PATENT DOCUMENT

Publication Number: US-9588371-B2
Application Number: US-201414497252-A
Country: US
Kind Code: B2

Title: Flipped panel displays with black column spacers

Abstract:
A liquid crystal display may have a thin-film transistor layer with an array of pixel electrode structures for applying electric fields to a liquid crystal layer. The liquid crystal display may also have a color filter layer with an array of color filter elements. The color filter elements may allow the display to display color images. The color filter layer may be interposed between the thin-film transistor layer and a backlight. The liquid crystal layer may be sandwiched between the thin-film transistor layer and the color filter layer. The color filter layer may have a transparent substrate on which the color filter elements are formed. Black masking structures may be formed on a transparent overcoat layer that covers the color filter elements. Black column spacers may be formed from the same layer of material that forms the black masking structures.

Claims:
What is claimed is: 
     
       1. A display, comprising:
 a thin-film transistor layer, wherein the thin-film transistor layer comprises a transparent substrate on which a thin-film transistor and data lines are formed; 
 a backlight; 
 a color filter layer interposed between the backlight and the thin-film transistor layer; 
 a layer of liquid crystal material interposed between the thin-film transistor layer and the color filter layer, wherein the color filter layer includes:
 an additional transparent substrate; 
 color filter elements formed on the additional transparent substrate; 
 a coating layer formed on the color filter elements; and 
 black masking structures formed on the coating layer, wherein the black masking structures overlap the data lines; and 
 
 a black column spacer formed on the coating layer adjacent to the black masking structures, wherein the black column spacer overlaps the thin-film transistor, wherein the thin-film transistor layer further comprises an additional black masking structure interposed between the thin-film transistor and the transparent substrate, and wherein the additional black masking structure overlaps the black column spacer and the thin-film transistor. 
 
     
     
       2. The display defined in  claim 1  wherein the coating layer comprises a transparent overcoat layer having a lower surface adjacent to the color filter elements and having an opposing upper surface on which the black masking structures are formed. 
     
     
       3. The display defined in  claim 2  wherein the black masking structures are formed from a black polymer layer and wherein a portion of the black polymer layer forms the black column spacer. 
     
     
       4. The display defined in  claim 3  wherein the black column spacer extends from the color filter layer to the thin-film transistor layer through the layer of liquid crystal material. 
     
     
       5. The display defined in  claim 1  wherein the additional black masking structure in the thin-film transistor layer that overlaps the black column spacer and the thin-film transistor also overlaps at least one of the data lines and the black masking structures in the color filter layer. 
     
     
       6. The display defined in  claim 5  further comprising at least one transparent layer within the thin-film transistor layer that is interposed between the additional black masking structure in the thin-film transistor layer and the liquid crystal layer. 
     
     
       7. The display defined in  claim 6  wherein the at least one transparent layer comprises a gate insulator layer. 
     
     
       8. The display defined in  claim 7  further comprising a planarization layer between the additional black masking structure in the thin-film transistor layer and the gate insulator layer. 
     
     
       9. The display defined in  claim 8  wherein the color filter elements include red color filter elements, blue color filter elements, and green color filter elements. 
     
     
       10. The display defined in  claim 9  further comprising first and second polarizers, wherein the thin-film transistor layer, the liquid crystal layer, and the color filter layer are interposed between the first and second polarizers. 
     
     
       11. A display, comprising:
 a thin-film transistor layer having a data line and a black masking structure that overlaps the data line; 
 a color filter layer; 
 a layer of liquid crystal material interposed between the thin-film transistor layer and the color filter layer, wherein the color filter layer includes color filter elements covered with a transparent overcoat layer and a grid of black masking material on the transparent overcoat layer; and 
 a black column spacer on the transparent overcoat layer in an opening in the grid, wherein the black masking structure in the thin-film transistor layer overlaps the black masking material in the color-filter layer and the black column spacer. 
 
     
     
       12. The display defined in  claim 11  further comprising:
 a backlight, wherein the color filter layer is interposed between the thin-film transistor layer and the backlight. 
 
     
     
       13. The display defined in  claim 12  wherein the color filter layer comprises a transparent substrate on which the color filter elements are formed and wherein the color filter elements include red, green, and blue color filter elements. 
     
     
       14. The display defined in  claim 13  wherein the grid of black masking material has a plurality of openings that are aligned with respective color filter elements among the color filter elements on the transparent substrate. 
     
     
       15. The display defined in  claim 14 , wherein the grid of black masking material overlaps borders between the red, green, and blue color filter elements.

Description:
This application claims the benefit of provisional patent application No. 61/989,467 filed May 6, 2014, 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 include displays for presenting information to users. 
     Displays such as liquid crystal displays may have a thin-film transistor layer that contains thin-film transistor circuitry and pixel electrodes. Liquid crystal displays may also have color filter layers. A color filter layer may have an array of color filter elements of different colors. A layer of liquid crystal material is sandwiched between the thin-film transistor layer and the color filter layer. The thin-film transistor layer is used to apply electric fields to the liquid crystal layer with the pixel electrodes. The color filter layer allows the display to display color images for a user. 
     To form a satisfactory display, the color filter layer should be aligned with the thin-film transistor layer. Alignment challenges and other issues should be addressed to ensure satisfactory display performance. If care is not taken, a display may be dim or may present images that appear washed out to a user. 
     It would therefore be desirable to be able to provide improved displays. 
     SUMMARY 
     An electronic device may be provided with a display. The display may be a liquid crystal display. The liquid crystal display may have a backlight that provides illumination for the display. 
     The liquid crystal display may have a thin-film transistor layer with an array of pixel electrode structures for applying electric fields to pixel-sized regions of a liquid crystal layer. The liquid crystal display may also have a color filter layer with an array of color filter elements. The color filter elements may be aligned with the array of pixel electrode structures and may allow the display to display color images. The color filter layer may be interposed between the thin-film transistor layer and the backlight. The liquid crystal layer may be sandwiched between the thin-film transistor layer and the color filter layer. 
     The color filter layer may have a transparent substrate on which the color filter elements are formed. Black masking structures may be formed on a transparent overcoat layer that covers the color filter elements. The black masking structures may have openings that are aligned with respective color filter elements. Black column spacers that extend from the color filter layer to the thin-film transistor layer through the liquid crystal layer may be formed from the same layer of material that forms the black masking structures. 
    
    
     
       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. 
         FIG. 2  is a perspective view of a portable electronic device such as a cellular telephone or other small portable device with a display in accordance with an embodiment. 
         FIG. 3  is a perspective view of an illustrative tablet computer with a display in accordance with an embodiment. 
         FIG. 4  is a perspective view of a display with an optional stand in accordance with an embodiment. 
         FIG. 5  is a cross-sectional side view of an illustrative display in accordance with an embodiment. 
         FIG. 6  is as cross-sectional side view of an edge portion of a display showing how the display may have inactive and active areas in accordance with an embodiment. 
         FIG. 7  is a cross-sectional side view of an illustrative display having a thin-film transistor layer on top of a color filter layer in accordance with an embodiment. 
         FIG. 8  is a cross-sectional side view of an illustrative display with black masking structures in accordance with an embodiment. 
         FIG. 9  is a cross-sectional side view of an illustrative display with black column spacers in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Illustrative electronic devices of the types that may be provided with displays are shown in  FIGS. 1, 2, 3, and 4 . 
     Electronic device  10  of  FIG. 1  has the shape of a laptop computer and has upper housing  12 A and lower housing  12 B with components such as keyboard  16  and touchpad  18 . Device  10  has hinge structures  20  (sometimes referred to as a clutch barrel) to allow upper housing  12 A to rotate in directions  22  about rotational axis  24  relative to lower housing  12 B. Display  14  is mounted in housing  12 A. Upper housing  12 A, which may sometimes be referred to as a display housing or lid, is placed in a closed position by rotating upper housing  12 A towards lower housing  12 B about rotational axis  24 . 
       FIG. 2  shows an illustrative configuration for electronic device  10  based on 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  has opposing front and rear surfaces. Display  14  is mounted on a front face of housing  12 . Display  14  may have an exterior layer that includes openings for components such as button  26  and speaker port  28 . Device  10  may, if desired, be a compact device such as a wrist-mounted device or pendant device (as examples). 
     In the example of  FIG. 3 , electronic device  10  is a tablet computer. In electronic device  10  of  FIG. 3 , housing  12  has opposing planar front and rear surfaces. Display  14  is mounted on the front surface of housing  12 . As shown in  FIG. 3 , display  14  has an opening to accommodate button  26 . 
       FIG. 4  shows an illustrative configuration for electronic device  10  in which device  10  is a computer display, a computer that has an integrated computer display, or a television. Display  14  is mounted on a front face of housing  12 . With this is of arrangement, housing  12  for device  10  may be mounted on a wall or may have an optional structure such as support stand  30  to support device  10  on a flat surface such as a table or desk. 
     Display  14  may be a liquid crystal display or a display formed using other suitable display technologies. A cross-sectional side view of an illustrative configuration for display  14  of device  10  (e.g., a liquid crystal display for the devices of  FIG. 1 ,  FIG. 2 ,  FIG. 3 ,  FIG. 4  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 of housing  12 ). 
     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 (innermost) polarizer layer  60  and upper (outermost) 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, outer substrate layer  56  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 . Inner substrate layer  58  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. 
     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. 
     Display  14  may have an array of display pixels (e.g., a rectangular array having rows and columns) for displaying images to a viewer. Vertical signal lines called data lines may be used to carry display data to respective columns of display pixels. Horizontal signal lines called gate lines  206  may be used to carry gate line signals (sometimes referred to as gate control signals or gate signals) to respective rows of display pixels. The outline of the array of display pixels in display  14  defines an active area for display  14 . The active area may have a rectangular shape and may be surrounded by an inactive border region. An inactive border area may, for example, run along one edge, two edges, three edges, or all four edges of the active area. 
     A cross-sectional side view of an illustrative electronic device having a display such as display  14  of  FIG. 5  is shown in  FIG. 6 . As shown in  FIG. 6 , images may be displayed on central active area AA of display  14 . Inactive area IA may have a rectangular ring shape that runs around the rectangular periphery of active area AA. To avoid unsightly bezel structures in device  10 , it may be desirable to keep inactive area IA free of overlapping housing structures, bezels, or other potentially unattractive border structures. 
       FIG. 7  shows a detailed cross-sectional side view of display  100  (e.g., a display of the type that may be used in implementing display  14  of  FIGS. 1, 2, 3, and 4 ). Displays such as display  100  of  FIG. 7  in which the thin-film transistor (TFT) layer  56  is closer to a user  99  viewing display  100  than the color filter (CF) layer  58  and in which color filter laser  58  is interposed between TFT laser  56  and backlight  42  are sometimes referred to as flipped panel displays. 
     As shown in  FIG. 7 , TFT layer  56  may include a TFT substrate  102 - 1  (e.g., a glass substrate layer), TFT black masking structures  106  formed on substrate  102 - 1 , a planarization layer  104  (e.g., a spin-on glass layer, sometimes referred to herein as an SOG layer) formed on substrate  102 - 1  over black masking structures  106 , a gate insulating (GI) layer  150  formed on planarization layer  104 , conductive data line structures  152  formed on layer  150 , dielectric layers  154  formed on layer  150  over the data line structures  152 , a power supply layer  156  (e.g., a common voltage Vcom layer) formed over layers  154 , an insulating layer  158  formed on Vcom layer  156 , and pixel electrode structures  160  formed on insulating layer  158 . Voltages applied on the pixel electrode structures  160  may control the liquid crystal (LC) material  52  that is sandwiched between TFT layer  56  and CF layer  58 . 
     CF layer  58  may include a CF substrate  102 - 2  (e.g., a glass substrate layer), CF black masking structures  116  formed on substrate  102 - 2 , color filter elements  108  (e.g., red color filter elements  108 -R, green color filter elements  108 -G, blue color filter elements  108 -G, and other types of color filter elements) formed on substrate  102 - 2  corresponding to each respective display pixel, and a color filter array overcoat laser  110  formed over the color filter elements  108 . Overcoat layer  110  may be formed form a clear polymer or other transparent materials. 
     During TFT-to-CF layer bonding operations, misalignment may cause the TFT structures to be laterally shifted in one direction (as indicated by arrow at  105 ) while causing the CF structures to be laterally shifted in an opposite direction as indicated by arrow  115 ). This can cause the TFT black masking structures  106  to shift to new position  106 ′ while causing the CF black masking structures  116  to shift to new position  116 ′. This type of misalignment can undesirably reduce the display pixel aperture ratio (AR). Even without any lateral misalignment, the off-axis AR is limited by the width Wx of the CF black masking material  116 . 
     It may be desirable to decrease the width Wx of CF black masking structure  116  to improve aperture ratio metrics. However, doing so would exacerbate color washout issues associated with adjacent display pixels. As shown in  FIG. 7 , the vertical distance between pixel electrode  160  and CF black masking structure  116  is defined by height Hx. 
     One way of improving reducing color washout is to reduce the vertical distance between pixel electrode  160  and CF black masking structure  116 .  FIG. 8  shows one suitable arrangement in which CF black masking structure  117  is formed on overcoat layer  110 . Formed in this way, the distance between structures  160  and  117  is reduced (i.e., Hy is less than Hx), which allows the width Wy of CF black masking structure  117  to be reduced (i.e., Wy is less than Wx) while maintaining the same color washout margin. Reducing the width of CF black masking structure  117  in this way can therefore help improve the on axis and/or off-axis aperture ratio of display  100 . Black masking structures  117  may surround respective color filter elements (e.g., black masking structures  117  may form a grid or other pattern with openings that are aligned with respective color filter elements to allow colored light from those elements to pass through the display). The black masking structures form borders for the pixels in the display and prevent undesired color mixing effects that might otherwise arise when light from adjacent pixels mixes due to inadequate separation between adjacent pixels. 
       FIG. 9  shows another suitable arrangement in which column spacer structures such as column spacer structures  119  are formed at the same time as the CF black masking structures  117  (e.g., using a half-tone photolithographic mask). Column spacer structures  119  may also be formed using opaque material with the desired optical density and are therefore sometimes referred to as black column spacers (BCS). Spacers  117  and  119  may be formed from an opaque material such as black photoimageable polymer. Column spacer  119  may be firmed directly beneath a thin-film transistor such as transistor  200 . Transistor  200  may serve as a gating switch that can be selectively turned on to pass desired voltages to corresponding pixel electrode structures  160 . A TFT black masking structure  210  may be formed over column spacer structure  119  and an adjacent masking structure  117  lying directly beneath a corresponding data line  152 . If desired, column spacer  119  may be formed using transparent material. 
     The foregoing is merely illustrative and various modifications can be made by those skilled in the art without departing from the scope and spirit of the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20140925
Publication Date: 20170307
Grant Date: 20170307
Priority Date: 20140506
Inventors: YANG BYUNG DUK
LI FLORA M.
PARK KWANG SOON
HUNG MING-CHIN
CHANG SHIH-CHANG
KIM YONG KWAN
CHANG YOUNG CHEOL
Assignee: APPLE INC
CPC Classifications: [{"code": "G02F1/1368", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133516", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/136209", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133512", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133509", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F2001/133519", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/13394", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133519", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133512", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/1368", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/136209", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133512", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133509", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133519", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/13394", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133509", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133516", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 54367752