JP2000131694A - Liquid crystal display - Google Patents

Abstract

(57) Abstract: The present invention is applied to a display system requiring a pretilt angle, such as a twisted nematic system, in which the optical alignment of a liquid crystal layer LC is set to a predetermined pretilt angle even when the initial alignment angle is 0 °. To align the liquid crystal. A first substrate SUB1 on which a first alignment film ORI1 is formed, a second substrate SUB2 on which a second alignment film ORI2 is formed, and a facing gap between the first substrate and the second substrate. And at least one of the first and second alignment films ORI1 and ORI2 has a liquid crystal alignment control ability provided by irradiation of linearly polarized light. In a pixel to be displayed, at least one of the first and second alignment films ORI1 and ORI2, which is in contact with the liquid crystal layer LC, has an inclination θ in the alignment direction of the liquid crystal molecules constituting the liquid crystal layer LC.

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 device, and more particularly to a liquid crystal display device having an alignment film provided with an alignment control function by irradiation of linearly polarized light.

[0002]

2. Description of the Related Art A liquid crystal display device has been widely used as a display device capable of high-definition and color display for a notebook computer or a display monitor.

[0003] Representative liquid crystal display devices include a simple matrix type using a liquid crystal panel in which a liquid crystal layer is sandwiched between a pair of substrates on which parallel electrodes formed so as to intersect with each other on the inner surface, and a pair of liquid crystal displays. 2. Description of the Related Art An active matrix system using a liquid crystal display element (also simply referred to as a liquid crystal panel) having a switching element such as a thin film transistor (hereinafter, referred to as a thin film transistor) for selecting a pixel unit on one side of a substrate is known.

An active matrix type liquid crystal display device is provided with a non-linear element (switching element) corresponding to each of a plurality of pixel electrodes arranged in a matrix. Since the liquid crystal in each pixel is theoretically always driven (duty ratio 1.0), the contrast is better than that of a simple matrix system employing a time-division driving system. It is not a technology. A typical switching element is a thin film transistor (TFT).

[0005] An active matrix type liquid crystal display device using thin film transistors is known, for example, from Japanese Patent Application Laid-Open No. 63-309921.

On the other hand, as a typical example of the method of aligning liquid crystal, an organic alignment film having an alignment control function by rubbing an organic polymer film such as polyimide has been known and put to practical use (Japanese Patent Application Laid-Open No. Sho 50/1985). -83051, JP-A-51-65
960, etc.).

Further, as known examples of aligning liquid crystal by light, US Pat. No. 4,974,941, JP-A-5-34699, JP-A-6-281937 and JP-A-7-247319 are known. is there.

[0008]

A practical means for aligning liquid crystals on a substrate in a liquid crystal display device is a rubbing method in which an alignment film is rubbed with a cloth (rubbing cloth). However, since the rubbing cloth directly contacts the surface of the alignment film in the alignment treatment by the rubbing method (the treatment for imparting the alignment control ability), static electricity may be generated in the alignment film or the alignment film surface may be contaminated. Static electricity generated in the alignment film may destroy a thin film transistor (TFT) or change its switching characteristics.

When contamination occurs on the surface of the alignment film, local frequency dependence of the threshold voltage becomes non-uniform, the voltage holding ratio decreases, the pretilt angle changes, and the liquid crystal alignment changes. Furthermore, as the size of the substrate increases, it becomes difficult to control the load during rubbing over the entire substrate, so that the rubbing may cause scratches and unevenness on the large substrate. In addition, the thin film rubbed with the rubbing cloth generates fine shavings, which become a large source of dust in the clean room where the liquid crystal display device is manufactured, which may reduce the yield of other manufacturing processes. There is also a big problem of becoming.

In addition, the surface of the substrate has irregularities (steps) due to the structure of the electrodes and active elements, and in the rubbing treatment, some parts are not rubbed due to the steps. This leads to light leakage in black display, leading to a decrease in contrast. These problems become more pronounced as the size of the substrate increases.

On the other hand, as described above, instead of such a contact type liquid crystal alignment method, there is known an optical alignment technique capable of achieving alignment of the liquid crystal without contacting the alignment film surface. However, applying the photo-alignment film to a practical liquid crystal display has the following problems.

That is, there is a problem that the liquid crystal in contact with the alignment film has a small pretilt angle, and is difficult to be applied to a display method such as a twisted nematic method or a super twisted nematic method which requires a pretilt angle. When there is no pretilt angle in the twisted nematic method, when an electric field is applied, a domain is generated because the rising direction of the liquid crystal is not determined.

Regarding pretilt control in optical alignment, a method of irradiating linearly polarized light twice is known as in SID95 Digest, page 877. In other words, the surface of the alignment film is irradiated with linearly polarized light perpendicular to the substrate to determine two pretilt angle directions facing the alignment film, and then the polarization direction perpendicular to the polarization direction of the primary irradiation is determined. The surface of the alignment film is irradiated with the linearly polarized light so as to be inclined at a certain angle.

Further, as disclosed in Japanese Patent Application Laid-Open No. 10-123531, it is assumed that in an alignment film made of a polycyclohexane-based material or polyvinyl fluorocinnamate, the pretilt angle can be controlled by a combination of thermal annealing and irradiation energy. I have.

However, these methods have problems that light irradiation must be performed twice or that the material of the alignment film is limited in heat resistance and the like.

An object of the present invention is to solve the above problems,
It is an object of the present invention to provide a liquid crystal display device which realizes good display by controlling the rising direction of liquid crystal when an electric field is applied even if the photo-alignment film has no pretilt angle.

[0017]

To achieve the above object, the present invention uses the following means. That is, it was found that by irradiating polarized light to an alignment film made of a polymer containing a polyimide or a photochromic site to align the liquid crystal, a uniform display can be obtained even near the step structure on the substrate. In addition, a streak pattern generated by rubbing the alignment film surface like rubbing may be generated and display quality may be impaired, but by aligning the liquid crystal with an alignment film provided with alignment control ability by light irradiation. , Such streaks do not occur.

When a polyimide alignment film is provided with an alignment control function by light irradiation, the pretilt angle is almost zero. In this case, in order to perform twisted nematic display by the photo-alignment method, polarized light is irradiated so that liquid crystals are arranged in a predetermined direction on the alignment film. However, in this case, when an electric field is applied to the liquid crystal, a domain occurs because the liquid crystal molecules on the alignment film have no pretilt angle. That is, in a liquid crystal display device represented by the twisted nematic method, when an electric field is applied in a direction perpendicular to the substrate, the liquid crystal molecules on the alignment film need to have a pretilt angle, which is an inclination angle from the substrate.

Therefore, in the present invention, a domain is prevented from being generated when switching the liquid crystal by inclining the surface of the alignment film in contact with the liquid crystal layer in a direction in which a pretilt angle is desired.

FIGS. 1 to 4 are schematic views for explaining a typical example of the basic structure of the present invention. In the figures, SUB1 is a first substrate, GI is a gate insulating film, ITO1 is a pixel electrode (transparent electrode). ), ORI1 is a first alignment film, SUB2 is a second substrate, OC is an overcoat film, ITO2 is a common electrode (transparent electrode), ORI2 is a second alignment film, and LC is a liquid crystal layer. Note that in a simple matrix type liquid crystal display device, IT
O1 corresponds to one stripe electrode, and ITO2 corresponds to the other stripe electrode.

FIG. 1 shows that the surface of the alignment film in contact with the liquid crystal layer is inclined by changing the thickness of the transparent electrodes ITO1 and ITO2 formed on the first and second substrates in the pixel.
(A) is an example in which the present invention is applied to a super twisted nematic liquid crystal display device, in which one stripe electrode ITO1 and the other stripe electrode ITO1 formed on a liquid crystal layer LC side of a first substrate SUB1 and a second substrate SUB2, respectively. The thickness of the stripe electrode ITO2 is changed within the pixel so that the stripe electrode ITO2 is inclined so that the angles θ ₁ and θ ₂ correspond to the pretilt angles of the liquid crystal molecules constituting the liquid crystal layer LC. As a result, the liquid crystal molecules forming the liquid crystal LC are aligned at a desired pretilt angle on the surfaces of the alignment films ORI1 and ORI2 which are formed with a uniform thickness on the upper surfaces of the stripe electrodes ITO1 and ITO2 and which are in contact with the liquid crystal layer LC. The angles θ ₁ and θ ₂ are the pixel electrodes ITO1 and ITO2 of the twisted nematic type described with reference to FIG.
Are larger than the angles θ ₃ and θ ₄ when the thickness of the substrate is changed.

That is, FIG. 1B shows the case where the present invention is applied to a twisted nematic liquid crystal display device.
Liquid crystal layer LC of first substrate SUB1 and second substrate SUB2
The pixel electrode ITO1 and the common electrode I formed on the
The thickness of TO2 is changed in the pixel so that the angles θ ₃ and θ ₄ correspond to the pretilt angles of the liquid crystal molecules constituting the liquid crystal layer LC.

FIG. 2 shows that the thickness of only the pixel electrode formed on the first substrate is changed within the pixel to give an inclination angle θ _5, and comes into contact with the liquid crystal layer LC of the first alignment film formed on the first substrate SUB1. The surface has a pretilt angle. This configuration example corresponds to the second substrate S in the liquid crystal display device of FIG.
This corresponds to a case where the thickness of the common electrode ITO2 of the UB2 in the pixel is constant.

FIG. 3 shows that the thickness of the gate insulating film GI formed on the first substrate SUB1 and the thickness of the overcoat film OC formed on the second substrate SUB2 are inclined in the pixel, and the inclination angles θ ₆ and θ _{7 respectively.} And a pretilt angle is given to a surface in contact with the liquid crystal layer LC.

FIG. 4 shows the first substrate SUB1 and the second substrate S
The tilt angles θ ₈ and θ ₉ are given to the liquid crystal layer side inner surface in the pixel of UB2, and the pre-tilt angle is given to the surface in contact with the liquid crystal layer LC.

As shown in FIGS. 1 to 4, by tilting the substrate surface in contact with the alignment film in a direction in which the liquid crystal molecules are desired to have a pretilt angle, it is possible to prevent the generation of domains when switching the liquid crystal. it can. In other words, even if the pretilt angle is 0 ° in the optical alignment treatment, the liquid crystal molecules can be tilted from 1 ° to 5 ° or more by tilting the surface in contact with the liquid crystal to control the rising direction by the electric field of the liquid crystal. it can. Specifically, it is sufficient that the surface in contact with the liquid crystal molecules is inclined, and this may be performed by changing the thickness of the electrode, the insulating film, or the protective film, or may be performed by tilting the substrate surface. The present invention is an effective method when a pretilt angle is required, and is not limited to the twisted nematic method.

Hereinafter, typical configuration examples of the present invention are listed as follows. That is, (1) the first substrate on which the first alignment film is formed, the second substrate on which the second alignment film is formed, and the opposing gap between the first substrate and the second substrate A liquid crystal layer comprising a liquid crystal composition, wherein at least one of the first and second alignment films has a liquid crystal alignment control ability imparted by irradiation of linearly polarized light, and a pixel to be displayed The surface of at least one of the first and second alignment films which is in contact with the liquid crystal layer has a gradient in the alignment direction of the liquid crystal molecules constituting the liquid crystal layer.

This configuration is particularly suitable for application to a super twisted nematic liquid crystal display device. Even if the pre-tilt angle is 0 ° in the optical alignment treatment, the liquid crystal molecules are reduced from 1 ° by the inclination of the surface in contact with the liquid crystal. By tilting the liquid crystal by 5 ° or more, the rising direction of the liquid crystal by the electric field can be controlled.

(2) a first alignment film having a scanning signal electrode, a video signal electrode, a pixel electrode, and an active element, and a first alignment film formed on each of the electrodes and the active element directly or via an insulating layer; A second alignment film having a substrate, a common electrode and a color filter, and a second alignment film formed directly or via an insulating layer on the common electrode and the color filter;
And a liquid crystal layer made of a liquid crystal composition sandwiched between opposing gaps between the first substrate and the second substrate, wherein the pixel electrode and the common electrode are substantially the same as the liquid crystal layer. External control means for arranging as if applying an electric field perpendicular to the surfaces of both substrates, connecting to the scanning signal electrode and the video signal electrode, and arbitrarily controlling the magnitude of the electric field according to a display pattern, In a liquid crystal display device comprising: a polarizing unit that changes optical characteristics according to an alignment state of the liquid crystal layer, at least one of the first and second alignment films includes:
The first and second substrates having a liquid crystal alignment control ability given by irradiation of linearly polarized light and being in contact with the first and second alignment films of the liquid crystal layer in a pixel to be displayed. At least a part of the substrate surface was inclined in the orientation direction of the liquid crystal molecules constituting the liquid crystal layer.

This configuration is particularly suitable for application to a twisted nematic type active matrix type liquid crystal display device. Even if the pretilt angle is 0 ° in the optical alignment treatment, the liquid crystal molecules are inclined by the inclination of the surface in contact with the liquid crystal. 1 ° to 5 °,
Alternatively, the rising direction can be controlled by tilting the liquid crystal more than that.

(3) In the pixel in (1) or (2), a part of at least one transparent electrode surface in contact with the alignment film of the liquid crystal layer is inclined in the alignment direction of liquid crystal molecules constituting the liquid crystal layer. Was.

Part of the transparent electrode is achieved by changing the thickness of a pixel electrode formed in a display pixel.

(4) This is achieved by changing the thickness of one or both of the gate insulating film and the overcoat film formed on the substrate in the pixel in (1) or (2).

(5) This is achieved by giving the surface of the substrate a slope in the pixel in (1) or (2).

(6) The inclination angle in each of the above items is
The angle is in the range of 1 ° or more and 20 ° or less, which is an angle at which no domain occurs.

(7) The alignment film in each of the above items was made of a polyimide polymer.

It should be noted that the present invention is not limited to the configurations described in the above items, and various changes can be made without departing from the scope of the technical idea of the present invention.

[0038]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the drawings described below, those having the same functions are denoted by the same reference numerals, and the repeated description thereof will be omitted.

FIG. 5 is a plan view of one pixel around an active matrix type liquid crystal display device using a thin film transistor as a switching element as an example of a liquid crystal display device to which the present invention is applied.

Pixels of this type of liquid crystal display device are formed in a region surrounded by a gate line GL which is a scanning signal line and a data line DL which is a video signal line intersecting the gate line GL. Part of the gate electrode GT
And a semiconductor layer AS made of amorphous Si and a drain electrode SD
2. Thin film transistor T composed of source electrode SD1
FT is formed, and a gate line GL is connected to the gate electrode GT.
However, the data line DL is connected to the drain electrode SD2.

The pixel electrode I
A film TO1 is formed, and a source electrode SD1 is connected to the pixel electrode ITO1.

The symbol d shown in parentheses in FIG.
1, d2 and d3 are conductive films, and signal lines or electrodes indicated by the same reference numerals are formed simultaneously by the same material.

FIG. 6 is a sectional view taken along the line AA of FIG. 5 for explaining the first embodiment of the liquid crystal display device according to the present invention.
5, the same reference numerals as those in FIG. 5 correspond to the same parts, SUB1 is a first substrate, SUB2 is a second substrate, GI is a gate insulating film, PSV is a protective insulating film, ORI1 is a first alignment film, B
M is a black matrix, FIL (R) red filter,
FIL (G) green filter (blue filter is not shown), OC is an overcoat film, ITO2 is a common electrode, O
RI2 is the second alignment film, LC is the liquid crystal layer, POL1, PO
L2 indicates a polarizing plate.

In this embodiment, the inclination angle is given by changing the thickness of the pixel electrode ITO1 formed on the first substrate SUB1 and the thickness of the common electrode ITO2 formed on the second substrate SUB2 within the pixel. Therefore, the first alignment film ORI1 and the second alignment film ORI2 formed on the pixel electrode ITO1 and the common electrode ITO2 are formed on the pixel electrode ITO1 and the common electrode I2.
The liquid crystal molecules of the liquid crystal layer LC in contact with the inclined surface of TO2 are inclined at the pretilt angle.

With this configuration, the alignment films ORI1, ORI
(2) By tilting the liquid crystal molecules from 1 ° to 5 ° or more by tilting the surface in contact with the liquid crystal even if the pretilt angle is 0 ° when the alignment control ability is given by the optical alignment treatment, In addition, the rising direction of the liquid crystal due to the electric field can be controlled.

FIG. 7 is a sectional view taken along line AA of FIG. 5 for explaining a second embodiment of the liquid crystal display device according to the present invention.
In the figure, the same reference numerals as those in FIG. 6 correspond to the same parts.

In this embodiment, the inclination angle is given by changing the thickness of the gate insulating film GI formed on the first substrate SUB1 and the thickness of the overcoat film OC formed on the second substrate SUB2 within the pixel. Therefore, the first alignment film OR formed via the pixel electrode ITO1 and the common electrode ITO2 formed on the gate insulating film GI and the overcoat film OC.
I1 and the second alignment film ORI2 are inclined according to the inclined surfaces of the gate insulating film GI and the overcoat film OC, and the liquid crystal molecules of the liquid crystal layer LC in contact with the inclined surfaces are oriented at the pretilt angle.

With this configuration, the alignment films ORI1, ORI
(2) By tilting the liquid crystal molecules from 1 ° to 5 ° or more by tilting the surface in contact with the liquid crystal even if the pretilt angle is 0 ° when the alignment control ability is given by the optical alignment treatment, In addition, the rising direction of the liquid crystal due to the electric field can be controlled.

FIG. 8 is a sectional view taken along the line AA of FIG. 5 for explaining a third embodiment of the liquid crystal display device according to the present invention.
6, the same reference numerals as those in FIGS. 6 and 7 correspond to the same parts.

In this embodiment, the inclination angle is given by changing the thickness of the first substrate SUB1 and the second substrate SUB2 within the pixel. Therefore, the first substrate SUB1 and the second
Gate insulating film GI, overcoat film O on substrate SUB2
C, and a first alignment film ORI1 and a second alignment film OR formed via the pixel electrode ITO1 and the common electrode ITO2.
I2 is inclined according to the inclined surfaces of the first substrate SUB1 and the second substrate SUB2, and the liquid crystal molecules of the liquid crystal layer LC in contact with the inclined surfaces are oriented at the pretilt angle.

With this configuration, the alignment films ORI1, ORI
(2) By tilting the liquid crystal molecules from 1 ° to 5 ° or more by tilting the surface in contact with the liquid crystal even if the pretilt angle is 0 ° when the alignment control ability is given by the optical alignment treatment, In addition, the rising direction of the liquid crystal due to the electric field can be controlled.

In the present invention, the orientation film can be inclined by combining the above embodiments, and only one of the first substrate SUB1 and the second substrate SUB2 can be used. The configuration of each of the above-described embodiments may be provided.

Hereinafter, specific examples of the liquid crystal display device to which the present invention is applied will be described with reference to FIGS.

Specific Example 1 PX in FIG. 9 corresponds to the pixel electrode ITO1, AOF on the gate electrode GT is an anodic oxide film of aluminum, d0
Indicates a contact layer. In FIG. 10, PNL denotes a liquid crystal panel constituting a liquid crystal display device, AR denotes a matrix portion (display area) of the liquid crystal panel, SL denotes a seal pattern for bonding the first and second substrates together, and INJ denotes a liquid crystal display. The entrance, Tg and Td indicate terminal groups, and LN indicates a cutting line. In FIG. 11, PCB1 is a multilayer printed board on which a data line driving circuit H and a scanning line driving circuit V are mounted.
CB2 is a multilayer board on which a power supply circuit is mounted, and TCP is a drive I
Tape carrier package with C, TTB, TT
M indicates a connection terminal, FC indicates a flat cable, and CJ indicates a connector connected to a host computer.

In the manufacture of this liquid crystal display device, a plurality of devices (unit liquid crystal panels) are simultaneously processed on a single glass substrate and then divided in order to improve the throughput if the size is small, and if the size is large, the device is large. reduced after processing a glass substrate of a size standardized in any breed for manufacturing facilities shared is sized to suit each model, in either case the glass is cut through the one way process. Here, the latter example is shown.

In any case, in the completed state, the external connection terminal groups Tg and Td (subscripts are omitted) are present (the upper and left sides in FIG. 10) on the second substrate SU so as to expose them.
The size of B2 is limited inside the first substrate SUB1. The terminal groups Tg and Td are respectively a scanning circuit connection terminal GTM and a data signal circuit connection terminal DTM described later.
And a plurality of the lead wiring portions are collectively named for a unit of a tape carrier package TCP on which an integrated circuit chip CHI as a driving IC is mounted. Td is a terminal group. The lead wiring from the matrix section of each group to the external connection terminal section is inclined as approaching both ends. This is for adjusting the terminals DTM and GTM of the display panel PNL to the arrangement pitch of the tape carrier package TCP and the connection terminal pitch of each package TCP.

First substrate SUB1 and second substrate SUB2
Between them, a seal pattern SL is formed along the edge except for the liquid crystal inlet INJ so as to seal the liquid crystal LC. The seal material of the seal pattern SL is made of, for example, epoxy resin.

The common transparent pixel electrode ITO2 on the side of the second substrate SUB2 is connected at least at one position to the lead-out wiring formed on the first substrate SUB1 side by silver paste at least at four corners of the panel in this example. Have been. This lead-out wiring is formed in the same manufacturing process as the later-described gate terminal GTM and drain terminal DTM.

The first alignment film ORI1, the second ORI2,
Pixel electrode ITO1 (PX), common transparent pixel electrode ITO
2. Each layer is formed inside the seal pattern SL.

The polarizing plates POL1 and POL2 are the first
Are formed on the outer surfaces of the substrate SUB1 and the second substrate SUB2. The liquid crystal layer LC is sealed in a region partitioned by the seal pattern SL between the first alignment film ORI1 and the second alignment film ORI2 for setting the direction of liquid crystal molecules. The first alignment film ORI1 is formed over the protective insulating film PSV on the second substrate SUB1 side.

In this liquid crystal display device, various layers are separately stacked on the first transparent glass substrate SUB1 side and the second substrate SUB2 side, and the seal pattern SL is formed on the second substrate SUB2.
Side, a first substrate SUB1 and a second substrate SUB2
After the liquid crystal is injected from the liquid crystal inlet INJ provided in the seal pattern SL, the liquid crystal inlet INJ is sealed with an epoxy resin or the like, and the upper and lower substrates are cut by cutting lines LN.

The thin film transistor TFT has a gate electrode G
When a positive bias is applied to T, the channel resistance between the source and the drain decreases, and when the bias is set to zero, the channel resistance increases.

Each pixel is provided with a thin film transistor TFT. The thin film transistor TFT has a gate electrode GT,
Gate insulating film GI, i-type (intrinsic: intrinsic:
The semiconductor device has an i-type semiconductor layer AS made of amorphous silicon (Si not doped with a conductivity type determining impurity), a pair of source electrode SD1, and a drain electrode SD2. The source,
It should be understood that the drain is originally determined by the bias polarity between them, and in the circuit of this liquid crystal display device, the polarity is inverted during operation, so that the source and drain are switched during operation. However, in the following description, one is fixed and the other is fixed as a drain for convenience.

The gate electrode GT is formed so as to protrude vertically from the scanning signal line GL (branched into a T-shape), and protrude beyond the active region of the thin film transistor TFT. This gate electrode GT is
It is formed continuously to the scanning signal line GL.
It is formed of a single-layer second conductive film g2. Second conductive film g
2 is, for example, an aluminum (Al) film formed by sputtering, on which an anodic oxide film A of Al is formed.
An OF is provided.

The gate electrode GT is formed to be larger than the i-type semiconductor layer AS so as to completely cover the i-type semiconductor layer AS (as viewed from below), and is designed so that external light or backlight light does not hit the i-type semiconductor layer AS. .

The scanning signal line GL is composed of the second conductive film g2. The second conductive film g2 of the scanning signal line GL is formed in the same manufacturing process as the second conductive film g2 of the gate electrode GT, and is integrally formed. Also, the scanning signal line GL
An anodic oxide film AOF of Al is also provided thereon.

The gate insulating film GI is made of a thin film transistor T
The FT is used as a gate insulating film for applying an electric field to the semiconductor layer AS together with the gate electrode GT. The insulating film GI is formed above the gate electrode GT and the scanning signal line GL. As the insulating film GI, for example, a silicon nitride film formed by plasma CVD is selected.
To a thickness of 0 to 2700 mm (in this example, about 2000 mm)
Formed so as to surround the entire display area AR,
The peripheral portion is removed to expose the external connection terminal.
The insulating film GI includes the scanning signal line GL and the video signal line D.
It also contributes to the electrical insulation of L.

The i-type semiconductor layer AS is formed here as an island independent of the thin film transistor TFT, and is made of amorphous silicon and has a thickness of 200 to 2200 ° (in this example,
(A film thickness of about 2000 °). The layer d0 is an N (+) type amorphous silicon semiconductor layer doped with phosphorus (P) for ohmic contact, and the i-type semiconductor layer A
S exists and is left only where the conductive layer d2 (d3) exists on the upper side. Although an amorphous silicon semiconductor layer is used here, a polycrystalline silicon semiconductor layer or a single crystal silicon semiconductor layer having high mobility may be used.

The i-type semiconductor layer AS is also provided between both intersections (crossover portions) between the scanning signal lines GL and the video signal lines DL. The i-type semiconductor layer AS at the intersection reduces a short circuit between the scanning signal line GL and the video signal line DL at the intersection.

Each of the source electrode SD1 and the drain electrode SD2 is composed of a second conductive film d2 in contact with the N (+) type semiconductor layer d0 and a third conductive film d3 formed thereon.

The second conductive film d2 is formed of a chromium (Cr) film formed by sputtering and has a thickness of 500 to 1000 ° (about 600 ° in this example). Since the stress increases when the Cr film is formed with a large film thickness, the thickness of the
It is formed in a range that does not exceed a certain thickness. In addition, this Cr
The film is used for the purpose of improving adhesion to the N (+) type semiconductor layer d0 and preventing Al of the third conductive film d3 from diffusing into the N (+) type semiconductor layer d0 (so-called barrier layer). Is done.

As the second conductive film d2, in addition to the Cr film, a refractory metal (Mo, Ti, Ta, W) film, a refractory metal silicide (MoSi ₂ , TiSi ₂ , TaSi ₂ , WS)
i ₂ ) A membrane may be used.

The third conductive film d3 is formed to a thickness of 3000 to 5000 ° by sputtering of Al (here, 4000 °).
Degree) is formed. The Al film has a smaller stress than the Cr film and can be formed to have a large thickness, and can reduce the resistance values of the source electrode SD1, the drain electrode SD2 and the video signal line DL, and can reduce the gate electrode GT and the i-type semiconductor. Layer AS
Has the function of ensuring that the vehicle gets over a step (improves step coverage).

After patterning the second conductive film d2 and the third conductive film d3 with the same mask pattern, an N (+) type is formed using the same mask or using the second conductive film d2 and the third conductive film d3 as a mask. The semiconductor layer d0 is removed. That is, in the N (+)-type semiconductor layer d0 remaining on the i-type semiconductor layer AS, portions other than the second conductive film d2 and the third conductive film d3 are removed by self-alignment. At this time, since the N (+) type semiconductor layer d0 is etched so as to completely remove the thickness thereof, the i-type semiconductor layer AS is also slightly etched at its surface, but the degree is controlled by the etching time. do it.

The video signal line DL is made of a second conductive film d2 and a third conductive film d of the same layer as the source electrode SD1 and the drain electrode SD2.
3.

On the second substrate SUB2 side, a black matrix BM is provided so that external light or backlight light does not enter the i-type semiconductor layer AS. The black matrix BM is made of a metal oxide having a high light-shielding property, for example, a metal oxide such as an aluminum film or a chromium film, or a pigment-dispersed organic material. Here, the chromium film is formed to a thickness of about 1300 mm by sputtering. Is done. Therefore, the i-type semiconductor layer AS of the thin film transistor TFT is sandwiched between the upper and lower black matrices BM and the large gate electrode GT, so that external natural light or backlight does not shine. The black matrix BM is formed in a grid around each pixel, and an effective display area of one pixel is partitioned by the grid black matrix. Therefore, the outline of each pixel is made clear by the black matrix BM, and the contrast is improved. That is, the black matrix BM also has a light shielding function for the i-type semiconductor layer AS.

It should be noted that the black matrix BM may be formed in a frame shape also in the peripheral portion. In this case, the pattern is formed continuously with the pattern of the display area AR provided with a plurality of openings in a dot shape. In this case, the peripheral black matrix BM is extended outside the seal pattern SL,
It prevents leakage light such as reflected light due to a mounting machine such as a personal computer from entering the display area AR. On the other hand, this black matrix BM is held, for example, about 0.3 to 1.0 mm inside the edge of the second substrate SUB2, and the second substrate SU
It is formed avoiding the cutting region of B2.

The overcoat film OC is made of, for example, a transparent resin material such as an acrylic resin and an epoxy resin.

As shown in FIG. 5, each pixel has two adjacent scanning signal lines (gate signal lines or horizontal signal lines).
It is arranged in an intersection area (in an area surrounded by four signal lines) between the GL and two adjacent video signal lines (drain signal lines or vertical signal lines) DL. Each pixel includes a thin film transistor TFT, a transparent pixel electrode ITO1, and a storage capacitor Cadd. The scanning signal lines GL extend in the left-right direction in FIG. The video signal lines DL extend in the up-down direction, and a plurality of video signal lines DL are arranged in the left-right direction.

The transparent pixel electrode ITO1 (PX) constitutes one of the pixel electrodes of the liquid crystal display. Transparent pixel electrode ITO1
Is connected to the source electrode SD1 of the thin film transistor TFT1. The transparent pixel electrode ITO1 is composed of a first conductive film d1, and the first conductive film d1 is a transparent conductive film (Indium-Tin) formed by sputtering.
-Oxide: ITO: Nesa film)
It is formed to a thickness of 2000 mm (here, a film thickness of about 1400 mm). At this time, the pixel electrode ITO1 was inclined with respect to the substrate at an inclination angle of 4 ° in the initial alignment direction of the liquid crystal, as described in the first embodiment.

As described above, the common electrode ITO2 is connected to the pixel electrode I provided for each pixel on the first substrate SUB1 side.
Opposed to TO1, the optical state of the liquid crystal layer LC is the potential difference (electric field) between each pixel electrode ITO1 and the common electrode ITO2.
Changes in response to The common electrode ITO2 is configured to apply a common voltage. Here, the common voltage is set to an intermediate DC potential between the minimum level drive voltage and the maximum level drive voltage applied to the video signal line DL, but the power supply voltage of the integrated circuit used in the data line drive circuit is If it is desired to reduce the voltage by about half, an AC voltage may be applied.

At this time, the common electrode ITO2 was inclined with respect to the substrate at an inclination angle of 4 ° in the initial alignment direction of the liquid crystal. The inclination direction of the transparent pixel electrode ITO1 is different from that of the transparent pixel electrode by 90 °, and the liquid crystal display mode is adapted to a twisted nematic mode which is a display mode of liquid crystal.

FIG. 12 is an exploded perspective view for explaining an overall configuration example of the liquid crystal display device according to the present embodiment.
Diffusion plate SPS, light guide resistant LCB, reflector R on the back of NL
M and a backlight case composed of a backlight fluorescent tube BL, and a shield case S serving as an upper frame.
Module MDL sandwiched between HD and lower case LCA
Fixed as The fluorescent tube BL is supplied with power from the inverter circuit board PCB3.

Next, a method for imparting liquid crystal alignment control capability to the alignment film will be described with reference to FIGS.

FIG. 13 is an explanatory view of a polarized light irradiation method for imparting liquid crystal alignment ability by irradiating light to the alignment film, and FIG. 10 is a conceptual diagram for obtaining polarized light for imparting liquid crystal alignment ability to the alignment film by light irradiation. is there.

13 and 14, reference numeral 100 denotes a light source preferably using a laser, 101 denotes an attenuator, 102 a relay optical system (102a is a first mirror, 102c is a second mirror, 102e is a third mirror, and 102b is a first mirror. Lens system, 102d is a second lens system), 103 is a homogenizer, 104 is a fourth mirror, 105 is a slit, 106
Denotes an imaging lens system, 107 denotes a holder, 108 denotes a polarization separating unit, 109 denotes a scanning unit, and 110 denotes an irradiation surface (alignment film).

The light emitted from the light source 100 passes through the attenuator 101, the relay optical system 102, the homogenizer 103, and the fourth mirror, and reaches the slit 105 after the light intensity on the cross section thereof is made uniform.

The slit 105 is a rectangular opening, and the cross section of the light passing therethrough is shaped into a rectangular beam pattern, introduced into the imaging lens system 106, and the light emitted from the imaging lens system 106 is also rectangular. A beam pattern BP is incident on the polarization beam splitting means 108.

The polarization separating means 108 is formed by forming a multilayer film on a quartz plate, and its polarization axis is a polarization axis AX _{P of} a P-wave of an incident light beam (light of a beam pattern BP emitted from the imaging lens system 106). Are held parallel to the optical axis of the incident light beam by the holder 107 while being inclined at a Brewster angle θ with respect to the optical axis of the incident light beam. The shape of the quartz plate is not limited to a rectangle.

As shown in FIG. 14, the polarization separating means 10
8 at the Brewster angle θ, the S-wave component B included in the incident light beam A of the beam pattern BP
The (polarization axis AX _S ) is selectively reflected by the polarization splitter 108.

Therefore, the light beam that reaches the irradiation surface 110 after passing through the polarization separation means 107 is only a P-wave component having the polarization axis AX _P.

The irradiation surface 110 is supported by a scanning stage 109 which is movable in two dimensions perpendicular to the optical axis of the irradiation light, and by moving the scanning stage 109 in the directions of arrows X and Y, the light beam pattern BP The irradiation surface 110 can be irradiated two-dimensionally in a range wider than the size.

When a polarization splitting plate having a multilayer film formed on the surface of a rectangular quartz plate (hereinafter also described by reference numeral 108) is used as the polarization splitting means 108, the polarization axis AX _{P of the} P wave is Either the short side may be made to coincide with the parallel surface (the short side and the irradiation surface are parallel) or the long side may be made to coincide (the long side and the irradiation surface are parallel). by matching the polarization axis AX _P wave, it is possible to irradiate the irradiated surface 110 of the large area efficiently.

Here, the irradiation effect when the rectangular polarization separation plate 108 is installed at a Brewster angle with the short side and the long side of the rectangular polarization separation plate 108 aligned with the irradiation surface 110 will be described.

In this case, the surface of the polyimide alignment film was irradiated with polarized UV light in order to use polyimide as the alignment film and align the liquid crystal on the surface. KrF excimer for light source
Laser-248 nm was used. At this time, irradiation was performed for 300 shots at an irradiation energy of 7.5 mJ / cm ² . The substrate can be scanned at a constant speed, and the feed speed of the substrate was set so that the irradiation surface was uniformly irradiated with 300 shots of polarized UV. The quartz plate with the multilayer film, which was installed at a Brewster's angle corresponding to the polarizing plate, was installed horizontally so as to be parallel to the substrate.

The polyimide used was a polyimide composed of pyromellitic dianhydride and 2,2-bis [4- (p-aminophenoxy) phenyl] propane, and had a glass transition temperature of about 320 ° C. there were.

For bonding the first and second substrates, 18
Although a curing temperature of 0 ° C. was given, the liquid crystal alignment ability was maintained. The thus obtained active matrix type liquid crystal display device had no domains and good display quality.

Example 2 This example has the same configuration as that of Example 1 except for the following. The pixel electrode ITO1 is connected to the source electrode SD1 of the thin film transistor TFT1. The transparent pixel electrode ITO1 is formed of a first conductive film d1, and the first conductive film d1 is formed of a transparent conductive film ITO formed by sputtering and has a thickness of 1000 to 2000 ° (here, 1
(Thickness of about 400 °). At this time, the pixel electrode ITO1 was inclined with respect to the substrate at an inclination angle of 6 ° in the initial alignment direction of the liquid crystal.

The common electrode ITO2 is connected to the first substrate SUB1.
The optical state of the liquid crystal layer LC changes in response to a potential difference (electric field) between each pixel electrode ITO1 and the common electrode ITO2, facing the transparent pixel electrode ITO1 provided for each pixel on the side. The common electrode ITO2 is configured to apply a common voltage. In this example, the common voltage is set to an intermediate DC potential between the minimum level drive voltage and the maximum level drive voltage applied to the video signal line DL, but the power supply voltage of the integrated circuit used in the video signal drive circuit is set. If it is desired to reduce by about half, an AC voltage may be applied.

At this time, the common electrode ITO2 was inclined with respect to the substrate at an inclination angle of 3 ° in the initial alignment direction of the liquid crystal. The inclination direction of the transparent pixel electrode ITO1 is different from that of the transparent pixel electrode by 90 °, and the liquid crystal display mode is adapted to a twisted nematic mode which is a display mode of liquid crystal.

In this example, polyimide was employed as the alignment film, and polarized UV was applied to the surface of the polyimide alignment film in order to align the liquid crystal on the surface. KrF excimer laser-248 nm was used as a light source. At this time, the irradiation energy
Irradiated 300 shots at 7.5 mJ / cm ² . The substrate can be scanned at a constant speed, and the feeding speed of the substrate was set so that the irradiated surface was uniformly irradiated with polarized light UV for 700 shots. The polarized light irradiation method and the polarized light irradiation device for aligning the liquid crystal in this example are shown in FIGS.
4 is the same as that described in FIG. The quartz plate with a multilayer film, which was installed at a Brewster angle corresponding to a polarizing plate, was installed horizontally so as to be parallel to the substrate.

The polyimide used had a chemical structure of pyromellitic dianhydride and diaminodiphenyl ether, and had a glass transition temperature of about 40.
It was 0 ° C.

180 ° for bonding the first and second substrates
Although the curing temperature of C was given, the liquid crystal alignment ability was maintained. The liquid crystal display thus obtained had no domains and good display quality.

In each of the above embodiments, the case where the present invention is applied to a so-called vertical electric field system in which an electric field substantially perpendicular to the substrate is applied to the liquid crystal layer to change the orientation direction of the liquid crystal molecules, The present invention is not limited to such a method, and can be applied to a so-called lateral electric field (IPS) method in which an electric field substantially parallel to the substrate is applied to the liquid crystal layer to change the orientation direction of the liquid crystal molecules.

[0105]

As described above, according to the present invention,
Even if the photo-alignment film does not have a pretilt angle, it controls the rising direction of the liquid crystal when an electric field is applied to achieve good display, and applies the liquid crystal optical alignment to a display method that requires a pretilt angle. In addition, a liquid crystal display device in which liquid crystal is uniformly aligned can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a typical basic configuration example of the present invention.

FIG. 2 is a schematic diagram illustrating a typical basic configuration example of the present invention.

FIG. 3 is a schematic diagram illustrating a typical basic configuration example of the present invention.

FIG. 4 is a schematic diagram illustrating a typical basic configuration example of the present invention.

FIG. 5 is a plan view around one pixel of an active matrix liquid crystal display device using a thin film transistor as a switching element, which is an example of a liquid crystal display device to which the present invention is applied.

FIG. 6 is a cross-sectional view taken along the line AA of FIG. 5 for explaining the first embodiment of the liquid crystal display device according to the present invention.

FIG. 7 is a sectional view taken along line AA of FIG. 5 for explaining a second embodiment of the liquid crystal display device according to the present invention.

FIG. 8 is a sectional view taken along line AA of FIG. 5 for explaining a third embodiment of the liquid crystal display device according to the present invention.

FIG. 9 is a cross-sectional view illustrating a configuration of a thin film transistor portion of a liquid crystal display device to which the present invention is applied.

FIG. 10 is a plan view of a liquid crystal display device to which the present invention is applied.

FIG. 11 is a plan view illustrating a configuration of a liquid crystal panel and a drive circuit board portion of a liquid crystal display device to which the present invention is applied.

FIG. 12 is an exploded perspective view illustrating an example of the overall configuration of a liquid crystal display device to which the present invention is applied.

FIG. 13 is an explanatory view of a polarized light irradiation method for imparting a liquid crystal alignment ability by light irradiation to an alignment film.

FIG. 14 is a conceptual diagram for obtaining polarized light for imparting liquid crystal alignment ability by light irradiation on an alignment film.

[Explanation of symbols]

 PNL Liquid crystal panel SUB1 First substrate SUB2 Second substrate SL Seal pattern INJ Liquid crystal injection port AR Display area Tg, Td Terminal group g2, d2, d3 Conductive film GI Gate insulating film AS i-type semiconductor layer PSV Protective insulating film BM Black Matrix FIL (R), FIL (G) Color filter ITO2 Common electrode ITO1 Pixel electrode (PX) ORI1, ORI2 Alignment film LC Liquid crystal layer.

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Shigeru Matsuyama 3300 Hayano, Mobara-shi, Chiba F-term in the Electronic Devices Division, Hitachi, Ltd. (Reference) 2H090 HB04X HB08Y HB13X KA05 KA08 LA01 LA04 LA09 LA15 MA11 MB14

Claims (2)

[Claims] A first substrate on which a first alignment film is formed, a second substrate on which a second alignment film is formed, and a gap between the first substrate and the second substrate facing each other. A liquid crystal layer comprising a liquid crystal composition, wherein at least one of the first and second alignment films has a liquid crystal alignment control ability given by irradiation of linearly polarized light, and a pixel to be displayed Wherein at least one of the first and second alignment films, which is in contact with the liquid crystal layer, has an inclination in the alignment direction of liquid crystal molecules constituting the liquid crystal layer. 2. A scanning signal electrode, a video signal electrode, a pixel electrode,
A first substrate having a first alignment film formed directly or via an insulating layer on each of the electrodes and the active element; a common electrode and a color filter; Second on the filter directly or via an insulating layer
A second substrate having an alignment film formed thereon, and a liquid crystal layer made of a liquid crystal composition sandwiched in a facing gap between the first substrate and the second substrate, wherein the pixel electrode and the common electrode are Arranged so as to apply an electric field substantially perpendicular to the surfaces of the two substrates to the liquid crystal layer, connected to the scanning signal electrode and the video signal electrode, and arbitrarily controlling the magnitude of the electric field according to a display pattern A liquid crystal display device comprising: an external control unit for performing the operation; and a polarizing unit that changes optical characteristics according to an alignment state of the liquid crystal layer. At least one of the first and second alignment films is linearly polarized. The liquid crystal layer has a liquid crystal alignment control function provided by light irradiation, and the first liquid crystal layer of the liquid crystal layer in a pixel to be displayed.
A liquid crystal display device characterized in that at least a portion of at least one of the first and second substrates in contact with the second alignment film has a tilt in an alignment direction of liquid crystal molecules constituting the liquid crystal layer.