JPH04338721A - Reflection type optical modulation panel and projection type display device - Google Patents

Abstract

PURPOSE:To realize the projection type display device which provides high output and high efficiency, makes a display of high quality, and generates a small noise. CONSTITUTION:The panel consists of a matrix substrate which has switching transistors 40, picture element electrodes 41, etc., on a glass plate 20, a transparent glass plate 24 which has a transparent electrode 25, and an optical modulation layer 23 which is sandwiched between them, and a dielectric films 42 and a dielectric multi-layered film mirror 43 which have their surfaces flattened are formed on the picture element electrodes 41.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection type display device that uses an active matrix liquid crystal panel to project and display television images on a screen.

0002

2. Description of the Related Art Recently, with the improvement of the video software supply environment and the increasing definition of images such as high-definition, there has been an increasing demand for projection type display devices that can display a large screen with a high number of pixels.

[0003] Also in liquid crystal projectors that enlarge and display images on a liquid crystal panel, high-density liquid crystal panels are being developed to increase the number of pixels. 13, No. 58, pp. 49-5
There is an active matrix reflective liquid crystal panel reported in No. 4. As shown in FIG. 2, this liquid crystal panel includes a matrix substrate having a configuration in which a switching transistor 21 and a reflective pixel electrode 22 are provided on a glass substrate 20, a transparent glass plate 24 having a light shielding film 26 and a transparent electrode 25, It is composed of a liquid crystal layer 23 sandwiched between them. The reflective pixel electrode 22 is made of aluminum metal, and the light shielding film 26 that prevents light from irradiating the switching transistor 21 is generally made of chromium metal.

In this reflective liquid crystal panel, the light flux incident from the transparent glass plate 24 side is modulated by the liquid crystal layer 23 and reflected by the reflective pixel electrode 22, so that the modulated light is extracted as reflected light. In the reflective type, the reflective pixel electrode can be formed on the switching transistor, unlike the conventional transmissive liquid crystal panel, which has a structure in which a switching transistor and a transmissive pixel electrode are formed in parallel on the panel surface. Therefore, there is an advantage that the panel size can be considerably reduced with the same number of pixels, and the proportion of the light modulation section within the panel surface can be made relatively large.

[0005]

However, the above-mentioned reflective liquid crystal panel has many problems. One is the low light utilization efficiency. The reflectance of the aluminum surface of the reflective pixel electrode is as low as approximately 88%, and the light shielding film is placed so as to overlap the reflective pixel electrode to a sufficient extent to sufficiently prevent light from irradiating the switching transistor. Efficiency decreases. For example, even if a highly reflective metal such as silver is used for the reflective pixel electrode, it is difficult to eliminate the reduction in efficiency caused by the light shielding film. Furthermore, when the reflective pixel electrode is made of aluminum, it is difficult to flatten the surface because the material is brittle, and low specular reflection efficiency due to surface irregularities also becomes a factor in reducing efficiency.

Another problem is that cooling is required to prevent the panel from increasing in temperature. Since the aluminum of the reflective pixel electrode has a visible light absorption rate of about 12%, and the chromium of the light shielding layer has a visible light absorption rate of about 60%, the temperature of the liquid crystal panel increases. In this case, the off-resistance of the switching transistor decreases, and the resistivity and arrangement state of the liquid crystal material change, resulting in a decrease in display quality. To prevent this, cooling such as liquid cooling or air cooling is required, which results in increased noise, increased device size, and increased power consumption.

Furthermore, when dealing with a high-power luminous flux,
In addition to the above problems, there arises the problem of a decrease in contrast ratio. FIG. 3 is a diagram showing the relationship between panel illuminance and contrast ratio for a reflective light modulation panel similar to that in FIG. 2. Even under conditions of sufficient forced air cooling, the panel temperature increases as the amount of light incident on the panel increases, and the contrast ratio decreases accordingly. Also, as the amount of light increases,
Irradiation of the switching transistor by a small amount of light passing between the light shielding film and the reflective pixel electrode cannot be ignored, and the contrast ratio decreases due to the photoconduction phenomenon of the semiconductor. Projection display devices for presentations need to be visible even in bright places, and projection display devices for theaters need to be able to be viewed by a large number of people, each of which requires extremely high output. The problem of a decrease in contrast ratio becomes even more noticeable.

[0008] Recently, PDLC (Polymer Dispersion), in which liquid crystals are dispersed in polymers and incident light is modulated by the degree of scattering, has been developed.
There is a new mode of light modulation material called (persed liquid crystal), which is attracting a lot of attention because of its high light utilization efficiency. It is conceivable to use a material that modulates such light according to the degree of scattering in a conventional reflective light modulation panel, but in this case, the scattered light easily passes between the light shielding film and the reflective electrode, This combination is difficult to use because it lowers the off-resistance of the switching transistor.

The reflective light modulation panel and projection type liquid crystal display device according to the present invention solves these problems.
The purpose is to provide a projection type display device with high output, high efficiency, high quality display, and low noise.

0010

[Means for Solving the Problems] The reflective light modulation panel of the present invention includes a first support plate having a transparent electrode and high visible light transmittance, a plurality of pixel electrodes, and one support plate for driving each pixel electrode. A reflective mode light modulation panel comprising a second support plate having the above switching element and a light modulation layer sandwiched between both support plates, wherein the light modulation layer is sandwiched between the second support plate and the light modulation layer. is characterized in that an optical separation dielectric layer is formed that optically separates the light modulation layer side and the second support plate side and has the function of reflecting incident light from the first support plate side. shall be.

[0011] In the above preferred embodiment, the optical isolation dielectric layer includes a dielectric film formed on the second support plate and having a flattened surface, and a dielectric multilayer mirror formed on the dielectric film. characterized by something. Furthermore, the dielectric film is characterized in that it is a ferroelectric material and/or a material with a high visible light absorption rate. Alternatively, a material having a high visible light absorption rate is further inserted between the dielectric film and the dielectric multilayer mirror.

In addition, the preferred embodiment described above is characterized in that the optical isolation dielectric layer is a dielectric multilayer mirror formed on the planarized pixel electrode. Furthermore, a dielectric film having a high visible light absorption rate is inserted between the pixel electrode and the dielectric multilayer mirror.

[0013] The light modulating layer is characterized in that it is a liquid crystal composite material that modulates the incident light flux depending on the degree of scattering.

[0014] The second support plate is a single-crystal silicon substrate, and the switching element is formed using the single-crystal silicon substrate.

The projection type display device of the present invention includes a light source device that generates a light beam containing three primary color lights, a color light separator that separates the light beam into each primary color light beam, and a color light separator that modulates each of the separated primary color light beams. A projection display device comprising: a reflective light modulation panel that includes display information; and a projection lens that projects a modulated light beam onto a screen; The reflection type light modulation panel is characterized in that the reflection wavelength range of the dielectric multilayer mirror included in the reflective light modulation panel corresponds to the wavelength range of the primary color light beam separated by the color light separator.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A reflective light modulation panel and a projection display device according to the present invention will be explained in detail below with reference to the drawings.

The reflective light modulation panel of the present invention is particularly driven by an active matrix method using switching transistors. FIG. 1 shows the configuration of the equivalent circuit on the panel and its peripheral parts in this case. A switching transistor 10 is formed for each pixel, and when turned on by the Y driver, a signal voltage is written into the liquid crystal capacitor 11 by the X driver. In addition, in order to prevent voltage drop due to liquid crystal leakage, etc., a holding capacity of 1
2 is provided in parallel with the liquid crystal capacitor 11. In addition to this, active matrix methods include those in which an MIM element is provided for each pixel, and those in which a diode element is provided for each pixel.
The present invention can also be used for these.

A first embodiment of a reflective light modulation panel according to the present invention is shown in FIG. A matrix substrate having a switching transistor 40, a pixel electrode 41, etc. on a glass plate 20, and a transparent glass plate 2 having a transparent electrode 25.
4 and a light modulation layer 23 containing a liquid crystal material sandwiched between them, and a dielectric film 42 with a flattened surface and a dielectric multilayer mirror 43 are formed on the pixel electrode 41. .

When a signal potential is applied to the pixel electrode 41 through the switching transistor 40, a potential difference is generated between the transparent electrode 25 and the pixel electrode 41, and this voltage is applied to the light modulating layer 23 containing the liquid crystal material and the dielectric multilayer mirror 43. The dielectric film 42 divides the capacitance, and the alignment direction of the liquid crystal molecules changes depending on the voltage applied to the light modulation layer 23. When a readout light beam is incident from the transparent glass plate 24 side, it is modulated by liquid crystal molecules while passing through the light modulation layer 23, and is reflected by the dielectric multilayer mirror 43.
After being reflected by the light modulating layer 23, the light is modulated again by the light modulating layer 23 and then taken out. Since the dielectric multilayer mirror 43 can have a reflectance of 99% or more by appropriate design, the reflective light modulation panel of this configuration has negligible light absorption and almost no temperature rise. Further, the amount of light irradiation to the switching transistor 40 is also very small.

[0020] For the light modulation layer 23, a liquid crystal material or a liquid crystal composite material is used. In the case of liquid crystal materials, for example, there are nematic liquid crystals that are oriented in a twisted structure or a structure that is almost perpendicular to the substrate, and when polarized light is incident, the polarization state is changed by increasing or decreasing the retardation of the light modulation layer. . A liquid crystal composite material is a composite of liquid crystal with a polymeric material or an inorganic material, and includes materials such as PDLC that modulate light by scattering and transmitting it.

A suitable mode for the reflective light modulation panel is the so-called normally black mode, in which black is displayed when no voltage is applied, and white is displayed when voltage is applied. When the normally white mode is used, since the pixel electrodes 41 are discrete, it is difficult to apply a voltage to the entire light modulation layer 23 for black display, and the contrast ratio of the display becomes low.

When the signal line from the X-driver is passed between the pixel electrodes 41, the signal potential to other pixels applies a voltage to the light modulation layer 23 corresponding to the gap between the pixel electrodes 41, thereby improving the display quality. worsen. Therefore, in this configuration, it is better to pass the signal line under the pixel electrode. However, in this case, signals to other pixel electrodes affect the pixel electrode 41, causing crosstalk and vertical unevenness, so as a special driving method, a line inversion drive in which the polarity is reversed for each horizontal line is used. use In line inversion driving, the influence of the video signal on other pixels becomes a high frequency alternating current electric field.
Since the change is faster than the response speed of liquid crystal molecules, it hardly affects the display.

The dielectric film 42 is made of silicon nitride (S), for example.
i3N4), silicon oxide (SiO2), and its surface is flattened by polishing so that the dielectric multilayer mirror 43 formed thereon is formed flat. If the planarization is insufficient, the specular reflection efficiency of the dielectric multilayer mirror will be low, resulting in a low light modulation efficiency.

When this dielectric film 42 is formed of a material with a high dielectric constant such as a ferroelectric, such as titanium oxide (TiO2) or barium titanate (BaTiO3), a voltage is applied to the dielectric film 42 by capacitance division. The voltage is lower, reducing the overall voltage requirement. Further, the unevenness of the electrode 41 causes unevenness in the voltage applied to the light modulation layer 23 within one pixel, but this can be considerably reduced by using a material with a high dielectric constant. Furthermore, when the dielectric constant is high, the electric field wraps around more, and a voltage is applied to the liquid crystal molecules even in a portion slightly off the top of the pixel electrode 41, increasing the actual light modulation area and increasing the modulation efficiency.

As mentioned above, most of the read light is extracted by reflection by the dielectric multilayer mirror 22, but since the reflectance of the dielectric multilayer mirror cannot be made completely 100%, a small amount of the read light is extracted by the dielectric multilayer mirror 22. The light flux passes through the switching transistor 4
irradiated to 0. If an aluminum metal film with high reflectivity is used as the pixel electrode 41, the amount of irradiated light will be considerably reduced, but when a very large amount of light is irradiated, the light flux that passes between the pixel electrodes will lower the off-resistance of the switching transistor 40. and reduce display quality. Therefore, if a material with high visible light absorption rate, such as cadmium telluride (CdTe), praseodymium manganate (PrMnO3), or niobium oxide (NbO) is used as the dielectric film 42,
It is possible to completely cut out the irradiation light. In particular, when the light modulation layer 23 is made of a material such as PDLC that modulates light according to the degree of scattering, the scattered light easily passes through due to the angular dependence of the dielectric multilayer mirror, so it absorbs visible light. The effect of using a material with a high index is very large.

A second embodiment of the reflective liquid crystal light valve according to the present invention is shown in FIG. In this configuration, a dielectric film 50 having a high visible light absorption rate is inserted between the dielectric multilayer mirror 43 and the dielectric film 42 of the first embodiment. The effect is the same as in the case of using a material with high visible light absorption rate for the dielectric film 42 in the first embodiment. However, in this case, there is no need to planarize the dielectric film 50 with a high visible light absorption rate, so there is a large degree of freedom in selecting the material of the dielectric film 50 with a high visible light absorption rate. For example, even materials that cannot be polished, such as organic materials with pigments dispersed therein or dyed gelatin, can be used. Further, even a black material with low adhesion strength to the pixel electrode 41 can be used. A third embodiment of the reflective light modulation panel according to the present invention is shown in FIG. In this case, the flattened pixel electrode 41
A dielectric film 50 with a high visible light absorption rate and a dielectric multilayer mirror 43 are laminated thereon. When aluminum is used as the pixel electrode 41, it is easy to manufacture because aluminum is relatively brittle and easy to polish. Furthermore, compared to the second embodiment, since the dielectric film 42 in FIG. 5 is not provided, the voltage applied to the light modulation layer 23 increases accordingly, and the required maximum voltage can be reduced. In addition, since the electric field applied to the light modulation layer 23 within the pixel is uniform, the display quality is good. Although the dielectric film 50 with a high visible light absorption rate is shown in FIG. 6, it may be omitted if light leakage to the switching transistor 40 is not a problem.

Fourth in the reflective light modulation panel of the present invention
An example of this is shown in FIG. In the other embodiments described above, a matrix substrate in which thin film transistors were formed on a glass plate was used, but in this embodiment, a single crystal silicon substrate 70 is used. Switching transistor 7 made using single crystal silicon substrate 70
Although No. 1 has very good characteristics, it tends to be prone to deterioration in characteristics against light. However, in this configuration, almost all of the incident light is transmitted to the dielectric multilayer mirror 43.
Since the light is shielded by the dielectric film 50 having a high visible light absorption rate, no deterioration of characteristics occurs. Further, it is possible to incorporate the X-driver and Y-driver shown in FIG. 2 on the single crystal silicon substrate 70, and the structure around the panel becomes extremely simple.

The dielectric multilayer mirror formed on the pixel electrode generally has a structure in which dielectric films with a high refractive index and dielectric films with a low refractive index are alternately laminated. On the other hand, the optical thickness of each film is 1/4 wavelength. FIGS. 8, 9, and 10 are diagrams showing examples of wavelength-reflectance characteristics of dielectric multilayer mirrors that reflect green light, red light, and blue light, respectively. The characteristics are shown when a total of 15 layers are stacked, using TiO2 for the high refractive index film and SiO2 for the low refractive index film. In order to increase the reflectance, it is sufficient to increase the number of layers. For example, if you increase the number of layers to 20, the reflectance will be 99.8% in the range of 50 nm before and after the reflection center wavelength.
That's all. Next, a projection display device using the above-mentioned reflective light modulation panel will be explained. FIG. 11 is a perspective view showing a first embodiment of the projection display device of the present invention. This configuration was devised for the case where a material such as PDLC that modulates light according to the degree of scattering is used as the light modulation layer of a reflective light modulation panel. Light source device 11
0, the light beam from a light source lamp such as a halogen lamp, metal halide lamp, or xenon lamp is converted into a nearly parallel light beam by a parabolic reflector, and unnecessary wavelength ranges such as infrared and ultraviolet light are removed by a filter before being emitted. The light beam separation prism 111 is constructed by placing the slopes of two triangular prisms with a slight gap between them, and the light beam from the light source device 110 is totally reflected on the slope of one of the triangular prisms, resulting in color light separation. prism 112
Inject it into the Color light separation prism 112 shown in FIG.
has a square prism shape with four triangular prisms glued together, and has a red reflective multilayer interference filter and a blue reflective multilayer interference filter inside in a cross shape, so the three primary colors of the incident light beam are separated into three directions. be done. The separated primary color lights are each directed to a reflective liquid crystal panel 113 (there is another reflective light modulation panel on the other side of the color light separation prism 112), and after being modulated, they are directed to the color light separation prism 1 again.
12 and is synthesized following the path in the opposite direction. The beam then reaches the slope where it is totally reflected at the beginning of the beam splitting prism 111, but since the angle of incidence on the slope at this time is smaller than at the beginning, most of the beam passes through, and similarly, almost all of the beam passes through the other triangular prism. is transmitted. The modulated light that has passed through the beam separation prism 111 enters a projection lens 114 and is projected onto a screen 115. Among the light beams modulated by the reflective light modulation panel 113 that modulates the incident light beam by the degree of scattering, the specularly reflected light reaches the screen 115, but the scattered light does not enter the projection lens 114, or Even if it is incident, it will not reach the screen 115 because it will be blocked by the aperture in the projection lens 114.

When using a light modulation layer such as PDLC that modulates light according to the degree of scattering in a reflective light modulation panel, the problem is that the light reflected from the surface of the glass plate used in the light modulation panel, etc. This is to reduce the contrast ratio of the display. In such an optical system, the reflective light modulation panel 1
13, color light separation prism 112, light beam separation prism 11
When the respective glass material parts of 1 are brought into close contact with oil or optical glue whose refractive indexes are matched, reflected light at the interface is eliminated, making it easy to obtain a high contrast ratio.

A second embodiment of the projection type display device of the present invention is shown in FIG. In this configuration, for example, ECB (electrically
controlled birefringen
ce) mode, which modulates light by changing the polarization direction. The substantially parallel light beam emitted from the light source device 110 enters the color beam splitter 121 by the polarizing beam splitter 120, where the p-polarized light is transmitted and the s-polarized light is reflected. Of the s-polarized light including the three primary colors incident on the color light separation prism 121, the green light is transmitted to the reflective light modulation panel 1 for green color.
22G, the red light and blue light are reflected by the multilayer interference filter included in the color light separation prism 121 and the interface between the glass material and the air, and are reflected by the red reflective light modulation panel 122R and the blue reflective light modulation panel 122R, respectively. 122B. The reflected primary color lights whose polarization state has been modulated are combined by a color light separation prism 121, and only the p-polarized light is transmitted by a polarization beam splitter 120.
The light will be analyzed. This analyzed light beam is projected through the projection lens 114 to form a color image on the screen.

[0031]

As described above based on the embodiments, the reflective light modulation panel and projection display device of the present invention have the following three main effects.

[0032] Since the reflectance of incident light to the panel is high, the aperture ratio is high, and a light modulation material with a high light utilization efficiency such as a liquid crystal composite can be used, the overall light utilization efficiency is very high. . In turn, the power consumption of the projection display device can be reduced.

[0033] Since almost no light flux is absorbed by the light modulation panel, there is no need to cool the panel, and noise is reduced.

[0034] Since there is no problem of display quality deterioration due to temperature rise of the light modulation panel or light irradiation to the switching transistor, it is possible to input a high power luminous flux to the light modulation panel.
Therefore, it is possible to realize a high-output projection display device that can be easily viewed even in a bright place.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an equivalent circuit on an active matrix optical modulation panel using switching transistors and the configuration of its peripheral parts.

FIG. 2 is a schematic cross-sectional view showing the configuration of a conventional reflective light modulation panel.

FIG. 3 is a diagram showing the relationship between panel illuminance and display contrast ratio in a conventional reflective light modulation panel.

FIG. 4 is a schematic cross-sectional view showing a first embodiment of a reflective light modulation panel according to the present invention.

FIG. 5 is a schematic cross-sectional view showing a second embodiment of the reflective light modulation panel according to the present invention.

FIG. 6 is a schematic cross-sectional view showing a third embodiment of the reflective light modulation panel according to the present invention.

FIG. 7 is a schematic cross-sectional view showing a fourth embodiment of a reflective light modulation panel according to the present invention.

FIG. 8 is a diagram showing wavelength-reflectance characteristics of a dielectric multilayer mirror that reflects green light.

FIG. 9 is a diagram showing wavelength-reflectance characteristics of a dielectric multilayer mirror that reflects red light.

FIG. 10 is a diagram showing wavelength-reflectance characteristics of a dielectric multilayer mirror that reflects blue light.

FIG. 11 is a structural perspective view showing a first embodiment of a projection type display device of the present invention.

FIG. 12 is a structural perspective view showing a second embodiment of the projection display device of the present invention.

[Explanation of symbols]

10, 21, 40, 71... Switching transistor 11... Liquid crystal capacitor 12... Holding capacitor 20... Glass plate 22... Reflective pixel electrode 23... Light modulation layer 24... Transparent glass Plate 25...Transparent electrode 26...Light shielding film 41...Pixel electrode 42...Dielectric film 43...Dielectric multilayer mirror 50...Dielectric film 70 with high visible light absorption rate . . . Single crystal silicon substrate 110 . . . Light source device 111 . ...Polarizing beam splitter

Claims (10)

[Claims] 1. A first support plate having a transparent electrode with high visible light transmittance; a second support plate having a plurality of pixel electrodes and one or more switching elements for driving each pixel electrode; In a light modulation panel used in a reflective mode, the light modulation layer is sandwiched between support plates, and between the second support plate and the light modulation layer, the light modulation layer side and the second support plate are disposed between the second support plate and the light modulation layer. A reflective light modulation panel characterized in that an optical isolation dielectric layer is formed that optically isolates the plate sides and reflects incident light from the first support plate side. 2. The optical separation dielectric layer is a dielectric film formed on the second support plate and having a flattened surface, and a dielectric multilayer mirror formed thereon. The reflective light modulation panel according to claim 1. 3. The reflective light modulation panel according to claim 2, wherein the dielectric film is ferroelectric. 4. The reflective light modulation panel according to claim 2, wherein the dielectric film is made of a material with high visible light absorption rate. 5. The reflective light modulation panel according to claim 2, wherein a substance having a high visible light absorption rate is inserted between the dielectric film and the dielectric multilayer mirror. . 6. The reflective light modulation panel according to claim 1, wherein the optical isolation dielectric layer is a dielectric multilayer mirror formed on the planarized pixel electrode. 7. The optical isolation dielectric layer is a dielectric film having a high visible light absorption rate formed on the planarized pixel electrode, and a dielectric multilayer mirror formed thereon. The reflective light modulation panel according to claim 1, characterized by: 8. The reflective material according to claim 1, 2, 3, 4, 5, 6, or 7, wherein the light modulating layer is a liquid crystal composite material that modulates the incident light flux by the degree of scattering. type light modulation panel. 9. Claims 1, 2, 3, and 4, wherein the second support plate is a single-crystal silicon substrate, and the switching element is formed using the single-crystal silicon substrate. , 5, 6, 7 or 8. 10. A light source device that generates a light beam containing three primary color lights, a color light separator that separates the light beam into each primary color light beam, and modulates each of the separated primary color light beams to include display information. A projection type display device comprising a reflective light modulation panel and a projection lens for projecting a modulated light beam onto a screen, wherein the reflective light modulation panel is characterized by the following: , or 9, wherein the reflection wavelength range of the dielectric multilayer mirror included in the reflective light modulation panel is in the wavelength range of the primary color light beam separated by the color light separator. A projection type display device characterized by being compatible.