JPH09258242A - Liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display element which is high in numerical aperture, bright, has an excellent visual angle characteristic and is producible at a low cost. SOLUTION: A TFT(thin-film transistor) connected to a gate electrode wiring 10, drain electrode wiring 14, gate electrode wiring 10 and drain electrode wiring 14 and common electrode wiring 16 exist on one side of an insulating layer 23. A comb-shaped source electrode 15 and comb-shaped electrodes 16a of the common electrode wiring meshed with each other exist on the other side of the insulating layer 13. The source electrode 15 is electrically connected to the source part 15a of the TFT 7 via a contact hole 15 and the comb-shaped part 16a of the common electrode electrically connected to the common electrode wiring 16 via a contact hole 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a portable information terminal, a personal computer, a word processor, which can be viewed by a large number of people.
A flat display used for amusement equipment or a television, a display board using the shutter effect,
Alternatively, the present invention relates to a liquid crystal display element that can be used for windows, doors, walls and the like.

[0002]

2. Description of the Related Art As a liquid crystal display element, an active matrix type is known. In this active matrix type liquid crystal display device, thin film transistors (hereinafter referred to as TFTs) are formed in a matrix on an insulating substrate such as glass which is one of a pair of substrates arranged to face each other with a liquid crystal layer interposed therebetween. This is a configuration using this as a switching element. Such an active matrix type liquid crystal display device (TFT-LCD) is highly expected as a flat panel display because it can obtain high image quality.

The above-mentioned active matrix type liquid crystal display element uses transparent electrodes which are respectively formed on a pair of substrates as electrodes for driving a liquid crystal layer and which are arranged to face each other. The arrangement of the electrodes facing each other is to make the direction of the electric field applied to the liquid crystal substantially perpendicular to the substrate surface, and to adopt a display system represented by a twisted nematic display system.

In addition to the method in which the direction of the electric field applied to the liquid crystal is substantially perpendicular to the substrate surface, a method in which the direction of the electric field applied to the liquid crystal is substantially parallel to the substrate surface is used as a pair of combs. A method using a circular electrode has been proposed (Japanese Patent Publication No. 63-21907). In this proposed method, a liquid crystal layer provided between a pair of substrates is driven by a pair of interdigitated comb-shaped electrodes formed on one substrate, and the plane where the comb-shaped electrodes are present. And the plane where bus lines such as signal lines and scanning lines exist are the same.

[0005]

By the way, in the case of the conventional proposed liquid crystal display element, since the plane where the comb-shaped electrode exists and the plane where the bus line exists are the same, the comb-shaped electrode and the bus line are A gap for insulation is required between them. Moreover, since the comb-shaped electrodes that interlock with each other are used to drive the liquid crystal layer, it is difficult to increase the effective area through which light can pass. Therefore, there is a problem that the aperture ratio, which is the area ratio of light transmission of the display screen, decreases.

In principle, the aperture ratio can be increased to a practical level by reducing the electrode width of the comb-shaped electrode from the usual 10 μm to about 1 to 2 μm. It is extremely difficult to form the film uniformly and without any disconnection. That is, since the comb-shaped electrodes that occlude alternately are used, there is a trade-off relationship between the aperture ratio and the manufacturing yield, and it is difficult to manufacture a liquid crystal display element having a bright image at low cost.

The present invention solves the problems of the prior art as described above, and provides an active matrix type liquid crystal display device which has a high aperture ratio and is bright, has excellent viewing angle characteristics, and can be manufactured at low cost. The purpose is to provide.

[0008]

In a liquid crystal display element of the present invention, a scanning line, a signal line, a switching element connected to the scanning line and the signal line, and a common electrode are present on one side of an insulating layer. On the other side of the insulating layer, the first
The comb-shaped electrode and the second comb-shaped electrode exist, and the output terminal of the switching element and the first comb-shaped electrode are connected by a contact hole provided in the insulating layer, and the common A liquid crystal layer is sandwiched between a first substrate having a structure in which an electrode and the second comb-like electrode are connected by a second contact hole provided in the insulating layer, and the first substrate. And a second substrate disposed so as to face each other, and a lateral electric field is applied to the liquid crystal layer by the first comb-shaped electrode and the second comb-shaped electrode, thereby achieving the above object. To be done.

In the liquid crystal display element of the present invention, the insulating layer may be made of a resist material.

In the liquid crystal display element of the present invention, the insulating layer is formed in a concavo-convex structure having line-shaped convex portions, and both side surfaces of the convex portions are sloped surfaces, and at least the first surface is formed on the sloped surface. The comb teeth of the first comb-shaped electrode and the comb teeth of the second comb-shaped electrode may face each other.

The operation of the present invention will be described below.

In the present invention, the electrode structure is three-dimensionally constructed. Specifically, it is as follows.

In the liquid crystal display element of the present invention, the scanning line, the signal line, the switching element connected to the scanning line and the signal line, and the common electrode are present on one side of the insulating layer. A contact in which a first comb-shaped electrode and a second comb-shaped electrode that interlock with each other are present on the other side, and the output terminal of the switching element and the first comb-shaped electrode are provided in the insulating layer. A first substrate having a structure in which the common electrode and the second comb-shaped electrode are connected by a hole, and the common electrode and the second comb-shaped electrode are connected by a second contact hole provided in the insulating layer; It is arranged so as to face the substrate with a liquid crystal layer interposed therebetween. Therefore, it has a structure in which bus lines such as scanning lines and signal lines and the first and second comb-shaped electrodes are arranged on different planes, and the first and second comb-shaped electrodes are partially formed on the bus line. Even if the structures overlap, there is no short circuit.

When the insulating layer has a concavo-convex structure and both side surfaces of the convex portion are inclined, the comb teeth of the first and second comb-shaped electrodes are formed facing each other on the inclined surface. Then, the comb teeth form an angle with the substrate surface.

[0015]

Embodiments of the present invention will be specifically described below. Note that the present invention is not limited to the following embodiments.

(Embodiment 1) FIGS. 1 and 2 are a plan view and a sectional view showing a unit pixel of a liquid crystal display element according to Embodiment 1. As shown in FIG. FIG. 2 is a cross-sectional view of the portion indicated by the alternate long and short dash line in FIG. The configuration of this liquid crystal display element will be described along with the manufacturing process.

On the glass substrate 1, a gate electrode wiring 10 as a scanning line and a common electrode wiring 1 as a common electrode are provided.
6 was made of Cr together. A part of the gate electrode wiring 10 constitutes the gate electrode of the TFT 7.

Next, a gate insulating film 20 made of a silicon nitride (SiN) film was formed so as to cover these electrode wirings 10 and 16.

Next, the amorphous silicon (a-Si) film 3 is formed on the gate electrode wiring 10 with the gate insulating film 20 interposed therebetween.
Formed 0. This is the active layer of the TFT 7.

Next, on the a-Si film 30, the a
The drain electrode wiring 14 as a signal line and the source portion 15a of the TFT 7 are overlapped with a part of the -Si film 30.
Are both formed of Mo. A part of the drain electrode wiring 14 constitutes a drain part of the TFT 7 overlapping a part of the a-Si film 30.

Next, a protective insulating film 23 made of a polymer film using a resist material was formed on the substrate 1 so as to cover the drain electrode wiring 14 and the source portion 15a.

Next, contact holes 5 and 6 were formed in the insulating film 23 at two locations, on the source portion 15a and on the common electrode wiring 16.

Next, a comb-shaped source electrode (first comb-shaped electrode) 15 and a comb-shaped portion (second comb-shaped electrode) 16a of the common electrode were formed on the insulating film 23. At this time, the source electrode 15 is connected to the TFT through one of the contact holes 5
7 is electrically connected to the source portion 15a, and the comb-shaped portion 16a of the common electrode is electrically connected to the common electrode wiring 16 through the other contact hole 6.

An insulating film 23 separates the comb-shaped portion 16a of the comb-like common electrode used for display and the source electrode 15 from other bus lines such as the drain electrode wiring 14 and the source electrode wiring 10. Because
The comb-shaped portion 16 of the common electrode that is also comb-shaped on the bus line
a and a part of the source electrode 15 can be formed,
The aperture ratio can be increased. That is, the planar aperture ratio can be improved.

An alignment film OR made of polyimide was formed on the surface of an active matrix substrate having unit pixels arranged as described above arranged in a matrix, and the surface was rubbed.

Prior to or after the production of this active matrix substrate, a counter substrate having an alignment film OR on the surface of which the same rubbing treatment is applied is formed on the glass substrate 2. The two substrates are arranged so as to face each other, and the liquid crystal layer 3 is provided between the two substrates. Then, polarizing plates were arranged on the outer sides of both substrates.

1 and 2 show the directions in which liquid crystal molecules are directed when no electric potential is applied to the source electrode 15 and the comb-shaped portion 16a of the common electrode, that is, when there is no electric field. At the time of no electric field, the long axis (optical axis) of the liquid crystal molecules 4 has a slight angle with respect to the longitudinal direction of the striped source electrode 15 and the comb-shaped portion 16a of the common electrode. That is, the liquid crystal molecules 4 are aligned such that the angle between the long axis of the liquid crystal molecules 4 and the direction of the electric field (perpendicular to the longitudinal direction of the comb-shaped portions of the source electrode and the common electrode) is 45 ° or more and less than 90 °. There is. The orientations of the liquid crystal molecules 4 at the interfaces with the upper and lower substrates 1 and 2 were parallel to each other. In addition, the liquid crystal molecule 4
Has a positive dielectric anisotropy.

In the liquid crystal display device in such a state, TF
When a voltage is applied to the gate electrode of T7 to turn on the TFT 7, a voltage is applied to the source electrode 15 and the source electrode 1
An electric field E1 is induced between the comb-shaped portions 16a of the 5-common electrodes. Then, as shown in FIGS. 3 and 4, the liquid crystal molecules 4 turn in the direction of the electric field. Therefore, the upper and lower substrates 1,
When the polarization transmission axes of the two polarizing plates arranged outside of 2 are arranged at a predetermined angle, it becomes possible to change the light transmittance by applying an electric field.

Therefore, in the liquid crystal display element of the present embodiment, the gate electrode wiring 10, the drain electrode wiring 14, the TFT 7 connected to the gate electrode wiring 10 and the drain electrode wiring 14, and the common electrode wiring 16 are the insulating layer 23. On the other side of the insulating layer 23, which is present on one side, the source electrode 15 and the comb-shaped electrode 1 of the common electrode wiring which interlock with each other.
6a is present. Therefore, the gate electrode wiring 1
0, the drain electrode wiring 14 and other bus lines and the source electrode 15 and the common electrode wiring comb-shaped electrode 16a are arranged on different planes, and the source electrode 15 and the common electrode wiring are comb-shaped on the bus line. Even if the electrode 16a is covered with each part, no short circuit occurs.
Therefore, the electrode area used for display can be made larger than that of the conventional active element substrate having a structure in which the bus line and the comb-shaped electrode are arranged on the same plane. That is, the aperture ratio in the horizontal direction can be improved.

Further, in the liquid crystal display element of the present embodiment, it is possible to provide a display with contrast even without the transparent electrodes which are arranged oppositely, which is conventionally required. Therefore, the manufacturing cost can be reduced because all the steps related to the formation of the transparent electrode can be omitted. Furthermore, in the conventional display method in which transparent electrodes are arranged opposite to each other, a dark state is obtained by raising the major axis of liquid crystal molecules from the substrate interface by applying a voltage and setting the birefringence phase difference to 0. The viewing angle direction in which the phase difference becomes 0 is only the front direction, that is, the direction perpendicular to the substrate interface, and the birefringence phase difference appears when it is slightly inclined. Therefore, in the normally white type display, there is a problem that light leaks and the contrast is lowered, and the contrast change is opposite to the potential change and the contrast is inverted depending on the gradation level. However, in the liquid crystal display element of the present embodiment, the long axis of the liquid crystal molecules is substantially parallel to the substrate and does not rise even when a voltage is applied, and therefore the change in brightness when changing the viewing angle direction is small, This has the effect of significantly improving the viewing angle characteristics.

Further, since the overlapping portion of the source electrode 15 and the common electrode 16 acts as an additional capacitance connected in parallel with the liquid crystal capacitance, the ability to hold the liquid crystal applied voltage can be improved.

Since the present invention adopts a structure in which the common electrode wiring 16, the gate electrode wiring 10, and the drain electrode wiring 14 are separated from the source electrode 15 and the comb-shaped portion 16a of the common electrode by the insulating layer 23, The degree of freedom in designing the plane pattern of each electrode sandwiching the insulating layer 23 is increased, and the electrode shape is not limited to this embodiment, and various structures can be adopted.

(Embodiment 2) In Embodiment 2, as shown in FIG. 5, a comb-shaped portion 1 of a common electrode for displaying is provided.
This is a case where the shape of the insulating layer 23 for separating the 6a and the source electrode 15 from the TFT 7 and the gate electrode wiring 10 has an uneven structure.

In the second embodiment, as shown in FIG. 5, an insulating layer is formed in a concavo-convex structure along the direction in which the comb-shaped portions 16a of the common electrode and the comb teeth of the source electrode 15 are arranged. Then, the comb-shaped portions of the common electrode 16a and the comb-shaped teeth of the source electrode 15 are alternately located on each convex portion of the insulating layer, and the comb-shaped portions of the common electrode are arranged so that the comb teeth face each other. 16a and the source electrode 15 are formed. Note that the insulating layer 23 having a concavo-convex structure is formed simultaneously with the manufacturing process of the insulating layer 23 in Embodiment 1, that is, when the insulating layer 23 is patterned by a resist or when a contact hole is formed in the insulating layer 23. You can Further, when the pattern formation of the insulating layer 23 and the formation of the contact hole are performed at the same time, it may be performed at the same time.

With this structure, the two comb-shaped electrodes are arranged on the slopes of the convex portions, so that the aperture ratio when the liquid crystal display element is observed from above the substrate is increased. That is, the aperture ratio can be improved by utilizing the vertical direction. Further, as shown in FIG. 6, the extent to which the electric lines of force indicated by broken lines run in the direction perpendicular to the substrate is reduced, and the black level is improved. This will be explained in more detail below. In the case where the source electrode and the comb-shaped portion of the common electrode are on the same plane as in the first embodiment, light leakage occurs on the comb-shaped electrode because it occurs on the comb-shaped electrode in the direction perpendicular to the substrate surface. (When the polarizing plate is parallel Nicole)
Occurs and the contrast deteriorates. On the other hand, in the case of the present embodiment, since the vertical component of the lines of electric force is reduced,
It is possible to prevent the liquid crystal molecules from moving in the horizontal direction and the contrast from being deteriorated.

The uneven structure as described above may be the structure shown in FIG. That is, each convex portion is formed in a trapezoidal shape,
It is also possible to separate the two on the trapezoidal convex portions so that the comb teeth of the common electrode 16 a and the comb teeth of the source electrode 15 are arranged.

When the insulating layer has a concavo-convex structure as in the second embodiment, the liquid crystal layer above the convex portion has a slow response because electric lines of force do not reach sufficiently, so that the thickness of the liquid crystal layer is small. It is preferably 5 times or less the height of the convex portion.

The driving method and substrate material applicable to the present invention will be described below.

(Driving Method) As a driving method applicable to the present invention, a driving method such as active driving of a three-terminal element such as TFT and a two-terminal element such as MIM can be applied.
In particular, amorphous Si and low or high temperature p-Si
Various transistors can be used in which the semiconductor layer is made of a material that has been conventionally used.

(Substrate Material) As the substrate material, a transparent solid that transmits visible light may be used, and a glass, quartz, plastic substrate or the like may be used.

[0041]

As described above in detail, in the case of the present invention, the electrode structure is three-dimensionally configured in the horizontal electric field driving type liquid crystal display mode, so that the aperture ratio is high and the viewing angle characteristics are high. It is possible to provide an excellent liquid crystal display element that can be manufactured at low cost.

[Brief description of drawings]

FIG. 1 is a plan view (when a voltage is OFF) showing a liquid crystal display element according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view (when the voltage is OFF) showing the liquid crystal display element according to the first embodiment of the present invention.

FIG. 3 is a plan view (at the time of voltage ON) showing the liquid crystal display element according to the first embodiment of the present invention.

FIG. 4 is a cross-sectional view (at voltage ON) showing the liquid crystal display element according to the first embodiment of the present invention.

FIG. 5 is a cross-sectional view showing an active matrix substrate of a liquid crystal display element of Embodiment 2 of the present invention.

FIG. 6 is a schematic diagram showing lines of electric force when a voltage is applied in the second embodiment of the present invention.

FIG. 7 is a cross-sectional view showing another active matrix substrate in the liquid crystal display element of Embodiment 2 of the present invention.

[Explanation of symbols]

 1, 2 Glass substrate 3 Liquid crystal layer 4 Liquid crystal molecule 5, 6 Contact hole 7 TFT 10 Gate electrode wiring (scanning line) 14 Drain electrode wiring (signal line) 15a Source part 15 Source electrode (first comb-shaped electrode) 16a Common Comb-shaped part of electrode (second comb-shaped electrode) 16 Common electrode wiring (common electrode) 20 Gate insulating film 23 Insulating film 30 Amorphous silicon (a-Si) film

Claims (3)

[Claims] 1. A scanning line, a signal line, a switching element connected to the scanning line and the signal line, and a common electrode are present on one side of the insulating layer, and are on the other side of the insulating layer, and are connected to each other. There is a first comb-shaped electrode and a second comb-shaped electrode that occlude,
Moreover, the output terminal of the switching element and the first comb-shaped electrode are connected by a contact hole provided in the insulating layer, and the common electrode and the second comb-shaped electrode are connected to the insulating layer. A first substrate connected by a second contact hole provided in the first substrate, and a second substrate disposed opposite to the first substrate with a liquid crystal layer interposed therebetween. A liquid crystal display element in which a lateral electric field is applied to a liquid crystal layer by the first comb-shaped electrode and the second comb-shaped electrode. 2. The liquid crystal display element according to claim 1, wherein the insulating layer is formed of a resist material. 3. The insulating layer is formed into a concavo-convex structure having line-shaped convex portions, and both side surfaces of the convex portions are sloped surfaces, and at least the sloped surface of the first comb-shaped electrode is formed. The liquid crystal display device according to claim 1, wherein the comb teeth and the comb teeth of the second comb-shaped electrode face each other.