JP3530811B2 - Reflective light modulation panel and projection display - Google Patents

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 for projecting and displaying a television image or the like on a screen using an active matrix liquid crystal panel.

[0002]

2. Description of the Related Art Recently, a demand for a projection type display device capable of displaying a large screen with a large number of pixels has been increased with the improvement of the environment for supplying the image software and the high definition of the image as seen in the high definition.

In a liquid crystal projector for enlarging and displaying an image on a liquid crystal panel, a high-density liquid crystal panel has been developed to increase the number of pixels. For example, see Technical Report of the Television Society of Japan. 13, No. 58, pp. 49-5
There is an active matrix type reflective liquid crystal panel reported in No. As shown in FIG. 2, this liquid crystal panel includes a matrix substrate having a switching transistor 21 and a reflective pixel electrode 22 provided on a glass substrate 20, a transparent glass plate 24 having a light shielding film 26 and a transparent electrode 25. The liquid crystal layer 23 is sandwiched between them. The reflective pixel electrode 22 is made of aluminum metal, and the light shield film 26 for preventing light irradiation to the switching transistor 21 is generally made of chromium metal.

In this reflection type 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 having a structure in which the switching transistor and the transmissive pixel electrode are formed in parallel on the panel surface. Therefore, with the same number of pixels, there is an advantage that the panel size can be made considerably small, and the ratio of the light modulator in the panel surface can be made relatively large.

[0005]

However, the above-mentioned reflective liquid crystal panel has many problems. One is that the light utilization efficiency is low. The reflectance of the aluminum surface of the reflective pixel electrode is as low as about 88%, and the light shielding film is placed so as to overlap the reflective pixel electrode to prevent light irradiation to the switching transistor sufficiently. Efficiency is low. For example, even if a metal having a high reflectance such as silver is used for the reflective pixel electrode, it is difficult to eliminate the efficiency reduction due to the light shielding film. Further, when the reflective pixel electrode is aluminum, it is difficult to flatten the surface because the material is brittle, and the low regular reflection efficiency due to the unevenness of the surface also causes a decrease in efficiency.

Another problem is that cooling is required to prevent the panel temperature from rising. 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 rises. Then, the off resistance of the switching transistor is reduced, and the specific resistance and arrangement state of the liquid crystal material are changed, so that the display quality is degraded. In order to prevent this, cooling such as liquid cooling or air cooling is necessary, resulting in increased noise, larger device size, and increased power consumption.

Further, when dealing with high power luminous flux,
In addition to the above problems, there is a problem that the contrast ratio is lowered. FIG. 3 is a diagram showing the relationship between the panel illuminance and the contrast ratio for the same reflection type light modulation panel as in FIG. Even under the condition of sufficient forced air cooling, the panel temperature rises as the amount of light incident on the panel increases, and the contrast ratio decreases accordingly. Further, as the amount of light increases, irradiation of the switching transistor with a slight amount of light flux passing between the light shielding film and the reflective pixel electrode cannot be ignored, and the contrast ratio is lowered due to the photoconduction phenomenon of the semiconductor. In the projection type display device for presentation, it is necessary to be visible even in a bright place, and in the projection type display device for theater, there are requirements such that a large number of people can appreciate it, and each requires a very high output. The problem of lowering the contrast ratio becomes more significant.

Recently, a PDLC (Polymer Disp) in which a liquid crystal is dispersed in a polymer and incident light is modulated by a scattering degree.
There is a new mode of light modulation material called ersed Liquid Crystal), and it is attracting much attention because of its high light utilization efficiency. It is conceivable to use a material that modulates such light with the degree of scattering in a conventional reflection-type light modulation panel. In this case, scattered light easily passes between the light shielding film and the reflection electrode, Since it reduces the off resistance of the switching transistor, it is difficult to use this combination.

The reflection type light modulation panel and the projection type liquid crystal display device according to the present invention solve such problems.
It is an object of the invention to provide a projection type display device having high output and high efficiency, high quality display and low noise.

[0010]

A reflection type light modulation panel of the present invention comprises a first support plate having a transparent electrode, a plurality of pixel electrodes arranged in a matrix and a switching element for controlling the pixel electrode. A second support plate having the first support plate and the first support plate
And a light modulation layer sandwiched between the second support plate, and a driver circuit writes a signal voltage to the pixel electrode via the switching element to modulate the light modulation layer between the transparent electrode and the pixel electrode. A reflection type light modulation panel formed by reflecting incident light from the side of the first support plate through the light modulation layer, wherein the second support plate is made of single crystal silicon forming a switching element, and the second support is formed. Between the plurality of pixel electrodes of the plate and the light modulation layer, a dielectric multilayer mirror having a function of selectively reflecting the wavelength range of light incident from the first support plate side is arranged. It is characterized by

Further, the reflection type light modulation panel of the present invention is characterized in that a dielectric film having a high visible light absorptivity is provided under the dielectric multilayer film mirror.

Further, the reflection type light modulation panel of the present invention is provided in a projection type display device.

[0013]

[0014]

[0015]

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The reflection type light modulation panel and the projection type display device of the present invention will be described below in detail with reference to the drawings.

The reflection type light modulation panel of the present invention is driven by an active matrix system using a switching transistor. FIG. 1 shows a configuration of an equivalent circuit on the panel and its peripheral portion in this case. A switching transistor 10 is formed for each pixel, and a signal voltage is written to the liquid crystal capacitance 11 by the X driver when it is turned on by the Y driver. Further, in order to prevent a voltage drop due to liquid crystal leakage, etc., the storage capacitor 1
2 is provided in parallel with the liquid crystal capacitor 11. In addition to this, the active matrix system includes a system in which a MIM element is provided for each pixel and a system in which a diode element is provided.
The present invention can also be used for these.

A first embodiment of the reflection type light modulation panel according to the present invention is shown in FIG. A transparent glass plate 2 having a transparent substrate 25 and a matrix substrate having a structure including switching transistors 40, pixel electrodes 41, etc. on the glass plate 20.
4 and a light modulation layer 23 containing a liquid crystal material sandwiched by them, and a dielectric film 42 and a dielectric multilayer film mirror 43 whose surfaces are flattened 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 the voltage is generated between the light modulation layer 23 containing a liquid crystal material and the dielectric multilayer film mirror 43. The capacitance is divided by the dielectric film 42, and the alignment direction of the liquid crystal molecules changes according to the voltage applied to the light modulation layer 23. When the light flux read from the transparent glass plate 24 side is incident, it is modulated by the liquid crystal molecules while passing through the light modulation layer 23, and the dielectric multilayer mirror 43.
After being reflected by, the light is modulated again by the light modulation layer 23 and then taken out. The reflectance of the dielectric multilayer film mirror 43 can be set to 99% or more by an appropriate design, so that the reflection type light modulation panel of this configuration can ignore the light absorption and hardly raise the temperature. Further, the light irradiation to the switching transistor 40 is very small.

A liquid crystal material or a liquid crystal composite material is used for the light modulation layer 23. In the case of a liquid crystal material, for example, there is one that orients a nematic liquid crystal in a twisted structure or a structure in a direction substantially perpendicular to the substrate, and makes polarized light incident and changes its polarization state by increasing or decreasing the retardation of the light modulation layer. . The liquid crystal composite material is a composite of liquid crystal with a polymer material or an inorganic material, and there is a material such as PDLC that modulates light by scattering and transmission.

As a mode of the reflection type light modulation panel, a so-called normally black mode in which black display is performed when no voltage is applied and white display is applied when voltage is applied is suitable. When the normally white mode is used, it is difficult to apply a voltage to the entire light modulation layer 23 in the case of black display because the pixel electrode 41 is discrete, and the display contrast ratio becomes low.

When a signal line from the X-driver is passed under the pixel electrodes 41, the signal potential to other pixels applies a voltage to the light modulation layer 23 corresponding to the pixel electrodes 41, and the display quality is improved. Aggravate. Therefore, in this configuration, it is better to pass the signal line below the pixel electrode. However, in this case, a signal to another pixel electrode affects the pixel electrode 41 to cause crosstalk and vertical unevenness. Therefore, as a special driving method, a line inversion drive in which the polarity is inverted for each horizontal line to be driven is performed. To use. In the line inversion drive, the influence of the video signal on other pixels is an AC electric field having a high frequency, and the change is faster than the response speed of the liquid crystal molecules, so that it hardly affects the display.

The dielectric film 42 is made of, for example, silicon nitride (S
i ₃ N ₄ ), an insulator such as silicon oxide (SiO ₂ ),
The surface is flattened by polishing so that the dielectric multilayer mirror 43 formed thereon is flat. If the planarization is not sufficient, the specular reflection efficiency of the dielectric multilayer film mirror will be low, and as a result, the light modulation efficiency will be low.

When this dielectric film 42 is formed of a substance having a high dielectric constant such as a ferroelectric substance, such as titanium oxide (TiO ₂ ) or barium titanate (BaTiO ₃ ), it is applied to the dielectric film 42 by capacitance division. The voltage applied is lower and the overall required voltage is lower. Further, the voltage applied to the light modulation layer 23 due to the unevenness of the electrode 41 causes unevenness in one pixel, but it can be considerably reduced by using a substance having a high dielectric constant. Further, when the dielectric constant is high, the wraparound of the electric field becomes large, and the voltage is applied to the liquid crystal molecules even in the part slightly off the pixel electrode 41, the actual light modulator increases, and the modulation efficiency increases.

As described above, most of the light read out by the dielectric multi-layer film mirror 43 is extracted by reflection, but the reflectance of the dielectric multi-layer film mirror cannot be completely set to 100%. Light flux is switching transistor 4
It is irradiated to 0. When an aluminum metal film having a high reflectance is used as the pixel electrode 41, the irradiation light amount is considerably reduced, but when a very large amount of light flux is irradiated, the light flux passing through between the pixel electrodes lowers the off resistance of the switching transistor 40. Reduce the display quality. Therefore, if a material having a high visible light absorption rate, such as cadmium telluride (CdTe), praseodymium manganate (PrMnO3), or niobium oxide (NbO), is used as the dielectric film 42,
The irradiation light can be completely cut. Particularly when the light modulation layer 23 is a material such as PDLC that modulates light with the degree of scattering, scattered light is easily transmitted due to the angle dependency of the dielectric multilayer film mirror, and thus visible light absorption is achieved. The effect of using a high-rate material becomes very large.

A second embodiment of the reflective liquid crystal light valve according to the present invention is shown in FIG. In this structure, the 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 when the dielectric film 42 of the first embodiment is made of a substance having a high visible light absorption rate. However, in this case, since it is not necessary to flatten the dielectric film 50 having a high visible light absorption rate, the dielectric film 50 having a high visible light absorption rate has a high degree of freedom in material selection. For example, an organic substance in which a pigment is dispersed or a dyed gelatin that cannot be polished can be used. Further, it is possible to use a black material having a low adhesion strength to the pixel electrode 41.

FIG. 6 shows a third embodiment of the reflection type light modulation panel according to the present invention. In this case, the dielectric film 50 having a high visible light absorption coefficient and the dielectric multilayer film mirror 43 are laminated on the flattened pixel electrode 41. When aluminum is used as the pixel electrode 41, aluminum is relatively fragile and easy to polish, so that it is easy to manufacture. Further, compared with the second embodiment, since the dielectric film 42 in FIG. 5 is not provided, the voltage applied to the light modulation layer 23 is increased accordingly, and the required maximum voltage can be reduced. In addition, since the electric field applied to the light modulation layer 23 in the pixel becomes uniform, the display quality is good. Although the dielectric film 50 having a high visible light absorption rate is shown in FIG. 6, it may be omitted if light leakage to the switching transistor 40 does not cause a problem.

Fourth Embodiment of Reflective Light Modulation Panel of the Present Invention
An example of the above is shown in FIG. In the other embodiments described above, a matrix substrate having thin film transistors formed thereon is used, but in this embodiment, a single crystal silicon substrate 70 is used. The switching transistor 71 formed by using the single crystal silicon substrate 70 has very good characteristics, but tends to easily deteriorate in characteristics with respect to light. However, in this configuration, almost all of the incident light is the dielectric multilayer mirror 4
3 and the dielectric film 50 having a high visible light absorptivity, the characteristics are not deteriorated. Further, the X-driver and the Y-driver shown in FIG. 2 can be formed on the single crystal silicon substrate 70, and the structure around the panel becomes very simple.

The dielectric multi-layer film mirror formed on the pixel electrode generally has a structure in which high-refractive index dielectric films and low-refractive index dielectric films are alternately laminated, and has a center wavelength for reflection. On the other hand, the optical thickness of each film is ¼ wavelength. 8, 9 and 10 show green light, red light,
It is a figure which shows the example of the wavelength-reflectance characteristic of the dielectric multilayer mirror which reflects blue light. The characteristics are shown when TiO _{2 is used} for the high refractive index film and SiO ₂ is used for the low refractive index film, and a total of 15 layers are laminated. In order to increase the reflectance, the number of layers may be increased. For example, when the number of layers is 20, the reflectance is 99.50 in the range of 50 nm around the reflection center wavelength.
8% or more.

Next, a projection type display device using the above reflection type light modulation panel will be described. FIG. 11 is a configuration perspective view showing the first embodiment of the projection type display device of the present invention. This configuration is devised for the case where a light modulating layer such as PDLC that modulates light with a scattering degree is used as the light modulating layer of the reflective light modulating panel. Light source device 11
0 emits a light beam from a light source lamp such as a halogen lamp, a metal halide lamp, or a xenon lamp as a substantially parallel light beam by a parabolic reflector after removing unnecessary wavelength regions such as infrared rays and ultraviolet rays by a filter. The light beam separating prism 111 is formed by arranging the slanting surfaces of two triangular prisms with a slight gap therebetween, and totally reflects the light flux from the light source device 110 on the slanting surface of one of the triangular prisms. Prism 112
Incident on. The color light separating prism 112 shown in FIG.
Is a quadrangular prism with four triangular prisms stuck together, and has a red reflection multilayer interference filter and a blue reflection multilayer interference filter in a cross shape, so the three primary colors of the incident light beam are separated in three directions. To be done. The separated primary color lights respectively go to the reflection type liquid crystal panel 113 (the other reflection type light modulation panel is located on the other side of the color light separation prism 112), and after being modulated, enter the color light separation prism 112 again. , And is synthesized by following the opposite path. Then, the light reaches the inclined surface that is totally reflected at the beginning of the light beam separating prism 111. However, since the incident angle to the inclined surface at this time is smaller than that at the beginning, most of the light flux is transmitted, and the other triangular prism is also almost the same. Is transparent. The modulated light that has passed through the light beam separating prism 111 enters the projection lens 114, and the screen 115
Projected on. Of the light flux modulated by the reflection-type light modulation panel 113 that modulates the incident light flux 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 the light enters, it is blocked by the diaphragm in the projection lens 114 and does not reach the screen 115.

When a light modulation layer, such as PDLC, which modulates light with a scattering degree is used in a reflection type light modulation panel, a problem is that surface reflection light from a glass plate or the like used in the light modulation panel is This is to reduce the display contrast ratio. In such an optical system, the reflection-type light modulation panel 1
13, color light separating prism 112, light beam separating prism 11
When the respective glass material portions of No. 1 are adhered to each other with oil or optical glue whose refractive index is matched, the reflected light at the interface is eliminated and it is easy to obtain a high contrast ratio.

A second embodiment of the projection type display device of the present invention is shown in FIG. This structure is used as a light modulation layer of a reflective light modulation panel, for example, an ECB (electrical call).
y controlled birefringenc
e) Designed for the case of using a light such as a mode that modulates light with a change in polarization direction. Light source device 1
The substantially parallel light flux emitted from the beam splitter 10 is transmitted through the polarization beam splitter 120 as p-polarized light and reflected as s-polarized light, and enters the color light separation prism 121. Of the s-polarized light including the three primary color lights that have entered the color light separation prism 121, the green light is transmitted and the reflection type light modulation panel 12 for green is used.
After reaching 2G, the red light and the blue light are separated into the colored light separating prism 1
The light is reflected by the multilayer interference filter included in 21 and the interface between the glass material and air, and enters the red reflection light modulation panel 122R and the blue reflection light modulation panel 122B, respectively. Then, the respective primary color lights whose polarization states have been modulated and reflected are combined by the color light separation prism 121, and only p-polarized light is transmitted by the polarization beam splitter 120,
Be analyzed. The light flux thus detected is projected through the projection lens 114 to form a color image on the screen.

[0033]

As described above with reference to the embodiments, the reflection type light modulation panel and the projection type display device of the present invention have three main effects as described below.

Since the reflectance of incident light to the panel is high, the aperture ratio is high, and a light modulating material having a high light utilization rate such as a liquid crystal composite can be used, the overall light utilization efficiency is very high. . As a result, the power consumption of the projection display device can be reduced.

Since there is almost no light beam absorbed by the light modulation panel, cooling of the panel is unnecessary and noise is low.

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

[Brief description of drawings]

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

FIG. 2 is a schematic sectional view showing a configuration of a conventional reflection-type 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 sectional view showing a first embodiment of the reflection-type light modulation panel according to the present invention.

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

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

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

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

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

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

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

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

[Explanation of symbols]

10, 21, 40, 71 ... Switching transistor 11 ... Liquid crystal capacitance 12 ... Storage capacitance 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 having high visible light absorption rate・ ・ ・ Single crystal silicon substrate 110 ・ ・ ・ Light source device 111 ・ ・ ・ Ray separation prisms 112, 121 ・ ・ ・ Color light separation prism 113 ・ ・ ・ Reflective light modulation panel 114 ・ ・ ・ Projection lens 115 ・ ・ ・ Screen 120・ ・ ・ Polarizing beam splitter 122R ・ ・ ・ Red reflection type light modulation panel 122G ・ ・ ・ Green reflection type light modulation panel 122B ・ ・ ・ Blue reflection type light modulation panel

Claims (3)

(57) [Claims] 1. A first support plate having a transparent electrode, a plurality of pixel electrodes arranged in a matrix, and a second support plate having a switching element for controlling the pixel electrodes.
A light modulation layer sandwiched between the first and second support plates,
A signal voltage is written to the pixel electrode via the switching element by the driver circuit, the light modulation layer between the transparent electrode and the pixel electrode is modulated, and the incident light from the first support plate side is changed to the light modulation layer. In the reflection-type light modulation panel that is reflected by the second support plate, the second support plate is made of single-crystal silicon that forms a switching element, and the second support plate is provided between the plurality of pixel electrodes and the light modulation layer. , Incident from the side of the first support plate
A reflection-type light modulation panel, characterized in that a dielectric multi-layer film mirror having an action of selectively reflecting the wavelength range of the generated light is arranged. 2. The reflection-type light modulation panel according to claim 1, further comprising a dielectric film having a high visible light absorption rate under the dielectric multilayer film mirror. 3. A projection type comprising: a light source; a reflective light modulation panel according to claim 1 for modulating light from the light source; and a projection lens for projecting the modulated light. Display device.