JPH07306409A - Reflective liquid crystal display - Google Patents

Abstract

(57) [Summary] [Object] To provide an active matrix reflective liquid crystal display device capable of preventing light leakage without impairing the drive voltage of liquid crystal. A dielectric mirror 5 is arranged between a reflective pixel electrode 6 and an active element 60, and light entering from a gap between the reflective pixel electrodes in a certain direction of an active element below the reflective pixel electrode is reflected by the dielectric mirror 5. Let Since the dielectric mirror is not provided between the pixel electrode and the liquid crystal, the voltage applied to the pixel electrode is never attenuated by the dielectric mirror.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflective liquid crystal display device using an active matrix reflective liquid crystal element, and more particularly to a reflective liquid crystal display device that can be used in a projection display device. The present invention also relates to a projection type liquid crystal display device using this reflection type liquid crystal display device.

[0002]

2. Description of the Related Art As a conventional reflection type liquid crystal display device using a reflection type liquid crystal element, there is one described in JP-A-4-338721. As shown in FIG. 4, the reflective liquid crystal element disclosed in the publication flattens the surface of the active element 16 between the pixel electrode 30 to which a voltage is applied by the active element 16 and the liquid crystal layer 8. A dielectric layer 35 and a dielectric mirror 34 composed of a dielectric multilayer film are provided.

In this prior art, when an active matrix type reflective liquid crystal element having an active element such as a TFT or a MOS under a pixel electrode (on the side not facing the liquid crystal) is used as a projection type display device. It has the effect of solving the problems that arise. That is, when the liquid crystal element is exposed to intense irradiation light, light may leak into the reflective substrate through the gap between the reflective pixel electrodes separately arranged on the reflective substrate. Therefore, there is a problem of a so-called light leak phenomenon in which the charge of the pixel electrode leaks due to the reduction of the off resistance of the active element, the generation of photocarriers, etc., and the liquid crystal drive voltage is reduced. In response to such a phenomenon, according to the above-described technique, by covering the surface of the reflective substrate with the dielectric mirror, the light hitting the gap between the reflective pixel electrodes is reflected, which is effective in preventing light leakage. .

[0004]

However, the reflection type liquid crystal display device having the above-mentioned conventional dielectric mirror has the following problems.

That is, the dielectric mirror is formed of a multilayer film in which thin films of substances having different refractive indexes such as titanium dioxide and silicon dioxide are alternately stacked. Further, as the number of layers of the multilayer film increases, the reflectance of the dielectric mirror increases. However, this multilayer film
It is also a very good insulator, and an increase in the total number of the multilayer films is accompanied by a decrease in electric capacity and an increase in electric resistance.
However, in the prior art, since the dielectric mirror is arranged on the pixel electrode, that is, between the liquid crystal and the pixel electrode, the pixel electrode and the counter electrode facing the pixel electrode via the liquid crystal layer are provided. Since the voltage applied during the period is also shared and applied to the dielectric mirror, the drive voltage of the liquid crystal is impaired and the drive becomes difficult. That is, there is a trade-off relationship between the effect of reflection of the dielectric mirror for preventing light leakage and the adverse effect of the voltage drop. This point was not taken into consideration in the above-mentioned conventional technology.

An object of the present invention is to provide a reflective liquid crystal display device which does not deteriorate the display characteristics even when exposed to strong light without damaging the driving voltage of the liquid crystal.

[0007]

To achieve the above object, a first aspect of the present invention is a reflection type liquid crystal display device for projecting reflected light from a reflection type liquid crystal element, wherein A feature is that a dielectric mirror is arranged between the reflective pixel electrode and the active element.

A second aspect of the present invention is, in a reflective liquid crystal display device for projecting reflected light from a reflective liquid crystal element, a dielectric mirror is installed only in a gap between reflective pixel electrodes. It is characterized by

Further, according to a third aspect of the present invention, in a reflective liquid crystal display device, in a reflective liquid crystal display device which projects reflected light from a reflective liquid crystal element, a visible light is present between a reflective pixel electrode and an active element. A feature is that a dielectric layer that absorbs light is provided.

[0010]

When a dielectric mirror is arranged between the reflective pixel electrode and the active element of the reflective liquid crystal element, light entering through the gap between the reflective pixel electrodes in the direction of the active element below the reflective pixel electrode is reflected by the dielectric mirror. Is reflected. Since the dielectric mirror is not located between the pixel electrode and the liquid crystal, the voltage applied to the pixel electrode is never attenuated by the dielectric mirror.
In particular, when a polymer-dispersed liquid crystal that does not require an alignment film is used as the liquid crystal, the voltage of the pixel electrodes can be entirely applied to the liquid crystal. Therefore, there is an effect of preventing light leakage without impairing the liquid crystal drive voltage.

The effect of preventing light leakage is the same when the dielectric mirror is installed in the gap between the reflective pixel electrodes. Therefore, if a dielectric mirror is provided at least in the area between the pixel electrodes, light leakage from that portion to the active element is prevented, so that light leakage can be prevented.

[0012]

Embodiments of the present invention will now be described with reference to the drawings.

(Embodiment 1) FIG. 1 is a sectional structural view of Embodiment 1 of a reflective liquid crystal device of the present invention. In this embodiment, a monolithic IC substrate is used as the reflection substrate 31, an aluminum pixel electrode 6 provided on the reflection substrate 31, a transparent electrode 9 facing the aluminum pixel electrode 6 and a glass substrate 10 which is a transparent substrate supporting the transparent electrode 9. , The reflective substrate 31 and the glass substrate 10
Polymer dispersed liquid crystal 8 disposed so as to be sandwiched between
It is configured to have and.

With such a structure, a voltage is applied to the polymer-dispersed liquid crystal 8 between the aluminum pixel electrode 6 and the transparent electrode 9 facing it. This polymer-dispersed liquid crystal 8 is
It has a characteristic that it takes a scattering state when no voltage is applied, and the scattering property decreases and changes to a transmission state as the applied voltage increases.

The reflective substrate 16 is formed by forming a MOS transistor as an active element 60 for driving a liquid crystal on a silicon substrate. That is, on the p-type well 2 of the silicon substrate 1, the drain diffusion layer 12, the drain electrode 14, the source diffusion layer 13, the source electrode 4, the polysilicon gate 3 are formed.
To form a MOS transistor. Further, a spin-on-glass insulating layer 15 is provided for interlayer insulation. Further, a dielectric mirror layer 5 in which titanium oxide and silicon oxide are alternately laminated is provided below the aluminum pixel electrode 6. Since it is possible to form a stable film on the dielectric mirror 5 when it is formed on a flat surface, a spin-on-glass layer that is etched back or a surface-polished silicon oxide layer is further provided as a base of the dielectric mirror layer 5. It is desirable to keep. The electric signal controlled by the MOS transistor is applied to the aluminum pixel electrode 6 through the through hole contact 11, and a voltage is applied to the polymer dispersed liquid crystal 8 between the transparent electrode 9 and the opposed transparent electrode 9 to disperse the polymer dispersed liquid crystal 8. The liquid crystal 8 is driven.

The optical thickness of the thin film of titanium oxide and silicon oxide forming the dielectric mirror 5 is 1/4 of the wavelength of the light to be reflected. Therefore, in order to reflect the entire visible light, it is necessary to combine and stack thin films having a wide range of optical thicknesses. However, if a dielectric mirror that selectively reflects only red, blue, and green light, respectively, the total film thickness can be reduced, and the film thickness is approximately 1/3 of that that reflects all visible light. Mu. This reduction in film thickness is achieved by the manufacturing process of the reflective substrate 16 described above.
It is possible to reduce the extent to which the diameter of the through-hole contact 11 is larger than the diameter of the bottom thereof just below the aluminum pixel electrode,
It is preferable because the flat area of the aluminum pixel electrode can be easily secured.
Therefore, a red reflective liquid crystal display element 23, a blue reflective liquid crystal display element 25, and a green reflective liquid crystal display element 2 each having a dielectric mirror that reflects only red, blue, and green light, respectively.
4 is used to form the projection type liquid crystal display device shown in FIG.

The projection type liquid crystal display device shown in FIG. 2 has a light source system 17a for emitting projection light, a modulator 70 for modulating incident light according to an image signal and reflecting the light, and a modulator 70 for modulating the incident light. The screen 28 for projecting the reflected light and the optical system 4 for guiding the projected light from the light source system 17a to the modulator 70 and the reflected light from the modulator 70 to the screen 28.
0 and a driving device 50 for driving the modulator 70.

The light source system 17a includes a light source 17 and a parabolic mirror 1 for emitting light emitted from the light source 17 as parallel light.
8 and.

The optical system 40 is placed at the focal position of the condenser lens 19 for condensing the projection light from the light source system 17a, the mirror 29 for deflecting the light from the condenser lens toward the modulator 70, and the condenser lens 19. A first diaphragm 20 that narrows light that does not pass through the focus, a lens 21 that condenses the light that has passed through the first diaphragm 20 into parallel light, and collects the reflected light from the modulator 70. The second diaphragm 26, which is placed at the focal position of the lens 21 and narrows the light that does not pass through the focal point
And a projection lens 27 for projecting the light that has passed through the second diaphragm 26 onto the screen.

The modulator 70 includes a dichroic prism 22 for decomposing incident light into three components of red, blue and green, and red light disposed on three side surfaces of the dichroic prism 22 according to light emitted from the dichroic prism 22. Reflective liquid crystal display element 23,
It has a reflective liquid crystal display element 25 for blue and a reflective liquid crystal display element 24 for green.

The driving device 50 is constituted by these liquid crystal display elements 2
For 3-25, the transmission / scattering state of each pixel is driven according to the image signal.

In this apparatus, the light from the light source 17 is converted into parallel rays by the parabolic mirror 18, and then the condenser lens 1 is used.
The light enters the dichroic prism 22 through the mirror 9, the mirror 29, the first diaphragm 20, and the lens 21. In the dichroic prism 22, the light is separated into three components of red, blue and green, and the dichroic prism 22 is divided according to each color.
Directed to the three sides of the. In the reflective liquid crystal display element 23 for red, the reflective liquid crystal display element 25 for blue, and the reflective liquid crystal display element 24 for green, the incident light of each color is respectively modulated according to the image signal. Then, the modulated reflected lights of the respective colors are again combined by the dichroic prism 22, pass through the lens 21, the second diaphragm 26, and the projection lens 27, and are projected on the screen 28.

At this time, the three reflective liquid crystal elements 23 are
-25 is in a scattered or reflected state depending on the image signal for each pixel. Of these, the light specularly reflected is the lens 21.
Is focused at the position of the second diaphragm 26, passes through the diaphragm 26,
It reaches the screen 28 through the projection lens 27. On the other hand, most of the scattered light is not condensed at the position of the second diaphragm 26, is almost blocked, and does not reach the screen 28. Therefore, the three reflective liquid crystal display elements 23 are
A bright / dark state can be created for each color on the screen 28 in accordance with the scattering / reflection state of −25, and a color image can be projected by combining them.

In this embodiment, each liquid crystal element 2 of the modulator 70 is
In 3-25, since the dielectric mirror 5 that reflects at least a part of visible light including the gap between the pixel electrodes 6 is disposed under the pixel electrodes 6, the liquid crystal is driven. It is possible to prevent light leakage from occurring in the active matrix element. Moreover, the pixel electrode 6 and the polymer dispersed liquid crystal 8
Since the dielectric mirror 5 does not exist between and, the drive voltage applied to the liquid crystal is not impaired at all.

(Embodiment 2) FIG. 3 is a sectional structural view of Embodiment 2 of the reflective liquid crystal display element of the present invention. In this example,
Basically, it has the same structure as the device of the first embodiment shown in FIG. Therefore, the characteristic points of this embodiment different from the first embodiment will be mainly described here. That is, the feature of this embodiment is that the dielectric mirror 32 is provided in the gap between the aluminum pixel electrodes 6 on the reflective substrate 33. This dielectric mirror 32 may be one that reflects the entire emission wavelength range of the light source or one that reflects only the light of the emitted color, as in the first embodiment.

Since the dielectric mirror 32 is provided in this embodiment, the dielectric mirror 5 may be replaced with a dielectric layer having no mirror structure. The dielectric layer may be, for example, a polyimide layer. In this case, a substance that absorbs light may be further mixed as in Example 3 described later. As described above, by providing the substance that absorbs light, it is possible to suppress the generation of stray light due to multiple reflection in the dielectric layer and scattering.

(Embodiment 3) The embodiment 3 of the reflection type liquid crystal display element of the present invention has a sectional structure in which a black polyimide layer is provided instead of the dielectric mirror layer 5 of FIG. The black polyimide layer is a mixture of polyimide and black dye. Incidentally, depending on the wavelength component of the irradiation light,
Dyes such as red, blue and green may be selectively used.

The polyimide has an effect of reducing unevenness of the base and also has an effect of flattening the aluminum pixel electrode formed thereon to obtain a high reflectance. However, in order to make this effect more remarkable, it is desirable to provide a spin-on glass layer etched back or a surface-polished silicon oxide layer on the base of the polyimide layer, as described in the first embodiment. In order to ensure long-term reliability of the polyimide layer, it is desirable to provide an inorganic dielectric layer between the polyimide layer and the aluminum pixel electrode.

In each of the above embodiments, the polymer dispersed liquid crystal is used as an example of the liquid crystal, but the present invention is not limited to this. It can be similarly applied to a reflective liquid crystal element using twisted nematic liquid crystal. Further, the present invention is
The present invention is not limited to the projection type display device, but can be applied to the direct-view type display device.

In the first embodiment, a dielectric layer that absorbs at least a part of visible light may be further arranged. Further, instead of the dielectric mirror, a dielectric layer that absorbs at least a part of visible light may be arranged.

Further, in the second embodiment, instead of the dielectric mirror arranged in the gap between the pixel electrodes, a dielectric layer absorbing at least part of visible light may be arranged.

[0032]

According to the present invention, a dielectric mirror that reflects at least a portion of visible light under a pixel electrode or in a gap between pixel electrodes and a dielectric that absorbs at least a portion of visible light. By disposing the body layer, light leakage can be prevented from occurring in the active matrix element that drives the liquid crystal, without impairing the drive voltage applied to the liquid crystal.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure of a reflective liquid crystal display element of Example 1 of the present invention.

FIG. 2 is an explanatory diagram showing a configuration of a position type embodiment of a projection type display device using the reflection type liquid crystal display element of the present invention.

FIG. 3 is a cross-sectional view showing the structure of a reflective liquid crystal display element of Example 2 of the present invention.

FIG. 4 is a cross-sectional view of a reflective liquid crystal display device according to a conventional technique.

[Explanation of symbols]

1 ... Silicon substrate, 2 ... P-type well, 3 ... Polysilicon gate, 4 ... Source electrode, 5 ... Dielectric mirror layer, 6 ... Aluminum pixel electrode, 7 ... Dielectric mirror, 8 ... Polymer dispersed liquid crystal, 9 ... transparent electrode, 10 ... glass substrate, 11 ... through-hole contact, 12 ... drain diffusion layer, 13 ... source diffusion layer, 14 ... drain electrode, 15 ... first spin-on-glass insulating layer, 16 ... active element, 17 ... light source , 18 ... Parabolic mirror, 19 ... Condenser lens, 20 ... First diaphragm,
21 ... Lens, 22 ... Cross dichroic prism,
23 ... Red reflective liquid crystal display element, 24 ... Green reflective liquid crystal display element, 25 ... Blue reflective liquid crystal display element, 26
... second diaphragm, 27 ... projection lens, 28 ... screen,
29 ... Mirror, 30 ... Pixel electrode, 31 ... Reflective substrate, 32 ... Dielectric mirror, 33 Reflective substrate, 34 ... Dielectric mirror, 35
... Dielectric film, 40 ... Optical system, 50 ... Driving device, 60 ... Active element, 70 ... Modulator.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hideo Sato Inventor Hide 1-1 Satoshi Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Minoru Hoshino 7-chome Omika-cho, Hitachi-shi, Ibaraki No. 1 Hitachi Ltd., Hitachi Research Laboratory (72) Inventor Shinichi Omura 7-1-1 Omika-cho, Hitachi City, Ibaraki Prefecture Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Naofumi Kakei, Oita Mika Hitachi City, Ibaraki Prefecture 7-1-1, Machi, Hitachi Co., Ltd. Hitachi Research Laboratory

Claims (7)

[Claims] 1. A liquid crystal is sandwiched between a transparent substrate and a reflective substrate,
In the reflective liquid crystal display element, wherein the reflective substrate has a plurality of pixel electrodes that are separated from each other, below the surface side of the pixel electrode that does not face the transparent substrate,
A liquid crystal display device having a dielectric mirror. 2. A liquid crystal is sandwiched between a transparent substrate and a reflective substrate,
The reflective liquid crystal display element, wherein the reflective substrate has a plurality of pixel electrodes separated from each other, wherein a dielectric mirror is provided in a gap between the separated pixel electrodes. 3. A liquid crystal is sandwiched between a transparent substrate and a reflective substrate,
The reflective substrate, in a reflective liquid crystal display element having a plurality of pixel electrodes separated from each other, below the surface side of the pixel electrode not facing the transparent substrate,
A liquid crystal display device comprising a dielectric that absorbs at least part of visible light. 4. A liquid crystal is sandwiched between a transparent substrate and a reflective substrate,
In the reflective liquid crystal display element, wherein the reflective substrate has a plurality of pixel electrodes separated from each other, a dielectric that absorbs at least a part of visible light is provided in a gap between the separated pixel electrodes. Reflective liquid crystal display device. 5. A reflection type liquid crystal display device according to claim 1, 2, 3 or 4, wherein the liquid crystal is a transmission / scattering type liquid crystal. 6. A light source system for emitting projected light, a modulator for modulating and reflecting incident light according to an image signal, a screen for projecting reflected light modulated by the modulator, and a light source. An optical system that guides the projection light from the system to the modulator and guides the reflected light from the modulator to the screen, wherein the modulator is the reflection type liquid crystal display according to claim 1. A projection type liquid crystal display device comprising an element and a driving device thereof. 7. The modulator according to claim 6, wherein the modulator is arranged on three side surfaces of the dichroic prism for separating incident light into three components of red, blue, and green, and the light emitted from the dichroic prism. And a reflective liquid crystal display element for blue, and a reflective liquid crystal display element for green.