JP2600171B2 - Liquid crystal matrix display device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal matrix display device for displaying a large number of characters, graphics, images and the like with high quality. Conventional technology Currently, word processors, personal computers, televisions, CAD / CA
Most of the display devices used for M etc. use a CRT (cathode ray tube), from monochrome devices that can display A4 full pages to devices that can display high-quality full colors. Various items ranging from 0.5 ″ to 40 ″ are used for office or recreational use.
However, a CRT has a large volume and is difficult to be reduced in thickness, and requires a high voltage. Therefore, a flat-panel large-capacity display device is strongly demanded. Plasma, electroluminescence, liquid crystal, and the like are typical examples of a flat panel display device, each of which has a configuration as shown in FIG. 2 and has parallel strip electrodes 3, 4 provided on a pair of substrates 1, 2. The display medium 5 is sandwiched therebetween to form a matrix panel. In a twisted nematic liquid crystal (hereinafter abbreviated as TN) type XY matrix panel, a matrix panel 8 is formed by providing polarizing plates 6 and 7 on each side of each substrate. When the panel 8 is used in the transmission mode, the display is viewed from the substrate 2 side using the back illumination light 9. The former two have problems such as a high driving voltage, an expensive driver circuit, and high power consumption. On the other hand, liquid crystals are widely used in calculators, watches, etc., but it is difficult to realize large-capacity display with a large number of pixels with cells having a simple matrix configuration due to the characteristics of liquid crystal materials. , To use a pair of polarizing plates,
It has disadvantages such as dark display. On the other hand, recently, ferroelectric liquid crystals have attracted attention due to their high speed. The ferroelectric liquid crystal has the following molecular structure: that the molecule has asymmetric carbon and is optically active. : Permanent dipole moment perpendicular to the molecular long axis exists close to the asymmetric carbon. And as a molecular system: found to satisfy conditions such as having a chiral smectic layer, and historically synthesized using the asymmetric carbon of active amyl alcohol and the permanent dipole moment of the carbonyl group DOBAMBC

[(S) 2-methylbutyl p- (pn-decyloxybenzylideneamino) cinnamate] is a typical example. Several display modes using a ferroelectric liquid crystal have also been proposed. That is, the helical structure disappears upon application of a voltage, and the light scattering property changes from light scattering when no voltage is applied to light transparency. The cell thickness is made sufficiently thinner than the pitch of the helical structure, the helical structure is forcibly erased by the wall effect, and the direction of the tilt angle of the molecule is reversed by applying a positive or negative voltage to use a pair of polarizing plates together. The one that obtains light and dark by the birefringence effect.
Using a chiral smectic liquid crystal having a tilt angle of about 45 ° in which a dichroic dye is dissolved, the polarization axis of at least one polarizing plate is aligned with the molecular axis of the liquid crystal, and a positive or negative voltage is applied. Inverts the direction of the tilt angle of the molecule to obtain bright and dark contrast with the dichroism of the dye. One that utilizes light scattering accompanied by intense molecular motion when the spontaneous polarization is reversed due to the reversal of the polarity of the electric field. The above-mentioned mode is called Transient-Scattering-Mode (TSM), in which high-speed operation and bright display can be obtained because a polarizing plate is not required. In order to construct a light valve, it is necessary to make the cell thickness as thin as about 2 μm and maintain the gap with high precision and uniformity, which entails difficulties in cell production. However, TSM can construct a panel with a cell thickness of 5 μm or more. There is an advantage that the production of is easy. For details, see Katsumi Yoshino ETL, Ferroelectrics, Vol. 59, 1984, pp. 145-160 (Ka
tsumi Yoshino et al, Ferroelectrics, vol. 59.1984, p. 1
45-160). The TSM mode has the above features, but until now only the characteristics of a single optical shutter have been reported, and the cell configuration and drive for large-capacity display as a matrix type display panel have been reported. The law was undeveloped. In addition, the cell structure reported conventionally has insufficient light scattering performance, and further higher contrast has been required. Problems to be Solved by the Invention The present invention realizes a high display capacity matrix panel having a large display capacity having a binary or halftone using the transient light absorption effect of a ferroelectric liquid crystal in which a dichroic dye is dissolved. And a driving method. Means for Solving the Problems In order to solve the above problems, according to the present invention, a first electrode group in which a plurality of thin strip-shaped transparent electrodes are provided on a first transparent substrate in parallel with each other, A plurality of narrow strip-shaped transparent electrodes are provided on the second transparent substrate so as to face each other, and are arranged at a predetermined gap so as to be orthogonal to the first electrode group. A chiral smectic liquid crystal in which a dichroic dye is dissolved is interposed between the first electrode group and the second electrode group.
In a ferroelectric matrix liquid crystal display device configured to apply video signal voltages all at once to the electrode groups in parallel, the surface on the first transparent substrate and / or the second transparent substrate side has irregularities. The first,
The present invention proposes a liquid crystal matrix display device characterized in that the liquid crystal is brought into an intense light absorbing state by a selection signal applied between the second electrodes, and the liquid crystal is brought into a transparent state by a sufficiently long pulse. According to the above means, in the panel of the present invention, the liquid crystal molecules are oriented in a direction substantially parallel to the substrate and dichroic dyes are arranged by a sufficiently long DC voltage, so that polarized light oscillating in the direction perpendicular to the dye molecules is transmitted and a bright state is obtained. When the polarity of the applied voltage is switched, the arranged liquid crystal molecules, that is, the dichroic dye molecules are dynamically oriented in various directions, so that the light absorption increases.
The light shielding effect is improved. In the case of a substrate having an uneven surface, the light absorption at the time of switching the polarity of the voltage is further improved, so that a display with excellent contrast can be obtained. Embodiment Hereinafter, a liquid crystal matrix display device according to an embodiment of the present invention will be described with reference to the drawings. Using the photo-etch technology on the surface of the transparent glass substrate 10
Irregularities of ± 3 μm were regularly provided at a pitch of 20 μm. A strip-shaped transparent electrode (hereinafter abbreviated as ITO) 11 composed mainly of indium oxide having a pitch of 0.2 mm and a width of 0.17 mm is placed on the surface of the substrate.
A first substrate was prepared by providing 00 pieces. Another glass substrate 12 was prepared, and here, a band-shaped electrode 13 of ITO was formed in the same manner as above without forming irregularities on the surface to prepare a second substrate. These first
And the electrode surfaces of the second substrate face each other, and arranged so that the strip electrodes of each other are orthogonal to each other, and a dichroic dye composed mainly of a mixture of ester and pyrimidine was dissolved between both electrodes, Chiral smectic C at room temperature
An XY matrix panel 15 was formed by interposing a ferroelectric liquid crystal 14 showing a phase so as to have a thickness of 20 μm. A liquid crystal in which a dichroic dye is dissolved is hereinafter referred to as a GH liquid crystal. Although not shown, the surface of the electrode is provided with an alignment film obtained by subjecting a polyimide resin to a known rubbing treatment in order to control the alignment of the liquid crystal molecules. The pitch of the mixed liquid crystal used at room temperature is about 3
At μm, the spontaneous polarization is that of 20 nC / cm ² . Each electrode of the panel is connected to a data signal source and a scanning signal source, and x-
A y-matrix display was constructed. The optical characteristics were examined by applying a matrix drive voltage based on a voltage averaging method, which is known for driving a TN matrix panel, to this device. Regarding the optical characteristics of the panel, the panel was irradiated with white light 16 from the back, and the luminance was measured from the direction perpendicular to the panel surface. One polarizing plate is provided on the surface of the panel on the measurement side such that the direction of the director of the molecule and the absorption axis coincide when a positive voltage is applied to the panel. A panel having no irregularities was also prepared, and the contrasts of the two panels were compared. In the panel having the unevenness with the driving waveform set to the number of scanning lines = 200 and the bias ratio = 3, the light / dark contrast ratio was 25 at the optimum voltage value V ₀ = 60 V, and a quite satisfactory value was obtained. Under the same conditions, the contrast of the conventional panel having no unevenness was 18 at most, and it was confirmed that the unevenness of the surface of the substrate contributed to the improvement of the contrast. In the two-field AC type applied voltage waveform,
In each field, a DC component is applied to the liquid crystal cell, and the spontaneous polarization of the liquid crystal is oriented in the direction of the electric field, so that the liquid crystal is untwisted and becomes transparent, but a high voltage in the opposite direction is applied to the selected pixel in the next field. As a result, when the spontaneous polarization is reversed, intense molecular motion occurs and the light becomes absorptive. On the other hand, in the non-selected pixels, the light absorption is not remarkable because the applied voltage is low. The reason that the contrast is improved by making the substrate surface uneven is that the dynamic molecular motion at the time of applying the voltage pulse becomes more prominent due to the unevenness of the substrate surface, and the light absorption increases due to the dye molecules being oriented in all directions. Is probably the cause. The normal TSM has a high light scattering degree in the forward direction, but it is desirable that the original light valve be light scattering or light absorbing backward. It can be said that the panel configuration of the present application having unevenness on the substrate is more suitable for a rear light source type display panel. If the pitch of the unevenness is too large than the cell thickness, the light absorption performance is reduced. The critical electric field E _C at which the spiral of the chiral smectic liquid crystal disappears is given by the following equation. Here, P: helical pitch, K: orientation elastic constant, Ps: spontaneous polarization. That is, when driving at low voltage, K is small, and P, Ps
The larger is better. Desirable characteristics in matrix display according to the display mode of the present application are as follows. : The liquid crystal is brought into a strong light absorbing state as soon as possible by polarity inversion by a selection pulse of a voltage as low as possible. : The absorption state achieved above can be maintained as long as possible for one field. : The non-selected pulse should not be in the absorption state as much as possible. Are required for high Δn (refractive index anisotropy), high tilt angle, and high
It is considered to be realized by a liquid crystal having characteristics such as Ps, low K, and low viscosity (η). Are related to the requirements of K, η, P, Ps, Δε
(Dielectric anisotropy), cell thickness (d), bias voltage applied during the non-selection period, and the like.
The drive signal waveform and the like are involved in a complicated manner. A similar parameter is involved from the beginning. When unevenness is provided on the substrate as in the present invention, it is involved in all of the above-mentioned, and the cell thickness, the depth of unevenness, the unevenness pitch depend on the liquid crystal material, the amount of dye added, the number of scanning lines, the supplyable voltage value, the pixel pitch, etc. Etc. need to be optimized. In the embodiment, one polarizing plate is used. However, the contrast can be obtained even if the polarizing plate is not used, though it is slightly small. It was also found that when the polarizing axes of the polarizing plates were provided in parallel on both sides of the substrates 10 and 12, the brightness was reduced but the contrast was further improved. The present invention improves the conventionally proposed TSM mode, improves the shutter effect of the panel by providing irregularities on at least one surface of the substrate, and adding a dichroic dye to the liquid crystal. This achieves a high contrast display. Further, this configuration is applied to a matrix panel, and a cell configuration and a driving method for displaying a panel having a large number of scanning lines with high contrast without substantially applying a DC voltage component to the liquid crystal are provided. As a result, the cell gap can be thickened, so that the cell can be easily manufactured, and the manufacturing yield of the panel can be increased. : By adopting the mode that causes the maximum light absorption at the time of field switching, the entire scanning line time (τ) can be allocated to domain switching, so that a large-capacity display having many scanning lines can be realized. : Since a DC voltage component is not substantially applied to the liquid crystal cell, a highly reliable display panel can be realized. It is also possible to realize a display having a halftone by modulating the peak value (V ₀ ) or the panel width τ (τ = T / m: T is the time of one field, m is the number of scanning lines). . : In the conventional TSM mode, the light scattering property is forward scattering, so the contrast cannot be obtained unless the back light source is irradiated from an oblique direction, and the illumination method is restricted. Increased. In the embodiment, the monochrome display is described. However, in this matrix display mode, since the light transmittance of the pixel is changed, it is easy to display a color image by providing a color filter for each pixel, as is well known. And a display with a high viewing angle can be obtained because of the GH liquid crystal.

[Brief description of the drawings]

FIG. 1A is a configuration diagram of a matrix display device of the present invention,
FIG. 1 (b) is a cross-sectional view of the panel of FIG. 1 taken along the line AA ', and FIG. 2 is a configuration diagram of a conventional TN type matrix display device. 10 …… Transparent substrate with uneven surface, 12 …… Transparent substrate,
13,11 ... Transparent row and column electrodes, 14 ... Ferroelectric liquid crystal added with dichroic dye, 15 ... Ferroelectric liquid crystal XY matrix panel, 16 ... Back light source.

Continuation of the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location G09G 3/36 G02F 1/137 510 (72) Inventor Hiroyuki Onishi 1006 Kazuma, Kadoma-shi Matsushita Electric Industrial Co., Ltd. (72) Inventor Kazuhiro Kamiten 1006 Kadoma Kadoma, Matsushita Electric Industrial Co., Ltd. (72) Inventor Yoshio Iwai 1006 Kadoma Kadoma, Matsushita Electric Industrial Co., Ltd. Address Matsushita Electric Industrial Co., Ltd. (56) Reference JP-A-58-173719 (JP, A) JP-A-53-77497 (JP, A)

Claims (5)

(57) [Claims] 1. A first electrode group in which a plurality of strip-shaped transparent electrodes are provided in parallel on a first transparent substrate, and a strip-shaped transparent electrode is provided on a second transparent substrate in opposition to the first electrode group. A chiral electrode in which a plurality of electrodes are provided in parallel with each other, and a dichroic dye is dissolved between the first electrode group and a second electrode group arranged at a predetermined gap so as to be orthogonal to the first electrode group A ferroelectric matrix liquid crystal display in which a smectic liquid crystal is sandwiched and a scanning pulse is sequentially applied to a first electrode group and a video signal voltage is simultaneously applied to a second electrode group in parallel. An apparatus, wherein a surface of a first transparent substrate and / or a surface of a second transparent substrate is processed to have irregularities, and a liquid crystal is formed by a selection signal applied between the first and second electrodes. Intense light absorption state, and liquid crystal The liquid crystal matrix display device which is characterized in that the transparent state. 2. The liquid crystal matrix display device according to claim 1, wherein the average pitch of the surface irregularities on the substrate side is smaller than the gap. 3. The liquid crystal matrix display device according to claim 1, wherein the surface irregularities on the substrate side are provided in advance on the substrate itself on which the electrodes are provided. 4. The liquid crystal matrix display device according to claim 1, wherein the surface irregularities on the substrate side are provided on an insulating film provided on the electrodes. 5. The method according to claim 1, wherein the signal voltage applied to the second electrode group is modulated with a peak value or a pulse width so as to display a halftone. The liquid crystal matrix display device according to item (1).