Classifications

• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
  • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
  • G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
  • G09G3/36—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using liquid crystals
  • G09G3/3611—Control of matrices with row and column drivers
  • G09G3/3622—Control of matrices with row and column drivers using a passive matrix
  • G09G3/3629—Control of matrices with row and column drivers using a passive matrix using liquid crystals having memory effects, e.g. ferroelectric liquid crystals
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K19/00—Liquid crystal materials
  • C09K19/52—Liquid crystal materials characterised by components which are not liquid crystals, e.g. additives with special physical aspect: solvents, solid particles
  • C09K19/58—Dopants or charge transfer agents
• • 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
  • G02F1/137—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
  • G02F1/13781—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 using smectic liquid crystals
• • 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
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2300/00—Aspects of the constitution of display devices
  • G09G2300/04—Structural and physical details of display devices
  • G09G2300/0469—Details of the physics of pixel operation
  • G09G2300/0478—Details of the physics of pixel operation related to liquid crystal pixels
  • G09G2300/0482—Use of memory effects in nematic liquid crystals
  • G09G2300/0486—Cholesteric liquid crystals, including chiral-nematic liquid crystals, with transitions between focal conic, planar, and homeotropic states
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2310/00—Command of the display device
  • G09G2310/06—Details of flat display driving waveforms

Definitions

• the present invention relates to the field of liquid crystal optical devices.
• the present invention was made at the Laboratory of Solid State Physics of the University of Paris Sud, laboratory associated with the NATIONAL CENTER FOR SCIENTIFIC RESEARCH number 04 0002.
• the present invention relates more precisely to so-called bistable liquid crystal optical devices, that is to say devices in which the molecules of liquid crystals are capable of alternately occupying two stable states, under the effect of an external command. .
• bistable optical devices lend themselves in particular to the production of multiplex displays.
• Cheng et al describes for example a nematic liquid crystal device having two volume stable states switched by an external electric control field. The process described in this document has not been applied in practice. It has a very slow switching time and generally reveals many texture defects. Applied Physic Letters 36, 899 (1980), NA Clark et al describes another bistable optical device using crystals
• the present invention now aims to provide a new bistable liquid crystal optical device having better performance than the prior art.
• An important object of the present invention is to provide a bistable optical device with fast switching liquid crystal.
• Another important object of the present invention is to provide a bistable liquid crystal optical device designed to be easily controlled by an external electric field.
• Means capable of applying, to the device, electric field pulses perpendicular to the plates, oriented alternately in one direction then in the other.
• the device comprises electrical supply means designed to apply successively to the device:
• control pulse of lower amplitude than the control signal, and of polarity chosen according to the required final state.
• the optical device in which the control electrodes are arranged in N rows and M columns defining a matrix of NM pixels at their intersections, is characterized in that the control signals are applied successively to the N row electrodes, while at the end of each control signal, control pulses of respectively chosen polarity are applied simultaneously to all of the M column electrodes.
• the pulses necessary for multiplexing the liquid crystal device are thus much simpler than those used in the past, in particular for the multiplexing of ferroelectric smectics C *.
• control signal can comprise two successive square pulses of opposite polarity or else comprise a series of high frequency pulses.
• the amplitude of the control signal is between 1 and 100 volts, typically between 10 and 20 volts, while the duration of the control signal is greater than l ⁇ s, typically between 20 and 50 ⁇ s.
• the amplitude of the control pulses is between 0.1 and 10 volts, typically between 0.1 and 5 volts, while the duration of the control pulses is greater than 10 ⁇ s, typically between 0.1 and 10 volts.
• the start of the control pulses may coincide with the end of the control signal.
• the start of the control printouts can precede the end of the control signal.
• control pulses persist after the end of the control signal for at least 10 to 50 ⁇ s.
• FIG. 1 represents a general schematic view of an optical device according to the present invention
• FIG. 7 schematically represents an example of control signals and control signals in accordance with the present invention
• FIG. 8 represents in table form, the various states obtained as a function of the control signals applied
• FIG. 9 schematically represents a matrix display controlled by multiplexing in accordance with the present invention.
• FIG. 10 represents a general schematic view of an alternative embodiment of an optical device according to the present invention.
• FIG. 11 and FIG. 12 schematically represent two textures capable of being occupied by the liquid crystal molecules in the context of this variant
• the known basic structure of the optical device used comprises, as shown diagrammatically in the appended FIG. 1, a cell 10 formed by two parallel transparent plates 12, 14, for example made of glass, separated by a shim of constant thickness (not shown in the figure 1) and between which is placed a liquid crystal material 20.
• the plates 12, 14 are provided on their internal facing surfaces, adjacent to the liquid crystal, with electrically conductive and optically transparent electrodes. Such an electrode is shown diagrammatically in the form of a strip 18, for the plate 14, in FIG. 1.
• the homologous electrode provided on the plate 12 is referenced 19.
• Electrical supply means 30 are connected between the electrodes provided on the two plates 12, 14, to apply a controlled electric field to the liquid crystal material 20.
• the optical device according to the present invention has three essential characteristics:
• liquid crystal molecules are capable of alternately occupying at least two states
• the power supply means 30 are coupled to the electrodes 18, 19 so as to apply to the device electric field pulses perpendicular to the plates, oriented alternately in one direction then in the other.
• Bistability can have different origins.
• the bistability may be due to a surface treatment of the plates 12, 14.
• This surface treatment can be formed for example by the deposition of a polymer on the internal surfaces facing the plates 12, 14 followed by two rubs of the polymer inclined between them.
• the surface treatment can be formed by controlling the roughness of the surface of the plates 12, 14 (controlling the thickness of the roughness and its average incidence or average wavelength) as taught in French patent application n ° 87 17660 published under the number 2624985.
• the bistability may also be due to the properties of the liquid crystal; they may, for example, be non-ferroelectric Smectics C. Bistability can also be obtained by the combination of a surface treatment associated with the properties of the liquid crystal.
• the liquid crystal 20 used in the context of the invention can be a nematic, a choesteric, a non-ferroelectric C smectic or a ferroelectric C smectic.
• the sign of chirality is defined by the sign of the choiesteric helix obtained by dissolving the chirai ion in the nematic liquid crystal 5CB, as explained in document 3.
• This document shows that one can shift the chiraiity in volume under the action of a continuous electric field but does not reveal the transient action on the surface on the bistable surfaces due to electric field pulses.
• the chiral ions added to the liquid crystal can be formed from many known compounds having chiral properties. Among these compounds, there may be mentioned as examples:
• the orientation of the liquid crystal molecules is controlled on the surface and not in volume, by application of the electric field pulses by the means 30.
• the chiral ions In the absence of an electric field, the chiral ions, electrically compensated by their counterions, form a homogeneous and neutral whole in a liquid crystal cell 20 placed between the two plates 12, 14.
• the liquid crystal material is a nematic, that a single type of chiral ion is used and that the plates 12 and 14 are treated to favor a planar anchoring, parallel to the electrodes, in a direction p
• the nematic becomes a choiesteric, that is to say has a spontaneous twist.
• this twist corresponds to a complete revolution of the azimuth (measured in the plane of the electrodes with respect to " p) for the thickness d between the plates 12, 14.
• the angle ⁇ (d) is then a simple linear dependence as shown in solid lines in FIG. 2.
• the chiral ions are entrained towards one of the electrodes, according to their polarity, where they accumulate over a thickness a "d.
• T is typically equal to K / L where L is of the order of 5 S
• r> T is expressed by the condition: K (2 ⁇ ) 2 / a> K / L i.e. a ⁇ (2 ⁇ ) 2 L or a r- L.
• V> V s (d 2 / a 2 ) (K (2 ⁇ ) 2 / ⁇ ⁇ ) _. ( d 2 / ⁇ X)
• the characteristic times of nematics or cholesterics are 1 ms for lengths o characteristic a of l ⁇ m.
• a L ⁇ 0.1 ⁇ m (1000A)
• V is thus of the order of V ⁇ (d 2 / ⁇ x) ⁇ V (10 ⁇ 8/10 ⁇ 5 ) 10 ⁇ 5 ⁇ »100 Volt
• the threshold V is in principle independent of the concentration since it is linked only to the transport phenomenon.
• the influence of the concentration of chiral ions is hidden in the initial angle of rotation of the cell (2 ⁇ in the example given here) which corresponds to a concentration C. chiral ion.
• the ions are concentrated in a thickness a.
• the step of the choiesteric in this region is a / x.
• the density couple kx 2 / a 2 integrated into the thickness a gives a surf torque ace r> x 2 Tmax.
• V C 0 (a / L).
• the described principle of surface tilting controlled by electrical pulses allows rapid control of the state of a liquid crystal cell.
• the information writing time will be compared to T (OlO ⁇ s).
• the liquid crystal texture in volume follows the change in surface orientation with its own time ⁇ ", * ⁇ > ⁇ d 2 / K ( ⁇ r) 2 , longer than since d> L.
• the cell behaves like an integrator of time constant adjustable by the thickness d.
• a nematic liquid crystal can be doped with two kinds of chiral ions to achieve an electrically and mechanically neutral mixture.
• ions can be obtained from a "bi-chiral" molecule (containing for example two asymmetric carbons) soluble in organic medium, easily dissociable, and of which the two ions and against ion (ie of opposite electrical polarities ), are each chiral and chirally opposite to each other (no screw on the left and no screw on the right).
• a "bi-chiral" molecule containing for example two asymmetric carbons
• organic medium easily dissociable
• the two ions and against ion ie of opposite electrical polarities
• the two electrodes 18 and 19 are treated to give two possible directions of molecular orientation p and p ′ parallel two by two from one plate to the other, and at 45 ° one of the other on the same plate.
• the electric field E is zero.
• the system is a nematic oriented uniformly in a first state along p. This state is stable.
• the chiral ions are quickly moved against the electrodes, the positive ions to the cathode and the negative ions to the anode. They create couples of surface T of opposite signs with respect to each normal oriented to each respective surface since their chiralites are opposite, but of the same sign with respect to a common reference system. This sign corresponds to the easy rotation which brings p on p ', at 45 °.
• a reverse torque is applied to the liquid crystal molecules, the system returns to the p state at the surface.
• the final orientation state of the nematic in volume is the initial uniform p stable state.
• the system is bistable. b) Waveguide mode.
• Cells containing a dichroic dye whose absorption depends on the angle with the polarization of the light, can be controlled by surface rotation. d) Multi-mode operation.
• multistable electrodes defined by anchoring directions " p, p ', p", etc.
• a series of electric field pulses of the same sign will rotate the system from p to p 'then p ".
• a series of electric field pulses of opposite sign will cause the system to return to p.
• a first voltage pulse V makes it possible to pass from pa p '.
• a second voltage pulse V of the same polarity allows to go from p 'to p ".
• a voltage pulse of reverse polarity -V allows to go from p" to ⁇ p * '.
• a second voltage pulse -V with the same polarity as the last pulse cited, makes it possible to go from p 1 to p.
• the electrical sign is chosen so that the ions are transported by the display field towards the electrode which does not turn over, for example towards the electrode which remains in the state p during a desired tilting from pp to p'p '.
• the direction of chirality is also chosen so that the surface torque transmitted on the defective electrode changes from p to p' in the easy direction to 45 °.
• the concentration of chiral ion is adjusted so that the polar effect disappears.
• NON-FERROELECTRIC C BISTABLE SMECTIC DISPLAYS The bistability of the display in two states as proposed by Lagerwaal and Ckark with ferroelectric Cs in Applied Physics Letters 36, 899, (1980) is also a potential property of non-ferroelectric C smectics. The problem with these smectics is however that so far we did not know how to control them electrically to pass from one state to another.
• 5CB ambient nemati ⁇
• BBQ benzyl quininium bromide
• APL phenyl lactic acid
• the concentrations of BBQ and APL were 0.5% and 1.8% respectively.
• the cell had a thickness of 6 ⁇ m, in waveguide mode having a bistable surface and a monostable surface.
• the bistable surface was obtained by an evaporation of SiO near the transition region, as indicated in the document Monkade, Boix, Durand, Europhysics Letters, 5, 697 (1988) in one case and by two evaporations crossed SiO at 45 ° in another case.
• the second monostable orientation was obtained conventionally by evaporation of thick SiO at 60 °.
• the electrodes were conventional ITO on glass. (Baitracon de Balzens). Before the application of an electric field, the cell showed two kinds of domains confirming the existence of two possible surface states on the bistable electrode.
• the inventors observed a surface tilt threshold from one bistable state to another, for square pulses of 100V and 40 ⁇ s. The sample then becomes homogeneous, showing the surface orientation selected by the polarity of the last control pulse.
• the light establishment time (i.e. the volume rotation time ⁇ ) is much longer than the time x 40 ⁇ s). It is worth around 50ms, typical time of diffusion of the orientation of
• the inventors also produced a symmetrical cell made of the same mixture of 5 CB + BBQ +
• This curve shows that V decreases slightly when x increases, from 120V at 30 ⁇ s to 80V at 300 ⁇ s, as expected.
• the contrast between crossed polarizers is strong ( ⁇ _> 20) without being optimized.
• the time for establishment of light through the cell was Torde of 50 ms, as in the 1st experiment.
• 5CB which is a dielectrically positive body, tending to align itself along the applied electric field.
• This orientation is used secondarily in the display, to help cross the potential barrier of the surface orientations, weaker for an oblique (or hometotropic) orientation than planar.
• the integration time of the nematic volume can be chosen longer, by adjusting the thickness or the material; it must be compared to the image time r 40ms.
• the system potentially allows the creation of high definition multiplex video matrix displays.
• liquid crystal optical device comprising chiral ions dissolved in the liquid crystal material and electrical supply means capable of applying to the device electric field pulses perpendicular to the plates.
• the device more precisely comprises two kinds of chiral ions chirally opposed to each other (no screw on the left and no screw on the right).
• a voltage pulse is applied between the electrodes of the device, and therefore an electric field is applied perpendicular to the plates, the chiral ions are moved against the electrodes, the positive ions towards the cathode and the negative ions towards the anode .
• the chiralites of these chiral ions are of opposite signs with respect to each normal oriented to each respective surface since their chiralites are opposite, but of the same sign with respect to a common reference system.
• a voltage pulse of given polarity thus makes it possible to pass the liquid crystal from a first stable state into a second stable state.
• a voltage pulse of opposite polarity makes it possible to pass the liquid crystal inversely from the second stable state to the first stable state.
• control signal which generates an electric field normal to the plates, defines a homogeneous, homeotropic orientation, by coupling with the molecules of a crystal material with positive dielectric anisotropy.
• Figure 7 An example of successive command and control signals according to the present invention is shown in Figure 7 attached.
• the control signal Ca is applied at time 1 and ends at time 2. It lasts time x.
• the control signal Ca is formed by a succession of pulses of opposite polarities (two pulses Cal and Ca2 according to FIG. 7) having the function of breaking the anchoring of the liquid crystal molecules on the plates and of defining a substantially homogeneous texture.
• liquid crystal preferably homeotropic, while retaining a substantially homogeneous distribution of chiral ions in the cell.
• the control signal must therefore have an amplitude V which exceeds a threshold V as a function of the time x of application, that is to say
• the amplitude of the control signal Ca is preferably between 1 and 100 volts, typically 10 and 20 volts.
• control signal Ca is advantageously greater than 1 ⁇ s, typically between 20 and 50 ⁇ s.
• the control signal Ca can be a high frequency signal.
• the control signal Ca is followed by a pulse Co, called a control pulse, of amplitude _ + v, less than V s (X).
• of the Co control pulse may be weak. In practice, one can take 0.1 volts ⁇ v ⁇ 10 volts, typically 0.1 volts ⁇ v ⁇ 5 volts.
• the Co control pulse is maintained between times 2 and
• the control pulse Co makes it possible to control the polarity of the field in the cell between instants 2 and 3 where the system will switch from the homogeneous homeotropic orientation obtained by the control signal Ca of amplitude V at time 2, towards one of the states A or B.
• the Co control pulse makes it possible, depending on its polarity, to attract a first type or second type of chiral ions to a first plate and vice versa for the second.
• a positive control pulse Co causes the switching from A to B and a negative control pulse Co causes the switching from B to A.
• control signal Ca of amplitude V breaks the surface orientation
• control pulse Co controls by its sign the final state A or B.
• the switching table obtained is given in FIG. 8 where we have assumed . V. ⁇ V (x).
• a matrix display comprising N row electrodes referenced 18-1 to 18-N on a first plate and M column electrodes referenced 19-1 to 19-M on the second plate.
• Each pixel defined by the intersection of a row electrode and a column electrode is identified by its coordinates i, j.
• the multiplexing method according to the present invention is as follows.
• Each line 18-1 to 18-N, for example line i, is successively opened by exciting it with a control signal Ca of amplitude V (V
• the whole line i is erased, the molecules of the liquid crystal take on a homeotropic orientation.
• control pulses Co of amplitude _ + v are sent in parallel on all the columns M simultaneously, according to the desired state of the different pixels, i, j (1 j M) of the line i.
• the control pulses Co of amplitude + _ v are applied just at the end of the control signal Ca of amplitude V.
• the pixels i, j (1 j ⁇ ) of this line are then placed in states A or B, following the sign of the small control pulse v.
• the Co control pulse persists 10 to 50 ⁇ s after the end of the Ca control signal.
• line i we will successively open lines i + 1, i + 2, etc., which will be erased and rewritten, to draw the new image.
• Each line is therefore successively erased, by a control signal Ca of amplitude V during time x, and rewritten by a control pulse Co of amplitude v during time x 'which follows x.
• the total time to erase and write a line is therefore, according to the aforementioned process: ⁇ + ⁇ ', adjustable by varying the control signal Ca and the control pulse Co.
• the total time to erase and write a complete image is then N (x + ⁇ ').
• bistable display system described above can be multiplexed very simply by the means proposed by the present invention.
• each line electrode is sequentially excited by an AC control signal of amplitude V between 1 and 100 volts, typically 10 and 20 volts of duration greater than 1 ⁇ s, typically between 20 and 50 ⁇ s, which breaks surface orientation and erases the line.
• the final state of the pixels only depends on the polarity of the control pulse Co.
• a new bistable nematic liquid crystal display device has previously been described, using two distinct surface orientation states p and p 'on each electrode, that is to say two non-aligned anchors.
• the switching between these two states is controlled by an electric field pulse which first breaks the surface anchoring, above a threshold value.
• the undoped liquid crystal returns at random to one or the other of the two surface states.
• the degeneration is lifted, the nematic, returning to equilibrium, takes a surface orientation turned from p to p 'with the ion of chirality 0 and from p' to p with l 'ion of chiraiity ⁇ 0.
• the sign of chiralites is linked to the sign of the electric charges of the ions, and therefore to the direction (sign) of the electric field.
• the inventors also propose another variant of the device, similar to the previous one, with regard to bistability, the use of a nematic, its doping with chiral ion and the breaking of surface orientations, using an anisotropy nematic. positive dielectric.
• this variant of the device differs from the previous one, by the fact that it uses simple and not double nematic anchors, but of different strength on the two electrodes. These anchors define two bistable textures in volume, but of different twist. The switching between these two textures is produced by a rotation of 180 ° on a single electrode, by the electrochiral mechanism already described.
• the detection of the optical contrast required for the display is made by using, as the case may be, the rotary power, the ellipticity or the reflection of light.
• the device represented in FIG. 10 comprises a liquid crystal cell 10, doped with chiral ions, and a nonionic choiesteric substance, for possibly adjusting a spontaneous twist of the textures, (see below).
• the electrodes 18, 19 are produced on glass slides 12, 14 treated with ITO, so as to be conductive and transparent.
• the surfaces of the electrodes 18, 19 are treated to obtain a single planar (molecules in the plane of the electrodes) or quasi-planar orientation (oblique molecules, but with projection F defined in the plane). This can be achieved for example by oblique evaporation of SiO, according to a conventional process. It is thus possible to use other methods, for example a rubbed polymer.
• the treatment on the surface of the electrodes must be adapted to obtain a strong planar anchoring on one of the two electrodes 18, 19 (it will be little sensitive to the electric field) and a weaker anchoring on the other electrode (which will be the most sensitive to the electric field). These two almost planar orientations are preferably parallel to each other.
• the inventors carried out tests with a nematic formed of 5CB (pentylcyanobiphenyl) which has a positive dielectric anisotropy and which is therefore oriented along the applied field E.
• the doping in chiral ions consisted of a mixture of 0.21% by mass of phenyl lactic acid and 0.04% by mass of Benzyl quininium bromide.
• the difference between the textures "u” and “t” can be observed by the appearance, in the twisted texture "t", of rotary power and ellipticity for the transmitted light, properties which do not exist for the texture not twisted "u”. This ellipticity and this power are described below.
• the cell is then placed between crossed linear polarizers parallel and perpendicular to the planar direction F.
• the pitch is of the order of magnitude of the optical wavelengths ⁇ , (very thin cell, or ⁇ large (infrared) on can also detect rotation by a total Bragg reflection of circularly polarized light in the texture "t".
• Polarized light is sent to the cell in the direction F of planar orientation of the input face, either the strong or weak anchor face.
• the light is elliptically polarized (figure 13).
• the major axis of the ellipse has turned by an angle B.
• the ellipticity is defined by the angle X of the diagonal of the rectangle which circumscribes the ellipse.
• This device has on each electrode surface a single planar anchor, instead of two separate anchors, and comprises a spontaneously twisted nematic liquid crystal (therefore "choiesteric").
• This liquid crystal cell has two bistable textures (of the same energy), one uniform "u”, the other "t", twisted by half a turn.
• the sign of the twisted twisted texture "t" compared to "u” is controlled by the sign of the spontaneous twist of the choiesteric.
• the simple planar anchors on the two surfaces are chosen with different energies.

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• 1990
  • 1990-09-19 FR FR9011547A patent/FR2666908B2/fr not_active Expired - Lifetime
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