JP2003195331A - Active matrix type display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the alignment deviation problem between a first substrate and a second substrate. <P>SOLUTION: In an active matrix type display device in which liquid crystal 200 is sealed between the first substrate 100 and the second substrate 500 and a thin film transistor (TFT 11) is provided in each pixel, this device is provided with the TFT 11, a reflection electrode 74C which is formed with an insulator layer covering over the pertinent TFT 11 and is connected to the TFT 11, a color filter 54A which is formed on the pertinent reflection electrode 74C and a transparent electrode 55 which is formed on the pertinent color filter 54 at the side of the first substrate 100. <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 an active matrix type display device having a thin film transistor in each pixel.

[0002]

2. Description of the Related Art A flat panel display such as a general reflection type active matrix type display device (hereinafter, abbreviated as reflection type LCD) is capable of thinning, downsizing and weight saving and low power consumption. Etc. have already been adopted as a display unit of various devices for many devices including portable information devices. An LCD or the like in which each pixel is provided with a thin film transistor or the like as a switching element is called an active matrix type, and since this panel surely maintains the display content of each pixel, high definition display and high display It is used as a display device for realizing quality.

FIG. 5 shows an equivalent circuit for pixels of an active matrix LCD. Each pixel includes a thin film transistor 11 (TFT) connected to a gate line and a data line, and when the TFT is turned on by a selection signal output to the gate line, data corresponding to display contents is output from the data line through the TFT. Liquid crystal capacity 1
2 (Clc). Here, since it is necessary to surely hold the written display data from the time when the TFT is selected and the data is written to the time when the TFT is selected again, it is necessary to securely hold the written display data to the TFT.
An auxiliary capacitor 13 (Csc) is connected in parallel with c.

FIG. 6 shows a planar structure of a pixel portion on a TFT formation substrate (first substrate 100) of a conventional LCD, and FIG. 7 shows the LCD at a position along line XX of FIG.
The cross-sectional structure of is shown. The LCD has a structure in which liquid crystal is sealed between the first and second substrates. In the active matrix LCD, the T-shaped matrix is formed on the first substrate 100.
The FT 11, the pixel electrode 74, etc. are arranged, and the first substrate 100
The common voltage Vcom is applied to the second substrate 500, which is disposed opposite to
The common electrode 56 to which is applied, the color filter 54, and the like are formed. Then, each pixel electrode 74 and the liquid crystal 20
The liquid crystal capacitance Clc is driven for each pixel by a voltage applied between the common electrode 56 and the common electrode 56 that face each other with 0 interposed therebetween. BM is a black matrix area.

As shown in FIG. 7, the TFT provided on the first substrate 100 side for each pixel has a so-called top gate type TF in which the gate electrode 60 is located above the active layer 64.
T. The active layer 64 of the TFT is shown on the substrate 100 in FIG.
A gate insulating layer 66 is formed so as to cover the active layer 64, and a gate line which also serves as the gate electrode 60 is formed on the gate insulating layer 66. The active layer 64 has a channel region at a position facing the gate electrode 60, and the drain region 64d and the source region 6 in which impurities are implanted on both sides of the channel region.
4s are formed.

The drain region 64d of the active layer 64 is connected to the drain electrode 70 which also serves as a data line, through a contact hole formed in the interlayer insulating layer 68 which covers the gate electrode 60.

A flattening insulating layer 72 is formed so as to cover the data lines and the drain electrode 70, and the source region 64s of the active layer 64 has ITO (Indium Tin Oxide) on the flattening insulating layer 72. Pixel electrode 7 composed of etc.
4 is connected via a contact hole.

The source region 64s of the active layer 64 further includes
It also serves as the first electrode 80 of the auxiliary capacitance Csc provided in each pixel, and further extends from the contact region with the pixel electrode 74, as shown in FIG. Second auxiliary capacitance Csc
The electrode 84 is simultaneously formed in the same layer as the gate electrode 60 as shown in FIG. 7, and is formed in another region with a predetermined gap from the gate electrode 60. The gate insulating layer 66 also serves as a dielectric between the first electrode 80 and the second electrode 84. In addition, the second electrode 84 of the auxiliary capacitance Csc is
As shown in FIG. 6, each pixel is not independent, extends in the row direction in the pixel region like the gate line 60, and a predetermined auxiliary capacitance voltage Vsc is applied.

By providing the auxiliary capacitance Csc in each pixel in this way, during the non-selection period of the TFT, the auxiliary capacitance Csc holds the charge corresponding to the display content to be applied to the liquid crystal capacitance Clc. Therefore, it is possible to suppress the potential variation of the pixel electrode 74 and retain the display content.

[0010]

However, in the reflective LCD structure described above, the TFT 11 is provided on the first substrate 100 side, and the color filter 54 is formed on the second substrate 500 side facing the first substrate 100. Has been done.

Here, the first substrate 100 and the second substrate 500.
There was a slight misalignment (about ± 3 μm) between and. However, no conventional product has such a size that such misalignment poses a problem. Therefore, conventionally, the color filter 54A is formed on the upper substrate (second substrate 500) side that is easy to process.

However, when the size is reduced to, for example, a size smaller than 5 inches, the above-mentioned misalignment becomes a problem.

[0013]

In view of the above problems, an active matrix type display device of the present invention has a liquid crystal sealed between a first substrate and a second substrate and each pixel is provided with a thin film transistor. A thin film transistor on the first substrate side, a reflective electrode formed via an insulating layer covering the thin film transistor, connected to the thin film transistor, a color filter formed on the reflective electrode, and formed on the color filter. And a transparent electrode that is formed.

Further, the present invention is characterized in that the transparent electrode on the color filter is in an electrically floating state.

Further, a capacitance is generated between the reflective electrode and the transparent electrode, and the potential of the reflective electrode is varied, so that the potential of the transparent electrode can be varied.

Further, the capacitance is set to be 5 times or more the liquid crystal capacitance.

Furthermore, it is characterized in that the capacitance is set to 10 times or more the liquid crystal capacitance.

With such a structure, in the present invention, the reflective LCD is used.
In the above, by disposing the color filter on the side of the first substrate, it is possible to prevent the occurrence of a problem due to misalignment in the step of attaching the first substrate and the second substrate.

Then, the reflective electrode under the color filter and the thin film transistor are contact-connected, the transparent electrode (pixel electrode) on the color filter is electrically floated, and the transparent electrode and the reflective electrode are capacitively coupled to each other. Since it is possible to vary the voltage of, for example, as compared with the one in which a contact hole is formed in the reflective electrode and the transparent electrode and the thin film transistor are contact-connected, there is no contact hole penetrating the color filter, and therefore a higher aperture is achieved. It can be rationalized.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a reflection type active matrix display device of the present invention will be described below with reference to the drawings.

(First Embodiment) The first embodiment will be described in detail below.

FIG. 1 shows a reflection type active matrix type display device (hereinafter referred to as reflection type LC) according to a first embodiment of the present invention.
The sectional structure of D) is shown. The same components as those of the conventional configuration are designated by the same reference numerals to simplify the description.

The LCD includes a liquid crystal 2 between a first substrate 100 and a second substrate 500 made of a transparent insulating material such as glass.
It is configured by laminating together 00.

Here, the equivalent circuit of each pixel is the same as that of FIG. 5, and each pixel is provided with a thin film transistor 11 (TFT) connected to a gate line and a data line, and is selected by a selection signal output to the gate line. When the TFT is turned on, data corresponding to the display content is supplied from the data line to the liquid crystal capacitor (Clc) through the TFT. Here, since it is necessary to reliably hold the written display data during a period from when the TFT is selected and data is written to when the TFT is again selected,
An auxiliary capacitance (Csc) is connected in parallel with the liquid crystal capacitance Clc.

FIG. 1A shows an LCD according to this embodiment.
The cross-sectional structure of is shown. The LCD has a structure in which a liquid crystal 200 is sealed between a first substrate 100 and a second substrate 500, and a TFT provided for each pixel on the first substrate 100 side.
Is a so-called top gate type TF in which the gate electrode 60 is located above the active layer 64, as shown in FIG.
T. The active layer 64 of the TFT is shown on the substrate 100 in FIG.
This active layer 64 is patterned as shown in FIG.
And a gate insulating layer 66 is formed to cover the gate insulating layer 6
A gate line that also serves as the gate electrode 60 is formed on the gate electrode 6. The active layer 64 has a channel region at a position facing the gate electrode 60, and a drain region 64d and a source region 64s in which impurities are implanted are formed on both sides of the channel region.

The drain region 64d of the active layer 64 is connected to the drain electrode 70 which also serves as a data line, through a contact hole formed in the interlayer insulating layer 68 which covers the gate electrode 60.

A flattening insulating layer 72 is formed so as to cover the data lines and the drain electrode 70, and the source region 64s of the active layer 64 has a reflective electrode made of Al or the like on the flattening insulating layer 72. A (pixel electrode) 74A is formed.

Further, an insulating layer is formed so as to cover the reflective electrode 74A, and the color filter 54A is formed on the insulating layer.
Are formed.

Here, the feature of the first embodiment of the present invention is that a transparent electrode (pixel electrode) 55 is formed on the color filter 54A, and a reflection formed under the transparent electrode 55 and the color filter 54A. The electrode 74A and the TF
That is, the connection was made through a contact hole common to T11.

When the color filter 54A is arranged on the side of the first substrate 100 as described above, the reflective electrode 7 for reflecting light is provided.
4A must be below the color filter 54A, and the reflective electrode 74A formed below the color filter 54A increases the distance to the liquid crystal 200.
The driving ability due to is reduced, and in the worst case, it may not be possible to drive.

Therefore, in the present invention, the transparent electrode 55 connected to the reflective electrode 74A is arranged on the color filter 54A. In addition, the TFT 11 (source region 64
s) is connected to the TFT 11 through a contact hole 55A of the transparent electrode 55 and a common contact hole. The contact hole is formed so as to penetrate through the reflective electrode 74A, the color filter 54A, the transparent electrode 55 and the insulating layer at one time in one step, and the TFT 11 is formed.
Connected to. Although not shown in the drawings, the TFT 11 and the reflective electrode 74A are connected to each other through a first contact hole, and the reflective electrode 74A and the transparent electrode 55 are connected through a second contact hole.
It is also possible to connect and to contact with each other, but in this case, the number of manufacturing steps is further increased.

Here, FIG. 1B shows the reflective electrode 74.
It is a figure which shows the state which carried out the contact connection of A and the said transparent electrode 55, the outer dimensions of the said reflective electrode 74A and the said transparent electrode 55 are substantially equal, and the contact hole dimension is the same.

Since the contact hole 55A connects the transparent electrode 55 and the TFT 11, the reflective electrode does not exist. Therefore, a light shielding plate (not shown) may be provided.

Then, an insulating layer is formed so as to cover the transparent electrode 55, and the liquid crystal 200 is sealed with the first substrate 100 and the second substrate 500 facing the first substrate 100. Formed reflective LCD.

The common voltage Vcom is applied to the second substrate 500.
A common electrode 56 composed of an ITO electrode to which is applied is formed. The common electrode 5 that faces each pixel electrode (the reflective electrode 74A and the transparent electrode 55) with the liquid crystal 200 interposed therebetween.
The liquid crystal capacitance Clc is set for each pixel by the voltage applied between
To drive.

With the above structure, in the reflective LCD of the first embodiment, the color filter 54A is arranged on the side of the first substrate, so that the misalignment in the step of attaching the first substrate and the second substrate is misaligned. It is possible to suppress the occurrence of a problem due to, and it becomes possible to drive with high accuracy.

Further, on the color filter 54A,
By disposing the transparent electrode 55 commonly connected to the TFT 11 and the reflective electrode 74A, the liquid crystal capacitance Clc can be reliably formed between the TFT 11 and the common electrode 56 formed on the second substrate side.

(Second Embodiment) A second embodiment of the present invention will be described with reference to the drawings. The same components as those in the first embodiment are designated by the same reference numerals to simplify the description.

Here, the feature of the second embodiment is that the configuration in which the color filter 54A is arranged on the first substrate 100 side is the same as that of the first embodiment, but in the present embodiment,
That is, the TFT 11 and the transparent electrode 55 are connected to each other without contacting the reflective electrode 74B.

That is, as shown in FIG. 2A, the reflective electrode 74B below the color filter 54A is connected in the row direction, and a predetermined voltage (Vcom voltage) is applied and fixed to a constant voltage. As a result, the reflective electrode 74B and the transparent electrode 55 form an auxiliary capacitance C1 (= Csc). An auxiliary capacitance electrode 64t integrated with the active layer of the TFT 11 (continuous with the source region 64s) may be provided below the reflective electrode 74B to serve as the auxiliary capacitance C2.

With the above structure, in the reflective LCD of the second embodiment, the entire reflective electrode can be used as the auxiliary capacitance, so that even if the pixel size is small, the entire liquid crystal capacitance can be reliably ensured. it can.

Here, FIG. 2B shows the reflective electrode 74.
FIG. 6B is a diagram showing a state in which B and the transparent electrode 55 are contact-connected to each other, and the outer dimensions of the reflective electrode 74B and the transparent electrode 55 are substantially equal to each other, and the transparent electrode is formed through a contact hole 55C formed in the reflective electrode 74B. The contact portion 55B of 55 is contact-connected to the TFT 11 (source region 64s). In the present embodiment, as shown in FIG. 2, the first electrode 80 and the second electrode 84 forming the auxiliary capacitance Csc made of a polysilicon film are omitted, but they may be installed in the same manner as in FIG. Absent. In this case, by increasing the number of layers, the capacity can be increased.

(Third Embodiment) Further, a third embodiment of the present invention will be described with reference to the drawings. The same components as those in the first and second embodiments are designated by the same reference numerals to simplify the description.

The feature of the third embodiment is that the color filter 54 is provided on the first substrate 100 side as shown in FIG.
The arrangement of A is similar to that of the first and second embodiments, but in this embodiment, the TFT 11
That is, the (source region 64s) and the reflective electrode 74C are contact-connected. FIG. 4 is an equivalent circuit of FIG.

That is, as shown in FIG. 3, the reflective electrode 74C below the color filter 54A and the TFT 11 are contact-connected, and the transparent electrode 55 on the color filter 54A is connected.
Are not connected to other electrodes and are electrically floating. The voltage of the transparent electrode 55 is changed by capacitive coupling between the transparent electrode 55 and the reflective electrode 74C.

Here, the capacitance C3 between the reflective electrode 74C and the transparent electrode 55 is the capacitance C between the transparent electrode 55 and the common electrode 56.
It is desirable to be sufficiently larger than lc. If the capacitance C3 is small, it becomes necessary to amplify the voltage applied to the transparent electrode 55. For example, when the capacitance C3 is set to 5 times or more of the liquid crystal capacitance Clc (5Clc≤C3), the drive IC used for a normal LCD can be used as it is.

Further, when the capacitance C3 is set to be 10 times or more of the liquid crystal capacitance Clc (10Clc≤C3), it can be diverted without changing the operating voltage of the drive IC, which is more convenient.

In order to increase the capacitance C3, the concentration of the adhesive contained in the color filter 54 is increased to 1 μm or less, more preferably 0.5 μm or less. Further, it is also effective to use a gelatin material having a higher dielectric constant as the material of the color filter 54, instead of acrylic material.

With the above structure, in the reflective LCD of the third embodiment, the contact hole (region that does not contribute to display) penetrating the color filter 54A is formed as in the first and second embodiments. Since it does not exist, a higher aperture ratio can be achieved.

In this embodiment, the distance between the reflective electrode 74C and the transparent electrode 55 should be as short as possible. Therefore,
It is advisable to omit the insulating film on the reflective electrode 74C and dispose the color filter 54A directly on the reflective electrode 74C. Further, at this time, it is desirable to use an acrylic resin for the color filter in terms of surface flatness and insulation.

[0051]

According to the present invention, in the reflective LCD, the color filter is arranged on the first substrate side,
It is possible to prevent the occurrence of problems due to misalignment in the step of bonding the first substrate and the second substrate, and it is possible to drive with high accuracy.

Then, the reflective electrode under the color filter and the thin film transistor are contact-connected, the transparent electrode (pixel electrode) on the color filter is brought into an electrically floating state, and the transparent electrode and the reflective electrode are capacitively coupled to each other. Since it is possible to vary the voltage of, for example, as compared with the one in which a contact hole is formed in the reflective electrode and the transparent electrode and the thin film transistor are contact-connected, there is no contact hole penetrating the color filter, and therefore a higher aperture is achieved. It can be rationalized.

[Brief description of drawings]

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

FIG. 2 is a sectional view showing a configuration of an active matrix type display device according to a second embodiment of the present invention.

FIG. 3 is a sectional view showing a configuration of an active matrix type display device according to a third embodiment of the present invention.

FIG. 4 is a diagram showing an equivalent circuit per pixel of an active matrix type liquid crystal display device according to a third embodiment of the present invention.

FIG. 5 is a diagram showing an equivalent circuit per pixel of a conventional active matrix type liquid crystal display device.

FIG. 6 is a diagram showing a schematic planar structure of a pixel region in a conventional active matrix type liquid crystal display device.

7 is a diagram showing a schematic cross-sectional structure of the liquid crystal display device at a position along line XX in FIG.

[Explanation of symbols]

11 thin film transistor (TFT), 54A color filter, 55 transparent electrode, 55A contact part, 55
B contact part, 56 common electrode, 64t auxiliary capacitance electrode, 74A reflective electrode, 74B reflective electrode, 74C
Reflective electrode, 100 first substrate, 200 liquid crystal, 500 second substrate

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2H091 FA02Y GA02 KA10 LA12                 2H092 GA17 GA29 HA04 HA05 JA24                       JB69 NA27 PA08

Claims (5)

[Claims] 1. An active matrix display device in which a liquid crystal is sealed between a first substrate and a second substrate and a thin film transistor is provided in each pixel, wherein a thin film transistor is provided on the first substrate side and an insulating layer covering the thin film transistor. And a color filter formed on the reflective electrode, and a transparent electrode formed on the color filter. Display device. 2. The active matrix type display device according to claim 1, wherein the transparent electrode on the color filter is in an electrically floating state. 3. A capacitance is generated between the reflection electrode and the transparent electrode, and the potential of the reflection electrode is changed,
The active matrix display device according to claim 2, wherein the potential of the transparent electrode is variable. 4. The active matrix type display device according to claim 3, wherein the capacitance is set to 5 times or more the liquid crystal capacitance. 5. The active matrix type display device according to claim 3, wherein the capacitance is set to be 10 times or more the liquid crystal capacitance.