JP2007121505A - Reflection type liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reflection type liquid crystal display capable of maintaining uniformity of a displayed image and maintaining high display quality even when intense readout light is made incident. <P>SOLUTION: In the reflection type liquid crystal display having a liquid crystal display cell 2 wherein a semiconductor substrate 4 having a plurality of reflection type pixel electrodes 4A formed in a matrix shape on the surface thereof and a transparent substrate 6 having a transparent common electrode 6A formed on the surface thereof are disposed so that the pixel electrodes and the common electrode are opposed to each other at a prescribed interval of a gap and a liquid crystal 8 is encapsulated in the gap and a transparent dust preventing substrate 36 provided on the transparent substrate side of the liquid crystal display cell, a heat conductive cell housing 22 is provided so as to enclose at least surrounding of the liquid crystal display cell and the cell housing supports a peripheral part of the dust preventing substrate so that a slow axis is radially generated in the dust preventing substrate during operation. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a reflective liquid crystal display device used as a basic part of a projector, a projection TV or the like, and in particular, a reflection capable of maintaining high display quality by preventing occurrence of luminance unevenness due to temperature rise during use. The present invention relates to a liquid crystal display device.

  In general, liquid crystal display devices are widely used as basic components for projectors and projection TVs. In recent years, in particular, a reflective pixel electrode arranged in a matrix and a CMOS transistor driving circuit for supplying voltage to the pixel electrode are formed on a silicon substrate, and the silicon substrate and a transparent glass substrate on which a common electrode is formed. A reflective liquid crystal display device using a liquid crystal display cell called an LCOS (Liquid Crystal On Silicon) element in which the liquid crystal is sealed between them is attracting attention because of the high quality of the display image. Has been.

  Such a reflective liquid crystal display device is configured by housing the liquid crystal display cell described above together with a flexible printed circuit board (FPC) in a metal or resin package. The reflective liquid crystal display device described above is installed in a projector or a projection TV, and an image displayed on the liquid crystal display cell is enlarged and projected. At this time, strong light from the light source causes the liquid crystal display cell. The temperature rises and the display quality deteriorates.

  That is, when a reflective liquid crystal display device is incorporated in a projector or the like and irradiated with readout light from a light source, a part of the light is absorbed and the temperature rises. When the temperature rise of the liquid crystal display cell is increased, a large thermal stress is generated on the transparent substrate to cause birefringence, and display quality is deteriorated. The generation of the thermal stress is caused when a temperature distribution is generated on the transparent substrate. Specifically, the readout light from the light source is applied to the image display portion, and the temperature of the silicon substrate that absorbs a part of this light is raised. The temperature of the transparent substrate bonded to the silicon substrate also rises. This temperature rise is large in the central portion where the image display area is present and small in the peripheral portion. As a result, as described above, a temperature distribution occurs and birefringence due to thermal stress occurs in the transparent substrate. This birefringence hinders the control of the readout light using the birefringence of the liquid crystal, causes a deviation from the correct display luminance level, and degrades the display quality.

Therefore, in Patent Document 1, in a liquid crystal display device using a liquid crystal display cell with a dust-proof glass, display quality due to a temperature change, in particular, measures against displacement of the liquid crystal display cell are taken by matching the linear expansion coefficient of the element constituent members. It has been.
Further, in Patent Document 2, in the projection type liquid crystal display device, in order to prevent the occurrence of birefringence that deteriorates the display quality, the linear expansion coefficient or the photoelastic constant is set to a certain value or less for the second transparent substrate. It is disclosed.

JP 2001-195006 A JP 2001-290120 A

The above-described conventional liquid crystal display device has been designed in consideration of the deterioration in display quality due to the temperature rise as described above. However, the display image is required to have higher density and higher brightness, and a high-output light source is used. As a result, it is difficult to maintain good image quality.
In particular, in the liquid crystal display device of Patent Document 1, sufficient measures are not taken for the deterioration in display quality caused by the birefringence of the transparent substrate and the dust-proof glass caused by the temperature rise.
In addition, in the liquid crystal display device of Patent Document 2, there are few transparent substrates that satisfy the linear expansion coefficient and the photoelastic constant defined here, and the cost is high. Furthermore, in the liquid crystal display device of Patent Document 2, sufficient measures have not been taken to reduce the display quality due to birefringence caused by the temperature rise of the transparent substrate used in the liquid crystal display cell.

  The present invention has been devised to pay attention to the above problems and to effectively solve them. An object of the present invention is to provide a reflective liquid crystal display device capable of maintaining the uniformity of a display image and maintaining high-quality display quality even when strong readout light is incident.

  According to a first aspect of the present invention, there is provided a semiconductor substrate having a plurality of reflective pixel electrodes formed in a matrix on the surface, and a transparent substrate having a transparent common electrode formed on the surface, the pixel electrode and the common electrode, Is disposed so as to face each other with a predetermined gap, and includes a liquid crystal display cell in which liquid crystal is sealed in the gap, and a transparent dustproof substrate provided on the transparent substrate side of the liquid crystal display cell. In the reflection type liquid crystal display device, a thermally conductive cell housing is provided so as to surround at least the periphery of the liquid crystal display cell, and the cell housing is configured so that a radial slow axis is generated in the dustproof substrate during operation. A reflection type liquid crystal display device characterized in that it is configured to support a peripheral portion.

In this case, as defined in claim 2, a visible light absorbing film for absorbing visible light may be formed on the periphery of the dust-proof substrate.
Further, as defined in claim 3, the dust-proof substrate and the transparent substrate may be bonded together with a transparent adhesive.

  According to the reflective liquid crystal display device of the present invention, the cell housing is provided so as to surround at least the periphery of the liquid crystal display cell, and the cell housing has a dustproof state in which a slow axis is radially generated on the dustproof substrate during operation. Since it is configured to support the peripheral part of the substrate, the birefringence due to the stress generated by the temperature distribution of the transparent substrate can be optically canceled by the birefringence generated by the transparent dustproof substrate provided opposite to this. Therefore, even when strong readout light is incident, the uniformity of the display image can be maintained and high-quality display quality can be maintained.

Hereinafter, an embodiment of a reflective liquid crystal display device according to the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic sectional view showing a liquid crystal display cell used in a reflective liquid crystal display device according to the present invention, FIG. 2 is a sectional view showing a first embodiment of the reflective liquid crystal display device according to the present invention, and FIG. It is a schematic diagram which shows the state of the slow axis which arises.
First, a liquid crystal display cell used in a reflective liquid crystal display device will be described with reference to FIG. The liquid crystal display cell 2 is encapsulated between a semiconductor substrate 4 made of, for example, a silicon substrate, a transparent substrate 6 made of, for example, a transparent glass substrate disposed opposite thereto, and the semiconductor substrate 4 and the transparent substrate 6. The liquid crystal 8 is mainly composed.

  Specifically, a plurality of reflective pixel electrodes 4A made of, for example, an aluminum alloy are arranged in a matrix on the surface of the semiconductor substrate 4 on the liquid crystal 8 side, and the pixel corresponding to each pixel electrode 4A. A drive circuit 4B including a switching transistor for driving the electrode 4A is formed. A signal voltage is applied to the corresponding pixel electrode 4A by the drive circuit 4B.

  A transparent common electrode 6A made of, for example, ITO is formed on the surface of the transparent substrate 6 on the liquid crystal 8 side, and an antireflection film 6B is formed on the opposite surface. The semiconductor substrate 4 and the transparent substrate 6 are disposed to face each other with a predetermined gap so that the pixel electrode 4A and the common electrode 6A face each other, and the liquid crystal 8 is sealed in the gap. The peripheral portions of both the substrates 4 and 6 are liquid-tightly joined by a sealing adhesive 10 that also functions as a spacer. The thickness of the seal adhesive 10 is, for example, about 5 μm. The readout light L1 is incident from the transparent substrate 6 side.

A flexible wiring board 12 is connected to the side portion of the semiconductor substrate 4 to supply necessary electrical signals to the drive circuit 4B and the common electrode 6A.
In the image display operation of the liquid crystal cell 2, a signal voltage corresponding to the image is applied between the pixel electrode 4A connected to the drive circuit 4B formed on the semiconductor substrate 4 and the common electrode 6A formed on the transparent substrate 6. This is done by changing the polarization direction of the liquid crystal 8. That is, the readout light L is incident on the liquid crystal 8 through the transparent substrate 6, and then reflected and emitted from the pixel electrode 4A. Image display is performed by changing the polarization direction of the light. In the liquid crystal display cell 2, since the pixel electrodes 4A are arranged in a two-dimensional matrix, two-dimensional image display can be performed as described above by selectively driving the pixel electrodes 4A. it can.

<First embodiment>
Next, the liquid crystal display device of the first embodiment in which the liquid crystal display cell 2 is incorporated will be described with reference to FIG. In FIG. 2, the structure of the liquid crystal display cell 2 is shown in a simplified manner.
As shown in FIG. 2, the liquid crystal display device 20A according to the first embodiment includes a metal cell housing 22 made of, for example, stainless steel, which is provided so as to surround the liquid crystal display cell 2 and has a good thermal conductivity. is doing. Specifically, a plate-like cell base 24 is connected and attached to the bottom of the cell housing 22. On the cell base 24, the semiconductor substrate 4 side of the liquid crystal display cell 2 is fixedly attached to the cell base 24 with an adhesive 28 having good thermal conductivity with a spacer 26 interposed in the periphery. As the adhesive 28, for example, a silicone gel can be used.

  A heat sink 32 made of, for example, aluminum is joined to the lower surface of the cell base 24 via a heat radiating sheet 30, and the heat sink 32 is provided with a number of heat radiating fins 32 </ b> A for promoting heat radiation.

  On the other hand, an upper portion of the cell housing 22 is opened, and an attachment step 34 is formed inside the opening. In this opening, a transparent dustproof substrate 36 made of, for example, a glass plate is provided so as to face the transparent substrate 6. Specifically, the dust-proof substrate 36 has its peripheral portion supported by the mounting step 34, and is adhered by interposing a thermal conductive adhesive 38 having a good soft thermal conductivity therebetween, and the cell housing. 22 is attached. This prevents stress from being generated in the dust-proof substrate 36 at the time of bonding, and increases the thermal contact area with the cell housing 22 (reducing thermal resistance). A temperature distribution is set so that the temperature of the peripheral portion of the dust-proof substrate 36 in contact with the temperature increases, and the slow axis is generated radially. Anti-reflection films 36A and 36B are provided on the upper and lower surfaces of the dust-proof substrate 36, respectively.

  As the material of the dustproof substrate 36, the same material as that of the transparent substrate 6, for example, the same glass plate is preferably used. As a result, when the liquid crystal display cell 2 is operated, the entire liquid crystal display cell 2 becomes a heating element due to Joule heat or the like, and the transparent substrate 6 is a semiconductor made of a silicon substrate which is a heat generation source via the liquid crystal 8. Since the substrate 4 is in contact with the surface, the temperature of the central portion of the transparent substrate 6 serving as the central portion of the heating element is higher than that of the peripheral portion.

  On the other hand, since the dust-proof substrate 36 is transparent, a lot of light is transmitted. However, the periphery of the dust-proof substrate 36 is attached to the mounting step 34 of the cell housing 22 that is heated by heat from the liquid crystal display cell 2 side. Since it is supported by being bonded via the heat conductive adhesive 38 having good heat conductivity, it is heated by the heat from the cell housing 22, and as a result, contrary to the temperature distribution of the transparent substrate 6, The temperature distribution is such that the temperature of the part is higher than that of the central part.

The plate-like cell base 24 is preferably made of Kovar (an alloy of iron, nickel, and cobalt, which has a thermal expansion coefficient close to that of glass or silicon). The coefficient of thermal expansion of Kovar is 49 × 10 ⁻⁷ / ° C. The thermal conductivity of Kovar is 17 W / m ° C. Incidentally, the coefficient of thermal expansion of the semiconductor substrate 4 made of a silicon substrate is 32 × 10 ⁻⁷ / ° C. As the transparent substrate 6 made of a glass substrate, # 1737 (trade name) manufactured by Corning Inc. can be used, and the coefficient of thermal expansion is 38 × 10 ⁻⁷ / ° C.

  As described above, the same glass plate as the transparent substrate 6 of the liquid crystal display cell 2 is used for the dust-proof substrate 36, and anti-reflection films 36A and 36B are formed on both sides of the dust-proof substrate 36. There is almost no absorption, and even when the reading light L is irradiated, the temperature rise of the dust-proof substrate alone hardly occurs. Further, as described above, since the soft heat conductive adhesive 38 is used for bonding the dustproof substrate 36 to the cell housing 22, no stress is generated during bonding, and the thermal contact area with the cell housing 22. Contrary to the transparent substrate 6 of the liquid crystal display cell 2, the temperature distribution can be made such that the temperature of the peripheral portion in contact with the cell housing 22 is increased during light irradiation.

  In other words, as described above, the transparent substrate 6 of the liquid crystal display cell 2 has a temperature distribution in which the central portion side (central portion side) of the transparent substrate 6 is hotter than the peripheral portion due to its characteristics. The dustproof substrate 36 has a reverse temperature distribution, that is, a temperature distribution in which the peripheral portion is hotter than the central portion, and thereby, birefringence due to stress generated by the temperature distribution of the transparent substrate 6 is provided opposite to the transparent substrate 6. Since it can be optically canceled by the birefringence generated by the dust-proof substrate 36, even when strong readout light is incident, the uniformity of the display image can be maintained and the high-quality display quality can be maintained.

The reflective liquid crystal display device 20A configured as described above is incorporated in a color separation / synthesis optical system (not shown) such as a projector (not shown). This color separation / synthesis optical system guides the readout light L emitted from a light source (not shown) to the liquid crystal display cell 2 of the reflective liquid crystal display device 20A and modulates it with an image signal emitted from the liquid crystal display cell 2. The readout light is projected onto a screen (not shown) to display an image.
A projector was constructed using the liquid crystal display device 20A produced as described above, and was actually operated to evaluate the quality of the display image.

The size of the liquid crystal display cell 2 in the reflective liquid crystal display device 20A of the first embodiment is 1.3 inches diagonal (aspect ratio 4: 3). The optical system used has a brightness of 8000 lm (lumen) on the screen, and the amount of light incident on the reflective liquid crystal display device 20A is 15W.
The uniformity of the projected image was evaluated as the display quality. The illuminance at the four corners and the center of the screen was measured, and the image uniformity was evaluated as “(maximum illuminance−minimum illuminance) / central illuminance”. The results are shown in Table 1.

As shown in Table 1, when the dust-proof substrate 36 was attached to the cell housing 22 with the heat conductive adhesive 38 having high heat conductivity, the uniformity of the image was most excellent. This result is due to the birefringence generated by the attachment of the dustproof substrate 36 and the temperature distribution caused thereby.
In the absence of the dust-proof substrate 36, the uniformity of the image is poor because of the temperature distribution that causes the temperature of the central portion of the transparent substrate 6 of the liquid crystal display cell 2 to be high during strong light irradiation, resulting in birefringence. is there. The stress generated by the temperature distribution in the transparent substrate 6 of the liquid crystal display cell 2 is a tensile stress, and the direction in which the refractive index is large (slow axis) is distributed in a circular shape. The state at this time is shown in FIG. In addition, the arrow in FIG. 3 has shown the direction where a refractive index is large.

On the other hand, since the dust-proof substrate 36 has a temperature distribution that increases the temperature of the peripheral portion, the resulting stress becomes a compressive stress, and the slow axis is distributed radially. The state at this time is shown in FIG. As a result, a phase difference caused by birefringence is generated in the opposite direction between the transparent substrate 6 and the dust-proof substrate 36 of the liquid crystal display cell 2, and this phase difference optically cancels out, thereby improving image uniformity. it can. That is, since the incident polarized light is arranged in the horizontal or vertical direction, the portion that is parallel or orthogonal to the incident polarized light becomes dark with a phase difference of zero, and the maximum phase difference occurs at a portion where the angle is 45 degrees with the incident polarized light, It becomes brighter. Since the phase difference is reversed between FIG. 3 (A) and FIG. 3 (B), the addition is canceled.
Accordingly, the birefringence of the transparent substrate 6 and the dust-proof substrate 36 of the liquid crystal display cell 2 always cancel each other optically, so that the uniformity of the image is increased even in a projector or the like in which the intensity of the readout light L is increased and the brightness is increased. Can be maintained.

Next, a second embodiment of the present invention will be described.
FIG. 4 is a sectional view showing a second embodiment of the reflective liquid crystal display device according to the present invention. In FIG. 4, the same components as those shown in FIG.
In the reflective liquid crystal display device 20B of the second embodiment, a visible light absorbing film 40 that absorbs visible light is formed on the peripheral side of the dust-proof substrate 36 in addition to the antireflective film 36B. Other configurations are the same as those of the first embodiment. Here, the visible light absorbing film 40 is formed with a predetermined width along the outer peripheral side of the lower side (liquid crystal display cell 2 side) of the dustproof substrate 36.

The visible light absorbing film 40 can be formed by forming a metal Cr by a vacuum film forming process and then patterning it by etching. A portion where the visible light absorbing film 40 is formed is preferably an outer peripheral portion from 27.4 × 20.8 mm on the outer periphery of 0.5 mm from the pixel area 26.4 × 19.8 mm of the silicon substrate.
Here, a projector similar to that of the first embodiment was configured using the reflective liquid crystal display device 20B, and the uniformity of the projected image was similarly evaluated. The results are shown in Table 2.

As shown in Table 2 above, the Cr film as the visible light absorbing film 40 increases the heat absorption at the periphery of the dust-proof substrate 36, and the birefringence of the dust-proof substrate 36 due to the temperature distribution increases. Similarly to the example, the birefringence of the transparent substrate 6 of the liquid crystal display cell 2 cancels out, and the image uniformity can be further improved.
In addition, since the Cr film functions as an image display frame, it also serves to shield the periphery of the pixel area. Therefore, the portion where the visible light absorption film 40 is formed is determined by the incident angle of the readout light L from the optical system, and the Cr film thickness that provides the optimum absorption rate is determined accordingly.

<Third embodiment>
Next, a third embodiment of the present invention will be described.
FIG. 5 is a sectional view showing a third embodiment of the reflective liquid crystal display device according to the present invention. In FIG. 5, the same components as those shown in FIGS. 2 and 4 are denoted by the same reference numerals.
In the reflective liquid crystal display device 20C of the third embodiment, both members are bonded together with an optically transparent adhesive 42 interposed between the dustproof substrate 36 and the transparent substrate 6 of the liquid crystal display cell 2. In this case, the antireflection film 36B (see FIG. 2) on the cell side of the dustproof substrate 36 bonded with the adhesive 40 and the antireflection film 6B (see FIG. 1) on the upper surface of the transparent substrate 6 of the liquid crystal display cell 2 are Can be omitted. Other configurations are the same as those of the second embodiment.

  A projector similar to that of the first example was constructed using the liquid crystal display device 20C, and the image uniformity of the projected image was also evaluated. The image uniformity in this case was as good as 21%. Heat exchange is performed by bonding the dust-proof substrate 36 and the transparent substrate 6 of the liquid crystal display cell 2, but birefringence can be canceled as in the first and second embodiments.

It is a schematic sectional drawing which shows the liquid crystal display cell used for the reflection type liquid crystal display device which concerns on this invention. 1 is a cross-sectional view showing a first embodiment of a reflective liquid crystal display device according to the present invention. It is a schematic diagram which shows the state of the slow axis which arises in a dustproof board | substrate. It is sectional drawing which shows 2nd Example of the reflection type liquid crystal display device based on this invention. It is sectional drawing which shows 3rd Example of the reflection type liquid crystal display device which concerns on this invention.

Explanation of symbols

2 ... Liquid crystal display cell, 4 ... Semiconductor substrate, 4A ... Pixel electrode, 6 ... Transparent substrate, 6A ... Common electrode, 8 ... Liquid crystal, 20A, 20B, 20C ... Liquid crystal display device, 22 ... Cell housing, 24 ... Cell base, 36 ... Dust-proof substrate, 38 ... Thermally conductive adhesive, 40 ... Visible light absorbing film, 42 ... Transparent adhesive, L ... Reading light.

Claims (3)

A semiconductor substrate having a plurality of reflective pixel electrodes formed in a matrix on the surface, and a transparent substrate having a transparent common electrode formed on the surface, the pixel electrode and the common electrode having a predetermined gap. A liquid crystal display cell that is disposed so as to face each other and encloses liquid crystal in the gap;
In a reflective liquid crystal display device having a transparent dustproof substrate provided on the transparent substrate side of the liquid crystal display cell,
A structure in which a thermally conductive cell housing is provided so as to surround at least the periphery of the liquid crystal display cell, and the cell housing supports a peripheral portion of the dustproof substrate so that a slow axis is radially generated in the dustproof substrate during operation. A reflection-type liquid crystal display device.   2. The reflection type liquid crystal display device according to claim 1, wherein a visible light absorption film for absorbing visible light is formed on the peripheral side of the dustproof substrate. 3. The reflective liquid crystal display device according to claim 1, wherein the dustproof substrate and the transparent substrate are bonded together with a transparent adhesive.

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