JP3208363B2 - Liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display (LCD) for performing display utilizing the electro-optical anisotropy of liquid crystal.
More particularly, the present invention relates to a liquid crystal display device which has improved viewing angle characteristics, brightness and contrast and has achieved a reduction in response speed.

[0002]

2. Description of the Related Art LCDs have advantages of small size, thin shape, low power consumption, and the like, and are being put to practical use in fields such as OA equipment and AV equipment. In particular, an active matrix type using a thin film transistor (hereinafter abbreviated as TFT) as a switching element can perform static driving with a duty ratio of 100% in principle in a multiplex manner, and has a large screen and a high-definition moving image display. Used in

A TFT is a field-effect transistor, is arranged in a matrix on a substrate, and is connected to a display electrode forming one of pixel capacitances using a liquid crystal as a dielectric layer. The TFTs are simultaneously turned on / off for the same row by a gate line, and a pixel signal voltage is supplied from a drain line, and a display voltage specified in a matrix is charged to a pixel capacitance with the TFT turned on. Is done. The display electrode and the TFT are formed on the same substrate, and the common electrode, which is the other of the pixel capacitors, is formed entirely on another substrate that is opposed to the liquid crystal layer. That is, the liquid crystal and the common electrode are partitioned by the display electrode to form a display pixel. The voltage charged in the pixel capacitance is insulated by the off resistance of the TFT for one field or one frame period until the next turn on of the TFT. The liquid crystal has electro-optical anisotropy, and the transmittance is controlled according to the voltage applied to the pixel capacitance. By controlling the transmittance for each display pixel, these light and dark areas are visually recognized as a display image.

The initial alignment state of the liquid crystal is further determined by an alignment film provided at the interface between the two substrates. For example, there is a twisted nematic (TN) system in which a nematic phase having a positive dielectric anisotropy is used as a liquid crystal and an orientation vector is twisted at 90 ° between both substrates. Usually, a polarizing plate is provided outside both substrates, and in the TN system, the polarization axis of each polarizing plate coincides with the alignment direction on the respective substrate side. Therefore, when no voltage is applied, the linearly polarized light that has passed through one of the polarizing plates is in a form that follows the twisted orientation of the liquid crystal,
It turns in the liquid crystal layer and is emitted from the other polarizing plate, and the display is recognized as white. Then, by applying a voltage to the pixel capacitance to form an electric field in the liquid crystal layer, the liquid crystal changes its orientation so as to be parallel to the electric field due to its dielectric anisotropy, and the twist arrangement is broken. As a result, the incident linearly polarized light is no longer rotated in the liquid crystal layer, the amount of light emitted from the other polarizing plate is reduced, and the display is temporarily turned black. As described above, a system in which white is displayed after no voltage is applied and then black is applied in response to voltage application is called a normally white mode, which is the mainstream of TN cells.

FIGS. 3 and 4 show the structure of a unit pixel portion of a conventional liquid crystal display device. FIG. 3 is a plan view, and FIG.
It is sectional drawing which followed the G line. On the substrate (100), C
gate electrode (10) made of metal such as r, Ta, Mo, etc.
1) is formed, over which SiNx or / and S
A gate insulating film (102) made of iO2 or the like is formed. On the gate insulating film (102), p-Si (10
3) is formed. The p-Si (103) has S patterned thereon in the shape of the gate electrode (101).
Using an injection stopper (104) such as iO2, phosphorus,
(N-) low concentration (L-) containing low concentration of impurities such as arsenic
D (Lightly doped) region (LD), and (N +) source and drain regions (S, D) containing a high concentration of impurities are formed outside the region (LD). Immediately below the injection stopper (104) is an intrinsic layer containing substantially no impurities, and serves as a channel region (CH).
An interlayer insulating film (105) made of SiNx or the like is formed to cover the p-Si (13), and the interlayer insulating film (10) is formed.
5) On the source electrode (10) made of Al, Mo, etc.
6) and a drain electrode (107) are formed and connected to the source region (S) and the drain region (D) via contact holes formed in the interlayer insulating film (105), respectively. On the entire surface covering this TFT, SOG (SPIN O
N GLASS), BPSG (BORO-PH-OSPHO SILICATE GLAS
S), a flattening insulating film (108) of acrylic resin or the like is formed. ITO on the flattening insulating film (108)
A display electrode (109) for driving a liquid crystal made of a transparent conductive film such as indium tin oxide (indium tin oxide) is formed.
08) is connected to the source electrode (106) via the contact hole opened.

An alignment film (120) made of a polymer film such as polyimide is formed on the entire surface covering all of them, and the initial alignment of the liquid crystal is controlled by a predetermined rubbing treatment.
On the other hand, a common electrode (131) formed entirely of ITO is provided on another glass substrate (130) provided at a position facing the substrate (100) with the liquid crystal layer interposed therebetween. 131), an alignment film (133) of polyimide or the like is formed thereon and subjected to a rubbing treatment.

Here, a nematic phase having a negative dielectric anisotropy is used for the liquid crystal (140), and the alignment film (120, 1) is used.
33) DAP (deformation) using a vertical alignment film
of vertically aligned phase) type. The DAP type is a voltage controlled birefringence (ECB).
This is one of the d birefringence systems in which the transmittance is controlled by utilizing the difference in the refractive index between the major axis and the minor axis of the liquid crystal molecules, that is, birefringence. In the DAP type, when a voltage is applied, incident linearly polarized light that has passed through one of the orthogonally arranged polarizing plates is converted into elliptically polarized light by birefringence in the liquid crystal layer, and the retardation amount according to the electric field intensity of the liquid crystal layer, that is, the ordinary light component in the liquid crystal By controlling the difference between the phase velocities of the light beam and the extraordinary light component, light is emitted from the other polarizing plate at a desired transmittance. In this case, the display changes from black to white by increasing the applied voltage from the state where no voltage is applied, so that the normally black mode is set.

[0008]

As described above, in a liquid crystal display device, by applying a desired voltage to a liquid crystal loaded between a pair of substrates on which predetermined electrodes are formed, the light in the liquid crystal layer is reduced. The desired transmittance or hue is obtained by controlling the rotation or birefringence of the image, and a display image is created. That is, by controlling the amount of retardation by changing the orientation of the liquid crystal,
In the TN system, the transmitted light intensity can be adjusted, and E
In the CB method, the hue can be separated by controlling the spectral intensity depending on the wavelength. The amount of retardation depends on the angle between the major axis of the liquid crystal molecules and the direction of the electric field. Therefore, even if the angle between the electric field and the long axis of the liquid crystal molecules is primarily controlled by adjusting the electric field strength, the retardation is relatively dependent on the angle that the observer visually recognizes, that is, depending on the viewing angle. When the amount changes and the viewing angle changes, the transmitted light intensity or the hue also changes, which has been a so-called viewing angle dependency problem.

[0009] In addition, there has been a problem that the brightness and contrast are reduced and the response speed is slow.

[0010]

SUMMARY OF THE INVENTION The present invention has been made to solve these problems, and a liquid crystal layer having vertically aligned liquid crystal molecules is provided between a plurality of display electrodes and a counter electrode. A vertical alignment type liquid crystal display device in which the alignment of the liquid crystal molecules is controlled by an electric field, wherein an alignment control window is provided in each of the display electrode and the counter electrode.

Further, it is preferable that the angle formed by the edge of the display electrode and the orientation control window of the counter electrode and the angle formed by the orientation control window of the counter electrode and the orientation control window of the display electrode are each smaller than 45 °. This is a characteristic configuration. Further, the orientation control window on the display electrode side is formed of a Y-shaped and an inverted Y-shaped slit separately provided at an upper portion and a lower portion of the display electrode, respectively. The V-shaped and Y-shaped slits surrounding the Y-shaped slit and the inverted V-shaped and inverted Y-shaped slits surrounding the inverted Y-shaped slit are formed. The slit and the inverted Y-shaped slit are connected to each other.

Thus, the effect of the edge is reduced, and the viewing angle characteristic, brightness and contrast are improved.
The response speed can be increased.

[0013]

1 and 2 show a unit pixel structure of a liquid crystal display according to an embodiment of the present invention. 1 is a plan view, and FIG. 2 is a cross-sectional view along the line AA in FIG. A gate electrode (11) made of a metal such as Cr, Ta, or Mo is formed on a substrate (10), and is covered with SiNx.
And / or a gate insulating film made of SiO2 or the like (12)
Are formed. On the gate insulating film (12), p-
Si (13) is formed. p-Si (13) is
Using an injection stopper (14) such as SiO2 patterned in the shape of the gate electrode (11) thereon,
(N-) lightly doped (LD) regions (LD) containing impurities such as phosphorus and arsenic at a low concentration, and (N +) source and drain regions (LDs) also containing impurities at a high concentration outside thereof. S, D) are formed. Immediately below the injection stopper (14) is an intrinsic layer containing substantially no impurities, and serves as a channel region (CH). An interlayer insulating film (15) made of SiNx or the like is formed to cover the p-Si (13), and the interlayer insulating film (1) is formed.
5) On the source electrode (16) made of Al, Mo, etc.
And a drain electrode (17) are formed and connected to the source region (S) and the drain region (D) via contact holes formed in the interlayer insulating film (15), respectively. On the entire surface covering this TFT, SOG (SPIN ON GLAS
S), a flattening insulating film (18) of BPSG (BORO-PH-OSPHOSILICATE GLASS), acrylic resin or the like is formed.
An ITO (indium tin oxi) is formed on the planarizing insulating film (18).
de) and other display electrodes (1)
9) is formed, and is connected to the source electrode (16) via a contact hole formed in the planarizing insulating film (18).

An alignment film (20) made of a polymer film such as polyimide is formed on the entire surface covering all of them.
On the other hand, a common electrode (31) formed entirely of ITO is provided on another glass substrate (30) provided at a position facing the substrate (10) with the liquid crystal layer interposed therebetween. 31) An alignment film (33) of polyimide or the like is formed on 31). In the present invention, the alignment films (20) and (33)
The liquid crystal (40) is selected so that the liquid crystal molecules (41) are vertical.

In the present embodiment, as shown by the solid line in FIG. 1, an alignment control window (19a) formed of a Y-shaped slit is formed above the display electrode (19), and symmetrically with this. An orientation control window (19b) formed of an inverted Y-shaped slit is formed below the display electrode (19). On the other hand, the common electrode (31) has a V-shaped slit (32a) surrounding the Y-shaped slit (19a) at a position corresponding to the upper part of the display electrode (19) as shown by a broken line in FIG. An inverted V-shaped slit (32a) and an inverted V-shaped slit (32a) are formed at a position corresponding to the lower part of the display electrode (19) to surround the inverted Y-shaped slit (19b). A Y-shaped slit (32b) is formed. The Y-shaped slit (32b) and the inverted Y-shaped slit (32d) are connected, and the four slits (32a), (32b), (32c), and (32d) are used to control the orientation control window (32) on the common electrode side. ).

Further, in the present invention, as shown in FIG. 1, the angles .theta.1, .theta.4 between the edge of the display electrode (19) and the orientation control window (32c) on the common electrode side, and the angle on the common electrode side. The angles θ2, θ3, θ5, θ6 formed by the orientation control window (32c) and the orientation control window (19b) on the display electrode side are:
All are set to be smaller than 45 °. The angles shown here are shown only for the lower right corner of the display electrode (19), but for the other three corners, all angles are similarly 45 °.
It is set to be smaller.

In the case of the above configuration, the alignment control windows (19a) and (19b) on the display electrode side are located just above the alignment control windows (19a) and (19b).
Immediately below the alignment control window (32) on the common electrode side, since one of the electrodes is missing, an electric field enough to incline the liquid crystal molecules (41) is not applied. ) Are vertically oriented. However, an electric field indicated by a dotted line in FIG. 2 is generated near these alignment control windows,
The alignment of the liquid crystal molecules (41) is controlled in a direction whose major axis is perpendicular to the electric field. Similarly, also at the edge of the display electrode (19), the alignment of the liquid crystal molecules (41) is controlled in a direction whose major axis is perpendicular to the electric field, and the inclination of these liquid crystal molecules is extended to the internal liquid crystal by the continuity of the liquid crystal. Convey. Therefore, as shown by the arrow in FIG. 1, the alignment control direction of the liquid crystal molecule (41) is determined by the display electrode edge and the alignment control window (19) on the display electrode side.
a) and (19b), and the alignment control window (3
The direction is perpendicular to any of 2).

As is clear from FIG. 1, the display electrode (1
Since the alignment control window is formed in the vertical direction in the central part of 9), the alignment of the liquid crystal molecules (41) is controlled in the same right or left direction, and no alignment failure occurs in this region. However, since the alignment control windows are formed obliquely in the upper and lower portions, the alignment direction of the liquid crystal molecules is also tilted accordingly. For example, at the lower right corner of the display electrode (19), the liquid crystal molecules (41) are in the direction indicated by the arrow a at the right edge of the display electrode, and at the arrow b at the edge of the alignment control window 32d.
It becomes the direction shown by. However, since the alignment direction of the liquid crystal molecules (41) is perpendicular to the display electrode edge and the alignment control window, the angle between the arrow a and the arrow b is θ4. In a region between the alignment control window 19b and the alignment control window 32d, an arrow c indicating the alignment direction of the liquid crystal molecules (41) is displayed.
The angle between the arrow and the arrow d is θ3. Hereinafter, similarly, the angle between the alignment directions of the liquid crystal molecules (41) at both edges is
In a region between the alignment control window (19b) and the alignment control window (32c), θ2 is obtained, and in a region between the alignment control window (32c) and the lower edge of the display electrode, θ1 is obtained.

If there is only one vertical alignment control window in the center as the alignment control window, the alignment direction of the liquid crystal molecules at the right edge of the display electrode and the alignment direction at the lower edge are 90 °.
In the vicinity of the edge, the liquid crystal molecules change their directions extremely. For this reason, poor alignment occurs in these regions. However, as described above, since the angles θ1, θ2, θ3, θ4, θ5, and θ6 are all set to be smaller than 45 °, it is difficult to change the direction of the liquid crystal molecules by 45 ° or more in all the regions. Absent. For this reason, alignment defects at both ends of the display electrode (19) can be reduced. This allows for brightness,
The contrast, response, and viewing angle characteristics are improved.

[0020]

As is clear from the above description, an orientation control window is provided for both the display electrode and the counter electrode, and the angle formed between the display electrode edge and the counter electrode-side orientation control window, the counter electrode-side orientation control window, and the display. The angles formed by the electrode-side orientation control windows are 4
Since the angle is set to be smaller than 5 °, it is possible to prevent poor alignment and to improve brightness, contrast, response, and viewing angle characteristics.

[Brief description of the drawings]

FIG. 1 is a plan view of a unit pixel portion of a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a plan view of a unit pixel portion of a conventional liquid crystal display device.

FIG. 4 is a sectional view taken along line GG of FIG. 3;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Substrate 11 Gate electrode 12 Gate insulating film 13 p-si 14 Injection stopper 15 Interlayer insulating film 16 Source electrode 17 Drain electrode 19 Display electrode 19a, 19b Display electrode side alignment control window 20 Alignment film 30 Glass substrate 31 Common electrode 32, 32a , 32b, 32c, 32d Opposing electrode side alignment control window 33 Alignment film 40 Liquid crystal 41 Liquid crystal molecule

Claims (6)

(57) [Claims] A vertical alignment type liquid crystal display device in which a liquid crystal layer having liquid crystal molecules vertically aligned is provided between a plurality of display electrodes and a counter electrode, and the alignment of the liquid crystal molecules is controlled by an electric field. An orientation control window is provided on each of the display electrode and the counter electrode, and an edge of the display electrode and an orientation control window of the counter electrode are provided .
The angle to be formed, the orientation control window of the counter electrode and the table
The angle between the alignment control windows of the indicator electrodes is smaller than 45 °
The liquid crystal display device, characterized in that brewing. 2. The display device according to claim 1, wherein the counter electrode has a plurality of alignment control windows, and the display electrode has an alignment control window.
2. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is provided in a region of the display electrode facing between alignment control windows provided in the counter electrode. 3. A vertical alignment type liquid crystal display device in which a liquid crystal layer having liquid crystal molecules vertically aligned is provided between a plurality of display electrodes and a counter electrode, and the alignment of the liquid crystal molecules is controlled by an electric field. The counter electrode has first and second alignment control means for dividing an alignment control direction of the liquid crystal molecules, and the display electrode opposed between the first and second alignment control means. the region, the alignment control direction of the liquid crystal molecules have a third orientation control means for dividing the first or second edge and the opposing electrode of the display electrode
Angle with the orientation control means, and the
A third arrangement of the first or second alignment control means and the display electrode;
A liquid crystal display device, wherein the angles formed by the direction control means are each smaller than 45 ° . Wherein said third orientation control means, the liquid crystal display device according to claim 3, characterized in that the slit-like orientation control window. 5. The apparatus according to claim 3, wherein said first and second alignment control means are slit-shaped alignment control windows.
Alternatively, the liquid crystal display device according to claim 4. 6. The alignment control window on the display electrode side includes a Y-shaped slit and an inverted Y-shaped slit provided separately at an upper portion and a lower portion of the display electrode, respectively. The window is composed of V-shaped and Y-shaped slits surrounding the Y-shaped slit and inverted V-shaped and inverted Y-shaped slits surrounding the inverted Y-shaped slit. the liquid crystal display device according to claim 1, wherein the shaped slit and the reverse Y-shaped slit, characterized in that it is connected.