Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
  • G02F1/137—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering
  • G02F1/139—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering based on orientation effects in which the liquid crystal remains transparent
  • G02F1/1391—Bistable or multi-stable liquid crystal cells
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
  • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
  • G02F1/1333—Constructional arrangements; Manufacturing methods
  • G02F1/1337—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers
  • G02F1/133753—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers with different alignment orientations or pretilt angles on a same surface, e.g. for grey scale or improved viewing angle
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
  • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
  • G02F1/1333—Constructional arrangements; Manufacturing methods
  • G02F1/1337—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers
  • G02F1/133711—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers by organic films, e.g. polymeric films
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
  • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
  • G02F1/1333—Constructional arrangements; Manufacturing methods
  • G02F1/1337—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers
  • G02F1/133734—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers by obliquely evaporated films, e.g. Si or SiO2 films

Definitions

• Cell comprising a controlled anchoring plate for nematic liquid crystals and method for producing such a plate
• the present invention relates to the field of monostable and multistable devices based on nematic liquid crystals.
• Films thermally polymerized and subjected to rubbing make it possible, for example, to obtain a direction of alignment of the nematic molecules which is coincident with the direction of rubbing, as described in [1] and [2].
• This first type of treatment makes it possible to obtain surfaces with a uniform texture.
• This modeling is based on a relaxation process of excess elastic energy in the volume associated with the morphology of the anisotropic surface obtained by the rubbing process.
• Anisotropic surfaces can also be obtained by means of an oblique deposition of SiO on a solid substrate, produced under vacuum and finely controlled.
• This technique it is possible to obtain different types of anchors (planar monostable, oblique monostable and oblique bistable).
• the type of anchoring obtained depends on the deposition parameters, essentially on the thickness of the SiO layer and the deposition angle.
• the anchoring properties on the surfaces obtained by this latter technique can be part of a generalization of the Berreman model.
• a more recent surface treatment technique is linear photopolymerization (PPL).
• a photosensitive polymer film is, according to this technique, polymerized by means of linearly polarized UV light.
• the resulting anchoring direction is usually perpendicular to the polarization direction of the incident UV light, as mentioned by M. Shadt et al. ([6]).
• bistable display devices have been proposed controlled by flexoelectric effect (see documents PCT / FR91 / 00496, WO92 / 00546 and US-5 357 358), or by electrochiral effect (see documents PCT / FR91 / 00052 and W091 / 11747).
• bistable device An example of a bistable device can also be found in French patent application FR-95 13324 "bistable display device based on nematic liquid crystals allowing shades of gray”.
• This device is based on the creation of an erasable network of surface defects on a suitable substrate. It uses a weak azimuth anchor constituting a quasi-bistable planar anchor. This type of anchoring is obtained from a monostable surface having an easy axis n 0 which corresponds to a very flat minimum of surface energy. The slightly oblique anchoring directions with respect to n 0 therefore correspond to nematic surface states having only an energy slightly greater than the minimum energy corresponding to an orientation of the nematic along the easy axis n 0 .
• the topology of this type of anchoring allows electrical control (creation or removal) of surface defects ( ⁇ walls), these defects acting as depolarizers for light.
• the operating mode of these different devices is based on the possibility of switching between two (or more) different optical states corresponding to different configurations of surface directors and therefore to different volume textures.
• the fact that the change in optical state of the cell is linked to a change in the state of the nematic on a surface makes it possible to obtain excellent performance in terms of electrical response time. Indeed, the surface dynamics are faster by an order of magnitude than the volume dynamics of the nematic liquid crystal, previously used in nematic devices.
• bistable anchors The possibility of improving the technology of nematic liquid crystal devices using bistable anchors today depends on the development of a new surface treatment which produces surface bistability and which is easily operable in an industrial process.
• the present invention proposes to meet this expectation More generally, it provides a surface treatment which makes it possible to obtain azimuthal bistable anchors, planar quasi-bistable anchors or inclined anchors for nematic liquid crystals in which the anchoring direction or directions are finely controlled
• liquid crystal cell comprising at least one plate with controlled anchoring, comprising at least two superimposed layers each having an alignment effect on the nematic molecules located in the vicinity of the same surface. of the plate, these two layers not having the same direction of alignment
• Other techniques for obtaining surfaces with bistable anchors for nematics have been proposed
• a process proposed according to the invention is a process for producing a plate with controlled anchoring on its upper face, in which the following steps are carried out: a) production of a first layer capable of producing a first alignment effect on its upper face in a first planar direction; b) deposition on this first layer of a second layer capable of producing, optionally after an additional treatment, a second alignment effect on its upper face in a second direction different from the first, the second layer being capable of transmitting on its upper side part of the first alignment effect induced by the first layer.
• FIG. 1 is a sectional view of a plate according to the invention, the section plane being perpendicular to the mean plane of the plate and parallel to a main vector of undulations of a lower SiO layer according to the present invention;
• - Figure 2 shows an orthonormal coordinate system linked to a nematic display device according to the invention, in which there is an orientation director of nematic surface molecules;
• - Figure 3 is a graph illustrating the dependence of an azimuthal anchoring direction of nematic molecules as a function of a duration of exposure of a plate according to the invention to polarized UV light;
• FIG. 4 is a photograph of a bistable cell according to the invention, observed between two crossed polarizers and in which the optical axis of a straight region is aligned with one of the two polarizers;
• FIG. 5 is a photograph of the same bistable cell, rotated so that a light extinction condition is obtained for a region on the left.
• anchoring competition means that the direction of the nematic surface molecules results from the effect exerted by several anchoring sources corresponding to different anchoring directions. As it is reported in the document [10], in the case of zenital anchors, a competition of anchors results in changes of orientation which are second order.
• FIG. 1 shows a bistable anchor plate 100 according to the present invention.
• the bistable plate 100 is one of the two opposite plates of a sandwich cell of known type.
• the second plate of this sandwich cell not shown, is for example a homeotropic anchoring plate.
• This type of structure is commonly called a "hybrid" structure.
• the bistable plate 100 can also be part of any type of liquid crystal cell.
• the first plate of a sandwich cell whose second plate is a bistable anchoring plate which is identical to it, or whose second plate is monostable with finely controlled anchoring in accordance with the invention, the relative orientations of the anchors of the plate 100 and of the second plate of the sandwich cell which can be adapted as a function of the desired effect.
• the plate 110 is preferably an isotropic confinement plate made of conductive ITO glass.
• the plate 110 is provided according to the invention with a two-layer coating
• the first layer is a layer of SiO, referenced 120, which has surface grooves which extend perpendicular to the section plane of FIG. 1, laterally offset one with respect to to the other according to a constant deviation ⁇ .
• the second layer is a film 130 of photopolymer deposited on the layer 120 of SiO.
• the SiO layer 120 is produced according to a known mode of vacuum deposition, with a deposition rate of 5 A / s and with an angle of 75 ° between the deposition beam and the normal to the surface of the glass plate 110 using a quartz balance perpendicular to the deposition beam and a deposition time of approximately 20 seconds.
• such a deposit gives rise to a layer consisting of an alternation of longitudinal bosses 124 and longitudinal depressions 126.
• the bosses 124 and the depressions 126 are directed in the same main direction contained in the plane of the glass plate 110. This main direction is perpendicular to the SiO beam during deposition.
• the distribution of the longitudinal bosses 124 and the depressions 126 perpendicular to this main direction is uniform. Two consecutive boss peaks 124 are thus always separated by the same distance ⁇ , at any point on the plate 100.
• the points of maximum depth of two consecutive longitudinal recesses 126 are separated by this same distance ⁇ .
• the morphology of the layer 120 thus obtained is therefore uniform and unidirectional.
• Each boss 124 and depression 126 has a substantially rounded contour, and each time has symmetry with respect to a central plane
• An amplitude A of this sinusoidal curve is defined as being the distance measured vertically between one of its vertices and one of its points of maximum depth.
• Such a substrate 120 alone would constitute a unidirectional planar anchoring surface, in said main direction, for a usual nematic material.
• the anisotropy of the SiO film as well obtained could be revealed by a well defined uniform planar alignment, perpendicular to the SiO deposition beam ([9]).
• the upper surface of the layer 120 is therefore flat enough to allow good deposition of the polymer film produced on a roll.
• the photopolymer constituting layer 130 is a PVMC (Poly
• the layer 130 of polymer thus deposited does not have an absolutely constant thickness.
• the thickness of the layer 130 is greater in the depressions 126 than at the vertices 124, so that the polymer tends to fill the depressions 126.
• the upper surface 132 of the layer 130 also has a sinusoidal contour in the plane of the figure 1.
• This sinusoidal contour 132 has an amplitude Aeff, measured in the same way as that of the layer 120 of SiO, which is substantially less than the amplitude A of the layer 120. This amplitude Aeff is uniform over the surface 133.
• the upper curve 132 is, like the curve 122, substantially sinusoidal, of the same wavelength ⁇ , Aeff is therefore the effective amplitude of the curve 132 or, in other words, of the surface grooving taking into account the fact that the Polymer film 130 smooths the initial topography of the SiO 123 surface.
• the morphology of the surface 133 of the layer 130 therefore differs from that of the layer 120 in that its amplitude Aeff is smaller.
• the polymer layer 130 is then linearly polymerized, so as to induce a nematic attraction in the direction perpendicular to that of the coating of SiO.
• Such an anchoring force in a direction perpendicular to said main direction is preferably obtained by photopolymerization linearly polarized in said main direction of the plane of the plate 110.
• the duration of exposure of the layer 130 to UV will depend on the anchoring force sought.
• the linear photopolymerization of the PVMC film was carried out by exposure to broad spectrum ultraviolet light emitted by three 15 watt OSRAM fluorescent lamps, referenced HNS-OFR. These samples to be treated were placed at a distance of approximately 10 cm from the lamps. The incident light was linearly polarized using an Oriel 27320 UV dichroic polarizer.
• the plate 100 constitutes the lower plate of a hybrid sandwich cell
• the upper plate not shown, is produced from a plate of conductive ITO glass, coated on its face lower DMOAP (dimethyl-octadecyl-3- (trimethoxysilil) propylammonium-chloride), so as to obtain a homeotropic anchoring.
• DMOAP dimethyl-octadecyl-3- (trimethoxysilil) propylammonium-chloride
• a bistable anchoring plate in accordance with the invention can be used in the composition of any other device using these bistable anchoring properties of nematics.
• An anchoring competition is therefore obtained between two superimposed anisotropic films 120 and 130 each having an alignment effect, and coating the same isotropic substrate 110.
• the layer 130 of polymer has an average thickness I.
• I the average thickness of a range critical I thicknesses in which there is a bistable anchor in two degenerate directions.
• an X axis coincides with the planar orientation direction referenced P, induced by the layer 120 of SiO, that is to say the main orientation of the plate of SiO 120.
• the Y axis coincides with the planar orientation induced by the linear photopolymerization process, referenced L, and the axis Z is directed towards the volume of the nematic material 150 perpendicular to the plane of the glass plate 100.
• nematic 150 / plate 100 we can then define, as shown in FIG. 2, an azimuthal angle ⁇ between the nematic director n and the x axis parallel to the planar orientation direction induced by the SiO layer.
• k is the elastic constant of the volume of nematic crystal 150.
• w S ⁇ o can be modulated by varying I
• the anchoring force exerted by the photopolymer film 130 on the nematic liquid crystal 150 depends on the duration of exposure to UV, which is thus used as a control parameter to modulate the azimuthal orientation of nematic liquid crystals
• w s , o> 0 means that the orientation induced by the layer 120 of SiO is parallel to the X axis (direction P), while w P ⁇ ⁇ > 0 means that the polymer layer 130 tends orient the director along the Y axis (direction L)
• the term 1 / 4.b.in 4 ⁇ introduced by AL Alexe-lonescu et al. ([13]) is typical in the case of disordered surfaces. It is linked to the effect of the random distribution of molecules in the orientation film 130.
• the model gives a degenerate solution ⁇ ⁇ in two directions.
• the azimuthal surface anisotropy induced by the linear photopolymerization (PPL) process is a non-monotonic function of the exposure time.
• the thickness of the film 130 of photopolymer was controlled by varying the concentration of PVMC in a suitable solvent such as an NMP: N-methyl Pirrolidone and the thickness actually obtained has been verified by an ellipsometry technique ([12]).
• the inventors have found that with a concentration of PVMC of 0.2%, the nematic alignment always corresponds to the direction P, whatever the time of exposure to UV: the nematic anchoring is imposed by the layer of SiO .
• the inventors have found a first critical thickness l c of the layer 130 of approximately 30 A, corresponding to a PVMC concentration of 0.25%.
• the inventors found that with a concentration of PVMC of 0.3%, which defines a second critical length l s of approximately 100 A, the nematic alignment always corresponds to the direction L after exposure to UV. Without UV treatment, a degenerate primary orientation of the non-critical liquid crystal is obtained from this thickness.
• I s and l c depend on the polymeric material and the roughness of the anisotropic SiO layer.
• the average thickness must be in the case described here between 30 A and 100 A.
• a range of thicknesses of the photopolymer layer giving rise to such a result may have a lower limit l c of a few tens of Angstroms and an upper limit l s of a few hundred Angstroms.
• Figures 4 and 5 are two photographs of a bistable plate.
• the invention is not limited to the specific case of plates with bistable or quasi-bistable anchors, but extends to the case of plates with controlled monostable anchoring.
• the inventors also carried out experiments in the case where the angle between P and L is not perpendicular.
• the inventors have chosen for example an angle of approximately 45 ° between P and L. In this case they have also found a change in the angle ⁇ which evolves from the direction P towards the direction L when the exposure time UV increases, with a thickness of photo-polymers between l c and l s .
• This possibility of controlling the direction of a monostable anchor is particularly useful in any type of cell where there is a need for a monostable anchor plate whose orientation is finely controlled.
• a possibility of obtaining a quasi-bistable anchoring is given, in the previously described case of a photo-polymer layer 130 on an anisotropic substrate 120, by a bistable alignment very close to that of the lower substrate 120.
• the method according to the invention for obtaining anchors of bistable or quasi-bistable nematic liquid crystals is based on the concept of anchoring competition between two alignment sources having different types of interaction with the liquid crystalline material.
• bistable anchors which can be obtained by this method are suitable for use in a bistable nematic device flexo-electrically controlled (document PCT / FR91 / 00496, document WO92 / 00546, patent US-5,357,358), in a bistable nematic device controlled by electro-chiral effect (document PCT / FR91 / 00052, document W091 / 11747) and in any other bistable electro-optical device based on the nematic surface bistability.
• planar quasi-bistable nematic anchors such as those required in the device of the document Bistable display device based on nematic liquid crystals allowing shades of gray can also be obtained.
• the inventors used a coating of SiO 120 deposited under vacuum as the first competitive alignment layer, the implementation of the invention does not necessarily require such treatment. Any other anisotropic substrate on which it is possible to deposit a second thin anisotropic film can be used. Mechanically rubbed substrates could be good candidates provided an appropriate roughness is reached.
• the second competitive alignment layer is constituted by an organic coating film 130 photo-polymerized by UV (PVMC or similar), which can be sprayed or applied by spin coating on the glass substrate.
• PVMC photo-polymerized by UV
• This film may be substituted by any other anisotropic film sufficiently thin to allow the anchoring competition.

Landscapes

• Physics & Mathematics (AREA)
• Nonlinear Science (AREA)
• Chemical & Material Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Mathematical Physics (AREA)
• Liquid Crystal (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=9506554

Family Applications (1)

Country Status (4)

Family Cites Families (3)

• 1997
  • 1997-05-02 FR FR9705466A patent/FR2762915B1/fr not_active Expired - Fee Related
• 1998
  • 1998-04-30 WO PCT/FR1998/000878 patent/WO1998050820A1/fr not_active Application Discontinuation
  • 1998-04-30 EP EP98922910A patent/EP0910812A1/de not_active Withdrawn
  • 1998-04-30 JP JP10547773A patent/JP2000513836A/ja active Pending

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events