JP2003255392A - Reflection type liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve problems in a reflection type LCD (liquid crystal display) that, when a reflection display electrode of the LCD is flat, light is reflected in a fixed direction and hence the viewing angle cannot be broadened and, moreover, that a TFT (thin film transistor) and the reflection display electrode comes in contact at a single spot and hence contact failures are brought about in the LCD. <P>SOLUTION: In this reflection type liquid crystal display, a plurality of contact parts of the reflection display electrode and the TFT for driving a pixel are provided almost over the whole surface of the reflection display electrode. As a result, since the surface of the display electrode is made to have an uneven cross-sectional shape, incoming light is reflected to many directions to broaden the viewing angle. Moreover, contact failures are reduced and pixels are prevented from becoming defective. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflective liquid crystal display device using a thin film transistor (hereinafter referred to as "TFT") as a switching element and having a reflective display electrode connected to the TFT. .

[0002]

2. Description of the Related Art Liquid crystal display devices are classified into a transmissive type in which light from the back surface is transmitted and displayed, and a reflective type in which light incident from the viewer side is reflected by a reflective display electrode for display.

In the following, regarding the conventional display device, the TFT
An example of a reflective liquid crystal display device provided with will be described. FIG. 5 shows a plan view in the vicinity of a display pixel region of a conventional reflective liquid crystal display device. A plurality of gate signal lines 151 arranged in the row direction,
TFTs are provided near the intersections with the drain signal lines 152 arranged in the column direction. TFT is the active layer 1
13 and the gate electrode 111. Gate electrode 1
11 is integrally connected to a part of the gate signal line 151,
A gate signal is supplied via the gate signal line 151.
The drain 113d of the active layer 113 is the drain signal line 1
A drain signal, which is a video signal, is supplied to the drain electrode 116, which is a part of the reference numeral 52, via a contact and a drain signal line 152. Source 11 of active layer
3s is connected to the reflective display electrode 120 via the contact CT.

FIG. 6 shows a sectional view taken along the line CC in FIG. On an insulating substrate 110 made of quartz glass, alkali-free glass or the like, an active layer 113 made of an island-shaped polycrystalline silicon film, a gate insulating film 112 made of a SiN film and a SiO2 film, and a refractory metal such as Cr or Mo. A gate electrode 111 made of is sequentially formed. The active layer 113 is provided with a channel 113c below the gate electrode 111, and a source 113s and a drain 113d formed by ion implantation on both sides of the channel 113c. The above is the configuration of the TFT.

Then, the gate insulating film 112 and the active layer 11 are formed.
An interlayer insulating film 115 in which a SiO2 film, a SiN film, and a SiO2 film are laminated is formed on the entire surface of 3. The drain 11 is formed in the contact hole provided in the interlayer insulating film 115.
Al alone or Mo and Al at the position corresponding to 3d
A drain electrode 11 formed by filling a metal in which
6, the drain signal line 152 is formed. Then, a flattening insulating film 119 made of, for example, an organic resin is formed on the entire surface. A contact hole CT is formed at a position corresponding to the source 113s of the planarization insulating film 119 and the interlayer insulating film 115.
And a reflective display electrode 120 made of a reflective conductive material such as Al is connected to the source 113s. An alignment film 121 that aligns the liquid crystal 136 is formed thereon. In FIG. 5, the reflective display electrode 120 is shown by a dotted line for easy understanding, but the position where it is formed is the upper layer of the planarization insulating film 119 as shown in FIG. The above is the configuration of the insulating substrate 110 including the TFT.

A counter electrode substrate 130 is arranged opposite to the insulating substrate 110. The counter electrode substrate 130 is provided with a color filter 131 showing each color such as red (R), green (G), and blue (B), a counter electrode 132, and an alignment film 133 on the side where the liquid crystal 136 is arranged, and on the opposite side. A retardation plate 134 and a polarizing plate 135 are provided on the substrate 130.

The insulative substrate 110 and the counter electrode substrate 130 are adhered to each other by a seal adhesive (not shown) around the periphery, and the formed voids are filled with the liquid crystal 136 to complete the liquid crystal display device.

In FIG. 6, the natural light 101 incident from the outside is incident from the retardation plate 135 on the side of the observer 100, as shown by the arrow, and the polarizing plate 134 and the counter electrode substrate 13 are provided.
0, color filter 131, counter electrode 132, alignment film 1
33, liquid crystal 136, alignment film 121 on the TFT substrate 110
Is reflected by the reflective display electrode 120 and again emitted from the phase difference plate 135 on the counter electrode substrate 130.
Enter the 0s.

[0009]

By the way, in the case of the conventional liquid crystal display device, since the reflective display electrode is flat, the reflected light is also emitted at a certain angle. It has the drawback of narrowing the viewing angle.

Since it is necessary to make the opening of the pixel large, the p-Si of the TFT is made as small as possible, and the pixel electrode and T
There was one contact CT with the FT in one pixel.
For this reason, there is a problem that contact defects are likely to occur due to dust, misalignment of the mask during the manufacturing process, and the number of pixel defects increases.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems. First, a plurality of gate signal lines and a plurality of drain signal lines are arranged on an insulating substrate so as to intersect each other. A display device comprising a thin film transistor connected to both signal lines and a reflective display electrode connected to the thin film transistor and made of a reflective material, wherein a plurality of contacts between the reflective display electrode and the thin film transistor are provided, and the reflective display electrode is provided. This is solved by making the surface uneven.

In the reflective liquid crystal display device having the above structure, the entire surface of the pixel electrode can be used, unlike the transmissive liquid crystal display device in which the light from the illuminating device provided under the substrate is transmitted through the transparent electrode for observation. . That is, increasing the number of contacts and increasing the contact area does not affect the aperture ratio. Since the reflective display electrode is in contact with the semiconductor layer, the position of the contact is recessed and the surface has an uneven shape. By providing a plurality of these contacts, a plurality of concavities and convexities can be provided, and the incident angle can be reflected in multiple directions, and the range in which the display of the reflective liquid crystal display device can be observed, that is, the viewing angle can be widened. Since the unevenness is formed at the same time when the contact is formed, a separate process for forming the unevenness is unnecessary, and a reflective liquid crystal display device having a wide viewing angle can be manufactured at low cost. Further, since the number of contacts increases, there is a feature that contact defects can be reduced.

The contact is provided over substantially the entire surface of the reflective display electrode.

Thus, light can be reflected uniformly in each direction.

A semiconductor layer forming the thin film transistor is provided on substantially the entire surface below the reflective display electrode.

Further, the reflective display electrode and the semiconductor layer are in contact with each other through a pad provided in the same layer as the drain signal line.

Further, the reflective display electrode and the semiconductor layer are in contact with each other through a pad provided in the same layer as the gate signal line.

By appropriately selecting the layer forming the pad, the depth of the unevenness of the reflective display electrode can be appropriately set, and it is possible to prevent the optical path difference of the light from being remarkably different between the apex and the bottom of the unevenness. Display can be realized.

[0019]

DETAILED DESCRIPTION OF THE INVENTION A reflective liquid crystal display device according to a first embodiment of the present invention will be described below. FIG. 1 is a plan view showing the vicinity of a display pixel area of a reflective liquid crystal display device of the present invention. A plurality of gate signal lines 51 arranged in the row direction,
TFTs are provided near the intersections with the drain signal lines 52 arranged in the column direction. The TFT has an active layer 13
And a gate electrode 11. The gate electrode 11 is integrally connected to a part of the gate signal line 51, and a gate signal is supplied via the gate signal line 51. The drain 13d of the active layer 13 is connected to the drain electrode 16 which is a part of the drain signal line 52 through a contact, and the drain signal which is a video signal is supplied through the drain signal line 52. The source 13s of the active layer is connected to the reflective display electrode 20 via the contact 17.

The characteristic point of this embodiment is that the active layer 13 of the TFT connected to the reflective display electrode 20, especially the source 13s.
Lies almost all under the reflective display electrode 20, and a large number of contact holes 17 between the reflective display electrode and the TFT are provided. Since a large number of contact holes 17 are arranged over almost the entire surface of the reflective display electrode 20, even if one contact has poor conduction due to dust or the like, if the other contact is good, the TFT and the reflective display electrode are The conduction of 20 does not disappear. Therefore, contact defects can be reduced and pixel defects can be significantly reduced. The surface of the reflective display electrode on the contact hole 17 has an uneven shape, and the incident light can be reflected in multiple directions, and a wide viewing angle can be obtained. In this embodiment, as shown in the drawing, circular contact holes are arranged in a matrix. Further, as will be described later in detail, the opening width (diameter in the present embodiment) of the contact hole in the minor axis direction is formed to be twice the film thickness of the reflective display electrode or more.

FIG. 2 shows a sectional view taken along the line AA in FIG. On an insulating substrate 10 made of quartz glass, alkali-free glass or the like, an active layer 13 made of an island-shaped polycrystalline silicon film, a gate insulating film 1 made of a SiN film and a SiO2 film.
2, and a gate electrode 11 made of a refractory metal such as Cr or Mo is sequentially formed. The active layer 13 is provided with a channel 13c below the gate electrode 11 and a source 13s and a drain 13d formed by ion implantation on both sides of the channel 13c. The above is the configuration of the TFT.

An inter-layer insulating film 15 is formed on the entire surface of the gate insulating film 12 and the active layer 13 by laminating a SiO2 film, a SiN film and a SiO2 film. A drain electrode 16 and a drain signal line 52 are formed in the contact hole provided in the interlayer insulating film 15 at a position corresponding to the drain 13d by filling Al alone or a metal in which Mo and Al are sequentially stacked. Then, a flattening insulating film 19 made of, for example, an organic resin is formed on the entire surface. A contact hole 17 is provided at a position corresponding to the source 13s of the flattening insulating film 19 and the interlayer insulating film 15, and a reflective display electrode 20 made of a reflective conductive material such as Al is connected to the source 13s. An alignment film 21 for aligning the liquid crystal 36 is formed thereon. In FIG. 1, the reflective display electrode 20 is shown by a dotted line for easy understanding, but the position where it is formed is the upper layer of the flattening insulating film 19 as shown in FIG. The above is the insulating substrate 1 provided with the TFT
0 configuration.

Referring to FIG. 2B, the counter electrode substrate 30 is arranged to face the insulating substrate 10. Counter electrode substrate 30
Is provided with a color filter 31, a counter electrode 32, and an alignment film 33, each of which has a color of red (R), green (G), blue (B), etc., on the side where the liquid crystal 36 is arranged, and on the opposite side of the substrate 30. Includes a retardation plate 34 and a polarizing plate 35.

The periphery of the insulating substrate 10 and the counter electrode substrate 30 are adhered by a seal adhesive (not shown), and the formed voids are filled with liquid crystal 36 to complete the liquid crystal display device.

Natural light 101 incident from the outside is shown in FIG.
As indicated by an arrow in (b), the light enters from the polarizing plate 35 on the observer 100 side, and the retardation plate 34, the counter electrode substrate 30, the color filter 31, the counter electrode 32, the alignment film 33, and the liquid crystal 3 are incident.
6. It passes through the alignment film 21 on the TFT substrate 10 and reaches the reflective display electrode made of a reflective material and having an uneven shape.
The reached light is reflected by the reflective display electrode. The unevenness of the reflective electrode scatters the direction of reflection and expands the viewing angle. In the case of a reflective liquid crystal display device, incident light 101 is reflected by the reflective display electrode 20 from the observer 100 side, and pixels are displayed by the reflected light 102.
Even if many contacts are provided, the aperture ratio is not affected at all.

Next, a method of forming the contact 17 will be described. If the contacts 17 of this embodiment are formed simultaneously in the same step, the contact hole forming step can be completed in one time as in the conventional case. Also, the plurality of contact holes may be formed, for example, twice. By forming the contact holes separately, the risk of occurrence of defects in the forming process is dispersed, and the merit of improving the yield is increased. In this case, if the contact holes in the odd columns are first formed and the contact holes in the even columns are formed by shifting the same mask, the contact holes can be formed by the same mask. In this case, the contact and the counter electrode pad (electrode connecting the glass substrate 10 on the TFT side and the counter electrode substrate 30: not shown) and the external circuit connecting terminal (glass substrate 10) are formed simultaneously with this mask. And a terminal for connecting an external control circuit to an FPC (Flexible Printed Circuit): not shown) is preferable. The counter electrode pad and the external circuit connection terminal have a size of, for example, about 200 μm. On the other hand, since the contact hole is several μm to several tens of μm at the most, even if the mask is displaced by about one row of the contact hole, there is no great trouble in forming the counter electrode pad and the external circuit connecting terminal.

The contact hole 17 is formed so that its opening width in the minor axis direction (inner diameter in this embodiment) is at least twice the film thickness of the reflective display electrode 20. As a result, the reflective display electrode 20 is not embedded in the contact hole, but the reflective display electrode is formed so as to cover the inner wall of the contact hole in a shape along the inner wall of the contact hole, and the surface thereof has an uneven shape. In order to make the unevenness gentle, the inner diameter of the contact hole is set to the reflective display electrode 2.
It is preferable to secure a film thickness of 0 or more, which is 3 times or more, preferably 5 times or more.

The contact hole may be formed by wet etching, and the inner wall of the contact hole may be tapered as gently as possible. For example, flattening film 1
A mask is formed on 9, and the flattening film 19 is wet-etched for the first time, and then the interlayer insulating film 15 and the gate insulating film 12 are wet-etched for the second time. If the etchant for the second wet etching is selected to have a small selection ratio to the flattening film 19, and the inner wall of the flattening film 19 is slightly etched at the same time as the insulating film 15 and the gate insulating film 12, a gentle taper shape is obtained. You can do it.

Here, the structure itself for widening the viewing angle by making the surface of the reflective display electrode uneven is a conventionally known structure, but according to the present invention, the reflective display electrode is provided by providing a large number of contacts. The unevenness of is realized. Conventionally, the flattening film under the reflective display electrode is etched to form the uneven shape of the reflective display electrode. In this case, since the etching depths for forming the contact hole of the reflective display electrode and for forming the concavo-convex shape are different, a photoetching step is separately required. However, according to the present invention, since the contact formation and the concavo-convex formation can be performed in one photo-etching step using a normal planarization film, the manufacturing process can be simplified.

Next, a reflective liquid crystal display device according to the second embodiment of the present invention will be described. FIG. 3 shows a plan view of the vicinity of the display pixel area of this embodiment. FIG. 3A is a plan view, and FIG. 3B is a sectional view taken along line BB. The same components as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted. The characteristic point of this embodiment is the planar shape of the contact hole. In this embodiment, the elongated contact holes 18 are formed over substantially the entire surface of the reflective display electrode 20, and are arranged side by side in the column direction. The contact hole 18c at the center is a rectangle long in the column direction (even if it is a rectangle, the corners are rounded if it is actually formed as a contact hole by design), and the contact holes 18s arranged on both sides of the contact hole 18c are spread outward. Is bent to. The bending angle of the contact hole 18s is larger as it is arranged outside. By bending in this way, the contact holes, and by extension, the sloping surface of the unevenness of the surface of the reflective display electrode, face in various directions, so that, for example, in comparison with arranging all parallel linear contact holes in parallel, , A wider viewing angle can be obtained.

The contact hole is provided over almost the entire surface of the reflective display electrode in order to prevent the deviation of the reflected light, and the contact hole is not buried by the reflective display electrode so that the surface of the reflective display electrode becomes uneven. Once formed, any shape and arrangement is feasible.

The arrangement of the contact holes is not limited to the above-described first and second embodiments, and various patterns may be used. For example, it may be arranged randomly in each pixel, but since it is a contact with the reflective display electrode, it must be formed in at least the same area in each pixel.

Next, a third embodiment of the present application will be described. FIG. 4 is a sectional view of this embodiment. The plan view of this embodiment is the same as FIG. 1A or FIG. The characteristic point of this embodiment is that the reflective display electrode 20 and the active layer 1 are
The pad 40 is disposed between the reflective display electrode 20 and the active layer 13 and the pad 40 is disposed between the reflective display electrode 20 and the active layer 13. When the reflective display electrode is formed so as to cover the contact hole, if the unevenness is too deep, the optical path difference (difference in the distance from the light entering the liquid crystal to the light exiting) between the top and bottom of the unevenness becomes large. In this embodiment, by inserting the pad 40, an excessive optical path difference is eliminated and a good display is performed. Of course, if the interlayer insulating film 15 and the planarizing film 19 are sufficiently thin and the optical path difference does not matter, the pad 40 need not be provided. If the pad 40 is provided in the same layer as the existing conductive layer such as the drain electrode 16 or the gate electrode 11, it is not necessary to increase the number of additional manufacturing steps. The layer to be the same layer may be determined according to the depth of the unevenness formed on the reflective electrode surface. If the lower conductive layer and the pad 40 are formed in the same layer, the contact 17 (18) becomes deeper, so that the irregularities on the surface of the reflective display electrode 20 also become deeper. The unevenness is
As described above, if the depth is too deep, the optical path difference becomes excessive, and if it is too shallow, the effect of widening the viewing angle becomes difficult to be obtained. When the planarization insulating film 19 is 2000 Å or more and 4000 Å or less, the pad 40 is on the interlayer insulating film 19, that is, the drain electrode 1.
It is preferable to form the same layer as 6. The planarization insulating film 19 is 200
When it is less than 0 Å, the pad 40 is preferably provided on the interlayer insulating film 15, that is, in the same layer as the gate electrode 11. of course,
The material of the pad 40 need not be the same as that of the drain electrode 16 and the gate electrode 11, and may be any other conductive material such as metal or polysilicon into which impurities are introduced.

Although the auxiliary capacitor is not shown in the embodiment of the present application, it goes without saying that the auxiliary capacitor may be arranged if necessary. At this time, the auxiliary capacitance may be formed in the same layer as the gate electrode 11 and the contact may be arranged while avoiding the portion, or the auxiliary capacitance may be arranged in a mesh shape between the contacts 17 shown in FIG. good. Further, a conductive layer may be arranged between the active layer 13 and the substrate 10.

[0035]

As described above, according to the present invention,
Since a plurality of contacts for electrically connecting the reflective display electrode and the thin film transistor are provided, even if one contact is defective in conduction due to dust or the like, if the other contact is good, the TFT and the reflective display electrode can be connected. There is no loss of continuity. Therefore, contact defects can be reduced and pixel defects can be significantly reduced. In addition, the surface of the reflective display electrode on the contact hole 17 has an uneven shape, so that incident light can be reflected in multiple directions, and a wide viewing angle can be obtained. In particular, since it is a reflective display device, the entire surface of the pixel electrode can be used, unlike a transmissive liquid crystal display device in which light from an illumination device provided below the substrate is transmitted through a transparent electrode for observation. That is, increasing the number of contacts and increasing the contact area does not affect the aperture ratio.

Further, since the contact is provided over almost the entire surface of the reflective display electrode, the reflected light is uniformly reflected in various directions, and good viewing angle characteristics can be obtained.

Further, since the reflective display electrode and the semiconductor layer are electrically connected via the pad, the depth of the unevenness on the surface of the reflective display electrode can be made the optimum depth from the viewpoint of the optical path difference and the widening of the viewing angle. The quality can be improved.

If the side wall of the contact hole is tapered, it can be reflected in more directions.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of the present invention.

FIG. 2 is a sectional view showing an embodiment of the present invention.

FIG. 3 is a plan view showing an embodiment of the present invention, and FIG.
FIG.

FIG. 4 is a cross-sectional view showing an embodiment of the present invention.

FIG. 5 is a plan view illustrating a conventional technique.

FIG. 6 is a cross-sectional view illustrating a conventional technique.

[Explanation of symbols]

10 Insulating substrate 11 Gate electrode 13 Active layer 13s source 13d drain 13c channel 15 Interlayer insulation film 17 contact holes 19 Flattening insulation film 20 reflective display electrode 36 LCD 100 observer 101 incident light 102 reflected light

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takeo Yoshimura             2-5-3 Keihan Hondori, Moriguchi City, Osaka Prefecture             Within Yo Denki Co., Ltd. F term (reference) 2H091 FA14Y FB08 FD02 GA01                       GA02 LA19 LA30                 2H092 GA17 GA29 GA30 HA05 JA24                       JB07 JB56 MA13 MA17 NA01                       NA12 NA13                 5F110 AA26 AA30 BB01 CC02 DD02                       DD03 EE04 FF02 FF03 GG02                       GG13 HJ13 HL03 HL04 HL08                       HL11 HL14 HM12 HM18 HM20                       NN03 NN23 NN24 NN27 NN72

Claims (5)

[Claims] 1. A plurality of thin film transistors connected to the gate signal line and the drain signal line, wherein a plurality of gate signal lines and a plurality of drain signal lines intersect with each other on an insulating substrate, and the thin film transistors. A reflective liquid crystal display device comprising: a reflective display electrode made of a reflective material and connected to a plurality of contacts for electrically connecting the reflective display electrode and the thin film transistor, the reflective display electrode surface being formed by the contact. A reflective liquid crystal display device having an uneven shape. 2. The reflective liquid crystal display device according to claim 1, wherein the contact is provided over substantially the entire surface of the reflective display electrode. 3. The reflective liquid crystal display device according to claim 2, wherein a semiconductor layer forming the thin film transistor is provided on substantially the entire surface below the reflective display electrode. 4. The reflective display electrode and the semiconductor layer are
2. The reflection type liquid crystal display device according to claim 1, wherein the reflection type liquid crystal display device is electrically connected through a pad made of a conductor to form the unevenness of the surface of the reflection display electrode shallowly. 5. The reflective liquid crystal display device according to claim 4, wherein the pad is provided in the same layer as the drain signal line or the gate signal line.