such a defect of the additional capacitance portion, some pixels in the display element are always turned on (lit) regardless of a video signal to be displayed, and display quality is degraded. Therefore, the defective additional capacity portion (divided portion) is deleted. That is, a laser beam is irradiated from the side of the transparent substrate 12 in FIG. 4 so that a focal point of 2 to 10 μm is formed near the pixel electrode of the bridging piece 32 in the defective additional capacitance section 30, and cut off from the pixel electrode 15.

[Problem to be Solved by the Invention] In the conventionally proposed liquid crystal display element, when one divided portion of the defective additional capacitance portion 30 is laser-cut, the capacitance value of the additional capacitance portion becomes 2/3 of the set value. Will decrease. Therefore, the potential of the pixel electrode with respect to the common electrode deviates from the set value, and the luminance of the pixel changes. When performing simple monochrome display, there is not much problem. However, when performing high-quality multi-gradation display, the gradation of pixels is shifted, and display quality is deteriorated.

An object of the present invention is to enable a defective pixel to be relieved by a method that does not change the luminance of the pixel when the insulation of the additional capacitance section becomes defective.

"Means for Solving the Problems" A plurality of source buses and a plurality of gate buses are formed at equal intervals on a transparent substrate in directions orthogonal to each other,
A thin film transistor connected to the intersecting source bus and gate bus corresponding to each of the intersecting positions is formed at one corner of a mesh surrounded by the source bus and the gate bus, and is connected to a drain electrode of the transistor. A pixel electrode is formed widely in the mesh, an end of the pixel electrode is extended so as to overlap a lower side of a gate bus to which an adjacent thin film transistor is connected, and is in contact with a lower surface of the gate bus. In the liquid crystal display device according to the present invention, in a liquid crystal display device in which a gate insulating film is uniformly formed so as to cover the extension and an additional capacitance portion is formed between the extension and the gate bus opposed to the extension. The extended portion of the pixel electrode is formed of a plurality of comb-shaped electrodes, and in any one of the comb-shaped electrodes, an electrode in contact with the pixel electrode is provided. The first portion and the second portion for laser welding are respectively formed on the upper surface of the comb-shaped electrode and the pixel electrode facing each other across the gap portion. The gate insulating film is formed so as to cover the first and second electrodes and fill the gap, and overlaps the first and second electrodes and a part of the gap on the gate insulating film. Then, a third electrode for laser welding is formed.

Embodiment An embodiment of the present invention will be described with reference to FIG. 1 to FIG. In these drawings, parts corresponding to those in FIGS. 4 to 8 are denoted by the same reference numerals, and redundant description will be omitted. In this embodiment, in the comb tooth-shaped electrode 15b1, the pixel electrode 15
The gap portion 40 is formed by lacking a part of the electrode in contact with. On each upper surface of the bridging piece 32 in which the gap portion 40 is formed and the pixel electrode 15 opposite to each other with the gap portion 40 interposed therebetween, a first melting point metal (for example, chromium, molybdenum, or the like) for laser welding is used. , Second electrodes 41 and 42 are formed, respectively. This refractory metal may be the same as the well-known refractory material laminated thereon to reduce the resistance value of the source bus, and is patterned in the same step. A gate insulating film 22 is deposited so as to cover the first and second electrodes 41 and 42 and fill the gap 40. On the gate insulating film 22, first and second electrodes 41 and 42 are provided.
The third electrode 43 for laser welding is formed so as to overlap with a part of the gap portion 40. The third electrode 43 is formed of the same material (for example, aluminum) as the gate bus 18 using the gate bus.
Patterned simultaneously with 18.

Capacitor C _1a is formed between the toothed electrode 15b1 and the gate bus 18 of the comb. Further, capacitors C _1b and C _1c are formed between the first and second electrodes 41 and 42 and the third electrode 43, respectively. These three capacitors are connected in series as shown in FIG. By using the sign of the capacitor as it is to represent the capacitance value of each capacitor, For simplicity, _let C _1b C _1c (2) Capacitors C ₂ and C ₃ are respectively formed between the comb tooth-shaped electrodes 15b2 and 15b3 and the gate bus 18 as in the related art.
FIG. 2A shows one pixel and an equivalent circuit around the pixel.

Both set to C the capacitance value for easy of the capacitors C ₂ and C _3.

C ₂ = C ₃ = C (4) If the additional capacitance value is represented by C _T , then C _T = C ₁ + 2C (5).

When the capacitor C ₃ is short-circuited, the toothed electrode comb
The vicinity of the pixel electrode 15 of the bridging piece 32 of 15b3 is laser-cut as shown by a cutting portion 44 in FIG. 3A. Also, from the side of the transparent substrate 12 or 11 shown in FIG. 3, a laser welder is provided at the central portion of each of the third electrode 43 and the first electrode 41 and the second electrode 42 facing the third electrode 43 (positions indicated by crosses in FIG. 1A). By irradiating a laser beam with a (welding machine using a laser beam), the two electrodes facing each other are electrically connected by a molten metal 45 or 46 as shown in FIG. 3B. As a result, the capacitors C _1b and C _1c are short-circuited, the combined capacitance is C ₁ = C _1a , and the additional capacitance is C _T ′ = C + C _1a . It is necessary to set the additional capacitance C _T '= C + C _1a after the repair substantially equal to the additional capacitance value C _T = C ₁ + 2C of the normal expression (5). Therefore, (C _T '=) C + C _1a = C ₁ + 2C (= C _T ) (6) On the other hand, even if the capacitor C _1a is short-circuited, the additional capacitance value C _T ″ = C _1b / 2C at the time is normal. Additional capacitance value C _T
Must be set to be approximately equal to Therefore, (C _T ″ =) C _1b / 2 + 2C = C ₁ + 2C (= C _T ) (7) From equation (7), C ₁ = C _1b / 2 (8) From equation (8) and equation (3), C _1a = ∞ (9) Practically, it is sufficient if C _1a ≫C _1b / 2 (9 ′), and from equation (6), C _1a = C ₁ + C (6 ′) (6 ′) By substituting equation (8) into the equation, C _1a = C _1b / 2 + C (10)

Let's explain by giving numerical examples for easy understanding. Now, C
_{If 1b} = 0.5 pF, then C _1a ≫0.25 pF from equation (9 ′). Therefore, considering equation (10), C = 1.0 pF
Then, C _1a = 0.25 + 1.0 = 1.25pF1.2pF,
Equation (9 ') can be satisfied with a rough approximation. Therefore, C _1b = 0.
5. Set C = 1.0 and C _1a = 1.2 pF. From the equation (8), the combined capacitance C ₁ is C ₁ = C _1b /2=0.25 pF. However, since the capacitance value of each of the above capacitors is approximate, C ₁ is (3)
It is better to find it more accurately than the formula, Becomes If C _T , C _T ′, C _T ″ are obtained from the equations (5), (6), and (7), respectively, C _T = C ₁ + 2C = 0.21 + 2 × 1 = 2.21 pF (12) C _T ′ = C + C _1a = 1 + 1.20 = 2.20 pF (13) C _T ″ = C _1b / 2 + 2 C = 0.25 + 2 = 2.25 pF (14), and the additional capacitance C _T ′ after repair and the additional capacitance C _T ″ after C _1a short-circuit It can be seen that it is almost equal to the normal additional capacity C _T.

In the above description, the comb tooth-shaped electrode 15b of the additional capacitance portion 30 has been described.
Each of 1, 15b2 and 15b3 has a narrow bridging piece 32 on the pixel electrode 15 side and has a constricted shape. However, the present invention is not limited to this shape, and may have any shape. For example, the simplest shape may be a rectangular comb-shaped electrode having no constriction. As described above, the shapes of the first to third electrodes may be arbitrary. Also, the number of comb-shaped electrodes is not limited to three,
Any number may be used.

According to "Effect of the Invention" The present invention, one of the divided additional capacitance C ₂ or
Even one of C ₃ becomes defective insulation, the bridge 32 of the defective capacitor cut by laser cutting, instead, between the first electrode and the third electrode and the second electrode and the third electrode during into conduction by Rezaweruda a may be approximately equal to the value of the normal additional capacitance values after the repair by adding an additional capacitance C _1a made between the comb tooth-shaped electrode 15b1 and the gate bus 18 .

Further, even if the additional capacitance _C1a is short-circuited, the total additional capacitance value can be made substantially equal to the normal value without special repair.

Therefore, in any of the above cases, the luminance of the corresponding pixel hardly changes from that of a normal pixel, and excellent multi-stage display is possible.

[Brief description of the drawings]

1A and 1B are a plan view and a BB cross-sectional view, respectively, showing a main part of an embodiment of the present invention, and FIG. 2 is a pixel electrode of FIG.
FIG. 3A shows an electrical equivalent circuit diagram of a main part surrounding the comb 15 and FIG. 3 shows a case where there is an insulation failure between the comb tooth-shaped electrode 15b3 and the gate bus 18 in FIG. FIG. 3B is a plan view showing a state where the pixel electrode 15 is separated from the pixel electrode 15 by laser cutting.
Are connected to the first electrode 41 of FIG.
FIG. 3A is a cross-sectional view taken along the line BB of FIG. 3A showing a state where the electrodes 43 and the second electrode 42 and the third electrode 43 are electrically connected, and FIG. 5, FIG. 5 is an equivalent circuit diagram of the liquid crystal display element, FIG. 6 is a plan view of a main part of the already proposed liquid crystal display element, and FIG. 7 is AA of FIG.
FIG. 8 is a sectional view taken along the line BB of FIG.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Teizo Yukawa 4-3-1 Takatsukadai, Nishi-ku, Kobe-shi, Hyogo )

Claims (1)

(57) [Claims] 1. A plurality of source buses and a plurality of gate buses are formed on a transparent substrate at equal intervals in a direction orthogonal to each other, and the source buses and the gate buses intersecting each other corresponding to the positions of the intersections. A thin film transistor connected to the source bus and the gate bus is formed at a corner in a mesh surrounded by the source bus and the gate bus, and a pixel electrode connected to a drain electrode of the transistor is formed widely in the mesh, and an end of the pixel electrode is formed. Is extended so as to overlap the lower side of the gate bus connected to the adjacent thin film transistor, is in contact with the lower surface of the gate bus, and a gate insulating film is uniformly formed so as to cover the pixel electrode and its extension. In a liquid crystal display device in which an additional capacitance portion is formed between the extension portion and the gate bus opposed to the extension portion, a plurality of extension portions of the pixel electrode are provided. In any one of the comb tooth-shaped electrodes, a part of the electrode in contact with the pixel electrode is missing to form a gap, and the gap is formed. On the upper surface on the gap side of the opposing comb tooth-shaped electrode and pixel electrode, a laser weld
The first and second electrodes are respectively formed, and the gate insulating film is formed so as to cover the first and second electrodes and fill the gap, and the first and second electrodes and the gate electrode are formed on the gate insulating film. A liquid crystal display element, wherein a third electrode for laser welding is formed so as to overlap with a part of the gap.