JP3158111B2 - Active matrix display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an active matrix display device having a spacer which does not affect display.

[0002]

2. Description of the Related Art Conventionally, in a small-sized display device using a display medium such as a liquid crystal, in order to keep a layer thickness of a liquid crystal layer between two substrates constituting the display device constant, a peripheral portion between the two substrates is required. A spacer such as glass fiber is mixed into a sealant sandwiched between the substrates. When the spacer is mixed with the sealant, the display screen is not affected by the spacer. However, in a display device having a large screen of 3 inches or more, since the thickness of the liquid crystal layer is not constant, spacers are also mixed in the liquid crystal layer in the display portion.

FIG. 5 is a schematic sectional view of a conventional typical active matrix type liquid crystal display device in which spacers are mixed in a liquid crystal layer, and FIG. 7 is a plan view of an active matrix substrate constituting the display device. . This display device
It is a twisted nematic (TN) type. In this display device, as shown in FIG. 7, each rectangular region formed by the gate bus line 5 and the source bus line 6 has
The picture element electrode 3 is formed. As shown in FIG. 5, each picture element electrode 3 is formed on an insulating substrate 1, and a thin film transistor (hereinafter, referred to as "TFT") 2 is connected to the picture element electrode 3 as a switching element. A counter electrode 13 is formed on a counter substrate 10 facing the substrate 1, and a voltage is applied to the liquid crystal layer 8 between the picture element electrode 3 and the counter electrode 13. Between the substrate 1 and the substrate 10, a spacer 17 for keeping the thickness of the liquid crystal layer 8 constant is interposed.

Further, an active matrix display device shown in the schematic sectional view of FIG. 6 in which the aperture ratio of the display device is increased is known. In the display device shown in FIG.
The pixel electrode 3 and the TFT 2 are electrically connected via a contact hole provided in the insulating film 4. 6, the thickness of the liquid crystal layer 8 between the substrates 1 and 10 is kept constant by the spacer 17.

[0005]

The display devices shown in FIGS. 5 and 6 are usually of a white or transparent type. When a white or transparent spacer is used, there is a problem that when displaying black, the spacer portion becomes white, and the alignment ratio of liquid crystal molecules in the vicinity thereof is disturbed, so that the contrast ratio is greatly reduced. The use of such white or transparent spacers has a very serious problem since it has a bad influence on display quality.

In order to solve such a problem, use of a black spacer has been studied. However, since the hardness of the black spacer is not sufficiently high, there is a problem that the thickness of the liquid crystal layer cannot be kept uniform with high accuracy over a long period of time. Moreover, the problem caused by the disorder of the alignment of the liquid crystal molecules due to the use of the spacer remains unsolved.

As a solution to this problem, there is a display device described in US Pat. No. 4,904,056. In this display device, the light shielding layers formed on the source bus wiring and the gate bus wiring also function as spacers. However, in this display device, since a spacer made of a polymer material is used, the spacer is easily peeled, deformed, or the like. Therefore, there is a problem that the reliability of the display device is reduced.

An object of the present invention is to provide an active matrix display device having a spacer which does not adversely affect display and which has high reliability.

[0009]

In order to achieve the above object, an active matrix display device according to a first aspect of the present invention comprises a pair of insulating substrates and one of the substrates, which is vertically and horizontally wired. A bus line, an insulating film covering the bus line, a pixel electrode disposed on the insulating film, a display medium sealed between the pair of substrates, and keeping a distance between the pair of substrates constant. And a spacer for maintaining the spacer, wherein the spacer is formed on the bus wiring by an electrodeposition method, and a side portion of the spacer is supported by the insulating film. I have.

The bus wiring on which the spacers are formed may be a source bus wiring.

Further, the bus line on which the spacer is formed may be a gate bus line.

According to the active matrix display device of the present invention, in an active matrix display device in which bus lines and picture element electrodes are formed via an insulating film, spacers are formed on the bus lines by an electrodeposition method. Thus, since the spacer is formed on the bus wiring which does not contribute to the display, the image quality does not deteriorate due to the presence of the spacer. Also, since the spacer is formed by the electrodeposition method, it is formed with high pattern accuracy on the bus wiring,
Moreover, it has high adhesion. Therefore, the spacer does not peel off. Further, according to the electrodeposition method, since a spacer having a uniform layer thickness is formed, the uniformity of the layer thickness of the display medium can be increased to within a range of ± 0.1 μm.

[0013] Further, since the side portion of the spacer is supported by the insulating film, the spacer can be reinforced, the uniformity of the layer thickness of the display medium can be further improved, and over a long period of time. The layer thickness of the display medium can be kept uniform.

Further, since the gate bus wiring is formed of a material having a lower resistance than the source bus wiring, it is possible to perform electrodeposition at a low voltage on the gate bus wiring and to form a spacer having a more uniform layer thickness. Can be.

[0015]

Embodiments of the present invention will be described below.

(Reference Example) FIG. 1 shows a sectional view of a reference example of the active matrix display device of the present invention. FIG. 2 is a plan view of an active matrix substrate included in the display device of FIG. The reference example has a configuration similar to that of the display device of FIG. 5, but differs from the display device of FIG. 5 in that a spacer 18 is formed on a bus line.

The reference example is a transmission type TN mode active matrix display device, in which a pair of glass substrates 1 and 1
0, and a liquid crystal layer 8 as a display medium sealed between the substrates 1 and 10. A gate bus wiring 5 is provided on the substrate 1.
And a source bus line 6 intersecting the gate insulating film 9 therebetween. A gate electrode 7 branches from the gate bus line 5, and the TFT 2 is formed on the gate electrode 7. Gate bus line 5 and the gate electrode 7 is made of Ta, the gate insulating film 9 is made of SiN _X. The source bus line 6 is made of Ti.

The TFT 2 is manufactured by a known method. A channel layer 21 made of amorphous silicon (a-Si) is formed on the gate electrode 7 with the gate insulating film 9 interposed therebetween. An etching stopper 22 is formed above the gate electrode 7 on the channel layer 21, and a source electrode 23 and a drain electrode 24 are formed on both sides of the channel layer 21 with a contact layer 25 interposed therebetween. The source electrode 23 branches from the source bus line 6 and extends on the TFT 2. The contact layer 25 is made of n ⁺ type amorphous silicon. Source electrode 23 and drain electrode 24
Are formed at the same time as the source bus lines 6, and therefore are also made of Ti.

On the source bus wiring 6 and the source electrode 23, a spacer 18 formed by an electrodeposition method is formed. The spacer 18 is made of an organic polymer.

It is not necessary to form the spacers 18 on all the source bus lines 6 and all the source electrodes 23.
As few spacers 1 as possible to make the layer thickness of
8 may be formed.

FIGS. 4A and 4B show the cell configuration of this display device, that is, the rubbing directions of the two alignment films 27 and the polarization axes of the respective polarizing plates. FIG. 4A shows the case of the normally white mode, and FIG. 4B shows the case of the normally black mode. In FIG. 4, the solid line o indicates the direction of the polarization axis of the upper polarizer, and the arrow m indicates the rubbing direction of the alignment film on the upper substrate. Similarly, the broken line p indicates the direction of the polarization axis of the lower polarizing plate, and the arrow n indicates the rubbing direction of the alignment film on the lower substrate. As shown in FIG. 4, the twist angle of the liquid crystal molecules in the liquid crystal layer 8 is 90 degrees.

Table 1 shows the display characteristics of the active matrix display device of the reference example. For comparison, Comparative Example 1 shows the display characteristics of the conventional display device shown in FIG.

[0023]

[Table 1] In Table 1 and the following tables, the display luminance is the panel transmittance of light when a display device is driven to obtain a maximum contrast ratio and white display is performed.

As shown in Table 1, in the reference example, the spacer 1
Since the presence of 8 does not affect the display, a high contrast ratio is obtained, and when applied to a color display device, the color purity is increased and the image quality is improved. Further, since the layer thickness of each spacer 18 is also constant, the liquid crystal layer 8 having a uniform layer thickness over the entire display device is obtained.

It can be seen that the effect of improving the contrast ratio is greater in the normally black mode than in the normally white mode. In addition, it has been confirmed that similar effects can be obtained when different liquid crystal materials are used and when different cell configurations are used.

Although the spacer 18 is formed on the source bus line 6 and the source electrode 23 in the reference example, it can be formed on the gate bus line 5. Since the gate bus line 5 is formed of a material having a lower resistance than the source bus line 6, electrodeposition at a low voltage becomes possible, and the spacer 18 having a more uniform layer thickness can be formed.

(Embodiment) The active matrix display device of this embodiment has the same structure as that of the display device of FIG. 6, except that the spacer 18 is formed on the bus wiring. Display device.

In this embodiment, in order to increase the aperture ratio of the display device, the picture element electrode 3 is provided on the insulating film 4 covering the TFT 2, and the picture element electrode 3 and the TFT 2 are in contact holes provided in the insulating film 4. 26 are electrically connected. In this embodiment, the spacers 18 are formed on the source bus lines 6 and the source electrodes 23 by an electrodeposition method. The cell configuration of the present embodiment is the same as that of FIG. In the present embodiment, it is desirable to form the spacers 18 in as small a number as possible so that the layer thickness of the liquid crystal layer 8 can be made constant so that the liquid crystal layer 8 can spread over the entire display device.

Table 2 shows the display characteristics of the active matrix display device of the present embodiment. For comparison, Comparative Example 2 shows the display characteristics of the conventional display device shown in FIG.

[0030]

[Table 2] In the present embodiment, since the presence of the spacer 18 does not affect the display, a high contrast ratio is obtained, and when applied to a color display device, the color purity is increased and the image quality is improved. Further, since the layer thickness of each spacer 18 is also constant, the liquid crystal layer 8 having a uniform layer thickness over the entire display device is obtained.

Further, since the side portions of the spacers 18 are supported by the insulating film 4, the spacers 18 can be reinforced and the uniformity of the thickness of the liquid crystal layer 8 can be further improved. , The thickness of the liquid crystal layer 8 can be kept uniform.

In this embodiment, the effect of improving the contrast ratio is larger in the normally black mode than in the normally white mode.
In addition, it has been confirmed that similar effects can be obtained when different liquid crystal materials are used and when different cell configurations are used.

In the present embodiment, the spacer 18 is formed on the source bus line 6 and the source electrode 23, but may be formed on the gate bus line 5. Gate bus wiring 5
Is formed of a material having a lower resistance than the source bus wiring 6, electrodeposition at a low voltage becomes possible, and the spacer 18 having a more uniform layer thickness can be formed.

In the above embodiment, a display device using a TFT in which a gate electrode is formed below and a source electrode and a drain electrode are formed above has been described. However, the gate electrode is formed above the source electrode and the drain electrode. Can also be applied to a display device using a TFT formed below.

In the above embodiment, the transmission type display device has been described. However, it has been confirmed that the same effect can be obtained in the case of the reflection type display device. In addition, the same study was performed for the case where the layer thickness of the spacer was changed from 1 to 10 μm by the electrodeposition method.

[0036]

According to the active matrix display device of the present invention, in an active matrix display device in which bus lines and picture element electrodes are formed via an insulating film, spacers are formed on the bus lines by electrodeposition. Thus, since the spacers are provided in the portions that do not contribute to the display, the reduction of the contrast ratio and the disturbance of the alignment of the liquid crystal molecules due to the spacers do not occur. Further, since the thickness of each spacer is constant, the thickness of the liquid crystal layer is constant over the entire display device. Therefore, an active matrix display device having high image quality can be obtained.

Further, since the side portion of the spacer is supported by the insulating film, the spacer can be reinforced, the uniformity of the layer thickness of the display medium can be further improved, and over a long period of time. The layer thickness of the display medium can be kept uniform.

Further, since the gate bus wiring is formed of a material having a lower resistance than the source bus wiring, it is possible to perform electrodeposition at a low voltage on the gate bus wiring and to form a spacer having a more uniform layer thickness. Can be.

[Brief description of the drawings]

FIG. 1 is a sectional view of a reference example of an active matrix display device of the present invention.

FIG. 2 is a plan view of an active matrix substrate included in the display device of FIG.

FIG. 3 is a sectional view of an embodiment of the active matrix display device of the present invention.

FIG. 4A is a view in FIG. 1 in a normally white mode.
4 is a diagram showing a cell configuration of the active matrix display device shown in FIG. 3 and FIG. 3B is a diagram showing a cell configuration of the active matrix display device shown in FIG. 1 and FIG. 3 in a normally black mode.

FIG. 5 is a sectional view of an active matrix display device having a conventional spacer.

FIG. 6 is a sectional view of an active matrix display device having a conventional spacer.

FIG. 7 is a plan view of an active matrix substrate included in the display device of FIGS. 5 and 6;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 insulating substrate 2 TFT 3 picture element electrode 4 insulating film 5 gate bus wiring 6 source bus wiring 7 gate electrode 8 liquid crystal layer 9 gate insulating film 10 insulating substrate (counter substrate) 13 counter electrode 17 spacer 18 spacer 21 channel layer 22 Etching stopper 23 Source electrode 24 Drain electrode 25 Contact layer 26 Contact hole 27 Alignment film

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G02F 1/1339 G02F 1/1343 G02F 1/1362 G02F 1/1333

Claims (1)

(57) [Claims] 1. A pair of insulating substrates, a bus wiring laid vertically and horizontally on one of the substrates, an insulating film covering the bus wiring, and a picture element electrode disposed on the insulating film. In an active matrix display device having a display medium sealed between the pair of substrates and a spacer for keeping a distance between the pair of substrates constant, the spacer is formed on the bus wiring by an electrodeposition method. An active matrix display device, wherein the spacer is supported on its side by the insulating film.