JP3268786B2 - Reflection type light modulation panel and projection type display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type light modulation panel and a projection type display device for projecting a television image or the like on a screen using the reflection type light modulation panel.

[0002]

2. Description of the Related Art In recent years, with the enhancement of a video software supply environment and high definition of a video as seen in a high-definition television, a demand for a projection display device capable of displaying a large screen with a large number of pixels has been increasing.

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 in order to increase the number of pixels. For example, the technical report of the Institute of Television Engineers of Japan, vol. 13, No. 58 pp. 49-5
No. 4, there is an active matrix type reflection type liquid crystal panel. 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 reflection pixel electrode 22 is made of aluminum metal, and the light shielding film 26 for preventing light irradiation on the switching transistor 21 is generally made of chromium metal.

In this reflection type liquid crystal panel, a light beam incident from the transparent glass plate 24 is modulated by the liquid crystal layer 23 and reflected by the reflection pixel electrode 22, so that the modulated light is extracted as reflected light. In the reflection type, the reflection pixel electrode can be formed on the switching transistor, unlike the transmission type liquid crystal panel in which the switching transistor and the transmission pixel electrode are formed in parallel on the panel surface, which is a conventional technique. Therefore, there is an advantage that the panel size can be considerably reduced with the same number of pixels, and the ratio of the light modulation section 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 use 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 arranged so as to slightly overlap the reflective pixel electrode in order to sufficiently prevent light irradiation on the switching transistor. Efficiency is reduced. For example, even if a metal having a high reflectance such as silver is used as 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 made of aluminum, it is difficult to planarize the surface because the material is brittle, and the low regular reflection efficiency due to unevenness on the surface also causes a reduction in efficiency.

Another problem is that cooling is required to prevent the temperature of the panel from rising. Since the aluminum of the reflective pixel electrode has a visible light absorption of about 12% and the chromium of the light shielding layer has a visible light absorption of about 60%, the temperature of the liquid crystal panel increases. Then, the off-resistance of the switching transistor is reduced, and the specific resistance and the arrangement state of the liquid crystal material are changed, so that the display quality is reduced. In order to prevent this, cooling such as liquid cooling or air cooling is required. As a result, noise increases, the device becomes large, and power consumption increases.

Further, when handling a high-power light beam,
In addition to the above problems, there is a problem of a decrease in contrast ratio. FIG. 3 is a diagram showing the relationship between the panel illuminance and the contrast ratio for the reflection type light modulation panel similar to 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, the irradiation of the switching transistor with 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 photoconductive phenomenon of the semiconductor. Projection display devices for presentations need to be visible even in bright places, and projection display devices for theaters have the requirement that they can be viewed by a large number of people. The problem of lowering the contrast ratio becomes even more pronounced.

Recently, a PDLC (Polymer Disp) which disperses a liquid crystal in a polymer and modulates incident light with a degree of scattering.
There is a new mode of light modulating material called an “erected liquid crystal”, which has attracted much attention because of its high light use efficiency. It is conceivable to use a material that modulates such light with a degree of scattering in a conventional reflection type light modulation panel.In this case, the scattered light easily passes between the light shielding film and the reflection electrode, Since this 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 present invention to provide a projection display device having high output, high efficiency, high quality display, and low noise.

[0010]

A reflection type light modulation panel according to 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 electrodes. A second support plate having the first support plate
And a light modulating layer sandwiched between second support plates, a driver circuit writes a signal voltage to a pixel electrode via the switching element, modulates the light modulating layer between the transparent electrode and the pixel electrode. A reflection-type light modulation panel configured to reflect incident light from the first support plate side through the light modulation layer, on the switching element of the second support plate, and with the plurality of pixel electrodes and the light; A dielectric multilayer mirror having a characteristic of selectively reflecting light in an incident wavelength range and having a function of reflecting incident light from the first support plate side is arranged between the modulation layer and the modulation layer. It is characterized by the following.

Further, the present invention is characterized in that the reflection type light modulation panel having the above-mentioned characteristics is used for a projection type display device.

[0012]

[0013]

[0014]

[0015]

[0016]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing a reflection type light modulation panel and a projection type display device according to the present invention.

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

FIG. 4 shows a first embodiment of the reflection type light modulation panel according to the present invention. A matrix substrate having a configuration including a switching transistor 40 and a pixel electrode 41 on a glass plate 20; and a transparent glass plate 2 having a transparent electrode 25
4 and a light modulating layer 23 containing a liquid crystal material sandwiched therebetween. On the pixel electrode 41, a dielectric film 42 having a flat surface and a dielectric multilayer mirror 43 are formed. .

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 applied to the light modulating layer 23 containing a liquid crystal material and the dielectric multilayer mirror 43. The direction of arrangement of the liquid crystal molecules is changed according to the voltage applied to the light modulation layer 23 by the capacitance division by the dielectric film 42. When a light beam read out from the transparent glass plate 24 enters, the light beam is modulated by liquid crystal molecules while passing through the light modulation layer 23, and the dielectric multilayer mirror 43 is formed.
After being reflected by the light modulation layer 23, the light is again extracted and taken out. The reflectivity of the dielectric multilayer mirror 43 can be made 99% or more by an appropriate design. Therefore, the reflection type light modulation panel of this configuration can ignore light absorption and has almost no temperature rise. Further, the light irradiation on the switching transistor 40 is very small.

For the light modulation layer 23, a liquid crystal material or a liquid crystal composite material is used. In the case of a liquid crystal material, for example, there is a liquid crystal material in which a nematic liquid crystal is oriented in a twisted structure or a structure substantially perpendicular to a substrate, and polarized light is made incident to change the polarization state by increasing or decreasing the retardation of the light modulation layer. . The liquid crystal composite material is a material in which liquid crystal is composited with a polymer material or an inorganic substance, and for example, 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 performed when a voltage is applied, is suitable. 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 in the case of black display, and the contrast ratio of display is reduced.

When a signal line from an X-driver is passed through a lower portion between the pixel electrodes 41, a signal potential to another pixel applies a voltage to the light modulation layer 23 between the pixel electrodes 41, and the display quality is improved. Worsen. Therefore, in this configuration, it is better to pass the signal line under the pixel electrode. However, in this case, a signal to another pixel electrode affects the pixel electrode 41 and causes crosstalk and unevenness in the vertical direction. As a special driving method, a line inversion drive in which the polarity is inverted for each horizontal line is performed. Used. In the line inversion drive, the influence from the video signal on the other pixels becomes an AC electric field having a high frequency, and the change is faster than the response speed of the liquid crystal molecules.

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 formed flat. If the planarization is not sufficient, the specular reflection efficiency of the dielectric multilayer mirror will be low, and as a result, the light modulation efficiency will be low.

When the dielectric film 42 is formed of a substance having a high dielectric constant such as a ferroelectric, for example, titanium oxide (TiO ₂ ) or barium titanate (BaTiO ₃ ), the dielectric film 42 is applied to the dielectric film 42 by capacitance division. And the overall required voltage is reduced. Further, the voltage applied to the light modulation layer 23 due to the unevenness of the electrode 41 causes unevenness within one pixel, but 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 a voltage is applied to the liquid crystal molecules even in a portion slightly off the pixel electrode 41, the actual light modulation section increases, and the modulation efficiency increases.

As described above, most of the light read out by the dielectric multilayer mirror 43 is taken out by reflection, but the reflectance of the dielectric multilayer mirror cannot be made completely 100%, so that a slight amount is obtained. Light flux is switching transistor 4
It is irradiated to 0. If an aluminum metal film having high reflectivity is used as the pixel electrode 41, the irradiation light amount is considerably reduced, but when a very large amount of light beam is irradiated, the light beam passing between the pixel electrodes reduces the off resistance of the switching transistor 40. To degrade the display quality. Therefore, if a material having high visible light absorption, for example, cadmium telluride (CdTe), praseodymium manganate (PrMnO3), or niobium oxide (NbO) is used as the dielectric film 42,
Irradiation light can be completely cut. In particular, when the light modulating layer 23 is made of a material such as PDLC that modulates light according to the degree of scattering, the scattered light is easily transmitted due to the angle dependence of the dielectric multilayer mirror, so that the visible light is absorbed. The effect of using a material with a high rate is very large.

FIG. 5 shows a second embodiment of the reflection type liquid crystal light valve according to the present invention. In this configuration, a dielectric film 50 having a high visible light absorptivity is inserted between the dielectric multilayer mirror 43 and the dielectric film 42 of the first embodiment. The effect is the same as the case where a substance having a high visible light absorption rate is used for the dielectric film 42 in the first embodiment. However, in this case, since it is not necessary to planarize the dielectric film 50 having a high visible light absorption rate, the degree of freedom in material selection of the dielectric film 50 having a high visible light absorption rate is large. For example, even those which cannot be polished, such as an organic substance in which a pigment is dispersed or dyed gelatin, can be used. Further, even a black material having low adhesion strength to the pixel electrode 41 can be used. FIG. 6 shows a third embodiment of the reflection type light modulation panel according to the present invention. In this case, the flattened pixel electrode 4
A dielectric film 50 having a high visible light absorptance and a dielectric multilayer mirror 43 are laminated on the first substrate 1. When aluminum is used for the pixel electrode 41, aluminum is relatively fragile and easily polished, so that it is easy to manufacture. Further, as compared with the second embodiment, since there is no dielectric film 42 in FIG. 5, the voltage applied to the light modulation layer 23 increases by that much, and the required maximum voltage can be reduced. In addition, the light modulation layer 23 in the pixel
Since the electric field applied to the substrate becomes uniform, the display quality is good.
FIG. 6 shows the dielectric film 50 having a high visible light absorptance, but may be omitted if light leakage to the switching transistor 40 does not matter.

The fourth aspect of the reflection type light modulation panel of the present invention.
7 is shown in FIG. In the other embodiments described above, the matrix substrate used is a thin film transistor formed on a glass plate. In this embodiment, a single crystal silicon substrate 70 is used. The switching transistor 71 manufactured 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 reflected by the dielectric multilayer mirror 4.
3 and is shielded by the dielectric film 50 having a high visible light absorptance, so that the characteristics do not deteriorate. 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.

A dielectric multilayer mirror formed on a pixel electrode generally has a structure in which a dielectric film having a high refractive index and a dielectric film having a low refractive index are alternately laminated. On the other hand, the optical thickness of each film is 1/4 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 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 stacked are shown. In order to increase the reflectance, the number of layers may be increased. For example, when the number of layers is 20 and the reflectance is 99.99 within a range of 50 nm before and after the central wavelength of reflection.
8% or more. Next, a projection display device using the above-mentioned reflection type light modulation panel will be described. FIG. 11 is a configuration perspective view showing a first embodiment of the projection display apparatus of the present invention. This configuration is devised for a case where a light modulation layer such as PDLC that modulates light with a degree of scattering is used as a light modulation layer of a reflection type light modulation panel. The light source device 110 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 using a parabolic reflector, after removing unnecessary wavelength ranges such as infrared rays and ultraviolet rays by a filter. I do. The light beam splitting prism 111 is formed by arranging the slopes of two triangular prisms with a slight gap therebetween. The light beam from the light source device 110 is totally reflected by the slope of one of the triangular prisms, and color light separation is performed. The light is incident on the prism 112. The color light separation prism 112 shown in FIG. 11 has a quadrangular prism shape in which four triangular prisms are laminated, and has a red reflection multilayer film interference filter and a blue reflection multilayer film interference filter in a cross shape, so that it is incident. The three primary colors of the light beam are separated in three directions. Each of the separated primary color light is directed to the reflection type liquid crystal panel 113 (there is another reflection type light modulation panel on the other side of the color light separation prism 112), and after being modulated, enters the color light separation prism 112 again. , And are synthesized by following a path in the reverse direction. Then, the light reaches the slope totally reflected at the beginning of the light beam splitting prism 111. At this time, the incident angle with respect to the slope is smaller than that at the beginning, so that most of the light flux is transmitted. Is transmitted. The modulated light that has passed through the light beam splitting prism 111 enters the projection lens 114 and
15 is projected. Among the light beams modulated by the reflection type light modulation panel 113 that modulates the incident light beam according to 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, the light does not reach the screen 115 because it is blocked by the stop in the projection lens 114.

When a light modulating layer, such as PDLC, which modulates light with a degree of scattering is used for a reflection type light modulating panel, a problem is that surface reflected light from a glass plate or the like used for the light modulating panel is a problem. This is to lower the contrast ratio of the display. In such an optical system, the reflection type light modulation panel 1
13, color light separation prism 112, light beam separation prism 11
When the respective glass parts are adhered to each other with oil or optical glue whose refractive index is matched, reflected light at the interface is eliminated and a high contrast ratio is easily obtained.

FIG. 12 shows a second embodiment of the projection type display apparatus according to the present invention. In this configuration, as a light modulation layer of a reflection type light modulation panel, for example, ECB (electrical) is used.
y controlled birefringenc
e) It is designed for the case of using a device such as a mode that modulates light by changing the polarization direction. Light source device 1
The substantially parallel light flux emitted from the light 10 is transmitted by the polarization beam splitter 120 so that p-polarized light is transmitted and s-polarized light is reflected and enters the color light separation prism 121. Of the s-polarized light including the three primary colors incident on the color light separating prism 121, green light is transmitted and the green reflective light modulation panel 12 is transmitted.
2G, the red light and the blue light are separated by the color light separating prism 1
The light is reflected by the multilayer interference filter included in 21 and the interface between the glass material and the air, and enters the red reflective light modulation panel 122R and the blue reflective light modulation panel 122B, respectively. Each primary color light whose polarization state has been modulated and reflected is synthesized by the color light separation prism 121, and only the p-polarized light is transmitted by the polarization beam splitter 120,
It is analyzed. The detected light flux is projected through the projection lens 114 and forms a color image on a screen.

[0031]

As described above, according to each embodiment, the reflection type light modulation panel and the projection type display device using the same have the following effects.

Since the light modulating material having a high reflectance of the light incident on the panel, a high aperture ratio, and a high light utilization factor 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 almost no light flux is absorbed by the light modulation panel, cooling of the panel becomes unnecessary and noise is reduced.

Since the problem of display quality deterioration due to temperature rise of the light modulation panel and light irradiation to the switching transistor is eliminated, a light beam of high power can be input to the light modulation panel.
Therefore, a high-output projection display device that can be easily recognized even in a bright place can be realized.

[Brief description of the drawings]

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

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 wavelength-reflectance characteristics of a dielectric multilayer mirror that reflects green light.

FIG. 9 is a diagram illustrating 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 configuration perspective view showing a first embodiment of a projection display device of the present invention.

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

[Explanation of symbols]

10, 21, 40, 71 switching transistor 11 liquid crystal capacitor 12 storage 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 coefficient ... Single-crystal silicon substrate 110 ... Light source device 111 ... Light beam splitting prism 112,121 ... Color light splitting prism 113 ... Reflection type light modulation panel 114 ... Projection lens 115 ... Screen 120・ ・ ・ Polarization beam splitter 122R ・ ・ ・ Reflection type light modulation panel for red 122G ・ ・ ・ Green reflection type light modulation panel 122B ・ ・ ・ Reflection type light modulation panel for blue

Continuation of the front page (56) References JP-A-64-7221 (JP, A) JP-A-2-253235 (JP, A) JP-A-3-107818 (JP, A) JP-A-1-94322 (JP) JP-A-2-85825 (JP, A) JP-A-2-501334 (JP, A)

Claims (2)

(57) [Claims] A first support plate having a transparent electrode; a second support plate having a plurality of pixel electrodes arranged in a matrix and a switching element for controlling the pixel electrodes;
A light modulation layer sandwiched between the first and second support plates,
A driver circuit writes a signal voltage to a pixel electrode via the switching element, modulates the light modulation layer between the transparent electrode and the pixel electrode, and transmits incident light from the first support plate side to the light modulation layer. In a reflection type light modulation panel that is reflected by passing through the switching element of the second support plate, and between the plurality of pixel electrodes and the light modulation layer, light of an incident wavelength range is selectively applied. A reflection type light modulation panel, comprising a dielectric multilayer mirror having a property of reflecting light incident on the first support plate and having a function of reflecting light incident from the first support plate side. 2. A projection display device 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. .