JPH11149071A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display of high definition by suppressing contrast irregularity being apt to occur in a liquid crystal panel exposed to high temp. such as a projection type display. SOLUTION: A contrast irregularity compensating plate 72, having the photoelastic coefficient of a change characteristic opposed to the change characteristic for temp. of a photoelastic coefficient possessed by the substrate of a liquid crystal cell, is arranged by closely approaching or being in contact with the liquid crystal cell 30 interposing a liquid crystal layer 37 between two substrates 32, 33 and the change of the irregularity of optical stress due to the temp. irregularity of the substrate is compensated by the contrast irregularity compensating plate 72.

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 which is exposed to a high temperature, for example, suitable for a projection type.

[0002]

2. Description of the Related Art In recent years, practical use of a liquid crystal display device which obtains high performance and high definition while having high density and large capacity has been attempted. Among these liquid crystal display devices, TFTs are used because there is no crosstalk between connected scanning electrodes, a high contrast display is obtained, a transmission type display is possible, and a large screen is easy. Active matrix type liquid crystal display device equipped with
In particular, polysilicon thin film transistors (hereinafter p-SiT)
In the case of using FT), the mobility of electrons in the p-Si TFT is high, the size of the driving element can be reduced as compared with those using other driving elements, and the aperture ratio of the pixel electrode can be improved. There is an advantage that the driving circuit is formed integrally on the active matrix substrate.

[0003] Accordingly, a driving IC or the like is not required, the mounting process can be saved, and the cost of the device can be reduced, and its development is promoted. A high-definition liquid crystal display device is created using such a TFT technology, and a large screen display can be easily achieved by enlarging and projecting using a projection lens. A projection TV and the like have been developed.

[0004]

In such a projection type liquid crystal display device, it is desired that the size of the liquid crystal display device be reduced in order to reduce the size, weight and cost of the projector device. On the other hand, in order to make the screen brighter, in addition to the improvement of the aperture ratio of the liquid crystal display device, the use of a light source with high luminance and high output and the improvement of the optical system efficiency have been performed. For this reason, light with extremely high illuminance is incident on the liquid crystal display device, and in addition to the temperature rise of the liquid crystal display device, in-plane temperature unevenness has been caused. This is particularly noticeable in the case of a 16: 9 aspect ratio that is horizontally longer than the 4: 3 aspect ratio display screen, and the glass substrates 11 and 12 and the single-panel type that constitute the liquid crystal display device 10 shown in FIG. Due to the photoelastic characteristics of the microlens array 13 used for projection, there is a problem that unevenness in contrast occurs on the projection screen due to stress distribution caused by unevenness in temperature in the plane.

The incident illuminance is often strong at the center and lower at the periphery. As shown in FIG. 3B, the contrast ratio of the center portion 17 and the side portion 18 of the display area 16 is reduced, and the diagonal cross-shaped contrast is reduced. A high ratio portion 19 results. This is because the current mainstream TN liquid crystal has the same structure as a device for observing a stress distribution due to photoelasticity of an object because the polarizing plates 14 and 15 are disposed before and after the liquid crystal display device.

[0006] In addition, as the size of the liquid crystal display device becomes smaller and the resolution becomes higher, the microlens array substrate 13 is used to improve the effective aperture ratio in order to compensate for the smaller aperture ratio. When the microlens array substrate is bonded to the front substrate 12, the photoelastic effect is proportional to the thickness of the glass substrate, so that there is a problem that the contrast unevenness is more likely to occur by the thickness of the microlens substrate.

Accordingly, an object of the present invention is to provide a liquid crystal display device capable of suppressing cost-last unevenness due to stress unevenness due to in-plane temperature unevenness.

[0008]

According to the present invention, there is provided a liquid crystal cell having a liquid crystal layer sandwiched between two substrates, and a photoelastic structure which is disposed close to or in contact with the liquid crystal cell. An object of the present invention is to provide a liquid crystal display device comprising a contrast unevenness compensator having a photoelastic coefficient having a change characteristic opposite to a change characteristic of a coefficient with respect to temperature.

Further, a first electrode substrate having pixel electrodes arranged in a matrix and a first electrode substrate having a counter electrode are provided.
And a second electrode substrate having a liquid crystal layer disposed in the gap with the second electrode substrate opposed to the first electrode substrate with a gap therebetween, wherein the first and second electrode substrates have different photoelastic coefficients and signs. A liquid crystal display device characterized in that an unevenness compensating plate is attached to at least one of a first electrode substrate and a second electrode substrate via an adhesive layer.

Furthermore, a liquid crystal display device characterized in that a microlens array is bonded to the first or second electrode substrate via an adhesive layer.

Furthermore, a liquid crystal display device characterized in that a polarizing plate or a polarizing plate and a retardation plate are integrally attached to a contrast unevenness compensating plate.

Further, the present invention provides a liquid crystal display device characterized in that the above-mentioned polarizing plate or the polarizing plate and the retardation plate are integrated, but an antireflection film is formed on the light emitting interface.

Further, the present invention provides a liquid crystal display device characterized in that the contrast unevenness compensating plate is a microlens array.

As described above, the present invention provides a liquid crystal display device generated by irradiation with a high-luminance light source by combining a contrast unevenness compensator having a photoelastic coefficient having a sign different from that of a substrate of a liquid crystal cell. It can act so as to cancel out stress unevenness due to temperature unevenness in the inside.

The photoelastic effect on the light transmitted through the substrate is remarkably exhibited by the stress and strain of the substrate. Therefore, when stress strain occurs in the substrate due to uneven temperature of the substrate, the stress becomes uneven according to the strain. However, if a plate having a photoelastic coefficient having a different sign from the photoelastic coefficient of the substrate is arranged close to or in contact with the substrate, the photoelastic effect mutually cancels out. Therefore, by using this plate-like body as a contrast unevenness compensating plate, it is possible to improve stress unevenness and improve display contrast.

The photoelastic effect generated depends on the product of the photoelastic coefficient and the thickness of the plate. For example, two glass liquid crystal substrates sandwiching a liquid crystal layer constituting a liquid crystal cell have a positive photoelastic coefficient. On the other hand, since the liquid crystal layer is as thin as several μm, unevenness in stress with respect to temperature is caused by these two glass substrates. Depends on. The thickness of the substrate is 0.5 mm to 2 mm, and when combined with a glass microlens array, the overall thickness increases accordingly. The contrast unevenness compensating plate is made of a material having a negative photoelastic coefficient, such as an acrylic resin, and the photoelastic effect can be offset by selecting the thickness.

Further, according to the present invention, a microlens array substrate is laminated on a second electrode substrate which is a front substrate to increase an effective aperture ratio, and a third substrate which performs contrast unevenness compensation is a rear substrate which is a third substrate. By adhering to the first electrode substrate side, even if dust or dust adheres to the liquid crystal display device, the effect that the projected image is hardly affected can be achieved.
This is to improve display image quality.

Then, a polarizing plate or a polarizing plate and a retardation plate integrated with each other are bonded to a third substrate bonded to the first electrode substrate side, and an antireflection film is formed on an emission interface. In addition to improving the transmittance by reducing the reflection loss, it is possible to avoid an increase in leak current of the pixel switching element due to interface reflected light.

Further, by forming the microlens array plate from a material having a photoelastic coefficient having a sign different from that of the liquid crystal substrate, the microlens array plate can also serve as a contrast unevenness compensating plate. The installation of the compensator can be omitted.

[0020]

FIG. 1 is a block diagram showing an embodiment of the present invention.
This will be described with reference to FIG.

FIG. 1 is a schematic sectional view of a liquid crystal display panel, and FIG.
FIG. 3 is a schematic sectional view of a main part of a liquid crystal cell. In the figure, an active matrix type liquid crystal display panel 20 has a microlens array substrate 71 on the front surface of a liquid crystal cell 30, a contrast unevenness compensator 72 on the back surface, and polarizing plates 70 and 74 on both outer surfaces.

The liquid crystal cell 30 has p-SiT as a driving element.
An active matrix substrate 32 as a first electrode substrate and a counter substrate 3 as a second electrode substrate using FT31
3, a nematic liquid crystal 37 as a liquid crystal composition is held via an alignment film (not shown) made of polyimide.

Here, the active matrix substrate 32
Has a p-Si TFT 31 on a glass substrate 38. The p-Si TFT 31 is formed as follows.
That is, an amorphous silicon (hereinafter referred to as a-Si) film is formed on the glass substrate 38 by the CVD method.
A -Si film is formed on a polycrystalline silicon (hereinafter, referred to as p-Si) film by a laser annealing method, and is further patterned to form a semiconductor layer 40 in an island shape so as to have a matrix shape. Next, a first insulating layer 41 serving as a gate insulating film is coated on the semiconductor layer 40, and p-Si
A scanning line (not shown) for applying a scanning signal to the TFT 31 and a part thereof. After forming a gate electrode 42 and an auxiliary capacitance electrode 43 for applying a gate voltage, impurities are implanted into the semiconductor layer by self-alignment. Source area 4
After the formation of Os and the drain region 40d, the second insulating layer 45 is covered.

Here, the p-Si TFT 31 is nc
low impurity concentration region between the active layer and the source and drain regions in some cases constituted by h transistors (n ^- region) formed to LLD (Lightly Doped Drain) for the mutual structure is desirable n ^- region of Impurity implantation is
This was performed in a step different from that for the drain region.

It is desirable that a scanning line driving circuit and a signal line driving circuit described later have an n-ch and p-ch CMOS structure. Therefore, in order to form the source region 40s and the drain region 40d, impurities must be implanted. , Nc
h and p-ch. Furthermore, p-SiT
A signal line 44 for applying a video signal to the FT 31 is patterned and connected to the drain region 40d through the first contact hole 46. The first contact hole is also formed in the source region 40s using the same material as the signal line 44. Connect at 48.

A third insulating layer 51 is formed thereon,
Is formed, and a fourth insulating layer 52 is further formed, and a contact hole is formed at the same position as the second contact hole 49, and the contact hole 49 is formed.
, The source region 40s and the pixel electrode 47 made of indium tin oxide (hereinafter referred to as ITO) were connected. Further, a scanning line driving circuit (not shown) connected to a lead line of the scanning line 42 is provided on two adjacent sides of the display region when the pixel electrodes 47 on the active matrix substrate 32 are arranged in a matrix. A signal line driving circuit (not shown) connected to the lead line of the signal line 44 is formed.

On the other hand, the opposing substrate 33 is formed by forming a light-shielding member such as chromium (Cr) on a glass substrate 60 and forming a pattern in a matrix so as to face the p-Si TFT 31 on the active matrix substrate 32. A light-shielding layer 61 is formed, and a counter electrode 62 made of ITO is formed on the front surface by a sputtering method. Subsequently, the active matrix substrate 32
And the counter electrode 33 side of the counter substrate 33 and the counter electrode 6
The alignment films 63 and 64 made of polyimide are printed and applied to the entire surface on the second side, and rubbing is performed. In the active matrix substrate 32, a UV curable sealant 65 is applied by printing using a dispenser to the adhesive area around the display area except for the liquid crystal injection port.
After the counter substrate 33 is stacked on 2 and aligned, and the pressure is applied so that the gap between the two substrates 32 and 33 becomes uniform,
Irradiation of ultraviolet rays cures the sealant 65 to form an empty liquid crystal cell.

Next, a nematic liquid crystal 37 is injected from the liquid crystal injection port into the gap between the empty liquid crystal cells, and the liquid crystal injection port is sealed to complete the liquid crystal cell.

Then, a 2 mm-thick ion exchange glass microlens array substrate 71 is placed on the opposite substrate 33.
Was adjusted to match the pixels via an ultraviolet-curable adhesive, and then fixed by irradiation with ultraviolet light. The microlens array substrate 71 has a large number of convex lens microlenses 71a arranged on one surface. When the substrate is glass, the convex lens portion is formed by ion exchange. Each convex lens is arranged corresponding to the pixel of the liquid crystal cell, and one lens corresponds to each pixel of red, green, and blue in the single-panel color display.

Further, an acrylic resin substrate 72 having a thickness of 1 to 2 mm was adhered to the active matrix substrate 32 via an ultraviolet-curable adhesive as a contrast unevenness compensating plate and fixed by irradiating ultraviolet rays. Further, an acrylic resin substrate 7
In No. 2, a polarizing plate 74 having an antireflection layer 75 formed on the surface side was adhered via an adhesive layer.

As described above, the positive photoelastic coefficient (2.6 to 3.7 cm ² / dyne in the operating temperature range) of the glass active matrix substrate 32, the counter substrate 33, and the glass microlens array substrate 71 is obtained. An acrylic resin contrast unevenness compensating plate 72 having a negative photoelastic coefficient 72 (−6 cm ²⁾
/ Dyne), the linearly polarized light after the incident-side polarizing plate 70, which is a cause of contrast unevenness caused by uneven temperature caused by the incidence of high illuminance light from the side of the microlens array substrate 71, is applied to the liquid crystal panel. Elliptical polarization during transmission is suppressed.

Contrast unevenness means that in the case of black display, if there is no stress due to temperature unevenness, in the case of TN liquid crystal, light that has become linearly polarized by the polarizing plate on the incident side is only blocked by the polarizing plate 74 on the outgoing side and the contrast is almost one. However, when temperature unevenness occurs, a phase difference is generated when the light passes through a liquid crystal panel (glass substrate), resulting in uneven contrast in which a small contrast portion and a high-contrast band portion are formed. For example, as shown in FIG. 3, the phenomenon occurs vertically symmetrically.
When the temperature exceeds (the temperature difference between the center and the surroundings), it becomes noticeable visually.

The angular phase difference δ of two polarized lights having polarization planes orthogonal to each other due to the photoelastic effect is defined as t with respect to the substrate thickness, and when the stress state in the thickness direction is uniform and unchanged, Since the optical path length is n1 t for polarized light in the σ1 direction and n2 t (n1 and n2 are refractive indexes for orthogonal polarized lights) for polarized light in the σ2 direction, δ = (2π / λ) (n1 -N2) .t where n1-n0 = Aσ1 + Bσ2 n2 -n0 = Bσ1 + Aσ2 n0 between the above n1 and n2 and the main stress n0: refractive index in a no-stress state A: direct stress light constant B: lateral stress Δ = (2π / λ) · (AB) · (σ1−σ2) · t C = AB δ = (2π / λ) · C · (σ1−σ2) · tC: photoelastic coefficient

Therefore, in order to cancel the angular phase difference caused by the in-plane stress generated by the temperature unevenness of the liquid crystal panel, the product of the total thickness of the member having a positive photoelastic coefficient and the photoelastic coefficient is equal. Thus, it can be seen that the product of the thickness of the member having the negative photoelastic coefficient and the photoelastic coefficient may be set.

The polysilicon TFT 3 shown in FIG.
In the liquid crystal panel using 1, the active matrix substrate 3
The reflected light at the output interface of No. 2 is incident from the back surface of the pixel TFT, and a leak current is likely to occur. For this reason, a polarizing plate 73 is stuck on the interface on the emission side, and a polarizing plate with an anti-reflection film is stuck on the acrylic resin substrate 72 in order to reduce the leak current by forming the anti-reflection film 75 on this emission interface. Is more desirable.

Of course, the output side polarizing plate 73 is not attached to the liquid crystal panel but is separated from the liquid crystal panel.
Needless to say, an antireflection film may be provided on the substrate.

Further, the spectral characteristics of the antireflection film are p
It is desirable to lower the reflectance on the blue side where the absorption coefficient of -Si is high.

Considering the combination with a polarizing screen, when the orientation of the liquid crystal is rubbing at 45 degrees, a polarizing plate is laminated with a polarizing plate such that the polarizing axis is rotated by 45 degrees to match the polarizing screen. It goes without saying that an anti-reflection film may be attached and bonded.

Further, in the projection type display device, there is a problem that the display quality is deteriorated by dust or dirt accumulated on the display device due to large projection by the projection lens. However, as shown in FIG. Since the microlens array substrate and the acrylic resin substrate are arranged on the emission side, the position of dust and dust is shifted from the focus position, so that there is an advantage that deterioration of display quality is suppressed.

In another embodiment of the present invention, the microlens array substrate is configured to also serve as a contrast unevenness compensating plate. As shown in FIG.
When the microlens array substrate 80 formed on one surface is formed of an acrylic resin, the refractive index is 1.54, so even if the lens side is adhered to the glass substrate of the liquid crystal cell, the adhesive has a refractive index of 1.34. The use of the fluororesin does not impair the lens function. As described above, the acrylic resin has the opposite characteristic of the change of the photoelastic coefficient with respect to the temperature of glass. Therefore, by selecting an appropriate thickness, the contrast unevenness can be sufficiently removed.

It is needless to say that the present invention is also effective for a device using no microlens. Needless to say, an acrylic resin substrate serving as a contrast unevenness compensating plate may be attached to both the incident side and the outgoing side in order to suppress the influence of dust and dirt in the case of a liquid crystal panel not using a microlens. In this case, the thickness of the front and rear acrylic resins may be experimentally optimized based on the above relational expression. Further, it is needless to say that the contrast unevenness compensating plate can be formed of a material other than the acrylic resin, and various modifications can be made without departing from the present invention.

FIG. 5 shows another embodiment of the present invention. A phase difference plate 76, a polarizing plate 74, and an antireflection film 75 provided on a contrast unevenness compensating plate 72 for expanding a viewing angle and preventing coloring are provided. This shows an integrally formed structure, and by bonding this to a liquid crystal panel, manufacturing can be simplified.

[0043]

As described above, according to the present invention, it is possible to suppress the uneven contrast caused by the uneven temperature caused by the incidence of the high illuminance light on the projection type liquid crystal panel. realizable.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a liquid crystal panel according to an embodiment of the present invention;

FIG. 2 is a schematic sectional view of a liquid crystal cell according to an embodiment of the present invention;

3 (a) is a schematic sectional view illustrating a conventional example, and FIG. 3 (b) is a schematic plan view illustrating contrast unevenness of a projected image.

FIG. 4 is a schematic sectional view of a contrast unevenness compensator according to another embodiment of the present invention.

FIG. 5 is a schematic cross-sectional view of a contrast unevenness compensator according to another embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 20: liquid crystal panel 30: liquid crystal cell 31: TFT 32: active matrix substrate 33: counter substrate 70, 74: polarizing plate 71: microlens array substrate 72: contrast unevenness compensating plate 75: anti-reflection film

──────────────────────────────────────────────────続 き Continued on front page (51) Int.Cl. ⁶ Identification code FI // G02B 5/30 G02B 5/30

Claims (6)

[Claims] A liquid crystal cell having a liquid crystal layer sandwiched between two substrates; and a liquid crystal cell disposed close to or in contact with the liquid crystal cell, wherein the photoelastic coefficient of the substrate of the liquid crystal cell is opposite to a change characteristic with respect to temperature. A liquid crystal display device comprising: a contrast unevenness compensating plate having a photoelastic coefficient of change characteristics of the liquid crystal. 2. A first electrode substrate having pixel electrodes arranged in a matrix, and a first electrode substrate having a counter electrode, wherein the first electrode substrate is opposed to the first electrode substrate with a gap therebetween, and a liquid crystal layer is arranged in the gap. In the liquid crystal display device having the first and second electrode substrates, a contrast unevenness compensating plate having a different sign from the photoelastic coefficient of the first and second electrode substrates is bonded to at least one of the first and second electrode substrates. A liquid crystal display device characterized by being laminated via layers. 3. The liquid crystal display device according to claim 2, wherein a microlens array is bonded to the first or second electrode substrate via an adhesive layer. 4. The liquid crystal display device according to claim 2, wherein a polarizing plate or a polarizing plate and a phase difference plate are integrally attached to the contrast unevenness compensating plate. 5. The liquid crystal display device according to claim 4, wherein an anti-reflection film is formed on a light emitting surface of the polarizing plate or a combination of the polarizing plate and the retardation plate. 6. The liquid crystal display device according to claim 1, wherein the contrast unevenness compensating plate is a microlens array.