JPH0679201B2 - Projection type liquid crystal display - Google Patents

Description

The present invention relates to a projection type display device of a system using a liquid crystal light valve.

[Conventional technology]

In recent years, there has been a strong demand for large-screen displays for conference materials and scene displays in remote conference systems, various control panel displays for air traffic control, and other high-definition televisions, and displays in this field have relatively large display pixels. In addition to using a mosaic array type display in which lamps and small-scale liquid crystal panels are integrated in a large screen display, a projection type display is used. As for the projection type display, for example, a CRT projector and a liquid crystal light valve of a system that projects a high-intensity cathode ray tube (hereinafter abbreviated as CRT) as described in Nikkei Electronics September 5, 1977 page 58 and subsequent pages. A projection-type liquid crystal display device of the type using is known as a practical one.

[Problems to be solved by the invention]

The CRT projector directly projects the CRT screen,
Although the display brightness is not always sufficient, it is possible to display a moving image like a normal television. However, a CRT having a high-luminance enough to be projected does not have sufficient resolution represented by the number of scans and cannot be used for document display such as conference materials. On the other hand, the projection type liquid crystal display device has a feature that a bright display can be obtained because a light source dedicated to projection can be used. There are several types of projection type liquid crystal display devices, and they are classified according to the image writing system to the liquid crystal light valve. The first method is the laser thermal writing method.This method is a method of squeezing the laser very finely and irradiating it on the liquid crystal light valve, raising the temperature of the liquid crystal substance at that point and thermally writing. While high-resolution display can be performed, it has a drawback that the writing speed is slow and a moving image cannot be displayed because it is necessary to scan and write with a laser by dot sequential scanning. The second method is the CRT optical writing method.This method projects a CRT screen on a liquid crystal light valve having a photoconductor layer and converts the light and shade image of light into the intensity of voltage to produce the electro-optical effect of liquid crystal. This is a method of writing an image based on the liquid crystal light valve. Therefore, although it is possible to display a moving image like the CRT display, there is a drawback in the resolution limited by the number of scanning lines. The third method is a method in which an array of charge-coupled devices, generally called CCD, is laminated with liquid crystal, and the charge distribution formed by an electric signal is converted into an image on the liquid crystal light valve by using the electro-optical effect of the liquid crystal. Is. With this method, charge transfer can be performed at high speed, so moving images can be displayed up to about 1000 × 1000 pixels, but resolution is not always sufficient due to diffusion of charges during transfer to the liquid crystal layer. As described above, the conventional projection displays are insufficient in either high-speed writability capable of displaying a moving image or high resolution capable of displaying a high-quality image.

An object of the present invention is to provide a projection display device of high brightness, high resolution, and high speed writing, which is capable of displaying a moving image with a large screen and high quality.

[Means for solving problems]

The projection type liquid crystal display device of the present invention has an active matrix structure in which a switching element is attached to each pixel electrode,
In addition, a plurality of liquid crystal light valves having a structure other than the pixel electrode as a light-shielding portion are formed so that the pixel portions of the projection image formed by the projection light projected on each liquid crystal light valve do not overlap each other and a gap is formed. It is characterized by having been placed without.

[Action / Principle]

The projection type liquid crystal display device of the present invention is a projection type display device of a type in which an image written in a liquid crystal light valve is projected on a screen using a projection light source and a projection optical system. A liquid crystal light valve has a structure in which a substrate having pixel electrodes forming a large number of pixels and another substrate with electrodes are opposed to each other and a liquid crystal material is sandwiched between the substrates, and the pixel electrodes have thin film transistors or thin film diodes. Alternatively, a switching element represented by a two-terminal element having a metal-insulator-metal (MIM) structure is attached. These switching elements apply a voltage corresponding to the signal of the liquid crystal material even when the line-sequential scanning drive is not performed, or the voltage applied to the liquid crystal material layer of the selected pixel and the liquid crystal material layer of the non-selected pixel are applied. It has the effect of increasing the ratio with the applied voltage, and as a result, even if the number of scans is increased to about 1000 or more, the selected state and the non-selected state of the liquid crystal substance layer are clearly distinguished. It becomes possible to write the image. Of course, since the response time of the switching element is sufficiently short, it is possible to carry out so-called refresh driving in which all scanning for one cycle is completed within 30 milliseconds and this is repeated, and moving image display such as television display is also possible. However, the portion of the switching element attached to each pixel electrode does not function as a pixel, and a signal electrode to the switching element is also required, which reduces the area ratio of the pixel region occupied in the liquid crystal light valve. In particular, when a thin film transistor is used as a switching element, the signal electrodes are required in an XY matrix, and this influence is great. That is, the pixels cannot be arranged densely, and the display resolution is reduced. However, in the liquid crystal light valve used in the projection type liquid crystal display device of the present invention, since the light shield is provided in the region other than these pixel electrodes, in the projected image on the screen, the projection light except the pixel portion is projected. Is a dark area that does not reach. For example, by using two liquid crystal light valves in which the pixel electrode portions are arranged in a checkerboard pattern, the pixel portion in the projection image of another liquid crystal light valve is positioned in the dark portion in the projection image of one liquid crystal light valve. By projecting, a high-resolution display in which pixels are densely arranged on the screen is realized.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a front view showing the structure of a part of two liquid crystal light valves used in an embodiment of the projection type liquid crystal display device of the present invention. In FIG. 1, 1 and 2 are glass substrates facing each other, and both substrates are sealed at the periphery with an epoxy adhesive 3 mixed with spacer particles having a diameter of 8 μm.
A liquid crystal material layer (nematic liquid crystal ZLI-
1565 (Merck) 4 is held. (While it has a so-called twisted nematic structure,
Since the alignment treatment film and the like are not essential to the present invention and are complicated, they are omitted in FIG. 1 and the description. A strip-shaped transparent electrode 11 made of indium oxide is formed on the inner surface of one glass substrate 1, and a transparent pixel electrode 5 made of indium oxide is formed on the inner surface of the other glass substrate 2. MIM using tantalum oxide as an insulator for each pixel electrode 5
The element 6 is mounted as a switching element. Reference numeral 21 is a signal electrode for driving the MIM element, which is made of tantalum. On the outer surface of the glass substrate 2, a light-shielding film made of aluminum is formed in a region inside the seal 3 other than a region facing the pixel electrode 5 (not shown). In the liquid crystal light valve having the active matrix structure having such a structure, line sequential driving can be performed by scanning about 1000 electrodes, and the light transmittance of the pixel electrode 5 portion can be changed according to the image signal applied to the signal electrode 11. Change. The number of electrodes in this embodiment is 500 scanning electrodes 21, 1000 image signal electrodes 11,
Therefore, the number of pixels (the number of pixel electrodes) is 500 × 1000. The structure of the projection type liquid crystal display device of this embodiment is shown in FIG. In FIG. 2, 31 and 32 are the liquid crystal light valves of FIG. 1, 37, 38 and 39, 40 are sets of two polarizing plates whose polarization directions are parallel to each other, and the liquid crystal light valves are twisted nematic. It is inserted to make it work. Projection light having the xenon lamp 30 as a light source is incident on two liquid crystal light valves via a half mirror 33 and a mirror 34, and an image thereof is projected on a screen 36 by a projection lens 35. The projected image is obtained by enlarging the shape / arrangement of the pixels (pixel electrodes) in FIG. 1 as it is. According to the projection type liquid crystal display device in FIG. 2, as shown in FIG. The image 41 of the pixel array and the image 42 of the pixel array of the second liquid crystal light valve are projected in a dense pixel arrangement without overlapping each other. In this example, the screen
It is possible to display a movie on the 36 with a high resolution of 1000 x 1000.
In this embodiment, the liquid crystal light valve is provided with a light-shielding film made of an aluminum film in order to obtain a particularly high display contrast. For example, in a twist nematic liquid crystal operation mode, two polarizing plates are polarized in parallel directions. In such a case, the liquid crystal is always in a light-shielding state except for the pixel electrode portion, and this serves as a light-shielding portion, so that no special light-shielding film need be provided. Also, the third
The figure shows that the switching element part for the projected image remains as a non-pixel part, but it is possible to eliminate such non-pixel region by making the transparent pixel electrode rectangular or square in a liquid crystal light valve, for example. Is. FIG. 4 is a diagram for explaining this, and shows the shape of the pixel electrode portion of the liquid crystal light valve. In FIG. 4, 51 is a transparent pixel electrode, and 52 is a metal signal electrode, which correspond to 5 and 21 in FIG. 1, respectively. Further, 53 is a metal electrode corresponding to the upper electrode of the MIM element, and 54 is the MIM element section. It can be easily understood that the pixel electrode shape as described above eliminates the defect that the projected image of the switching element portion as illustrated in FIG. 3 remains as a non-pixel portion. However, in FIG.
The gap between the adjacent pixel electrodes running in the direction orthogonal to is also left as a non-pixel portion in the projected image on the screen. An example of a method for removing such non-pixel portions to obtain a dense pixel arrangement on the screen will be described with reference to FIG. FIG. 5 is a diagram showing a shape of a pixel electrode portion of a liquid crystal light valve in a projection type liquid crystal display device of a system using three liquid crystal light valves. In FIG.
Reference numerals 51, 52, 53 and 54 are transparent pixel electrodes, metal signal electrodes, metal electrodes and MIM element portions corresponding to the same numbered portions in FIG. 4, respectively. FIG. 6 is a diagram showing a state in which pixels are densely arranged without a gap when three electrode-shaped liquid crystal light valves as shown in FIG. 5 are used for projection display, and 61, 62 and 63 are respectively the first and A pixel formed by the second and third liquid crystal light valves is shown. In addition, by setting red, green, and blue color filters to the three liquid crystal light valves, and setting 61, 62, and 63 in FIG. 6 as red, green, and blue pixels, respectively, high resolution It can be easily understood that full color display is possible.

FIG. 7 is a diagram showing the configuration of another embodiment of the present invention, 73 is a polarization beam splitter, and the other parts having the same reference numerals indicate the same parts as in FIG. However, in the configuration shown in FIG. 7, the two polarized beams split by the polarizing beam splitter 73 have their polarization directions orthogonal to each other, and the two polarizing plates 38 and 40 are attached to the twisted nematic. Type of liquid crystal light valve 31 or
It is installed so that the polarization direction of the polarized beam incident on 32 is parallel to the polarization direction. In the projection type liquid crystal display device having the structure as shown in FIG. 7, compared with the structure shown in FIG. 2, the amount of light is reduced to about half by the respective polarizing plates before the projected light enters the liquid crystal light valve. Since almost all of the projected light from the light enters the liquid crystal light valve, a display screen with extremely high brightness can be obtained.

〔The invention's effect〕

It has been described in the above embodiments that various modifications can be made to the projection type liquid crystal display device of the present invention, particularly the liquid crystal light valve used in the same device in order to obtain a high quality and high resolution projected image. Even in such a case, according to the present invention, a projection type liquid crystal display device of high resolution and high speed writing capable of displaying moving images with a large screen and high quality can be obtained. Particularly, in a method using a polarization beam splitter, a projection type liquid crystal of extremely high brightness is obtained. This has the effect of obtaining a display device.

[Brief description of drawings]

FIG. 1 is a front view showing a part of the structure of a liquid crystal light valve showing an embodiment of the projection type liquid crystal display device of the present invention, FIG. 2 is a view showing the configuration of the display device, and FIG. 3 is a projection image. FIG. 4 is a diagram showing the pixel arrangement, FIGS. 4 and 5 are diagrams showing the electrode shape of another liquid crystal light valve, FIG. 6 is a diagram showing the pixel arrangement in a projected image by three liquid crystal light valves, and FIG. It is a block diagram of the display apparatus in another Example. 1, 2 is a substrate, 3 is a seal part, 4 is a liquid crystal material layer, 5 is a pixel electrode, 6 is a switching element, 11 and 21 are signal electrodes, 30 is a light source, 31 and 32 are liquid crystal light valves, and 33 is a half mirror. , 3
4 is a mirror, 35 is a projection lens, 36 is a screen, 37, 38, 3
Reference numerals 9 and 40 are polarizing plates, and reference numerals 41 and 42 are images of pixel arrays of the first and second liquid crystal light valves, respectively. 51 is a pixel electrode, 52
Is a signal electrode, 53 is a metal electrode, 54 is a switching element, 6
Reference numerals 1, 62 and 63 are images of pixel arrangements of the first, second and third liquid crystal light valves, respectively, and 73 is a polarization beam splitter.

Claims (1)

[Claims] 1. A plurality of liquid crystal light valves having an active matrix structure in which a switching element is attached to each pixel electrode, and having a structure in which a region other than the pixel electrode is a light shielding portion is projected on each liquid crystal light valve. A projection-type liquid crystal display device, characterized in that it is arranged so that pixel portions of a projected image formed by projection light do not overlap each other and no gap is formed.