Classifications

• • 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
  • C09K19/0225—Ferroelectric
• • 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
  • G02F1/1416—Details of the smectic layer structure, e.g. bookshelf, chevron, C1 and C2
• • 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
  • G02F1/133749—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers for low pretilt angles, i.e. lower than 15 degrees
• • 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
  • G02F1/13706—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 the liquid crystal having positive dielectric anisotropy

Definitions

• the replacement of the cathode ray tube (picture tube) with a flat screen requires a display technology that simultaneously has high image resolution, ie more than 1000 lines, high image brightness (> 200 Cd / m 2 ), high contrast (> 100: 1), a high image frequency (> 60 Hz), sufficient color display (> 16 million colors), a large image format (> 40 cm screen diagonal), low power consumption and a wide viewing angle enable and also inexpensive to produce. So far, there is no technology that fully fulfills all of these features at the same time.
• Tsukuda, TFT / LCD Liquid Crystal Displays Addressed by Thin-Film Transistors, Gordon and Breach 1996, ISBN 2-919875-01-9 and the literature cited therein; SID Symposium 1997, ISSN-0097-966X, pages 7 to 10, 15 to 18, 47 to 51, 213 to 216, 383 to 386, 397 to 404 and the literature cited therein.
• PDP Plasma Display Panel
• PALC Phase Change RAM
• ELD Electro Luminescent Display
• FED Field Emission Display
• the individual picture elements (pixels) of an LC display are usually arranged in an x, y matrix, which is arranged by a series of electrodes
• This arrangement of the pixels is usually referred to as a passive matrix.
• Various multiplexing schemes have been developed for addressing, as described, for example, in Displays 1993, Vol. 14, No. 2, pp. 86-93 and contacts 1993 (2), pp. 3-14.
• Passive matrix addressing has the advantage of simpler manufacture of the display and the associated low manufacturing costs, but the disadvantage that passive addressing can always be done line by line, which means that the addressing time of the entire screen is N lines is N times the row addressing time. With the usual line addressing times of approx. 50 microseconds, this means a screen addressing time of approx. 60 milliseconds with, for example, HDTV standard (High Definition TV, 1152 lines), ie a maximum frame rate of approx. 16 Hz.
• HDTV standard High Definition TV, 1152 lines
• AMLCD active matrix technology
• An electrically non-linear element for example a thin-film transistor, is integrated on each pixel of the active matrix substrate.
• the nonlinear element can also be diodes, metal insulator metal, etc. Act elements which are advantageously produced using thin-film processes and are described in the relevant literature, see e.g. T. Tsukuda, TFT / LCD: Liquid Crystal Displays Addressed by Thin-Film Transistors, Gordon and Breach 1996, ISBN 2-919875-01-9 and the literature cited therein.
• Active matrix LCDs are usually operated with nematic liquid crystals in TN (twisted nematics), ECB (electrically controlled birefringence), VA (vertically aligned) or IPS (in plane switching) mode.
• TN twisted nematics
• ECB electrically controlled birefringence
• VA vertical aligned
• IPS in plane switching
• the active matrix generates an electric field of individual strength at each pixel, which produces a change in orientation and thus a change in birefringence, which in turn is visible in polarized light.
• a serious disadvantage of this method is the lack of video capability due to the long switching times of nematic liquid crystals.
• liquid crystal displays based on a combination of ferroelectric liquid crystal materials and active matrix elements have been proposed, see e.g. WO 97/12355 or Ferroelectrics 1996, 179, 141-152, W.J.A.M. Hartmann, IEEE Trans. Electron. Devices 1989, 36, (9; Pt. 1), 1895-9.
• Hartmann used a combination of the so-called 'quasi-bookshelf geometry' (QBG) from FLC and a TFT (thin-film transistor) active matrix and at the same time received a high switching speed, grayscale and high transmission.
• QBG 'quasi-bookshelf geometry'
• TFT thin-film transistor
• a disadvantage of this approach is the appearance of a stripe texture on the display that limits the contrast and brightness of this cell (see Fig. 8 in the above quotation).
• the disadvantageous stripe texture can be corrected by treatment with a high electrical voltage (20-50 V) in the nematic or cholesteric phase (see p. 168 of the above quotation); however, such field treatment is not suitable for the mass production of screens and generally does not lead to temperature-stable textures.
• this method only results in switching in an angular range of up to a maximum of the simple tilt angle, which in the case of Nito et. al. The material used is approx. 22 ° (see p. 165 Fig. 6) and thus only results in a transmission of a maximum of 50% of the transmission of two parallel polarizers.
• the spontaneous polarization P in the liquid crystal layer is preferably between 0.1 and 15 nC / cm 2 .
• the tilt angle Tiw is preferably between 9 and 40 ° in the liquid crystal layer.
• the ratio of the product of anchorage strength and the sine of the tilt angle to the spontaneous polarization is preferably less than 20 V / ⁇ m.
• the object is further achieved by a monostable ferroelectric active matrix display containing a liquid crystal layer in chevron C1 geometry in the form of a monodomain with a clearly defined direction of the layer normals z of the SmC * phase, the pretilt angle Prw being at least 5 ° and that The ratio of the pretilt angle to the tipping angle (Prw / truck) is greater than 0.7.
• the object is further achieved by a monostable ferroelectric active matrix display containing a liquid crystal layer in bookshelf geometry in the form of a mono-domain with a clearly defined direction of the layer normal z of the smC * phase, the pretilt angle Prw being at least 1 °.
• a monostable ferroelectric avtiv matrix display containing a liquid crystal layer in the form of a monodomain with a clearly defined direction of the layer normal z of the smC * phase, which has the following properties:
• the liquid crystal layer preferably has one or more, in particular all, of the following features:
• the angle between the layer normal z of the smC * phase and the preferred direction n of the nematic or cholesteric phase (N * phase) is in a range of 0.5 to 1.0 times the smC * tilt angle, at least however 5 °,
• the ferroelectric liquid crystal layer has a phase sequence
• the active matrix FLCD according to the invention preferably contains, as an optically active layer, a ferroelectrically liquid-crystalline medium (liquid-crystal phase) with a phase sequence of
• phase has a range of existence (phase range) of at most 2 ° C., preferably at most 1 ° C., particularly preferably at most 0.5 ° C.
• phase range a range of existence (phase range) of at most 2 ° C., preferably at most 1 ° C., particularly preferably at most 0.5 ° C.
• the asterisk (*) on the phase label indicates that it is a chiral phase.
• the displays are preferably produced by a process in which the liquid crystal layer is introduced into the space between a rubbed upper substrate plate and a rubbed lower substrate plate of the active matrix display, the rubbing directions on the upper and lower substrate plates being essentially parallel, and the Liquid crystal phase cools from the isotropic phase, with an electrical voltage being present on the display at least during the phase transition N * - »smC * or N * ⁇ smA * ⁇ smC * .
• the FLC mixture is filled into an active matrix display.
• the manufacture and components of such an AM display is described in detail in the Tsukuda literature listed above.
• the thickness of the FLC layer is only 0.7 to 2.5, preferably 1-2 ⁇ m.
• the rubbing directions on the upper and lower substrate plates are essentially parallel.
• the term "substantially parallel” includes anti-parallel or weak, i.e. friction directions crossed by up to 10 °.
• the preferred n-director (which indicates the preferred direction of the molecular longitudinal axes) is located in the rubbing direction of the cell, whereas the z-director (which indicates the preferred direction of the smectic layer normal) is inclined approximately by the amount of the tilt angle Rubbing direction is located.
• This constellation is exactly the opposite of the usual bistable cell according to Clark and Lagerwall, where the z-director lies in the rubbing direction.
• the display thus obtained appears completely dark with a suitable angle of rotation between crossed polarizers.
• a control voltage of only a few volts is applied, it appears bright, whereby the brightness can be varied continuously over the voltage and, when saturated, has almost the brightness of two parallel polarizing foils.
• the angle between the preferred direction of the nematic (or cholesteric) phase and the layer normal (z director) is ideally and therefore preferably the tilt angle of the smectic C phase, or at least substantially the tilt angle.
• “In essence” in the sense of this invention preferably means a value range from half to the full, particularly preferably 0.5 to 1 times the tilt angle, but at least 5 °.
• the ferroelectric active matrix liquid crystal display according to the invention is highly practical, in particular for TV and HDTV or multimedia, since it agrees high transmission, short switching times, gray scale and therefore full color capability, cost-effective production and a wide temperature range.
• the display can preferably be operated at voltages of ⁇ 10 volts, preferably ⁇ 8 V, particularly preferably ⁇ 5 V.
• the characteristic curve (transmission plotted against voltage) of the liquid crystal mixture should be flat enough on the one hand to address the gray values with the available voltages, on the other hand the saturation voltage should not be too high.
• the saturation voltage V90 at which 90% of the maximum transmission is reached, should not be too high so that the display can be operated with voltages below 30V, preferably below 15 V, preferably below 10 V, particularly preferably below 8 V, especially below 5 V. .
• the maximum transmission of the cell should generally be at least 40% (based on an empty cell between two parallel polarization foils), preferably at least 50%, preferably at least 70%, particularly preferably at least 80%, especially at least 90%.
• the T, V- Characteristic curve should be strictly monotonically increasing (with increasing voltage). A decrease in transmission after reaching a transmission maximum is not desirable.
• the subject of this invention is therefore the selection of liquid crystals and mixtures thereof with suitable material parameters for the advantageous setting of the characteristic curve.
• the invention further relates to a monostable active matrix FLC display, in which an optimal characteristic is obtained by the selection of liquid crystals or their mixtures through a targeted combination of several material properties of the ferroelectric liquid crystal, and the use of liquid crystal mixtures of these properties for active Matrix FLC displays.
• IC integrated circuit
• the characteristic curve of the ferroelectric liquid crystal cell according to the invention is influenced by a number of parameters, which should preferably take on their own or in combination preferred value ranges so that optimal switching conditions are achieved.
• this involves spontaneous polarization (P), the tilt angle (Tiw), the layer tilt angle (truck), the pretilt angle (Ptw), the anchorage strength (AS), the dielectric anisotropy (DA), and also the layer rotation angle (Sdw), the cell thickness (d), the helical pitch of the cholesteric phase (pitch) and the smectic C * phase, and the optical anisotropy (OA).
• the characteristic (T, V) should preferably have the following properties.
• the characteristic curve is not influenced or only influenced to a very small extent by the rotational viscosity, instead, e.g. the saturation voltage V90 is strongly determined by the spontaneous polarization (P) and the anchoring strength (AS).
• the spontaneous polarization (P) should preferably be between 0.1 nC / cm 2 and 15 nC / cm 2 (here the absolute amount of P is always meant), preferably between 0.2 and 10 nC / cm 2 , preferably 0.4 to 8 nC / cm 2 0.5 to 6 nC / cm 2 is particularly preferred, especially 0.8 to 3.5 nC / cm 2 .
• the tilt angle should preferably be in the range from 9 ° to 45 °, preferably between 12 ° and 35 °, preferably 14 ° to 31 °, particularly preferably 17 ° to 27 °, especially 19 ° to 25 °.
• the absolute amount of dielectric anisotropy should preferably be less than 3 (three), preferably less than 2.5, particularly preferably less than 1.8, especially less than 1.2.
• the product of the anchoring energy (AS) and the sine of the tilt angle divided by the spontaneous polarization (P) should preferably be less than 20 V / ⁇ m, preferably less than 15 V / ⁇ m, preferably less than 12 V / ⁇ m, particularly preferably less than 9 V / ⁇ m, especially less than 6 V / ⁇ m.
• the parameter specifications relate to at least one temperature in the working range of the ferroelectric liquid crystal display.
• the display according to the invention can be operated not only in the area of the smectic C * phase, but also, at least in part, in the area of another tilted smectic phase, with analogous transmission of the properties mentioned above.
• the monostable active matrix FLC display according to the invention can be in the Chevron C1, the Chevron C2 or the bookshelf or quasi-bookshelf Arrangement (or 'geometry') are operated.
• the preferred combination of value ranges for spontaneous polarization and tilt angle applies to all three geometries:
• the pitch of the cholesteric helix should be longer than 50 ⁇ m in a temperature range of 5 ° above the transition to the smectic phase or, in the case of a smaller range of existence of the cholesteric phase, preferably in the range of 80% of this range of existence.
• the Layer tilt angle (truck) together with the pretilt angle (Ptw) preferably have the following relation to the tilt angle (Tiw): the ratio WR from the sum of the pretilt angle and layer tilt angle to the tilt angle (i.e. (truck + Ptw) / Tiw) should generally be at least 0.1 , preferably at least 0.15, preferably at least 0.25, particularly preferably at least 0.5, especially at least 0.7.
• the amount of dielectric anisotropy DA should be less than 3.
• the C2 geometry is preferred over C1 and 'bookshelf.
• the pretile angle should be at least 5 ° with a suitable position tilt angle, since otherwise no switching occurs at low voltage.
• the tipping angle (truck) and the pretilt angle (Prw) should advantageously have the following relationship: the ratio of the pretilt angle and the tipping angle should be greater than 0.7.
• the pretilt angle should generally be at least 1 °, preferably at least 2 °. Particularly preferably, the pretilt angle should be at least 1 °, the spontaneous polarization should be at least 0.1 nC / cm 2 , at most 15 nC / cm 2 and the tilt angle should be at least 12 °.
• the spontaneous polarization in the tables above can also preferably be 0.1 to 15 nC / cm 2 .
• a mixture particularly suitable for use in the display according to the invention has at least six (6), preferably at least eight (8), particularly preferably at least nine (9), especially at least eleven (11) components, which are selected such that the spontaneous polarization is between 0.1 and 15 nC / cm 2 , the tilt angle is between 17 ° and 27 °, the ratio of the tilt angle to the tilt angle is at least 0.3, the pitch of the chiral nematic phase is at least 50 ⁇ m (range of 5 ° C above the phase transition), which Absolute amount of dielectric anisotropy is less than 3, and the phase sequence
• a glass substrate coated with transparent - conductive indium tin oxide is patterned in a photolithographic process, so that an electrode pattern is obtained.
• Electrode structures are used for the electrical control of the display by means of a function generator, and so the switching behavior of a thin film transistor is simulated.
• Two such structured glass panes, which form the top and bottom of the display - that is, the carrier plates - are provided with orientation layers, these are rubbed and with the help of an adhesive frame with the addition of a concentration of 0.5% by weight spacer balls with a diameter of 1, 3 ⁇ m assembled.
• the adhesive is cured by careful heating, the liquid crystal mixture is filled at 100 ° C. by capillary forces and the cell is brought to a temperature above the IN * phase transition by slow cooling. At this
• the cell is now powered by monopolar pulses with a length of 10 ms and a spacing of 30 ms with voltages of variable amplitude by means of a function generator (model Wavetech) and amplifier (manufacturer: Krohn-Hite) wired, and the transmission is measured using a photodiode and oscilloscope.
• This characteristic curve generally shows a saturation of the transmission at high voltages, this value is referred to as 100%.
• V10 is now the threshold voltage at which the brightness is just 10% of the saturation transmission
• V90 is the voltage at which 90% of the saturation transmission is achieved.
• the empirical anchoring strength AS is obtained from the value for V90 obtained in Example 2, the layer thickness and the spontaneous polarization according to the following formula.
• An FLC display with a cell thickness of 1.25 ⁇ m is provided with an FLC mixture with the phase sequence lN * -smC * , which has the following physical data:
• An FLC display with a cell thickness of 1.25 ⁇ m is equipped with an FLC mixture with the phase sequence lN * -smC *, which has the following physical data: Geometry: C2
• An FLC display with a cell thickness of 1.25 ⁇ m is filled with an FLC mixture with the phase sequence l-N * - smA * (with a range of existence ⁇ 2 °) -smC *, which has the following physical data:
• An FLC display with a cell thickness of 1.25 ⁇ m is provided with an FLC mixture with the phase sequence lN * -smC * , which has the following physical data:
• Advantageous characteristic curves are obtained at low values of AS * sin (Tiw) / P, in particular at AS * sin (Tiw) / P ⁇ 20 V / ⁇ m, preferably ⁇ 16 V / ⁇ m.
• An FLC display with a cell thickness of 1.25 ⁇ m is provided with an FLC mixture with the phase sequence lN * -smC * , which has the following physical data:
• An FLC display with a cell thickness of 1.25 ⁇ m will have the following physical data with an FLC mixture with the phase sequence lN * -smC ⁇ :
• T V characteristics (characteristic curves) are obtained when the pretilt angle is varied:
• Prw is at least 5 °, Prw / truck greater than 0.7.

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• 1998
  • 1998-06-08 DE DE19825487A patent/DE19825487A1/de not_active Withdrawn
• 1999
  • 1999-06-08 JP JP2000553862A patent/JP4728479B2/ja not_active Expired - Fee Related
  • 1999-06-08 EP EP10180673A patent/EP2348356A1/de not_active Withdrawn
  • 1999-06-08 WO PCT/EP1999/003941 patent/WO1999064925A1/de not_active Ceased
  • 1999-06-08 US US09/701,986 patent/US6661494B1/en not_active Expired - Lifetime
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