PATENT DOCUMENT

Publication Number: US-9128327-B2
Application Number: US-201313891021-A
Country: US
Kind Code: B2

Title: Stress insensitive liquid crystal display

Abstract:
A display is provided that has upper and lower polarizers, a color filter layer, a liquid crystal layer, and a thin-film transistor layer. The color filter layer and thin-film transistor layer may be formed from materials such as glass that are subject to stress-induced birefringence. To reduce light leakage that reduces display performance, one or more internal layers may be incorporated into the display to help ensure that linearly polarized backlight that passes through the display is not undesirably converted into elliptically polarized light. The internal layers may include a thin-film polarizer layer that forms a coating on the color filter layer, a thin-film polarizer layer that forms a coating on the thin-film-transistor layer, a retarder layer that is formed as a coating on the color filter layer, and a retarder layer that is formed as a coating on the thin-film-transistor layer.

Claims:
What is claimed is:  
     
       1. A display having display pixels of different respective display pixel colors, the display comprising:
 an upper polarizer; 
 a lower polarizer; 
 a liquid crystal layer; 
 a first glass layer interposed between the upper polarizer and the liquid crystal layer, wherein the first glass layer comprises a color filter layer having color filter elements of different thicknesses for the different respective display pixel color; 
 a second glass layer interposed between the lower polarizer and the liquid crystal layer; and 
 a birefringent retarder layer located between the first and second glass layers to help counteract light polarization state changes associated with passing backlight through the liquid crystal layer, wherein the birefringent retarder layer has different thicknesses for different respective display pixel colors, wherein a combined thickness of the color filter element and the birefringement retarder layer is different for each of the respective display pixel colors, and wherein the birefringement retarder layer is interposed between the liquid crystal layer and the second glass layer. 
 
     
     
       2. The display defined in  claim 1  wherein the liquid crystal layer has different thickness for different respective display pixel colors. 
     
     
       3. The display defined in  claim 1  wherein the second glass layer comprises a thin-film-transition layer. 
     
     
       4. The display defined in  claim 1 , wherein the display pixel colors comprise red, green, and blue display peixel colors, and wherein the combined thickness of the color filter element and the birefringent retarder layer for the blue display pixel color is greater than the combined thickness of the color filter layer and the birefringent retarder layer for the red display pixel color and is greater then the combined thickness of the color filter layer and the birefringent retarder layer for the green display pixel color. 
     
     
       5. A display having display pixels of different respective display pixel colors, the display comprising:
 an upper polarized; 
 a lower polarizer; 
 a liquid crystal layer, wherein the liquid crystal layer has different thicknesses for different respective display pixel color; 
 a first glass layer interposed between the upper polarizer and the liquid crystal layer; 
 a second glass layer interposed between the lower polarized and the liquid crystal layer; 
 a birefringent retarder layer is interposed between the second glass layer and the liquid crystal layer, wherein the biefringement retarder layer has different thicknesses for the different respective display pixel colors, wherein the birefringement retarder layer and the liquid crystal layer are configured to help counteract light polarization state changes associated with passing backlight through the liquid crystal layer; and 
 an overcoat layer formed over the birefringement retarder layer, wherein the overcoat layer has different thicknesses for the different respective display pixel colors, correspond to the different thicknesses of the liquid crystal layer. 
 
     
     
       6. The display defined in  claim 5  wherein the first glass layer comprises of a color filter layer and wherein the color filter layer has color filter elements of different thicknesses for different respective display pixel colors. 
     
     
       7. The display defined in  claim 5  wherein the second glass layer comprises a thin-film-transistor layer. 
     
     
       8. The display defined in  claim 7  wherein the first glass layer comprises a color filter layer and wherein the color filter layer has color filter elements of different thicknesses for different respective display pixel colors. 
     
     
       9. A display having an array of display pixels of different respective display pixel colors, comprising:
 an upper polarizer; 
 a lower polarizer 
 a liquid crystal layer; 
 a first transparent layer interposed between the upper polarized and the liquid crystal layer, wherein the first transparent layer comprises a color filter layer with color filter elements of different colors for the different respective display pixel colors; 
 a second transparent layer interposed between the lower polarized and the liquid crystal layer, wherein the second transparent layer compises a thin-film transitor layer; and 
 a waveplate layer located between the first and second transparent layers, wherein the waveplate layer has different thicknesses for different respective display pixel colors, and wherein the waveplate layer is interposed between the liquid crystal layer and the thin-film transistor layer. 
 
     
     
       10. The display defined in  claim 9  wherein the liquid crystal layer has different thicknesses for different respective display pixel colors. 
     
     
       11. The method defined in  claim 9 , wherein an optical axis of the waveplate layer is parallel to an optical axis of the liquid crystal layer. 
     
     
       12. A display having display pixels of different respective display pixel colors, the display comprising:
 a upper polarizer; 
 a lower polarizer; 
 a liquid crystal layer; 
 a first glass layer interposed between the upper polarizer and the liquid crystal layer, wherein the first glass layer comprises a color filter layer with color filter elements of defferent thicknesses for different respective display display pixel colors; 
 a second glass layer interposed between the lower polarizer and the liquid crystal layer, wherein the second glass layer comprises a thin-film transistor layer; and 
 a birefringent retarder layer located between the first and second glass layers, wherein the birefringent retarder layer has different has different birefringence values for the different respective display pixel colors and is configured to help counteract light polarization state changes associated with passing backlight through the liquid crystal layer, wherein the display emits a different respective color of light for each respective display pixel color, wherein the birefringent retarder layer is configured to counteract the polarization state changes such that polarization states of each of the different respective color of light emitted form the display are the same, and wherein the birefringent retarder layer is interposed between the liquid crystal layer and the second glass layer and has different thicknesses for the different respective display pixel colors. 
 
     
     
       13. The display defined in  claim 12  wherein the liquid crystal layer has different thicknesses for different respective display pixel colors.

Description:
This application is a continuation-in-part of patent application Ser. No. 13/622,973, filed Sep. 19, 2012, which is hereby incorporated by reference herein in its entirety. 
    
    
     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. An electronic device may have a housing such as a housing formed from plastic or metal. Components for the electronic device such as display components may be mounted in the housing. 
     It can be challenging to incorporate a display into the housing of an electronic device. Size and weight are often important considerations in designing electronic devices. In some mounting configurations, standoffs, housing walls, display bezels and other structures may press against a display, leading to bending. If care is not taken, optical effects such as stress-induced birefringence may cause a display to exhibit undesired light leakage. 
     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. The display may have upper and lower polarizers. A color filter layer, a liquid crystal layer, and a thin-film transistor layer may be interposed between the upper and lower polarizers. A backlight unit may provide backlight that passes through the layers of the display. 
     The color filter layer and thin-film transistor layer may be formed from materials such as glass that are subject to stress-induced birefringence when the display is mounted in a housing for the electronic device. Light leakage may be reduced by incorporating one or more internal layers into the display to help ensure that linearly polarized backlight that passes through the display is not undesirably converted into elliptically polarized light. 
     The internal layers of the display may include a thin-film polarizer layer that forms a coating on the color filter layer and/or a thin-film polarizer layer that forms a coating on the thin-film-transistor layer. If desired, the internal layers may include a retarder layer (waveplate) that is formed as a coating on the color filter layer or thin-film-transistor layer. The retarder layer may be configured to counteract polarization state changes that are produced by backlight traveling through the liquid crystal layer. 
     The retarder layer and liquid crystal layer may be provided with different thicknesses and the retarder layer may be configured to exhibit different birefringence values in display pixels of different colors to counteract wavelength-dependent birefringence in the liquid crystal layer. 
     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 schematic diagram of an illustrative electronic device with a display in accordance with an embodiment of the present invention. 
         FIG. 5  is a cross-sectional side view of an illustrative display in accordance with an embodiment of the present invention. 
         FIG. 6  is a cross-sectional side view of a display layer such as a layer of glass in a thin-film-transistor layer or color filter layer showing how stress-induced birefringence may be generated upon application of tensile stress to the layer of glass. 
         FIG. 7  is a cross-sectional side view of a display layer such as a layer of glass in a thin-film-transistor layer of color filter layer showing how stress-induced birefringence may be generated upon application of compressive stress to the layer of glass. 
         FIG. 8  is a cross-sectional side view of a layer of material such as a layer of glass that has been subjected to bending and that exhibits stress-induced birefringence in a display. 
         FIG. 9  is a cross-sectional side view of a display with layers of glass that have been subjected to bending due to forces imparted by mounting the display in a device housing in accordance with an embodiment of the present invention. 
         FIG. 10A  is a cross-sectional diagram of display layers in a conventional liquid crystal display. 
         FIG. 10B  is a Poincare sphere showing how the polarization of backlight may vary when passing through the conventional display layers of  FIG. 9A  when the layers are subject to stress-induced birefringence. 
         FIG. 11A  is a cross-sectional diagram of display layers in a liquid crystal display with one or more internal polarization layers to help reduce light leakage due to stress-induced birefringence in accordance with an embodiment of the present invention. 
         FIG. 11B  is a Poincare sphere showing how the polarization of backlight may vary when passing through the display layers of  FIG. 11A  in the presence of stress-induced birefringence in some of the layers in accordance with an embodiment of the present invention. 
         FIG. 12A  is a cross-sectional diagram of display layers in a liquid crystal display with an internal retarder formed as a coating on an inner (lower) surface of a color filter layer in accordance with an embodiment of the present invention. 
         FIG. 12B  is a Poincare sphere showing how the polarization of backlight may vary when passing through the display layers of  FIG. 12A  in the presence of stress-induced birefringence in some of the layers in accordance with an embodiment of the present invention. 
         FIG. 13A  is a cross-sectional diagram of display layers in a liquid crystal display with an internal retarder formed as a coating on an inner (upper) surface of a thin-film transistor layer in accordance with an embodiment of the present invention. 
         FIG. 13B  is a Poincare sphere showing how the polarization of backlight may vary when passing through the display layers of  FIG. 13A  in the presence of stress-induced birefringence in some of the layers in accordance with an embodiment of the present invention. 
         FIG. 14  is a cross-sectional diagram of display layers in a liquid crystal display with different birefringent retarder layer thicknesses for display pixels of different respective display pixel colors in accordance with an embodiment of the present invention. 
         FIG. 15  is a Poincare sphere showing how the polarization of backlight may evolve when passing through the thin-film transistor layer and liquid crystal layer of the display layers of  FIG. 14  in accordance with an embodiment of the present invention. 
         FIG. 16  is a Poincare sphere showing how the polarization of backlight may continue to evolve when passing through the retarder layers and color filter layer of  FIG. 14  in accordance with an embodiment of the present invention. 
         FIG. 17  is a table showing illustrative thicknesses and properties that may be associated with the structures of  FIG. 14  in accordance with an embodiment of the present invention. 
         FIG. 18  is a cross-sectional diagram of an illustrative display with different retarder thicknesses and different color filter element thicknesses that result in different respective liquid crystal thicknesses for display pixels of different colors in accordance with an embodiment of the present invention. 
         FIG. 19  is a cross-sectional diagram of an illustrative display with different retarder thicknesses that result in different respective liquid crystal thicknesses for display pixels of different colors in accordance with an embodiment of the present invention. 
         FIG. 20  is a table showing illustrative thicknesses and properties that may be associated with the structures in a display with different liquid crystal thicknesses and different retarder thicknesses for different respective display pixel colors in accordance with an embodiment of the present invention. 
         FIG. 21  is a table showing illustrative thicknesses and properties that may be associated with the structures in a display with different liquid crystal thicknesses and different retarder thicknesses for different respective display pixel colors in which limits have been placed on retarder thickness variations in accordance with an embodiment of the present invention. 
         FIG. 22  is a cross-sectional diagram of an illustrative display with different retarder birefringence values for display pixels of different colors in accordance with an embodiment of the present invention. 
         FIG. 23  is a diagram showing how the structures of  FIG. 22  may be fabricated by adjusting substrate temperatures during ultraviolet light curing of liquid crystal monomer precursor material to form retarder regions with different birefringence values in accordance with an embodiment of the present invention. 
         FIG. 24  is a table showing illustrative properties that may be associated with a structure of the type shown in  FIG. 22  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 , and  3 . 
       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 a display cover layer or other exterior layer that includes openings for components such as button  26 . Openings may also be formed in a display cover layer or other display layer 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 a cover layer or other external layer with an opening to accommodate button  26  (as an example). 
     The illustrative configurations for device  10  that are shown in  FIGS. 1 ,  2 , and  3  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. 
     Displays for device  10  may, in general, include image pixels formed from light-emitting diodes (LEDs), organic LEDs (OLEDs), plasma cells, electrowetting pixels, electrophoretic pixels, liquid crystal display (LCD) components, or other suitable image pixel structures. In some situations, it may be desirable to use LCD components to form display  14 , so configurations for display  14  in which display  14  is a liquid crystal display are sometimes described herein as an example. It may also be desirable to provide displays such as display  14  with backlight structures, so configurations for display  14  that include a backlight unit may sometimes be described herein as an example. Other types of display technology may be used in device  10  if desired. The use of liquid crystal display structures and backlight structures in device  10  is merely illustrative. 
     A display cover layer may cover the surface of display  14  or a display layer such as a color filter layer or other portion of a display may be used as the outermost (or nearly outermost) layer in display  14 . A display cover layer or other outer display layer may be formed from a transparent glass sheet, a clear plastic layer, or other transparent member. 
     Touch sensor components such as an array of capacitive touch sensor electrodes formed from transparent materials such as indium tin oxide may be formed on the underside of a display cover layer, may be formed on a separate display layer such as a glass or polymer touch sensor substrate, or may be integrated into other display layers (e.g., substrate layers such as a thin-film transistor layer). 
     A schematic diagram of an illustrative configuration that may be used for electronic device  10  is shown in  FIG. 4 . As shown in  FIG. 4 , electronic device  10  may include control circuitry  28 . Control circuitry  28  may include storage and processing circuitry for controlling the operation of device  10 . Control circuitry  28  may, for example, include storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Control circuitry  28  may include processing circuitry based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio codec chips, application specific integrated circuits, etc. 
     Control circuitry  28  may be used to run software on device  10 , such as operating system software and application software. Using this software, control circuitry  28  may present information to a user of electronic device  10  on display  14 . When presenting information to a user on display  14 , sensor signals and other information may be used by control circuitry  28  in making adjustments to the strength of backlight illumination that is used for display  14 . 
     Input-output circuitry  30  may be used to allow data to be supplied to device  10  and to allow data to be provided from device  10  to external devices. Input-output circuitry  30  may include communications circuitry  32 . Communications circuitry  32  may include wired communications circuitry for supporting communications using data ports in device  10 . Communications circuitry  32  may also include wireless communications circuits (e.g., circuitry for transmitting and receiving wireless radio-frequency signals using antennas). 
     Input-output circuitry  30  may also include input-output devices  34 . A user can control the operation of device  10  by supplying commands through input-output devices  34  and may receive status information and other output from device  10  using the output resources of input-output devices  34 . 
     Input-output devices  34  may include sensors and status indicators  36  such as an ambient light sensor, a proximity sensor, a temperature sensor, a pressure sensor, a magnetic sensor, an accelerometer, and light-emitting diodes and other components for gathering information about the environment in which device  10  is operating and providing information to a user of device  10  about the status of device  10 . 
     Audio components  38  may include speakers and tone generators for presenting sound to a user of device  10  and microphones for gathering user audio input. 
     Display  14  may be used to present images for a user such as text, video, and still images. Sensors  36  may include a touch sensor array that is formed as one of the layers in display  14 . 
     User input may be gathered using buttons and other input-output components  40  such as touch pad sensors, buttons, joysticks, click wheels, scrolling wheels, touch sensors such as sensors  36  in display  14 , key pads, keyboards, vibrators, cameras, and other input-output components. 
     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 backlight structures such as backlight unit  42  for producing backlight  44 . During operation, backlight  44  travels outwards (vertically upwards in dimension Z in the orientation of  FIG. 5 ) and passes through display pixel structures 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. 
     In a configuration in which display layers  46  are used in forming a liquid crystal display, 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  60  and upper polarizer layer  54 . 
     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 for providing display  14  with the ability to display color images. 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  28  (e.g., one or more integrated circuits such as components  68  on printed circuit  66  of  FIG. 5 ) 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 circuitry  68  to display driver integrated circuit  62  using a signal path such as a signal path formed from conductive metal traces in flexible printed circuit  64  (as an example). 
     Display driver integrated circuit  62  may be mounted on thin-film-transistor layer driver ledge  82  or elsewhere in device  10 . A flexible printed circuit cable such as flexible printed circuit  64  may be used in routing signals between printed circuit  66  and thin-film-transistor layer  60 . If desired, display driver integrated circuit  62  may be mounted on printed circuit  66  or flexible printed circuit  64 . Printed circuit  66  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). 
     Backlight structures  42  may include a light guide plate such as light guide plate  78 . Light guide plate  78  may be formed from a transparent material such as clear glass or plastic. During operation of backlight structures  42 , a light source such as light source  72  may generate light  74 . Light source  72  may be, for example, an array of light-emitting diodes. 
     Light  74  from light source  72  may be coupled into edge surface  76  of light guide plate  78  and may be distributed in dimensions X and Y throughout light guide plate  78  due to the principal of total internal reflection. Light guide plate  78  may include light-scattering features such as pits or bumps. The light-scattering features may be located on an upper surface and/or on an opposing lower surface of light guide plate  78 . 
     Light  74  that scatters upwards in direction Z from light guide plate  78  may serve as backlight  44  for display  14 . Light  74  that scatters downwards may be reflected back in the upwards direction by reflector  80 . Reflector  80  may be formed from a reflective material such as a layer of white plastic or other shiny materials. 
     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 . Optical films  70  may overlap the other structures in backlight unit  42  such as light guide plate  78  and reflector  80 . For example, if light guide plate  78  has a rectangular footprint in the X-Y plane of  FIG. 5 , optical films  70  and reflector  80  may have a matching rectangular footprint. 
     When display  14  is mounted in a housing, the layers of display  14  such as thin-film transistor layer  58  and color filter layer  56  (e.g., the glass layers of the display) may be subjected to stresses. Stress may be imparted by bending the layers of display  14  when display  14  is mounted within housing  12  (e.g., using standoffs, housing walls, internal frame structures, display bezels, adhesive, and other mounting and support structures). The optical behavior of the layers of display  14  when bent depends on the type of materials used in forming the display layers. 
     As shown in  FIG. 6 , when a glass layer such as glass layer  92  is subjected to tensile stress by pulling ends  90  of glass layer  92  in is opposing outward directions  94 , the glass layer may exhibit birefringence so that the optical axis (extraordinary axis) of the glass runs parallel to the direction of stress (i.e., horizontally within the page in the orientation of  FIG. 6 ). The ordinary axis of the glass layer may run perpendicular to the optical axis in the plane of glass layer  92 . 
     As shown in  FIG. 7 , when a glass layer such as glass layer  92  is subjected to compressive stress by pushing ends  90  of glass layer  92  in opposing inward directions  96 , the glass layer may exhibit birefringence so that the optical axis (extraordinary axis) of the glass runs parallel to the direction of stress (i.e., into the page in the orientation of  FIG. 6 ). The ordinary axis may run perpendicular to the extraordinary axis in the plane of layer  92 . 
     A bent layer of glass such as glass layer  92  of  FIG. 8  may exhibit compressive stress along top surface  98  (e.g., near the edge of glass layer  92 ) and may exhibit tensile stress along lower surface  100 . As a result, glass layer  92  may be characterized by an optical axis such as optical axis  102  that extends into the page of  FIG. 8  along upper surface  98  and an optical axis such as optical axis  104  that extends parallel to the page of  FIG. 8  along lower surface  100 . 
     As shown in  FIG. 9 , when the layers of display  14  such as color filter layer  56  and thin-film-transistor layer  58  are mounted in device housing  12 , these layers may become bent (e.g., from forces introduced when mounting display  14  in housing  12 ). The bending of layers  56  and  58  may give rise to stress-induced birefringence. If care is not taken, this birefringence can adversely affect the performance of a display by causing light leakage when the display is viewed by a user. 
     Layers  56  and  58  may be glass layers or layers of other material with optical characteristics of the type described in connection with  FIGS. 6 ,  7 , and  8 . A layer of sealant such as sealant  106  (e.g., a bead of adhesive) may be interposed between color filter layer  56  and thin-film-transistor layer  58 . Sealant  106  may run around the periphery of display  14  in a rectangular ring and may surround and enclose liquid crystal material  52 . The presence of sealant  106  may cause the tensile stress on the lower surface of layer  56  to counteract the compressive stress on the upper surface of layer  58 . This compensation of stresses may cause optical axis  108  of layer  56  near the edge of layer  56  (e.g., in edge region ER) to point into the page of  FIG. 9  and may cause optical axis  110  of layer  58  near the edge of layer  58  (e.g., in edge region ER) to lie in the plane of layer  58  (lying within the page and pointing to the right in the example of  FIG. 9 ). The perpendicular optical axes of layers  58  and  56  (particularly prevalent in edge regions ER) may lead to changes in the polarization state of backlight passing through these layers that cause light leakage in conventional displays. 
       FIG. 10A  is a cross-sectional side view of a conventional display having glass layers that may be subject to stress-induced birefringence. As shown in  FIG. 10 , the display of  FIG. 10A  is a liquid crystal display in which liquid crystal layer  116  is sandwiched between thin-film-transistor layer  114  and color filter layer  118 . The display has upper and lower polarizers located respectively above and below the layers of  FIG. 10 . A backlight may generate backlight  112  that travels vertically upwards through the display in direction Z. Upon passing through the lower polarizer (i.e., at point A of  FIG. 10 ), backlight  112  may be linearly polarized (i.e., the lower polarizer may impart a linear polarization on backlight  112 ). The polarization of light  112  may then be affected by passing from point A to point B through thin-film-transistor layer  114  (which is exhibiting stress-induced birefringence), by passing from point B to point C through liquid crystal  116  (which is birefringent), and by passing from point C to point D through color filter layer  118  (which is exhibiting stress-induced birefringence). The upper and lower polarizers in the display do not typically exhibit stress-induced birefringence and are not shown in  FIG. 10A . 
     The polarization state of backlight  112  as backlight  112  travels through the layers of the conventional display of  FIG. 10A  is illustrated in the Poincare sphere of  FIG. 10B . In a Poincare sphere, linear polarization states are represented by points on equatorial line  130 . Point  132  represents right-hand circularly polarized light. Point  134  represents left-hand circularly polarized light. Intermediate points on the Poincare sphere represent various types of elliptically polarized light. 
     Each of the layers of  FIG. 10A and 10B  has an optical axis that is aligned in a different direction. In the Poincare sphere representation of  FIG. 10B , thin-film transistor layer  114  is characterized by optical axis  122 , color filter layer  118  is characterized by optical axis  124 , and liquid crystal layer  116  is characterized by optical axis  120 . On the Poincare sphere, azimuthal angle α of a vector each point P on equatorial line  130  is equal to 2θ, where θ is equal to an actual physical angle (e.g., an azimuthal angle in real space that is associated with the orientation of an optical axis for a display layer or an angle associated with the polarization of light such as light  112  that is passing through the display). As a result, a pair of axes such as thin-film-transistor axis  122  and liquid crystal layer axis  120  that appear to be perpendicular to each other in the Poincare sphere representation of  FIG. 10B  are, within the real-life coordinate system of the display, oriented at a 45° angle with respect to each other. Similarly, a pair of axes such as thin-film-transistor axis  122  and color filter layer axis  124  that appear to be separated by 180° in the Poincare sphere representation of  FIG. 10B  are, within the real-life coordinate system of the display, oriented at a 90° angle with respect to each other (i.e., axis  124  is perpendicular to axis  122 ). 
     The behavior of the polarization of light  112  is affected by the orientation of each optical axis and the thickness of each layer in the display of  FIG. 10A . As shown in  FIG. 10B , light  112  is initially linearly polarized (point A). Following passage through layer  114 , the polarization of light  112  is represented by point B on the Poincare sphere of  FIG. 10B  (i.e., light  112  is transformed from linearly polarized light to elliptically polarized light due to the stress-induced birefringence of layer  114 ). Visually, the transition from point A to point B along line  140  on the surface of the Poincare sphere is associated with rotation of point A about thin-film-transistor layer optical axis  122  on the surface of the sphere. Following passage of light  112  through layer  114 , light  112  passes through liquid crystal layer  116 . Layer  116  causes the polarization of light  112  to move from point B to point C along line  142  on the Poincare sphere of  FIG. 10B  (rotating about liquid crystal layer optical axis  120 ). 
     After traveling through liquid crystal layer  116 , light  112  passes through layer  118 . The birefringence of layer  118  causes the polarization of light  112  to change from the polarization state represented by point C to the polarization state represented by point D along line  144  of the Poincare sphere of  FIG. 10B  (rotating about color filter layer optical axis  124 ). 
     If liquid crystal layer  116  had not been present, the polarization state changes associated with lines  144  and  140  would have canceled each other out, resulting in minimal changes to the linear polarization of light  112  (i.e., light  112  would have remain linearly polarized with a polarization state represented by point A and the display would have operated satisfactorily). Because of the presence of liquid crystal layer  116  and the associated transition of the polarization state of light  112  from point B to point C, however, light  112  at point D (i.e., light  112  exiting the upper surface of color filter layer  118  of  FIG. 10A ) is substantially elliptically polarized, rather than being linearly polarized as desired. When this elliptically polarized light passes through the upper polarizer, the fact that the light is not linearly polarized as expected allows some of the light to leak out from the upper surface of the display through the upper polarizer, even when the electric field being applied to liquid crystal layer  116  is attempting to display a black display pixel. Display performance in conventional displays is therefore limited by the inability of conventional displays to satisfactorily display black images in the presence of stress-induced birefringence in the layers of the display. 
     Illustrative display configurations with designs that address the shortcomings of conventional displays in handling stress-induced birefringence are shown in  FIGS. 11 ,  12 , and  13 . 
     As shown in the example of  FIG. 11A , display  14  may be provided with one or more internal polarizer layers such as layer  146  and/or layer  146 ′. The layers of display  14  that are shown in  FIG. 11A  may be sandwiched between upper and lower polarizers (not shown in  FIG. 11A ) such as upper polarizer  54  and lower polarizer  60 . Layers such as layers  146  and/or layer  146 ′ may be implemented as thin-film coatings on glass substrates. For example, internal polarizer  146  may be formed as a thin-film coating on the upper surface of thin-film-transistor layer  58  and internal polarizer  146 ′ may be formed as a thin-film coating on the lower surface of color filter layer  56 . Examples of thin-film polarizer coatings that may be used for forming polarizers such as polarizers  146  and  146 ′ of  FIG. 11A  include polymers containing optically anisotropic dyes that are characterized by different absorption coefficients in different lateral dimensions within the plane of display  14 . The thickness of the thin-film coatings used in forming the internal polarizer(s) for display  14  may be, for example, less than 10 microns, less than 3 microns, less than 2 microns, or less than 1 micron. 
     The behavior of the polarization of display backlight such as light  44  is affected by the orientation of each optical axis and the thickness of each layer in display  14 . Optical axis  150  of  FIG. 11B  may be associated with thin-film-transistor layer  58 , which may exhibit stress-induced birefringence. Optical axis  152  of  FIG. 11B  may be associated with the liquid crystal layer  52 . Optical axis  154  of  FIG. 11B  may be associated with polarizer layer  146  and may be associated with color filter layer  56 , which may exhibit stress-induced birefringence. 
     As shown in  FIG. 11B , light  112  is initially linearly polarized (point A). Following passage through thin-film-transistor layer  58 , the polarization of light  44  may be represented by point B on the Poincare sphere of  FIG. 11B  (i.e., light  44  may be transformed from linearly polarized light to elliptically polarized light due to the stress-induced birefringence of layer  58 ). The transition from point A to point B along line  156  on the surface of the Poincare sphere of  FIG. 11B  is associated with rotation about thin-film-transistor layer optical axis  150 . Following passage of light  44  through layer  58 , light  44  may pass through polarizer layer  146  to point B′. The transition of the polarization state of light  44  when traveling from point B to B′ through polarizer layer  146  of  FIG. 11A  is represented by the transition from elliptically polarized polarization state B to linearly polarized polarization state B′ in  FIG. 11B  along line  158 . 
     Due to the presence of linear polarizer layer  146 , light  44  in polarization state B′ is characterized by linear polarization. As a result, light  44  will be less elliptically polarized (more linearly polarized) upon passing through layers  52  and  56  than in conventional display arrangements. As shown in  FIG. 11B , the transition of the polarization state of light  44  when traveling from point B′ to point C through liquid crystal layer  52  of  FIG. 11A  may be represented by line  160  and the transition of the polarization state of light  44  when traveling from point C to point D through color filter layer  56  may be represented by line  162 . Although light  44  is elliptically polarized at point D, light  44  at point D is more linearly polarized than conventional light D of  FIGS. 10A and 10B , thereby reducing light leakage and improving the performance of display  14 . 
     If desired, lower internal polarizer  146  may be supplemented by adding an upper internal polarizer such as polarizer  146 ′ of  FIG. 11A . Upper polarizer  146 ′ may also be used alone (e.g., instead of lower internal polarizer  146 ). Whether polarizer layer  146  is used alone, polarizer  146 ′ is used alone, or polarizers  146  and  146 ′ are used together, the presence of internal polarizer material adjacent to liquid crystal layer  52  may help remove the birefringence effects of the glass layers in display  14  such as layer  58 , thereby reducing the ellipticity of the polarized light exiting layer  56  and improving display performance. 
       FIG. 12A  is a diagram of another illustrative configuration that may be used for the middle layers of display  14  between upper polarizer  54  and lower polarizer  60 . As shown in the example of  FIG. 12A , display  14  may be provided with an internal retarder layer such as retarder layer  178  (sometimes referred to as a wave plate, birefringent layer, or birefringent coating). The polarization change that is imposed on light  44  by retarder  178  may be configured to be equal and opposite to that of liquid crystal layer  52  (as an example). Internal retarder layers such as retarder layer  178  may be implemented as a coating on the lower surface of color filter layer  56  (e.g., a thin-film coating of a liquid crystal polymer or other birefringent material). The thickness of the thin-film coating used in forming an internal retarder such as retarder  178  for display  14  may be, for example, less than 10 microns, less than 3 microns, less than 2 microns, or less than 1 micron. 
     The behavior of the polarization of display backlight such as light  44  is affected by the orientation of each optical axis and the thickness of each layer in display  14 . Optical axis  150  of  FIG. 12B  may represent the optical axis of thin-film-transistor layer  58 , which may exhibit stress-induced birefringence. Optical axis  152  of  FIG. 12B  may be associated with liquid crystal layer  52 . Optical axis  154  of  FIG. 12B  may represent the optical axis of color filter layer  56 , which may exhibit stress-induced birefringence. Optical axis  176  of  FIG. 12B  may be associated with retarder  178  (i.e., retarder  178  may have an optical axis that is perpendicular to the optical axis of liquid crystal layer  52  when measured in degrees θ). 
     As shown in  FIG. 12B , light  112  is initially linearly polarized (point A). Following passage through thin-film-transistor layer  58 , the polarization of light  44  may be represented by point B on the Poincare sphere of  FIG. 12B  (i.e., light  44  may be transformed from linearly polarized light to elliptically polarized light due to the stress-induced birefringence of layer  58 ). The transition from point A to point B along line  156  on the surface of the Poincare sphere of  FIG. 12B  is associated with rotation about thin-film-transistor layer optical axis  150 . 
     Following passage of light  44  through layer  58 , light  44  may pass through liquid crystal layer  52  to point B′. The transition of the polarization state of light  44  when traveling from point B to B′ through liquid crystal layer  52  of  FIG. 12A  is represented by the transition from elliptically polarized polarization state B to elliptically polarized polarization state B′ in  FIG. 12B  along line  170 . 
     Due to the presence of birefringent retarder  178 , the polarization state of light  44  returns to state B as light passes through retarder  178  from point B′ to C of  FIG. 12A , effectively reversing the polarization transition associated with passing through liquid crystal layer  52 . The transition of the polarization state of light  44  when traveling from point B′ to C through retarder  178  is represented by the transition from elliptically polarized polarization state B′ to elliptically polarized polarization state C. As shown in  FIG. 12B , line  172 , which is associated with rotation about retarder optical axis  176 , which is perpendicular to optical axis  152  in e (i.e., in the layers of display  14 ), retraces (in reverse direction) the course of line  170 , thereby counteracting and neutralizing the polarization state changes associated with passing backlight  44  through liquid crystal layer  52 . 
     Following passage of light  44  through retarder  178 , light  44  passes through color filter layer  56 . As shown in  FIG. 12B , the transition of the polarization state of light  44  when traveling from point C to point D through color filter layer  56  may be represented by line  174 , which is associated with rotation about color filter optical axis  154 . Because transition  172  brings the polarization state of light  44  back to point B from point B′, transition  174  causes the polarization of light  44  to return to its original state (i.e., point D is associated with the same linearly polarized light state as original point A). As a result, display performance will not be degraded due to an elliptical light polarization state as light  44  exits the upper surface of color filter layer  56 . 
     In the illustrative configuration of  FIG. 13A , the internal retarder (retarder  178 ′) has been formed on the upper surface of thin-film-transistor layer  58 , rather than the lower surface of color filter layer  56 . With this type of arrangement, the polarization state transition from B′ to C returns light  44  to the same polarization state (point C) as the arrangement of  FIG. 12A , but does so by following transition line  172 ′ of  FIG. 13B  (associated with rotation about optical axis  176 ′ of retarder  178 ′) rather than by following transition line  172  of  FIG. 12B . In the configuration of  FIG. 12A , the optical axis of retarder  178  is perpendicular to the optical axis of liquid crystal layer  52  (i.e., separated by α=180° and θ=90°). In the configuration of  FIG. 13A , the optical axis of retarder  178 ′ is parallel to the optical axis of liquid crystal layer  52 . 
     The birefringence of liquid crystal layer  52  may be wavelength dependent (i.e., liquid crystal layer  52  may exhibit dispersion in its refractive index). As a result, there may be larger values of Δn (the index of refraction difference between the extraordinary axis index ne and the ordinary axis index no) at shorter wavelengths of light than at longer wavelengths of light. To ensure that the retarder in display  14  (and/or other structures in display  14 ) can adequately counteract light polarization state changes caused by passing the backlight through the liquid crystal layer in display pixels of all colors (red, green, and blue) in the display, the birefringent retarder layer structures and/or other structures such as liquid crystal layer structures in display  14  can be provided with different configurations for display pixels of different respective display pixel colors. 
     Consider, as an example, illustrative display  14  of  FIG. 14 . As shown in  FIG. 14 , display  14  contains an array of display pixels of different colors such as red display pixels DP-R, green display pixel DP-G, and blue display pixel DP-B. Black matrix BM forms an opaque grid of rectangular openings. Color filter elements (e.g., colored polyimide) of different colors such as red element R, green element G, and blue element B are formed in the openings of the black matrix. Retarder  178 ″ has different heights (thicknesses) for different respective display pixel colors. Red display pixel DP has relatively thin color filter element R, so retarder  178 ″ has a relatively large thickness d 1  for red display pixel DP-R. Green and blue filter elements have respective thicknesses that give rise to different respective thicknesses d 2  and d 3  of retarder  178 ″ in green display pixel DP-G and blue display pixel DP-B. The different retarder thicknesses for the different colors of display pixels in display  14  help compensate for wavelength dependence in the birefringence of liquid crystal layer  52 . 
       FIG. 15  is a Poincare sphere showing how the polarization of backlight may vary when passing through the thin-film transistor layer  58  and liquid crystal layer  52  of the display layers of  FIG. 14 . Initially, the polarization of red pixel light is at point AR, the polarization of green pixel light is at point AG, and the polarization of blue light is at point AB. Following passage of the light through layer  58  of  FIG. 14  and the corresponding rotation about thin-film-transistor optical axis  150  in the sphere of  FIG. 15 , the polarization of red pixel light is represented by point BR, the polarization of green pixel light is represented by point BG, and the polarization of blue pixel light is represented by point BB. After the light passes through liquid crystal layer  52 , which exhibits wavelength-dependent birefringence, the polarization states of the red, green, and blue pixels become different. As shown in  FIG. 15 , following rotation about liquid crystal optical axis  152 , red pixel light is represented by point BR′, green pixel light is represented by point BG′, and blue pixel light is represented by point BB′. These points have different polarization states due to dispersion. 
     The dispersion of the liquid crystal layer can be counteracted using different thicknesses for retarder  178 ″ in pixels of different colors. 
       FIG. 16  shows how following passage of light through the retarder layers of different thicknesses (and following rotation about retarder optical axis  176 ″ of  FIG. 16 ), point BR′ rotates to the position indicated by point CR, point BG′ rotates to the position indicated by point CG, and point BB′ rotates to the position indicated by point CB. Different amounts of rotation are associated with display pixels of different colors due to the different thicknesses of the retarder layer in each differently colored display pixel. The resulting polarization states represented by points CR, CG, and CB are the same (i.e., dispersion effects have been compensated). Accordingly, following passage of the light through the color filter elements R, B, and G (which don&#39;t affect the polarization states) and passage through color filter layer  56  (and associated rotation about color filter optical axis  154  of  FIG. 16 ), red pixel light has polarization state DR, green pixel light has polarization state DG, and blue pixel light has polarization state DB. The polarization states DR, DG, and DB are equal, indicating that wavelength dependent effects in the birefringence of liquid crystal layer  52  have been removed from display  14 . 
     The table of  FIG. 17  shows illustrative thicknesses and properties that may be associated with the structures of  FIG. 14 . The entries of column I show different display pixel center wavelengths for display  14 . The entries of column II show how the liquid crystal thickness in this example is constant across different display pixels. The entries of column III show the wavelength dependence of the birefringence of the liquid crystal layer. The entries of column IV show the value of Δn*d of the liquid crystal layer for different pixel colors. The entries of column V show how the retarder thickness varies as a function of pixel color. The entries of column VI show how the birefringence of the retarder material itself may be somewhat wavelength dependent. The entries of column VII show the value of Δn*d for the retarder at different pixel colors. Retardation is equal to 2Π*Δn*d/λ (where λ represents wavelength). The entries of column VIII show the value of Δn*d taking into account both retardation in the liquid crystal and in the retarder. Dividing by λ to compute a number proportional to retardation (i.e., Δn*d/λ) gives the entries of column IX. The entries of column IX are all equal, demonstrating that the wavelength dependence of the liquid crystal layer birefringence has been counteracted by the wavelength dependence of the retarder and the different respective retarder thicknesses d 1 , d 2 , and d 3  for differently colored display pixels. 
     If desired, the liquid crystal layer thickness can be configured to be different for display pixels of different colors, as shown in  FIGS. 18 and 19 . The different liquid crystal layer thicknesses can help counteract the wavelength dependence of the liquid crystal layer birefringence. In the example of  FIG. 18 , color filter elements R, G, and B have different thicknesses and retarder structures  178 ″ have different thicknesses (Z 1 , Z 2 , and Z 3 ) for different pixel colors, resulting in different liquid crystal layer thicknesses h 1 , h 2 , and h 3 . In the arrangement of  FIG. 18 , clear non-birefringent polymer overcoat layer OC may lie between layer  178 ″ and layer  52 . 
     In the arrangement of  FIG. 19 , overcoat OC is interposed between the color filter elements and layer  178 ″. Other configurations for adjusting the retarder thicknesses and/or the thicknesses of the liquid crystal layers in display pixels of different colors may be used, if desired. 
       FIG. 20  is a table showing how display  14  may be configured to provide liquid crystal layer  52  with different thicknesses. The entries of column II of the table of  FIG. 20  show the different liquid crystal layer thicknesses that may be produced for different display pixel colors. The entries of column V show how the retarder thicknesses can be varied to ensure that the entries of column IX do not exhibit any wavelength dependence. In the example of  FIG. 21 , the maximum variation of retarder thickness that is allowed has been limited (e.g., to facilitate processing). As shown by the entries of column IX in  FIG. 21 , a small (acceptable) amount light leakage may result in this scenario. 
       FIG. 22  is a cross-sectional diagram of an illustrative display with different retarder birefringence values for display pixels of different colors. As shown in  FIG. 22 , retarder layer  178 ″ may (as an example) have the same thickness Z0 for each pixel color, but may have different birefringence values Δn1, Δn2, and Δn3. Displays may also be formed that have different liquid crystal thicknesses and/or different retarder thicknesses in addition to different birefringence values for different pixel colors. 
       FIG. 23  shows how a structure of the type shown in  FIG. 22  may be formed. Retarder layer  178 ″ may be formed by applying ultraviolet light to liquid crystal monomer layer LC. Layer LC may be formed from a liquid precursor material that is polymerized to form retarder layer  178 ″ upon exposure to ultraviolet (UV) light. At higher temperatures, the birefringence of the resulting retarder material will be lower than at lower temperatures. 
     As shown in  FIG. 23 , photolithographic masks may be used to expose red pixels to UV light while maintaining the retarder precursor material at a first temperature TR, may be used to expose green pixels to UV light while maintaining the retarder precursor material at a second temperature TG that is different from the first temperature, and may then be used to expose blue pixels to UV light while maintaining the retarder precursor material at a third temperature TB that is different from the first and second temperatures. As an example, TR may be more than TG, which may be more than TB. Larger substrate temperatures tend to reduce the amount of birefringence (i.e., the magnitude of Δn) in layer  178 ″. 
     As shown in column VI of  FIG. 24 , the use of different temperatures during ultraviolet light curing of the retarder precursor material to form retarder layer  178 ″ causes the retarder to exhibit different Δn values (birefringence values) for display pixels of different colors. These Δn values may be configured to counteract the wavelength dependence of the birefringence of liquid crystal layer  52 , as shown in column IX of  FIG. 24 . 
     The birefringent retarder layer with different thicknesses for different pixel colors may be located above or below the liquid crystal layer (e.g., when using a uniform liquid crystal layer thickness and/or when using a liquid crystal layer thickness that varies for different display pixel colors and/or when using a constant retarder thickness and/or when using a retarder thickness that varies for different display pixel colors and/or when using a retarder of a constant Δn value for different display color pixels and/or when using a retarder with different Δn values for different display color pixels). Any of the structures and layouts of the foregoing embodiments (e.g., the order of layers, the thicknesses of the liquid crystal layer, the thicknesses of the retarder, the birefringence values of the retarder, etc.) may be used in combination with the structures and layouts of any other of the foregoing embodiments. 
     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: 20130509
Publication Date: 20150908
Grant Date: 20150908
Priority Date: 20120919
Inventors: YANG YOUNG CHEOL
CHEN CHENG
Assignee: APPLE INC
CPC Classifications: [{"code": "G02F1/133528", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/13363", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133371", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F2001/133638", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F2001/133565", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133528", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133528", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133371", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133565", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133565", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133638", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133371", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133638", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/13363", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/13363", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 50274143