JP2000147462A - Active matrix type liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the brightness of a display screen by specifying an angle to be formed by long axial directions of liquid crystal molecules in the intermediate layer of a liquid crystal layer and the boundary line between subpixels to prevent the generation of slipping offs of lights of the boundary part between the subpixels and to raise an opening ratio. SOLUTION: This active matrix type liquid crystal display device holds a liquid crystal layer between two sheets of insulated substrates placed opposite to each other and has plural pixels arranged in a matrix shape and each pixel is constituted of subpixels of at least two or more and a voltage control means impressing voltages whose magnitudes are different with each other is formed in each pixel. When the angle to be formed by the long axial directions of the liquid crystal melecules in the intermediate layer of liquid crystal layer and the boundary line between the subpixels is defined as ϕ, the ϕ does not include 0 deg. and the upper limit value of the ϕ is made to be 30 deg. so that the disturbance of the arrangement of the liquid molecules becomes small even when the arrangement of the liquid molecules of this part is affected by the inclined longitudinal electric field of the boundary part of the electrodes of the subpixels.

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 liquid crystal display device which can be used as a flat display of AV / OA equipment.

[0002]

2. Description of the Related Art At present, display devices using liquid crystals have been applied in various fields such as viewfinders of video cameras, pocket TVs, and information display terminals such as high-definition projection TVs, personal computers, and word processors. Active development and commercialization. Among them, a typical one is an active matrix type liquid crystal display element, which has attracted much attention because it can realize colorization and high image quality. The structure is such that a switching element is provided for each of the pixel electrodes arranged on the matrix, and an electric signal for controlling the optical characteristics of the liquid crystal is independently supplied to each pixel electrode via the switching elements. As a switching element, an element using a thin film transistor (TFT) is mainly used. This active matrix type has the major feature that high contrast is maintained even when a large-capacity display is performed. In particular, in recent years, the market demand has been extremely high, such as laptop computers, notebook computers, and even engineering workstations. Developed and commercialized as the favorite of large-capacity, large-capacity full-color displays.

In such an active matrix type liquid crystal display device, a liquid crystal display mode widely used includes a TN (Twisted Nematic) type NW (Normally).
White) mode. In the TN mode, two panels having a structure in which liquid crystal molecules are twisted by 90 ° between substrates sandwiching a liquid crystal layer are used.
It is sandwiched between two polarizing plates. In the NW mode, the two polarizing plates are arranged so that their polarization axes are orthogonal to each other, and one of the polarizing plates is parallel or perpendicular to the long axis direction of the liquid crystal molecules in contact with one substrate. ing.
In this case, no voltage is applied, or white display is performed at a voltage lower than the threshold voltage, and when a higher voltage is applied,
The light transmittance gradually decreases, and the display becomes black. Such display characteristics are obtained because, when a voltage is applied to the liquid crystal panel, the liquid crystal molecules try to align in the direction of the electric field while untwisting the twisted structure. This is because the polarization state changes and the light transmittance is modulated. However, even in the same molecular alignment state, the polarization state of the transmitted light changes depending on the incident direction of the light incident on the liquid crystal panel, so that the light transmittance differs depending on the incident direction. That is, the characteristics of the liquid crystal panel have a viewing angle dependency. This viewing angle characteristic causes a luminance inversion phenomenon when the viewpoint is inclined obliquely to the main viewing angle direction (the major axis direction of the liquid crystal molecules in the intermediate layer of the liquid crystal layer). That is, in this display mode, a phenomenon in which the display luminance at a certain voltage becomes brighter than the luminance at a lower voltage, and in particular, the luminance reversal phenomenon when a high voltage is applied for a black display is caused by a liquid crystal panel. This is an important issue in terms of image quality.

In order to solve this problem, one pixel electrode is divided into a plurality of sub-pixels, and a voltage applied to a liquid crystal layer of each sub-pixel is changed by a control capacitor provided between the sub-pixels. There has been proposed a method (hereinafter, referred to as a pixel division method) for improving a viewing angle characteristic by displaying a good multi-tone display with a wide viewing angle. The principle of this pixel division method will be briefly described. FIG. 5 is an equivalent circuit of a typical pixel division configuration. As shown in the figure, the pixel is divided into two sub-pixels, and the drain electrode (D) of the TFT is directly connected to the sub-pixel 1 (Clc1). On the other hand, the drain electrode (D) is connected to the sub-pixel 2 (Clc2) via the control capacitor (Ccon). Accordingly, the same voltage value is supplied to the sub-pixel 1 as the driving voltage (Vd) supplied from the TFT,
In the sub-pixel 2, a part of the driving voltage is controlled by the control capacitance (Cco
n). That is, the driving voltages Vlc1 and Vlc2 supplied to the sub-pixel 1 and the sub-pixel 2 are Vlc1 = VdVlc2 = Vd * Ccon / (Cl
c2 + Ccon), and clearly, Vlc1> Vlc
2. Therefore, the driving voltage-luminance characteristic when the viewpoint is inclined by 30 ° in the main viewing angle direction is, as shown in FIG.
The characteristic of (1) causes luminance inversion similarly to the sub-pixel 1, but shifts to a higher voltage side as compared with the sub-pixel 1. As a result, the driving voltage-luminance characteristics of all the pixels are obtained by combining the characteristics of the two sub-pixels, and the conventionally observed luminance inversion phenomenon disappears. As described above, the pixel division method has a great effect of improving the viewing angle characteristics of the liquid crystal display device.

As an example of a liquid crystal display device using this pixel division method, Japanese Patent Application Laid-Open No. 5-289108, "Liquid Crystal Display Device and Manufacturing Method Thereof," is shown, and a plan view of a thin film transistor substrate used therein is shown in FIG. ), And the alternate long and short dash line b-
FIG. 7B is a cross-sectional view of the liquid crystal display device at b ′. The sub-pixel electrodes 2a, 2a correspond to the respective intersections of the plurality of scanning lines (gate lines) 16 and the plurality of signal lines (source lines) 17.
b and a thin film transistor (TFT) are formed.
A control capacitor 19 is provided between the sub-pixel electrodes 2a and 2b.
b and the control capacitor electrode 20. In FIG. B, reference numeral 4 denotes a first insulator layer, which functions as a gate insulating film. Reference numeral 6 denotes a second insulator layer. Then, in order to arrange the liquid crystal molecules in a predetermined direction, an alignment film is applied to the array substrate 1 and the opposite substrate 13 on which the transparent electrode film 11 and the light-shielding band 12 are laminated, and then a rubbing process is performed. The two substrates are bonded so as to keep a gap of several μm, and a liquid crystal is injected between them. Polarizing plates are attached one by one to the outside of both planes of the manufactured liquid crystal cell, and a backlight (light source) is arranged on one of the polarizing plates.

[0006]

However, the liquid crystal display element using this pixel division method has a problem that the response characteristics are deteriorated due to the difference in the division direction of the pixel electrode region. As an example, FIG. 8 shows a case where the major axis direction of the liquid crystal molecules of the liquid crystal intermediate layer and the direction of the boundary line between the sub-pixels are parallel to each other. 7A and 7B are a cross-sectional view and a plan view of a boundary portion between sub-pixel electrodes indicated by a dashed line cc ′ in the TFT substrate of FIG. 7, and show a state of liquid crystal molecules 18 in an intermediate layer of a liquid crystal layer. ing. FIG. 1 shows a white display, FIG. 4 shows a black display, and FIG.
FIG. 3C illustrates a transition state between white display and black display in order, and illustrates a state where the liquid crystal molecules 18 are arranged with respect to the electric field. As shown in FIG. 8A, in the case of white display, the liquid crystal molecules 18 in the intermediate layer are arranged at an angle (tilt angle) of several degrees with respect to the counter electrode 19. When the applied voltage is switched to black display, the tilt angle of the liquid crystal molecules 18 on the pixel electrode rises gradually due to the electric field between the sub-pixel electrodes 2 a and 2 b and the counter electrode 19. on the other hand,
As shown by the broken lines in FIG. 8- (2), the sub-pixel electrodes 2a, 2a
An oblique vertical electric field is generated at the boundary portion b, and the arrangement of the liquid crystal molecules 18 in this portion is affected. As a result, FIG.
The portions arranged along the oblique vertical electric field as in (2) and (3) have an arrangement opposite to that of the other portions, and at that boundary, light leakage occurs and the device shines white. However, due to the elastic influence of the surrounding normal sequence molecules, the reverse sequence domain disappears immediately as shown in FIG. As described above, even if the applied voltage is switched from white display to black display, there is a time lag until the display completely becomes black. For this reason, the response characteristic deteriorates, and the displayed image appears as an afterimage. In order to solve this, if the control capacitor electrode is formed using an opaque material, the portion between the sub-pixels is shielded from light, and the response characteristic is improved. However, there is a problem in that transmitted light decreases by the amount of the control capacitor electrode, that is, the aperture ratio (area ratio of the light transmitting portion in all pixels) decreases, and the display luminance decreases.

[0007]

In order to solve the above-mentioned problems, an active matrix type liquid crystal display device of the present invention has a liquid crystal layer sandwiched between two opposing insulating substrates and is arranged in a plurality of matrixes. Each pixel is composed of at least two or more sub-pixels, and each pixel has
Voltage control means for applying voltages of different magnitudes is formed. Even if the arrangement of liquid crystal molecules in this portion is affected by the oblique vertical electric field at the boundary between the sub-pixel electrodes, the arrangement of the liquid crystal molecules is affected. When the angle between the major axis direction of the liquid crystal molecules in the intermediate layer of the liquid crystal layer and the boundary line between the sub-pixels is φ so that the disturbance of φ is small, φ does not include 0 ° and the upper limit of φ The value is 30 °. In addition, all or some of the sub-pixels are connected in series with a liquid crystal capacitor formed by each sub-pixel,
By forming control capacitances of different sizes, it becomes voltage control means. The voltage control means is formed by forming control capacitors of different sizes between a control electrode to which a modulation signal is supplied and each of the sub-pixel electrodes.

As an example, as shown in FIG. 9, by setting the major axis direction of the liquid crystal molecules in the intermediate layer of the liquid crystal layer and the dividing direction of the sub-pixel electrode to be parallel (FIG. 9- (1)), The angle between the direction of the oblique vertical electric field generated between 2a and 2b and the counter electrode 19 and the major axis direction of the liquid crystal molecules 21 is 90 °. Therefore, even if the liquid crystal molecules are affected by the oblique vertical electric field as shown in FIGS.
Light leakage does not occur.

Accordingly, the present invention is able to drastically solve the above-mentioned problems of the liquid crystal display element, and aims to provide a liquid crystal display element having no display image and high display luminance.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments according to the present invention will be described in detail with reference to the drawings. FIG.
FIG. 1 is a schematic plan view of a TFT pixel portion of a thin film transistor array substrate used for a liquid crystal display element of a first reference example for explaining the present invention. FIG. 2B is a cross-sectional view of the liquid crystal display device taken along a dashed line aa ′ in FIG. In the first reference example, as shown in FIG. 1, the array substrate 1 is formed using ITO (InOx-SnOx) in which the sub-pixel electrodes 2a and 2b are deposited by a sputtering method.
Patterned on top. Here, the boundary line between the sub-pixel electrodes 2a and 2b is formed by a straight line in one predetermined direction. After the gate electrode 3a is formed using chromium, silicon nitride (Si) is used as the first insulator layer 4 serving as a gate insulating film of the TFT.
Nx) is laminated thereon. Next, amorphous silicon (α-Si) is laminated on the semiconductor layer 5 that controls the switching function of the TFT by a plasma CVD method. 6 is the second
It was an insulator layer and was patterned with silicon nitride (SiNx). Thereafter, the first insulator layer 4 and the semiconductor layer 5 are dry-etched to provide openings 7a and 7b, thereby exposing a part of the sub-pixel electrode 2a. Next, a source electrode 8a, a drain electrode 8b, a storage capacitor electrode 8d, and a control capacitor electrode 8 are formed using two layers of titanium / aluminum (Ti / Al) deposited by a sputtering method.
e is simultaneously patterned. At the same time, the semiconductor layer 5 is etched. At this time, through the opening 7a,
The sub-pixel electrode 2a and the drain electrode 8b are coupled, and the sub-pixel electrode 2a and the storage capacitor electrode 8d are similarly coupled via the opening 7b. Then, a control capacitor 9a is formed between the control capacitor electrode 8e and the sub-pixel electrode 2b, and a storage capacitor 10 is formed between the preceding gate electrode 3a and the storage capacitor electrode 8d. Note that the storage capacitor 10 is provided for maintaining characteristics of the voltage supplied to the pixel. An alignment film is applied to the thin film transistor array substrate thus completed, the opposite substrate 13 on which the transparent electrode film 11 and the light-shielding band 12 are laminated, and the long axis direction of the liquid crystal molecules of the liquid crystal intermediate layer and the boundary between the sub-pixels are aligned. A rubbing process is performed in the direction shown in the figure so that the rubbing process is parallel. Thereafter, a gap of about 5 μm is formed and bonded, and a liquid crystal is injected between them to manufacture a liquid crystal display element.

When the lighting image inspection of this liquid crystal display element was performed, no light leakage occurred at the boundary between the sub-pixels, and there was no need to provide a light-shielding band. Can be made.

Next, a first embodiment according to the present invention will be described with reference to the drawings. FIG. 2 is a schematic plan view of a TFT pixel portion of a thin film transistor array substrate used for the liquid crystal display device according to the first embodiment of the present invention. In the first embodiment, ITO (InOx−) in which the sub-pixel electrodes 2a and 2b are deposited by a sputtering method is used.
Using SnOx), a pattern was formed on the array substrate 1 in a shape as shown in FIG. Other manufacturing methods of the thin film transistor array substrate and the liquid crystal display element are exactly the same as those of the first embodiment. Here, the boundary line between the sub-pixels forms an angle of 30 ° with the long axis direction of the liquid crystal molecules of the liquid crystal intermediate layer.

When a lighting image inspection of this liquid crystal display element was performed, a high quality liquid crystal display element could be manufactured as in the reference example. When a liquid crystal display element was manufactured by changing the angle (φ) formed between the boundary between the sub-pixels and the major axis direction of the liquid crystal molecules in the liquid crystal intermediate layer, the light intensity was 0 ° ≦ φ ≦ 45 °. It was found that no omission occurred.

Next, a second embodiment according to the present invention will be described. FIG. 3 is a schematic plan view of a TFT pixel portion of a thin film transistor array substrate used for a liquid crystal display device of a second reference example. The method of manufacturing the thin film transistor array substrate and the liquid crystal display element is exactly the same as in the first reference example. However, the drain electrodes 8b and 8c and the control capacitance electrodes 8e and 8f are formed for the pixel electrodes 2a and 2b, respectively. This equivalent circuit is shown in FIG. The control capacitors (Cst1, Cst2) 9a and 9b are respectively pixel capacitors (Clc1, Cl1).
It is formed in parallel with c2) and is electrically connected to the (n-1) th scanning line 14. The parasitic capacitances (Cgd1, Cgd2) connected to the n-th scanning line 15 correspond to the drain electrodes 8b, 8g.
It is formed between the c-th and n-th scanning lines 15. Similarly, FIG. 4 shows signal waveforms applied to the (n-1) th and nth scanning lines. TFT on-potential Vgt, TFT off-potential Vg
b, four potentials of compensation potentials Vge (+) and Vge (-), and the compensation potentials Vge (+) and Vge (-) are applied alternately for each scanning line. Thereby, TF
The potential Vs of the pixel electrode at the moment when T is turned on is the potential change of the n-th scanning line 15 through the parasitic capacitance (Cgd) − (Vgt
-Vgb) * Cgd / (Cgd + Cst + Clc) and n via the storage capacity (Cst)
-1 potential change of scanning line 14+ (Vgb-Vge (-)) * Cgd / (Cgd + C
st + Clc). Therefore, the pixel voltage Vlc
Is V when the pixel electrode potential is higher than the counter potential Vcom.
Vlc (+) = Vs + [Cst * (Vgb-Vge (-))-Cgd * (Vgt-Vgb)] / Ctot-Vc
om Vlc (-) = Vs- [Cst * (Vge (+)-Vgb) + Cgd * (Vgbt-Vgb)] / Ctot-V
com. Here, Ctot = Cgd + Cst + Clc. Therefore, C
When st / Ctot or Cgd / Ctot is set to a different value for each sub-pixel, the liquid crystal application voltages Vlc1 and Vlc2 of the sub-pixels formed by the sub-pixel electrodes 2a and 2b can be set to different values.

For the second reference example, Cst1 and Cs1
This is made possible by the difference between t2 and Clc1 and Clc2. With the above configuration and driving method, the same effect as the pixel division method used in the first reference example and the first embodiment can be obtained.

With respect to the liquid crystal display device using this thin film transistor array substrate, when the angle (φ) formed between the boundary between the pixel electrodes 2a and 2b and the major axis direction of the liquid crystal molecules in the liquid crystal intermediate layer was changed, the angle was 0 °. It was found that light leakage did not occur in the range of ≦ φ ≦ 45 °, and a high-quality liquid crystal display element could be manufactured as in the first reference example.

The present invention can be employed not only in a configuration in which a pixel region is divided into two sub-pixels, but also in a configuration in which the pixel region is divided into three or more. In addition, the angle φ formed by the major axis direction of the liquid crystal molecules in the liquid crystal intermediate layer and not the entire boundary line between the subpixels and the major axis direction of the liquid crystal molecules in the liquid crystal intermediate layer does not include 0 °.
The present invention is effective if the upper limit of the angle is 30 °.

[0018]

As described above, the liquid crystal display device according to the present invention can be used in an active matrix type liquid crystal display device having a pixel division structure capable of realizing a wide viewing angle, with a simple structure and the same manufacturing process as in the prior art, in terms of image quality. It is possible to prevent light leakage at the boundary between the sub-pixels, which is a problem of the above, and it is not necessary to provide a light-shielding band at the boundary between the sub-pixels, so that the aperture ratio is increased and the brightness of the display screen is improved. can do.

[Brief description of the drawings]

FIG. 1A is a plan view showing a configuration of a thin film transistor substrate of a liquid crystal display element according to a first reference example of the present invention; FIG.

FIG. 2 is a plan view showing a configuration of a thin film transistor substrate of the liquid crystal display element according to Embodiment 1 of the present invention.

FIG. 3 is a plan view showing a configuration of a thin film transistor substrate of a liquid crystal display element according to a second reference example of the present invention.

FIG. 4 is an equivalent circuit diagram of a liquid crystal display element according to a second reference example of the present invention.

FIG. 5 is an equivalent circuit diagram of one pixel of a TFT liquid crystal display element subjected to a pixel division method.

FIG. 6 is a luminance-driving voltage characteristic diagram of the TFT liquid crystal display element subjected to the pixel division method when the viewpoint is inclined at 30 ° in the main viewing angle direction.

FIG. 7A is a plan view showing a configuration of a thin film transistor substrate of a conventional liquid crystal display element, and FIG.

FIG. 8A is a diagram illustrating a state of liquid crystal molecules in a liquid crystal intermediate layer when a driving voltage is applied, in a case where a major axis direction of liquid crystal molecules in the liquid crystal layer intermediate layer and a boundary line between sub-pixels are perpendicular to each other. 7 Cross-sectional view taken along dashed-dotted line cc '.

FIG. 9A is a cross-sectional view illustrating a state of the liquid crystal molecules of the liquid crystal intermediate layer when a driving voltage is applied when the major axis direction of the liquid crystal molecules of the liquid crystal layer intermediate layer and the boundary line of the sub-pixel are parallel. (B) is the same plan view

[Explanation of symbols]

 Reference Signs List 1 array substrate 2a pixel electrode 2b pixel electrode 3 gate electrode 4 first insulator layer 5 semiconductor layer 6 second insulator layer 7a opening 7b opening 8a source electrode 8b drain electrode 8c drain electrode 8d storage capacitor electrode 8e control capacitor electrode 8f Control capacitor electrode 9a Control capacitor 9b Control capacitor 10 Storage capacitor 11 Transparent electrode film 12 Shielding band 13 Counter substrate 14 n-1st scan line 15 nth scan line 16 Scan line (gate line) 17 Signal line (source line) 18 Liquid crystal molecules 19 Counter electrode

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Yoneharu Takubo 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] A liquid crystal layer is sandwiched between two opposing insulating substrates, and has a plurality of pixels arranged in a matrix. Each pixel is composed of at least two or more sub-pixels. The pixel is an active matrix type liquid crystal display element in which voltage control means for applying voltages of different magnitudes to each other are formed, and the liquid crystal in this portion is formed by an oblique vertical electric field at the boundary between the sub-pixel electrodes. Even if the arrangement of the molecules is affected, the angle formed by the major axis direction of the liquid crystal molecules in the intermediate layer of the liquid crystal layer and the boundary between the sub-pixels is φ so that the disturbance of the arrangement of the liquid crystal molecules is reduced. Wherein φ does not include 0 °, and the upper limit value of φ is set to 30 °. 2. A liquid crystal layer sandwiched between two opposing insulating substrates, comprising a plurality of pixels arranged in a matrix, wherein each of said pixels is composed of at least two or more sub-pixels. The pixel is an active matrix type liquid crystal display element in which voltage control means for applying voltages of different magnitudes to each other are formed, and the liquid crystal in this portion is formed by an oblique vertical electric field at the boundary between the sub-pixel electrodes. Even if the arrangement of the molecules is affected, the angle formed by the major axis direction of the liquid crystal molecules in the intermediate layer of the liquid crystal layer and the boundary between the sub-pixels is φ so that the disturbance of the arrangement of the liquid crystal molecules is reduced. Does not include 0 °, the upper limit value of φ is 30 °,
Further, a control capacitor of a different size is formed in all or a part of each of the sub-pixels in series with a liquid crystal capacitor formed by each of the sub-pixels, thereby providing the voltage control means. Active matrix type liquid crystal display device. 3. A liquid crystal layer sandwiched between two opposing insulating substrates, a plurality of pixels arranged in a matrix, and each pixel is constituted by at least two or more sub-pixels. The pixel is an active matrix type liquid crystal display element in which voltage control means for applying voltages of different magnitudes to each other are formed, and the liquid crystal in this portion is formed by an oblique vertical electric field at the boundary between the sub-pixel electrodes. Even if the arrangement of the molecules is affected, the angle formed by the major axis direction of the liquid crystal molecules in the intermediate layer of the liquid crystal layer and the boundary between the sub-pixels is φ so that the disturbance of the arrangement of the liquid crystal molecules is reduced. Does not include 0 °, the upper limit value of φ is 30 °,
An active matrix type liquid crystal display device, wherein a control capacitor of a different size is formed between a control electrode to which a modulation signal is supplied and each of the sub-pixel electrodes, thereby serving as the voltage control means.