JPH05210114A - Active matrix liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain a high display grade by preventing the generation of the discrination by a reverse tilt in both parts of a picture element electrode part near a signal line and a picture element electrode part near a scanning line. CONSTITUTION:A source guard electrode wiring 21 is formed around the periphery of the picture element electrode 17 and along a source bus wiring 20 as a signal line and a gate guard electrode wiring 3 is formed around the periphery of the picture element electrode 17 and along a gate bus wiring 2 as a scanning line. The source guard electrode wiring 21 and the gate guard electrode wiring are placed in the state of insulating the two guard electrode wirings 21 and with each other. The potentials which can most effectively decrease the influence acting on the electric field of the liquid crystal layer part on the picture element electrode 17 for each of the source bus wiring 20 and the gate bus wiring 2 are independently applied to the two guard electrode wirings 21, 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix liquid crystal display device using a thin film transistor (hereinafter referred to as TFT).

[0002]

2. Description of the Related Art FIG. 8 is a sectional view of a conventional active matrix liquid crystal display device. FIG. 6 is a plan view of an active matrix substrate 150 used in this display device,
FIG. 7 is a plan view of the counter substrate 160. In the active matrix substrate 150, TFTs 102 and picture element electrodes 103 are provided in a matrix on a first insulating substrate 101 made of glass or the like. As shown in FIG.
A gate bus line 114 for supplying a scanning signal is provided at T102.
And a source bus line 115 for supplying a video signal is connected. As shown in FIG. 8, a passivation film as a protective film is further provided on the entire surface of the substrate 101, and an alignment film 104 usually made of a polyimide film is formed on the passivation film. This alignment film 1
Numeral 04 is subjected to orientation treatment by a rubbing method.

In the counter substrate 160, a light-shielding film 120 is formed by forming a chromium film on the second insulating substrate 105 made of glass or the like by a sputtering method and patterning it in a shape shown by hatching in FIG. ing. The light shielding film 120 has a function of blocking light leaking from the active matrix substrate 150.

An opening 121 is opened in the light shielding film 120, and this opening 121 serves as an effective display portion. And
On the light shielding film 120, a counter electrode 106 made of a transparent electrode is formed on almost the entire surface, and on the counter electrode 106,
An alignment film 107 that has been subjected to an alignment treatment is formed. Plastic beads 109 are interposed as spacers between the active matrix substrate 150 and the counter substrate 160 to keep the distance between the substrates 150 and 160 constant. In addition, the liquid crystal layer 110 is provided between the active matrix substrate 150 and the counter substrate 160 so that the sealing resin 10
It is enclosed by 8.

In this active matrix liquid crystal display device, a liquid crystal layer 110 and alignment films 104 and 107 are present between a pixel electrode 103 and a counter electrode 106 in FIG. 8, and a capacitor is formed by these. .. One electrode of the capacitor is the pixel electrode 103 and the other is the counter electrode 106. Referring to FIG. 6, the pixel electrode 10
The drain electrode of the TFT 102 is connected to 3.
The source electrode of the TFT 102 has a source bus line 115.
Are connected. The gate bus wiring 114 and the source bus wiring 115 are connected to the electrode terminals outside the sealing resin 108, respectively.

In order to drive the active matrix liquid crystal display device of FIG. 8, a scanning pulse signal is sequentially input from the uppermost gate bus wiring 114 in FIG. 6, and the respective TFTs 102 connected to the gate bus wiring 114 are driven. Turn on. When a video signal is input from the source bus line 115 in synchronization with this scan pulse signal, a voltage is applied to each pixel electrode 103 and the counter electrode 106, and the orientation of the liquid crystal molecules in the liquid crystal layer 110 changes, resulting in a display. Is done.

In the active matrix liquid crystal display device of FIG. 8, when no voltage is applied, as shown in FIG.
The liquid crystal molecules 130 of the liquid crystal layer 110 are oriented with their molecular axes oriented in a fixed direction. In this specification, the case where the dielectric anisotropy of the liquid crystal layer 110 is positive will be described as an example. In this case, when no voltage is applied, the molecular axes of the liquid crystal molecules 130 are aligned with the pretilt angle θ with respect to the surface of the pixel electrode 103. On the other hand, when a voltage is applied, the molecular axis of the liquid crystal molecule 130 changes its alignment state substantially perpendicular to the surface of the picture element electrode 103. When the dielectric anisotropy is negative, the direction of the molecular axis of the liquid crystal molecule 130 is opposite between when the voltage is applied and when the voltage is not applied, but the liquid crystal molecule 130 is similarly oriented. change. The pretilt angle θ is set so that the directions of the alignment change of the liquid crystal molecules 130 are the same when a voltage is applied and a uniform display is performed.

In the conventional active matrix liquid crystal display device, the electric field of the liquid crystal layer 110 is generated between the picture element electrode 103 and the counter electrode 106, and as shown in FIG. In, the electric force line 132 is likely to be distorted. Due to the distortion of the electric lines of force 132,
As shown in FIG. 10 (B), the liquid crystal molecules 130 undergo reverse tilt in which the liquid crystal molecules 130 are oriented in the opposite direction to the direction of the pretilt angle θ at the end of the pixel electrode 103, as shown by an arrow 133 in FIG. 10 (B). At the position, the reverse tilt causes disclination. When this disclination occurs, liquid crystal molecules 130 are generated at that portion.
However, the light control is not performed normally, and the display quality is impaired due to a decrease in contrast and the like.

Therefore, in order to solve this difficulty, the applicant of the present application, as shown in FIGS. 11 and 12, has the pixel electrodes 217 on the active matrix substrate and the source bus wiring 22.
0 and the gate bus wiring 202, the pixel electrode 21
A display device in which a guard electrode 221 is provided so as to surround No. 7 has been previously proposed (Japanese Patent Application No. 3-88088). Figure 1
1 shows a plan view of the proposed active matrix liquid crystal display device having the guard electrode, and FIG. 12 shows a sectional view of the display device.

In this display device, the pixel electrode 217
An insulating film 219 is formed on the periphery of the insulating film 219, and a guard electrode 221 is formed on the insulating film 219. Picture element electrode 217
The electric field in the peripheral portion of is affected by the potential of the source bus line 220 as a signal line, that is, the electric field 234 from the source bus line 220 toward the pixel electrode 217. Therefore, the lines of electric force at the ends of the picture element electrodes 217 are distorted from the desired shape perpendicular to the substrate, and a lateral component parallel to the substrate appears as shown by lines of electric force 233.
Therefore, the potential of the guard electrode 221 is set to the source bus line 2
The potential of the source bus line 220 and the guard electrode 221 are set by setting the potential in which the lateral component in the opposite direction to the lateral component of the electric force line 233 that appears due to the influence of the potential of 20 is present.
Each of the potentials cancels the influence of the electric field 234 on the electric force line 233 at the end of the pixel electrode 217. Therefore, the lines of electric force formed in the liquid crystal layer portion on the pixel electrode can be made close to an ideal shape perpendicular to the substrate, and the occurrence of disclination in the effective display portion can be suppressed. You can

[0011]

However, in the proposed display device, since the guard electrodes are integrally formed and have substantially the same potential, one of the source bus line and the gate bus line is used. Is generated in the direction toward the center of the picture element, and the electric field from the other is generated in the direction toward the outside of the picture element. When the potential is such that it appears in the liquid crystal layer portion on the electrode, there is a problem that it can effectively contribute only to one of the source bus line and the gate bus line for the following reason.

The reason is that, for example, when the potential of the pixel electrode 217 is -4V, the potential of the source bus wiring 220 is + 6V, and the potential of the gate bus wiring 202 is -10V, the potential of the guard electrode 221 is set to -1V. Then, the lines of electric force 232 formed on the pixel electrode portion near the gate bus wiring 202 are close to the vertical direction with respect to the substrate, but are formed on the pixel electrode portion near the source bus wiring 220. This is because the lines of electric force 233 remain distorted, and thus the occurrence of disclination cannot be completely prevented.

The present invention has been made to solve such a problem, and discriminates due to reverse tilt in both the pixel electrode portion near the signal line and the pixel electrode portion near the scanning line. It is an object of the present invention to provide an active matrix liquid crystal display device which can prevent the occurrence of cation and has a high display quality.

[0014]

In the active matrix liquid crystal display device of the present invention, a liquid crystal layer is sandwiched between alignment films formed on the inner surfaces of a pair of insulating substrates facing each other, and one of the pair of substrates is sandwiched. In an active matrix liquid crystal display device in which picture element electrodes are arranged in a matrix on the inner surface of one substrate, and signal lines and scanning lines are wired around the picture element electrodes, the periphery of the picture element electrodes Signal line guard electrode wiring is formed along the signal line, and scanning line guard electrode wiring is formed along the scanning line along the periphery of the pixel electrode. Line guard electrode wiring and the scanning line guard electrode wiring,
The two guard electrode wirings are connected to the external electrode terminals while being insulated from each other, and the potentials are independently applied to the two guard electrode wirings, whereby the above object can be achieved.

[0015]

According to the present invention, the signal line guard electrode wiring is formed along the periphery of the picture element electrode and along the signal line, and also along the periphery of the picture element electrode and along the scanning line. The scanning line guard electrode wiring is formed, and the signal line guard electrode wiring and the scanning line guard electrode wiring exist in a state in which the two guard electrode wirings are insulated from each other. For this reason,
Either the potential of the signal line or the scanning line is lower than the pixel electrode potential, a lateral component of the electric field is generated outward from the pixel electrode, and the other potential is higher than the pixel electrode potential and the inside of the pixel electrode Even if there is a lateral component of the electric field that faces toward, the potentials that can most effectively reduce the effect on the electric field of the liquid crystal layer part on the pixel electrode for both the signal line and the scanning line are guarded. It is possible to provide the electrode wiring independently.

[0016]

EXAMPLES Examples of the present invention will be described below.

FIG. 1 is a plan view of an active matrix substrate which constitutes the display device of this embodiment, and FIG.
3C is a plan view showing a manufacturing process of the active matrix substrate, and FIGS. 3A to 3C are respectively FIGS.
3C is a sectional view taken along line III-III in FIG. 3C, and FIG.
FIG. 3 is a sectional view taken along line III-III of FIG. The active matrix liquid crystal display device of this embodiment will be described according to the manufacturing process.

As shown in FIG. 3A, the glass substrate 10
A Ta metal thin film was formed on the top by a sputtering method.
This Ta metal thin film is formed by photolithography on the gate bus wiring 2 and the gate bus branch line 2 shown in FIG.
a, patterning was performed in the shape of the gate guard electrode wiring 3. TF with the tip of gate bus branch line 2a formed later
It functions as a gate electrode of T1 (see FIG. 1).

Next, a silicon nitride film, a non-doped amorphous silicon film, and an n ⁺ type amorphous silicon film were sequentially formed on the entire surface of this substrate by the plasma CVD method. This silicon nitride film is the gate insulating film 1 of FIG.
It becomes 2. The non-doped amorphous silicon film and the n ⁺ type amorphous silicon film were patterned to form a semiconductor layer 13 and a contact layer 14 at the tip of the gate bus branch line 2a as shown in FIG. 2B.

Next, a Ti metal thin film was formed on the entire surface of this substrate. This metal thin film is patterned, and the pattern shown in FIG.
The source electrode 15 and the drain electrode 1 having the shape shown in FIG.
6, source bus wiring 20 and source guard electrode wiring 21
Formed. At this time, the central portion of the contact layer 14 is also removed by etching, and divided into a portion below the source electrode 15 and a portion below the drain electrode 16. With the above, the TFT 1 is completed.

Next, a silicon nitride film is formed on the entire surface of this substrate by the plasma CVD method, and patterning is performed to form a protective film 18 on the TFT 1 as shown in FIG. 3 (D).
Formed. Polyimide may be used as a material for this protective film. In this case, polyimide is applied with a spinner, and then firing patterning is performed.

Next, an ITO film is formed on the entire surface of this substrate and patterned to form a pixel electrode 17 having the shape shown in FIG. 1, and further an alignment film 24 (see FIG. 4) is formed. As a result, the active matrix substrate 30 is completed. FIG. 4 is a sectional view taken along the line IV-IV in FIG.

On the other hand, the active matrix substrate 30
As shown in FIG. 4, the counter substrate 40 combined with the light shielding film 44 and the transparent counter electrode 4 is provided on the glass substrate 41.
2 and the alignment film 43 in this order from the substrate 41 side. The alignment film 43 has been rubbed. This rubbing treatment is performed by the alignment films 24 of both the substrates 30 and 40.
It is applied to both 43. The rubbing process is performed on both substrates 30,
This is done to set the pretilt angle of the liquid crystal molecules of the liquid crystal layer 50 enclosed between 40.

The active matrix substrate 30 and the counter substrate 40 produced as described above are both substrates 30, 4
The liquid crystal layer 50 is sealed between 0, and the layers are bonded as shown in FIG. As a result, the active matrix liquid crystal display device of this embodiment is completed. At this time, the gate guard electrode 3, the source guard electrode 21, the source bus wiring 20
The gate bus line 2 and the gate bus line 2 are individually connected to the external electrode terminals 31 disposed outside the sealing resin for enclosing the liquid crystal layer 50.

Therefore, in the active matrix liquid crystal display device having this structure, for example, when the pixel electrode potential is -4V, the gate bus wiring potential is -10V, the source bus wiring potential is + 2V, and the counter electrode potential is 0V. , If the potential of the gate guard electrode is -1 V and the potential of the source guard electrode is -7 V, the influence of the potential of the gate guard electrode on the electric field of the liquid crystal layer on the pixel electrode and the potential of the gate bus wiring are The influence of the liquid crystal layer portion on the electrode on the electric field is canceled out. On the other hand, the influence of the potential of the source guard electrode on the electric field of the liquid crystal layer portion on the picture element electrode and the influence of the potential of the source bus line on the electric field of the liquid crystal layer portion on the picture element electrode cancel each other out. As a result, the distortion like the electric flux lines 233 in FIG. 12 that occurs in the case of the above-described conventional example is reduced, and as shown in FIG. 4, the electric flux lines have an ideal shape in which the electric flux lines are substantially perpendicular to the substrate. It becomes closer to the potential force line 60 and reverse tilt of the liquid crystal molecules is prevented. Therefore, good display quality can be obtained in the effective display portion which is smaller than the pixel electrode and is desired to be as close to the size of the pixel electrode as possible.

[0026]

According to the present invention, reverse tilt can be prevented from occurring in the liquid crystal layer portion on the pixel electrode, and disclination can be prevented from occurring in the effective display portion. Therefore, it is possible to provide an active matrix liquid crystal display device having good contrast and high display quality.

[Brief description of drawings]

FIG. 1 is a plan view of an active matrix substrate used in an embodiment of an active matrix liquid crystal display device of the present invention.

2A to 2C are plan views showing a manufacturing process of the active matrix substrate of FIG.

3A to 3D are cross-sectional views showing the same manufacturing process.

FIG. 4 is a cross-sectional view showing directions of lines of electric force of the active matrix liquid crystal display device of the present invention.

FIG. 5 is a diagram showing a state of bonding an active matrix substrate and a counter substrate.

FIG. 6 is a plan view showing a conventional active matrix substrate.

FIG. 7 is a plan view of a conventional counter substrate.

FIG. 8 is a cross-sectional view of a conventional active matrix liquid crystal display device.

FIG. 9 is a cross-sectional view showing an alignment direction of liquid crystal molecules in a conventional active matrix liquid crystal display device.

10A is a cross-sectional view showing the direction of lines of electric force in a conventional active matrix liquid crystal display device, and FIG. 10B is a cross-sectional view showing a state in which disclination occurs on an effective display portion.

FIG. 11 is a plan view of an active matrix substrate in an active matrix liquid crystal display device previously proposed by the applicant of the present application.

12 is a cross-sectional view showing directions of lines of electric force of the active matrix liquid crystal display device of FIG.

[Explanation of symbols]

 1 TFT 2 gate bus wiring 3 gate guard electrode wiring 20 source bus electrode wiring 21 source guard electrode wiring 10, 41 glass substrate 17 pixel electrode 30 active matrix substrate 31 external electrode terminal 40 counter substrate 42 counter electrode 50 liquid crystal layer

Claims (1)

[Claims] 1. A liquid crystal layer is sandwiched between alignment films formed on the inner surfaces of a pair of opposed insulating substrates, and the pixel electrodes are arranged in a matrix on the inner surface of one of the pair of substrates. In the active matrix liquid crystal display device in which the signal line and the scanning line are wired along the periphery of the picture element electrode, a signal line guard passing along the circumference of the picture element electrode and along the signal line. Electrode wiring is formed, scanning line guard electrode wiring is formed along the scanning line and around the pixel electrode, and the signal line guard electrode wiring and the scanning line guard electrode wiring are formed. However, the active matrix liquid crystal display device is configured such that both guard electrode wirings are connected to external electrode terminals while being insulated from each other, and a potential is independently applied to both guard electrode wirings.