JPS6364030A - Matrix display device - Google Patents

Abstract

PURPOSE:To contrive the reduction of a cost by interposing a quest host liquid crystal layer, whose light transmittance is increased when a voltage is applied, between a first transparent band-shaped electrodes and picture element electrodes and providing photoconductive elements between a second band-shaped electrodes intersected orthogonally with the first band-shaped electrodes and picture element electrodes. CONSTITUTION:The electrode surface side of a first transparent substrate 1 having narrow band-shaped transparent electrodes 3 and that of a second transparent substrate 2 where photoconductive elements 7 are interposed between narrow band-shaped electrodes 4 and picture element electrodes 5 and 6 face each other, and electrodes 3 and 4 are arranged orthogonally to each other to constitute X-Y matrix electrodes, and a GH liquid crystal 8 is held between electrodes 3 and 4. A voltage applying means is provided for electrodes 3 and 4, and a reflecting plate 16 is provided on the rear face of the substrate 2 if electrodes 5 and 6 are transparent. The liquid crystal 8 is used as a light valve in such a manner to change the quantity of light projected to the element 7, and the electric resistance of the element 7 is non-linearly changed, thereby amplifying the rates of voltages applied to turned-on picture elements and turned-off picture elements.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a flat X-Y matrix display device, and is suitable for use in office display devices with binary display, or wall type display devices with halftones. It can be used for color TVs, etc., and is particularly characterized by low cost and high image quality.

2. Description of the Related Art Conventionally, typical flat panel display devices include plasma displays, Furano CRTs, fluorescent display tubes, and liquid crystal displays. The first three types are light-emitting types, and currently have problems such as low luminous efficiency, relatively high driving voltage, and difficulty in increasing their size. On the other hand, liquid crystal display devices are being actively developed toward full-color and large-sized devices due to low voltage, low power consumption, and ease of increasing size. To achieve a full-color display with a liquid crystal, the liquid crystal is usually used simply as a light pulp, and a color image is created by additive color mixture on a two-dimensional surface by providing red, blue, and green color filters in the form of strips or dots. Is displayed. Figure 4 shows the conventional X using twisted nematic (hereinafter abbreviated as TN) liquid crystal display mode.
-The configuration and operation of the Y matrix type panel will be described.

FIG. 5 is a front view of FIG. 4 and shows the arrangement of row electrodes 3 and column electrodes 140. The TN type matrix panel 15 has a nematic liquid crystal 18 having a positive dielectric constant anisotropy sandwiched between transparent row electrodes 3 and transparent column electrodes 14 made of indium oxide, etc., which are respectively provided on a pair of glass substrates vi1 and vi2. A pair of polarizing plates 10° 1) are provided on the outside of the glass substrates 1 and 2. When constructing a color panel, one layer of red, blue, and green color filters are regularly provided on each row or column electrode. Although the panel 15 is shown in a simplified manner, an alignment treatment layer is usually provided on the row or column electrodes, or on the color filter layer if there is one color filter layer, for regulating the alignment of liquid crystal molecules. On the surface of each substrate, the liquid crystal molecules are arranged parallel to the substrate, and the direction of arrangement of the molecules is approximately 90° different between one substrate and the other in the case of normal TN mode, The direction in which the molecules are arranged is gradually twisted from one substrate to the other, and the surfaces of the side substrates are pre-aligned so that a twist of approximately 90° is produced between the side substrates. For example, S B E other than normal TN mode
(Super Birefringence Effe
(abbreviation for ct) mode, the torsion angle of the above molecules is 180° ~
Sometimes it is used at 360°.

The above is an example of a conventional liquid crystal matrix panel, but the biggest difficulty with conventional technology is (1) generally a simple X-Y matrix) In an IJ display panel, N scanning lines (here For example, when a panel with row electrodes 3) is driven by a line-sequential signal, the ratio R of the effective value voltage applied between the electrodes sandwiching the pixel to be turned on and the pixel to be turned off is determined by the so-called voltage averaging method. When the driving method is adopted and optimized to maximize R, R = ((N”” + 1)/ (N”” −
1)) ””. In other words, in a panel with a simple matrix configuration, the Kukostalk voltage is applied even to off-pixels, resulting in a decrease in contrast. For example, N=
In the case of 100 lines, R = 1.1, and the on pixel has 10% L of the effective value voltage applied between the electrodes corresponding to the off pixel.
Display contrast must be achieved with this 10% voltage difference without applying any additional voltage.

That is, unless the display medium used in a simple matrix panel has sharp luminance-voltage characteristics and clear threshold characteristics, a display with excellent contrast cannot be achieved. In conventional TN cells, this sharpness is insufficient, so N
= 64 (R = 1.134), the reality is that the contrast is not comparable to that of an active matrix panel. On the other hand, in a TN cell, as shown in the cited example, the light transmission characteristics of the cell generally depend on the wavelength of light, resulting in so-called optical rotational dispersion, and the brightness-voltage characteristics vary considerably depending on the wavelength.

In addition, when a dielectric layer called a color filter is provided on a transparent electrode as shown in the figure, the filter layer must be inserted in series with the liquid crystal, so the on and off voltage applied between the electrodes is There was a drawback that the voltage ratio was further reduced in the liquid crystal layer, and the contrast of the color panel was considerably worse than that of the monochrome panel.

(2) In order to overcome the poor contrast, viewing angle, color reproducibility, etc. of the simple XY matrix type display spring, a panel configuration called an active matrix is adopted. In an active matrix display panel, a thin film transistor (hereinafter referred to as TP) is installed at each pixel point that makes up the matrix.
3-terminal switch elements such as T), PN junctions, metal-insulator-metal (hereinafter abbreviated as MIM), etc.
By providing a terminal nonlinear resistance element, the poor threshold characteristics of the liquid crystal itself can be overcome, and high contrast and excellent color reproducibility are achieved. However, the biggest drawback of active matrix panels is that the panel cost is high because it is difficult to manufacture active matrix arrays at low cost and with high yield.

Problems to be Solved by the Invention The present invention seeks to solve the above-mentioned problems of the poor contrast of conventional liquid crystal simple matrix display devices and the high cost of liquid crystal active matrix display devices.

Means for Solving the Problems In the present invention, a guest-host liquid crystal layer whose light transmittance increases when a voltage is applied is sandwiched between a first transparent band-shaped chamber () and a pixel electrode, and the pixel electrode A second strip electrode is provided in a direction perpendicular to the first strip electrode, a photoconductive element is provided between the second strip electrode and the pixel electrode, and a voltage applying means is provided to the first and second electrodes. The present invention aims to solve the problems of the conventional method by using a matrix display device having a similar structure.

Effect: The above means solves the problems of poor contrast of conventional liquid crystal simple matrix display devices and high cost of liquid crystal active matrix display devices, and makes it possible to realize high-capacity, high-quality display with a low-cost panel.

Embodiment An embodiment of the matrix display device of the present invention will be described below with reference to the drawings.

The matrix display device of the present invention is basically of a reflective type. First, the panel configuration will be explained according to FIG. 1. A photoconductive element 7 is placed between the electrode surface side of the first transparent substrate 1 having the thin strip-shaped transparent electrode 3 and the thin strip-shaped electrode 4 and the pixel electrode 5.6.
The electrode surfaces of the second transparent substrate 2 with a A GH liquid crystal 8 is sandwiched between the two electrodes. As an example of the GH liquid crystal, a nematic liquid crystal having positive dielectric anisotropy and dichroic dye dissolved therein is initially aligned almost horizontally on both plates. A polarizing plate is provided on the outside of the first substrate 1 as required. The illumination light illuminates the first substrate side on which the display is viewed. Although not shown in FIG. 1, the strip-shaped electrode groups on the first and second substrates are provided with means for applying a voltage. With the above configuration, the GH liquid crystal layer and the photoconductive element are inserted in series between the XY matrix electrodes.

Details of the photoconductive element array on the second substrate side, which is important in the present invention, are shown in FIG. A strip-shaped transparent or opaque busbar electrode 4 is provided on a transparent substrate 2, and pixel electrodes 5.6 are provided on both sides of the busbar electrode 4, and a photoconductive element layer 7 is provided so as to straddle the busbar electrode 4 and the pixel electrode 5.6. ing. There are two types of methods for inserting the photoconductive element N7 between the bus bar electrode 4 and the pixel electrodes 5 and 6: a surface type and a bulk type, and the example shown in FIG. 2 shows the surface type. In FIG. 2, the photoconductive element layer 7 is provided in a strip-like pattern, but it may be provided over the entire display area. FIG. 3 shows one pixel section in which a photoconductive element is provided in a bulk type.

Here, the electrode 9 connecting the pixel electrodes is also transparent like the pixel electrodes 5.6, and the photoconductive layer 7 is sandwiched between the busbar electrode 4 and the transparent electrode 9.

This allows the photoconductive layer to utilize its photoconductivity in the film thickness direction. In this case as well, the photoconductive element layer may be provided over the entire display area.

Above, we have described the surface type and bulk type photoconductive elements, but the point is that in the present invention, the photoconductive element and the GH liquid crystal are inserted in series between the electric gaps, so capacitive coupling is used. In order to suppress the voltage distribution to the liquid crystal as much as possible, it is desirable that the capacitance of the photoconductive element be as small as possible compared to that of the liquid crystal element.
In the bulk type, it is important to reduce the overlapping area of both electrodes (region 10 in FIG. 3). Although FIGS. 2 and 3 show a configuration in which one pixel electrode is divided into two, it goes without saying that the number of pixel electrodes may be one per pixel.

Furthermore, the order in which the photoconductive element, busbar electrodes, and pixel electrodes are provided is not limited to the above-mentioned order. The transparent electrode used in the present invention includes indium oxide, tin oxide,
A thin metal film can be used, and the transparent electrode film may be used for the strip-shaped electrode group or pixel electrode on the second substrate side, or an opaque gold TI4 film such as aluminum, chromium, gold, tantalum, or nichrome may be used. You can.

When the pixel electrode 5.6 is transparent, a reflective plate 16 is provided behind the second substrate vi2. When the pixel electrodes 5 and 6 are light reflective, the reflective plate 16 is not necessarily required.

Here, illustration of an alignment film for aligning liquid crystal molecules in a specific direction and at an appropriate tilt angle (to prevent disclination defects) with respect to the electrode surface is omitted. Molecular orientation treatment involves coating an organic thin film such as polyimide on the electrode surface, drying it, and then rubbing it in one direction with a cloth.
This is carried out by a known method such as diagonally depositing SiO or the like on the electrode surface or adsorbing a molecular alignment agent onto the substrate by dipping or the like.

In the present invention, a negative type GH liquid crystal is used, which uses no or only one polarizing plate and whose light transmittance is increased by voltage. This is because in a mode that requires two polarizing plates, such as a TN or SBE liquid crystal mode, the intensity of the light beam is modulated only after passing through the two polarizing plates. Since the polarizing plate usually has to be installed on the outside of the substrate, the photoconductive element must be installed outside the polarizing plate, and when the pixel is small, the photoconductive element that corresponds exactly to the pixel passes through the pixel. It becomes difficult to irradiate the substrate with light, and the resolution inevitably deteriorates by the thickness of the substrate. In this respect, in the GH liquid crystal mode, a photoconductive element can be formed on the inner surface of the substrate, so a display with excellent resolution can be obtained.

Various kinds of GH liquid crystals can be used in the present invention.

Namely, (1) a nematic liquid crystal with a positive dielectric constant anisotropy (hereinafter abbreviated as Δε) is initially oriented parallel to the substrate and then oriented perpendicularly to the substrate by applying a voltage; (2) a nematic liquid crystal with a positive dielectric constant anisotropy (hereinafter abbreviated as Δε); (3) A nematic liquid crystal with a negative Δε is initially aligned perpendicular to the substrate and is turned perpendicular to the substrate by applying a voltage. (4) A type in which the chiral smectic liquid crystal is initially aligned horizontally on the substrate and then oriented horizontally but in a different direction depending on the polarity of the applied voltage. (5) A nematic-cholesterlink mixed liquid crystal with a positive Δε in a focal conic or Grandjean orientation state when no voltage is applied, and which can be oriented perpendicularly to the substrate by applying a voltage; (7), (1) Negative nematic cholesteric mixed liquid crystal in a focal conic or Grandjean alignment state with no voltage applied, which is made to orient horizontally to the substrate by applying a voltage.
) Two layers of liquid crystal layers are stacked and arranged so that the liquid crystal molecular axes of each layer are orthogonal to each other, and when a voltage is applied, the liquid crystal molecules of each layer are oriented perpendicular to the substrate (5) to (7)
There is no need to use a polarizing plate. Of course, since it is a GH liquid crystal mode, in any of the modes (1) to (7) above, there are two positive or negative colors that have anisotropy in absorption of visible light in the long axis direction and short axis direction of the molecule. A color dye is added to the liquid crystal.

The photoconductive elements include organic photoconductors such as polyvinylcarbazone and phthalocyanine, cadmium selenide (CdSe), cadmium selenium (CdS),
Inorganic photoconductors such as silicon (Si) and selenium (Se) can be used.

The reason why high contrast can be obtained by the matrix panel of the present invention will be explained.

When a voltage is applied to the electrodes of the matrix panel of the present invention (for example, the first thin strip electrode is used as a scanning electrode and the busbar electrode on the second substrate is used as a signal electrode) by a known voltage averaging method, a photoconductive element and an OH A voltage is applied to the series system of liquid crystal layers.

Here, the signal obtained by the voltage averaging method means that when selecting an electrode,
±■ for pixels that should be turned on. , ±(
12/a) Voltages are applied to the row and column electrodes so that xVo (the number of scanning electrodes when not selected) is applied.

In the voltage averaging method, the ratio (R) of the effective value voltage applied between each electrode of an on pixel (here, the pixel to which a larger voltage is applied is called an on pixel) and an off pixel is determined first. As mentioned, R = ((N””+ t)/ (N”” −
1)) However, the actual voltage applied to the liquid crystal layer is reduced by the amount applied to the photoconductive element. However, some voltage difference can be applied to the on and off pixels. The liquid crystal is negative type (a mode in which the transmittance increases as voltage is applied: in OH liquid crystal that uses a polarizing plate, it can be set to negative mode by appropriately arranging the polarization axis of the polarizing plate with respect to the liquid crystal molecule axis)
In this case, the light transmittance is improved in ON pixels to which a larger voltage is applied.

As a result, stronger light is applied to the photoconductive element, and the electrical resistance of the photoconductive element is further reduced.As a result, an increasingly stronger voltage is applied to the ON pixel, the transmittance is further improved, and the resistance of the photoconductive element is further reduced. In other words, feedback is applied to the ON pixel, and the voltage that was distributed to the photoconductive element is increasingly applied to the liquid crystal layer side. However, in an off pixel, for example, if the voltage applied to the liquid crystal layer is below the threshold value, the light transmittance does not change, and therefore the resistance of the photoconductive element does not change either, and no feedback occurs and the light transmittance decreases. remains low. In other words, by using OH liquid crystal as a light pulp, the amount of light irradiated to the photoconductive element is changed, and by non-linearly changing the electrical resistance of the photoconductive element, the ratio of the voltage applied to the on pixel and the off pixel is amplified. This means that it is possible. As a result, it is freed from the constraints imposed by the voltage averaging method, and high contrast and wide viewing angles can be obtained even in large-capacity displays with a large number of scanning lines (N). High image quality such as color reproducibility can be achieved.

Effects of the Invention Conventional simple matrix liquid crystal display devices have a simple panel configuration and are therefore low in cost, but as the number of scanning lines (N) increases, the ratio of voltages applied to on pixels and off pixels decreases to 1.
Because the camera is close to In addition, in TN mode and SBE mode, matrix drive is possible to some extent because the threshold characteristics are relatively steep, but in OH liquid crystal mode, TN mode has a relatively steep threshold characteristic.
Although it is more advantageous than SBE or SBE, it is not suitable for matrix driving due to insufficient threshold characteristics. However, in the present invention, unlike TN and SBE, OH liquid crystal does not require a polarizing plate or can change the light transmittance even with just one polarizing plate, so it is suitable for combination with a photoconductive element. It can now be used effectively for matrix display. Conventionally, an active matrix has been used as a method that does not cause a decrease in contrast even in large-capacity display with a large number of scanning lines N. In liquid crystal active matrix display devices, high contrast and wide color reproducibility have been demonstrated, and liquid crystal color TVs have been put into practical use. However, in order to manufacture an active matrix array, active matrix arrays require the formation of thin films of semiconductors, insulators, metals, etc. several times, and the photo process of converting these thin films with high precision many times, which increases manufacturing costs. There is a problem of deterioration in yield, and in particular, in order to manufacture large panels of A4 size or larger using active matrix, not only the cost increases but also the fact is that a satisfactory device itself has not been developed yet. In the present invention, even on the substrate side having the photoconductive element array, 1 to 3
By using a batting process with different steps, it is possible to construct a matrix panel that is much simpler and has a higher yield than conventional active matrix forming technology, and provides high image quality at a low cost.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a matrix liquid crystal display device of the present invention, FIG. 2 is a partially enlarged front view of a photoconductive element array used in the matrix panel of FIG. 1, and FIG. FIG. 4 is a perspective view of a conventional transmission type liquid crystal display device, and FIG. 5 is a front view of the electrode portion of FIG. 4. 1.2...Transparent substrate, 3,14...Transparent electrode, 4...Busbar electrode, 5,6...
...Pixel electrode, 7...Photoconductive element layer, 8...
...GH liquid crystal layer, 10.1) ...Polarizing plate, 1
2...Light source, 15...Conventional liquid crystal X-
Y matrix panel, 16...Reflector, 18.
...TN liquid crystal layer. Name of agent Patent attorney Toshio Nakao Number 3 Figure 14 Figure 5

Claims (8)

[Claims] (1) A guest-host liquid crystal layer whose light transmittance increases when a voltage is applied is sandwiched between the first transparent band-shaped electrode and the pixel electrode, and on the pixel electrode side there is a liquid crystal layer extending in a direction perpendicular to the first band-shaped electrode. 1. A matrix display device comprising two strip-shaped electrodes, a photoconductive element provided between the second strip-shaped electrode and a pixel electrode, and voltage applying means provided to the first and second electrodes. (2) The matrix display device according to claim (1), wherein a photoconductive element is provided at each pixel point constituted by the first strip electrode and the pixel electrode. (3) The photoconductive element must be made of an organic photoconductor such as polyvinylcarbazole or phthalocyanine, or an inorganic photoconductor such as cadmium selenide (CdSe), cadmium selenium (CdS), silicon (Si), or selenium (Se). A matrix display device according to claim (1), characterized in that: (4) A dichroic dye is added to the guest-host liquid crystal selected from nematic liquid crystal with positive dielectric anisotropy, nematic liquid crystal with negative dielectric anisotropy, nematic-cholesteric mixed liquid crystal, and chiral smectic liquid crystal. A matrix display device according to claim (1), characterized in that the matrix display device comprises: (5) The matrix display device according to claim (1), wherein the first strip electrode or the pixel electrode is provided with red, blue, and green color filters. (6) Claim (1) characterized in that at least a polarizing plate is provided on the substrate side having the first strip electrode.
The matrix display device described in Section 1. (7) When the pixel electrode is transparent, a light reflecting plate is provided behind the second substrate.
) The matrix display device described in item 2. (8) Between the first strip electrode and the second strip electrode, when selecting the electrode, ±V_0 for pixels to be turned on, ±(1-2/a)×V_0 for pixels to be turned off, When not selected |
Claim (1) characterized in that the device is configured so that a voltage of V_0/a| (where a=√N+1, a real number, N is the number of the first to second strip electrodes) is applied. The matrix display device described.