WO2017172578A1 - Dispositifs et procédés à cristaux liquides homéotropes chiraux stabilisés par un polymère à commutation rapide - Google Patents

Dispositifs et procédés à cristaux liquides homéotropes chiraux stabilisés par un polymère à commutation rapide Download PDF

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WO2017172578A1
WO2017172578A1 PCT/US2017/024246 US2017024246W WO2017172578A1 WO 2017172578 A1 WO2017172578 A1 WO 2017172578A1 US 2017024246 W US2017024246 W US 2017024246W WO 2017172578 A1 WO2017172578 A1 WO 2017172578A1
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liquid crystal
substrate
substrates
voltage
psch
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Liang-Chy Chien
Kai-Han Chang
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Kent State University
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    • 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
    • C09K19/586—Optically active dopants; chiral dopants
    • C09K19/588—Heterocyclic compounds
    • 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
    • C09K19/02—Liquid crystal materials characterised by optical, electrical or physical properties of the components, in general
    • 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
    • C09K19/04—Liquid crystal materials characterised by the chemical structure of the liquid crystal components, e.g. by a specific unit
    • C09K19/42—Mixtures of liquid crystal compounds covered by two or more of the preceding groups C09K19/06 - C09K19/40
    • 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
    • C09K19/54—Additives having no specific mesophase characterised by their chemical composition
    • C09K19/56—Aligning agents
    • 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
    • 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
    • C09K19/586—Optically active dopants; chiral dopants
    • 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
    • C09K19/54—Additives having no specific mesophase characterised by their chemical composition
    • C09K19/542—Macromolecular compounds
    • C09K2019/548—Macromolecular compounds stabilizing the alignment; Polymer stabilized alignment

Definitions

  • the present invention relates to a new mode of liquid crystal electro-optical devices. More particularly, the present invention relates to liquid crystal electro-optical devices utilizing surface-localized polymer structures to improve the dynamic response of a chiral homeo tropic mode.
  • Liquid crystals are widely used in flat panel displays because of several benefits such as low power consumption, high resolution, and easy mass panel production with large size.
  • various LCD modes have been developed.
  • a chiral nematic liquid crystal display with homeotropic alignment and negative dielectric anisotropy CH mode
  • Chiral nematic liquid crystal material with negative dielectric anisotropy is injected in liquid crystal cell.
  • the liquid crystal cell is placed between crossed polarizers.
  • the liquid crystal molecules are vertically aligned, which gives a good dark state.
  • the liquid crystal director forms a twist structure and enables the light to pass through.
  • This mode provides excellent contrast ratio because of the good dark state of vertical aligned (VA) mode and has the benefit of achromatic characteristic of twisted nematic (TN) mode.
  • VA vertical aligned
  • TN achromatic characteristic of twisted nematic
  • the present invention provides a polymer stabilized chiral homeotropic (PSCH) mode, that effectively resolves the problems with this LCD mode that resulted in slow rise time.
  • the invention provides liquid crystal electro-optical devices using PSCH mode, which provide a good dark state and fast response speed, obtained by optimizing polymerization conditions such as, the concentration of reactive monomer, light intensity and dosage of polymerization, polymerization with curing voltage to obtain a pretilt angle, and patterned electrodes for wide angle view as well as combinations thereof. Furthermore, the liquid crystal electro-optical devices using the PSCH mode also preserve the benefit of low power consumption, while providing the improved performance.
  • a liquid crystal device comprises a first substrate that is spaced apart from a second substrate by a predetermined distance. At least one electrode is disposed on the inner surface of the first or second substrate. An alignment layer disposed on the first and second substrates, and a liquid crystal material is interposed between the substrates.
  • the liquid crystal material comprises cholesteric liquid crystal molecules of negative dielectric anisotropy.
  • a polymer structure is disposed in the cholesteric liquid crystal material and positioned proximate the inner surface of the first and second substrates.
  • the invention also provides a polymer stabilization method of forming a fast response chiral homeotropic liquid crystal device.
  • the method comprises forming a polymer structure deposited in a liquid crystal cell comprising a first substrate and a second substrate that are spaced apart.
  • a chiral nematic liquid crystal and reactive monomer mixture is disposed between the first substrate and second substrate.
  • the reactive monomer is polymerized in a predetermined manner to form a plurality of polymer fibrils or protrusions on the first substrate and second substrate.
  • the polymerized chiral homeotropic device appears in a dark state when no voltage is applied between electrodes, such as pixel and counter electrodes. The application of a voltage across the cell produces a field-induced twist structure in the chiral nematic liquid crystal to produce a bright state.
  • FIG. 1 is a schematic illustration of field-off/dark state and field-on/bright state of a PSCH mode LCD cell according to an example of the invention.
  • FIGS. 2A-2D are the polarizing optical microscope (POM) images of a CH mode cell at 2A:field-off state and 2B:field-on state (14.5V) and a PSCH mode cell at 2C:field-off state (curing condition: 4V 1kHz, metal halide lamp 35mW/cm , 10-12 minutes) and 2D:field-on state (16.9V).
  • the scalar bar in each are 50 ⁇ .
  • FIGS. 3A-3D are plots of 3A:static voltage response, 3B:cell images of dark and bright states on a light box, with the scalar bar is 5mm, 3C:plots of rise time transmittance curves and 3D:fall time transmittance curves of CH mode and PSCH mode (Curing condition: 4V 1kHz, metal halide lamp 35mW/cm , 10-12 minutes).
  • FIGS. 4A-4F are POM images of field-off state of the PSCH mode polymerized at different applied voltages: 4A:0V; 4B:2V; 4C:3V; 4D:4V; 4E:5V and 4F: 15V.
  • the scalar bar in each are 50 ⁇ .
  • FIGS. 5A-5C are the plots of 5A:static voltage response of PSCH mode polymerized at different applied voltages, 5B:rise time transmittance curves and 5C:fall time transmittance curves of different curing voltages.
  • FIGS. 6A and 6B are SEM images of the surface morphology of the polymerized monomer in the liquid crystal mixture for different curing voltages of 6A:0V, 35mW/cm 2 and 6B: 4V, 35mW/cm 2 .
  • FIGS. 7A-7D are POM images of field-off state of PSCH mode polymerized at different UV intensities of 7A:5mW/cm 2 ; 7B: 15mW/cm 2 ; 7C:25mW/cm 2 and 7D: 35mW/cm 2 .
  • the scalar bars in each are 50 ⁇ .
  • FIGS. 8A-8B are plots of PSCH mode polymerized at different UV intensities: 8 A: rise time transmittance curve 8B:fall time transmittance curve.
  • FIGS. 9A-9B are SEM images of the surface morphology of the polymerized monomer in the liquid crystal mixture for different curing intensity of 9A:4V, 5mW/cm and 9B: 4V, 35mW/cm 2 .
  • FIGS. 10A-10D show POM images of CH and PSCH modes in a patterned- ITO vertical alignment (PVA) cell configuration for 10A:field-off state of CH mode; 10B:field-on state (12.4V) of CH mode; 10C:field-off state of PSCH mode and 10D:field-on state (13V) of PSCH mode, wherein the scalar bars in each are 50 ⁇ .
  • FIG. 10E shows a schematic illustration of electrode pattern and cell structure (PSCH curing condition: 4V 1kHz, settling time 5 minutes before UV curing with a metal halide lamp at 35mW/cm for 10-12 minutes.
  • FIGS. 11A-11D show the electro-optical properties of CH and PSCH modes in PVA cell configuration for 1 lA:static voltage response; 1 lB ell images of the CH and PSCH modes; the scalar bar is 5mm; l lC:rise time transmittance and HD:fall time transmittance curve (Curing condition: 4V 1kHz, metal halide lamp 35mW/cm , 10-12 minutes).
  • FIGS. 12A and 12B are the plots of CH and PSCH modes in top-down electrode configuration, static responses with voltage ramping up and down for hysteresis study, with 12A:CH mode and 12B:PSCH mode.
  • a fast-switching polymer- stabilized chiral homeotropic (PSCH) LC cell 10 according to an example as shown in FIGS. 1A and IB, comprises a pair of polarizers 12 crossed at 90 degrees with respect to their transmission axes, adjacent two substrates 14 such as glass.
  • the substrates 14 may be constructed of rigid or flexible materials.
  • One or both substrates may have a patterned electrode 16 formed thereon.
  • electrodes 16 are formed on both substrates and may comprise a transparent conductive oxide layer being lithographically processed with a desired pattern.
  • the electrode pattern 16 on the top and bottom substrates 14 may be a square electrode with a size of 5mm by 5mm, but any suitable electrode pattern or dimensions may be used.
  • the cell gap between the substrates 14 may be controlled with 5 ⁇ spacer for example.
  • the ratio between cell gap d and cholesteric pitch p (d/p) may be controlled to be about 0.25 ⁇ 0.02, but other suitable d/p may be used.
  • the ratio of d/p may be varied for various applications, such as for bistable displays or guest- host devices.
  • the PSCH cell 10 of this example includes a treated vertical alignment layer 18 formed on the interior of the top and bottom substrates 14.
  • the vertical alignment layers 18 may be formed of at least one material for providing vertical alignment of the LC materials, such as a polyimide or other suitable material.
  • the material SE-1211(Nissan Chemical) with a thickness of about -20 nm disposed on the surface of the substrates 14 and pixel/counter electrodes 16 may be suitable.
  • the fringe field switching also provides for a wide viewing angle.
  • the vertical alignment layer 18 is treated to create anisotropy and produce a predetermined tilt angle in the LC material.
  • suitable materials and thicknesses for the alignment layers 18 may be used, such as other polyimides or the like.
  • the SE-1211 material produces a high pretilt angle which can be controlled by varying the rubbing strength or baking temperature of a the polymer SE-1211 for example.
  • the alignment layers 18 may have two moieties, an alkyl side chain that promotes vertical and a backbone that promotes planar alignment.
  • the alignment layers 18 are rubbed with velvet cloth. The rubbing directions of top and bottom substrates are aligned in an anti-parallel configuration.
  • the alignment from layers 18 may be provided in other suitable manners other than rubbing, such as using printing techniques or in other suitable manners.
  • the thickness of the alignment layers 18 may be from about lOnm to 60 nm for example.
  • the chiral nematic (CH) material 20 has a negative dielectric anisotropy nematic liquid crystal and chiral dopant.
  • the amount of reactive monomer may be in the range of 0.1 - 2.0% in the mixture for example, or more particularly from about 0.5-1.0%.
  • the polymerized chiral nematic liquid crystal material results in formation of a polymer structure localized on the interior surfaces of top and bottom substrates 14.
  • FIGS. 1A and IB the switching of PSCH mode is shown between the dark state in FIG. 1A and the bright state in FIG. IB.
  • the liquid crystal molecules 20 are generally in an orientation perpendicular to the substrates 14, both adjacent the substrates 14 and toward the center of the cell 10.
  • the vertical alignment is provided by the deposited alignment layers 18 on the surfaces of substrates 14. Under crossed polarizers 12 it shows a dark state.
  • the liquid crystal molecules When an electric field is applied, because of the negative dielectric anisotropy and chiral dopant in the CH mixture, the liquid crystal molecules have a twist structure as shown in FIG. IB. As seen in FIG. IB, the liquid crystal molecules orientation near the substrates 14 is constrained due to surface constraints imposed by the polymer structure 22. The polymer structure is positioned near the surfaces of the substrates 14. The liquid crystal molecules 20 have the twist structure toward the center of the cell 10. In the configuration of FIG. IB, the cell 10 shows the bright state under crossed polarizers 12. If desired, additional material layers may be provided in association with cell 10, such as an insulating layer disposed on an electrode formed on a substrate, such as an insulating layer on the counter electrode of the lower or bottom substrate 14. Such an insulating layer may be formed of a silicon oxide or other suitable material, having a thickness of between 5 - 50 nm, or other suitable thickness.
  • a chiral nematic liquid crystal having a high twisting power such as in the range of 30-150 ⁇ 1 , or more particularly, from about 100-150 um "1 .
  • the formulated chiral nematic mixture used for comparison comprises a nematic liquid crystal LCT12312 (99.962%), a chiral dopant R5011 (0.038%).
  • the amount of chiral dopant may be in the range of 0.01- 0.1% for example.
  • the polymerization condition for these mixtures included exposing the polymerizable mixture to UV light (metal halide lamp) at 35mW/cm for 10-12 minutes with applied voltage.
  • Polarizing optical microscopy was used to compare the dynamic response difference between CH mode and PSCH mode, as shown in FIG. 2.
  • FIG. 2 being polarizing optical microscope (POM) images of a CH mode cell at field-off state in FIG. 2A, CH mode cell at field-on state (14.5V) in FIG. 2B, and for the PSCH mode cell of the invention at field-off state (curing condition: 4V 1kHz, metal halide lamp 35mW/cm , 10-12 minutes) in FIG. 2C and field-on state (16.9V) in FIG. 2D.
  • the scalar bar at the bottom right in FIGS. 2A - 2D is 50 ⁇ for reference.
  • FIG. 2B the POM image of field-on state of the CH mode shows a defect annihilation process.
  • the present invention has effectively suppressed the defect generation and annihilation as shown in FIG. 2D.
  • the dark state of PSCH mode as shown in the POM image of FIG. 2C shows slight light leakage but appears acceptable as shown in the cell image in FIG. 3B.
  • FIG. 3A there is shown the static voltage response of the CH cell at 30, and the static voltage response of the PSCH cell at 32.
  • the CH and PSCH cell images of dark and bright states on a light box are shown in FIG. 3B, with the scalar bar at the bottom right of each being 5mm for reference.
  • FIG. 3C shows plots of rise time transmittance curve for the CH cell at 40, and the rise time transmittance curve of the PSCH cell at 42.
  • FIG. 3D shows plots of fall time transmittance curve for the CH cell at 50, and the rise time transmittance curve of the PSCH cell at 52, using the curing condition: 4V 1kHz, metal halide lamp 35mW/cm , 10-12 minutes.
  • the static voltage response and response time measurements are presented for both the CH mode cell and PSCH mode cell according to the invention.
  • Both the CH and PSCH modes have similar behavior of voltage dependence of transmittance as seen in FIG 3A.
  • the PSCH mode requires slightly larger driving voltage than that of the CH mode.
  • the rise and fall times of the CH and PSCH mode cells are measured without warm-up voltage, and shown in FIGS 3C and 3D.
  • the rise time of CH mode at 40 is 72.5 milliseconds, while that of PSCH mode at 42 is 7.4 milliseconds.
  • the fall time of CH mode at 50 is 9.7 milliseconds, while that of PSCH mode at 52 is 6.6 milliseconds.
  • the sum of rise time and fall time is improved by 83% with the PSCH mode of the invention.
  • FIGS. 4 The effect of curing voltage is shown in FIGS. 4, and can be controlled to provide optimized response speed without surrendering the good dark state of CH mode.
  • the curing voltages 0V, 2V, 3V, 4V, 5V, and 15V are tested and results shown in FIGS. 4A - 4F.
  • the frequency of the curing voltages applied to the prepared cells is 1 kHz and the waveform is a square wave. Other suitable voltage frequencies or waveforms may be used.
  • the light source used for polymerization is a metal halide lamp (Loctite).
  • the polymerization intensity is 35mW/cm and the curing duration is 10-12 minutes.
  • the dark state is observed using polarizing optical microscopy as shown in the images of FIG.
  • the POM images of FIG. 4 are of the field-off state of the PSCH mode polymerized at different applied voltages of 0V in FIG. 4A, 2V in FIG. 4B, 3V in FIG. 4C, 4V in FIG. 4D, 5V in FIG. 4E and 15V in FIG. 4F.
  • the scalar bar at the bottom right of each image is 50 ⁇ for reference and the curing conditions for the sample cells was using a metal halide lamp 35 mW/cm for 10-12 minutes.
  • the curing voltage is larger than the threshold voltage (2.15V in this example)
  • the polymer structure starts to disturb the dark state at field-off condition.
  • the disturbance of dark state is seen to be more significant when the curing voltage is larger than about 5V in this example.
  • the curing voltage is below about 5V in this example, the dark state is effectively preserved, while providing significantly improved performance in rise and fall times as noted above.
  • the curing voltage is thus selected in order to maintain high contrast ratio with good dark state, while also resulting in the improved performance in rise and fall times.
  • the curing voltage may be selected to be in the range of 1.0-2.5 times the threshold voltage. Threshold voltage is generally in the range of 1.5-2.5V for example.
  • FIGS. 5A - 5C The static voltage response and dynamic response of the PSCH mode cells at different applied voltages are presented in FIGS. 5A - 5C.
  • curve 60 is shown for a 0V curing voltage
  • curve 62 for 2V
  • curve 64 for 3V
  • curve 66 for 4V
  • curve 68 for 5V
  • curve 70 for 15V curing voltage.
  • the twist structure of the chiral nematic liquid crystal is held by the polymer structure formed by the particular polymerization of the reactive monomer in the mixture. This ability for the created polymer structure to stabilize the twist structure results in lower driving voltage requirements to switch between dark and bright states.
  • the rise times for different curing voltages are shown, with curve 80 is shown for a 0V curing voltage, curve 82 for 2V, curve 84 for 3V, curve 86 for 4V, curve 88 for 5V and curve 90 for 15V curing voltage.
  • the rise time measurements of FIG. 5B show that the higher curing voltage the better optical bounce suppression. Though attempts to suppress optical bounce have used a warm-up voltage (Vio, voltage for switching the device to 10% transmittance), this requires higher power consumption. In the device 10 of the invention, the rise time measurements show that the higher curing voltage the better optical bounce suppression, without use of any warm-up voltage. The elimination of any required warm- up voltage provides a significant benefit.
  • the PSCH mode in this example has the best rise time of 7.4 milliseconds when cured at about 4V and best fall time of 6.6 milliseconds with a curing voltage of about 5V. Minimum light leakage at zero voltage is achieved when the curing voltage is smaller than about 5 V.
  • the fall times for different curing voltages are shown, with curve 100 is shown for a OV curing voltage, curve 102 for 2V, curve 104 for 3V, curve 106 for 4V, curve 108 for 5V and curve 110 for 15V curing voltage.
  • the polymerization can be optimized to provide the best balance between rise and fall times.
  • the surface morphology of the formed polymer network is shown using scanning electron microscopy (SEM) as seen in FIGS. 6A - 6B.
  • SEM scanning electron microscopy
  • the polymerization of the monomer in the formulated mixture of chiral nematic liquid crystal and reactive monomer produces a polymer structure disposed in the cholesteric liquid crystal material and positioned proximate the inner surfaces of top and bottom substrates 12.
  • the height of the formed structures may be between 50 - 200nm for example, or more particularly about 80 to 120nm.
  • shape of the fibrils, fibers or protrusions may not be round per se, in general the diameter of the polymer fibrils, fibers or protrusions is between 0.05 and 5.0 ⁇ , and more particularly are between 0.08 - 2 ⁇ or around lum. Other suitable dimensions may be acceptable.
  • the polymer structure 22 reduces the pretilt angle degeneracy of the chiral nematic liquid crystal and hence substantially eliminates the defect generation and annihilation during the switch on period. As seen in FIG.
  • the polymerization when cured with no applied voltage and a UV intensity of 35mW/cm , the polymerization does not result in formation of the polymer fibrils, fibers or protrusions formed upon the surface of each alignment layer 18, but at an applied voltage of 4V and a UV intensity of 35mW/cm , the polymer fibrils, fibers or protrusions formed upon the surface of each alignment layer 18 as seen in FIG. 6B.
  • the UV intensity of polymerization is studied in order to optimize the electro- optical performance of the PSCH mode cell 10 of the invention.
  • Four various UV intensities are tested: 5mW/cm 2 , 15mW/cm 2 , 25mW/cm 2 , 35mW/cm 2 with a metal halide lamp (Loctite).
  • Lictite metal halide lamp
  • total UV dosage is controlled at 27 J/cm for curing.
  • the dark state of each curing intensity is observed with polarizing optical microscopy as shown in FIGS. 7A- 7D for each of these different intensities respectively. As seen in FIG. 7, when the curing intensity 5mW/cm in FIG. 7 A, up to 15mW/cm 2 in FIG.
  • FIG. 7B shows that the field-off condition provides better dark state than 35mW/cm as in FIG. 7D.
  • the scalar bar at the bottom right of each image is 50 ⁇ for reference.
  • the effect on dynamic rise and decay times is shown in FIGS. 8 A and 8B. In FIG. 8 A, the rise times for different curing intensities are
  • curve 120 shown for 5mW/cm
  • curve 122 for 15mW/cm
  • curve 124 for
  • FIG. 8A indicates that the suppression of optical bounce at the rising period is improved with increasing in UV curing intensity.
  • FIG. 8B the fall times for different curing intensities are shown, with
  • FIGS. 9A and 9B The effect on the surface morphology of the polymer network based on different curing intensities is shown in FIGS. 9A and 9B.
  • a lower and higher curing intensity were evaluated at an applied voltage of 4V, being 5mW/cm in FIG. 9A and 35 mW/cm" in FIG. 9B.
  • FIG. 9A at the smaller intensity, the formation of polymer fibrils, fibers or protrusions upon the surface of each alignment layer 18 is not dense enough to enhance the anchoring of the chiral nematic liquid crystal, which leads to higher optical bounce.
  • each alignment layer 18 is dense enough to enhance the anchoring of the chiral nematic liquid crystal, which reduces optical bounce and improves rise and decay times of the cell 10.
  • the fast turn on and turn off times are provided by the increased anchoring energy produced by the polymer structure.
  • Example 4 The invention also provides for facilitating producing a wide view angle.
  • an interdigitated electrode configuration for viewing angle enhancement is used.
  • both the CH and PSCH modes are demonstrated using a patterned-ITO vertical alignment (PVA) configuration.
  • the first substrate 12 is sputtered with transparent oxide conductive layer and the second substrate 12 is sputtered with transparent oxide conductive layer and patterned with interdigitated electrode.
  • the electrode width and spacing in this example is 7 ⁇ and 13 ⁇ . Both substrates have an alignment layer 18 of polyimide coated on top of electrode that provides vertical alignment.
  • the formulated chiral nematic mixture used for comparison consists of a nematic liquid crystal LCT12312 (99.962%), and a chiral dopant R5011 (0.038%).
  • the polymerization condition for the PSCH cell is 35mW/cm for 10-12 minutes using a metal halide lamp (Loctite).
  • the field-on and field-off states of CH and PSCH modes in PVA configuration are shown in FIGS. 10A - 10D.
  • a schematic illustration of the interdigitated electrode configuration for viewing angle enhancement is shown in FIG. 10E.
  • the scalar bar at the bottom right in FIGS. 10A - 10D is 50 ⁇ for reference.
  • the POM images of the CH and PSCH modes in patterned-ITO vertical alignment (PVA) cell configuration in FIG. 10 show the field-off state of the CH mode cell in FIG. 10A, and the field-on state (12.4V) of the CH mode cell in FIG. 10B.
  • the CH mode cell exhibits disclination defects at field-on state and hence, needs more time for the rising period.
  • the field-off state of the PSCH mode cell is shown in FIG. IOC and the field-on state (13V) of the PSCH mode cell (PSCH curing condition: 4V 1kHz, settling time 5 minutes before UV curing with a metal halide lamp at 35mW/cm for 10- 12 minutes) is shown in FIG. 10D.
  • the PSCH mode cell in a PVA cell configuration shows no defect annihilation and improves the switching speed at field-on state as seen in FIG. 10D, and provides a significant improvement as compared with the CH mode cell.
  • FIGS. 11 A, 11C and 11D The static voltage response, rise time and fall time measurements for the CH and PSCH cells of this example are illustrated in FIGS. 11 A, 11C and 11D respectively, and off/on states for each of the CH and PSCH cells of this example are shown in FIG. 11B.
  • the curing conditions for the PSCH cell were 4V 1kHz, metal halide lamp 35mW/cm", 10-12 minutes for this example.
  • the scalar bar at the bottom right in FIG. 1 IB is 5 mm for reference.
  • FIG. 11 A static voltage response curve shows that PSCH mode 142 requires slightly higher operating voltage than CH mode 140 in a PVA cell configuration. Both CH 150 and PSCH 152 modes show less severe optical bounce at field-on state (FIG. 11C).
  • the average rise time measured without warm up voltage of CH mode in PVA configuration is 46.8 milliseconds, while the average rise time of PSCH mode in PVA configuration is 12.1 milliseconds.
  • the improvement of rise time is 74% for the PSCH mode cell of the invention.
  • the fall time of CH mode 160 is 6.7 milliseconds and that of PSCH mode 162 is 7.0 milliseconds.
  • the liquid crystal mixture formulation is the same as Example 4.
  • the electrode structure of interdigitated pattern was extended into plural domains to increase the viewing angle range.
  • the present invention can be applied on to patterned electrode configurations to improve the viewing angle property of the device.
  • the PSCH cell as compared to the CH cell is evaluated to demonstrate that with polymer structure inside the cell, the PSCH mode exhibits hysteresis-free characteristics in voltage ramping up and down.
  • the PSCH and CH modes in a top-down electrode configuration show static response with voltage ramping up 170 and down 172 of the CH mode cell in FIG. 12A, while the static response with voltage ramping up 180 and down 182 of the PSCH mode cell (cured at 4V, 35mW/cm 2 ) in FIG. 12B.
  • the materials used in these examples are the same as in Example 1.
  • Example 7 The devices of the present invention also exhibit good voltage holding ratio (VHR) stability.
  • the VHR measurements were made using a HP Elsicon VHR- 100.
  • the VHR is measured with pulse of amplitude 10V and pulse width 64 ⁇ 8.
  • the frequency of the pulse is 60 Hz.
  • Both CH mode and PSCH mode (Curing voltage: 4V 1kHz, Curing intensity: 35mW/cm , 10-12 minutes) have measured VHR value 0.987 right after the samples were fabricated. After two months, CH mode has a VHR value 0.984 and the PSCH mode has a VHR value 0.983, indicating good VHR performance.
  • the PSCH mode of the invention can be used in both transmissive displays and reflective displays, and by varying the ratio between cell gap d and cholesteric pitch p (d/p), this mode can be further applied to bistable displays and guest-host devices.
  • the invention may be in association with displays, such as direct view displays, wearable devices or other spatial light modulating devices such as beam steering devices, holographic devices, projection displays or other optical devices.

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  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Organic Chemistry (AREA)
  • Liquid Crystal (AREA)

Abstract

L'invention concerne des dispositifs à cristaux liquides homéotropes chiraux stabilisés par un polymère à commutation rapide (PSCH) et des procédés de production de tels dispositifs. La structure de cette invention comprend une paire de substrats de verre sur lesquels a été pulvérisée une couche conductrice transparente et qui sont revêtus d'une couche d'alignement homéotrope. Un mélange de cristaux liquides cholestériques dopé avec une petite quantité de monomère réactif est pris en sandwich entre les substrats. Par polymérisation des molécules de monomère réactives entre les substrats ou à la surface de ceux-ci pour former un réseau polymère prédéterminé, un rebond optique et un processus d'annihilation de défauts pendant la commutation sont supprimés, et des dispositifs électro-optiques à cristaux liquides ayant un temps de réponse rapide sont obtenus.
PCT/US2017/024246 2016-03-29 2017-03-27 Dispositifs et procédés à cristaux liquides homéotropes chiraux stabilisés par un polymère à commutation rapide WO2017172578A1 (fr)

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US5606442A (en) * 1993-05-14 1997-02-25 Tektronix, Inc. Low electro-optic threshold liquid crystal cell and method of fabricating same
US7652731B2 (en) * 2006-05-16 2010-01-26 Kent State University Polymer enhanced cholesteric electro-optical devices
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