JPH06250224A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To maintain the uniformity of a liquid crystal cell gap and to prevent light leakage by suppressing the hillock of the guard ring metallic layer provided in the active matrix type liquid crystal display device. CONSTITUTION:This active matrix type liquid crystal display device has a first substrate 1, a second substrate 21 arranged opposite to this first substrate 1 and a liquid crystal layer 16 held between these first and second substrates 1 and 21. A display region including matrixtype pixel electrodes 11 and thin-film transistors for driving the respective pixel electrodes 11 is formed on the first substrate 1. Further, the surface of the first substrate 1 is provided with a guard ring metallic layer 9 enclosing this display region. Rugged level differences 17 are provided along the lower part of the guard ring metallic layer 9 to prevent the generation of the hillock. These rugged level differences 17 are formed at <=0.5mm intervals. The rugged level differences 17 are provided at an interlayer insulating film 6 interposed between the first substrate 1 and the guard ring metallic layer 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix type liquid crystal display device in which a plurality of pixels each having a switching transistor are arranged in a matrix. More specifically, it relates to a guard ring structure surrounding a display area.

[0002]

2. Description of the Related Art To clarify the background of the present invention, the structure of a conventional active matrix type liquid crystal display device will be briefly described with reference to FIG. As shown, the glass substrate 10
0 is a thin film transistor (TF) for driving a pixel.
T) 101, a gate line 102 for supplying a selection signal to the TFT 101, a signal line 103 for similarly supplying an image signal, a pixel electrode 104, etc. are formed.
Further, a guard ring metal layer 105 is formed so as to surround the display area including the TFT 101 and the pixel electrode 104. A counter substrate 106 is bonded to the glass substrate 100 with a sealing material 107 with a predetermined gap. A counter electrode 108 is formed on the inner surface of the counter substrate 106. Lower glass substrate 100 and upper counter substrate 106
A liquid crystal layer 109 is held between and, and is made of, for example, nematic liquid crystal with twist alignment. Seal material 1
07 is arranged along the peripheral portions of both substrates 100 and 106 in a state of being aligned with the guard ring metal layer 105 described above.

The metal layer 105 surrounds the inner display area and serves as a guard ring to electrically protect the TFT 101. In addition, the thickness of the liquid crystal layer 109 is made uniform by aligning with the sealing material 107 and absorbing and flattening the wiring steps existing on the surface of the glass substrate 100. That is, the guard ring metal layer 105 has a function of protecting the TFT and the like from electrostatic damage in the manufacturing process, and has a function of uniformly controlling the liquid crystal cell gap, so that the yield and the display image quality can be improved. Further, the guard ring metal layer 105 also functions as a light shielding layer.

[0004]

However, in the above-mentioned conventional structure, since the guard ring is composed of the metal layer 105 formed on the relatively flat surface of the glass substrate 100,
There is a problem that so-called hill rock is likely to occur when heat treatment is applied in a post process or the like. This hillock is caused by electromigration or stress migration of the substance forming the metal layer 105, and hillrock having a protrusion shape is generated at the metal grain boundary portion. When hilllock occurs, the flatness of the surface of the metal layer 105 is impaired, and the thickness of the sealing material 107 varies, which causes a liquid crystal cell gap defect. Further, in some cases, the hill lock impairs the light-shielding property of the metal layer 105, which causes so-called light leakage. Since the light leakage of the guard ring is far from the display area including the pixel electrodes and the like, it does not directly affect the display image, but when a backlight or the like is incorporated, the light leakage from the periphery of the display area deteriorates the display quality. The occurrence of this hillock becomes a serious problem especially when aluminum is used as the constituent material of the metal layer 105. 40 for aluminum metal
Hill locks are easily generated even by heat treatment at a relatively low temperature of about 0 ° C.

[0005]

In view of the above-mentioned problems of the prior art, the present invention can suppress the occurrence of hillocks even if a heat treatment is applied to the guard ring metal layer, thereby preventing liquid crystal cell gap defects and light leakage. An object of the present invention is to provide a liquid crystal display device that does not have a liquid crystal display device. The following measures have been taken in order to achieve this object. That is, the liquid crystal display device according to the present invention has, as a basic constituent element, a first substrate, a second substrate arranged to face the first substrate, and between the first and second substrates. And a retained liquid crystal. A display region including a matrix of pixel electrodes and thin film transistors driving each pixel electrode is formed on the first substrate. A feature of the present invention is that a metal layer surrounding the display area is provided on the first substrate, and uneven steps are provided along the metal layer in the underlying layer. Preferably, the uneven steps are formed at intervals of 0.5 mm or less. This uneven step is provided in, for example, an interlayer insulating film interposed between the first substrate and the metal layer. Further, the metal layer is provided so as to be aligned with a sealing material that bonds the first and second substrates to each other. Further, the metal layer is formed of the same material as the extraction electrode for external connection.

[0006]

According to the present invention, uneven steps are provided along the lower portion of the guard ring metal layer surrounding the display area at intervals of, for example, 0.5 mm or less. The presence of these uneven steps makes it difficult for the substance forming the metal layer to migrate, so that the occurrence of hillocks is suppressed. Therefore, even if the sealing material is arranged in alignment with the guard ring metal layer, the flatness of the surface of the metal layer is maintained, so that the liquid crystal cell gap defect is reduced. Moreover, the light leakage caused by the hill rock can be improved. On the other hand, when the guard ring metal layer is arranged over a relatively flat glass substrate surface in a large area as in the conventional case, migration is likely to occur and hill lock frequently occurs.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a liquid crystal display device according to the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic sectional view showing the basic configuration of an active matrix type liquid crystal display device according to the present invention. As shown in the figure, thin film transistors (TFTs) are integrally formed on an insulating substrate 1 made of glass, quartz or the like. Only two TFTs 2 and 3 are shown for the sake of clarity. One T
The FT2 is used for switching and driving the corresponding pixel, and the other TFT3 constitutes a driving circuit for sequentially selectively driving the matrix array of pixels. Each TFT is composed of a polycrystalline silicon film 4 which is patterned in a predetermined shape. The polycrystalline silicon film 4 is formed with a thickness of 50 nm by the LP-CVD method, for example. A gate electrode G is formed on the polycrystalline silicon film 4 via a gate insulating film 5 made of SiO ₂ . The gate electrode G of the pixel TFT 2 is a gate line (not shown)
Has been extended from. The gate electrode G and the gate line are simultaneously formed by the LP-CVD method, and are made of an impurity-doped polycrystalline silicon film having a thickness of 350 nm.
A first interlayer insulating film 6 is covered thereover. The first interlayer insulating film 6 is made of a PSG film having a thickness of 600 nm formed by the AP-CVD method, for example. Further, an aluminum film having a thickness of, for example, 600 nm is formed thereon by sputtering. This aluminum film is patterned into a predetermined shape to form the signal line 7, the wiring electrode 8, the guard ring metal layer 9, and the like. The signal line 7 is electrically connected to the source region S of the pixel TFT 2 through a contact hole provided in the first interlayer insulating film 6. Similarly, the wiring electrode 8 is electrically connected to the source region S and the drain region D of the drive circuit TFT 3 via the contact hole provided in the first interlayer insulating film 6. A second interlayer insulating film 10 is formed on the aluminum film. The second interlayer insulating film 10 has a thickness of, for example, 400 by the AP-CVD method.
It consists of a PSG film deposited to a thickness of nm. Furthermore, a transparent conductive film made of ITO or the like is formed thereon by sputtering to a thickness of 150 nm. This transparent conductive film is patterned into a predetermined shape to become the pixel electrode 11. The pixel electrode 11 is electrically connected to the drain region D of the pixel TFT 2 through a contact hole provided in the second interlayer insulating film 10 and the first interlayer insulating film 6.

A counter substrate 21 is arranged to face the insulating substrate 1 with a predetermined gap therebetween. The counter substrate 21 is bonded to the insulating substrate 1 by the sealing material 12. The sealing material 12 is formed by screen printing or the like on the guard ring metal layer 9
It is arranged so as to match with. On the inner surface of the counter substrate 21, a black mask 13 is patterned in a predetermined shape.
Then, the whole surface counter electrode 15 is formed so as to be stacked via the insulating film 14. Black mask 13 is TFT2 or TF
The patterning is formed so as to shield T3 from light. The black mask 13 and the insulating substrate 1 formed on the counter substrate 21 side
A region other than the pixel electrode 11 is covered with the guard ring metal layer 9 formed on the side to obtain a desired light shielding structure.
Finally, the liquid crystal layer 16 is provided between the counter substrate 21 and the insulating substrate 1.
Is enclosed and held. The liquid crystal layer 16 is made of twisted nematic liquid crystal, for example.

The guard ring metal layer 9, which is a feature of the present invention, is provided so as to surround the display area including the TFT 2 and the pixel electrode 11. As described above, the guard ring metal layer 9 is patterned at the same time as the signal line 7 and the wiring electrode 8 and is made of the same material of aluminum having a thickness of 600 nm. The guard ring metal layer 9 electrically protects the TFT2 and TFT3 on the inner side, and at the same time, the sealing material 1
The adhesion area is flattened by aligning with No. 2. An uneven step 17 is provided along the lower part of the guard ring metal layer 9. In this example, the uneven step 17 is provided on the first interlayer insulating film 6 interposed between the insulating substrate 1 and the metal layer 9. By interposing the uneven step 17, aluminum migration is suppressed and hill lock is prevented from occurring.

FIG. 2 is a plan view of the active matrix type liquid crystal display device shown in FIG. As shown in the figure, pixel electrodes 11 are arranged in a matrix in the display region 18 surrounded by the guard ring metal layer 9 to form individual liquid crystal pixels. A pixel TFT 2 is connected to each pixel electrode 11. A gate line 19 is connected to the gate electrode of each pixel TFT 2, and a signal line 7 is also connected to the source electrode. The plurality of gate lines 19 are connected to the vertical driving circuit 22, while the plurality of signal lines 7 are connected.
Is connected to the horizontal drive circuit 23. The vertical drive circuit 22 selects the pixel TFTs 2 line-sequentially via the gate line 19, and the horizontal drive circuit 23 selects the corresponding pixel electrode 1 via the signal line 7 and the selected pixel TFT 2.
1 to supply the image signal. The vertical drive circuit 22 and the horizontal drive circuit 23 are integrated circuits having the TFT 3 as a constituent element as described above.

A lead-out electrode 24 for external connection is also formed in the peripheral portion of the insulating substrate 1 and intersects the guard ring metal layer 9 to connect to the vertical drive circuit 22 and the horizontal drive circuit 23. The extraction electrode 24 is made of the same aluminum film as the guard ring metal layer 9. For ease of understanding, an enlarged pattern shape of the intersection of the extraction electrode 24 and the guard ring metal layer 9 is shown. As shown in the drawing, the strip of the guard ring metal layer 9 is partially removed, and the extraction electrode 24 extends in this portion. The separated metal layers 9 are connected to each other by, for example, a polycrystalline silicon film 25 which is patterned into a predetermined shape. This polycrystalline silicon film 25
Is formed at the same time as the gate electrode and the gate line, and is insulated from the metal layer 9 and the extraction electrode 24 by the first interlayer insulating film. The lead-out electrode 24 is wired from the vertical drive circuit 22 or the horizontal drive circuit 23 toward the outside of the sealing material in order to make an electrical connection to the outside. Therefore, the middle portion of the extraction electrode 24 straddles the seal area. In this structure, the guard ring metal layer 9 is provided close to both sides of the extraction electrode 24 in the seal region. Therefore, it is possible to substantially flatten the entire sealing area. That is, the extraction electrode 24 and the guard ring metal layer 9 are formed of aluminum having the same film thickness, and the step is removed.

An uneven step 17 is provided along the band of the guard ring metal layer 9. In this example, the uneven step 17 is a 100 μm square hole provided in the first interlayer insulating film located under the metal layer 9. The individual holes are arranged at 100 μm intervals. Such holes can be formed by selective etching of the first interlayer insulating film. The unevenness 17 reduces the stress in the aluminum film and prevents migration from occurring. For example, even if a heat treatment of about 400 ° C. is applied in the step after depositing the aluminum film, no aluminum hillock is generated in the guard ring region. As described above, according to the present invention, it is possible to provide a liquid crystal display device that employs a guard ring made of metal and can suppress the occurrence of hillocks even when heat treatment is applied, and that does not cause defects in the liquid crystal cell gap or light leakage. it can.

On the other hand, as a comparative example, a liquid crystal display device was prepared in the same manner as in the above-mentioned example except that no hole was formed in the first interlayer insulating film located under the guard ring metal layer made of aluminum. In this case, hillocks frequently occurred in the guard ring metal layer in the subsequent heat treatment. Therefore, due to the defective liquid crystal cell gap and the light leakage in the guard ring portion, almost no good product was obtained and the yield was very low.

Although the aluminum film having a thickness of 600 nm is used as the guard ring metal layer in the above-mentioned embodiments, the present invention is not limited to this.
Any material may be used as long as it has sufficiently low resistance and is the same material as the extraction electrode to the outside. The light-shielding property of the guard ring metal layer is such that the transmittance is 1% or less, preferably 0.1% or less in the visible light region (400 nm to 700 nm). In addition to aluminum (Al), Cr, Ni, Ta, Ti,
Metals such as W, Cu, Mo, Pt, and Pd, alloys thereof, and silicide can be used. It is sufficient that the thickness of each material satisfies a predetermined light-shielding property, and generally 50
nm or more.

Further, in the present embodiment, as shown in FIG. 2, the shape of the uneven step provided in the lower part of the guard ring metal layer is such that square holes of 100 μm square are arranged at 100 μm intervals. It is not limited to this. Generally, any shape may be used as long as uneven steps can be arranged at intervals of 0.5 mm or less. If the distance is set to 0.5 mm or more, the effect of suppressing migration will be reduced. As another example, holes of 500 μm square may be used, or stripe-shaped grooves with intervals of 50 μm may be used. Further, a circular opening having a diameter of 100 μm may be used.

In this embodiment, the semiconductor layer of the TFT, the gate electrode and the gate line are made of polycrystalline silicon, the gate insulating film is made of SiO ₂ , and the signal line is made of aluminum. It is not limited. Amorphous silicon may be used for the semiconductor layer of the TFT. The gate electrode and the gate line are, for example, silicide, polycide, and the metal is Ta or A.
1, Cr, etc. may be used. The gate insulating film is, for example, Si
N, tantalum oxide or the like can be used. For the signal line, for example, Ta, Cr, Mo, Ni or the like can be used.
In addition, the present invention is a planar type thin film transistor,
It is needless to say that the present invention can be applied to an active matrix type liquid crystal display device using either a normal stagger type or an inverted stagger type.

[0017]

As described above, according to the present invention, the uneven steps are provided at intervals of at least 0.5 mm along the lower portion of the guard ring metal layer surrounding the display area.
The unevenness causes the stress to be alleviated, so that migration is less likely to occur and the occurrence of hill rock is suppressed. Therefore, the flatness of the guard ring metal layer at the interface with the sealing material can be maintained and the occurrence of liquid crystal cell gap defects can be prevented. Further, the light leakage of the guard ring metal layer due to the hilllock, which has been a problem in the past, is greatly improved. Even if heat treatment is applied after forming the guard ring metal layer, hilllock does not occur, and it is possible to provide a liquid crystal display device in which there is no defect in the liquid crystal cell gap or light leakage.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of an active matrix type liquid crystal display device according to the present invention.

FIG. 2 is a plan view of the active matrix type liquid crystal display device shown in FIG.

FIG. 3 is a cross-sectional view showing a configuration of a conventional active matrix type liquid crystal display device.

[Explanation of symbols]

 1 Insulating Substrate 2 TFT 3 TFT 4 Polycrystalline Silicon Film 5 Gate Insulating Film 6 First Interlayer Insulating Film 7 Signal Line 8 Wiring Electrode 9 Guard Ring Metal Layer 10 Second Interlayer Insulating Film 11 Pixel Electrode 12 Sealing Material 13 Black Mask 15 Counter electrode 16 Liquid crystal 17 Concavo-convex step 18 Display area 19 Gate line 21 Counter substrate 22 Vertical drive circuit 23 Horizontal drive circuit 24 Extraction electrode 25 Polycrystalline silicon film

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H01L 29/784

Claims (5)

[Claims] 1. A first substrate, a second substrate facing the first substrate, and a liquid crystal held between the first and second substrates. In a liquid crystal display device in which a display region including a matrix of pixel electrodes and thin film transistors for driving each pixel electrode is formed on a substrate, a metal layer surrounding the display region is provided on the first substrate, and the metal layer is provided. A liquid crystal display device characterized in that an uneven step is provided along the lower part of the. 2. The liquid crystal display device according to claim 1, wherein the uneven steps are formed at intervals of 0.5 mm or less. 3. The liquid crystal display device according to claim 1, wherein the uneven step is provided in an interlayer insulating film interposed between the first substrate and the metal layer. 4. The liquid crystal display device according to claim 1, wherein the metal layer is provided in alignment with a sealing material that bonds the first and second substrates to each other. 5. The liquid crystal display device according to claim 1, wherein the metal layer is formed of the same material as a lead electrode for external connection.