DE2132948A1 - Cell array containing nematic liquid crystals - Google Patents

Description

Applicant: Stuttgart, June 28, 1971

Hughes Aircraft Company P 234-9 S / kg

Centinela Avenue and

Teale Street

Culver City, Calif., V.St.A.

Cell array containing nematic liquid crystals

The invention relates to a cell array containing nematic liquid crystals.

Numerous nematic liquid crystals "are presently known, all of which have the special property of being sensitive to suitable electric fields in limited areas and forming areas or locations which can be identified and used as images which can be displayed in various ways.
In order to facilitate the explanation of the present invention,

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It should be noted that liquid crystals can be divided into three groups, namely the nematic, smectic and cholesteric liquid crystals, and that the present invention is primarily concerned with the use of nematic liquid crystals Advantage to be applied. Thus, the present invention relates in the broadest sense, despite the intensive ψ work that has so far been spent on liquid crystals, in particular nematic liquid crystals, unknown applications for such the nematic liquid crystals "

In particular, nematic liquid crystals have the common property that they are in a wide temperature range, known as the nematic realm, have a liquid crystal structure »In the nematic Area, the crystals can be influenced by electric fields of sufficient strength in such a way that that an image generation takes place within the ^ ristalle3b. The best understood mechanism of the Imaging has been referred to as "dynamic scattering" by nematic liquid crystal molecules «Bei this dynamic scattering leads to the formation of turbulence within the nematic liquid crystal, by which the optical reflective or transmissive power of the crystal is changed. As already mentioned, the image generation can take place with the help of an electric field and it needs the image = generation not necessarily a consequence of a "dynamic

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Scattering "because other effects of the electric field, which are currently being investigated, for ore; r ~ uiaß ν ·; η image-defining areas or areas within the nematic liquid crystals, “The present invention makes in a basic sense of an electric field for imaging within nematic liquid crystals Use regardless of the specific way in which the field is used to form the image-defining Areas leads, and is therefore not limited to the use of such crystals in the working area of dynamic Limited spread.

In the invention, "according to the timing, there were different nematic liquid crystals, either alone or in combination with other nematic ones Liquid crystals]! or other substances such that a "substance containing nematic liquid crystals" is used became. Various kinds of such substances containing nematic liquid crystals have been used, to achieve specific desired properties or the properties of nematic liquid crystals to modify. As will be explained in detail later, those containing nematic liquid crystals fall Substances that are best suited for the purposes of the invention generally fall into three different categories Categories related to the appearance of a thin layer of various nematic liquid crystals containing substances and the effect of an imaging electric field on this appearance differentiate. One category includes substances that

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contain nematic liquid crystals or consist of such liquid crystals "which form an essentially transparent, that is to say colorless or clear, layer in which an electric field by dynamic scattering can generate, for example, a milky white image. A second category includes substances that are in the are essentially the same as the substances of the first category, but contain, in addition to a nematic liquid crystal, a small amount of a colesteric material, so that an essentially transparent layer is formed which, by means of an emulsion storage effect, has an electric field excited, for example milky white, stray field in the The third category also includes substances such as are also included in the first category, but which, in addition to a nematic liquid crystal, contain a pleochroic or dichroic dye which is the one indicated by a Electric field modifiable substance gives the coloring of the dye, so that the image excited by the electric field takes on the coloring of the dye.Examples of nematic fluids

"Sigkristalle containing substances that are falling into these three categories _t given later in detail.

A knowledge of the prior art that can facilitate understanding of the present invention can be obtained by studying the existing literature. Papers have appeared that deal with the ways in which nematic and non-nematic

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Substances containing liquid crystals react to the application of an electric field. Thereof some essays are particularly instructive and attention is drawn to these essays. In particular contains an article by Heilmeier, Zanoni and Barton entitled "Dynamic Scattering in Nematic Liquid Crystals", published in "Applied Physics Letters", Vol. 13, No. 1 (July 1968), pages 4-6 and 4-7 »a report on a imaging dynamic scattering effect found in anisylidene para-aminophenyl acetate and other nematic liquid crystals. In an essay by Heilmeier, Zanoni and Barton with the title "Dynamic Scattering: A New Electrooptic Effect in Certain Classes of Nematic Liquid Crystals ", published in Proc IEEE, Vol. 56, No. 7 (July 1968), pages 1162 to 1171, it is stated that the term "liquid crystals" means substances denotes whose r-heological behavior corresponds to that of a Liquid is the same, but its optical behavior in a certain temperature range is that of a crystalline one Condition is the same. According to an article by Heilmeier and Zanoni entitled "Guest-Host Interactions In Nematic Liquid Crystal, A New Electro-OptjLC Effect ", published in" Applied Physics Letters ", Vol. 13, No. 3 (Aug 1968), pages 91 and 92, became nematic p-n-butoxybenzoic acid as Y / irt for a dichroic Dye, namely methyl red, is used. As stated in this paper, a suitable electric field cause a change in the color of the resulting solution from red-orange to money when the solution is below Using polarized white light viewed in transparency.

In an essay "A Hew Electric-Field Controlled, ^:; .o Reflective Optical Storage Effect in Mixed Liquid: ': Crystal Systems" by Heilmeier and Goldmacher, he. appeared in "Applied Physics Letters", Vol. 13, No. 4: (August 15, 1968), pages 132 and 133 »it is stated that a Iltissig crystal, which is composed of 90% by weight of anisylidene, p-aminophenyl acetate and 10% by weight .% Chole3terylnonanoat is, its optical state may change from milky-white _f transparent to when it is exposed to a suitable stationary or low frequency electric field of suitable strength. It is also stated therein that the material can be brought back to its clear or translucent state by applying a higher frequency electric field, whereby an extinction of the color change is achieved,

An article by Tan Raalte entitled "Reflective Liquid Crystal television Display" appeared in Proc. IEEE, Vol. 56, No. 12 (December 1968), pages 2146 to 2149, reports the study of the properties of liquid crystals using a cathode ray tube to drive a liquid crystal display in real time. According to this paper, the nematic liquid crystal became anisylidene-p-ainophenyl acetate investigated and found that the use of dynamic scattering in nematic liquid crystals for flat television walls is suitable for displaying images which are also visible in very bright surroundings. The control of the Flüssigkrisballdarstellung was performed using fine wires ^(25/1 Jn) ₁ varsn the semi-randomly so embedded in a glass plate,

that they formed a mosaic that made the electrical connection zv / inchen the electron beam in the evacuation tone Cathode ray tube and the liquid crystal outside the cathode ray tube, the one between the mosaic and a tin oxide coated glass plate was included.

In an essay by Kelker and Scheurle entitled "A Liquid-Crystalline (Nematic) Phase with a Particularly Low Solidification Point", published in "Angew. Chem · Boarding school Edit. ", Vol. 8, No. 11 (1969), pp. 884 and 885, is treated with N- (p-Ivlethoxybenzylidene) -p-n-butylaniline, which is chemically homogeneous, stable and is a nematic substance that is still liquid at room temperature "

Other published articles are of interest, but it is not possible to list all of them here. However attention should still be paid to the essays by Heilmeier, Zanoni and Barton, entitled "Further Studies of the Dynamic Scattering Mode in Nematic Liquid Crystals", published in "IEEE Transactions on Electron Devices", Vol. ED-17, No. 1 (January 1970), pages 22-26, and von Heilmeier with the title "Liquid-Crystal Display Devices", published in "Scientific American" April 1970 edition, Pages 100 to 106 are addressed. These papers describe a light reflective cell array that can be viewed in a wide range of lighting conditions. Another essay by Heilmeier with the Title "Transient Behavior of Don; ais in Liquid Crystals", published in "Journal of Chemical Physics", Vol. 44, Hr. (January 15, 1966), pages 644-647 deals with this

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Transition behavior of two typical nematic liquid crystals, namely of p-azoxyanisole and p-butoxybenzoic acid in a cell, the electrically conductive, orthogonally arranged strips of tin oxide on transparent Has plates, which strips for applying electric fields to the examined liquid crystals be put on tension.

Another essay by Heilmeier, Castellano and Zanoni k entitled "Guest-Host Interactions in Nematic Liquid Crystals", published in "Molecular Crystals and Liquid Crystals "Vol. 8 (1969) beginning on page 293 treats various nematic liquid crystals as hosts for various dyes. Among the "treated" compounds are p-n-butoxybenzoic acid containing 1% by weight of methyl red and p-ethoxybenzylidene-p'-aminobenzonitrile with a content of 1% by weight indophenol blue,

All of these reviews are of interest because they illustrate the extensive work that has been done on liquid crystals. However, none of these essays are in any V / else a teaching or suggestion for a W photoactivation of images within nematic liquid crystals containing substances "

British patent specification 1,123,117 deals with, inter alia, a Cell in which a layer of cholesteric liquid crystals containing substance is photoactivated by, for example, a photoconductive layer made of cadmium sulfide visible light is excited in this layer

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to generate a ph.otoleitend.es image that has a corresponding Image generated within the cholesteric liquid crystal. It will be the use of one Cell for display purposes. The patent specification however, deals exclusively with the use of cholesteric Liquid crystals and relies on variations in the properties of cholesteric liquid crystals compared to nematic liquid crystals. Ea is It is easy to see that the different properties of nematic and cholesteric liquid crystals are numerous differing technological factors bring with it, so that the present invention, which deals with the use of nematic liquid crystals, the wishes or demands of certain special applications can meet that in the use of cholesteric liquid crystals either to a lesser extent or cannot be met at all.

In contrast to the prior art, the invention is concerned with the photoactivation of image-forming Effects in substances containing nematic liquid crystals that are either pure or mixed or cholesteric ^ liquid crystals or dyes may contain, through the application of photoconductive Material. Depending on the type of substances used, different image-forming effects can occur within the substance containing the nematic liquid crystals are caused by in a suitable manner a photoconduction is excited in a photoconductive material.

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Mo invention consists in the fact that with a nematic Cell arrangement containing liquid crystals between two spaced apart electrodes containing a first layer of a nematic liquid crystal Substance and a second layer of photoconductive material are arranged and together with the electrodes form a sandwich structure and that at least one of the electrodes for light with a ^ is permeable to the wavelength to which the photoconductive material is sensitive «,

Thus, the invention is a cell array is provided that both _t a nematic liquid crystal containing substance as well as a photoconductive material contains and which is constructed so that it comprises a photoactivation of the photoconductive material by incident light and a transmission or reflection of light in various V / also enables, for example, by light scattering, light refraction and / or color change of the substance containing the nematic liquid crystals, Qe according to the type of use of the cell, P to reproduce images generated within the substance containing liquid crystals. So far, the combination of photoconductive material and cells with substances containing nematic liquid crystals, which did contain liquid crystals but no photoconductive material, had a comparatively low practical value and the results, advantages and benefits could not be achieved with them, such as those obtained with cell arrangements according to the Invention can be achieved.

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Cell arrangements constructed according to the invention can be used for a variety of different purposes, for which known cell arrangements are similar! however deviating construction are completely unsuitable. The application of the cell arrangements depends primarily on their construction as well as on the materials used for the elements forming the cell arrangement have been used. Some possible applications include information recording use and Playback in real time, for optical switching and for Bilddarsteliimn :.

Accordingly, the cell arrangements according to the invention and use a new field for the Use of substances containing nematic liquid crystals opened up. It is of a new species urd Mode of production, by an electric one Triggerable effects within the nematic field Liquid crystals made use of which have a photoactivation a photoconductive material in such Y / eip < includes that thereby a change in the liquid crystals containing substance applied electric fields is caused. You can use c * invention-'r: ~; aßenzellanordn-ii.j Bildinf ormationer g / l ... ^ h Reflection or transmission of the image information erhcV - η will·

Further details and refinements of the invention result from the following description of the aarges in the drawing! ¹ *; - ". Lten execution beiai) ie3.e · The the

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The description and features to be taken from the drawing can be used in other embodiments of the invention can be used individually or collectively in any combination. It is not to scale depiction

Pig. 1 shows a cross section through a perspective

illustrated cell arrangement according to the invention,

w Fig. 2 and 3 arrangements for displaying images with a

Cell arrangement according to Fig. 1 with the cell arrangement penetrating light in a schematic Depiction,

4- a cross section through a further embodiment of a cell arrangement according to the invention,

FIGS. 5 'and 6 are schematic representations of the application the cell arrangement according to FIG. 4 in connection with a cathode ray tube,

fc. 7 shows a cross section through a third embodiment

form of a cell arrangement according to the invention,

Fig. 8 is a schematic representation of the application of the cell array of FIG. 7 _T

9 shows a cross section through a fourth embodiment of a cell arrangement according to the invention,

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FIG. 10 shows a perspective illustration of a cell arrangement according to FIG Invention and its use,

Pig. 11 details of a sixth embodiment of a cell arrangement according to the invention,

Fig. 12 is a graph of the light transmission properties various substances containing nematic liquid crystals,

13 shows a schematic representation of a further one Application of a cell arrangement according to the invention and

14 shows a cross section through a final cell arrangement according to the invention.

The basic embodiment shown in FIG a cell arrangement 10 according to the invention consists of a plate 12, an electrode 14-, a layer 16 of a nematic liquid crystal, a layer 18 of photoconductive material, an electrode 20 and a plate 22. With the electrodes 14 · and 20 one can be set Voltage source 24 via lines and a switch 26 connected. When the switch 26 is closed, the voltage source 24 generates a potential difference between electrodes 14- and 20 and consequently an electric field in the space between the electrodes, in which the layers 16 and 18 are located * The plates 12 and 22 are made of a material such as quartz or glass,

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which is essentially transparent and electrically non-conductive. The electrodes 14 and 20 consist of one electrically conductive material like tin oxide, commonly known as nesa, that is thin enough to be used for certain Light wavelengths to be essentially transparent. Layer 16 exists in this embodiment made of zinc sulfide, which has a high specific resistance. The zinc sulfide layer 18 can also if necessary be doped with copper in order to not only use them for ultra-

k violet -kLcht, but also for blue visible To make light sensitive. It is true that this doping increases the resistivity of this layer significantly reduced, however, the application range of the cell arrangement containing the zinc sulfide layer be expanded significantly. The layer 18 was placed on the electrode 20 in a vacuum chamber Applying the conventional technique by applying phosphor grade zinc sulfide to the electrode 20 im Vacuum evaporation process at a pressure of 10 "" Torr and a deposition rate of 1 to .2 A / s. In this case it was the zinc sulfide layer 18 with a thickness of about 0.5 "to 1 / in

P brought, however, the thickness of the layer 18 can be sen limits can be varied, the layer 16 consists of in this case from N (p-methoxybenzylidene) -p-n-butylaniline, a nematic liquid crystal, and has a thickness of about 12 to 15 / I'm ο the plates 12 and 22 are on suitable, not shown manner held at a distance from one another, for example by an annular Spacer 28 made of an electrically insulating material, such as a putty compound,

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or by insulating! Spacers which are attached near the edges on those sides of the plates that are opposite each other · In this case ϊ .'- ιΐι c ■■>(.>',!', Tom ixnh (I Io Z ο 11 o / i ^ i λ or (Jn u / ig oino IJuaav / icri structure in which the layers 16 and 18 are enclosed one behind the other between the plates 12 and 22 with the electrodes 14 and 20 applied.

From a qualitative point of view, cell arrangements are behind the invention for a satisfactory operation only a relatively small energy requirement. Measurements were taken made of a test cell with a sandwich structure, the tin oxide electrodes, a zinc sulfide layer of 0.6 ^ m thick and a liquid crystal layer of 15 / tm Thickness of N- (p-ketho: cybenzylidine) -p-n-butylaniline, by the cell light with a wavelength of 367 mn, which with the help of a filter from the light of a 200 V / r mercury vapor lamp isolated and a projected beam of visible light is used to measure the transmittance of visible light became. With a voltage in the range of 70 to 80 V applied to the electrodes of the cell, the transmission dropped of the visible light through the cell to the minimum value (saturation) in about 0.1 s, which corresponds to an energy of

corresponds to only 0.12 mJ / cm of exposure to ultraviolet light in order to achieve saturation. Similar results were subjected to a pulse-shaped exposure to ultraviolet Light of 0.10 mJ / cm and it was achieved with the use of pulses of ultraviolet light of 20 to 200 ms duration, no reciprocity error observed. Shorter pulses of ultraviolet light of 50 / ^ s duration

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gave qualitatively comparable results. In the 70 "to 80 V range, an exposure was short Impulse images in the liquid crystal due to maximum dynamic scattering within approx. 100 ms the end of the exposure pulse and the images faded within about 2.5 s.

At this point it should be explained what applies to all the cell arrangements shown in the drawing,

^ That layers 16 and 18 of the cell each have the flow a current between the electrodes 14 and 20 after opposes a certain resistance to the application of a voltage. The one introduced by each shift Resistance depends on the resistivity of each layer, assuming that each layer is has a certain thickness. The resistance of the layer 16 is large in relation to the resistance of the layer 18 enough that there is a significant voltage drop across layer 16 so that the voltage drop across the Layer 18, which is the difference between that applied to the electrodes of the cell array Voltage and the voltage drop across layer 16

ψ acts, proportionally a \ if a value is reduced which is smaller than the voltage applied to the electrodes ^ ologto. The current flowing through the layers in the absence of a photoconductor applied in dor Jo.hioht 18 is limited and, according to the invention, insufficient, up; to generate an electrical fold somewhere in layer 18 that is strong enough to produce an image or. To evoke images. In fact, the resistors serve

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ciii / iU, dim ui existing between electrodes 14- and 20; Distribute the level generated by then applying the voltage to the light, IG and 18 in such a way that a change in the voltage drop at layer 18, which occurs by causing photoconduction in this layer, results in a voltage drop and consequently the electrical image at layer 16 is also changed. It is of fundamental importance that by changing the resistance and tj .; dor layer 18, the voltage drop at and the el fj «-: i.rijohe field in layer 16 can be increased. Layer 18 can be analyzed analytically as a plurality of x'hot.H / ideröüunden are described, which are electrically connected in parallel, and are composed of adjacent areas of the layer 18, each of which extends from one,. ν string extends to the other side of the layer 18 by L-ujenken the resistance value of each Any diüiicr .VLa heat area, namely by reducing the Irish resistance by creating a PhuüoLeitung, it is possible to increase the electric field in an adjacent area of the layer 16 to generate uii -iov't oiii image, this is the way, aal 'AuIII of Law "at the same time in some, but not anicren regions of the layer 16, an image being formed KIJ _it n;.. ■ ;;;!', the image representation and in the desired ki'h filhri ;. the This type of image generation in layers iuiuvj Irinr-ac: r !. '' Lüssigkristalle is already known, abfi.'jentiti from the creation of the image by generating e Liifj ^ ϊΊιot; oIo i.tung in layer 18 of photoconductive LlaWr.uiL , which forms the new and fundamental basis of the present invention.

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In the case of the cell arrangement 10, the electrodes W and 20 were produced by spraying a solution containing a tin saline onto each of the plates 12 and 22 with simultaneous heating of the plates. The method for producing the tin oxide electrodes is not optimal because it is not very clean, and if the electrode 20 is not as pure as possible, defective parts can occur in the zinc sulfide layer 18 applied later. It is desirable, however, that the layer 18, whatever material it may be made of, is of excellent quality and free from defects which can be attributed to the material of the electrodes 20 and the method used to produce them. Care should therefore be taken in this regard to obtain the most suitable cell arrangement for the intended purpose. Since the two plates 12 and 22 can be brought to a relatively high temperature when the tin oxide is applied in the manner described above, the selection of the various materials which can be used for the cell plates is relatively limited and, for practical reasons, can be used with regard to the Requirements placed on a cell array according to the invention should be limited to hard glass or t ^ uarz, although in some cases it might be desirable to use other materials for the plates The electrodes can therefore also be made of other electrically conductive materials

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special properties in terms of light transmission which are thought to be used individually or in combination. For example, can vapor-deposited platinum layers with a sheet resistance of a few thousand olim with an optical transparency from 40 to 6Ow used for transmitted light will. Other electrodes can be on glass or other materials, such as clear synthetic Polymers, made by using lethal reactive oxides or ketals are sprayed on. So can electrodes for example by spraying a selected uetal oxide onto a plate, followed by vapor deposition von Lietall in a vacuum and another spraying of the the same or a different selected metal oxide can be produced in order to produce a multilayer electrode form. For example, electrodes can be formed by forming a first layer of vapor-deposited titanium oxide, a second layer of vapor-deposited metal such as copper, silver, gold, palladium, tin or a mixture of these Metals and a third layer of vapor-deposited titanium oxide are made on a plate »In this case Electrode, each layer is kept so thin that a multilayer electrode of satisfactory optical transparency is achieved for at least certain wavelengths of the light rays. In every pail there must be spectrophotometry Curve, that is the optical transmittance or reflectivity as a function of the Wavelength, of the selected electrode material meet the special requirements for the desired application of a cell arrangement «It is a gold alloy crack layering known from Libbey-Owens- ^ ord,

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which is referred to as 81-E-Electr.ically Conducting Coating, which can be used as an electrode material in place of tin oxide. This special coating can be applied to glass without significantly changing the optical properties of the glass, and has spectrophotometric properties of light transmission and reflection depending on the wavelength, which can be used with advantage »The light transmission - % transmission of such a coating, measured using light incident perpendicular to the coating, in the range of 0.32 to 3.10 / tun wavelength is of interest. The optical transmittance of such a coating is between 4-5 and 70% in the wavelength range from 4-00 to 700 nm with a transmittance of 70% in the range between 560 and 600 nm. At 567 nm, the optical transmittance is about 35% and it can therefore, such a coating can be used in conjunction with a photoconductive layer 18 made of zinc sulfide with reasonable efficiency.

^ The used in the cell array Zinksulfidscliicht 'has a steep absorption edge and it does not absorb the zinc sulphide light in the ultraviolet region, but in the visible range and in the infrared region of the spectrum _o The degree of light absorption in the ultraviolet range through the zinc sulfide depends on the wavelength of the light from, that is used to activate the zinc sulfide, and the optimal conditions for photoactivation are therefore determined experimentally. In order to achieve the best effectiveness, the layer 18, whether it is made of zinc sulfide or another

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Material is made with such a thickness that the photoconductivity, which is caused by the absorption of photons in the layer material, and the resulting generation of charge carriers in the entire thickness of the layer occurs when exposed to light of a wavelength that leads to the best hesuitations for a given cell arrangement. Experimentally determined on the basis of measurements on a cell having a zinc sulfide layer 18 of 0.6 m in thickness and a layer 16 of N- (p-methoxybenzylidene) ~ pn-butylaniline was treated with a thickness of 12 to 15 / ⁱ m that the photon absorption in the layer 18 depends considerably on the wavelength of the light radiation which was used to activate the layer 18. Light with a wavelength of 400 nm is almost not absorbed by the layer and passes through this layer with essentially undiminished intensity. Light with a wavelength of 367 nm is absorbed to a greater extent by such a layer, so that the intensity of the light after Passage through the layer is only about 60% of the intensity of the light to which the cell was exposed. Light with a wavelength of 340 nm is very strongly absorbed within the layer, so that the intensity of the light after passing through the layer is only about Λ% of the intensity of the light to which the layer was exposed is reduced defined by the layer is numerically equal to 2.0 iat. That

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Material of which electrodes 14 and 20 "are made, absorbs some of that for activating; of the layer 18 used light in the near ultraviolet range, i.e. in the Range of wavelengths between 300 and 400 nm, and thus slightly influences the response of the cell "order to the light used for photoactivation" Experimentally, it has been found that the cell arrangement tested has a maximum sensitivity when used of light in the near ultraviolet range of about 350 nm for photoactivation of the zinc sulfide clixch occurred.

As is known, different samples of zinc sulfide react different, albeit similar, on the light used for photoactivation, depending on the type and amount of impurities or dopants present in (any given sample. Remarks above amount a special zinc sulfide macerial that is used for ultraviolet Light is sensitive and can be activated by this light, but insensitive to light radiation whose wavelength is greater than that of ultraviolet Light, as is the case with light in the visible and infrared regions of the spectrum. Because of These facts, it is to be understood that the invention in no way relates to the use of ultraviolet light for the purpose of photoactivation is limited and that the Invention using zinc sulfide material and also other photoconductive materials will be jerv.'ix ^ light can, whose absorption property is part of those of the specific zinc sulfide layer 18 treated above differ specifically.

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The cell arrangement described so far is a very one simple execution foria and makes of certain specified Materials for their various parts use. Cell assemblies according to the invention can, however Assume a variety of different forms and, as will be discussed later, take advantage of other materials and make use of combinations of materials. In the embodiment of FIG. 1, the plates 12 and 22 are as well * the electrodes 14 and 20 essentially as well as the layers 16 and 18 for radiation in the visible range of the spectrum permeable. The materials from which the plates 12 and 22 and the electrodes 14 and 20 are made, are also essentially transparent to radiation in the range of ultraviolet light, whereas the material of the photoconductive layer 18 absorbs at least a portion of the same ultraviolet light, when exposed to this light in order to make it photoconductive when an electric field is applied will. The material of the nematic liquid crystal layer 16 is not transparent to the same ultraviolet light, so that in this case it is necessary to expose the photoconductive layer 18 to ultraviolet light, which is irradiated through the plate 22 with the electrode 20. If the layer 16 for the photo-activation light used is transparent, the exposure of the photoconductive layer 18 can generally from made from both sides of the cell.

A cell arrangement similar to the cell arrangement according to FIG may also be used with others for layer 16 instead of IT- (p-I £ ethoxybenzylidene) -p-n-butylaniline

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Substances take place. For example, anisylidene-p-aminophenyl acetate could be used instead, which for the purposes of the present invention has many properties similar to those of N- (p-methoxybenzylidene) -pn-butylaniline. Further examples of substances that can be used are p-methoxycinnamic acid with a content of 1% by weight of methyl red or p-iithoxybenzylidene-p * -aminobenzonitrite with a content of 1% by weight of indophenol blue. These substances are QUIRES ONLY h lent representative for many others who also used it able v /.

There were more test cells in the laboratory manufactured like that shown in Fig. 1 and thereby about a dozen different substances were used for layer 16, whereas for layer 18 it was always used Zinc sulfide was used so that valid comparisons could be made.

The test cells produced were of two types ^ Substances used that quickly lost any ™ image produced in it when the layer was photoactivated was interrupted by interrupting the exposure of layer 18 to the image-forming light. The other Art made use of substances for layer 16 that also retained an image produced in layer 16, after the photoactivation of layer 18 has ended. Such a test cell was used for the layer 16 is a nematic liquid crystal, which by adding 8 wt had been made. After this

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the exposure of the zinc sulfide layer 18 to the imaging ultraviolet light is ended In this pail, shift 16 was held during the Exposure of layer 18 produced image for a few more days "at. These stored images were at all times by applying a high frequency voltage of, for example 50 "to 80 Y with a frequency between 1000 and 10,000 Hz on the electrodes of the cell arrangement can be erased. Other substances containing nematic liquid crystals with smaller amounts of cholesteric compounds showed a more rapid loss of image that was only for was temporarily detained a few minutes before disappearing.

Instead of choleuteryl chloride, small amounts can also be used from cholesteryl nonanoate or other cholesteric substances to selected nematic liquid crystals to be added. The presence of cholesteric Modified substances in nematic liquid crystal structures their optical properties in various ways, but in each case the image is generated in the way that it is characteristic of nematic liquid crystals and not that of cholesteric ones Liquid crystals characteristic way.

The experimental obtained for such test cells Results make it clear that from a practical point of view, apart from certain limitations, it is subordinate Meaning, the use of a host made of different substances for the layer 16 ωohr is quite possible is, Not all substances used were listed,

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because a long list of these substances would not provide any additional information, the treatment of which would be necessary ο As mentioned, zinc sulfide was used as a photoconductive material in the test cells, which compared to many other photoconductive materials has a relatively high specific resistance and its specific resistance in this Example also in comparison to the specific resistance of the substances that are used for the liquid crystal layer 16 have been applied, is very high and is, for example, ten times. Practical considerations for the construction of the cells suggest that, for optimal results, in certain cases the resistivities of the materials for layers 16 and 18 are chosen so that the resistivities of the material for layer 18 are comparable to and preferably greater than the specific resistance of the substance of the layer 16 _o From the principle of invention, however, this ratio of the specific resistances is not of fundamental importance.

In addition to zinc sulfide ″, other photoconductive substances can also be used for the photoconductive layer 18. For example cadmium sulfide, gadmium selenide, selenium and antimony triselenide can be used for this purpose and can These substances too are brought to bear that they are relative have high specific resistances, which are high with doia resistivity are comparable to that of the box Use of zinc sulfide is achievable, Jo after the Way in which these substances would be used as layers. It is known that the specific objections do 1 violer

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photoconductive materials can vary considerably depending on how the material is made. I.l '; t; hodon to »' Jtouorung dos aj> ozifiachen 'resisted are known and it is possible to produce photoconductive substances in essentially pure or undoped form, in which case the resistivity is relatively high, or in doped poria, in which Case the specific resistance is relatively low.

It is generally preferred, though not essential, that the photoconductive material selected have a relatively high resistivity and be able to change that resistance considerably upon photoactivation, since such behavior, as will be readily seen, be very effective Operation of the cell assembly leads. By comparison, the ability of a given photoconductive material to change its resistivity significantly when it is made photoconductive can be at least as important, if not more important, than the resistivity in the dark as such, which is not in all cases one after the other Invention constructed cell arrangement needs to be particularly high. Typical zinc sulfide layers can be made with a resistivity of 10 ^ to 10 ^J <-cia or less. The optical properties of the zinc sulfide depend on the manner and manner in which the zinc sulfide has been made.

Zinc sulfide layers with a specific resistance

13 14-

from 10 ^ to 10 -.7.cm, which is about ten times the specific Resistances α of IT-Cp-Ke thoxybenzylidene) -p-n-butylaniline is, iet for use in the preferred ·; on

109884/1 107 * ^{/ #}

Embodiment of the invention is suitable because it is essentially transparent to light in the visible range and near infrared range of the spectrum and can be activated in the desired manner by light radiation in the ultraviolet range of the spectrum. Cadmium sulfide with a specific resistance of 10 to 10 -ilcm essentially permeable to light in the red and infrared range of the spectrum and can be activated by light radiation in the ultraviolet and blue range of the spectrum. In the case of cadmium sulfide, as in all other cases, the wavelengths of light used to generate and display the image are selected with respect to these optical properties in order to achieve the desired results. It can also be amorphous selenium with a specific resistance up to

/ j tr

10 ' Jlcm, which is essentially transparent to light in the far red and infrared regions of the spectrum and can be activated by light in the ultraviolet and visible regions of the spectrum. Antimony trisulfide can also be used and produced with a resistivity of up to 10 Jlcm. It is essentially transparent to light "in the infrared region of the spectrum and activatable by light in the visible and ultraviolet region of the spectrum.

It can also use organic photoconductive substances such as for example crystal violet with a specific one Resistance of 10 .Ul cm, indanthrone with a specific Resistance of about 10 »0 cm, the sodium salt of fluorescein with a resistivity of 10 ^. CL cm and metal-free phthalocyanine with one resistivity of 10 to 10 ^ .. learners used will.

10 9884/1187 ''''

Depending on the desired result, silicon, ßermanium and other photoconductive materials can also be used. If the photoconductive materials used, such as silicon and germanium, are semiconductors with moderate specific resistance, a pn junction can be formed in the semiconductor material, which can be reverse-biased by changing the polarity of the voltage applied to the electrodes of the cell accordingly is chosen in order in this way to effectively increase the specific resistance of the material near the pn junction _β

It is still possible to select the one selected for layer 18 photoconductive material and the material used for the electrode 20 to prepare so that an ohmic contact or a blocking contact (B.C.) is established between the electrode and the layer. In Fig. 1 a blocking contact B.G. specified to the alternative possibility of producing a lock * to indicate contact between the electrode 20 and the layer 18.

The production of a blocking contact between the Layer 18 and the electrode 20 can also be used in cases using a semiconductor material with medium Allow specific resistance for the layer 18 in which it would otherwise not be possible. (Technologically For example, medium resistivity cadmium sulfide may be used with a blocking contact electrode 20 instead of being provided with an electrode which forms an ear-quick contact, "which would also be possible, in order to the application of cadmium sulfide layers 18 with a

109884/1187

2Ί32948

medium, as opposed to a high, specific one To be able to use resistance in cell assemblies according to the invention. If a sporr contact is used the voltage applied to the electrodes of the cells must be correctly polarized in order for the current to flow through To complicate the photoconductive material layer · A Photoactivation of the photoconductive layer, which is provided with a blocking contact electrode, leads to a reduction in the effective specific resistance of the layer material, so that results similar to those obtained with a layer of a photoconductive material with a high specific resistance, that with an ohmic or non-vaporous one Contact is to be provided.

From the foregoing treatment of semiconductor materials, which is for illustrative purposes only and is in no way exhaustive it can be seen that the present invention generally includes cell assemblies having a photoconductive layer, Electrodes and means for generating a bias voltage, which are used to generate an image in nematic Substances containing liquid crystals by photoactivation diont.

In the arrangement according to FIG. 2, the cell 10 shown in FIG. 1 is visible to a source 30 Light and a screen 32 arranged. A source 34-image generating ultraviolet light supplies ultraviolet radiation to activate the photoconductive Layer 18 within the cell array 10. At. this

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Embodiment of the invention "is the photoconductive Layer 18 on the left side of the cell facing sources 30 and 34-. Hit help With this arrangement, images formed within the liquid crystal layer 16 of the cell array are mapped on the screen 32. It is Typically, the imaging light from the source 34 has a shorter wavelength than that of the Representation serving light from the source 30. When the nematic liquid crystal layer 16 for the light used for image formation is transparent, the Cell arrangement 10 can also be turned over so that layer 18 on the right, facing screen 32 Side of the cell arrangement 10 is located. Here is herself source 34 to the left of the array of cells, see above arranged that it irradiates the photoconductive layer 18 with light which the liquid crystal layer 16 penetrates.

In the arrangement of Fig. 3 is the cell arrangement According to FIG. 1 as well as in FIG. 2, between a source of light used for reproduction and a screen 32 arranged. Also in the optical path between the imaging source 34 and the cell and in the optical path between the display light cell 30 and the screen 32 a partially transparent mirror 36 is arranged. In in this case the photoconductive Schi ~ Vb is within the Cell on the ooite facing the screen and the liquid crystal layer arranged on the side of the cell facing the source 30. The partially permeable

109884/1187

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Spiegel 36 has, as indicated, »the 32igen3Chaft, that To transmit light from source 30 from screen 32, but to allow light from source 34 to cell 10 reflect. A half-silver-plated mirror can be used for this purpose, in which case half of the light reaching the mirror from the source 30 is reflected by the mirror and not the screen while half of the light coming from the source 34 penetrates the mirror and does not | reaches cell 10. However, a dichroic mirror is preferably used instead of the partially transparent mirror 36 Mirror is used, in which case most of the light reaching the mirror from source 30 passes through the mirror transferred to screen 32 and most of it of the light coming from the source 34 is reflected by the mirror in the direction of the cell 10 *

Fig. 4 shows a modified cell arrangement 10a a dichroic mirror 38 containing that supplied by source 34, for example, for imaging Lets serving light pass, but that serving for image reproduction, for example from the source "reflects delivered light. As shown in Fig. 4, this cell arrangement 10a can be used to form an image reproduce by reflection by placing the image in the photoconductive layer 18 through the dichroic mirror is enrolled through it and, as a result, in the Liquid crystal layer 16 produced an image by reflecting the light used for reproduction on the mirror so that it is visible will.

109884/1187

In the arrangement of FIG. 5, the cell 10a is in front 'Arranged a cathode ray tube ORÜJ and a lens. The light emanating from the screen of the cathode ray tube is directed onto the photoconductive layer of the cell in the manner illustrated in FIG focused »to write an image in the photoconductive layer, whereas that of the environment or A particular light source supplied light in the manner illustrated in Fig. 4 at the dichroic Mirror 38 is reflected to the resulting written in the nematic liquid crystal layer To reproduce the image. In the arrangement of Fig. 6, the cell 10a is with the faceplate of the cathode ray tube LOCATION connected by a disk 42 of optical fibers that carry the light from the screen of the cathode ray tube transferred to the photoconductive layer of the cell through its dichroic mirror.

The imaging light for operating the cell arrangement can also come from light sources other than a cathode ray tube supplied, for example, from a scanning source of coherent light, an electroluminescent panel, a planar matrix of selectively excited light emitting diodes and the like.

The cell arrangement 10b of FIG. 7 is the same. 1, but instead of the glass plate and the electrode 14, it is the cell arrangement according to FIG. 1 a metal mirror 12 ', for example from polished aluminum or chrome. The reflective surface of this mirror borders on the liquid-

1 187

crystal layer 16, but is itself, opaque, so that the cell must be used for imaging by reflection rather than transmission. the The cell arrangement according to FIG. 7 can be used in that shown in FIG Way can be used in which a partially transparent mirror 46, for example a semi-silver-plated or a dichroic mirror, is used to divert the imaging light from the source 34 k to reflect through the electrode 20 of the cell onto the photoconductive layer 18 and that of the reproduction transmitting light in both directions · The reproduction light emitted by the ambient light or a display light source is supplied to the mirror 12 'of the cell, which is shown in FIG located on the left, reflected to the right. The imaging light from the source 34- can be perpendicular or at an angle deviating from the vertical on the surface of the photoconductive layer 18 meet that is adjacent to the electrode 20.

Fig. 10 shows a modified cell arrangement 1Od that P differs from the cell arrangement according to FIG. 1 in that the individual electrode 14 is formed by a row parallel, strip-shaped electrodes 14 'replaced has been. Each electrode 14 'is connected to a corresponding one Switch S 24-connected to a potential source. A source of 4-8 imaging light, such as for example a scanning source of coherent light or a cathode ray tube, din the right side of the Cell arrangement scanned horizontally, lxofort; a yourself horizontally moving light spot in οΐΐ, οα small area,

which runs across the cell arrangement like a grid · The switches S can be opened and closed electronically according to a program »for example during the interval of a horizontal scan. An image Q ¹ will appear within the liquid crystal layer 16 in front of a portion of an electrode 14- 'only if at any given time the spot ^ is aligned with the portion of the electrode 14-' and the switch for that particular electrode 14- 'is closed to connect the potential source to this electrode 14 *.

Figure 11 illustrates a portion of another r: i () di i'i HJorfcon / loluon / mortlnurif; 10e, perpendicular to the sides of the cell. In the case of the cell arrangement 10e, each of the large-area electrodes 14 · and 20 of the embodiment according to FIG. 1 is replaced by parallel, vertical and horizontal strip-shaped electrodes 14 · 'and 20'. This array of cells can be scanned by the imaging light in a manner similar to that described with reference to Figure 10, either vertically or horizontally, and can also be scanned obliquely to the vertical or horizontal direction, as desired Operating mode. By connecting a switch to each of the electrodes 14 'and 20 * and operating the switch to open or close lines leading to a voltage source, which voltage source can be connected to orthogonal electrode pairs with the aid of the switch, images inside the liquid crystal material can be displayed as required each point at which any pair of orthogonal electrodes intersect in the plan view of FIG. 11.

109884/1187

FIG. 12 illustrates the manner in which the transmission of the light used for reproduction passes through a given cell arrangement depends on the material, that is used for the nematic liquid crystal layer, as well as the intensity of the image-forming one Light incident on the photoconductive layer of the cell array. In Fig. 12 there are two separate light transmission curves A and B are shown illustrating the manner in which the transmission

k of the light used for reproduction through a "cell arrangement depends on the intensity of the image-forming light that hits the photoconductive Layer in the cell array occurs when two different types of nematic liquid crystals containing substances can be used for the nematic liquid crystal layer in the cell array. Curve A is typical of a cell made of a substance containing nematic liquid crystals, such as N- (p-methoxy-benzylidene) -p-n-butylaniline, uses without any addition of a pleochroism dye «The curve B is typical for a cell, those of a containing nematic liquid crystals

W uses substance that contains a pleochroic dye, such as p-llethoxyzintic acid and p-ethoxybenzylidene-p'-aminobenzonitrile with 1 wt Cell, which contains the various nematic liquid crystal-containing substances, increases or decreases as the intensity of the

109884/118?

photoconductive layer of the cell array incident, light used to generate images. Accordingly, it is possible to transmit the display light through a cell array increase or decrease by the. Intensity of the incident, used for image generation Light changes, either increased or decreased. Accordingly, a cell arrangement, which has the transmission characteristics of curve A or B, is easily used as an optical switch that lies in the path of the ray of a light used for reproduction, to the intensity of this To change the light beam by changing the intensity of the image-generating light that hits the photoconductive Layer of the tariff arrangement occurs "

13 illustrates an application of a cell array; with the help of which a correction of the color of a light beam is possible * In the case of the one shown The exemplary embodiment is a cell arrangement for this purpose used, which has a photoconductive layer made of cadmium sulfide, which is caused by incident blue light is activatable, and contains a nematic liquid crystal layer 16, which normally absorbs red light and, for example, from p-methoxycinnamic acid and p-ethoxybenzylidene-p'-aminobenzonitrile with 1 G ^ w, $ indophenol blue. One layer off This substance will normally look blue because of its indophenol blue content, but it will be colorless Look. ^ If at this layer a suitable one

1,988 * / 1'1 7

electric field is applied. Viie shown is an array of polarizing filters, one on each side of the cell, between a source of one Beams of red and blue light and a screen available so that the change in the color of the beam can be observed on the screen · By applying a appropriate voltage to the electrodes of the cell assembly and irradiating the cell with the red and the blue light of the light supplied by the source The cadmium sulfide can pass through the blue beam Light of the beam can be activated to change the color of the non-static liquid crystal layer · The more intense the blue light is in the beam, the more the cadmium sulfide is activated and the more it changes consequently the nematic liquid crystal layer changes its color.

The extent to which the red light that the cadmium sulfide layer easily penetrated, absorbed, determines the extent to which the liquid crystal layer is blue appears. The liquid crystal layer absorbs most of the red light when it is at its bluest is, and this condition is when, the photoconductive Layer is not activated · The liquid crystal layer absorbs the least red light when it is essentially colorless, and * this condition is before when the photoconductive layer is highly photoconductive

When the beam from the light source turns into such V / ei & e that the intensity of the blue changes

109884/1187

Light in relation to the intensity of the red light increases, the cadmium sulfide layer becomes different from the blue ones Light activated more strongly, oo that the liquid crystal layer becomes less blue and a larger proportion red light to the screen. The reverse situation occurs in the cell array when the The ray emanating from the source varies in such a way that the intensity of the blue light im Relation to the intensity of the red light decreases. Accordingly, the cell has a tendency to undergo any changes in the intensity ratio of that supplied by the source to correct or compensate for red and blue light in such a way that the color of the on The beam projected on the screen is kept constant, since the color of the light beam depends on the ratio depends on the intensities of the red and blue light in the beam. A similar correction changes in the color of a light beam can be made with light beams of various colors ίηάοκ. Cell arrays are used, their photoconductive and layers containing liquid crystals interact in a manner analogous to that explained above « As indicated in Fig. 13 by dashed lines, can an ilotfilter between the cell arrangement and dom Place the screen to ground to achieve yet another form of color control. With the one just described The device absorbs the hot filter blue light, whereas it absorbs that from the source of red and blue light, which is on the side of the cell array facing away from the screen, delivered red light to the screen

109884/1187

transmits. Accordingly, there may be a faint red image of the beam on a black background on the Screen can be observed when the intensity of the blue "light in the beam coming from the source is low. When the intensity of the blue light is in the beam coming from the source is high, the liquid crystal layer absorbs less red light than before, since the substance forming this layer has its blue color as a result of a stronger activation of the cadmium sulfide layer loses. Therefore, in this case the red "image of the beam on the screen becomes stronger. In feathers. Case, the fecal filter prevents the transmission of blue light to the screen. The proportion of blue light in the beam incident on the cell arrangement can can be changed by varying the amount of blue light supplied by the source or by varying suitable ones Filters can be provided between the source and the cell array.

9 illustrates a modified cell 10c _t in which the liquid crystal layer and the photoconductive layer do not adjoin one another, but are separated from one another. The illustrated cell structure "includes a thin, substantially opaque layer 50 of an electrically insulating material in which a mosaic of tiny, closely spaced circular dot areas 52 of electrically conductive metal are embedded. The dot areas $ 2 extend from one side of the layer ßO through the layer to its other side and can be transparent, semi-transparent, opaque or selective

109884/1187

be transparent. In the case of photoactivation of an area of the photoconductive material which touches one or more point areas 52, the point areas in contact with the activated areas of the layer 18 connect the electrode 20 through the photoactivated areas of the photoconductive layer to the circular areas or surface sections of the liquid crystal layer 16 to cause the formation of an image in this layer · It is ^J: easy to see that these cells arrangement is suitable for different purposes. Such a cell arrangement can, for example, be used in the same way as the cell arrangement according to FIG. 4 for projecting an image onto a screen with comparable, but possibly also slightly or significantly different results.The result obtained depends, for example, on the opacity of the point areas for the projection light , the number of dots per unit area, the type of activation of the photoconductive layer, for example by scanning the layer or covering the entire area of the layer with a cough of the photoactivating light, and so on.

If the dot areas 52 are opaque, you can they together with the opaque layer 50 to it are used to reflect the reproduction light back through the nematic liquid crystal layer 16, while the photoconductive layer 13 by image-forming Light is activated, then on the photoconductive layer through the plate 22 and the L'lektrocle 20 directed v / ird. That of representation dienoiuio LicuL; *.:.around

09384 / I 187

. to a wavelength have, the smaller than the wavelength (of the activation of the photoconductive layer 18 s dienendem Lichcen Y / hen the Darotellung with visible light and the activation with infrared light take place, can be applied a layer of silicon; 'the is doped in such a way that there is a pn over-

gang, which is essentially parallel to the. Surface and at the same time extending over the surface of the layer W 18. The pn-junction in the silicon is produced by, applying a voltage of appropriate polarity ah the elec trodes _t of the cell array in the reverse biased. If certain areas of the silicon layer are made phot-sliding by irradiating with infrared light, the loading of the pn junction in the blocking direction is reduced in the area of the activated surfaces, so that a localized decrease in the resistivity of the silicon material occurs, which is sufficient for a corresponding generation of To effect images in the nematic liquid crystal layer 16. For the same purpose, the layer 18 "of organic photo-

»Conductive substances are made by infrared light can be activated, such as crystal violet, Indanthrone or phthalocyanine.

Silicon and other photoconductive substances that are sensitive to infrared light can also be activated by light radiation of shorter wavelengths than infrared, for example by visible light. Therefore the opaque door layer yO serves in this case air, optical barrier between the ^{re-label 1} ;, flau hiroh dLti uema.fciaeft · ■ PlüsiiiskristailH-hicht; retLokfcie.vt, ,, LrJ, u X Ii- oiotoli> Lb-.Hulf! n iiuniohu to> ₄ nr anUiren Uiibti Ur -> oh \ ' \ " 50.

ι η ■> iv ι ι

1A- illustrates a modified cell 10f in which an electrode 20 "is used between the photoconductive layer 16 and the plate 22, which, in contrast to the electrodes 20 or 20 * in the previously discussed exemplary embodiments, does not extend over the entire surface of the photoconductive layer layer extends 18 but has a central opening, in the region of the photoconductive layer 18 is applied directly to the plate 22. "the opening in the _m electrode 20" is, in the illustrated embodiment, four mutually perpendicular sides of the electrode 20 'is limited in which is a four-sided tape of conductive material, which is arranged between opposite portions of the layer 18 and the plate 22 also take on other shapes with one or more openings. The image generation or image reproduction light can be transmitted through the opening in any direction so that none of this light impinges on the electrode 20 ". In this case, the electrode 20" need not necessarily be transparent, but can be opaque because the shape of the electrode makes it possible for the light which is used for image generation or reproduction to pass through the opening or openings in the electrode.

The existing in layers 16 and 18 electrical Fields necessarily take a different one in the layers Area distribution than in the case in which the the

l »38fU / 1 187

Z13Z94-8

Layer t8 touching electrode essentially extends over the same area as the layer 18. Nevertheless, the area of the layer 18, which is with of the opening in the electrode 20 "covers, are photoactivated and it is the electric field, which for a Photoconductivity is required in such an area on the potential difference between the electrodes 14 and 20 ", of which the electrode x 14 is located a first potential, the electrode 20 ″ is at a »wide potential, whereas the surface section the layer 18 within the electrode opening is at different points at different potentials, which »was close to the second potential, but from this potential by a small lateral one. Voltage drop that occurs in the surface of the layer as a result of the lateral resistance that occurs comprises the material of layer 18,

If the electrode opening is relatively small, it can be used for the layer 18 uses relatively high resistivity photoconductive material without grounding that an impermissibly large voltage drop in the Layer from the electrode 20 ″ to the various points of the layer 18 in the region of the electrode opening occurs. On the other hand, when the electrode opening is relatively is large, photoconductive material having a moderate or relatively low resistivity can be used are to be in the layer 18 a lower, lateral Voltage drop. In view of the lower lateral voltage drop that occurs when using of photoconductive material with less

109 ** 4 / 1-1 * 7

specific resistance is achievable, it is in the ■ preferable in most cases, regardless of the Size of the electrode opening use such a material. In Fig. 14 is indicated by a broken line indicated a pn junction that has been formed in the material of the photoconductive layer 18 and the extending over the entire surface of the layer and parallel extends to their opposite sides. The semiconductor layer material can be on either side of the n-type junction and on the opposite side Be side of the p-Iyp. Via pn junction can be applied in the reverse direction to an area to create high specific resistance on both sides of the junction, but not calibrated on the one side extends to the surface of the plate 22 and the electrode 20 ". The remainder of the layer" between the area of high resistivity and the layer surface, which is of the η-type or p- £ yp is semiconducting, causes a relatively small lateral voltage drop between the electrode 20 " and the respective position of the shift,

As mentioned earlier, substances containing nematic liquid crystals can be prepared which Forming image-defining surfaces that are phenomenologically do not necessarily derive from the various modes of operation detailed above are. In nematic liquid crystals, useful Images have been obtained at electric field strength values that are smaller and even significantly lower

10988Wt 187

, - 46 -

than those which are required, for example, in liquid crystals in order to generate dynamic * scattering. For example, it has been found that a cell having the structure shown in FIG. Uethoxybenzyliden) -pn-butylaniline and a zinc sulfide layer of etv / a 0.5 / Am contains thickness, provides the diffraction pattern of an image in the nematic Fiüssigkristall- W of the cell layer is formed by applying a voltage of only 2 to 10 V At these voltages, the resulting electric fields in the layers of the cell have a field strength that is far below that required to produce dynamic scattering in the nematic liquid crystal layer the "image" generated in the nematic liquid crystal layer is different in a projection arrangement as shown in example As shown in Fig. 2, can be observed on the screen. The "image" mentioned here consists of localized areas of the nematic liquid crystal layer, the shape and position of which corresponds to a photoconductive image pattern in the photoconductive layer and has been produced by the activation of the photoconductive material with ultraviolet light. The localized areas in the nematic liquid crystal layer are able, as a result of the different strengths of the electric field, to reduce the display light that is emitted by the! Cell is transferred, while breaking in other places the nematic liquid crystal layer

109884/1137

the display light leaves the cell essentially unbroken passes through.

In an experiment carried out with such a cell arrangement, a beam of coherent red light, emitted by a helium-neon laser and about 1 mm in diameter, was sent through the cell onto a screen where it had a bright red dot formed. Activation of the photoconductive layer with a pattern of ultraviolet light consisting of closely "adjacent parallel perpendicular lines with a density of 200 lines / mm," 200 refractive "image" lines / mm were generated in the nematic liquid crystal layer, so that one horizontal refraction of the beam of red light occurred by the image-forming light and additional red points were created on the screen horizontally on both sides of the bright red point originally produced on the screen of the first and following orders, where the 1st order beam points have about 5% of the brightness like the 0 ° order beam point, the 2nd order beam points have about J #> the brightness like the 1st order beam points, etc.

Pur is the specialist who is familiar with diffraction gratings immediately apparent that it is the one on the screen obtained sexton of beam spots is a pattern, which is characteristic of a diffraction grating. To the-

ORIGINAL INSPECTED

, ♦ - 48 -

after that in this case in the nematic Liquid crystal layers produced "all-in" images. Diffraction grating ", which is the Lo mark values Has property that it switched to Vahl in the way of the display light or can also be changed by simply changing the way in which the layer of photoconductive Material is activated. It goes without saying that * depending on There is also a need for other "gilder" in the nematic Plüesigkristallschicht can be generated.

The diffraction grating pattern just described can, as easily recognizable, rather than being displayed on a screen, more suitable for selective activation Sensor devices are used, such as a flat group of light-sensitive solid-state photodiodes, so that a digital, logical, optical readout of the light information using a coherent light beam can take place. Other uses are readily apparent to those skilled in the art of optical information display and it can be seen that the technique described is generally compatible with the known methods of optical Compatible with data processing.

A cell arrangement according to the invention can serve holograms also in the image plane are arranged a holographic system and high-speed recording and processing optical · The images in the cell array of a Holographic Systems provide the holographic image for the purposes Infonaationsverarbeitiings · ⁴

109884/1187

INSPECTED

49 -

In certain applications of such cell arrangements. and depending on the substances used, there is no need necessary to have the photoconductive material at the same time The time the imaging light is exposed to the light used for reproduction on the cell array is directed so that it is reflected or transmitted by the cell arrangement, because certain photoconductive substances, the photoconductivity still a certain Time after the activation by light has been stopped and are thereby able to do the to maintain images evoked in the substance containing nematic liquid crystals

Devices that make use of the invention Zellenanordnungea can in different ways memory - properties given v / ground. Certain photoconductive materials » ^'1, the hins'ichtllch their photo line Speichereigenschafteny ^v and certain liquid-containing substances that have been selected for their image storage properties can, having with memory properties or storage properties comprising liquid crystals containing substances or photoconductive materials are used. The storage property is that the photoconductivity in the Iiateo? Ial continues after the activation by light has been terminated, or the image in the substance containing liquid crystals ^! · Hold remains after the state generating the image - ^ has been terminated. / V *

A comparison of the properties of test cells constructed according to the invention with corresponding, however

109884/1187

21329 * 6

* 50 -

Technologically different ropes and display systems had favorable results in various respects and better results were obtained with the cell arrangements according to the invention than with the known ones Facilities achieved if such parameters as resolution, contrast, visibility and Brilliance of the picture, power requirements, size, cost factors, etc. must be taken into account.

The arrangements for image display that are dealt with here and are analogous to them can obviously be used to provide a dynamic image display of image information that changes over time. Images generated in different areas of bodies from different selected natal liquid crystals can be caused momentarily; are to appear, disappear and appear quickly wioder, namely substantially is a photoleiten- W used for the activation of the areas the material immediately as it is dictated by the rapid changes in the position or in the image pattern of a source bilderζengenden light, , and zv / ar everything in the manner as it has been dealt with above.

The suitable for the invention nematic liquid crystals containing substances may have in a nesatischen temperature range, the liquid form and may be liquid at room temperature crystalline or non · It is possible to combine two or more nematic liquid crystals in varying ratios to nematic Flüssigkristallsubatansen to

109884/1187

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• 21329 «

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that have unique nematic areas. Furthermore, devices can be used to contain a certain nematic liquid crystals To keep substance at a temperature at which the liquid is crystalline. When substances Finding uses that are solid at room temperature, using a cell array is a simple matter a suitable heating device for heating the substance used in the cell arrangement to a temperature in which the substance is located in the nematic boreioh. ~

In some cases, the photoconductive layers do not need to be continuous, but can consist of individual, layer sections arranged at a distance from one another exist. Cell arrangements of the most varied shapes and structures can be produced and used in can be used in various ways without doing so to leave the scope of the invention.

Therefore, it is understood that the invention, although it has been described with preferred embodiments, not limited to these Ausfünrungsbeispiele but AbweichungDη thereof are possible without departing from the scope of the invention.

103884/1187

Claims (18)

Γ "21329" Claims "'.' ·> ff 1, cells containing iiematic liquid crystals, characterized in that a first layer (16) of a substance containing nematic liquid crystals and a second layer between electrodes (14 and 20) which are spaced apart from one another (18) of a photoconductive material are arranged and together with the electrodes (14 and 20) form a sandwich structure and that at least one of the electrodes is transparent to light with a wavelength to which the photoconductive material is sensitive. 2. Cell arrangement according to claim 1, characterized in that that the resistivity of the substance containing the nematic liquid crystals is less than the resistivity of the photoconductive material in the non-illuminated state. 3. cell arrangement according to claim 2, characterized in that that the specific resistance of the unilluminated photoconductive material is about ten times of the specific resistance of the substance containing the nematic liquid crystals. 4. Cell arrangement according to one of the preceding claims, characterized in that at least one electrode is transparent. 109884/1187 2132S48 - 53 - 5. Cell arrangement Hack one of the preceding claims, characterized in that the photoconductive material by light of a certain Wavelength activatable and the substance containing nematic liquid crystals for light to a certain extent other wavelengths is transparent. 6 · Cell arrangement according to one of the preceding claims, characterized in that the nematic Substance containing liquid crystals and the photoconductive material in terms of their permeability have different properties for light of certain wavelengths 7 · Cell arrangement according to one of the preceding ^ claims, characterized in that the Electrodes (14 and 20) essentially over the extend the same area as the interposed layers (16 and 18) 8. Cell arrangement according to one of the preceding claims, characterized in that the substance containing nematic liquid crystals except at least a nematic liquid crystal a pleochroic one Contains dye 9 · cell arrangement according to one of claims 1 to 7 »that the nematic! Substance containing liquid crystals a cholesteric s ..! Includes apart from at least" i tfl neaatiachen liquid f Fabric. ·} 109884/1187 10. Cell arrangement according to one of the preceding claims, characterized in that the nematic Substance containing liquid crystals contains more than one nematic liquid crystal. 11. Cell arrangement according to one of the preceding claims, characterized in that between the second layer (18) and one of the "two electrodes (20) a blocking contact (B.C.) is located. 12. Cell arrangement according to one of claims 1 to 10, characterized in that there is a rectifying pn junction in the second layer (18). 13. Cell arrangement according to one of the preceding claims, characterized in that the first and the second Schiclrc (16 or 18) directly to one another adjoin. 14. Cell arrangement according to one of claims 1 to 12, characterized in that the first and second "Isolate layer (16 or 18) with a third layer, au3 the material existing layer (50) separated from each other containing conductive elements (52), which conductively conducts the first and second layers (16 and 18) through the third layer (50) to one another associate. 109884/1187 15 cell arrangement according to one of the preceding claims, characterized in that a dichroic mirror is attached to one of the "two electrodes (20) adjoins. 16. Cell arrangement according to one of the preceding claims, characterized ,, characterized in that at least one of the electrodes is opaque. . Cell arrangement according to one of the preceding claims, characterized in that a multiplicity of electrodes (20 ¹ ) are arranged on one side of the two layers (16 and 18) and at least one electrode (14) is arranged on the other side. 18. Arrangement for displaying images with a cell arrangement according to one of the preceding claims, characterized in that with the to both A voltage source (24) is connected to electrodes (14 and 20) arranged on the sides of the layers (16 and 18) with the help of which a voltage signal is applied to the layers, and the arrangement furthermore an image-generating light source (34) for Exposing the second layer (18) and one of the Light source (30) serving for image reproduction Bum exposure the first layer (16) comprises 19 · Arrangement according to claim 18, characterized in that in the path of one of the light sources (54) A partially transparent mirror is arranged for emitted light. 109884/1187