JPH07325322A - Thin-film transistor liquid crystal display device - Google Patents

Abstract

PURPOSE:To easily obtain a thin-film transistor(TFT) liquid crystal display device with which a wider visual field angle is obtainable by composing control capacitors of conductor patterns and pixel electrodes formed simultaneously with source and drain electrodes forming TFTs. CONSTITUTION:Insulating film layers of a silicon oxide film and silicon nitride film on transparent electrodes 2a are bored with contact holes 7 to expose part of the transparent electrodes 2a. The source electrodes 8a, drain electrodes 8b and additive capacitance electrodes 8c are simultaneously formed by using metals, such as aluminum. At this time, the drain electrodes 8b on the transparent electrodes 2a are so formed that the drain electrodes 8b and the transparent electrodes 2a are connected. On the other hand, the control capacitors 12 are formed between the drain electrodes 8b on the transparent electrodes 2b and the transparent electrodes 2b. Similarly, the additive capacitance electrodes 8c and the transparent electrodes 2a are so formed as to be connected via the contact holes 7 so that the additive capacitors 13 are formed between the gate electrodes 4 and the additive capacitance electrodes 8c of the previous stage.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a thin film transistor (T
The present invention relates to a liquid crystal display device driven by an FT) array substrate, and to a configuration for improving the viewing angle characteristics thereof.

[0002]

2. Description of the Related Art One pixel is divided into a plurality of sub-pixels, and a voltage applied to a liquid crystal layer of each sub-pixel is changed so that a good multi-gradation display can be performed with a wide viewing angle and a viewing angle characteristic can be improved. As a technology (conventional technology called pixel division method),
JP-A-61-166590 "Liquid crystal display element and driving method thereof", JP-A-62-182717 "Liquid crystal display device", or JP-A 2-12 "Pixel of liquid crystal display device and pixel of liquid crystal display device" There is a method of realizing gray scale ".

FIG. 7 shows a conventional normally white mode, that is, polarized lights arranged in front of and behind a liquid crystal display device so as to be in a bright state when no voltage is applied to the liquid crystal layer and in a dark state when a voltage is applied. 7 shows the luminance characteristic of the TFT liquid crystal display device in a mode in which the polarization axis of the plate is set, with respect to the driving voltage of the liquid crystal display device. FIG. 7 (a) shows the luminance characteristics with respect to the driving voltage when viewed from directly in front of the liquid crystal display device, and FIG. 7 (b) shows the driving voltage when the viewpoint is tilted downward 30 ° from the liquid crystal display device. Is a luminance characteristic with respect to.

FIG. 8 is a schematic view showing a viewpoint when measuring the viewing angle characteristics of the liquid crystal display device. The downward direction in FIG. 7 means that two liquid crystals are transparent as shown in FIG. 8 (a). FIG. 8B of the liquid crystal molecule 10a of each glass substrate sandwiched between the glass substrates 1a and 1b and viewed from the vertical direction of the glass substrates 1a and 1b.
When the orientation directions 21a and 21b shown in FIG.
FIG. 8 (a) (2) is a cross-sectional view of (b) taken along the line aa '.
A voltage is applied between the glass substrates 1a and 1b,
(Showing the one when 10a started up)
It is defined as when the viewpoint E is tilted to the right. Further, the angle here indicates the tilt angle θ of the viewpoint E from the perpendicular of the glass substrate 1b.

In the conventional liquid crystal display device as shown in FIG. 7 (a), when displaying 8 gradations, first of all, it is directly in front (0 °).
The brightness is divided into 8 equal parts (B1, B2, ………, B8),
Voltage level (V1, V2, ...) for each brightness level
..., V8) is set.

On the other hand, when the viewpoint is tilted downward by 30 ° as shown in FIG. 7 (b), the driving voltage-luminance characteristic is on the low voltage side as compared with the direct front (0 °) of FIG. 7 (a). With the shift
A new peak appears on the high voltage side. In this state, the brightness level (B1 ', B2', ..., B for each voltage level
Looking at 8 '), the difference between the brightness levels becomes large in the high brightness part (between B1' and B2 ', etc.), while the difference between the brightness levels becomes small in the low brightness part.

This is visually seen as a very dark image as compared with an image viewed from the front (called a blackout phenomenon). Furthermore, the brightness levels of B6 'and B7' are reversed by the new peak. This is called a gradation inversion phenomenon, and it looks like a negative image of a photograph by visual observation. As described above, in the conventional liquid crystal display device, there is a problem that gradation display is considerably deteriorated when the viewpoint is tilted downward.

Next, FIG. 9 shows a luminance characteristic with respect to a driving voltage of a liquid crystal display device by the pixel division method, and FIG. 11 is an equivalent circuit of a sectional configuration diagram of the TFT liquid crystal display device shown in FIG. As shown in FIG. 11, the pixel is divided into two sub-pixels 11a and 11b, and the sub-pixel (Clc1) 11a is directly
The drain electrode (D) of the TFT 14 is connected. on the other hand,
A control capacitor (Cc) 12 is connected to the drain electrode (D) in series with the sub-pixel (Clc2) 11b. Also, additional capacity (Cst)
13 is also connected to the drain electrode (D). As a result, the driving voltage (Vd) supplied from the TFT 14 is
The same voltage value is supplied to 1a, but in the sub-pixel 11b, part of the drive voltage is divided into the control capacitor (Cc) 12.
That is, the drive voltages Vlc1 and Vlc2 supplied to the sub-pixels 11a and 11b are

[0009]

[Formula 1] Vlc1 = Vd

[0010]

## EQU2 ## Vlc2 = Vd × Cc / (Clc2 + Cc) As a result, Vlc1> Vlc2.

As a result, the drive voltage-luminance characteristic is the same as that of FIG. 7A in the sub-pixel 11a when the viewpoint shown in FIG. The driving voltage-luminance characteristic of the above shifts to the high voltage side as compared with the sub-pixel 11a. As a result, the driving voltage-luminance characteristics of all the pixels 11c are characteristics in which the two are combined, and the inclination is as shown in FIG.
Looser compared to (a).

On the other hand, when the viewpoint shown in FIG. 9 (b) is tilted downward by 30 °, the sub-pixel 11a has the same characteristics as in FIG. 7 (b), but the sub-pixel 11b shifts to the high voltage side. To do. Then, in any of the sub-pixels 11a and 11b, a new peak appears on the high voltage side. As a result, the combined driving voltage-luminance characteristics of all the pixels 11c have a gentler slope than that of FIG. 7B.

Here, since the voltage value for shifting the driving voltage-luminance characteristic to the low voltage side by tilting the viewpoint from 0 ° to 30 ° downward is the same as that in the case of FIG. It can be seen that the difference between the brightness levels is more uniform than the difference between the brightness levels at the viewpoint of 30 ° in the configuration of the liquid crystal display device without the pixel division configuration. As a result, the conventionally observed blackout phenomenon is mitigated. Further, the peak on the high voltage side in the downward direction of 30 ° is a smooth characteristic in which the peaks of the respective sub-pixels cancel each other, and the characteristics of all pixels monotonically decrease. This eliminates the conventionally observed gradation inversion phenomenon. As described above, in the pixel division structure, the gradation effect is considerably improved in the downward viewpoint by these two effects as compared with the liquid crystal display device which is not the pixel division structure.

Next, a liquid crystal display device driven by thin film transistors will be described. 12 is a plan view of a conventional TFT liquid crystal display device, FIG. 13 is a sectional view of one pixel of the TFT liquid crystal display device taken along the line aa 'in FIG. 12, and FIG. 14 is a schematic view of the TFT liquid crystal display device of FIG. It is an equivalent circuit of one pixel.

A gate wiring group extends in the X direction and a source wiring group extends in the Y direction shown in FIG. The TFT 14 and the transparent electrode 2 connected to the TFT 14 exist at each intersection of the gate wiring and the source wiring. The TFT 14 functions as a switch element, and the transparent electrode 2 functions as a pixel electrode that drives liquid crystal molecules on the transparent electrode 2.

A TFT 14 on the gate wiring is turned on by a pulse signal sequentially applied to each gate wiring from the driving IC connected to the gate wiring end (Gn) shown in FIG. Then, the video signal supplied from the driving IC connected to the gate line end (Gn) through the source line end (S) is supplied to each transparent electrode (pixel electrode) 2 through the TFT 14 in the ON state. Further, the additional capacitor 13 is connected in parallel with the pixel 11. This additional capacitance 13 is
It is for improving the holding characteristic of the video signal supplied to the.

Next, an outline of the manufacturing process of the TFT array substrate having the inverted stagger structure will be described with reference to FIGS. First, the pixel 1 is placed on the transparent glass substrate 1a shown in FIG.
A transparent electrode (pixel electrode) 2 for driving the liquid crystal 1 is formed.
Next, a silicon oxide film 3 is deposited as an insulator. Then, the gate electrode 4 is formed of a metal such as chromium. Then, a silicon nitride film 5 which functions as a gate insulating film of the TFT 14 is deposited thereon. Next, the semiconductor layer 6 that constitutes the TFT 14 is formed. The semiconductor layer 6 is the gate electrode 4
The resistance value changes depending on the voltage applied to the element, and the function as a switching element is given.

Next, a contact hole 7 is opened in the insulating film layer of the silicon oxide film 3 and the silicon nitride film 5 on the transparent electrode (pixel electrode) 2 to expose a part of the transparent electrode (pixel electrode) 2. Next, using a metal such as aluminum, the source electrode 8a, the drain electrode 8b, and the additional capacitance electrode 8c (see FIG. 12)
Are formed at the same time. At this time, the drain electrode 8b is formed so that the drain electrode 8b and the transparent electrode (pixel electrode) 2 are connected to each other through the contact hole 7 formed on the transparent electrode (pixel electrode) 2, and the contact is similarly formed. The additional capacitance electrode 8c and the transparent electrode (pixel electrode) 2 are formed so as to be connected via the hole 7. Through the above steps, the TFT array substrate is completed. After that, the TFT array substrate is
Another glass substrate 1 having a transparent electrode 9 deposited on one surface
b and a gap of about 5 μm are formed and bonded together, and the liquid crystal 10 is injected therebetween.

[0019]

The cross-sectional configuration diagram of the TFT liquid crystal display device shown in FIG. 10 which has been subjected to the above-described conventional pixel division method and the equivalent circuit of one pixel shown in FIG.
This is quoted from Japanese Patent No. 348323. TFT of this configuration
14 has a staggered structure in which the gate electrode 4a is in the uppermost layer as shown in FIG. With this staggered TFT, 2
a is a drain electrode, also serves as an electrode of the subpixel 11a, 2b serves as an electrode of the subpixel 11b, 2c serves as a source electrode, and 8 serves as a source wiring. Then, the semiconductor layer 6 is formed thereon, and the silicon nitride film 5 serving as a gate insulating film is further formed thereon, and then the gate electrode 4a is formed.

Further, as shown in FIG. 10, the pixel electrode is divided into the electrodes 2a and 2b of the two sub-pixels 11a and 11b. Two
The first conductor 32 is formed below the electrodes 2a and 2b of the two sub-pixels 11a and 11b, with the second insulating film 33 interposed therebetween so as to partially overlap with each other in plan view. The first conductor 32 is connected to the electrode 2a of the first subpixel 11a via the contact hole 34 of the second insulating film 33. Further, the control capacitor 12 for dividing the drive voltage is formed between the first conductor 32 and the electrode 2b of the second subpixel 11b. In addition, the first sub-pixel 11
On the electrode 2a of a, the conductor pattern 4b formed simultaneously with the gate electrode 4a is formed through the silicon nitride film 5 as the gate insulating film. Between the conductor pattern 4b and the electrode 2b of the second sub-pixel 11b, the additional capacitance 13 for holding the liquid crystal applied voltage is formed. Here, the member 30 formed on the back surface of the first insulating film 31 is the semiconductor layer 6 from the back surface.
It is an opaque light-shielding film for preventing the resistance of the TFT when it is turned off from being lowered by being exposed to light.

In this way, the TF which has been subjected to the conventional pixel division method
Compared with the conventional TFT liquid crystal display device, the T liquid crystal display device needs to newly form a first conductor 32 and a second insulating film 33 as shown in FIG. 10 in addition to the conventional structure. Then, there was a problem that the manufacturing cost was improved.

The present invention solves such a conventional problem and makes it possible to manufacture a thin film transistor liquid crystal display device having a pixel division structure capable of widening the viewing angle by the same simple steps as those for a liquid crystal display layer having a normal structure. The purpose is to

[0023]

In order to achieve the above object, the first object of the present invention is to arrange a plurality of thin film transistors having an inverted stagger structure and a plurality of pixel electrodes in a matrix on a substrate which is a member. In a thin film transistor liquid crystal display device having a control capacitance connected in series with a pixel capacitance in a part of the pixel electrodes of the plurality of pixel electrodes,
It is characterized in that the electrode forming the control capacitor is composed of a conductive pattern and a pixel electrode which are formed simultaneously with the source-drain electrodes forming the thin film transistor.

According to an embodiment of the present invention, one inverted staggered thin film transistor driving a pixel electrode divided into two or more is arranged in a matrix on a substrate which is a member. Part or all of the divided pixel electrodes have a control capacitance connected in series with the subpixel capacitance.

[0025]

The present invention provides a TFT liquid crystal display device having a plurality of TFTs having a reverse stagger structure and a plurality of pixel electrodes, and having a control capacitor connected in series with a pixel capacitor in some of the pixel electrodes. At the time of fabrication, the control capacitance is formed by a conductive pattern and a pixel electrode that are formed at the same time as the source-drain electrodes forming the thin film transistor. body,
Alternatively, it is not necessary to form a new insulator, and the TFT liquid crystal display device can be manufactured at the same cost as the conventional one.

[0026]

FIG. 1 shows a TFT according to a first embodiment of the present invention.
2 is a plan configuration diagram of the liquid crystal display device, FIG. 2 is a sectional view of one pixel taken along line aa ′ in FIG. 1, and FIG. 3 is an equivalent circuit diagram of the TFT liquid crystal display device of FIG.

1 to 3, the same components as those of the conventional example shown in FIGS. 7 to 14 are designated by the same reference numerals.

The structure and manufacturing process of the TFT liquid crystal display device according to this embodiment will be described below with reference to FIGS.

First, on the transparent glass substrate 1a shown in FIG. 2, transparent electrodes 2a and 2b for driving the liquid crystal of the sub-pixels 11a and 11b.
To form. Next, a silicon oxide film 3 is deposited as an insulating film. Then, the gate electrode 4 is formed of a metal such as chromium. Then, a silicon nitride film 5 which functions as a gate insulating film of the TFT 14 is deposited thereon. Next, TFT14
The semiconductor layer 6 constituting the is formed. This semiconductor layer 6 is
The resistance value changes according to the voltage applied to the gate electrode 4, and the function as a switch element is given.

Next, a contact hole 7 is formed in the insulating film layer of the silicon oxide film 3 and the silicon nitride film 5 on the transparent electrode 2a.
Is opened to expose a part of the transparent electrode 2. Next, the source electrode 8a, the drain electrode 8b, and the additional capacitance electrode 8c (see FIG. 1) are simultaneously formed using a metal such as aluminum. At this time, the drain electrode 8b on the transparent electrode 2a is formed so that the drain electrode 8b and the transparent electrode 2a are connected via the contact hole 7 opened on the transparent electrode 2a.

On the other hand, the drain electrode 8b on the transparent electrode 2b
The control capacitance 12 is formed between the transparent electrode 2b and the transparent electrode 2b. Similarly, the additional capacitance electrode 8 is also provided through the contact hole 7.
It is formed so that c and the transparent electrode 2a are connected to each other so that the additional capacitance 13 is formed between the gate electrode 4 and the additional capacitance electrode 8c in the preceding stage. Through the above steps, the TFT array substrate is completed. Then, the glass substrate 1a is attached to the transparent electrode 9
Another transparent glass substrate 1b on which is deposited one surface
Then, a gap of about 5 μm is formed and the substrates are bonded together, and the liquid crystal 10 is injected therebetween.

As shown in the equivalent circuit of FIG. 3, the sub-pixel 11a
The driving voltage (Vd) supplied from the TFT 14 is directly supplied to the liquid crystal layer. On the other hand, the sub-pixel 11b has a TFT 14
Between the drain electrode 8b and the transparent electrode 2b of the control capacitor (Cc) 1
2 is formed, and this is connected in series with the capacitance (Clc2) of the subpixel 11b. Therefore, the drive voltage supplied from the TFT 14 is divided into the control capacitance 12 and the capacitance (Clc2) of the subpixel 11b. A lower voltage is applied to the liquid crystal of the sub-pixel 11b than the liquid crystal of the sub-pixel 11a. If this is expressed by an equation,

[0033]

[Formula 3] Vlc1 = Vd

[0034]

## EQU4 ## Vlc2 = Vd × (Cc / (Clc2 + Cc)) As a result, Vlc2 <Vlc1.

As described above, the pixel division structure is formed, and as described above, good gradation display is obtained from the downward viewpoint and the viewing angle characteristic is improved.

When the area ratio of the transparent electrodes 2a and 2b is set to about 6: 4 and the capacity ratio of the control capacitor 12 and the sub-pixel 11b is set to about 4: 6, a sufficiently wide viewing angle characteristic is obtained. can get.

With the above-described structure, it is not necessary to form a new conductor or a new insulator to form the control capacitor 12, and the pixel division structure of wide viewing angle can be obtained at the same cost as the conventional one. The TFT liquid crystal display device can be manufactured.

FIG. 4 shows the TF in the second embodiment of the present invention.
FIG. 5 is a plan configuration diagram of the T liquid crystal display device, FIG. 5 is a sectional view of one pixel taken along line aa ′ in FIG. 4, and FIG. 6 is an equivalent circuit diagram of the TFT liquid crystal display device in FIG.

Explaining the difference between this embodiment and the first embodiment, the structure of this embodiment is different from that of the first embodiment.
Source-drain electrodes 8a, 8b and additional capacitance electrode 8c
Simultaneously with the formation, the control capacitance electrode 8d is formed. The manufacturing process of this TFT liquid crystal display device is the same as that of the first embodiment. Control capacitors 12a and 12b are formed between the control capacitor electrode 8d and the transparent electrodes 2a and 2b, respectively.

As shown in the equivalent circuit of FIG. 6, the sub-pixel 11a
The driving voltage (Vd) supplied from the TFT 14 is directly supplied to the liquid crystal layer. On the other hand, the sub-pixel 11b has a TFT 14
Control capacitance (Cc) between the drain electrode (D) and the transparent electrode 2b of
Is formed, and this is connected in series with the capacitance (Clc2) of the sub-pixel 11b, the drive voltage supplied from the TFT 14 is divided into the control capacitances 12a and 12b and the pixel capacitance, and the sub-pixel 11b has A voltage lower than that of the sub-pixel 11a is applied. If this is expressed by an equation,

[0041]

[Equation 5] Vlc1 = Vd

[0042]

## EQU6 ## Vlc2 = Vd × (Cc / (Clc2 + Cc)) Here, Cc = 1 / ((1 / Cc1) + (1 / Cc2)) As a result, Vlc2 <Vlc1.

As a result, it is not necessary to form a new conductor or a new insulator to form the control capacitor, and it is possible to manufacture the TFT liquid crystal display device at the same cost as the conventional one.

In the embodiment of the present invention, the case where the pixel is divided into two sub-pixels has been described, but the present invention can be adopted not only in this configuration but also in a configuration in which it is divided into three or more.

[0045]

As described above, in the TFT liquid crystal display device of the present invention, the control capacitor is composed of the conductor pattern and the pixel electrode formed at the same time as the source-drain electrodes forming the TFT, or the thin film transistor is formed. Since the control capacitance is formed by using the conductor pattern and the pixel electrode that are formed at the same time as the gate electrode to be formed, the same process and cost can be achieved without forming a new conductor or insulator as in the conventional case. It is possible to provide a TFT liquid crystal display device having a wide viewing angle.

[Brief description of drawings]

FIG. 1 is a plan configuration diagram of a TFT liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of one pixel taken along the line aa ′ in FIG.

FIG. 3 is an equivalent circuit diagram of one pixel of the TFT liquid crystal display device of FIG.

FIG. 4 is a plan configuration diagram of a TFT liquid crystal display device according to a second embodiment of the present invention.

5 is a cross-sectional view of one pixel taken along the line aa ′ in FIG.

6 is an equivalent circuit diagram of one pixel of the TFT liquid crystal display device of FIG.

FIG. 7 is a luminance characteristic diagram with respect to a drive voltage when observed at each angle of θ = 0 ° and θ = 30 ° in a conventional normally white mode TFT liquid crystal display device.

FIG. 8 is a schematic diagram showing a viewpoint when measuring a viewing angle characteristic of a liquid crystal display device.

FIG. 9 is a luminance characteristic diagram with respect to a driving voltage of the liquid crystal display device when observed at each angle of θ = 0 ° and θ = 30 ° by the pixel division method.

FIG. 10 is a cross-sectional view of a conventional TFT liquid crystal display device having a pixel division structure.

11 is an equivalent circuit diagram of one pixel of the TFT liquid crystal display device having the pixel division structure of FIG.

FIG. 12 is a plan configuration diagram of a conventional TFT liquid crystal display device.

FIG. 13 is a cross-sectional view of one pixel of the TFT liquid crystal display device taken along the line aa ′ in FIG.

14 is an equivalent circuit diagram of one pixel of the TFT liquid crystal display device of FIG.

[Explanation of symbols]

1a, 1b ... glass substrate, 2, 2b, 9 ... transparent electrode,
2a ... transparent electrode (drain electrode), 2c ... source electrode,
3 ... Silicon oxide film, 4, 4a ... Gate electrode, 4b ... Conductor pattern, 5 ... Silicon nitride film, 6 ... Semiconductor layer, 7, 34 ... Contact hole, 8 ... Source wiring,
8a ... Source electrode, 8b ... Drain electrode, 8c ... Additional capacitance electrode, 8d ... Control capacitance electrode, 10 ... Liquid crystal, 10a
... Liquid crystal molecule, 11 ... Pixel, 11a, 11b ... Sub-pixel, 11c
... All pixels, 12 ... Control capacitance, 13 ... Additional capacitance, 14 ... Thin film transistor (TFT), 21a, 21b ... Alignment direction of liquid crystal molecules, 30 ... Shading film, 31 ... First insulating film, 32 ... First
Conductor, 33 ... Second insulating film.

Claims (3)

[Claims] 1. A plurality of thin film transistors having an inverted stagger structure and a plurality of pixel electrodes are arranged in a matrix on a substrate which is a member, and a pixel capacitance is provided in a part of the pixel electrodes of the plurality of pixel electrodes. In a thin film transistor liquid crystal display device having a control capacitor connected in series with the control capacitor, an electrode forming the control capacitor is composed of a conductor pattern and a pixel electrode formed at the same time as a source-drain electrode forming the thin film transistor. A thin film transistor liquid crystal display device characterized in that 2. A thin film transistor having an inverse stagger structure for driving pixel electrodes divided into two or more is arranged in a matrix on a substrate which is a member, and the thin film transistors among the pixel electrodes divided into two or more are arranged. 2. The thin film transistor liquid crystal display device according to claim 1, wherein some or all of the subpixel electrodes have a control capacitance connected in series with the subpixel capacitance. 3. A source that constitutes a part of the control capacitor
2. The thin film transistor liquid crystal display device according to claim 1, wherein a conductor pattern formed at the same time as the drain electrode is connected to a drain electrode forming a part of the thin film transistor.