Abstract
A liquid crystal device comprising a first substrate, a second substrate and a liquid crystal layer sandwiched between said first and second substrate; wherein an electrode structure is deposited on at least one of said first and second substrates, said electrode structure comprising: a first electrode layer; an insulating layer; a second electrode layer; wherein said electrode structure comprises holes extending through said second electrode layer and said insulating layer, such that said insulating layer is discontinuous, and wherein each hole is adapted to generate local fringe fields with azimuthal degenerate direction.
Claims
1. A liquid crystal device comprising a first substrate, a second substrate and a liquid crystal layer sandwiched between said first and second substrate; wherein an electrode structure is deposited on at least one of said first and second substrates, said electrode structure comprising: a first electrode layer; an insulating layer; a second electrode layer; wherein said electrode structure comprises holes extending through said second electrode layer and said insulating layer, such that said insulating layer is discontinuous, and wherein each hole is adapted to generate local fringe fields with azimuthal degenerate direction.
2. The liquid crystal device according to claim 1, wherein said second electrode layer comprises a plurality of electrodes comprising holes for generating local fringe fields with azimuthal degenerate direction, wherein said plurality of electrodes are electrically insulated of each other.
3. The liquid crystal device according to claim 1 or 2, wherein both of said first and second substrates comprise said layered electrode structure.
4. The liquid crystal device according to claim 3, wherein said holes of the second electrode layer on said first substrate have a first distribution and said holes of the second electrode layer on said second substrate have a second distribution.
5. The liquid crystal device according to claim 4, wherein said first distribution is different from said second distribution.
6. The liquid crystal device according to claim 4, wherein said second electrode layer on said first substrate and said second electrode layer on said first substrate are arranged so that the holes of the second electrode layer on said first substrate coincides with the holes of the second electrode layer on said second substrate.
7. The liquid crystal device according to claim 2, wherein said holes are circular.
8. The liquid crystal device according to claim 7, wherein said holes have a uniform distribution.
9. The liquid crystal device according to claim 1, wherein at least one of said first and second substrate is flexible.
10. The liquid crystal device according to claim 1, wherein one of said first and second substrates is transparent and one of said first and second substrates is a mirror.
11. (canceled)
12. The liquid crystal device according to claim 1, further comprising at least one photovoltaic semiconductor conversion layer.
13. (canceled)
14. The liquid crystal device according to claim 2, wherein the device is electronically driven by an active TFT matrix.
15. (canceled)
16. The liquid crystal device according to claim 1, wherein the liquid crystal layer comprises a polymer network having a pronounced splay-bend structure around said holes of said layered structured of said first and second portions.
17. (canceled)
18. The liquid crystal device according to claim 1, wherein the liquid crystal layer has a dielectric constant that is at least 2 times higher, or at least 5 times higher, or at least 10 times higher than the dielectric constant of the insulation layer.
19. The liquid crystal device according to claim 1, wherein said holes are filled with a material having a dielectric constant that is at least 2 times higher, or at least 5 times higher, or at least 10 times higher than a dielectric constant of the insulation layer.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0057] FIG. 1 A Cross-section of liquid crystal device, a prior of art, with electrode pattern for generating fringe field (FF), resulting Fringe Field Switching (FFS) of the liquid crystal.
[0058] FIG. 2 Is a perspective view of a prior of art liquid crystal sandwich cell, containing an electrode pattern for generating FF. The alignment layers deposited on the inner substrates' surface is not shown.
[0059] FIG. 3 Is a cross section of one-pixel electrode liquid crystal device, according to the invention, containing a layered electrode for generating AD-FFs, deposited on one of the substrate surfaces, which has circular holes in the second electrode and in the insulation layer, shown in FIG. 4.
[0060] FIG. 4 Magnified above view of a small area of the second electrode, containing holes 17 with circular form and uniform distribution over this electrode area.
[0061] FIG. 5 Perspective view of the generated AD-FFs around the circular holes in the layered electrode structure 17 (only the layered electrode is depicted but neither the discontinuous insulation or the alignment layer).
[0062] FIG. 6 Is a cross section of one-pixel electrode liquid crystal device, according to the invention, containing a layered electrode with holes in the structure shown in FIG. 4, for generating AD-FFs, resulting in AD-FF switching (AD-FFS) of liquid crystals.
[0063] FIG. 7 Schematic presentation of: a) field-off vertical orientation of liquid crystal molecules in the liquid crystal device, according to the invention (only the liquid crystal vertical alignment in the region adjacent to one of the substrates, bearing the layered electrode structure, is depicted). b) view of the device in field-off state placed between crossed linear polarisers, c) Feld-on orientation of the molecules of nematic liquid crystal, with positive dielectric anisotropy (Δε>0), at the substrate bearing the layered electrode structure with holes for generating of AD-FFs. View of the device in field-on state placed between d) crossed liner polarisers and e) crossed circular polarisers.
[0064] FIG. 8 Is a cross section of a liquid crystal device, according to the invention, with layered electrodes for generating AD-FFs, deposited on both inner substrates' surface, which holes in the second electrode a) coincide and b) are shifted with respect to each other.
[0065] FIG. 9 Is schematically illustrated a) cross section of a liquid crystal device, according to the invention, which contains a nematic liquid crystal with positive dielectric anisotropy (Δε>0) mixed with a dichroic dye and oriented in the field-off state vertically with respect to the device substrates (i.e. along the substrates normal). Field-off state of the device appears to be bright, due to the vertical orientation of the dichroic dye, with slight coloration, depending on the dissolved dye, b) Field-on state of the device. Negative (inverted) image of an amplified above view of an area of the liquid crystal device, in which the liquid crystal molecules, and thus the dichroic dye molecules, are oriented along the lines of the generated AD-FFs by the layered electrode structure illustrated in FIG. 4. (The white areas in the negative image corresponds to the dark ones in reality). Due to the degenerated local azimuthal distribution of the dye, the circular in the layered electrode structure appears dark (their dark colour depends on the dye), whereas the areas between the holes appears brighter with slight colouration.
[0066] FIG. 10 a) Cross section of field-off state of a cholesteric liquid crystal device, containing layered electrode structure, which has circular holes for generating AD-FFs, deposited on one of the device substrates, and a single electrode deposited on the other device substrate. The cholesteric liquid crystal is aligned in Uniform Standing Helix (USH) texture, which exhibits selective reflection of the light. b) Field-on state of the cholesteric device. AD-FFs-induced light scattering texture (focal conic “FC” texture) of the cholesteric liquid crystal layer, which is light scattering. c) Schematic presentation of the above view of the cholesetric helix distribution around one circular hole in the layered electrode in field-on state. d) Field-on state of the cholesteric device containing layered electrode structures deposited on both device substrates.
[0067] FIG. 11 Cross section of the field-off state of a liquid crystal device, according to the invention, containing Blue Phase (BP) liquid crystal with positive dielectric anisotropy (Δε>0) and inserted between two crossed polarisers. a) In field-off state, BP has optically isotropic properties (represented by sphere) and therefore, the device is dark. b) In field-on state, above a threshold voltage, the BP becomes birefringent (birefringent optical properties are represented by ellipsoid) and behaves as nematic with azimuthal degenerate alignment around the electrode holes, i.e. the field-on state of the device is bright. c) Cross section of the field-on state of the liquid crystal device, as depicted in a) but without polarisers and containing BP, in which a dichroic dye is dissolved. In the field-on state (the electric field is applied across the BP liquid crystal layer 16, the device possesses birefringent properties (represented here by the optical ellipsoids) and, therefore, is transparent with slight colouration. d) Schematic presentation of the field-on state of the device, with layered electrodes containing holes deposited onto both substrates, filled with BP containing a dichroic dye. The field-on state of the device, in which AD-FFs are generated by the layered electrodes, is dark with certain colouration.
[0068] FIG. 12 Computer simulation of the liquid crystal switching in a device a) with holes in the second electrode of layer electrode structure but with continuous insulation layer, according to the prior of art and b) with holes in the second electrode and insulation layer of the layered electrode structure (discontinuous insulation layer) having dielectric constant ε of the insulation layer and liquid crystal material 3 and 15, respectively.
[0069] FIG. 13 Magnified above view of 4-pixels LCD, according to the present invention, in which the common electrode of the layered electrode structure is joint for all 4 pixels and the holes in the second electrode and insulation layer are circular and uniformly distributed over the second electrode area. Each pixel may also have its own common electrode.
[0070] FIG. 14 X-Y matrix driven layered electrodes with columns X representing the common electrodes and columns X, representing the second electrodes and insulation layer with holes, according to the present invention.
[0071] FIG. 15 A magnified area of a layered electrode with X-Y matrix structure, deposited on a substrate (rigid or flexible, transparent, scattering or reflective), which pixels contains only one hole, which generally could be also a plurality of holes (c.f. FIG. 14). On top of the electrode is deposited alignment layer (not shown) covered by layer of photo-reactive liquid crystal layer 19. Applying voltage to selected pixels by appropriate driving of X-Y electrode matrix, the field-on state of these pixels will be memorised by illuminating the substrate with UV light, for instance.
[0072] FIG. 16 Schematic presentation of the device, according to the invention, where a photovoltaic semiconductor conversion layer (20) is inserted in between the pixel electrode (12) and the common electrode (10).
[0073] FIG. 17 Polarising microscope (PM) photos of one pixel sample containing a layered electrode deposited on one of the substrates with circular holes in the layered electrode. The holes have diameter 10 μm and are uniformly distributed over the layered electrode structure at distance 10 μm from each other. As seen, no changes of the brightness of the field-on state are observed when the sample is rotating between crossed polarisers.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0074] In FIGS. 1 and 2 is depicted a conventional LCD, according to prior of art, comprising two parallel glass substrates 1 and 2 assembled in a sandwich cell with predeterminate distance between them. On one of the inner substrates' surface facing to each other is disposed a layered electrode structure, which is generating fringe fields (FFs) for liquid crystal switching, the so-called Fringe Field Switching (FFS). The layered electrode structure comprises common electrode 3, which is covered by insulation layer 4 followed by deposition of transparent second comb-like electrodes (in form of parallel stripes, for instance) 5 (FIG. 2). On the top of the inner substrates' surface is deposited alignment layer 6 and 7. The FFs are generated between the common electrode 3 and second electrodes 5. The generated FFs are switching the molecules of liquid crystal 8, enclosed in between the two device substrates 1 and 2, which takes place in between the stripes of the second electrode and above the electrode stripes. However, the anisotropy of the switching direction of the liquid crystal molecules makes the viewing angle of the generated images angular dependent. Replacing the linear stripe electrodes in this electrode structure with chevron-like electrode structure, reduce substantially the azimuthal viewing angle dependence but it doesn't remove it completely! Hence, in order remove the viewing angle dependency, the switching of the liquid crystal molecules should take place equally in all azimuthal directions.
[0075] Moreover, the majority of conventional transmissive LCDs needs also two polarisers. However, this polarisers reduce the intensity of the transmitted light to about 50%. Therefore, there is also need of LCD modes, which do not require any polarisers resulting in a reduction of the power consumption of the back light illuminating source, a very important issue especially for portable electronic devices with incorporated LCDs. The use of dichroic days, for instance, having anisotropic absorption or reflecting properties, dissolved into the liquid crystal, is enabling to remove one or both polarisers of the LCD, thus improving the light transmission characteristics of LCD. [Heilmeier, G. H.; Zanoni, L. A. Guest-Host Interactions in Nematic Liquid Crystals. A New Electro-Optic Effect. Appl. Phys. Lett., 1968, 13, 91-92]. However, other absorbing objects, such as nano-rods for instance, with anisotropic light absorption properties in different light spectrum regions (UV, visible, infra-red) can be used as well.
[0076] The first embodiment, according the invention, is a liquid crystal device, schematically illustrated in FIG. 3 representing one pixel electrode device, comprising: two confining substrates 9 and 14, such as glass or plastic (rigid or flexible), which could be flat or curved substrates, at least one of them transparent, a liquid crystal bulk layer 16 arranged between said substrates 9 and 14. An electrode for generating azimuthally degenerated fringe fields (AD-FFs), depicted in FIG. 3, is deposited on the inner surface of one of the device substrates 9. This electrode has a layer structure comprising of common electrode 10 and insulation film 11 and second electrode 12, with circular holes 17 passing throughout both of them which are uniformly distributed over the pixel electrode area, as illustrated in FIG. 4. The layered electrode, containing circular holes 17 in the second electrode and in the insulation layer, is generating azimuthally degenerated fringe fields (AD-FFs), uniformly distributed over the pixel area with azimuthally degenerated direction around the holes 17 (see FIG. 5). The form of the holes could be also hexagon, square, triangular, etc. On top of the layered electrode, deposited on substrate 9, and on the inner surface of other substrate 14, is deposited alignment layer 13 and 15, respectively, for promoting a certain type of alignment of the liquid crystal 16, required by the liquid crystal switching mode used in the device, according to the present invention.
[0077] A skillful person may choose another form of the holes in the second electrode and provide different distribution of the generated AD-FFs over the device work area for achieving a particular device performance.
[0078] Another embodiment of the present invention is a liquid crystal device comprising two confining substrates 9 and 14 one of them bearing a layered electrode structure with, for generating AD-FFs, whereas on the other substrate surface, facing the layered electrode, is covered by a single electrode 18 (FIG. 6). On both electrodes are deposited alignment layers 13 and 15, respectively, for promoting certain alignment of the liquid crystal 16 enclosed between the confining device substrates 9 and 14 (FIG. 7a) (vertical alignment in this embodiment). Therefore, the device inserted in between two crossed linear or circular polarisers appears dark (FIG. 7b). The liquid crystal in this particular case is a nematic with positive dielectric anisotropy (Δε>0) and therefore the liquid crystal molecules will align along AD-FFs lines (FIG. 7c). Inserted between two crossed linear or circular polarisers, the liquid crystal device, according to the invention, will switched from dark field-off state (FIG. 7 a, b), due to field-off vertical alignment of the liquid crystal, to bright state (FIG. 7c-e), in which the liquid crystal molecules will be oriented along the FF lines (FIG. 7c) and hence will adopt azimuthally degenerated alignment of the local position of the liquid crystal optic axis. The bright state of the liquid crystal device, arising from the generated azimuthal orientation of the liquid crystal optic axes around the holes, provides 360° azimuthal viewing angle with constant contrast in the case of crossed circular polarisers. When crossed circular polarisers are used, much better contrast is achieved than with crossed linear polarisers (FIG. 7e, d). Adventitiously, the presence of electrodes on the both substrates in this embodiment makes it possible to apply electric field between the layered electrode on substrate 9 and the single electrode on substrate 14, enabling thus to reduce substantially the relaxation time of the liquid crystal after switching-off the AD-FFs.
[0079] Another embodiment of the present intention is a liquid crystal device, according to the invention, in which on both substrates' surfaces, facing to each other, are deposited layered electrodes (FIGS. 8a and b). The substrates of such liquid crystal device are assembled in such way that the holes in the second electrode of the layered electrode structures, deposited on both substrates, for certain applications either coincide (FIG. 8a) or not (FIG. 8b). It should be noted that besides the broad azimuthal viewing angle, the double sided layered electrodes device exhibits also improved polar viewing angle dependence.
[0080] In another embodiment of the invention instead of nematic liquid crystal, smectic liquid crystal may be used. In this case the switched-on state could be advantageously memorised and no polarisers are needed for visualisation of the displayed information.
[0081] Another embodiment of the present invention is a liquid crystal device, which also does not require any polarisers. The device comprises a nematic liquid crystal and for this particular application a dichroic dye(s) is (are) dissolved in the nematic, forming guest-host (GH) nematic liquid crystal mixture. Specific features of the used dichroic dye(s) is that it (they) absorb strongly light, which polarisation is along their long axis (positive dichroism) or perpendicular to it (negative dichroism). By proper choice of dye or combining properly the dyes dissolved in the liquid crystal, different absorption colours of the guest-host mixture could obtained. The liquid crystal device according to this embodiment of the invention has the same device architecture as the one of the previous embodiments illustrated on FIGS. 3-8. In the field-off state of the device, the orientation of the molecules of GH liquid crystal mixture, and thus of the dye molecules, is along the device substrates' normal, i.e. perpendicular to the device substrates (vertical alignment) (c.f. FIG. 9a). The dissolved dye(s) in the GH mixture is(are) possessing positive dichroism, which absorption in the field-off state, i.e. when the dye(s) molecules are oriented vertically with respect to the device substrates, is minimum and the GH liquid crystal mixture appears weakly coloured (BRIGHT state), depending on the dissolved dye(s). Under an applied electric field, the generated AD-FFs switch the molecules of GH liquid crystal mixture from vertical alignment to degenerate azimuthal alignment around the holes in the layered electrode. Such alignment of the GH molecules results in enhancement of the light absorption and the liquid crystal device, according to the present invention, appears dark (FIG. 9b). The colouration of this dark state, likewise the bright state, depends on the type of dissolved dye(s). Big advantage of the liquid crystal device with holes in the layered electrode, filled with GH nematic liquid crystal mixture, is that the device does not need any polarisers, which result in a substantial enhancement of the device brightness! Advantageously for certain applications, the liquid crystal device, with circular holes in the layered electrode and filled with GH liquid crystal mixture, according to the invention, is that it has improved optical characteristics, such as 360° degrees azimuthal viewing angle with constant contrast and enhanced brightness. For different application purposes the dichroic dopants may be selected to have absorption peak either in UV spectrum of the light or in the visible or IR spectrum.
[0082] According to another embodiment, the nematic liquid crystal host in the GH liquid crystal mixture is replaced by smectic liquid crystal. As consequence, the switched-on state of the device remains after the applied voltage to the layered electrode is turned-off, i.e. the device field-off scattering state becomes memorised.
[0083] According another embodiment of the present invention, in the liquid crystal device, described in the above embodiments, is formed a polymer network either by thermal-polymerisation or photo-polymerisation, or other polymerisation techniques such as radiation polymerisation, for instance. For certain applications is advantageously to use photo-polymerisation, according to which a certain small amount of photo-reactive monomer and photo-initiator are dissolved in the liquid crystal material 16 filling the space in between the device substrates 9 and 14. A weak electric field is applied to the liquid crystal device, so that AD-FFs are generated close to the electrodes and capable to switch the molecules of the liquid crystal mixture from the vertical alignment to locally degenerate azimuthal alignment but only within a tiny sub-region of the liquid crystal layer adjacent to the substrate. The strength of the applied electric should be such that the thickness of this sub-region is equal or smaller than the wavelength of the incoming light. The liquid crystal device is then exposed to UV light illumination and a polymer network from the photo-reactive monomer is formed into the liquid crystal layer 16. Such a polymer network, formed under application of weak electric field, stabilises the alignment of the liquid crystal molecules in this field-on state. Whereas the alignment of the liquid crystal molecules in the bulk, under application of such weak electric field will remain to a large extend vertical, within a sub-region of the liquid crystal layer, adjacent to the substrate bearing layered electrode, the molecules adopt alignment following the AD-FFs lines, i.e. alignment comprising splay and bend deformations with the periodicity of the holes in the layered electrode and deformation planes containing the AD-FF lines, i.e. being with local azimuthal degenerated orientation around the electrode holes. According to the present invention, after the applied electric field is turned-off, these splay-bend deformations of the liquid crystal 16 remain, due to the polymer network formed in the liquid crystal under UV light illumination in the field-on state of the liquid crystal device. However, as it is known, the splay and bend elastic deformations of the liquid crystals give rise to flexoelectric polarisation P.sub.flexo, which depends strongly on the strength of the curvature of splay-bend elastic deformations and liquid crystal material properties (i.e. the flexoelectric coefficients for splay and bend deformation of the liquid crystal). As seen from FIGS. 5 and 7c, the spay-bend deformations are quite strong, which means that the induced P.sub.flexo will be also large. P.sub.flexo in this embodiment is oriented perpendicular to the device substrates. When flexoelectric constants for splay and bend elastic deformations has the same sign then P.sub.flexo might be substantial and would strongly affect (facilitate) the relaxation process taking place in the field-off state! In the above described embodiment, containing a polymer network, such splay-bend deformations exist permanently around each hole in the layered electrode, giving rise to P.sub.flexo being oriented along the substrate normal. Advantageously, the polymer network stabilisation of the splay-bend deformations, around the holes in the layered electrode, will speed up the relaxation process in the described above embodiments of the present invention.
[0084] Yet another embodiment of the present invention is a liquid crystal device wherein a cholesteric liquid crystal is used instead of nematic (FIG. 10). As known the molecules of cholesteric liquid crystal possess a helical order, with helix axis perpendicular to the long axis of the molecules. Due to helical molecular order, the cholesteric liquid crystal exhibits optical properties different from those of nematic, such as selective light reflexion and rotation of the light polarisation. In a sandwich cell, cholesteric liquid crystal may adopt in field-off state different kind of textures, depending on the surface anchoring conditions. These textures are generally bistable and the orientation of their helix axis with respect to the confining substrates is different: [0085] Texture with helix oriented orthogonal to the substrates, so called uniform standing helix (USH) texture. [0086] Texture with helix uniformly alignment in the plane of the substrates, so called Uniform Lying helix (ULH) texture, in which the helix is oriented parallel to the confining device substrates and it is aligned in unique direction. [0087] Texture with helix randomly tilted (conical) orientation, so called Focal Conic (FC) texture.
[0088] When the cholesteric is with short pitch, shorter than the wavelength of the incident light, USH and ULH textures do not scatter light. USH texture is selectively reflecting the light (is coloured) and ULH texture is transparent. The FC texture, however, is strongly scattering the incident light. These cholesteric textures are bistable and the switching between them is possible by applying an electric field with appropriate strength, form and frequency. According to the invention, the cell gap of the liquid crystal devices illustrated in FIGS. 6 and 8, is filled with short pitch cholesteric liquid crystal 16. Alignment layer deposited onto the inner substrates' surfaces, promoting planar alignment, results in USH texture of the cholesteric (FIG. 10), i.e. with helix along the substrate normal and liquid crystal device exhibits selective light reflection but is optically transparent for the rest of the light spectrum, hence it appears optically transparent. For certain application purposes, the liquid crystal device, according to the invention, may have layered electrode with circular holes, uniformly distributed over the layered electrode area, deposited onto one or onto both of device substrates (FIGS. 3, 6 and 10). AD-FFs generated by the layered electrode have local azimuthal degenerate directions around the holes. Therefore, in the field-on state, the orientation of the cholesteric is changed from field-off USH texture, with helix being vertical to the substrate (FIG. 10a), to a texture with randomly(conically) oriented tilted helix (FIG. 10b-d). However, the cholesteric in conically oriented tilted helix (FC) texture scatter intensively the incoming light and the light scattering state has 360° azimuthal viewing angle with constant contrast. The field-on state is also bistable, i.e. it remains after switching off the applied electric field. Hence, the device according the invention switches from partially transparent (USH texture) or fully transparent (ULH texture) state to a scattering state (FC texture), which is bistable and has 360° degrees azimuthal viewing angle with constant contrast. Switching back to USH or ULH state (the coloured or transparent state field-off state, respectively) is realised by applying a proper electric field between the electrodes deposited onto both device substrates (e.g. FIGS. 6, 8 and 10).
[0089] Another embodiment of the present invention is a fast switching liquid crystal device, containing Blue Phase (BP) liquid crystal material, which, as known, have a short pitch helical molecular order along three orthogonal directions and therefore appears optically isotropic, i.e. optical properties represented by sphere (FIG. 11a). An applied electric field unwind the helical molecular order above a certain threshold voltage, likewise in cholesterics, and the BP material becomes optically equivalent to nematic liquid crystal, i.e. exhibits birefringence, represented by uniaxial ellipsoid (FIG. 11b). Therefore, inserted in between two crossed, linear or circular polarisers, the liquid crystal device containing BP liquid crystal appears DARK in the field-off. However, the field-on state of this device is BRIGHT, due to field-induced birefringence. Moreover, due to the azimuthal degeneracy of the AD-FFs, generated around the holes in the layered electrode of the device, the field-on BRIGHT state of the device appears viewing angle independent with constant contrast. A particularly important feature of this device is that the relaxation process, after turning-off the applied field, is very fast, due to the short pitch helical molecular order. Since the switching-on time dependents on the magnitude of the applied electric field, switching on- and off-times of this device, according to the present invention, are very fast.
[0090] Dissolving dichroic dye(s) in the BP liquid crystal, this device appears transparent under an applied electric field across the liquid crystal layer (FIG. 11c), and dark when AD-FFs are generated around the holes in the layered electrodes, deposited on the device substrates (FIG. 11d).
[0091] In another embodiment of the present invention, the layered electrode, containing holes for generation of AD-FFs, which are possessing degenerated azimuthal directions around the holes, could be applied not only in one pixel liquid crystal device but also in such device containing plurality of pixels with layered electrodes having holes (FIG. 13), which is driven by passive as well as by active TFT matrixes for switching of the liquid crystal by AD-FFs.
[0092] In another embodiment, according to the present invention, the layered electrode deposited on the device substrate 9 is forming X-Y electrode matrix, (FIG. 14), wherein the Y column electrodes 12 are playing the role of second electrodes and the X row electrodes 10 are playing the role of common electrodes of the layered electrodes, separated from each other by insulation layer 11. Both second electrode and insulation layer have holes passing throughout them. Such X-Y electrodes matrix might be deposited on one or on the both device substrates.
[0093] Another embodiment of the present invention, where the layered electrode with holes is used, according to the invention, is a device comprising a single substrate (FIG. 15), The device substrate 9 can be rigid or flexible, flat or curved, transparent, scattering or reflective, covered by alignment layer (not shown in the FIG. 15) on top of which is deposited liquid crystal material 19, being, but not limited to polymerisable nematic, which for some applications could be photo-polymerisable, i.e under an applied electric field, the generated AD-FFs, around the holes in the second electrode, generate an image, which becomes permanent after illumination of the device with light with a proper wavelength, due to photo-polymerisation of the nematic. The deposited liquid crystal material 19 on top of the layered electrode could be of such kind that it polymerises permanently under either temperature or different kind of radiation (x-ray, electron beam, etc.).
[0094] According another embodiment of the present invention, the liquid crystal material 19 deposited onto the layered electrode of the one substrate device, is of such kind that the generated image by AD-FFs becomes temporally memorised through, for example, gelation or hydrogen bounding of the liquid crystal by temperature or irradiation, such as x-ray, electron beam, etc
[0095] According another embodiment the single substrate device (shown in FIG. 15) can be covered, for protection or other purposes, via coating, lamination or other means.
[0096] Another embodiment of the present invention is where a photovoltaic semiconductor inversion layer (20) is deposited in between the second electrode (12) and common electrode (10) (FIG. 16). The photoconversion semiconductor material is known as Bulk Hetero Junction-BHJ. In dark, the photovoltaic film is insulator. However, when it is illuminated, electrons and holes are generated in the bulk of photovoltaic film, which results in a bias between the pixel electrode and common electrode, generating thus local fringe fields with azimuthal degenerate direction around each hole of the pixel electrode. The photovoltaic film could be a single layer of conventional or inverted kind. It could be also a tandem (multi-layer) of photovoltaic films properly arranged in series in order to enhance the photo-induced bias between the pixel electrode (12) and the common electrode (10).
[0097] A person being skilled in the art may apply the concept of layered electrode, which contains holes, according to the present invention, in different liquid crystal modes and devices where the liquid crystal is switching by AD-FFs. The following example is provided to a better understanding of the current invention. However, the general concept is not limited to the particular application given below.
Example 1
[0098] A sandwich cell comprising of two parallel glass plates is prepared and the space between them is filled with nematic liquid crystal material MLC 6686 (Merck) having positive dielectric anisotropy (Δε=10). On one of the glass substrates is deposited layered electrode structure comprising ITO common electrode (one single pixel device)), with thickness about 20 nm and covered by insulation SiOx film of thickness of 200 nm (such a thickness is necessary for avoiding pinholes in the oxide). On top of the SiOx film is deposited second electrode, represented by ITO film of 20 nm thickness having circular holes with diameter of 10 μm and such a distance between them. The holes are passing throughout the second electrode layer and insulation SiOx layer, preferably but not necessarily, throughout the entire insolation layer. The holes are uniformly distributed over the entire area of the layered electrode. On the inner surface of both substrates is finally deposit alignment layer made of polyamide material SE1211 (Nissan) for promoting field-off vertical alignment of the liquid crystal. Applying voltage to the layered electrode, AD-FFs are generated around each hole. The AD-FFs align the liquid crystal molecules along the field lines and therefore, azimuthal degenerated alignment of the liquid crystal takes place around each hole. Inserting the samples, described in this example, between two cross polarisers, the field-off state appears optically dark, due to vertical alignment of the liquid crystal, whereas the field-on state appears bright, due to azimuthal degenerated alignment of the liquid crystal around the holes in the layered electrode. On FIG. 16 is presented polarising microscope (PM) photographs of the sample inserted between two crossed linear polarisers and rotated between them. As seen, when the sample is rotated between the polarisers at 67°, the displayed image exhibits a constant contrast being viewing angle independent. Constant contrast and viewing angle independence of the display image retains at rotation angle of the sample even at 360° when the experimental cell is inserted between linear crossed polarisers. Between two crossed circular polarisers, the azimuthal viewing angle of the cell with constant contrast is found to be 360°.
Example 2
[0099] A device, according to the present invention is made of one glass substrate having a number of pixels each of them containing a layered electrode (e.g. FIG. 12), which is described in EXAMPLE 1. On top of the layered electrode is deposited first alignment layer made of polyamide material SE1211 (Nissan) for promoting field-off vertical alignment of the liquid crystal. Then on top of the alignment layer is deposited photo-reactive liquid crystal monomer such as RM257 (Merck), in which is dissolved photo initiator Irgacure 651. Due to the alignment layer and the air/liquid crystal interface, the molecules of the photo-reactive monomer align along the substrate normal. Applying voltage to a selected pixel(s), the alignment of the molecules of the photo-reactive liquid crystal monomer is reoriented from vertical to azimuthal (in-plane) degenerated alignment around the holes of selected pixel due to generated AD-FFs. Illuminating the device in field-on state with UV light, the photo-reactive monomer polymerise permanently and thus the orientation of the molecules of photo-reactive monomer becomes permanently frozen. Inserted in between two crossed linear polarisers, only the activated pixel(s) of the device in field-off state are bright, due to the azimuthal (in-plane) degenerated alignment of the molecules of the polymerised photo-reactive liquid crystal monomer. The rest of the device area is dark, due to the permanently polymerised vertical orientation of the photo-reactive liquid crystal monomer molecules.
