PATENT DOCUMENT

Publication Number: US-9488862-B2
Application Number: US-201313765656-A
Country: US
Kind Code: B2

Title: Displays with organic light-emitting diode backlight structures

Abstract:
An electronic device may be provided with a display. The display may include a liquid crystal display cell and an organic light-emitting diode backlight unit. The liquid crystal display cell may include a color filter layer, a liquid crystal layer, and a thin-film transistor layer. The organic light-emitting diode backlight unit may include organic emissive material formed on a substrate. The organic emissive material may generate backlight for liquid crystal display cell. Display pixels in the liquid crystal display cell may control the emission of the backlight from the display. The organic light-emitting diode backlight unit may be attached to the display using adhesive, laminated to a polarizer layer of the display cell, or may be integrated into the liquid crystal display cell. The backlight unit may include conductive vias or bent extended edge portions for coupling the backlight unit to control circuitry.

Claims:
What is claimed is: 
     
       1. A display, comprising:
 organic light-emitting diode backlight structures that generate backlight for the display; 
 display layers that include a layer of liquid crystal material that controls emission of the backlight from the display; 
 a polarizer layer that forms a layer of the organic light-emitting diode backlight structures, wherein the polarizer layer includes a circular polarizer and at least one additional polarizer, wherein the display layers comprise a display substrate interposed between the polarizer layer and the layer of liquid crystal material; and 
 at least one optical film interposed between the display substrate and the polarizer layer. 
 
     
     
       2. The display defined in  claim 1  wherein the organic light-emitting diode backlight structures are attached to the display layers by an adhesive that runs along at least one edge of the display. 
     
     
       3. The display defined in  claim 2  wherein the adhesive comprises pressure-sensitive adhesive. 
     
     
       4. The display defined in  claim 1  wherein the display layers further comprise:
 a thin-film-transistor layer; and 
 a color filter layer, wherein the layer of liquid crystal material is interposed between the thin-film-transistor layer and the color filter layer. 
 
     
     
       5. The display defined in  claim 4  wherein the polarizer layer is attached to the thin-film-transistor layer. 
     
     
       6. The display defined in  claim 1 , further comprising a chassis structure, wherein the organic light-emitting diode backlight structures are mounted to the chassis structure. 
     
     
       7. The display defined in  claim 6  wherein the organic light-emitting diode backlight structures are attached to the display layers by an adhesive that runs along at least one edge of the chassis structure. 
     
     
       8. The display defined in  claim 1  wherein the organic light-emitting diode backlight structures comprise a segmented organic light-emitting diode backlight unit. 
     
     
       9. The display defined in  claim 8  wherein the segmented organic light-emitting diode backlight unit comprises between one and one hundred organic-light-emitting diode backlight pixels. 
     
     
       10. The display defined in  claim 9  wherein each of the organic light emitting diode backlight pixels generates backlight for a plurality of display pixels. 
     
     
       11. A display, comprising
 a plurality of display layers that include a liquid crystal layer and a thin-film-transistor layer; 
 organic light-emitting diode backlight structures that are laminated to a surface of the plurality of display layers, wherein the organic light-emitting diode backlight structures provide backlight to the plurality of display layers; 
 at least one conductive via that electrically couples the organic light-emitting diode backlight structures to the thin-film-transistor layer; and 
 a polarizer layer interposed between the thin-film transistor layer and the organic light-emitting diode backlight structures, wherein the at least one conductive via passes through the polarizer layer. 
 
     
     
       12. The display defined in  claim 11  wherein the organic light-emitting diode backlight structures include an extended edge portion that extends beyond an edge of the plurality of display layers. 
     
     
       13. The display defined in  claim 12 , further comprising conductive contacts on the extended edge portion. 
     
     
       14. The display defined in  claim 13  wherein the extended edge portion is bent away from a plane defined by the plurality of display layers. 
     
     
       15. The display defined in  claim 11  wherein the organic light-emitting diode backlight structures comprise a segmented organic light-emitting diode backlight unit. 
     
     
       16. The display of  claim 11 , wherein control signals from the thin-film-transistor layer control the organic light-emitting diode backlight structures. 
     
     
       17. A display, comprising:
 a substrate having thin-film-transistor circuitry formed thereon; 
 organic emissive material on the substrate; 
 a layer of liquid crystal material, wherein the organic emissive material is interposed between the substrate and the layer of liquid crystal material; 
 thin-film transistor electrodes interposed between the layer of liquid crystal material and the organic emissive material; 
 a planarization layer interposed between the thin-film transistor electrodes and the organic emissive material; 
 a polarizer interposed between the organic emissive material and the planarization layer; and 
 at least one conductive via that couples conductive structures on the substrate to the thin-film-transistor electrodes. 
 
     
     
       18. The display defined in  claim 17 , wherein the thin-film-transistor electrodes are formed directly on the planarization layer. 
     
     
       19. The display defined in  claim 18 , further comprising an encapsulation layer formed over the organic emissive material. 
     
     
       20. The display defined in  claim 19 , further comprising a light polarizing layer interposed between the organic emissive material and the layer of liquid crystal material. 
     
     
       21. The display defined in  claim 20  wherein the light polarizing layer is formed on the planarization layer. 
     
     
       22. A display comprising:
 a liquid crystal display cell comprising an array of display pixels; and 
 an organic light-emitting diode backlight unit having a plurality of backlight pixels that share a common organic light-emitting diode layer and that provide white backlight to the entire array of display pixels, wherein each backlight pixel provides white backlight to a single corresponding display pixel in the array of display pixels, wherein each backlight pixel includes a plurality of color backlight sub-pixels and wherein, in combination, the plurality of color backlight sub-pixels in each backlight pixel are configured to generate the white backlight having a color temperature that is within a predetermined range of a desired color temperature. 
 
     
     
       23. The display defined in  claim 22  wherein the desired color temperature comprises the color temperature of a standard illuminant. 
     
     
       24. The display defined in  claim 23  wherein the predetermined range is between 6000K and 7000K. 
     
     
       25. A display comprising:
 a liquid crystal display cell having an array of display pixels, wherein the liquid crystal display cell comprises a thin-film transistor layer having thin-film transistors on a substrate and a color filter layer with a plurality of color filter elements that have associated transmission peak wavelengths; 
 an organic light-emitting diode backlight unit having an organic light-emitting diode layer comprising thin-film transistors on an additional substrate that receive control signals from the thin-film transistor layer in the liquid crystal display cell, wherein the organic light-emitting diode layer includes a plurality of backlight pixels that provide backlight to the entire array of display pixels, wherein each backlight pixel includes a plurality of color backlight sub-pixels and wherein, in combination, the plurality of color backlight sub-pixels are configured to generate backlight having a spectrum that includes emission peaks at emission peak wavelengths that correspond to the transmission peak wavelengths of the color filter elements; and 
 a polarizer interposed between the liquid crystal display cell and the organic light-emitting diode layer, wherein the thin-film transistors on the additional substrate receive the control signals from the thin-film transistor layer in the liquid crystal display cell through a via that extends through the polarizer. 
 
     
     
       26. The display defined in  claim 25 , wherein at least one of the emission peak wavelengths is within 30 nanometers of the transmission peak wavelength of a corresponding one of the plurality of color filter elements. 
     
     
       27. The display defined in  claim 25  wherein, for each backlight pixel, the plurality of color backlight sub-pixels comprises a first color backlight sub-pixel having a first width and a second color backlight sub-pixel having a second width and wherein the first width is larger than the second width. 
     
     
       28. The display defined in  claim 27  wherein the first color backlight sub-pixel is a blue backlight sub-pixel.

Description:
BACKGROUND 
     This relates generally to electronic devices, and more particularly, to electronic devices with displays. 
     Electronic devices often include displays. For example, cellular telephones and portable computers often include displays for presenting information to a user. 
     It can be challenging to form displays for electronic devices. Displays such as liquid crystal displays typically include backlight structures that include multiple light-emitting diodes that emit light into a light guide plate that distributes backlight for the display. Backlight generated by the backlight structures passes through electronically controlled liquid crystal material to generate images for presenting information to a user. 
     If care is not taken, backlight structures formed from light-emitting diodes and a light guide plate may be bulky. The housing of an electronic device can be adjusted to accommodate a bulky display with conventional backlight structures, but this can lead to undesirable enlargement of the size and weight of the housing and unappealing device aesthetics. 
     It would therefore be desirable to be able to provide improved displays for electronic devices. 
     SUMMARY 
     An electronic device may be provided with a display mounted within a housing. The display may include a liquid crystal display cell and a backlight unit that is formed from one or more organic light-emitting diodes. The liquid crystal display cell may include a color filter layer, a liquid crystal layer, a thin-film transistor layer, and one or more polarizer layers. The organic light-emitting diode backlight structures (OLED backlight structures) may provide backlight that illuminates the display layers. 
     The OLED backlight structures may be mounted in a chassis structure such as a plastic chassis that is attached to a liquid crystal display cell for the display. However, this is merely illustrative. If desired, the OLED backlight structures may be laminated to the liquid crystal display cell or the liquid crystal display cell may include integrated organic light-emitting diode backlight components. A polarizer layer for the display may be integrated onto the organic light-emitting diode backlight structures so that the OLED backlight structures generate polarized light that is provided to the liquid crystal display cell. 
     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device such as a laptop computer with a display in accordance with an embodiment of the present invention. 
         FIG. 2  is a perspective view of an illustrative electronic device such as a handheld electronic device with a display in accordance with an embodiment of the present invention. 
         FIG. 3  is a perspective view of an illustrative electronic device such as a tablet computer with a display in accordance with an embodiment of the present invention. 
         FIG. 4  is a perspective view of an illustrative electronic device such as a computer display with display structures in accordance with an embodiment of the present invention. 
         FIG. 5  is a cross-sectional side view of an illustrative display having organic light-emitting diode backlight structures in accordance with an embodiment of the present invention. 
         FIG. 6  is a cross-sectional side view of illustrative display layers and organic light-emitting diode backlight structures in accordance with an embodiment of the present invention. 
         FIG. 7  is a cross-sectional side view of illustrative top-emission organic light-emitting diode backlight structures in accordance with an embodiment of the present invention. 
         FIG. 8  is a cross-sectional side view of illustrative bottom-emission organic light-emitting backlight structures in accordance with an embodiment of the present invention. 
         FIG. 9  is a top view of illustrative organic light-emitting diode backlight structures showing how the organic light-emitting diode backlight structures may be horizontally segmented in accordance with an embodiment of the present invention. 
         FIG. 10  is a top view of illustrative organic light-emitting diode backlight structures showing how the organic light-emitting diode backlight structures may be horizontally and vertically segmented in accordance with an embodiment of the present invention. 
         FIG. 11  is a perspective view of illustrative organic light-emitting diode backlight structures and a corresponding chassis structure in accordance with an embodiment of the present invention. 
         FIG. 12  is a cross-sectional side view of illustrative display layers and organic light-emitting backlight structures showing how the organic light-emitting diode structures may be laminated to the display layers in accordance with an embodiment of the present invention. 
         FIG. 13  is a cross-sectional side view of illustrative display layers and organic light-emitting backlight structures showing how the organic light-emitting diode structures may be integrated into the display layers in accordance with an embodiment of the present invention. 
         FIG. 14  is a top view of a portion of an illustrative display having an array of color display pixels in accordance with an embodiment of the present invention. 
         FIG. 15  is a top view of a portion of illustrative organic light-emitting diode backlight structures showing how each backlight pixel may include multiple backlight sub-pixels in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices may include displays. The displays may be used to display images to a user. Illustrative electronic devices that may be provided with displays are shown in  FIGS. 1, 2, 3, and 4 . 
       FIG. 1  shows how electronic device  10  may have the shape of a laptop computer having upper housing  12 A and lower housing  12 B with components such as keyboard  16  and touchpad  18 . Device  10  may have hinge structures  20  that allow upper housing  12 A to rotate in directions  22  about rotational axis  24  relative to lower housing  12 B. Display  14  may be mounted in upper housing  12 A. Upper housing  12 A, which may sometimes referred to as a display housing or lid, may be placed in a closed position by rotating upper housing  12 A towards lower housing  12 B about rotational axis  24 . 
       FIG. 2  shows how electronic device  10  may be a handheld device such as a cellular telephone, music player, gaming device, navigation unit, or other compact device. In this type of configuration for device  10 , housing  12  may have opposing front and rear surfaces. Display  14  may be mounted on a front face of housing  12 . Display  14  may, if desired, have openings for components such as button  26 . Openings may also be formed in display  14  to accommodate a speaker port (see, e.g., speaker port  28  of  FIG. 2 ). 
       FIG. 3  shows how electronic device  10  may be a tablet computer. In electronic device  10  of  FIG. 3 , housing  12  may have opposing planar front and rear surfaces. Display  14  may be mounted on the front surface of housing  12 . As shown in  FIG. 3 , display  14  may have an opening to accommodate button  26  (as an example). 
       FIG. 4  shows how electronic device  10  may be a computer display or a computer that has been integrated into a computer display. With this type of arrangement, housing  12  for device  10  may be mounted on a support structure such as stand  27 . Display  14  may be mounted on a front face of housing  12 . 
     The illustrative configurations for device  10  that are shown in  FIGS. 1, 2, 3, and 4  are merely illustrative. In general, electronic device  10  may be a laptop computer, a computer monitor containing an embedded computer, a tablet computer, a cellular telephone, a media player, or other handheld or portable electronic device, a smaller device such as a wrist-watch device, a pendant device, a headphone or earpiece device, or other wearable or miniature device, a television, a computer display that does not contain an embedded computer, a gaming device, a navigation device, an embedded system such as a system in which electronic equipment with a display is mounted in a kiosk or automobile, equipment that implements the functionality of two or more of these devices, or other electronic equipment. 
     Housing  12  of device  10 , which is sometimes referred to as a case, may be formed of materials such as plastic, glass, ceramics, carbon-fiber composites and other fiber-based composites, metal (e.g., machined aluminum, stainless steel, or other metals), other materials, or a combination of these materials. Device  10  may be formed using a unibody construction in which most or all of housing  12  is formed from a single structural element (e.g., a piece of machined metal or a piece of molded plastic) or may be formed from multiple housing structures (e.g., outer housing structures that have been mounted to internal frame elements or other internal housing structures). 
     Display  14  may be a touch sensitive display that includes a touch sensor or may be insensitive to touch. Touch sensors for display  14  may be formed from an array of capacitive touch sensor electrodes, a resistive touch array, touch sensor structures based on acoustic touch, optical touch, or force-based touch technologies, or other suitable touch sensor components. 
     Display  14  for device  10  may include display pixels formed from liquid crystal display (LCD) components and organic light-emitting diode backlight structures. A display cover layer may cover the surface of display  14  or a display layer such as a color filter layer, polarizer layer, or other portion of a display may be used as the outermost (or nearly outermost) layer in display  14 . The outermost display layer may be formed from a transparent glass sheet, a clear plastic layer, or other transparent member. 
     A cross-sectional side view of an illustrative configuration that may be used for display  14  of device  10  (e.g., for display  14  of the devices of  FIG. 1 ,  FIG. 2 , or  FIG. 3  or other suitable electronic devices) is shown in  FIG. 5 . As shown in  FIG. 5 , display  14  may include one or more layers of touch sensitive components such as touch-sensitive layers  47  that are attached to a cover layer such as cover layer  49 . Cover layer  49  may be formed from a sheet of rigid or flexible transparent material such as glass or plastic. 
     Touch-sensitive layers  47  may be attached to cover layer  49  using an adhesive material such as optically clear adhesive (OCA)  43 . Adhesive  43  may be a liquid adhesive, light-cured adhesive, pressure-sensitive adhesive or other suitable adhesive. Touch-sensitive layers  47  may include touch sensor components such as an array of capacitive touch sensor electrodes formed from transparent materials such as indium tin oxide. 
     Display  14  may include display layers such as layers  46  (e.g. a liquid crystal display cell) for generating images to be displayed on display  14 . Display layers  46  may include polarizer layers, color filter layers, transistor layers, adhesive layers, layers of liquid crystal material, or other layers for generating display images. Display layers  46  may be attached to touch-sensitive layers  43  using adhesive such as optically clear adhesive  45 . Adhesive  45  may be a liquid adhesive, light-cured adhesive, pressure-sensitive adhesive or other suitable adhesive. 
     Display layers  46  may selectively block and transmit light that has been generated by light-generating structures such as organic light-emitting diode (OLED) backlight structures  42  (sometimes referred to herein as OLED backlight structures, OLED backlight unit, backlight unit or backlight structures) to form images to be viewed by a user of device  10 . OLED backlight structures  42  may include one, two, three, more than three, hundreds, thousands, hundreds of thousands, or more that hundreds of thousands of organic light-emitting elements formed from organic emissive material. 
     OLED backlight structures  42  may be attached to display layers  46  using an adhesive such as a pressure-sensitive adhesive that runs along one or more edges of structures  42 , may be laminated to display layers  46  using an optically clear adhesive sheet between structures  42  and layers  46 , or may be formed from organic light-emitting diode components that are integrated into display layers  46 . 
     OLED backlight structures  42  may be rigid or flexible OLED backlight structures (e.g., structures  42  may be formed on a rigid substrate such as glass or a flexible substrate). Display  14  may have a substantially rectangular shape or may have other shapes (e.g., a circular, oblong, or other irregular shape). OLED backlight structures  42  may have a shape that corresponds to the shape of display layers  46 . 
     OLED backlight structures  42  may have a thickness T that is substantially smaller than the thickness of a conventional LCD backlight unit. For example, thickness T of structures  42  may be between 150 microns and 200 microns, between 100 microns and 200 microns, less than 250 microns, or less than 650 microns (as examples). 
     A cross-sectional side view of an illustrative configuration that may be used for display layers  46  and OLED backlight structures  42  of display  14  (e.g., for display layers  46  and backlight structures  42  of  FIG. 5 , or other suitable display) is shown in  FIG. 6 . As shown in  FIG. 6 , OLED backlight structures  42  may be attached to display layers  46  using adhesive  60  (e.g., a pressure-sensitive adhesive, thermally cured adhesive, light-cured adhesive such as an ultra-violet light-cured adhesive, or other adhesive material) formed along one or more edges of structures  42 . Adhesive  60  may run along an edge of an active layer of backlight structures  42  (e.g., a substrate layer, a polarizer layer, etc.) or along a support structure such as a chassis structure for backlight structures  42 . In the example of  FIG. 6 , adhesive  60  attaches backlight structures  42  to a polarizer layer of display layers  46 . 
     OLED backlight unit  42  may produce backlight  44 . During operation of display  14 , backlight  44  travels outwards (vertically upwards in dimension Z in the orientation of  FIG. 6 ) and passes through display pixel structures  90  in display layers  46 . This illuminates any images that are being produced by the display pixels for viewing by a user. For example, backlight  44  may illuminate images on display layers  46  that are being viewed by viewer  48  in direction  50 . 
     Display layers  46  may be mounted in chassis structures such as a plastic chassis structure and/or a metal chassis structure to form a display module for mounting in housing  12  or display layers  46  may be mounted directly in housing  12  (e.g., by stacking display layers  46  into a recessed portion in housing  12 ). Display layers  46  may form a liquid crystal display or may be used in forming displays of other types. 
     Display layers  46  may include a liquid crystal layer such a liquid crystal layer  52 . Liquid crystal layer  52  may be sandwiched between display layers such as display layers  58  and  56 . Layers  56  and  58  may be interposed between lower polarizer layer  61  and upper polarizer layer  54 . If desired, upper polarizer layer  54  may be attached to an outer cover layer such as cover layer  49  ( FIG. 5 ). 
     Layers  58  and  56  may be formed from transparent substrate layers such as clear layers of glass or plastic. Layers  56  and  58  may be layers such as a thin-film transistor layer and/or a color filter layer. Conductive traces, color filter elements, transistors, and other circuits and structures may be formed on the substrates of layers  58  and  56  (e.g., to form a thin-film transistor layer and/or a color filter layer). Touch sensor electrodes may also be incorporated into layers such as layers  58  and  56  and/or touch sensor electrodes may be formed on other substrates. 
     With one illustrative configuration, layer  58  may be a thin-film transistor layer that includes an array of thin-film transistors and associated electrodes (display pixel electrodes) for applying electric fields to liquid crystal layer  52  and thereby displaying images on display  14 . Layer  56  may be a color filter layer that includes an array of color filter elements  56 ′ for providing display  14  with the ability to display color images. Color filter elements  56 ′ may each transmit light having a selected wavelength range around a peak transmission wavelength. For example, a red color filter element may transmit light have a range of wavelengths around a peak wavelength at or near 700 nanometers (nm). Color filter elements  56 ′ may include red color filter elements, blue color filter elements, green color filter elements, cyan color filter elements, magenta color filter elements and/or yellow color filter elements (as examples). If desired, layer  58  may be a color filter layer and layer  56  may be a thin-film transistor layer. 
     During operation of display  14  in device  10 , control circuitry for device  10  (e.g., one or more integrated circuits on a printed circuit) may be used to generate information to be displayed on display  14  (e.g., display data). The information to be displayed may be conveyed from the control circuitry to a display driver integrated circuit (e.g., a display driver integrated circuit mounted on TFT layer  58 ) for the display using a signal path such as a signal path formed from conductive metal traces in one or more flexible printed circuits. The display signals may be routed to electrodes on thin-film transistor layer  58  and/or to OLED backlight structures  42 . OLED backlight structures  42  may receive control signals directly from control circuitry or may receive control signals that are routed to OLED backlight structures  42  through a portion of display layers  46 . 
     Control signals provided to backlight structures  42  may turn on, turn off, increase brightness, decrease brightness, or otherwise adjust backlight  44  from some or all of backlight structures  42 . Backlight  44  passes through polarizer  61  and TFT layer  58  onto liquid crystal material  52 . 
     Control signals provided to display layers  46  may be used to operate electrodes  59  located on thin-film transistor layer  58 . Electrodes  59  may generate electric fields in liquid crystal material  52  that control the orientation of liquid crystals  52 ′ in liquid crystal layer  52 . In this way, liquid crystals  52 ′ may be rotated to selectively block and/or transmit various amounts of backlight  44  through each pixel  90 . 
     OLED backlight structures  42  may include organic-light-emitting diodes that generate polarized light to be provided to display layers  46 . In configurations in which OLED backlight structures include polarized light-emitting-diodes of this type, display layers  46  may be provided without a lower polarizer. 
     OLED backlight structures  42  may include color organic-light-emitting diodes that generate colored light to be provided to display layers  46 . In configurations in which OLED backlight structures include colored light-emitting-diodes of this type, display layers  46  may be provided without any color filter layer. However, this is merely illustrative. If desired, OLED backlight structures  42  may include colored light-emitting diodes that emit colors of light that are matched to the transmission spectra of the color filter elements in color filter layer  56 . For example, backlight structures  42  may generate backlight  44  having a continuous spectrum of colors in the visible range with one or more emission peaks at wavelengths corresponding to peak transmission wavelengths of the color filter elements. In this way, the power consumption of display  14  may be reduced by effectively reducing the amount of light that is generated by backlight structures  42  and absorbed by color filter layer  56 . 
     If desired, OLED backlight structures  42  may include colored light-emitting diodes that, in combination, generate white backlight for display  14  that has a color temperature that is matched to the color temperature of a desired white point for the display (e.g., the white points of the D55, D65, D75, F3, or other standard illuminants of the International Commission on Illumination (CIE)). 
       FIG. 7  is a cross-sectional view of OLED backlight structures  42  that are implemented in a top-emission configuration. In a configuration for display  14  of the type shown in  FIG. 7 , OLED backlight structures  42  include a substrate layer such as substrate layer  62 . Substrate layer  62  may be a polyimide layer that is temporarily carried on a glass carrier during manufacturing or may be a layer formed from glass or other suitable substrate materials. 
     Organic light-emitting diode (OLED) layer  64  is formed on an upper surface of substrate  62 . An encapsulation layer such as encapsulation layer  66  encapsulates organic light-emitting diode layer  64 . During operation, one or more individually controlled backlight pixels in organic light-emitting diode layer  64  generate backlight  44  to be provided to display layers  46 . 
     Structures  42  may include one or more polarizer layers such as polarizer layer  72 . Layer  72  may include a circular polarizer that suppresses reflections from metal signal lines in layer  64 . If desired, polarizer layer  61  of  FIG. 6  may be incorporated into polarizer layer  72  of OLED backlight structures  42 . In this way, OLED backlight structures  42  may provide polarized light to display layers  46 . 
     Organic light-emitting diode layer  64  may contain one or more thin-film transistors. The thin-film transistors may be formed from semiconductors such as amorphous silicon, polysilicon, or compound semiconductors (as examples). Signal lines (e.g., a grid of horizontal and vertical metal lines) may be used in applying control signals to the thin-film transistors. During operation, signals are applied to one or more organic light-emitting diodes in layer  64  using the signal lines so that backlight structures  42  generate backlight  44  of desired intensity and spatial distribution to be provided to the pixel structures (e.g., pixels  90  of  FIG. 5 ) of display layers  46 . 
     To enhance backlight performance for backlight structures  42 , backlight structures  42  may include optical films  70 . Optical films  70  may include diffuser layers for helping to homogenize backlight  44  and thereby reduce hotspots, compensation films for enhancing off-axis viewing, and brightness enhancement films (also sometimes referred to as turning films) for collimating backlight  44 . Display  14  may include other light diffusing features such as a roughened surface of a substrate layer of structures  42 , diffusive material in an adhesive that attaches polarizer  61  to TFT layer  58 , or a light diffusing adhesive that attaches structures  42  to display layers  46 . 
     In a configuration for display  14  of the type shown in  FIG. 8 , OLED backlight structures  42  are implemented in a bottom-emission arrangement. As shown in  FIG. 8 , OLED backlight structures  42  may include a transparent substrate layer such as glass layer  76 . A layer of organic light-emitting diode structures such as organic light-emitting diode layer  64  may be formed on the underside of glass layer  76 . An encapsulation layer such as encapsulation layer  66  may be used to encapsulate organic light-emitting diode layer  64 . 
     Encapsulation layer  66  may be formed from a layer of metal foil, metal foil covered with plastic, other metal structures, a glass layer, a thin-film encapsulation layer formed from a material such as silicon nitride, a layered stack of alternating polymer and ceramic materials, or other suitable material for encapsulating organic light-emitting diode layer  64 . Encapsulation layer  66  may help protect organic light-emitting diode layer  64  from environmental exposure by preventing water and oxygen from reaching organic emissive materials within organic light-emitting diode layer  64 . 
     Backlight  44  of desired intensity and spatial distribution from organic light-emitting diode layer  64  may be emitted upwards through transparent glass layer  76  to be provided to the pixel structures (e.g., pixels  90  of  FIG. 5 ) of display layer  46 . Backlight structures  42  may include a reflective layer such as reflector  74 . Reflector  74  may be attached to encapsulation layer  66  and may reflect light from layer  64  that has been emitted downward toward reflector  74  back upward to be used as backlight for display layers  46 . 
     Organic light-emitting diode backlight structures  42  may include a single OLED pixel, two OLED pixels, more than two OLED backlight pixels, between one and one hundred OLED backlight pixels, thousands of OLED backlight pixels, hundreds of thousands of OLED backlight pixels, millions of OLED backlight pixels or any other suitable number of OLED backlight pixels. OLED backlight pixels of structures  42  may be operated independently or in unison. 
       FIG. 9  is a top view of backlight structures  42  showing how structures  42  may form a segmented OLED backlight unit having horizontal backlight pixels  92 . Each horizontal backlight pixel  92  may provide backlight to one or more rows of display pixels  90 . In this way, the intensity of backlight that is provided to display layers  46  may be varied horizontally. Each display pixel  90  may control how much of the backlight that is provided by a horizontal backlight pixel  92  is released from the display for viewing by a user. However, the horizontal backlight pixels of  FIG. 9  are merely illustrative. If desired, other distributions of backlight pixels may be provided. 
     As shown in  FIG. 10 , structures  42  may be horizontally and vertically segmented using backlight pixels such as backlight pixels  94 . Each backlight pixel  94  may provide backlight to one or more display pixels  90 . If desired, a backlight pixel  94  may provide backlight to a single corresponding display pixel  90 , to multiple display pixels  90 , a subarray of display pixels  90 , or any suitable number of display pixels  90 . In this way, portions of the display that are used for displaying bright objects may be provided with bright backlight while portions of the display that are used to display dark objects such as black portions of an image may be provided with little or no backlight. Each display pixel  90  may control how much of the backlight that is provided by a backlight pixel  94  is released from the display for viewing by a user. 
     Each backlight pixel  94  may include one or more backlight sub-pixels that each generate light of a desired color. For example, each backlight pixel  94  may include a red backlight sub-pixel, a green backlight sub-pixel, a blue backlight sub-pixel, or other backlight sub-pixels. Backlight sub-pixels may each emit light having a wavelength range that corresponds to the range of transmitted wavelengths of a corresponding color filter element  56 ′ of color filter layer  56  of display layers  46 . Each backlight pixel  94  may include backlight sub-pixels having colors that, in combination, generate white light corresponding to a desired display white point or display light color temperature. 
     Individual backlight pixels such as pixels  92  or  94  may be controlled using directly driven (sequentially patterned) electrodes, vias from additional control circuitry to the electrodes, passively addressed rows and columns of electrodes or using active matrix technologies (as examples). 
     OLED backlight structures  42  may be mounted in a support structure such as chassis structure  900  of  FIG. 11 . Chassis structure  900  may be formed from a ring of plastic or other suitable material that surrounds structures  42  and that serves as an interface between structures  42  and other portions of display  14  and/or surrounding portions of housing  12 . If desired, chassis structure  900  may be formed from a plate of material that includes a rectangular recess to accommodate display structures such as structures  42 . Chassis structure  900  may be formed from housing structures (e.g., as part of a housing frame, part of a unibody housing such as a metal housing, etc.). The arrangement of  FIG. 11  in which chassis structure  900  surrounds OLED backlight structures  42  is merely illustrative. If desired, chassis structure  900  may only partially surround structures  42 . 
     Chassis structure  900  may be a plastic display chassis structure (sometimes referred to as a p-chassis). Chassis structure  900  may be used in supporting the layers and structures of display  14  such as OLED backlight structures  42 . If desired, other support structures such as a metal chassis structure (sometimes referred to as an m-chassis) may be used in supporting display  14 . 
     Chassis structure  900  may be formed from materials such as polycarbonate or may be formed from other suitable materials (e.g., other suitable thermoplastic polymers or plastics). Chassis structure  900  may be molded (e.g., using an injection molding process or other suitable molding process), machined, thermoformed, or may be formed using any other suitable fabrication process. This is, however, merely illustrative. If desired, chassis structure  900  may be formed from glass, ceramic, other materials, or a combination of these materials. 
     Chassis structure  900  may be attached to display layers  46  using, for example, adhesive  60  of  FIG. 6  that is interposed between an edge of chassis structure  900  and display layers  46 . 
       FIG. 12  is a cross-sectional view of display layers  46  and OLED backlight structures  42  showing how backlight structures  42  may be laminated to polarizer layer  61  of display layers  46 . In a configuration of the type shown in  FIG. 12 , backlight structures  42  may be attached to polarizer layer  61  using a layer of optically clear adhesive such as adhesive layer  99 . Backlight structures  42  may be provided with one or more conductive vias such as vias  96  that couple circuitry in backlight structures  42  to circuitry in thin-film transistor layer  58 . In this type of configuration, backlight structures  42  may receive control signals from TFT layer  58 . However, this is merely illustrative. If desired, OLED backlight structures  42  may include extended edge portions  42 E that extend beyond the edge of display layers  46 . 
     Extended edge portions  42 E may be formed from a flexible substrate portion of OLED backlight structures  42 . Extended edge portions  42 E may be bent away from the plane defined by the central portion of display  14 . Extended edge portions  42 E may include conductive contacts  98 . Contacts  98  may be coupled to additional circuitry in device  10 . For example, portions  42 E may be used to couple backlight structures  42  to one or more integrated circuits such as components  104  on printed circuit  102 . 
     Signals for controlling OLED backlight pixels (e.g., backlight pixels  92  of  FIG. 9  or backlight pixels  94  of  FIG. 10 ) may be conveyed from circuitry  104  to OLED backlight structures  42  using a signal path such as a signal path formed from conductive metal traces in flexible printed circuit  100  (as an example). However, this is merely illustrative. If desired, flexible printed circuit  100  may be used in routing signals between printed circuit  102  and thin-film transistor layer  58 . If desired, display  14  may include a driver integrated circuit mounted on printed circuit  102  or flexible printed circuit  100 . 
     Printed circuit  102  may be formed from a rigid printed circuit board (e.g., a layer of fiberglass-filled epoxy) or a flexible printed circuit (e.g., a flexible sheet of polyimide or other flexible polymer layer). However, these examples are merely illustrative. If desired printed circuits  100  and  102  may be formed from a combination of rigid and flexible printed circuit layers (e.g., printed circuit  102  may be formed from a rigid printed circuit board with a layer of flexible printed circuitry that extends from an edge of printed circuit  102  to form flexible printed circuitry  100  that attaches to thin-film transistor layer  58 ). Control circuitry such as printed circuit  102  and integrated circuit  104  may be coupled to display layers  46  and/or backlight structures  42  in any suitable configuration. 
       FIG. 13  is a cross-sectional view of display  14  showing how organic light-emitting diode backlight components may be integrated into the layers of a liquid crystal display. As shown in  FIG. 13 , display  14  may include a substrate such as thin-film-transistor substrate  112  (e.g., a glass substrate). Organic emissive material  108  may be formed on substrate  112 . Organic emissive material may be covered by an encapsulant such as thin-film encapsulation layer  114 . Organic emissive material  108  may be formed from organic plastics such as polyfluorene, a phosphorescent material, or other organic emissive materials. A planarization layer such as planarization layer  110  may be formed over thin-film encapsulation layer  114 . 
     If desired, thin-film-transistor electrodes  59  may be formed between planarization layer  110  and encapsulation layer  114 . Encapsulation layer  114  may be formed from a glass layer, a thin-film encapsulation layer formed from a material such as silicon nitride, a layered stack of alternating polymer and ceramic materials, or other suitable material for encapsulating organic emissive material  108 . 
     If desired, a light polarizing layer such as polarizer layer  61  may be formed between encapsulation layer  114  and planarization layer  110 . However, this is merely illustrative. Polarizer  61  may be formed above planarization layer  110  or in another position in display  14  that allows layer  61  to polarize light emitted from organic emissive material  108  before the light reaches liquid crystal layer  52 . In an integrated configuration of the type shown in  FIG. 13 , polarizer  61  may be implemented as a wire-grid polarizer with periodic wire structures having a size and a relative separation that are associated with the wavelength of light emitted by emissive material  108 . 
     An array of thin-film-transistor electrodes  59  (e.g., electrodes formed from indium tin oxide (ITO), a conductive polymer, or other transparent conductive material) may be formed over planarization layer  110 . Liquid crystal layer  52  may be formed over TFT electrodes  59  so that electric fields generated by electrodes  59  control the orientation of liquid crystals  52 ′, thereby controlling the amount of backlight  44  that exits display  14 . Display  14  may include one or more conductive vias such as via  118  that route signals between TFT electrodes  59  and conductive structures on TFT substrate  112 . 
     Display  14  may include circuitry such as thin-film-transistors and associated electrodes  116  on TFT substrate  112 . Electrodes  116  may be operated by control circuitry for device  10  (e.g., printed circuit  102  and integrated circuit  104  of  FIG. 12 ) to control emission of backlight  44  that is received from organic emissive material  108 . Display  14  may include one electrode  116  associated with each display pixel  90  each electrode  116  may control the emission of backlight  44  for multiple pixels  90 . 
       FIG. 14  is top view of a portion of display  14  showing how display pixels  90  may be combined to form a display pixel group for generating display light of a desired color. In the example of  FIG. 14 , display pixel group  900  includes four display pixels  90  (e.g., a red display pixel having a red color filter element, a blue display pixel having a red color filter element, and two green display pixels each having a green color filter element). Display pixels  90  of each pixel group  900  may be illuminated at various intensities to generate light of a desired color that is a combination of the colors of pixels (e.g., violet light or white light). In some scenarios, pixel groups  900  may be referred to as display pixels having display sub-pixels  90 . 
     The arrangement of  FIG. 14  is merely illustrative. If desired, display  14  may include three pixels  90  per pixel group  900 , four pixels  90  per pixel group  900 , two pixels  90  per pixel group  900 , or more than four pixels  90  per pixel group  900 . In configurations of the type shown in  FIG. 14  in which a pixel group includes four pixels  90 , the second green pixel can be replaced by a clear aperture (e.g., a pixel with a clear color filter element or no color filter element) or a pixel of a color other than red, green, or blue, such as yellow, cyan, or magenta. The fourth pixel may be a full color pixel or a color pixel having a color filter element with a reduced pigment in comparison with other color pixels. This type of reduced pigment pixel may help adjust the color of white light emitted by the display. 
     Display light having a wide range of colors can be produced by display  14  by generating white light using OLED backlight structures  42  and using liquid crystals  52 ′ ( FIG. 6 ) to vary the amount of that white light that is transmitted through the various pixels  90  in each pixel group. 
     In many display applications, it may be desirable to generate white display light. However, display light that appears white to the human eye may be composed of various combination of colored light (i.e., various spectral distributions of light appear white to the human eye). The spectrum of white light is often characterized by a “color temperature” or “white point”, which distinguishes these various white colors. For example, a “warm” white emits more red light than a “cool” white, which emits more blue light. Some display standards mandate or recommend the use of specific color temperatures or white points for white light. 
     The white point for display  14  may be controlled by using liquid crystals  52 ′ to set the balance of emitted light from red, green, and blue pixels  90  of each pixel group  900 . However, in order to improve the efficiency of display  14 , the materials and/or formation of OLED backlight structures  42  may be configured to emit backlight that is closely matched to the desired white point of the display. 
     As shown in  FIG. 15 , OLED backlight pixels  94  that produce backlight such as white backlight for display  14  may include multiple emitting components  94 ′ (sometimes referred to as backlight sub-pixels  94 ′) that individually emit red, green, blue, or other colors (e.g., yellow), so that, in combination, all the emitters  94 ′ produce a white light. By controlling the relative intensity of light generated by each emitter  94 ′, the color temperature of each backlight pixel  94  can be tuned to match the color temperature associated with a desired display white point such as the D65 white point (e.g., a display white point corresponding to a color temperature of near 6500 K (degrees Kelvin)). 
     In this way, the overall power consumed by the backlight may be reduced because liquid crystals  52 ′ can block little or no light from the backlight to generate light of the appropriate white point. To maximize the efficiency of the display, the color temperature of backlight emitted by OLED backlight structures  42  may be within 1500 K, within 500 K, within 250 K, within 100 K, or within 50 K of the color temperature of the desired display white point (as examples). For example, for a D65 white point, the backlight color temperature may be between 5000K and 8000 K, between 6000 K and 7000 K, or between 6250 K and 6750 K (as examples). 
     If desired, the relative intensities of light generated by backlight sub-pixels  94 ′ can be adjusted to generate white backlight having a spectrum with emission peaks at desired wavelengths. For example, OLED backlight structures  42  may be configured to emit white light having emission peaks at emission peak wavelengths corresponding to transmission peak wavelengths in the transmission spectra of display color filter elements  56 ′ (see, e.g.,  FIG. 6 ). In this way, the efficiency of display  14  may be improved because most or all of the backlight will be transmitted by the color filter elements. 
     White light generated using backlight sub-pixels  94 ′ may, for example, have a red emission peak, a blue emission peak, and a green emission peak. As examples, one or more of the emission peak wavelengths may be within 30 nm, within 20 nm, within 10 nm, within 5 nm, or within one nm of the transmission peak wavelength of a corresponding color filter element. 
     As shown in  FIG. 15 , each backlight sub-pixel  94 ′ may have a characteristic size such widths WP1 and WP2. The characteristic size of each backlight sub-pixel  94 ′ in a backlight pixel  94  may be the same as, or different than, the characteristic size of other sub-pixels in each backlight pixel  94 . 
     In the example of  FIG. 15 , the blue backlight sub-pixel has a characteristic size (e.g., width WP2) that is larger than the characteristic size (e.g., widths WP1) of backlight sub-pixels  94 ′ of other colors. In this way, a lower backlight luminance level and power may be required for generating images that include blue light. This type of arrangement may help reduce the power requirements and undesired heating of the OLED backlight structures that can reduce the lifetime of an OLED emitter. 
     The example of  FIG. 15  in which the blue backlight sub-pixel is larger than the red, green, and yellow backlight sub-pixels is merely illustrative. If desired, a backlight sub-pixel of any color may be provided with a larger or smaller area to increase the efficiency of the display. 
     The foregoing is merely illustrative of the principles of this invention and various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention.

Metadata:
Filing Date: 20130212
Publication Date: 20161108
Grant Date: 20161108
Priority Date: 20130212
Inventors: DOYLE DAVID A.
DRZAIC PAUL S.
GUILLOU JEAN-PIERRE S.
WURZEL JOSHUA G.
Assignee: APPLE INC
CPC Classifications: [{"code": "G02F2001/133624", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F2202/28", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133603", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133624", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F2202/28", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F2202/28", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133624", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133603", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133603", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 51297231