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
  • G02F1/133—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
• • 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
• • 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
• • 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
  • G02F1/1396—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 the liquid crystal being selectively controlled between a twisted state and a non-twisted state, e.g. TN-LC cell
  • G02F1/1397—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 the liquid crystal being selectively controlled between a twisted state and a non-twisted state, e.g. TN-LC cell the twist being substantially higher than 90°, e.g. STN-, SBE-, OMI-LC 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
  • G02F1/137—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
  • G02F1/141—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 using ferroelectric liquid crystals

Definitions

• the present invention relates to optical devices using liquid crystals. 5.
• the present invention was made in the Laboratory of
• the present * invention now aims to propose new means for defining, simply, reliably and economically, an oblique inclination of the liquid crystal molecules relative to a plate of the device.
• the present invention which is based on numerous theoretical studies and experimental observations, proposes for this purpose to define on a plate " of the device, a roughness of the order of molecular magnitude of the liquid crystal considered.
• the roughness thus defined on the plate of the device will be of the order of magnitude from 20 to 40 A.
• the inventors have determined that such roughness results in an order parameter gradient which induces an ordoelectric polarization, associated with a depolarizing field which tends to force the molecules of the crystal in an oblique orientation relative to the plate. More precisely still, by extending their research, the inventors have determined that, by defining a preferential direction of roughness, for example by depositing on the plate a rough coating by evaporation in a determined direction, it was possible to obtain both. controlled oblique orientation and azimuthal orientation of the liquid crystal, relative to the plates.
• the oblique orientation and the azimuthal orientation of the liquid crystal evolve continuously, in an obi plane relative to the plates as a function of the thickness of the roughness and of its preferential direction, that is to say in the case of an evaporation as a function of the direction of incidence.
• a bistable display with very low energy consumption can be obtained using a device comprising two parallel transparent plates, and a material comprising liquid crystal molecules placed between the two plates, at least one plates having on its surface adjacent to the liquid crystal a roughness of the order of molecular magnitude of the liquid crystal, the thickness and the orientation of the roughness being adapted to define two possible azimuthal orientations of the molecules of the liquid crystal, symmetrical with respect to to the preferred direction of roughness and of the order of 45 ° relative to this direction, and means making it possible to apply an electric field external to the device to cause the controlled tilting of the molecules from one azimuth orientation to the other.
• Document US-A-4 601 544 relates to a liquid crystal device having a bistable volume effect.
• Document FR-A-2 308 675 relates to micromachining, by means of an ion beam, of a coating deposited on the substrate of a liquid crystal cell.
• FIGS. 1 to 4 show, for four experiments, the azimuthal orientation Y and the oblique bearing ⁇ of the liquid crystal as a function of the angle of evaporation and the thickness of a deposit made on a plate,
• FIGS. 7, 8 and 9A, 9B schematically illustrate three applications of the invention , to nematic liquid crystal devices, and
• FIG. 10 shows curves illustrating the evolution of the oblique or ⁇ tion of a smectic liquid crystal, on each of the two faces of the device, depending on a thickness of SiO deposited.
• the present invention is based on the following theoretical analysis.
• Nematic liquid crystals can be considered as liquids of oriented electric quadrupoles for which one can write: relationship in which:
• - S represents the order parameter of the liquid crystal (S is between O and 1)
• - n is the unit vector representing the orientation of the molecules.
• the inventors proposed the idea of controlling the order parameter S, on the surface of a liquid crystal device, by depositing on a plate of the device small grains whose size is of the order of magnitude of the molecular size of the liquid crystal considered, that is to say of l '' from 20 to 40 A.
• the inventors have controlled the orientation of the liquid crystal for different pairs of evaporation angle and thickness of the deposited grains.
• the inventors have found that achieving a rough surface state by evaporation in a determined direction makes it possible to obtain not only an oblique orientation of the liquid crystal molecules relative to the plates, but also an azimuthal orientation which is controlled and variable with respect to to the direction of evaporation.
• the first results obtained are recorded in Figures 1 to 4 and 6 attached. These results are illustrated with reference to the geometric model represented in FIG. 5.
• This geometric model includes a coordinate system with three axes x, y and z, orthogonal to each other.
• the axes x, y extend parallel to the plate P considered.
• the z axis extends perpendicular to this plate P, in the direction of the volume of the liquid crystal.
• the direction of evaporation arbitrarily coincides with the plane defined by the x and z axes.
• the incidence of the direction of evaporation, which corresponds to the inclination between the direction of evaporation and the z axis is defined by the angle.
• the oblique orientation of the liquid crystal which corresponds to the inclination between the z axis and the longitudinal axis of the liquid crystal molecules is illustrated by the angle ⁇ in FIG. 5.
• the complement of this angle ⁇ is referenced ⁇ .
• the azimuthal orientation of the liquid crystal which corresponds to the inclination between the x axis and the projection on the xy plane of the longitudinal axis of the molecules is illustrated by the angle referenced ⁇ in FIG. 5.
• the evaporation angle c a gradual azimuthal rotation of the molecules in an oblique plane with respect to the plate P.
• the liquid crystal then passes from a domain for which the azimuthal orientation ⁇ equals 90 ° to an azimuthal domain for which can reach 0 °, that is to say a domain for which the molecules are oriented substantially parallel to the xz plane containing the direction of evaporation.
• azimuthal is accompanied by an increase in molecules; when T gradually goes from 90 ° to 0 °, ⁇ goes from 0 to about 20-30 °.
• the hatched range in FIG. 1 corresponds to the range of values of the evaporation angle c. and of the thickness of evaporation for which the azimuthal orientation varies progressively between 90 ° and 0 ° and the oblique orientation ⁇ varies progressively between 0 and approximately 20-30 °.
• FIG. 2 relates to tests carried out under the same operating conditions, that is to say deposition by evaporation of SiO on ordinary glass, for different values of evaporation angle and thickness of deposition, but with the difference of Figure 1, using liquid crystal 5 CB instead of MBBA.
• Figures 3 and 4 similarly represent the value of the azimuthal orientation as a function of the angle of evaporation o (and the thickness of deposition of SiO, on an ITO plate, respectively for liquid crystal MBBA d ' on the one hand, and 5CB on the other.
• Figures 2, 3 and 4 like Figure 1 above, reveal a range (hatched in the figures) of pairs of values, evaporation angle ⁇ (/ thickness of deposit, for which the orientation azimuthal ⁇ ? gradually goes from 90 ° to 0 °.
• FIG. 6 represents the simultaneous evolution of the azimuthal orientation T and of the oblique orientation ⁇ as a function of the thickness of a deposit of SiO evaporated on an ITO plate with an incidence p. 74 °, using a 5CB liquid crystal.
• the azimuthal orientation ⁇ passes progressively from 90 ° to 0 ° for a thickness of deposit substantially between 30 and 40 A.
• the oblique orientation ⁇ gradually rises from 0 to 20 ° for an evaporation thickness ranging from 30 to 40 A.
• the tests carried out by the inventors have made it possible to observe that the bare substrate, before evaporation, promotes a planar orientation, that is to say parallel to the surface, but degenerate.
• the average evaporated amount (of SiO) reaches 5 A, the azimuthal degeneration is lifted, but the anchoring remains planar.
• the nematic which turns in a oblique plane from its initial planar position, perpendicular to the direction of evaporation, to an oblique position towards the direction of evaporation.
• achieving a rough state on the plates capable of generating an order gradient, and from there thanks to the induced ordoelectric polarization, to request a raising of the liquid crystal in an oblique orientation orientation relative to the plates, can be operated by means other than evaporation, such as for example, by chemical attack, spraying, or even ion bombardment.
• the inventors have moreover determined that the molecules of the liquid crystal are capable of taking two symmetrical azimuthal orientations with respect to the plane xz containing the direction of evaporation.
• FIG. 8 We have thus schematically illustrated in FIG. 8 two azimuthal orientations symmetrical with respect to the plane xz defined by the direction of evaporation.
• the evaporation angle ⁇ and thickness evaporation on a plate so that the azimuthal orientation with respect to the xz plane is in the range of 45 ° T, it is easy, by applying an external electric field provoke the controlled tilting of the molecules from an azimuthal orientation to the other on said plate.
• both electrodes or plates have a state of
• a planar and parallel anchoring is defined on the two plates of the device, as illustrated in FIG. 9A.
• the angle of evaporation ⁇ (and the thickness of evaporation of a deposit are checked to place the liquid crystal in the vicinity of the hatched transition range in FIGS. 1 to 4.
• the liquid crystal is thus placed in the vicinity of an instability threshold, that is to say in the vicinity of an azimuthal tilting threshold.
• This arrangement facilitates the tilting of the liquid crystal towards a helical formation, by application of an external electric field, as is known per se and as illustrated diagrammatically in FIG. 9B
• Ferroelectric smectic C displays when they have a degenerate surface anchoring, theoretically allow two positions of symmetrical molecules with respect to the smectic layers. In one of these positions, the electric dipole of the molecules is oriented towards the electrode, in the other position, it is oriented towards the volume, by an external applied field. In theory, these two positions should be equivalent and allow the realization of bistable displays.
• the present invention makes it possible to cancel the chemical polarization by virtue of an ordoelectric polarization induced by the creation of a gradient of nematic order, in the smectic phase, of suitable sign and amplitude.
• FIG. 10 illustrates the orientation 0, - of the liquid crystal thus obtained on the lower and upper device plates for different thickness values of a deposit of SiO operated by evaporation at an incidence ⁇ of 81 ° on ITO plates separated by 3 ⁇ m, respectively for temperatures of 55 ° C and 48.0 ° C.

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• 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)

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• 1987
  • 1987-12-17 FR FR8717660A patent/FR2624985B1/fr not_active Expired - Fee Related
• 1988
  • 1988-12-16 JP JP50076389A patent/JPH03502969A/ja active Pending
  • 1988-12-16 EP EP19890900833 patent/EP0393128A1/de not_active Ceased
  • 1988-12-16 WO PCT/FR1988/000623 patent/WO1989005993A1/fr not_active Application Discontinuation

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