Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
  • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
  • G02F1/1333—Constructional arrangements; Manufacturing methods
  • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
  • G02F1/1336—Illuminating devices
  • G02F1/133602—Direct backlight
  • G02F1/133603—Direct backlight with LEDs
• • 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
  • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
  • G02F1/13356—Structural association of cells with optical devices, e.g. polarisers or reflectors characterised by the placement of the optical elements
  • G02F1/133565—Structural association of cells with optical devices, e.g. polarisers or reflectors characterised by the placement of the optical elements inside the LC elements, i.e. between the cell substrates
• • 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
  • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
  • G02F1/1336—Illuminating devices
  • G02F1/13362—Illuminating devices providing polarized light, e.g. by converting a polarisation component into another one
• • 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
  • G02F2202/00—Materials and properties
  • G02F2202/02—Materials and properties organic material

Definitions

• the present invention relates to an LCD display panel apt to modulate light emitted from a light source incorporated therein.
• Polymeric or organic light-emitting diodes (LEDs) used in image representation systems are known. These diodes are used to fabricate flat panel displays in which the intersections of rows and columns define picture elements (pixels) which are controlled individually by means of a matrix of switching devices, or scanned by means of a matrix of passive electrodes, thus taking advantage of the intrinsically nonlinear relationships among applied voltage current and photon flux generated by the emitting diode.
• diodes are also used as light source for display panels based on the modulation effects of liquid crystals on transmitted light.
• Object of the present invention is to solve the abovementioned problems of the known art providing an LCD display panel, comprising: - one or more supporting layers;
• the main advantage of the panel according to the present invention lies in the use of a backlight source consisting of organic light-emitting semiconductor diodes, and not resulting in a package of greater weight and bulkiness.
• This source is based on preferably organic electroluminescent materials and it is fabricated directly onto one of the substrates of the same panel.
• This fabricating technique determines a structure which is much thinner, lighter and more compact compared to that of the traditional flat LCD panels in which the backlighting is provided by a discrete and much bulkier package, usually consisting of one or more fluorescent tubes, light guides and diffusers.
• a second advantage of the present invention lies in that the display panel is sturdier and it consists of a reduced number of parts and components, with the entailed simplification of the production processes, which therefore are also more cost-effective.
• the LCD display panel according to the present invention is apt to be used in all those applications in which thickness, weight and power consumption are crucial.
• Exemplary fields and marketed products in which said panel is advantageously employable are: second- (GSM) and third- (UMTS) generation cell phones with connectivity to the Internet , global positioning systems (GPS), viewfinders, portable
• the reduction in the number of the parts and components also entails a reduction in the production, assembly and maintenance costs which are advantageous also for display devices in systems powered by main, or by other power supplies which are not particularly limited, desktop computer and TV monitors, programmable windows and decorative walls, navigation devices for motor vehicles, aircrafts and ships, devices for projecting virtual images on motor vehicle, aircraft and ship screens.
• the incorporation of a light source and of a modulator can be advantageous in order to implement a particularly effective optical processing element.
• figure 1 is a sectional perspective view of a first embodiment of the panel according to the present invention
• figure 2 is a sectional perspective view of a second embodiment of the panel according to the present invention
• figure 3 is an exploded perspective view of a display panel according to the present invention
• figure 4 is an examplary timing of the control signals of a panel according to the present invention.
• FIG. 1 a sectional perspective view of a first embodiment of the panel according to the present invention is illustrated.
• a first conductive layer 2 is deposited or grown on a first supporting layer 1, preferably made of materials like plastics, glass, quartz or metal, and of a thickness typically ranging from 100 ⁇ m to 1 mm.
• the layer 2 is itself made as a reflective metal layer .
• the layer 2 has a low work function, (e.g. Aluminum, Calcium, Barium, Lithium, Magnesium or Magnesium/Silver alloys). Said layer 2 can be made or treated to narrow mirror reflection and enhance light diffusion.
• the layer 2 also serves as a cathode for an emitting layer 3 made of a material emitting in the visible wavelengths of light (390-789 nm) which is deposited by spin coating, electrochemically, by inkjet printing or vacuum techniques,
• the emitting material can be of inorganic type, like e.g. ZnS, ZnSe, CdS, etc., or of organic polymer type, like e.g.
• Alq3 Aluminium (known as Alq3).
• Alq3 aluminium
• it can preferably be sandwiched between other two or more separation layers of material which facilitate electron and hole transport.
• dopants apt to accelerate the phosphorescence- enhancing radiative emission processes can be added as well.
• a second conductive layer 4 is overlapped to the layer 3.
• the layer 4 is of the transparent type and it also serves as anode, being characterized by a high work function.
• the constituent materials of said second conductive layer 4 may be of inorganic (e.g., Indium and/or Tin oxides in vacuum or from a liquid dispersion) or of organic type (polyaniline, deposited electrochemically or by spin coating).
• inorganic e.g., Indium and/or Tin oxides in vacuum or from a liquid dispersion
• organic type polyaniline, deposited electrochemically or by spin coating
• a transparent cathode can be made of a suitably doped polyaniline.
• a reflecting anode can be made, e.g., with a noble metal like gold. In this configuration, anodes can still be made with transparent materials. However should be overlapped to a further reflective layer. This further reflective layer can be a low cost reflecting metal like alluminium or silver or dielectric mirror.
• the light emitted by the emitting layer 3 can be monochromatic, polychromatic or white, unpolarized or partially or totally polarized.
• the layer 5 can be fabricated with a thin layer of prelaminated material, like e.g. the mylar.
• a third conductive layer 6 transparent and made, with lithography techniques, of an organic- or inorganic-type material, apt to define display panel rows.
• the panel according to the present invention further comprises one or more alignment layers 7, 9 for liquid crystals deposited according to techniques known to the art, like e.g. the spin-coating for organic materials (polyimide, polyamide, polyvinyl alcohol), and aligned by rubbing, or irradiation with (optionally polarized) light (visible or UV).
• organic materials polyimide, polyamide, polyvinyl alcohol
• irradiation with (optionally polarized) light visible or UV
• said alignment layers can be fabricated by sputtering or thermal evaporation of, e.g., Silicon oxides with a suitable incidence angle.
• a protective layer 11 optionally also serving as support, preferably made of plastics or vitreous material, it is deposited a fourth conductive layer 10 onto which the panel column electrodes are lithographically defined.
• a fourth conductive layer 10 Onto said conductive layer
• the second alignment layer 9 is deposited.
• the supporting layer 1 and the protective layer 11, with the layers deposited thereon, are assembled to form a panel as in the known LC art.
• a liquid crystal light- modulating layer 8 (modulator 8), sandwiched between the layers 1 and 11, can be injected from a slit in its isotropic phase and left to cool until it reaches a more ordered phase.
• the positions and/or the functions of the row and of the column electrodes are easily swappable therebetween, as it is apparent to those skilled in the art.
• the panel is sealed.
• a first polarizing layer 12 is laminated onto the outer side of the layer 11 . Moreover, also further layers, apt to improve the angle of sight and not shown in the figure, can be used.
• the liquid crystal can be of the guest-host type.
• a panel as the one hereto described can function in a transmissive as well as in a reflective mode.
• the first case the light is generated by the layer 3 when a sufficient voltage is applied onto the electrodes 2 and 4.
• the light is modulated by the liquid crystal layer 8 under the action of the commands (controls) applied onto the electrodes 6 and 10.
• the second case no electric field is applied between the electrodes 2 and 4, rather the environment light is modulated via the polarizing layer 12.
• the modulation effect can be the guest-host one.
• figure 2 is a sectional perspective view of a second embodiment of the panel according to the present invention.
• a second polarizing layer can be sandwiched between the layers 4, 5 .
• This polarizing layer can be fabricated overlapping a layer 13 of polymerized cholesteric liquid crystal to a quarter- wave foil 14.
• the dielectric layer 5 can be present as in the figure, precede the layer 5, or be absent.
• the liquid crystal e.g., a monoacrylate
• a chiral dopant e.g., a diacrylate
• said range ⁇ can be widened by modulating the pitch of the helical structure. This may be carried out by continuously varying the concentration of the chiral dopant.
• the component of the circular or helical polarization reflected by the Bragg reflector is diffused by the metallic cathode, fabricated so as to be diffusive to the utmost, and the luminous intensity is depolarized and again reflected towards the Bragg reflector, where once more one of the circular or helical polarizations is transmitted and the other one thereof is reflected.
• the light is generated by the emitting layer already in a polarized form, in order to be able to use a liquid crystal technology operating under polarized light.
• This may be effected conferring to the emitting conjugated polymer a directional order, typical of nematic phases, and optionally also a positional one, typical of smectic or hexatic phases.
• This order can be conferred by rubbing the emitting conjugated polymer or a related underlying layer (e.g. the poly(para- phenylenevinylene) or derivatives thereof) like a hole-transport layer or another dedicated layer.
• useful polymers are the polyamides, the polyimides, the polyvinylalcohol, the polyester, the polyaniline aligned with various rubbing techniques or the polytetrafluoroethylene hot-deposited by friction, as well as the photoalignable polymers.
• the alignment layer can be doped with charge transfer complexes like, e.g., the tetrathiafulvalene /7,7,8,8-tetracyanoquinodimethane complexes.
• the same emitting materials can be aligned (can be photoalignable conjugated polymers).
• the emitting layer can be already polymerized prior to the deposition or it can be polymerized in situ starting from mesogens.
• a fourth embodiment of the panel according to the present invention is provided in order to be able to use a liquid crystal technology operating under polarized light.
• the light emitted by the emitting layer (optionally already partially polarized) passes, before reaching the liquid crystal light-modulating layer, through a further layer fabricated with thin film techniques (spin-coating, spray or roll techniques) and serving as polarizer.
• This further layer comprises molecules (optionally polymerized) of a dichroic dye.
• said molecules have self-assembling properties and are, optionally or additionally, alignable, e.g. by rubbing techniques.
• the same technique for fabricating a thin film polarizer can be used to fabricate the polarizing layer 12.
• the latter besides being overlapped to the protective layer 11, can also be located at an intermediate position sandwiched between said layer 11 and the liquid crystal light-modulating layer 8.
• the availability of polarized light as obtained in the two abovedescribed embodiments enables to use a very wide range of modulation effects by the top liquid crystal layer.
• the guest-host effects can still be used, or "S" or “B” effects of the nematic liquid crystals, or twisted nematics (TN), supertwisted nematics (STN), hybrid alignment nematics (HAN) or in-plane switching nematics, as it is known in the art of the liquid nematic crystals, included those having surface or volume memory with the entailed bi- or multistability.
• liquid smectic-phase crystals like SmA*, SmC*, SmCA*, SmI*, SmLA* or the various subphases comprised thereamong can advantageously be used.
• a viable solution is to spatially subdivide the pixels, defined by the intersection of rows and columns, into subpixels related thereamong as the powers of two.
• the refresh period (frame) can be subdivided into several time subintervals having durations related thereamong as the powers of two. It is also possible to jointly use spatial and temporal subdivisions, adopting suitable subdivision ratios.
• the panel according to the present invention simply solves the temporal subdivision problem, as the response of the emitting layer is fast and the light can also be amplitude modulated. Hence, it is possible to write «fields» all alike in duration and therefore to modulate the intensity of the light emitted from the various fields according to ratio related thereamong as the powers of two.
• the light source can be controlled only after a "field" has been written.
• a greater panel luminosity, and lesser stresses in terms of current and of peak voltage can be provided thereto.
• figure 3 is a schematic perspective view of the panel according to the present invention.
• Figure 4 shows an exemplary timing of the selection signals in the case of a panel in which the liquid crystal modulator consists of 64 rows (and of a number of columns which is irrelevant to the ends of the description) and the light source is subdivided into eight strips.
• the emitting layer can be apt to emit solely at the pixel defined by the intersection of the row and column electrodes of the liquid crystal modulator. This can easily be carried out, e.g. by lithographic definition of one of the layers serving as electrode, preferably the layer indicated with 2 in the figure.
• a panel having the above characteristics could have various operation modes: - with memory and reflecting without its own lighting, with the advantage of a virtually nil consumption.
• a typical application can be that of a display panel of a portable phone displaying the name of the service provider or of an electronic notebook displaying a list of meetings; - with memory and transmitting with its own lighting, wherein the consumption is due to the sole inner light source, e.g. when any one key of a portable phone be pressed;
• the light source is advantageously fabricated overlapping several emitting layers, sequentially modulated, each emitting at a primary color wavelength of one of the primary colors. Therefor, further layers fabricated according to the techniques described in the present invention, yet not explicitly shown in the embodiments of figures 1 and 2, are required.
• the liquid crystal can modulate continuously, or a modulation technique analogous to the abovedescribed one can be adopted.
• color filters preferably in a number equal to three, e.g. defining stripes parallel the columns of the liquid crystal modulator, can be used. Said strips can be located above the emitting layer or onto the opposite layer 11.
• the pixel of the modulator can be subdivided in correspondence of the emitting stripes. hi order to provide a color image starting from a blue source it is advantageous to use two photoluminescent layers re-emitting preferably in the remaining two primary colors (green and red).
• Each switching device can be a three-terminal device like a thin film transistor, or a two-terminal device like a back to back diode.
• the material used to fabricate the switching devices can be amorphous Silicon, polycrystalline Silicon, or single-crystal Silicon, or a chalcogenide, or an organic semiconductor.
• the liquid crystal used is of nematic type, however it can also be of twisted nematic type, vertical alignment nematic, hybrid alignment nematic, plane commutation nematic, flexoelectric nematic, Smectic A*, Smectic C*, surface-stabilized in a "chevron", "bookshelf, or “quasi-bookshelf configuration, ferroelectric surface-stabilized in a twisted structure, or deformed-helix-ferroelectric, antiferroelectric with or without threshold.

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• Physics & Mathematics (AREA)
• Nonlinear Science (AREA)
• Mathematical Physics (AREA)
• Chemical & Material Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Electroluminescent Light Sources (AREA)

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Cited By (4)

Citations (7)

• 2001
  • 2001-03-12 IT IT2001RM000124A patent/ITRM20010124A1/it unknown
• 2002
  • 2002-02-21 WO PCT/IT2002/000105 patent/WO2002073306A1/en not_active Application Discontinuation
  • 2002-02-21 EP EP02707092A patent/EP1368696A1/en not_active Withdrawn

Patent Citations (7)

Non-Patent Citations (4)

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