JPH0727142B2 - Matrix display - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flat panel XY matrix display device, which is a binary display office display device or a wall-mounted color TV having halftone. It can be used for various purposes such as low cost and high image quality.

2. Description of the Related Art Conventionally, as flat panel display devices, plasma displays, flat CRTs, fluorescent display tubes, liquid crystals, etc. have been typical.
The former three are of the light emitting type and currently have low luminous efficiency.
It has problems such as relatively high drive voltage and difficulty in upsizing. On the other hand, the liquid crystal display device has low voltage, low power,
Due to the ease of upsizing, the development towards full-color upsizing is being actively pursued. In order to realize full-color display with liquid crystal, the liquid crystal is usually used simply as a light valve, and by providing red, blue, and green color filters in the form of strips or dots, a color image is produced by additive color mixture on a two-dimensional surface. Is displayed. Fig. 3 shows a conventional XY using a twisted nematic (TN) liquid crystal display mode.
The configuration and operation of the matrix type panel will be described. Fourth
The figure shows the arrangement of the row electrodes 3 and the column electrodes 14 in the front view of FIG. The TN type matrix panel 15 includes a pair of glass substrates 1 and 2, a transparent row electrode 3 and a transparent column electrode 14 each made of indium oxide, and a monomatch liquid crystal 8 having a positive dielectric anisotropy. It is sandwiched, and a pair of polarizing plates 10 and 11 are provided outside the glass substrates 1 and 2, respectively. When constructing a color panel, red, blue, and green color filter layers are regularly provided on the row electrodes or the column electrodes, respectively. Although the panel 15 is illustrated in a simplified manner, usually, an alignment treatment layer for regulating the alignment of liquid crystal molecules is provided on the row electrodes or the column electrodes or, if there is a color filter layer, on the color filter layer. On the surface of each substrate, the liquid crystal molecules are aligned almost parallel to the substrate, and the orientation direction of the molecules differs between the one substrate and the other substrate by approximately 90 ° in the normal TN mode. The molecular arrangement direction is gradually twisted from one substrate to the other substrate.
The surfaces of both substrates are pre-aligned so that a twist of approximately 90 ° occurs between both substrates. In other than the normal TN mode, for example, in the SBE (abbreviation of Super Birefringence Effect) mode, the twist angle of the molecule may be set to 180 ° to 360 °. Backlight source 12 for transmissive display
Is provided. When a linear light source such as a fluorescent lamp is used as the light source 12, a light diffusion plate is provided between the contribution and the liquid crystal panel in order to obtain uniform and even brightness on the two-dimensional display surface. . If the light source is a planar light source such as electroluminescence, the light diffusion plate is not necessary. The above is one example of the conventional liquid crystal matrix panel, but the biggest drawbacks of the conventional technology are: (1) Generally, in a simple XY matrix display panel,
When a panel having two scanning lines (here, for example, the row electrode 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 When a driving method called the so-called voltage averaging method is adopted and optimized so that R becomes maximum, R = {(N ^1/2 +1) / (N ^1/2 -1)} ^1/2 . That is, in a panel having a simple matrix structure, a crosstalk voltage is applied to off-pixels as well, resulting in a reduction in contrast. For example, in the case of N = 100, R = 1,1 and only 10% of the effective value voltage applied between the electrodes corresponding to the off pixels is applied to the ON pixel, and the voltage difference of 10% is displayed. You must be able to add contrast. In other words, the display medium used for the simple matrix panel cannot provide a display excellent in contrast unless the luminance-voltage characteristic is sharp and the threshold value is clear. In conventional TN cells, this sharpness is insufficient, so N = 64 (R =
However, the contrast is not comparable to that of active matrix panels. On the other hand, in the TN cell, as shown in the above-mentioned reference, the light transmission characteristics of the cell generally depend on the light wavelength, so-called optical dispersion occurs, and the luminance-voltage characteristic considerably differs depending on the wavelength. When a dielectric layer called a color filter is provided on the electrodes, the filter layer is inserted in series with the liquid crystal, so this voltage ratio of ON and OFF applied between the electrodes is different in the liquid crystal layer. Further, there is a drawback that the contrast of the color panel is deteriorated and the contrast of the color panel is considerably deteriorated as compared with the monochrome panel.

(2) In order to overcome the poor contrast, viewing angle, color reproducibility and the like of the simple XY matrix type display panel, a panel structure called an active matrix is adopted. In the active matrix display panel, a thin film transistor (hereinafter referred to as a TFT) is formed at each pixel point forming a matrix.
3 terminal switch element such as abbreviated) and 2 terminal non-linear resistance element such as P-N junction and metal-insulator-metal (abbreviated as MIM below) overcomes the poor threshold characteristics of liquid crystal itself. However, it has achieved high contrast and excellent color reproducibility. However, in the active matrix panel, it is difficult to manufacture the active matrix array with low cost and high yield, and thus the active matrix panel has the greatest difficulty in that the panel cost is high.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The present invention is intended to solve the above-mentioned problems of the conventional liquid crystal simple matrix display device having poor contrast and the high cost of the liquid crystal active matrix display device.

Means for Solving the Problems In the present invention, a first strip-shaped electrode provided with a photoconductive film and a second strip-shaped electrode arranged so that the first strip-shaped electrode and the first strip-shaped electrode are orthogonal to each other. A negative guest-host liquid crystal layer whose light transmittance is increased by a voltage is sandwiched therebetween, and means for applying a voltage to the first and second strip electrodes is provided. This is to solve the conventional problems.

By the above means, it is possible to solve the problems of poor contrast of conventional liquid crystal simple matrix display devices and high cost of liquid crystal active matrix display devices, and to realize high-capacity and high-quality display with a simple and low-cost panel configuration. Is.

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

The matrix display device of the present invention basically has a transmission type and a reflection type. First, a transmissive panel structure will be described with reference to FIG. A voltage is applied between the first strip-shaped electrode 4 provided with the photoconductive film 19 and the second strip-shaped electrode 3 arranged so that the first strip-shaped electrode and the first strip-shaped electrode are orthogonal to each other. Increasing negative type guest-host liquid crystal layer
18 is sandwiched. The first and second strip electrodes are XY
Each electrode is provided with a means for applying a voltage in a matrix configuration. As an example of the GH liquid crystal 18, a nematic liquid crystal having a positive dielectric anisotropy and in which a dichroic dye is dissolved is subjected to an initial alignment treatment substantially horizontally on both substrates. On the outside of the second substrate 2, a polarizing plate 10 having a polarization axis aligned with the liquid crystal molecular axis
Is provided. The light source 12 is provided outside the polarizing plate, and the display is observed through the first substrate provided with the photoconductive layer 19. With the above structure, the GH liquid crystal layer 18 and the photoconductive element 19 are inserted in series between the XY matrix electrodes. The above is an example of the transmissive display device. Next, the reflective panel structure will be described with reference to FIG. In this case, the reflection plate 20 is provided on the back surface of the first substrate 1 shown in FIG. 1 so that the second substrate 2 side is illuminated and the display is observed from the second substrate side. Of course, if the first strip electrode 4 is reflective, the back reflector 20 is not necessary. As the transparent electrode used in the present invention, indium oxide, tin oxide, a metal thin film or the like can be used, and the first strip-shaped electrode 4 which can be a reflective electrode itself is aluminum, chromium, gold, tantalum, nichrome or the like. The opaque metal film can be used. Here, an illustration of an alignment film for aligning liquid crystal molecules in a specific direction and having an appropriate tilt angle (to prevent disclination defects) with respect to the electrode surface is omitted. For molecular orientation treatment, an organic thin film such as polyimide is applied to the electrode surface, dried and then rubbed in one direction with a cloth, or the electrode surface is treated with Si.
It is carried out by a known method such as oblique vapor deposition of O or the like, or adsorption of a molecular orientation agent on the substrate by dipping or the like.

In the present invention, a GH liquid crystal in which the light transmittance is increased by not using a polarizing plate or by using only one sheet and increasing the voltage is used. This is because in a device that requires two polarizing plates such as the TN or SBE liquid crystal mode, the light beam is intensity-modulated only after passing through the two polarizing plates. Since the polarizing plate usually has to be provided on the outside of the substrate, the photoconductive element is provided on the outside of the polarizing plate. When the pixel is small, the pixel is passed through the photoconductive element that corresponds to the pixel. It becomes difficult to irradiate with light, and the resolution must be deteriorated by the thickness of the substrate. In this respect, in the GH liquid crystal mode, since the photoconductive layer can be formed on the inner surface of the substrate, a display with excellent resolution can be obtained.

Various types of GH liquid crystal 18 can be used in the present invention.
That is, (1) a nematic liquid crystal having a positive dielectric anisotropy (hereinafter abbreviated as Δε) is initially aligned parallel to the substrate and is oriented vertically to the substrate by applying a voltage, (2) nematic with a positive Δε The liquid crystal is initially aligned so that it is parallel to both substrates and twisted by 90 °, and the voltage is applied so that it is oriented vertically to the substrate. (3) Nematic liquid crystal with negative Δε is initially aligned vertically to the substrate and the voltage is applied. Those that are directed horizontally to the substrate by application, (4) Those that initially orient the chiral smectic liquid crystal horizontally to the substrate and are oriented horizontally but different directions to the substrate depending on the polarity of the applied voltage. (5) A Δε positive nematic-cholesteric mixed liquid crystal with no voltage applied and focus conic or Grandjean alignment oriented in a direction perpendicular to the substrate with voltage applied. Those which, (6) [Delta] [epsilon] is negative nematic - those which suited the horizontal direction to the substrate voltage application those focal conic or Grandjean alignment state of a cholesteric liquid crystal mixture in no voltage application, (7)
Two liquid crystal layers in the state of (1) are stacked so that the liquid crystal molecule axes of the respective layers are orthogonal to each other, and the liquid crystal molecules of the respective layers are oriented in the direction perpendicular to the substrate when a voltage is applied.
In (7), it is not necessary to use a polarizing plate. Of course, since it is the GH liquid crystal mode, in any of the above modes (1) to (7), two positive or negative colors having anisotropy in absorption of visible light in the major axis direction and the minor axis direction of the molecule. A sex dye is added to the liquid crystal.

Examples of the photoconductive element include organic photoconductors such as polyvinylcarbazole and phthalocyanine, or cadmium selenide (CdSe), cadmium sulfide (CdS), silicon (S
Inorganic photoconductors such as i) and selenium (Se) can be used. A transparent photoconductive layer is used in the transmissive display device of FIG. 1, and an opaque photoconductive film may be used in the reflective panel of FIG.

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

When a voltage according to a known voltage averaging method is applied to the electrodes of the matrix panel of the present invention (for example, the first strip-shaped electrode is a scanning electrode and the second strip-shaped electrode is a signal electrode), the photoconductive layer and the GH liquid crystal layer are connected in series. A voltage is applied to the system.

Here, the signal obtained by the voltage averaging method means ± V _{0 for} the pixel to be turned on and ± V for the pixel to be turned off when the scanning electrode is selected.
(1-2 / a) × V ₀ , when not selected | V ₀ / a | (however, Is a real number, N is the number of scan electrodes, and a driving method in which voltages are applied to the row and column electrodes so that a voltage is applied. In the case of the voltage averaging method, the ratio (R) of the effective value voltage applied between each electrode of the ON pixel (here, the pixel to which a higher voltage is applied is called the ON pixel) and the OFF pixel is first calculated. As mentioned above, R = {(N ^1/2 +1) / (N ^1/2 -1)} ^1/2 , but the actual voltage applied to the liquid crystal layer is reduced by the amount applied to the photoconductive layer. To do. However, some voltage difference can be applied to the ON and OFF pixels. The liquid crystal is a negative type (a mode in which the transmittance increases with the application of a voltage: in a GH liquid crystal that uses a polarizing plate, a negative type mode can be set if the polarizing axis of the polarizing plate is properly provided with respect to the molecular axis of the liquid crystal). Therefore, the light transmittance is improved in the ON pixel to which a larger voltage is applied. As a result, strong light is struck by the optical 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. That is, feedback is applied to the ON pixels, and the voltage component distributed to the photoconductive element is more and more applied to the liquid crystal layer side. However, in an off pixel, for example, if the voltage applied to the liquid crystal layer is a voltage equal to or lower than the threshold value, the light transmittance does not change here. Therefore, the resistance of the photoconductive element does not change and feedback does not occur. Remains low. That is, by using GH liquid crystal as a light valve, the light irradiation amount to the photoconductive element is changed, and the electric resistance of the photoconductive element is changed non-linearly to amplify the ratio of the voltage applied to the ON pixel and the OFF pixel. You can do that. As a result, it is possible to obtain a high contrast and a wide viewing angle even in a large-capacity display having a large number of scanning lines (N) without being restricted by the voltage averaging method. In the case of a color panel provided with a color filter, a wide range is obtained. Higher image quality such as color reproducibility can be realized.

EFFECTS OF THE INVENTION In the conventional simple matrix liquid crystal display device, the panel structure is simple, so the cost is low, but when the number of scanning lines (N) increases, the ratio of the voltage applied to the ON pixel and the OFF pixel is 1.
However, the deterioration of the contrast and the narrowing of the viewing angle were major problems. Also, since the threshold characteristics are relatively steep in TN mode and SBE mode, matrix driving can be performed to some extent, but the GH liquid crystal mode is more advantageous than TN and SBE in terms of viewing angle dependence, but the threshold characteristics are However, it was not suitable for matrix driving. However, in the present invention
Unlike TN and SBE, GH liquid crystal does not require a polarizing plate.
Since the light transmittance can be changed even with a single sheet, it is optimal for combination with a photoconductive element, and the present invention enables the GH liquid crystal to be effectively used for matrix display. Number of scanning lines N
Conventionally, an active matrix is provided as a method for preventing a reduction in contrast even in a large capacity display. In liquid crystal active matrix display devices, high contrast and wide color reproducibility have been demonstrated, and liquid crystal color TVs have been put to practical use. However, in active matrix, semiconductors, insulators,
It requires several photo processes to form thin films such as metal several times and to pattern these thin films with high accuracy, which causes problems such as increase in manufacturing cost and deterioration of yield. In the case of manufacturing a panel with an active matrix, the actual condition is that the device itself has not yet been developed, which is satisfactory while increasing the cost. According to the present invention, it is sufficient to provide a photoconductive layer on one electrode of a conventional simple matrix panel, which is much simpler and higher in yield than the conventional active matrix forming technology, and a matrix panel which provides high image quality at low cost. Can be configured.

[Brief description of drawings]

FIG. 1 is a perspective view of a transmissive matrix liquid crystal display device of the present invention, FIG. 2 is a perspective view of a reflective matrix panel of the present invention, and FIG. 3 is a perspective view of a conventional transmissive liquid crystal display device.
The figure is a front view of the electrode portion of FIG. 1,2 …… Transparent substrate, 3,4 …… Transparent electrode, 19 …… Photoconductive layer,
18 …… GH liquid crystal layer, 10,11 …… Polarizing plate, 12 …… Light source, 15…
... Conventional liquid crystal XY matrix panel, 8 ... TN liquid crystal layer, 20 ... Reflector, 14 ... Electrode.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Hiroyuki Onishi 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Shuko Oba 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. 56) References JP-A-59-129892 (JP, A) JP-A-61-290422 (JP, A) JP-A-62-127720 (JP, A) JP-A-62-235984 (JP, A)

Claims (8)

[Claims] 1. A first band-shaped electrode provided with a photoconductive film and a second band-shaped electrode arranged so that the first band-shaped electrode and the first band-shaped electrode are orthogonal to each other A matrix display device characterized in that a negative guest-host liquid crystal layer of increasing rate is sandwiched, and means for applying a voltage to the first and second strip electrodes is provided. 2. The photoconductive film is a polyvinylcarbazole-based organic photoconductor, a phthalocyanine-based organic photoconductor, or cadmium selenide (CdSe), or cadmium sulfide (Cd).
The matrix display device according to claim 1, wherein the matrix display device comprises one of an inorganic photoconductor of S), silicon (Si), and selenium (Se). 3. The matrix display device according to claim 1, wherein the second strip electrode is transparent. 4. The matrix display device according to claim 1, further comprising a reflector provided behind the first strip electrode. 5. The guest host liquid crystal is a nematic liquid crystal having a positive dielectric anisotropy, a nematic liquid crystal having a negative dielectric anisotropy, a nematic / cholesteric mixed liquid crystal, or a chiral smectic liquid crystal to which a dichroic dye is added. The matrix display device according to claim (1), characterized in that 6. The first or second strip electrodes are red, blue,
The matrix display device according to claim (1), characterized in that a green color filter is provided. 7. The matrix display device according to claim 1, wherein at least a polarizing plate is provided on the side of the substrate having the second strip electrode. 8. Between the first strip electrode and the second strip electrode, when selecting an electrode, ± V ₀ is for a pixel to be turned on and ± (1-2 / a) is for a pixel to be turned off. × V ₀ , when not selected | V ₀ /
a | The matrix display device according to claim (1), wherein a real number, N, is a voltage applied to the first or second strip electrodes.