PATENT DOCUMENT

Publication Number: US-9482905-B2
Application Number: US-201414307841-A
Country: US
Kind Code: B2

Title: Display with column spacer structures

Abstract:
A display may have a color filter layer and a thin-film transistor layer. A layer of liquid crystal material may be located between the color filter layer and the thin-film transistor layer. Column spacers may be formed on the color filter layer to maintain a desired gap between the color filter and thin-film transistor layers. Support pads may be used to support the column spacers. The column spacers and support pads may have comparable thicknesses. Different column spacers may be located at different portions of the support pads to allow the support pad size to be reduced while ensuring adequate support.

Claims:
What is claimed is: 
     
       1. A display, comprising:
 a color filter layer having an inner surface and an opposing outer surface, wherein the color filter layer includes a column spacer on the inner surface; 
 a thin-film transistor layer having a column spacer support pad for supporting the column spacer, wherein the column spacer support pad and the column spacer have heights that are within 30% of each other; 
 a layer of liquid crystal material between the color filter layer and the thin-film transistor layer; 
 a black matrix on the inner surface, wherein the column spacer is formed at least partly from color filter element material that overlaps the black matrix; and 
 an organic polymer overcoat layer on the color filter layer, wherein the organic polymer overcoat layer has first and second opposing sides, wherein the column spacer is formed on the first side of the organic polymer overcoat layer and wherein the black matrix is formed on the second side of the organic polymer overcoat layer. 
 
     
     
       2. The display defined in  claim 1  wherein the column spacer support pad is circular. 
     
     
       3. The display defined in  claim 2  wherein the column spacer is circular. 
     
     
       4. The display defined in  claim 3  wherein the column spacer support pad has a first diameter, wherein the column spacer has a second diameter, and wherein the second diameter is different than the first diameter. 
     
     
       5. The display defined in  claim 4  wherein the first diameter is greater than the second diameter. 
     
     
       6. The display defined in  claim 5  wherein the first diameter is more than 5 microns more than the second diameter. 
     
     
       7. The display defined in  claim 1  wherein the color filter layer comprises an array of color filter elements formed from color filter material. 
     
     
       8. The display defined in  claim 1  further comprising a subspacer column spacer on the inner surface of the color filter layer. 
     
     
       9. The display defined in  claim 8 , wherein the subspacer column spacer is separated from the thin-film transistor layer by a gap. 
     
     
       10. The display defined in  claim 1  further comprising:
 a subspacer column spacer on the inner surface of the color filter layer; and 
 a subspacer column spacer support pad under the subspacer column spacer. 
 
     
     
       11. The display defined in  claim 10  wherein the subspacer column spacer and the subspacer column spacer support pad are separated by a gap of 0.2 to 0.8 microns. 
     
     
       12. The display defined in  claim 11  wherein the subspacer column spacer has a laterally elongated shape and wherein the subspacer column spacer support pad has a laterally elongated shape that extends perpendicular to the laterally elongated shape of the subspacer column spacer. 
     
     
       13. The display defined in  claim 1  wherein the column spacer support pad and the column spacer have heights that differ by less than 10%. 
     
     
       14. The display defined in  claim 1 , wherein the column spacer is in direct contact with the first side of the organic polymer overcoat layer and the black matrix is in direct contact with the second side of the organic polymer overcoat layer. 
     
     
       15. A display, comprising:
 a substrate layer having an inner surface and an opposing outer surface, wherein the substrate layer includes a column spacer on the inner surface; 
 a thin-film transistor layer having a column spacer support pad for supporting the column spacer; 
 an array of pixels formed on the thin-film transistor layer; 
 a black matrix on the thin-film transistor layer that separates the pixels, wherein the column spacer support pad is formed on the thin-film transistor layer on top of the black matrix; 
 a layer of liquid crystal material between the substrate layer and the thin-film transistor layer; and 
 an array of color filter elements formed from color filter material on the thin-film transistor layer each of which overlaps a respective one of the pixels, wherein the column spacer support pad is formed at least partly from color filter element material. 
 
     
     
       16. A display, comprising:
 a color filter layer having an inner surface and an opposing outer surface, wherein the color filter layer has an array of color filter elements of different colors formed from color filter element material on the inner surface and wherein the array of color filter elements includes a first color filter element and a second color filter element; 
 a thin-film transistor layer; 
 a layer of liquid crystal material between the color filter layer and the thin-film transistor layer; 
 a plurality of column spacers on the inner surface of the color filter layer that are formed from the color filter element material, wherein the plurality of column spacers includes a first column spacer; 
 a plurality of column spacer support pads on the thin-film transistor layer, wherein each column spacer support pad supports a respective one of the column spacers; and 
 a black matrix on the color filter layer that defines openings for the color filter elements, wherein the column spacers overlap the black matrix, wherein a portion of the black matrix is interposed between the first and second color filter elements, wherein the first column spacer overlaps the portion of the black matrix, and wherein the first column spacer directly contacts the portion of the black matrix, the first color filter element, and the second color filter element. 
 
     
     
       17. The display defined in  claim 16  wherein the column spacer support pads and the column spacers have respective heights that differ by less than 20%. 
     
     
       18. The display defined in  claim 16 , wherein the column spacer directly contacts two surfaces of the first color filter element and two surfaces of the second color filter element. 
     
     
       19. The display defined in  claim 18 , wherein the first color filter element is a first color, wherein the second color filter element is a second color that is different than the first color, wherein the first column spacer comprises color filter element material that is a third color, and wherein the first color and the third color are the same.

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. 
     Liquid crystal displays contain a layer of liquid crystal material. Display pixels in a liquid crystal display contain thin-film transistors and electrodes for applying electric fields to the liquid crystal material. The strength of the electric field in a display pixel controls the polarization state of the liquid crystal material and thereby adjusts the brightness of the display pixel. 
     Substrate layers such as color filter layers and thin-film transistor layers are used in liquid crystal displays. The thin-film transistor layer contains an array of the thin-film transistors that are used in controlling electric fields in the liquid crystal layer. The color filter layer contains an array of color filter elements such as red, blue, and green elements. The color filter layer provides the display with the ability to display color images. 
     In an assembled display, the layer of liquid crystal material is sandwiched between the thin-film transistor layer and the color filter layer. Polyimide passivation layers cover the inner surface of the color filter layer and the upper surface of the thin-film transistor layer. An array of column spacers is formed on the inner surface of the color filter layer to maintain a desired gap between the color filter layer and the thin-film transistor layer. Column spacers are typically formed from hard organic materials such as photoresist. 
     During assembly operations, the layers of a liquid crystal display can be subjected to lateral forces. Even if great care is taken when handling the color filter layer and thin-film transistor layer, there is a possibility that these two layers will shift laterally with respect to each other. Lateral movement between the color filter layer and the thin-film transistor layer can cause damage to the display. For example, the column spacers can scratch the sensitive polyimide passivation layer material on the thin-film transistor layer, leading to undesirable visible artifacts on the display. 
     It would therefore be desirable to be able to provide electronic device displays with improved column spacer structures for minimizing scratches during lateral movement between display layers. 
     SUMMARY 
     A display may have a color filter layer with opposing outer and inner surfaces. The thin-film transistor layer may have an upper surface that faces the inner surface of the color filter layer. A layer of liquid crystal material may be located between the inner surface of the color filter layer and the upper surface of the thin-film transistor layer. 
     Column spacers may be formed on the color filter layer to maintain a desired separation between the color filter layer and the thin-film transistor layer. The columns spacers may include main column spacers that extend vertically across the entire liquid crystal layer and subspacer column spacers that extend vertically only partway across the liquid crystal layer. 
     Support pads may be formed on the surface of the thin-film transistor layer. The support pads may be used to support the column spacers. The support pads and column spacers may have comparable heights. 
     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. 
         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. 
         FIG. 3  is a perspective view of an illustrative electronic device such as a tablet computer with a display in accordance with an embodiment. 
         FIG. 4  is a perspective view of an illustrative electronic device such as a computer display with display structures 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 a top view of an array of display pixels in a display in accordance with an embodiment. 
         FIG. 7  is a cross-sectional side view of a portion of a thin-film transistor layer in accordance with an embodiment. 
         FIG. 8  is a cross-sectional side view of a portion of an illustrative display showing how column spacer structures can be configured in accordance with an embodiment. 
         FIG. 9  is a cross-sectional side view of a portion of a display having column spacers and column spacer support pads in accordance with an embodiment. 
         FIG. 10  is a cross-sectional side view of a portion of a display having a column spacer and a column spacer support pad that have shifted relative to each other in accordance with an embodiment. 
         FIG. 11  is a cross-sectional side view of a portion of a display having a subspacer in accordance with an embodiment. 
         FIG. 12  is a cross-sectional side view of a portion of a display having a subspacer structure with a subspacer support pad in accordance with an embodiment. 
         FIG. 13  is a top view of an illustrative column spacer and support pad in accordance with an embodiment. 
         FIG. 14  is a top view of a portion of a display showing where column spacer structures may be located relative to pixel structures in accordance with an embodiment. 
         FIG. 15  is a top view of a column spacer with a laterally elongated shape and a column support pad with a laterally elongated shape that crosses the column spacer at a right angle in accordance with an embodiment. 
         FIG. 16  is a top view of an oval laterally elongated column spacer and an oval laterally elongated support pad that cross the column spacer at a right angle in accordance with an embodiment. 
         FIG. 17  is a cross-sectional side view of a display substrate that has been provided with a black matrix in accordance with an embodiment. 
         FIG. 18  is a cross-sectional side view of the display substrate of  FIG. 17  following patterning of a red layer of color filter material to form a red color filer element in accordance with an embodiment. 
         FIG. 19  is a cross-sectional side view of the display substrate of  FIG. 18  following patterning of a green layer of color filter material to form a green color filter element in accordance with an embodiment. 
         FIG. 20  is a cross-sectional side view of the display substrate of  FIG. 19  following deposition of a patterned blue layer of color filter material to form a blue color filter element in accordance with an embodiment. 
         FIG. 21  is a cross-sectional side view of the display substrate of  FIG. 20  following deposition and patterning of a layer of color filter material to form a column spacer structure in accordance with an embodiment. 
         FIG. 22  is a cross-sectional side view of the display substrate of  FIG. 21  following deposition of an overcoat layer in accordance with an embodiment. 
         FIG. 23  is a top view of a portion of a display showing how column spacer structures may be located over a black matrix that has openings for color filter elements in accordance with an embodiment. 
         FIG. 24  is a cross-sectional side view of a portion of a display substrate in which a column spacer has been formed over an overcoat layer and over a black matrix on the underside of a color filter layer in accordance with an embodiment. 
         FIG. 25  is a cross-sectional side view of a portion of a display with a column spacer and a corresponding spacer support pad in accordance with an embodiment. 
         FIG. 26  is a cross-sectional side view of a portion of a display having spacer structures formed from a column spacer on the underside of a clear substrate layer and a corresponding support pad formed from color filter element material on a thin-film transistor layer over a black matrix in accordance with an embodiment. 
     
    
    
     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  includes display pixels formed from liquid crystal display (LCD) components or other suitable image pixel structures. 
     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 . 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 for display  14  of device  10  (e.g., for display  14  of 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 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 (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 to a display driver integrated circuit such as circuit  62 A or  62 B using a signal path such as a signal path formed from conductive metal traces in a rigid or flexible printed circuit such as printed circuit  64  (as an example). 
     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. 
     As shown in  FIG. 6 , display  14  may include a pixel array such as pixel array  92 . Pixel array  92  may be controlled using control signals produced by display driver circuitry. Display driver circuitry may be implemented using one or more integrated circuits (ICs) and may sometimes be referred to as a driver IC, display driver integrated circuit, or display driver. 
     During operation of device  10 , control circuitry in device  10  such as memory circuits, microprocessors, and other storage and processing circuitry may provide data to the display driver circuitry. The display driver circuitry may convert the data into signals for controlling the pixels of pixel array  92 . 
     Pixel array  92  may contain rows and columns of display pixels  90 . The circuitry of pixel array  92  may be controlled using signals such as data line signals on data lines D and gate line signals on gate lines G. 
     Pixels  90  in pixel array  92  may contain thin-film transistor circuitry (e.g., polysilicon transistor circuitry or amorphous silicon transistor circuitry) and associated structures for producing electric fields across liquid crystal layer  52  in display  14 . Each display pixel may have a respective thin-film transistor such as thin-film transistor  94  to control the application of electric fields to a respective pixel-sized portion  52 ′ of liquid crystal layer  52 . 
     The thin-film transistor structures that are used in forming pixels  90  may be located on a thin-film transistor substrate such as a layer of glass. The thin-film transistor substrate and the structures of display pixels  90  that are formed on the surface of the thin-film transistor substrate collectively form thin-film transistor layer  58  ( FIG. 5 ). 
     Gate driver circuitry may be used to generate gate signals on gate lines G. The gate driver circuitry may be formed from thin-film transistors on the thin-film transistor layer or may be implemented in separate integrated circuits. Gate driver circuitry may be located on both the left and right sides of pixel array  92  or on one side of pixel array  92  (as examples). 
     The data line signals on data lines D in pixel array  92  carry analog image data (e.g., voltages with magnitudes representing pixel brightness levels). During the process of displaying images on display  14 , a display driver integrated circuit may receive digital data from control circuitry and may produce corresponding analog data signals. The analog data signals may be demultiplexed and provided to data lines D. 
     The data line signals on data lines D are distributed to the columns of display pixels  90  in pixel array  92 . Gate line signals on gate lines G are provided to the rows of pixels  90  in pixel array  92  by associated gate driver circuitry. 
     The circuitry of display  14  such as demultiplexer circuitry, gate driver circuitry, and the circuitry of pixels  90  may be formed from conductive structures (e.g., metal lines and/or structures formed from transparent conductive materials such as indium tin oxide) and may include transistors such as transistor  94  that are fabricated on the thin-film transistor substrate layer of display  14 . The thin-film transistors may be, for example, polysilicon thin-film transistors or amorphous silicon transistors. 
     As shown in  FIG. 6 , pixels such as pixel  90  may be located at the intersection of each gate line G and data line D in array  92 . A data signal on each data line D may be supplied to terminal  96  from one of data lines D. Thin-film transistor  94  (e.g., a thin-film polysilicon transistor or an amorphous silicon transistor) may have a gate terminal such as gate  98  that receives gate line control signals on gate line signal path G. When a gate line control signal is asserted, transistor  94  will be turned on and the data signal at terminal  96  will be passed to node  100  as voltage Vp. Data for display  14  may be displayed in frames. Following assertion of the gate line signal in each row to pass data signals to the pixels of a that row, the gate line signal may be deasserted. In a subsequent display frame, the gate line signal for each row may again be asserted to turn on transistor  94  and capture new values of Vp. 
     Pixel  90  may have a signal storage element such as capacitor  102  or other charge storage element. Storage capacitor  102  may be used to store signal Vp in pixel  90  between frames (i.e., in the period of time between the assertion of successive gate signals). 
     Display  14  may have a common electrode coupled to node  104 . The common electrode (which is sometimes referred to as the Vcom electrode) may be used to distribute a common electrode voltage such as common electrode voltage Vcom to nodes such as node  104  in each pixel  90  of array  92 . As shown by illustrative electrode pattern  104 ′ of  FIG. 6 , Vcom electrode  104  may be implemented using a blanket film of a transparent conductive material such as indium tin oxide (i.e., electrode  104  may be formed from a layer of indium tin oxide that covers all of pixels  90  in array  92 ). 
     In each pixel  90 , capacitor  102  may be coupled between nodes  100  and  104 . A parallel capacitance arises across nodes  100  and  104  due to electrode structures in pixel  90  that are used in controlling the electric field through the liquid crystal material of the pixel (liquid crystal material  52 ′). As shown in  FIG. 6 , electrode structures  106  may be coupled to node  100 . The capacitance across liquid crystal material  52 ′ is associated with the capacitance between electrode structures  106  and common electrode Vcom at node  104 . During operation, electrode structures  106  may be used to apply a controlled electric field (i.e., a field having a magnitude proportional to Vp-Vcom) across pixel-sized liquid crystal material  52 ′ in pixel  90 . Due to the presence of storage capacitor  102  and the capacitance of material  52 ′, the value of Vp (and therefore the associated electric field across liquid crystal material  52 ′) may be maintained across nodes  106  and  104  for the duration of the frame. 
     The electric field that is produced across liquid crystal material  52 ′ causes a change in the orientations of the liquid crystals in liquid crystal material  52 ′. This changes the polarization of light passing through liquid crystal material  52 ′. The change in polarization may, in conjunction with polarizers  60  and  54  of  FIG. 5 , be used in controlling the amount of light  44  that is transmitted through each pixel  90  in array  92  of display  14 . 
     A cross-sectional side view of a portion of thin-film transistor layer  58  taken through transistor  94  in one of display pixels  90  is shown in  FIG. 7 . As shown in  FIG. 7 , thin-film transistor layer  58  may include thin-film transistor structures  58 A on substrate  58 B. Substrate  58 B may be a transparent sheet of material such as glass or other dielectric. Structures  58 A may include thin-film transistor  94 . Transistor  94  may have an active layer such as layer  110  (e.g. a layer of amorphous silicon or polysilicon). Dielectric passivation layer  112  may separate gate conductor  98  from active layer  110 . Passivation layer  114  may cover the conductive material of source-drain conductors  96  and  100 . An opening may be formed in passivation layer  114  to form a contact between terminal  96  and electrode layer  106 . 
     Common electrode (Vcom) layer  104  may be formed on the upper surface of dielectric planarization layer  116 . Passivation layer  118  may separate electrode layers  106  from common electrode layer  104 . Electrode layer  106  may be formed from a layer of transparent conductive material such as indium tin oxide and may be patterned to form finger-shaped electrodes (not shown in  FIG. 7 ). Common electrode layer  104  may be formed as a blanket film of transparent conductive material such as indium tin oxide that covers array  92 . Passivation layers such as layers  112 ,  114 , and  118  and planarization layer  116  may be formed from polymers such as photoresist, silicon oxide, silicon nitride, or other suitable dielectric layers. Gate electrode structures  98  and source and drain electrodes  100  and  96  may be formed from a conductive material such as metal. In scenarios in which electrodes  104  and  106  are formed from a transparent conductive material such as indium tin oxide, backlight  44  may pass through display  14  as shown in  FIG. 5  without being blocked by electrodes  104  and  106 . 
     The sheet resistance of indium tin oxide is relatively high compared to the sheet resistance of aluminum, copper, and other metals. To lower the effective resistance of the Vcom electrode, it may be desirable to form a grid of metal on top of thin-film transistor layer  58 . The grid of metal may be shorted to the indium tin oxide layer forming the Vcom electrode to reduce the effective resistance of the Vcom electrode. The grid of metal may have openings to accommodate the light passing through pixels  90 . The openings may be, for example, rectangular openings that are aligned with respective liquid crystal pixels  52 ′. 
     To maintain a desired gap for the liquid crystal material between the lower surface of color filter layer  56  and the upper surface of thin-film transistor layer  58 , display  14  may be provided with column spacer structures (sometimes referred to as post spacers). A cross-sectional side view of display  14  showing how column spacers  122  may be formed in an array on the lower (inner) surface of color filter layer  56  is shown in  FIG. 8 . As shown in  FIG. 8 , color filter layer  56  may include a transparent substrate layer such as clear glass layer  56 A. A layer of color filter elements (e.g., an array of red, blue, and green color filter elements formed from colored photoresists) such as layer  56 B may be formed on the inner surface of color filter layer  56 . A grid of opaque material such as black photoresist forms black matrix  124 . Black matrix  124  has a grid pattern with an array of openings such as opening  126 . Each opening  126  allows light  44  to pass for a different respective one of pixels  90 . 
     The presence of black matrix  124  may help delineate the boundaries between pixels (e.g., red, blue, and green pixels  90 ), so that light does not leak between adjacent pixels. The size of openings such as opening  126  in black matrix  124  (sometimes referred as the pixel “aperture”) is preferably as large as possible to enhance display brightness efficiency. If aperture  126  is too small, light  44  will be blocked from escaping display  14  and the images that are presented on display  14  will be undesirably dimmed. 
     Column spacers  122  in display  14  may be formed from a material such as a hardened photoimageable polymer. When handing display layer such as layers  56  and  58  during assembly of display  14 , there is a potential for layers  56  and  58  to slip with respect to each other. If care is not taken, column spacers may scratch sensitive material layers in a display such as a thin-film transistor polyimide passivation layer (e.g. layer  118  in the example of  FIG. 10 ). 
     To ensure that aperture  126  is not too small, it is desirable to minimize lateral dimensions WBM of black mask  124  and to maximize lateral dimensions WP of aperture  126 . In some conventional displays, wide black mask structures are formed over column spacers to prevent passivation layer scratches that are produced by the column spacers during assembly from becoming visible to a user. In these conventional displays, aperture size may be undesirably small. 
     To help minimize scratches and other display damage while maximizing pixel apertures, column spacer pad structures such as column spacer pads  130  can be formed on thin-film-transistor layer  58 . Column spacer pads  130  may be formed from the same material that is being used elsewhere on the surface of thin-film-transistor layer  58  to form a resistance-lowering Vcom conductive grid (i.e., pads  130  may be patterned on the surface of layer  58  using the same layer of metal that is being used to form common electrode metal grid lines on Vcom layer  104 ). 
     Column spacers  122  may be distributed across the display  14  to maintain a desired gap between layers  56  and  58 . Columns spacers  122  may include more than one type of structure. For example, some column spacer structures, such as the left-hand column spacer structure of  FIG. 8 , may extend all the way from thin-film transistor surface  132  to color filter layer surface  134 . By using column spacer thickness T 1  and column spacer support pad thickness T 2 , column spacer structures such as the left-hand column spacer structure of  FIG. 8  may establish a desired thickness T=T 1 +T 2  for liquid crystal layer  52 . Columns spacers such as the left-hand column spacer of  FIG. 8  that establish the separation T between thin-film transistor layer  58  and color filter layer  56  may sometimes be referred to as being the main columns spacers or main columns spacer structures for display  14 . 
     Other column spacer structures, which may sometimes be referred to as subspacer column spacer structures or subspacers may extend only partway between surfaces  134  and  132 . In the example of  FIG. 8 , the right-hand column spacer  122  is a subspacer. A gap GP separates upper surface  132  of thin-film transistor layer  58  from lower surface  136  of subspacer column spacer  122 . Because subspacer surfaces such as surface  136  of  FIG. 8  are separated from passivation layer  118  on the upper surface of thin-film transistor layer  58  by gap GP, the subspacers will tend not to scratch passivation layer  118 , even if there is lateral movement between layers  56  and  58  during assembly. 
     During use of device  10 , display  14  may be subjected to external pressure. For example, a user of device  10  may press against the surface of display  14  with a finger or other external object. Under pressure from the external object, color filter layer  56  may bow downwards towards surface  132  of thin-film transistor layer  58 . Due to the presence of subspacers  122  (e.g., a column spacer of the type shown in the right-hand side of  FIG. 8 ), color filter layer  56  and thin-film transistor layer  58  will be maintained a desired distance apart from each other. The presence of column spacer pads  130  may also help separate the subspacers from thin-film transistor layer  58  in configurations of the type shown in  FIG. 8 . 
     Subspacers may be formed in display  14  in any suitable ratio to the main column spacers. For example, there may be one, two or more, ten or more, 100 or more, 1000 or more, or 10,000 or more subspacers for each main column spacer in display  14 . Displays that only contain main column spacers and that are free of subspacers may also be used. 
     The main column spacers and the subspacers are blocked from view by a user of device  10  using overlapping regions of black matrix  124  in color filter element layer  56 B. Somewhat smaller regions of black matrix  124  may be used when covering subspacers than when covering main column spacers, because subspacers are not as prone to producing scratches as the main columns spacers when color filter layer  56  and thin-film transistor layer  58  slip with respect to each other during assembly. Nonetheless, it is generally desirable to maintain the size of the apertures associated with the subspacers relatively close in magnitude to the apertures associated with the main column spacers. The ability to increase the apertures such as aperture  126  of  FIG. 8  that are adjacent to the main column spacers may therefore have a substantial influence on the ability to increase aperture size for all pixels in display  14 . 
     Column spacer support pads  130  may be circular, oval, semicircular, rectangular, square, may have curved edges, may have straight edges, or may have a combination of curved and straight edges. 
     The size of aperture  126  can be maximized by minimizing the size of column spacer support pads  130 . With one suitable arrangement, columns spacer support pad size may be minimized by supporting different columns spacers  122  at different locations on different column spacer support pads  130 . This creates redundancy in the column support structures that allows some of the column spacers to slip off of their respective support pads without compromising the overall support functions of the column spacers. 
     If desired, display  14  may have column spacers and support pads that have comparable thicknesses. This type of arrangement is shown in  FIG. 9 . As shown in  FIG. 9 , column spacer  122  may have a thickness H 1  and column spacer support pad  130  may have thickness H 2 . The total thickness of column spacer  122  and support pad  130  (i.e., the thickness of liquid crystal layer  52 ) is thickness HT (i.e., HT=H 1 +H 2 ). The value of thickness HT may be 2.5 to 4 microns, 2 to 5 microns, 1.8 to 7 microns, more than 2.5 microns, less than 2.5 microns, more than 4 microns, or less than 4 microns (as examples). The value of H 2  may be 0.5 to 1.2 microns, 0.5 to 2 microns, or other suitable values. The value of H 1  may be equal to the value of HT minus the value of H 2 . The ratio of H 1 /H 2  may be in the range of 85/15 to 15/85, may be in the range of 70/30 to 30/70, may be in the range of 60/40 to 40/60, may be 50/50, or may have other suitable values. As shown in  FIG. 10 , when the values of H 1  and H 2  are relatively closed to each other (i.e., when H 1  and H 2  are equal and/or have values that are within 10% of each other, within 20% of each other, within 30% of each other, or within 40% or other value of each other), misalignment of column spacer  122  and support pad  130  may result in a configuration in which column spacer  122  hangs in liquid crystal layer  52  without contacting the surface of layer  58 . (Other columns spacers may be supported by their support pads, if desired) This avoids damage to the surface of layer  58  that might create visible artifacts. 
       FIG. 11  is a cross-sectional side view of an illustrative subspacer design that may be used in a display conjunction with the column spacer structures of  FIG. 9  or other column spacers. As shown in  FIG. 11 , subspacer  122 SUB may be separated from the surface of layer  58  by a gap H 3 . The value of H 3  may be 0.2 to 0.8 microns, 0.3 to 0.7 microns, or other suitable value. 
     In the illustrative configuration of  FIG. 12 , subspacer structures have been formed that include both a downwardly extending subspacer (subspacer  122 SUB) and an upwardly extending subspacer support pad  130 SUB. Subspacers of the type shown in  FIG. 12  may be used with displays having column spacers of the type shown in  FIG. 9  and other displays. 
     Column spacers, support pads, and subspacers may be circular (e.g., the footprint of these structures may have the shape of a circle), as shown in  FIG. 13 . In the example of  FIG. 13 , column spacer  122  has been formed on top of support pad  130 . Spacer  122  may have a diameter D 1  of about 5-9 microns, 3-12 microns, or 2-15 microns (as examples). Diameter D 3  of support pad  130  may be 8 microns more than D 1 , may be 2-10 microns more than D 1 , may be 0.5 to 10 microns more than D 1 , may be at least 5 microns more than D 1 , may be equal to D 1 , may be less than 10 microns more than D 1 , may be more than 6 microns more than D 1 , or may be any other suitable value. 
       FIG. 14  is a top view of a portion of display  14  showing how column spacer structures such as the structures of  FIG. 13  may overlap black matrix  124 . Black matrix  124  may have the shape of a grid with horizontal and vertical lines. The lines of black matrix  124  may separate individual color filter elements  200  for respective display pixels  90  (e.g., red color filter elements, green color filter elements, and blue color filter elements may overlap openings in the black matrix). Black matrix  124  and color filter elements  200  in a color filter array may, if desired, be formed on thin-film transistor layer (e.g., in a configuration in which the color filter for display  14  is formed as an integral portion of the thin-film transistor layer rather than being formed as a separate layer above liquid crystal layer  52 ). 
     If desired, column spacer  122  and support pad  130  (or a subspacer and subspacer support pad) may be laterally elongated and may be oriented at right angles to each other as illustrated in the top view of  FIG. 15 . In subspacer configurations, spacer  122  may be a subspacer and pad  130  may be a subspacer support pad that is vertically separated from spacer  122  by a gap such as gap H 3 . In the  FIG. 15  example, structures  122  and  130  have rectangular laterally elongated shapes that extend perpendicular to each other.  FIG. 16  shows how column spacer  122  and support pad  130  (or a subspacer and corresponding subspacer support pad) may have oval footprints that extend perpendicular to each other. Other shapes may be used if desired. Illustrative operations involved in forming column spacer structures (e.g., column spacer  122  and pad  130  of  FIG. 9  or other column spacer structures) are shown in  FIGS. 17, 18, 19, 20, 21, and 22 . 
     Initially, black matrix  124  may be formed on layer  56  ( FIG. 17 ). Black matrix  124  may have a grid shape with openings for color filter elements of different colors or may have other suitable shapes. 
     Following formation of layer  56 , a first layer of color filter elements may be formed. For example, a color filter element  200  of a particular color may be formed, as illustrated by color filter element  200  for a red pixel R in  FIG. 18 . 
     As shown in  FIG. 19 , a color filter element G for a green pixel may be formed after the color filter element for the red pixel has been formed. 
     Following formation of the red and green color filter elements  200  (or after forming color filter elements from color filter material of different colors), an additional color filter element such as blue color filter element  200  (i.e., element B) may be formed on layer  56 . Layer  56  may be a color filter layer. (If desired, black matrix and color filter element structures may also be formed on a thin-film transistor layer.) 
     Color filter elements  200  may be formed using a photoimageable polymer (e.g. a polymer dyed red, green, and blue for red, green, and blue color filter elements, respectively) or other suitable color filter element material. The color filter element materials used in forming elements  200  may be patterned using photolithography or other suitable techniques (e.g., shadow mask deposition, ink jet printing, etc.). These techniques may also be used in depositing other structures in display  14  (e.g., column spacer structures, support pads, black matrix, etc.). 
     After forming color filter elements  200 , an additional polymer element may be formed on layer  56 . As shown in  FIG. 21 , for example, an additional polymer structure (e.g., an additional structure formed from color filter element material) such as structure  202  may be formed on black matrix  124 . Structure  202  may be green, red, blue, clear, or other suitable color and may be formed from a color filter element material such as dyed photoimageable polymer material using photolithography or other suitable fabrication techniques. A polymer overcoat (e.g., an organic layer) may then be formed on layer  56  such as polymer overcoat  204  of  FIG. 22 . As shown in  FIG. 22 , the formation of structure  202  on layer  56  creates a raised protrusion on the surface of layer  56  that serves as column spacer  122 . 
       FIG. 23  is a top view of the structures of  FIG. 22  showing how column spacer  122  may be formed over black matrix  124  between respective color filter elements  200  for color filter layer  56 . 
     If desired, overcoat layer  204  may be formed under polymer structure  202  rather than over polymer structure  202 , as shown in  FIG. 24 . Column spacer  122  (or a subspacer) may overlap black matrix  124 , so that overcoat  204  is interposed between layer  56  and structure  202 . 
       FIG. 25  is a cross-sectional side view of a portion of display  14  in a configuration in which column spacer  122  has been formed by depositing an additional polymer structure (e.g., additional structure  202 ). Structure  202  may be formed from color filter element material (e.g., green color filter element material in the example of  FIG. 25 ). Column spacer structures, subspacers, and support pads may also be formed from different material (e.g., a photoimagable acrylic polymer adhesive or other material that is not used in forming color filter elements  200 ). Structure  202  is formed on top of black matrix  124  and is covered with overcoat layer  204 . As shown in  FIG. 25 , support pad  130  may be located between pixels. In particular, thin-film transistor layer  58  may contain electrodes and other circuitry associated with pixels such as pixels P 1 , P 2 , and P 3 . Pixels P 1 , P 2 , and P 3  are aligned with corresponding color filter elements  200  in color filter layer  200 . As shown in  FIG. 25 , support pad  130  may be located between pixels (i.e., between the electrodes and other circuitry on thin-film transistor layer  58  that is associated with pixels P 1  and P 2  in the example of  FIG. 25 ). In general, the surface areas of the column spacers is less than or equal to that of the support pads (see, e.g.,  FIG. 13 ). In the example of  FIG. 25 , column spacers such as column spacer  122  have been formed on color filter layer  56  and support pads such as support pad  130  have been formed on thin-film transistor layer  58 . If desired, a mixture of column spacers and support pads may be formed on color filter layer  56  and a corresponding mixture of respective support pads and column spacers may be formed on thin-filmed transistor layer  58 . Configurations in which column spacers  122  are formed on thin-film transistor layer  58  (e.g., in the position shown by pad  130  of  FIG. 25 ) and in which associated support pads  130  are formed on color filter layer  56  (e.g., in the position shown by spacer  122  of  FIG. 25 ) may also be used in forming display  14 . 
     In the illustrative configuration of  FIG. 26 , column spacer  122  has been formed from polymer structure  206  (e.g., a patterned photoimageable acrylic structure or other organic polymer) on layer  56  and support structure  130  has been formed from additional polymer structure  202  on layer  58 . Additional polymer structure  202  is formed on black matrix  124  (i.e., black matrix  124  is interposed between structure  202  and layer  58 ) and is covered with overcoat  204 . Layer  56  may be a clear substrate (e.g., a clear layer of glass or plastic) and need not contain color filter elements. Rather, color filter elements  200  of different colors (e.g., red, green, and blue) may be formed in an array on thin-film transistor layer  58  in alignment with respective pixels P 1 , P 2 , P 3 , etc. Black matrix  124  may have openings aligned with the color filter elements  200  and pixels. Column spacer  122  and support pad  130  (and, if desired, a subspacer and/or subspacer support pad formed using this arrangement) may overlaps black matrix. 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: 20140618
Publication Date: 20161101
Grant Date: 20161101
Priority Date: 20140618
Inventors: GE ZHIBING
HAM YEON SIK
CHEN CHENG
TAI CHIA HSUAN
DORJGOTOV ENKHAMGALAN
CHOI SANG UN
JIANG SHIH-CHYUAN FAN
Assignee: APPLE INC
CPC Classifications: [{"code": "G02F1/1368", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/13394", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133512", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F2001/136222", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F2001/13396", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F2001/13398", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133514", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133512", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/13398", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/136222", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/13394", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/13396", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/1333", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133514", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/136222", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133512", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133514", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/1368", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/13394", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/13396", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/13394", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 53274818