Method for treating the surface of an ionic amorphous material to control the orientation of liquid crystals, method for manufacturing multi-domain alignment liquid crystal cells

Abstract

The invention relates to a method for treating a surface of an ionic amorphous material (AM) for its use in the design of liquid crystal cells, the method comprising:  Arranging the surface of the ionic amorphous material (AM) in contact with at least a first geometrically structured electrode (A1, C1);  Applying a temperature to the ionic amorphous material (AM);  Applying a voltage to the terminals of the first electrode (A1, C1);  Generating a plasma (PL1) between two portions of the first electrode (A1, C1) from the presence of a gas and applying a given voltage to the terminals of the first electrode (A1, C1), the voltage applied to the terminals of the first electrode (A1, C1) and the plasma generated between two portions of the first electrode (PL1) being configured to modify the electrical properties of the ionic amorphous material (AM) in order to define a polarised zone (Z1);  Extracting the ionic amorphous material (AM').

Description

[0001] DESCRIPTION

[0002] METHOD FOR TREATING THE SURFACE OF AN IONIC AMORPHOUS MATERIAL FOR CONTROLLING THE ORIENTATION OF LIQUID CRYSTALS, METHOD FOR MANUFACTURING LIQUID CRYSTAL CELLS

[0003] MULTI-DOMAIN ALIGNMENT

[0004] Field of invention

[0005] The invention relates to a method for electrically treating the surface of an ionic amorphous material, such as glass, for use in the design of a liquid crystal cell so as to control the orientation of said liquid crystals. The field relates to that of liquid crystal cells and structures associated with liquid crystals for controlling in particular their orientation.

[0006] State of the art

[0007] There are various techniques for controlling the alignment properties of liquid crystals. Typically, a liquid crystal cell is sandwiched between different layers to hold the crystals and control their alignment. A widely used solution is based on the use of treated surfaces such as polymer surfaces to control liquid crystal alignment. These treated polymer surfaces govern the orientation of their alignment upon contact with the liquid crystals. However, it is difficult to achieve multi-domain orientations in the polymer. Indeed, polymer processing techniques for controlling liquid crystal alignment include a surface treatment involving a mechanical operation such as surface brushing.This technique does not allow defining regions in which the electrical or chemical properties of the polymers will be differentiated to orient the liquid crystals in different directions.

[0008] Currently, there is a technique called photoalignment that allows local control of liquid crystal alignments according to delimited regions of the polymer. These techniques require photoelectric treatment of the polymer by applying surface chemistry and light treatment of the polymer surface.

[0009] Furthermore, conventionally, these polymer-treated surfaces can be associated with structured layers comprising electrodes to form a screen matrix typically defining pixels / voxels of a display. These electrodes can also be associated with polarizers which can, for example, be configured to define light filters, in particular by using the birefringence properties of liquid crystals. The electrodes make it possible to control the dynamics of the liquid crystals and their alignment and therefore the induced properties of the light passing through a cell.

[0010] These solutions allow liquid crystals to be controlled within a localized space, for example in cells. To achieve this, the use of electrodes allows for local control of liquid crystal alignments. These electrodes allow, in particular, the application of local electromagnetic fields and the achievement of liquid crystal orientation effects for only a portion of the cells.

[0011] There are also possibilities to control alignment locally using masks. However, these solutions have the disadvantage of being poorly configurable.

[0012] Conventionally, a layer of glass can be used to provide a transparent support for the liquid crystal cells of a matrix and thus form an external protection.

[0013] These structures require great complexity in manufacturing and implementation. In addition, they require many components.

[0014] Furthermore, prior art technologies had the disadvantage of having low viewing angles. To increase the viewing angle, it is necessary to microscopically vary the alignment. Techniques have been developed and recently adapted to industrial methods in order to remedy this defect. However, for the moment, these are based on local polymer deposits, which is difficult to implement and does not allow for a result with optimal efficiency.

[0015] Summary of the invention According to one aspect the invention relates to a method of treating a surface of an ionic amorphous material (AM) comprising:

[0016] ■ Arrangement of said first surface of the ionic amorphous material in contact with or in the vicinity of at least one first geometrically structured electrode;

[0017] ■ Applying a temperature to said ionic amorphous material from a heat source to a first area of ​​said ionic amorphous material;

[0018] ■ Application of a voltage across the terminals of the first electrode of a predefined value for a given period;

[0019] ■ Generation of a surface plasma on the surface of the ionic amorphous material between at least two portions of the first electrode from the ionization of a gas located between said first surface of ionic amorphous material and different portions of the first electrode and the application of a given voltage across the terminals of the first electrode, said application of the voltage across the terminals of the first electrode and said generation of plasma being configured so as to modify the electrical properties of said ionic amorphous material to define at least one locally polarized zone between the different portions of the first electrode;

[0020] ■ Extraction of the treated ionic amorphous material.

[0021] One advantage is that it induces polarization of the glass charges within areas that can have dimensions of several hundred micrometers. The distance between two portions of the first electrode can be adapted according to the number of ionic charges included in the glass.

[0022] Another advantage is to define polarized zones according to desired electrical properties according to a given geometry. Defining polarized zones in the surface of the amorphous material makes it possible, for example, to control the orientation of liquid crystals sensitive to electric fields.

[0023] The proximity between the first ionic amorphous material surface and the first geometrically structured electrode may correspond to a distance between 0 and 500 microns.

[0024] According to one embodiment, the portions of the first electrode are separated by a distance of less than 500 micrometers when these distances are measured in a plane parallel to the plane of the treated surface.

[0025] In one embodiment, the plasma is a cold plasma or a dielectric barrier discharge type plasma. An advantage is that it allows the creation of a plasma from a common and easily accessible gas.

[0026] According to one embodiment, the first electrode comprises an anode arranged in contact with or near a first surface of the ionic amorphous material to be treated and a cathode arranged on or near the second surface of the ionic amorphous material, said gas confined between the first surface of the ionic amorphous material and the different electrode portions undergoing ionization forming plasma discharges.

[0027] According to one embodiment, the application of a voltage to the first electrode induces a displacement of the mobile cations under the surface of the ionic amorphous material towards the cathode and a displacement of the negative charge carriers comprising electrons and / or anions towards the first surface of said ionic amorphous material, said displacement of the negative charges at the surface of the ionic amorphous material generating the plasma at the surface of the ionic amorphous material and forming a surface current whose propagation orientation is controlled in the plane of said ionic amorphous material by the geometry of the anode.

[0028] According to one embodiment, the cathode is homogeneous in contact with the second surface of the ionic amorphous material.

[0029] According to one embodiment, the temperature induced by the heat source is between 150°C and 500°C.

[0030] According to one embodiment, the temperature induced by the heat source is between 180°C and 300°C.

[0031] According to one embodiment, the voltage applied to the terminals of the electrode is between 100V and 3000V.

[0032] According to one embodiment, the gas comprises nitrogen, argon or oxygen, the gas being subjected to a pressure of between 400 hPa and 2000 hPa.

[0033] According to one embodiment, the charge density within the ionic amorphous material, the voltage applied to the terminals of the first electrode and the charged plasma are configured to generate, for a predefined duration, displacements of the negative charges in directions parallel to the plane of the surface of the amorphous material, said displacements occurring in a thickness of the surface less than 3 micrometers.

[0034] According to one embodiment, the anode comprises a geometry configured to define polarized regions (Zpi) on the surface of the ionic amorphous material (MA), each region being comprised between the portions of the first electrode.

[0035] According to one embodiment, the anode comprises a geometry configured to define regions within which the surface currents generated at the surface of the ionic amorphous material induce the creation of a plurality of polarized zones delimited at least in part by the limits of each region, said polarized zones being created at the surface of the amorphous material.

[0036] According to one example, the regions circumscribed by the electrode portions having dimensions along each of the two axes in the plane of the surface greater than 5 micrometers.

[0037] According to one embodiment, the anode comprises a geometry forming cells closed by linear portions of said anode in which surface currents (S(Ch-)) are generated to induce circumscribed polarized zones on the surface of the ionic amorphous material, said circumscribed polarized zones comprising dimensions along each of the two axes in the plane of the surface of the ionic amorphous material greater than 2 micrometers and being defined by a direction of polarization induced by the direction of the surface currents (S(Ch-)).

[0038] According to another aspect, the invention relates to a treated ionic amorphous material comprising at least one electrically polarized zone, said electrically polarized zone being intended to receive liquid crystals.

[0039] According to one embodiment, the surface of a treated ionic amorphous material of the invention is produced using a method of the invention.

[0040] According to another aspect, the invention relates to a liquid crystal cell (LCC) characterized in that it comprises:

[0041] ■ a first surface of an ionic amorphous material treated according to the method of the invention;

[0042] ■ a second surface of a material arranged so as to maintain liquid crystals in a sandwich structure, ■ liquid crystals oriented according to the direction(s) of polarization of each polarized zone of said first surface.

[0043] According to one embodiment, the material having the second surface in contact with the liquid crystals comprises a multilayer structure having a first layer of polyimide material and a second layer of an amorphous material holding the first layer.

[0044] An advantage of using a polyimide layer is to homogenize the effect induced by the electrical charges of the second surface or to limit the heterogeneous effects on the alignments of the liquid crystals controlled by the first surface.

[0045] According to one embodiment, the second surface is a surface of an amorphous material treated according to the method of the invention, said second surface being secured to the first treated surface by means of fixing elements, the two surfaces being held together with a constant inter-surface thickness adapted to the dimensions of the liquid crystals.

[0046] According to one embodiment, the distance between the two planes between the first and second surfaces is between 5 and 10 micrometers.

[0047] According to one embodiment, the thickness of the area located between the two surfaces in which the liquid crystals are inserted is between 5 and 100 micrometers.

[0048] According to one embodiment, the ionic amorphous material is an ionic glass, such as a soda-calcium silicate ionic glass, or a glass comprising alkali or alkaline earth elements.

[0049] Brief description of the figures

[0050] Other characteristics and advantages of the invention will emerge on reading the detailed description which follows, with reference to the appended figures, which illustrate:

[0051] [Fig. 1]: an example of the main stages of the process for treating an ionic amorphous material for use with liquid crystals;

[0052] [Fig. 2]: An example of a multilayer structure for creating a treated ionized glass layer and its use in a liquid crystal cell to control the alignment of the liquid crystals; [Fig. 3]: An example of the formation of a surface plasma generated to polarize an ionic glass used for use with liquid crystal cells,

[0053] [Fig. 4]: an example of an amorphous material such as glass treated by the method of the invention comprising different zones having different polarizations.

[0054] Description of the invention

[0055] Process

[0056] Figure 1 describes the main steps of the method for treating a surface of an ionic amorphous material MA. The polarized amorphous material obtained by the method of the invention is advantageously used to structure liquid crystal cells. Given the correspondence between the electrical properties of the desired polarized amorphous material and the use of a configuration obtained to induce liquid crystal alignments, the method described below can refer to technical effects sought when said material will be used in a second step to structure a liquid crystal cell.

[0057] A first step of the method of the invention comprises an arrangement AGE of the surface of ionic amorphous material MA in contact with or in proximity to at least one first geometrically structured electrode Ai, Ci. A heat source is arranged to control the temperature of the amorphous material MA. The different layers thus arranged form a multilayer structure 1 shown in Figure 2. Such an arrangement of layers allows the implementation of the method of the invention.

[0058] A "surface of a material" is the geometric surface of the material and also the surface as a part of the material. In the following description, it is therefore considered that a treatment of the surface of a material induces a treatment in a given thickness of the material. Since the thickness considered remains negligible with regard to the transverse dimensions of the surface, the surface of the material denotes its transverse dimensions considered with the dimension corresponding to a thickness over a fraction of the total thickness of the material. Electrode

[0059] Figure 2 describes an embodiment of an arrangement AGEi of an electrode Ai, Ci with respect to a surface of an ionic amorphous material MA, such as glass, for its treatment by the method of the invention.

[0060] Thus, the arrangement AGEi represented by the multilayer structure 1 of Figure 2 illustrates the first step of the method of the invention in which a surface of an ionic amorphous material MA is arranged for its treatment in contact with an electrode Ai, Ci. The electrode Ai, Ci comprises an anode Ai and a cathode Ci. According to one example, the cathode Ci is arranged on one face of the ionic amorphous material MA and the anode Ai on the other face of the same ionic amorphous material MA. The electrode Ai, Ci is powered by a voltage source applied within the electrode Ai, Ci is controlled by the application of an electric voltage across the electrode 1, Ai, Ci.

[0061] Preferably, the anode Ai and the cathode Ci or the anode Ai or the cathode Ci are parts of a planar electrode. The geometry of the anode Ai is, for example, structured in the plane so as to induce desired electrical properties in the ionic amorphous material MA. It is therefore preferentially structured in a plane parallel to the plane of the surface of the ionized amorphous material MA. According to the example of Figure 1, the anode Ai is arranged on a surface portion Zi represents a section of the ionic amorphous material MA to be treated. In the example of Figure 1, the anode A1 is held between the surface of the ionized amorphous material MA and a layer of a substrate SAi having no electrical property, or at least negligible compared to the electrical properties of the ionic amorphous material MA. The layer of the substrate SAi is for example a non-ionic glass forming an electrical insulator.

[0062] According to one embodiment, an electrode Ai, Ci having a 2D geometry more easily allows 2D control of surface currents. Consequently, 2D control of currents makes it possible to induce the formation of multi-domains of liquid crystal alignments when the latter are close to the surface of the treated amorphous material.

[0063] This type of electrode Ai, Ci can be formed of micro-volumes delimited from each other by barriers formed of conductive materials having determined electrical potentials. For example, within one of these micro-volumes, the surface currents are multidirectional depending on the geometry of the volume and the applied voltage and the possible electrically charged gas that can occupy this volume. It is therefore understood that the method of the invention makes it possible to configure and induce multi-domain polarizations according to the configuration of the micro-volumes and their distribution with respect to each other.

[0064] The method of the invention therefore allows the formation of several alignment domains within the same micro-volume since it is possible to associate spatialized surface currents with regions to be polarized of an ionic amorphous material to induce in a second step alignments of objects sensitive to this polarization arranged near the polarized amorphous material. The geometry of the surface currents, that is to say the orientation of the surface currents, can be deduced by the use of simple electrostatic models and their modeling with respect to a given electrode geometry and the composition of the glass and other variable parameters for the implementation of the method of the invention, namely the temperature of the material, the applied voltage, etc.

[0065] Indeed, to control the shape of the surface currents generated on the surface of the ionic amorphous material MA and therefore the polarizations likely to be generated within the material and therefore the alignment domains of the liquid crystals that can be induced, it is possible to apply different electrical potentials in several regions of the electrode Ai, Ci. An alternative would be for example the use of several positive electrodes arranged according to a predefined configuration.

[0066] According to different embodiments, the voltage can be applied with a constant or variable value. An applied voltage having a continuous value makes it possible, for example, to obtain a first dynamic of charge migration within the amorphous material and the plasma. This dynamic can be, for example, adjusted according to the duration of application of the voltage to obtain a given surface current. An applied voltage having a variable value can be of interest in other use cases involving particular control of the dynamic of charge migration within the amorphous material or the plasma. In the latter case, the value of the voltage can be determined and / or controlled, for example, by a function implemented in an electronic card controlling the voltage source at the terminals of an electrode.The function can generate pulses with a given frequency or, in another example, the function can generate an alternating voltage in the form of a square-wave signal or a sinusoid. More generally, when a variable voltage is applied, the frequency, amplitude and phase of the voltage can be controlled according to a given function implemented by means of calculating and controlling the voltage.

[0067] According to one embodiment, different voltage values ​​are applied to the terminals of a plurality of electrodes in order to induce surface currents on the surface of the amorphous material. This possibility makes it possible to obtain polarized zones having different electrical properties depending on the zones considered.

[0068] According to one embodiment, the method of the invention can take into account the spatial variation of the applied electrical potential to enable control of the shapes or geometries of the surface currents generated on the surface of the ionic amorphous material MA. These shapes and / or these geometries correspond to orientations of surface currents forming parallel to the surface of the material. These shapes or geometries make it possible to induce polarizations capable of being generated within the material. These polarized zones thus induced make it possible, when using a treated material, to define different alignment domains of the liquid crystals CL.

[0069] According to one embodiment, the electrode Ai, Ci is of point or wire type. One interest is to design electrode geometries defining regions within which a control of spatialized surface currents is configurable.

[0070] Anode geometry

[0071] According to one embodiment, the anode Ai forms a grid as shown in Figure 2, the grid is a grid of which each branch has a given thickness and a predefined distance between two thicknesses. According to the example of Figure 1, the thickness of the branches of the grid of the anode Ai is 10 micrometers and the distance between two branches is 40 micrometers.

[0072] According to other examples, the width of the anode portions Ai in the plane parallel to the plane of the surface of the amorphous material MA is between 1 micrometer and 20 micrometers. According to one embodiment, the distance between the anode portions Ai in the plane parallel to the plane of the surface of the amorphous material MA is between 15 micrometers and 400 micrometers. An advantage of the invention is to allow the control of surface electric current generated by the formation of a plasma over distances that can reach several hundred micrometers. An interesting range is notably between 5 micrometers and 200 micrometers. These distances are notably difficult to control from electrodes because this assumes the use of electrode geometries that are difficult to implement with more reduced control of the addressed regions of the ionic amorphous material MA.

[0073] According to other embodiments, the structure of the anode Ai may take different forms, these may be more or less complex geometric shapes. For example, the anode Ai may comprise a structure having a geometric shape of a ring, a hollow shape, a shape having a plurality of parallel straight branches and more generally any other geometric shape inscribed in a plane. The geometric shape of the anode Ai may comprise a duplicated repeating pattern with the same dimensional properties, such as squares of the same size spaced a certain distance apart or with different dimensions such as squares nesting inside a larger square and providing space for a smaller square.

[0074] Thus, the electrode Ai, Ci and more specifically the anode Ai in the case of the example makes it possible to define regions within which the surface currents are controlled to form electrical polarizations within the ionic amorphous material MA.

[0075] Thus, the anode Ai may comprise a geometric shape having at least one symmetry, such as symmetry with respect to an axis or symmetry of revolution. According to another example, the anode Ai comprises a geometric shape such that a part of the anode Ai is obtained by a geometric transformation of another part of the anode Ai. According to one example, this transformation is a homothety. Thus, it is possible to generate concentric or nested shapes.

[0076] An advantage of shapes with repeating patterns is that they allow for polarized glass for applications with cell structures such as liquid crystal cells. These applications are particularly interesting for liquid crystal displays or the design of optical components.

[0077] The multilayer structure 1 of Figure 2 makes it possible to carry out a method of treating an ionic glass MA, the glass being an amorphous material particularly interesting for applications specific to defining liquid crystal cells. According to one example, a glass of the soda-calcium silicate glass type can be used.

[0078] The multilayer structure 1 of Figure 2 also includes the AGEi arrangement of a cathode Ci on the other surface of the ionic amorphous material MA. This AGEi arrangement of sandwich layers allows, when the electrode Ai, Ci is energized, to migrate electrons or anions into the ionic amorphous material MA.

[0079] Application of a temperature

[0080] In order to facilitate or make possible the migration of electrons or anions in the ionic amorphous material MA, a layer HTi is used to heat the surface of the ionic amorphous material MA. This source comprises for example a heating plate in order to heat the surface of the ionic amorphous material MA over a complete region defining the surface of the plate. Heating the surface of the ionic amorphous material MA makes it possible to facilitate the movement of electrons or anions within the surface of the amorphous material MA. The arrangement of the heat source HT1 can be achieved in different ways. According to one embodiment, a heating plate can be used. According to another embodiment, a temperature can be provided by radiation from a radiant source. According to another embodiment, the multilayer structure 1 is arranged within an adiabatic enclosure which allows the temperature of the ionic amorphous material MA to be controlled.

[0081] A second step of the method therefore comprises applying a given temperature to the ionic amorphous material MA from a heat source HTi to a first region Zi of said ionic amorphous material MA. The area may correspond to the entire surface of the ionic amorphous material MA.

[0082] Depending on the material chosen, the temperature can be varied to promote the movement of electrons or anions within the ionic amorphous material MA. The temperature can be varied within a preferred temperature range and must remain below the glass transition temperature of the ionic amorphous material MA.

[0083] Application of voltage

[0084] A third step comprises the application APPi of a voltage across the terminals of the first electrode Ai, Ci in order to generate an electric current intensity within the anode Ai and the cathode Ci. This step is preferably carried out simultaneously with the step of heating the material. This voltage can be controlled so as to promote the movement of charges within the ionic amorphous material MA. The period of application of the voltage is also parameterized according to the given case during a given period Td. The period can be configured according to the surface currents that are desired to be generated in order to obtain a desired polarization of the material MA.

[0085] One of the desired goals of the AGEi arrangement of this multilayer structure 1 and the thermoelectric configuration of the first steps of the process is the GENi generation of a surface plasma PLi on the surface of the ionic amorphous material MA between at least two portions of the anode Ai defining a confined micro-volume between these anode portions Ai.

[0086] Under the effect of the electric field and temperature, a depletion of alkali and / or alkaline earth metals is formed within the vitreous matrix over a thickness of a few micrometers on the anodic surface of the treated glass. This phenomenon is also known as "poling" on a glass in English terminology. The quantity of cations displaced by this charge separation mechanism defines the surface density of negative charge induced during the treatment. This surface charge density can be controlled by various parameters, including:

[0087] ■ the composition of the glass and in particular its concentration of alkaline elements,

[0088] ■ the treatment temperature,

[0089] ■ the applied voltage values, and

[0090] ■ the dimensions of the electrode.

[0091] According to one example, the electrode is a wire electrode of the tungsten wire type with a diameter of 80 μm. This electrode is placed in contact with a surface of soda-calcium silicate glass. The treatment is carried out at 240°C for a voltage of 1400V. The example of the ionic amorphous material MA in Figure 3 can be treated with the same configurations, namely a temperature of 240°C and a voltage of 1400V across the electrodes Ai, Ci.

[0092] Generation of a surface plasma

[0093] When the surface charge density is sufficient over a given domain, the ionization of the gas in contact with the charged surface allows the formation of plasmas and surface currents which cause an electric polarization effect in the plane of the surface of the glassy matrix.

[0094] The method of the invention makes it possible to define a configuration ensuring that a surface charge density generated during the treatment is sufficient to produce a static electric field of sufficient amplitude. The sufficient amplitude is defined according to the use case, such as the amplitude necessary to generate an orientation or an alignment of liquid crystals. Conversely, the method makes it possible to limit the surface charge density obtained in order to avoid damaging the ionic glass substrate.

[0095] We therefore understand the usefulness of creating electrode geometries defining micro-volumes within which it is possible to generate controlled surface currents induced by the formation of surface plasma.

[0096] The production of a plasma is promoted by the presence of an initially neutral gas confined between said at least two portions of the anode Ai when the voltage is applied and the heat is supplied to the ionic amorphous material MA. The application of the voltage and the heat make it possible to promote the ionization of the gas, thus forming a surface plasma.

[0097] The invention takes advantage of a chosen structuring of the electrode, in particular of the anode A1 so as to define confined regions of large dimensions relative to the electrode portions. The gas allows the formation of a plasma within which the displacement of the charges originating from the ionic amorphous material MA is possible. This displacement allows the formation of a surface current.

[0098] The method of the invention allows the formation of surface plasmas which allow the control over adjustable distances of the surface currents at the surface of the ionic amorphous material towards the positive electrode.

[0099] The regions of formation of these surface currents / plasmas define the electrically activated zones due to an electrical polarization of the material according to the direction of the currents formed. Thus, in the same region defined by the geometry of the electrode, several zones with different electrical polarizations can be generated.

[0100] Indeed, a region defined by the structuring of the electrode makes it possible to induce different polarization zones according to the displacements of the surface currents on the surface of the amorphous material delimited by said region. Typically, an electrode defining a parallelogram-shaped region makes it possible to define 4 triangular-shaped polarization zones, the surface currents being oriented from the center of the region towards each branch of the parallelogram. If the electrode has a circular shape, the polarization zone is defined according to a radial polarization geometry obtained thanks to surface currents oriented from the center of the circle towards the circumference of the circle.

[0101] The material thus modified allows, for example, control of the alignment of liquid crystals as detailed below.

[0102] According to the example of the grid in Figure 2, the polarization effect of the glass surface occurs on the contact areas between the grid and the glass and by the formation of surface plasmas in the micro-volumes of gas present at each gap of the grid. There are therefore two regions which are subject to different electrical stresses depending on the contact of the ionic amorphous material with the electrode or with the plasma.

[0103] To control the size of the treated surfaces, in addition to the parameters of glass composition, temperature, applied voltage and electrode geometry for controlling the surface charge density, a fifth parameter can be defined. The fifth parameter can be defined by the properties of the gas used, in particular its composition, its pressure and the size of the volume of gas in contact with the electrode and the glass surface to be treated.

[0104] When treating the surface of the ionic amorphous material, the temperature and voltage can be stopped so as to freeze the polarization in the treated amorphous material MA'.

[0105] For a single domain, a surface plasma can be controlled at micrometric scales ranging from 5 to 500 pm. The use of spatially controlled surface plasmas / currents at micrometric scales makes it possible to induce an electrical polarization of the surface of an ionic glass. The glass surface thus treated can then be used for applications aimed at controlling an object sensitive to static electromagnetic fields obtained by this polarization. One advantage of the invention is to use this type of glass treated with liquid crystals so as to force their alignment. Thus, the invention allows the formation of multi-domains of alignments of these liquid crystals.

[0106] The configuration of the multilayer structure 1 of Figure 2 allows preparation of the ionic glass MA surface by the use of surface plasmas induced by the thermoelectric treatment according to the operation described in Figure 3. One of the advantages of the invention is to use the geometry of the electrode Ai, Ci used to spatially control the directions of the surface currents of the ionic amorphous material MA. The geometry of the electrode Ai, Ci can therefore be adapted according to the desired application.

[0107] Figure 3 represents an ionic amorphous material MA comprising mobile cations of alkali or alkaline earth type. When it is heated and the electrode Ai, Ci is energized, the voltage across the anode promotes the migration of electrons or anions from the ionic amorphous material MA towards the surface as the arrows Ch- represent. Conversely, the positive charges, the cations Ch+ migrate towards the cathode Ci. The region located on the surface of the ionic amorphous material MA between two portions of anode Ai comprises a gas which, under the effect of the electromagnetic field generated locally by the electrode, promotes the creation of a charged surface plasma PLi. The plasma comprises electric charges created during the application of the electric field induced by the energization of the electrode Ai, Ci.Thus, the PLi plasma allows a displacement of charges within the plasma on the surface of the amorphous material in a plane parallel to the plane of the surface of the ionic amorphous material MA. The PLi Plasma has the effect of generating a surface current noted S(Ch-) between the surface of the ionic amorphous material (MA) and the portions of the electrode Ai. Figure 3 represents between each electrode A1 surface currents S(Ch-) having opposite directions under the same region comprising the plasma, the arrows representing the directions of the surface currents obtained thanks to the configuration of the electrodes. These opposite directions explain in particular the geometric triangle shapes obtained in Figure 4 when a grid-shaped electrode is used.

[0108] The generation of this PLi plasma is made possible in particular by the establishment of a zone having a sufficient dimension between the anode portions Ai. According to one example, at least two portions of the anode Ai are separated by a distance of between 5 micrometers and 500 micrometers. In a preferred embodiment, the anode portions Ai are organized to form closed confinement zones having the shape of a circle, square, rectangle, triangle or any other shape used according to the desired application.

[0109] Figure 3 also represents a surface of polarized amorphous material MA' obtained by means of the method of the invention. This surface is shown in top view with respect to the sectional view of the amorphous material MA shown above. This treated surface comprises alternating zones Zpi and Zp2 which are determined according to the electrical polarization of said zones. The zones Zp2 located under the anode Ai are polarized in a first direction in the plane of the polarized amorphous material MA' and the zones Zpi located under the plasma Ai are polarized in a second direction perpendicular to the first direction and also included in the plane of the polarized amorphous material MA'. Other types of polarizations can be obtained depending on the anode Ai used and more generally the geometry of the electrode Ai, Ci and the dimensions of the confined spaces between the anode portions Ai.In particular, it is possible to generate polarizations in different directions within a microvolume by controlling the direction and / or directions of the currents in the microvolume.

[0110] The PLi plasma thus formed on the surface of the ionic amorphous material MA makes it possible to modify the electrical properties of the latter to define at least one locally electrically polarized ionic zone Zi.

[0111] Thus, the geometry of the micro-volumes formed between the different anode portions Ai allows the control of the direction and / or the sense of the electric currents along the surface of the glass substrate, the effects of which will subsequently allow the control of the orientation of the liquid crystals when the substrate is used in the design of an LC liquid crystal cell. Thus, this type of substrate can then be used for the manufacture of a liquid crystal cell by eliminating the use of a polymer film during the manufacture of a liquid crystal cell.

[0112] Another advantage is the open possibility of manufacturing planar alignment multi-domains whose orientation axis and dimension are controlled by the glass substrate processing parameters.

[0113] Figure 4 illustrates an effect of multi-domain polarization of a treated amorphous material obtained between the anode portions Ai of a grid-type electrode such as that of Figure 3. The polarizations are differentiated according to the triangular-shaped regions falling within the micro-volumes between the grid-shaped traces which were in contact with the electrode A1.

[0114] Optical microscopy observation of the amorphous material between two crossed polarizers shows that the areas that have been in contact with the grid induce an orientation of the liquid crystals perpendicular to the surface of said amorphous material. In the area corresponding to the gap of the grid, 4 domains of distinct planar orientations and triangular shape Zp1 have formed. In each of these four triangular shaped domains Zp1, the orientation of the liquid crystals CL is planar and perpendicular to the nearest edge of the grid. The directions of each of the 4 zones Zp1 included within the same rectangular or square region delimited by the wire portions of the electrode include different directions.

[0115] The method of the invention makes it possible to control the duration of application of the surface treatment in order to obtain a desired polarization of the ionic amorphous material MA. When the treatment is finished, a step of extraction EXTi of the ionic amorphous material MA is carried out. The extraction EXTi consists of the separation of the ionic amorphous material MA from the other layers of the multilayer structure 1 of figure 1.

[0116] Figure 2 represents a surface of ionic amorphous material 2 also noted MA' thus obtained by the process of the invention. The ionic amorphous material MA' comprises two types of zones: Zpi and Zp2.

[0117] First zones Zpi correspond to the zones of the ionic amorphous material located between the anode portions A1. In these regions a first electrical polarization of the surface of the ionic amorphous material MA is induced by the method of the invention. Second zones Zp2 correspond to the zones of the ionic amorphous material which were located under the anode portions A1 or which were in contact with the anode portions Ai. In these regions a second electrical polarization of the surface of the ionic amorphous material MA' is induced by the method of the invention.

[0118] Use to define liquid crystal cells

[0119] The treated amorphous material MA' surface includes a structuring of induced polarized zones corresponding to the geometry of the electrode Ai, Ci. An advantage of the controlled polarization of certain zones is the creation of a static electromagnetic field within the polarized amorphous material MA'. This field makes it possible to control the alignment of liquid crystals that would be brought into contact with the surface of the polarized amorphous material MA'.

[0120] An example of liquid crystals whose orientation can be governed by a surface treated by the method of the invention is the family of nematic liquid crystals such as hexyl-biphenylcabonitrile.

[0121] Indeed, a consequence of the method of the invention is the development of a direct link between the direction of the currents during the thermoelectric polarization process and the direction of alignment of the liquid crystals CL obtained on the treated surface. The directions of the electric currents on the surface of the amorphous material are controlled by the configuration of the electrodes used during the method of the invention.

[0122] To achieve a homeotropic orientation perpendicular to the surface of the liquid crystals CL, a uniform electrode close to or in contact with the surface can be used.

[0123] For a planar orientation of the liquid crystals CL, the method of the invention can implement a configuration allowing the generation of currents having a majority component along the surface and perpendicular to the positive electrode in the surface plasma formation zone. In these zones the currents induced along the surface of the glass allow a planar alignment of the liquid crystals CL along the direction directly perpendicular to the positive electrode and parallel to the surface of the glass.

[0124] The invention also relates to the use of such a polarized amorphous material to define liquid crystal cells. A layer of ionic glass thus treated allows the manufacture of a liquid crystal cell having spatially controlled planar and non-planar orientation domains. The geometry of the surface currents of the treated glass controlled by means of the method of the invention allows spatial control of the alignment directions of the LC liquid crystals in interaction with the treated surface of the polarized glass used.

[0125] Such a liquid crystal cell 3 is obtained and represented in Figure 2. The cell 3 is delimited by the surface of the polarized amorphous material MA' according to the method of the invention.

[0126] The multilayer structure 3 of Figure 2 comprises in this example LC liquid crystals, said LC liquid crystals being held between two surfaces by means of a suitable geometry of said layers arranged on either side of the liquid crystals. A first layer of a polarized amorphous material MA' and a second a layer of polyimide material PI. An additional layer SLG of an amorphous material denoted MA2 can be used to hold the layer of polyimide PI.

[0127] The multilayer structure 3 in Figure 2 is also called an SCL liquid crystal cell.

[0128] An advantage of the invention is to define liquid crystal cells whose orientation is governed not by the surface state of a polymer, but by a static electric field. Depending on the orientation of this static electric field, the orientation of the liquid crystals can be governed so as to favor an alignment perpendicular or an alignment parallel to the plane of the surface of polarized amorphous material MA'.

[0129] According to one embodiment, the surface of the polarized amorphous material MA' is associated with elements making it possible to secure said surface with a second surface arranged in parallel. The region between the two surfaces defines a reception zone for receiving liquid crystals LC. The latter can be introduced by capillarity and be kept confined within the sandwich structure.

[0130] In the case where the two surfaces define a liquid crystal cell, the filling of the cell can be carried out in a vacuum oven. Once the vacuum is established, the cell is heated in order to pass the liquid crystal into the isotropic phase and obtain the filling of the cell. This technique is particularly effective on small cells. For larger cells, a pressurization technique known to those skilled in the art for filling can also be implemented.

[0131] According to one embodiment, the liquid crystal cell SCL comprises a second surface of an amorphous material arranged so as to maintain the liquid crystals within a sandwich structure with the first surface of the polarized amorphous material MA'. According to one example, the second layer comprises a first sub-layer of polyimide material PI and a second sub-layer SLG of an amorphous material MA2. In the latter case, the role of this second sub-layer is in particular to maintain the polyimide layer.

[0132] According to one embodiment, the second surface comprises a surface geometry adapted to form with the first surface a sandwich structure comprising an inter-surface space. The inter-surface space is designed to define a spacing adapted to accommodate liquid crystals in order to define a liquid crystal cell LC.

[0133] The first surface MA' and the second surface SLG, PI can be held together by means of a fixing means so as to secure the two surfaces together and to maintain a predefined distance between the two surfaces. An example of a fixing means is the use of micrometric glass beads mixed with a UV glue. The mixture is thus applied, for example, to the four corners of the two surfaces to be joined. The mixtures are then crosslinked by applying UV light. According to this example, the liquid crystals are introduced by capillary action between the two surfaces to be joined and are heated so that they are in their isotropic phase. As they cool, they then pass into the nematic phase and then naturally orient themselves according to the polarization of the material of the first surface.

[0134] An advantage of the invention is to modify the electrical properties of a material, for example a vitreous material such as glass, with the aim of controlling the optical properties of a liquid crystal cell. One interest is to custom-functionalize a glass for given applications.

[0135] The invention benefits from the fact that liquid crystals are sensitive to electric fields. One advantage is that it avoids the use of more complex solutions for controlling alignments using so-called "photo-alignment" techniques. For example, the invention makes it possible to avoid the use of a photosensitive dopant within the liquid crystals or the use of a polymer that has been treated by surface chemistry with a photosensitive molecule that will orient itself according to the polarization of the light.

[0136] The process makes it easier to make liquid crystal cells and requires fewer components.

[0137] The liquid crystal cell of the invention may be associated with a system generating an electric field controlling the orientation of the main axis of the liquid crystals. According to one example, transparent electrodes may also be implemented to control the electric field in order to orient the crystals to manage an alignment dynamic of said crystals as for the pixels of a display. The electrodes may be used to manage an alignment dynamic such as an alignment frequency.

[0138] Polarizers can be configured on either side of the liquid crystal cell to control the polarization of light passing through the liquid crystal cell. Thus, controlling the electric field and the polarizers allows for different uses of the liquid crystal cell that is illuminated by a light source.

[0139] According to one embodiment, the liquid crystal cell is associated with crossed optical polarizers.

[0140] The polarized amorphous material may be a glass also serving as a support and external surface of the liquid crystal cell.

[0141] Another advantage of the invention is to provide a solution that can be implemented in vertical alignment technologies that are increasingly used.

Claims

CLAIMS A process for treating a first surface of an ionic amorphous material (AM) comprising: ■ Arrangement (AGEi) of said first surface of the ionic amorphous material (MA) in contact with or near at least one first geometrically structured electrode (Ai, Ci); ■ Application (APPi) of a temperature said ionic amorphous material (MA) from a heat source (HTi) on a first zone (Zi) of said ionic amorphous material (MA); ■ Application (APP2) of a voltage across the terminals of the first electrode (Ai, Ci) of a predefined value for a given period (Td); ■ Generation (GEN1) of a plasma (PL1) on the surface of the ionic amorphous material (MA) from the ionization of a gas located between said first surface of ionic amorphous material and different portions of the first electrode (Ai, Ci) and the application of a given voltage across the terminals of the first electrode (Ai, Ci), said application (APP1) of the voltage across the terminals of the first electrode (Ai, Ci) and said generation (GEN1) of plasma (PL1) being configured so as to modify the electrical surface properties of said ionic amorphous material (MA) to define at least one area of ​​the surface (Zpi) locally polarized between the different portions of the first electrode (Ai, Ci); ■ Extraction (EXT1) of the treated ionic amorphous material (MA'); Said polarized ionic amorphous material (MA) being used to define a liquid crystal cell. A method for treating the surface of an ionic amorphous material (MA) according to claim 1, characterized in that said portions of the first electrode (Ai, Ci) are separated by a distance of less than 500 micrometers. A method for treating the surface of an ionic amorphous material (MA) according to any one of claims 1 to 2, characterized in that that the plasma is a cold plasma or a dielectric barrier discharge type plasma. Method for treating a surface of an ionic amorphous material (MA) according to any one of claims 1 to 3 characterized in that the first electrode (Ai, Ci) comprises an anode (Ai) arranged in contact with or near a first surface of the ionic amorphous material (MA) to be treated and a cathode (Ci) arranged on or near the second surface of the ionic amorphous material (MA), said gas confined between the first surface of the ionic amorphous material (MA) and the different portions of electrodes (Ai, Ci) undergoing ionization forming plasma discharges.A method for treating the surface of an ionic amorphous material (MA) according to any one of claims 1 to 4 characterized in that the application of a voltage to the first electrode (Ai, Ci) induces a displacement of mobile cations under the surface of the ionic amorphous material (MA) towards the cathode and a displacement of negative charge carriers comprising electrons and / or anions towards the first surface of said ionic amorphous material (MA), said displacement of negative charges on the surface of the ionic amorphous material (MA) generating the plasma (PL1) on the surface of the ionic amorphous material (MA) and forming a surface current (S(Ch-)) whose propagation orientation is controlled in the plane of said ionic amorphous material (MA) by the geometry of the anode (Ai).Method for treating a surface of an ionic amorphous material (MA) according to any one of claims 1 to 5 characterized in that the charge density within the ionic amorphous material (MA) and the voltage applied across the terminals of the first electrode (Ai, Ci) are configured to generate for a predefined time displacements of negative charges (S(Ch-)) along directions parallel to the plane of the surface of the amorphous material, said displacements occurring in a thickness of the surface less than 3 micrometers. Method for treating a surface of an ionic amorphous material (MA) according to any one of claims 5 to 6 characterized in that the anode (Ai) has a geometry configured to define regions within which the surface currents generated on the surface of the ionic amorphous material (MA) induce the creation of a plurality of polarized zones delimited at least in part by the limits of each region defined by the geometry of the anode (Ai), said polarized zones being created on the surface of the amorphous material (MA).A method for treating the surface of an ionic amorphous material (MA) according to any one of claims 5 to 7, characterized in that the anode (Ai) has a geometry forming cells closed by linear portions of said anode (Ai) in which surface currents (S(Ch-)) are generated to induce circumscribed polarized zones (Zpi) on the surface of the ionic amorphous material (MA), said circumscribed polarized zones (Zpi) having dimensions along each of the two axes in the plane of the surface of the ionic amorphous material (MA) greater than 2 micrometers and being defined by a polarization direction induced by the direction of the surface currents (S(Ch-)). The treated ionic amorphous material (MA') is characterized in that it comprises at least one electrically polarized zone (Zi), said electrically polarized zone (Zi) being intended to receive liquid crystals (CLi).Treated ionic amorphous material (MA') characterized in that said material is produced by means of a process of any one of claims 1 to 8. Liquid crystal cell (SCL) characterized in that it comprises:. ■ a first surface of a treated ionic amorphous material (MA') according to any one of claims 9 to 10; ■ a second surface of a material arranged to hold liquid crystals in a sandwich structure, ■ Liquid crystals oriented along the polarization direction(s) of each polarized zone (Zi) of said first surface. Liquid crystal cell (LCC) according to claim 11 characterized in that the material having the second surface in contact with the liquid crystals comprises a multilayer structure having a first layer of polyimide material and a second layer of an amorphous material holding the first layer. Liquid crystal cell (LCC) according to claim 12 characterized in that the second surface is a surface of an amorphous material (MA2) according to any one of claims 9 to 10, said second surface being attached to the first treated surface (MA') by means of fastening elements, the two surfaces being held together with a constant inter-surface thickness adapted to the dimensions of the liquid crystals.Liquid crystal cell (LCC) according to any one of claims 11 to 13 characterized in that the ionic amorphous material (Ma) is an ionic glass, such as a soda calcium silicate ionic glass, or a glass comprising alkali or alkaline earth elements.

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