Liquid crystal display device and projection-type display device

The problem to be solved is to suppress image quality degradation caused by polarizers and provide improved light fastness.To solve the above problem, the embodiment of the present invention is a liquid crystal display device. The liquid crystal display device includes a driving-side substrate 1 on which a drive transistor 5, pixel electrode 6 and orientation film are formed. The liquid crystal display device further includes an opposed-side substrate 2 on which an opposed electrode and orientation film are formed. The liquid crystal display device still further includes liquid crystal 4 filled between the pixel electrode 6 of the driving-side substrate 1 and opposed electrode of the opposed-side substrate 2. The liquid crystal display device still further includes a reflective inorganic polarizer 3 formed between the drive transistor 5 and pixel electrode 6 of the driving-side substrate 1. The embodiment of the present invention is also a projection-type display device using the liquid crystal display device.

TECHNICAL FIELD

The embodiment of the present invention relates to a liquid crystal display device with liquid crystal filled between a driving-side substrate and opposed-side substrate, and to a projection-type display device using the same.

BACKGROUND ART

A projection-type display device (projector) using a liquid crystal display device has an absorptive organic polarizer on the incident and emitting sides. That is,FIG. 7is a schematic sectional view describing a related art liquid crystal display device. In this liquid crystal display device, a drive transistor5, pixel electrode6and orientation film are formed on a driving-side substrate1. In the same device, an opposed electrode and orientation film are formed on an opposed-side substrate2. The liquid crystal display device is formed by first attaching the driving-side and opposed-side substrates1and2together with a predetermined gap therebetween and then filling liquid crystal4between the pixel electrode6of the driving-side substrate1and opposed electrode of the opposed-side substrate2. On the other hand, an incident-side organic polarizer11is disposed on the outside of the opposed-side substrate2, and an emitting-side polarizer12on the outside of the driving-side substrate1.

However, the organic polarizers11and12disposed on the incident and emitting sides entails the problems of color fading and image quality degradation with increasing light intensity. Color fading is caused by the breaking of the dye and iodine molecules contained in the organic polarizers. Image quality degradation results from the burning of the protective layer. In the technique disclosed in Japanese Patent Laid-Open No. Hei 10-133196, therefore, an organic pre-polarizer is provided to distribute the optical stress, thus alleviating such stress on the emitting-side polarizer.

Some liquid crystal display devices employ inorganic polarizers to avoid the aforementioned problem of light fastness and other problems with polarizers made of organic materials. A reflective inorganic polarizer may be used on the incident side. However, a reflective inorganic polarizer3, if disposed on the emitting side or on the outside of the driving-side substrate1, adversely affects the image quality as a result of the light returning from the polarizer striking the drive transistor5, as illustrated inFIG. 8.

A possible solution to avoiding the impact of the returning light under consideration is to dispose the emitting-side reflective inorganic polarizer3diagonally relative to the driving-side substrate1as illustrated inFIG. 9. However, this solution leads to a large device configuration.

On the other hand, absorptive inorganic polarizers have yet to reach a level of practical utility due to their characteristic problems in the visible range (blue range in particular).

DISCLOSURE OF INVENTION

The embodiment of the present invention has been devised in light of the foregoing problems. That is, the embodiment of the present invention is a liquid crystal display device which includes a driving-side substrate on which a drive transistor, pixel electrode and orientation film are formed. The liquid crystal display device further includes an opposed-side substrate on which an opposed electrode and orientation film are formed. The liquid crystal display device still further includes liquid crystal filled between the pixel electrode of the driving-side substrate and opposed electrode of the opposed-side substrate. The liquid crystal display device still further includes a reflective inorganic polarizer formed between the drive transistor and pixel electrode of the driving-side substrate.

In the embodiment of the present invention described above, a reflective inorganic polarizer is provided between the drive transistor and pixel electrode of the driving-side substrate, thus eliminating the need for any polarizer on the outside of the substrate. Further, even a reflective inorganic polarizer can prevent the returning light from the polarizer from entering the drive transistor if disposed between the drive transistor and pixel electrode.

Further, the embodiment of the present invention is a projection-type display device which includes a light source, condensing optical system and projection optical system. The condensing optical system guides light from the light source into a liquid crystal display device. The projection optical system enlarges and projects the light optically modulated by the liquid crystal display device. In order to form the liquid crystal display device, a driving-side substrate and opposed-side substrate are disposed parallel to each other so that orientation films adapted to orient liquid crystal are opposed to each other. Liquid crystal is filled between the driving-side substrate and opposed-side substrate. The driving-side substrate of the liquid crystal display device has a drive transistor and pixel electrode. A reflective inorganic polarizer is formed between the drive transistor and pixel electrode.

Still further, the embodiment of the present invention is a projection-type display device which includes a light source, condensing optical system and projection optical system. The condensing optical system separates light from the light source into a plurality of color beams and guides each color beam into one of a plurality of liquid crystal display devices associated with the color beam. The projection optical system enlarges and projects the light optically modulated by the liquid crystal display devices. In order to form each of the plurality of liquid crystal display devices, a driving-side substrate and opposed-side substrate are disposed parallel to each other so that orientation films adapted to orient liquid crystal are opposed to each other. Liquid crystal is filled between the driving-side substrate and opposed-side substrate. The driving-side substrate of each of the plurality of liquid crystal display devices has a drive transistor and pixel electrode. A reflective inorganic polarizer is formed between the drive transistor and pixel electrode.

In the embodiment of the present invention described above, a reflective inorganic polarizer is provided between the drive transistor and pixel electrode of the driving-side substrate of the liquid crystal display device in the projection-type display device. This eliminates the need for any polarizer on the outside of the substrate, thus allowing for reduction of the component count of the projection-type display device. Further, even a reflective inorganic polarizer can prevent the returning light from the polarizer from entering the drive transistor if disposed between the drive transistor and pixel electrode, thus ensuring improved image quality of the projection-type display device.

Therefore, the embodiment of the present invention offers the following effects. That is, a reflective polarizer can be used on the emitting side without causing any image quality degradation, thus allowing to achieve a higher level of light fastness and to provide a higher level of value to the panel. Further, if reflective polarizers are used on both the incident and emitting sides, there is no need for any separate polarizer, allowing for significant downsizing of the set.

BEST MODES FOR CARRYING OUT THE INVENTION

The preferred embodiment of the present invention will be described below with reference to the accompanying drawings.FIG. 1is a schematic sectional view describing a liquid crystal display device according to the present embodiment. That is, the liquid crystal display device according to the present embodiment includes the driving-side substrate1and opposed-side substrate2. The drive transistor5, pixel electrode6and orientation film are formed on the driving-side substrate1. The opposed electrode and orientation film are formed on the opposed-side substrate2. The liquid crystal display device further includes liquid crystal4. The liquid crystal4is filled between the pixel electrode6and opposed electrode with the driving-side substrate1and opposed-side substrate2attached together. The liquid crystal display device still further includes the reflective inorganic polarizer3. The reflective inorganic polarizer3is formed between the drive transistor5and pixel electrode6of the driving-side substrate1. In the liquid crystal display device illustrated inFIG. 1, an orientation film is formed on each of the opposed surfaces of the driving-side substrate1and opposed-side substrate2. However, such films are omitted for easier understanding of the description.

The driving-side substrate1has an active layer and insulating layer stacked thereon. These layers make up the drive transistor5on the glass substrate. The drive transistor5is formed for each pixel by the predetermined techniques such as photolithography and ion injection.

The pixel electrode6which has electrical continuity with the drive transistor5is controlled by the on/off switching of the drive transistor5. This permits control of the voltage applied to the liquid crystal4. Further, a light-shielding film61is formed above the drive transistor5to prevent undesired light from entering the drive transistor5.

In the related art configuration, a pixel electrode is formed above a drive transistor via insulating and light-shielding films. In the present embodiment, the reflective inorganic polarizer3is formed between the drive transistor5and pixel electrode6. That is, the polarizer disposed on the emitting side is made of an inorganic material. Moreover, the polarizer is fabricated integrally with the driving-side substrate1.

The layer on which the reflective inorganic polarizer3is disposed is not particularly limited. Preferably, however, the reflective inorganic polarizer3should be disposed on a planarizing layer51formed on top of the drive transistor5(on the incident side). Further, the layer of the reflective inorganic polarizer3should preferably be fully buried in a protective layer31and planarized to avoid any impact on the upper layers.

To fabricate a reflective inorganic polarizer, fine lines are formed on a transparent substrate made of glass, quartz, polymer or other material. The width, height and shape of the fine lines just have to be optimally selected according to the wavelengths of the respective colors (red, green and blue light beams).

The material of the fine lines should be selected from among those which permit patterning at a fine pitch from 100 nm to 500 nm to cover the entire visible range and which function as a reflective polarizer. Further, aluminum or other inorganic conductive material is particularly preferred in consideration of light fastness and other factors.

On the other hand, a material having a low refractive index should be used, to the extent possible, as the medium (protective film31) adapted to fill the gaps between the fine lines in consideration of ease of manufacturing and feasibility.

If a sufficient extinction ratio wanted for a polarizer may not be provided, for example, because of the materials used as the reflective inorganic polarizer3and the medium (protective film31) adapted to fill the gaps between the fine lines, the reflective inorganic polarizer3may be used as a pre-polarizer and incident and emitting polarizers may be separately provided. As described above, even if the reflective inorganic polarizer3which is fabricated integrally with the driving-side substrate1is used as a pre-polarizer, the reflective inorganic polarizer3is disposed closer to the liquid crystal4than the drive transistor5. This allows suppressing image quality degradation, thus ensuring significantly reduced optical stress on the organic polarizer separately disposed on the emitting side.

In the meantime, if the reflective inorganic polarizer3can be designed and manufactured to offer an excellent extinction ratio characteristic, the reflective inorganic polarizer3may be used as the main polarizer, thus eliminating the need for any other polarizer.

For example,FIG. 2is a schematic sectional view describing an example in which the reflective inorganic polarizers7and3are fabricated integrally with the substrates on the incident and emitting sides, respectively. In this example, the driving-side substrate1on the emitting side has the reflective inorganic polarizer3disposed between the drive transistor5and pixel electrode6. The opposed-side substrate2on the incident side has the reflective inorganic polarizer7formed on the side of the liquid crystal4.

The reflective inorganic polarizer7formed on the opposed-side substrate2is formed on the layer between the surface of the opposed-side substrate2and the orientation film. The reflective inorganic polarizer7is provided on the uniformly formed substrate surface or on the surface of the opposed electrode. As a result, the separately formed film-type reflective inorganic polarizer7may be attached. Alternatively, the reflective inorganic polarizer7may be formed by vapor deposition and photolithography. It should be noted that the fine lines of the reflective inorganic polarizers3and7provided respectively on the driving-side substrate1and opposed-side substrate2are actually orthogonal to each other. However, these lines are shown to run in the same direction inFIG. 2for easier understanding of the description.

As described above, the reflective inorganic polarizers3and7are fabricated integrally with the driving-side substrate1and opposed-side substrate2, respectively. As a result, there is no need for any separate polarizer, thus allowing manufacturing the polarizing and liquid crystal members fully integral with the panel.

The manufacturing method of the liquid crystal display device according to the embodiment of the present invention will be described next with reference toFIGS. 3 to 5. First, as illustrated inFIG. 3(a), given films are formed on a glass substrate10which serves as the driving-side substrate. These films are fabricated into the drive transistor5by photolithography, ion injection and other techniques.

Next, an insulating film (e.g., silicon oxide film) is formed on the drive transistor5as illustrated inFIG. 3(b). This film is planarized, for example, by CMP to form the planarizing layer51. It should be noted that the planarization in this step is important for the accurate formation of the fine lines of the reflective inorganic polarizer in the next step.

Next, fine lines30serving as the reflective inorganic polarizer are formed on the planarizing layer51as illustrated inFIG. 3(c). The fine lines30are formed in several steps. That is, a photosensitive material is applied in advance first. Then, the areas where the fine lines will be fabricated are removed by photolithography. Next, aluminum or other inorganic conductive material is deposited, for example, by vapor deposition. Finally, the photosensitive material is removed to form the fine lines30at a given pitch.

Next, an optical thin film material such as magnesium fluoride is filled between the fine lines to form the protective film31as illustrated inFIG. 4(a), thus planarizing the surface. As a result, the reflective inorganic polarizer3is formed.

Next, the light-shielding film61is formed on a portion of the planarized surface of the reflective inorganic polarizer3as illustrated inFIG. 4(b). This portion is associated with the drive transistor5. At the same time, a conductive electrode60is formed which has electrical continuity with the drive transistor5.

Next, an insulating film62made, for example, of silicon oxide is formed on the light-shielding film61as illustrated inFIG. 4(c). Then, the pixel electrode6is formed on the insulating film62. The pixel electrode6is a transparent electrode (ITO: Indium Tin Oxide). The pixel electrode6is connected to the conductive electrode60formed earlier to have electrical continuity with the drive transistor5. Then, an unshown orientation film is formed which is rubbed as necessary.

Next, an opposed electrode and unshown orientation film are formed on a glass substrate20which serves as the opposed-side substrate2as illustrated inFIG. 5(a). Then, the driving-side substrate1and opposed-side substrate2are disposed face-to-face with each other with a given gap therebetween. The given gap is controlled, for example, by the spacer mixed in the sealing agent used to attach the substrates together. Alternatively, the gap may be controlled by forming an OCS as necessary.

Then, the liquid crystal4is injected into the gap formed between the driving-side substrate1and opposed-side substrate2as illustrated inFIG. 5(b). This provides a complete liquid crystal display device.

It should be noted that if the reflective inorganic polarizer7is fabricated integrally with the opposed-side substrate2as illustrated inFIG. 2, the reflective inorganic polarizer7is provided at the time of forming the opposed-side substrate2. Then, the driving-side substrate1and opposed-side substrate2just have to be overlaid one on top of another in this condition, followed by liquid crystal injection.

Further, if the reflective inorganic polarizer7is fabricated integrally with the opposed-side substrate2as illustrated inFIG. 2, a given pattern may be left unremoved without fabricating some fine lines so that the unremoved pattern can serve also the purpose of a light-shielding film to be provided on the opposed-side substrate2for protection against stray light. Alternatively, some fine lines may be rotated 90 degrees to prevent the propagation of undesired light to the screen. Still alternatively, the patterns of the reflective inorganic polarizers3and7may be electrically grounded to avoid the development of undesired electric field.

The liquid crystal display device according to the present embodiment is used in a projection-type display device such as a projection-type liquid crystal projector as illustrated inFIG. 6.

A liquid crystal projector100illustrated inFIG. 6is a so-called three-plate projector. The liquid crystal projector100separates the light from the light source into three primary colors: i.e., red, blue and green. The liquid crystal projector100uses an LCD (liquid crystal display device) for each of the three colors to display a color image. Liquid crystal light bulbs, each for one of the three primary colors, correspond to the LCD illustrated inFIG. 1. In the description given below, an LCD adapted to receive the red light is denoted by reference numeral LCD125R, an LCD adapted to receive the green light by reference numeral LCD125G, and an LCD adapted to receive the blue light by reference numeral LCD125(b).

The LCDs125R and125(b) each have a liquid crystal layer formed, for example, by sealing liquid crystal with an inorganic sealing agent. These LCDs have no OCS (On Chip Spacer) adapted to control the liquid crystal layer to a given thickness. On the other hand, the LCD125G for the green light, a highly visible color, has a liquid crystal layer formed, for example, by sealing liquid crystal with an organic sealing agent, thus controlling the gap with accuracy using an OCS.

The liquid crystal projector100illustrated inFIG. 6includes a light source111adapted to emit light and first lens array112disposed on the emitting side of the light source111. The liquid crystal projector100further includes a mirror114adapted to reflect the light emitted from the first lens array112and change the optical path of the emitted light (optical path110) 90 degrees. The liquid crystal projector100still further includes a second lens array113adapted to receive the reflected light from the mirror114.

Here, the mirror114is preferably a total reflection mirror. The first and second lens arrays112and113have a plurality of micro lenses112M and113M, respectively. The micro lenses112M and113M are arranged two-dimensionally.

The first and second lens arrays112and113are adapted to provide uniform distribution of illuminance. These arrays can split the incident beam into a plurality of small luminous fluxes. It should be noted that an unshown UV (ultraviolet)/IR (infrared) cut filter may be provided between the light source111and first lens array112.

The light source111emits white light which contains red, blue and green beams wanted to display a color image. The light source111source111includes an unshown luminous body adapted to emit white light and reflector adapted to reflect and collect the light from the luminous body.

An ultra high pressure mercury lamp, halogen lamp, metal halide lamp or xenon lamp can be used, for example, as a luminous body. The reflector is preferably shaped to offer high light collecting efficiency. For example, the reflector has a rotationally symmetric concave surface such as spheroidal mirror or rotational parabolic surface. The light emission point of the luminous body is located at the focal point of the concave-surfaced reflector.

The white light emitted from the luminous body of the light source111is formed into an approximately parallel beam by the reflector and enters the total reflection mirror114via the first lens array112. The white light enters the second lens array113after its optical axis110has been bent 90 degrees by the total reflection mirror114.

The liquid crystal projector100illustrated inFIG. 6has a PS conversion element115, condenser lens116and dichroic mirror117on the emitting side of the second lens array113.

The PS conversion element115is an example of a polarization conversion element. The PS conversion element115has a plurality of phase difference plates115(a) provided at the positions associated with the boundaries between the adjacent micro lenses on the second lens array113. A half-wave plate is an example of the phase difference plate115(a).

The PS conversion element115separates the incident light into p- and s-polarization components. The PS conversion element115emits one of the polarizations (e.g., p-polarization component) without changing the polarization direction thereof. The PS conversion element115converts another polarization (e.g., s-polarization component) into the other polarization component (e.g., p-polarization component) by the action of the half-wave plates115(a) and emits the resultant polarization component.

The light from the PS conversion element115is collected by the condenser lens116and enters the dichroic mirror117. The dichroic mirror117reflects, for example, a red light beam LR in the incident light and transmits the other color beams, thus separating the incident light into the red beam LR and other color beams.

The liquid crystal projector100further has a mirror118, field lens124R, incident-side polarizer130I, LCD125R and emitting-side polarizer130S arranged along the optical path of the red beam LR separated by the dichroic mirror117.

Here, a total reflection mirror is used as the mirror118. The total reflection mirror118reflects the red beam LR, separated by the dichroic mirror117, toward the incident-side polarizer130I and LCD125R.

The incident-side polarizer130I transmits the portion of the incident red beam LR from the total reflection mirror118whose direction matches the direction of a polarization axis130a.

The LCD125R has the same construction as the aforementioned liquid crystal display device. The LCD125R spatially modulates the red beam LR, received via the incident-side polarizer130I provided as necessary, according to the input image data.

The emitting-side polarizer130S which is provided as necessary, on the other hand, transmits the portion of the modulated red beam LR from the LCD125R whose direction matches the direction of a polarization axis130b.

The liquid crystal projector100has a dichroic mirror119arranged along the optical path of the other color beams separated by the dichroic mirror117. The dichroic mirror119reflects a green beam LG of the incident light and transmits a blue beam LB thereof, thus separating the incident light into the green and blue beams LG and LB.

A field lens124G, the incident-side polarizer130I, the LCD125G and the emitting-side polarizer130S are provided along the optical path of the green beam LG separated by the dichroic mirror119. It should be noted that the incident-side polarizer130I and emitting-side polarizer130S are provided as necessary.

The incident-side polarizer130I transmits the portion of the incident green beam LG from the dichroic mirror119whose direction matches the direction of the polarization axis130a. The LCD125G spatially modulates the green beam LG received via the incident-side polarizer130I according to the input image data. The emitting-side polarizer130S transmits the portion of the modulated green beam LG from the LCD125G whose direction matches the direction of the polarization axis130b.

Further, a relay lens120, a mirror121, a relay lens122, a mirror123, a field lens124(b), the incident-side polarizer130I, the LCD125(b) and the emitting-side polarizer130S are provided along the optical path of the blue beam LB separated by the dichroic mirror119. It should be noted that the incident-side polarizer130I and emitting-side polarizer130S are provided as necessary.

The mirrors121and123are preferably total reflection mirrors. The total reflection mirror121reflects the blue beam LB, received via the relay lens120, toward the total reflection mirror123. The total reflection mirror123reflects the blue beam LB, reflected by the total reflection mirror121and received via the relay lens122, toward the incident-side polarizer130I and LCD125(b).

The incident-side polarizer130I transmits the portion of the incident green beam LG from the total reflection mirror123whose direction matches the direction of the polarization axis130a. The LCD125(b) spatially modulates the blue beam LB reflected by the total reflection mirror123and received via the field lens124(b) according to the input image data.

The emitting-side polarizer130S transmits the portion of the modulated blue beam LB from the LCD125(b) whose direction matches the direction of the polarization axis130b. A cross prism126is provided where the optical paths of the red, green and blue beams LR, LG and LB intersect each other. The cross prism126can combine these color beams.

The cross prism126includes, for example, four right angle prisms joined together. Each of the prisms has incident surfaces126R,126G and126B which receive the red, green and blue beams LR, LG and LB, respectively. Each of the prisms further has an emitting surface126T which emits the combined light of the red, green and blue beams LR, LG and LB.

In the liquid crystal projector100, the joined surface of each of the right angle prisms is coated with a dichroic film. As a result, the cross prism126transmits the incident green beam LG toward the emitting surface126T and reflects the red and blue beams LR and LB toward the emitting surface126T. This permits the cross prism126to combine the three color beams entering the incident surfaces126R,126G and126B to emit the combined beam from the emitting surface126T.

Further, the liquid crystal projector100has a projection lens127adapted to project the combined beam from the cross prism126toward a screen128. The projection lens127preferably includes a plurality of lenses and has zooming and focusing functions. The zooming function permits the adjustment of the image size projected onto the screen128.

A reflective inorganic polarizer is incorporated in the liquid crystal display device according to the present embodiment. Therefore, if the liquid crystal display device is used in the liquid crystal projector100configured as described above as its LCD and if the reflective inorganic polarizer is used as a pre-polarizer, the optical stress on the incident-side polarizer130I and emitting-side polarizer130S can be significantly reduced. This provides improved durability of the liquid crystal projector100as a whole.

In the meantime, if the reflective inorganic polarizer3can be designed and manufactured to offer an excellent extinction ratio characteristic, the reflective inorganic polarizer3may be used as the main polarizer, thus eliminating the need for the incident-side polarizer130I and emitting-side polarizer130S. This allows for reduction of the component count and downsizing of the liquid crystal projector100.

The embodiment of the present invention has been described with reference to an embodiment of a transmissive LCD and a projection-type display device associated therewith. However, a reflective LCD may be combined with a projection-type display device. Further, other projection-type display devices may also be used. Such projection-type display devices include one which uses a liquid crystal display device for each color of RGB and another which uses just one liquid crystal display device to display a monochrome image.