PATENT DOCUMENT

Publication Number: US-9612470-B2
Application Number: US-201414473342-A
Country: US
Kind Code: B2

Title: Display with column spacer structures

Abstract:
A display may have a layer of liquid crystal material between a color filter layer and a thin-film transistor layer. Column spacer structures may be formed between the color filter layer and the thin-film transistor layer to maintain a desired separation between the color filter and thin-film transistor layers. Column spacers may be deposited in column spacer regions of the color filter layer. The color filter layer may include rows of red, green, and blue color filter elements. Blue color filter material that forms blue color filter elements in the color filter layer may also be used to form a planar surface over red and green color filter elements in the column spacer regions. Using the blue color filter material to planarize the surface on which column spacers are formed ensures that the column spacers provide sufficient support for the display without requiring an additional planarization layer.

Claims:
What is claimed is: 
     
       1. A display, comprising:
 a color filter substrate; 
 a color filter array formed on the color filter substrate, wherein the color filter array comprises rows of color filter elements and wherein each row of color filter elements includes red color filter elements, green color filter elements, and blue color filter elements; 
 blue color filter material interposed between the rows of color filter elements, wherein the blue color filter material forms a plurality of planar surfaces between the rows of color filter elements, wherein the planar surfaces are separated from one another by gaps in the blue color filter material, and wherein each planar surface extends partially over adjacent color filter material of a different color; and 
 a column spacer formed on each planar surface. 
 
     
     
       2. The display defined in  claim 1  further comprising:
 a thin-film transistor layer having an upper surface; and 
 a liquid crystal layer between the color filter array and the upper surface, wherein the column spacers are located between the color filter array and the upper surface. 
 
     
     
       3. The display defined in  claim 1  further comprising a grid of opaque masking lines formed on the color filter substrate, wherein the grid of opaque masking lines comprises a plurality of openings, wherein each color filter element in the color filter array overlaps a corresponding one of the openings. 
     
     
       4. The display defined in  claim 3  wherein the blue color filter material overlaps the opaque masking lines between the rows of color filter elements. 
     
     
       5. The display defined in  claim 3  wherein each color filter element in the color filter array is separated from each neighboring color filter element in the color filter array by a boundary and wherein each of the column spacers is formed on a portion of the blue color filter material that overlaps the boundary. 
     
     
       6. The display defined in  claim 1  wherein the plurality of column spacers comprises main column spacers having a first thickness and subspacer column spacers having a second thickness, and wherein the first thickness is greater than the second thickness. 
     
     
       7. A display, comprising:
 a color filter substrate; 
 a color filter array formed on the color filter substrate, wherein the color filter array comprises rows of light-transmitting regions through which light exits the display, wherein the rows of light-transmitting regions are separated from each other by light-blocking regions, wherein the color filter array comprises color filter material of at least first and second colors in each light-blocking region, and wherein the color filter material of the first color has an extended portion that partially overlaps the color filter material of the second color in each light blocking region; and 
 a plurality of column spacers, wherein one of the column spacers is formed on the extended portion. 
 
     
     
       8. The display defined in  claim 7  wherein the color filter array comprises red, green, and blue color filter elements and wherein each of the red, green, and blue color filter elements overlaps a respective one of the light-transmitting regions. 
     
     
       9. The display defined in  claim 7  wherein the column spacers comprise pillars of photoresist. 
     
     
       10. The display defined in  claim 7  further comprising:
 a thin-film transistor layer; and 
 a layer of liquid crystal material between the color filter array and the thin-film transistor layer, wherein the column spacers are located between the color filter array and the thin-film transistor layer. 
 
     
     
       11. The display defined in  claim 7  further comprising a black matrix formed on the color filter substrate, wherein the black matrix comprises lines of opaque masking material in the light-blocking regions. 
     
     
       12. The display defined in  claim 11  wherein the first color comprises blue and the second color comprises red. 
     
     
       13. A method, comprising:
 depositing and patterning red color filter material on a color filter substrate of a display to form red color filter elements; 
 depositing and patterning green color filter material on the color filter substrate of the display to form green color filter elements; and 
 depositing and patterning blue color filter material on the color filter substrate of the display to form blue color filter elements, wherein depositing and patterning the blue color filter material comprises forming the blue color filter material over the red and green color filter elements to form planar surfaces over the red and green color filter elements with the blue color filter material, and wherein each planar surface extends partially over adjacent color filter material of a different color, and wherein the planar surfaces that extends partially are separated from one another by gaps in the blue color filter material. 
 
     
     
       14. The method defined in  claim 13  further comprising:
 forming a plurality of column spacers on the planar surfaces formed by the blue color filter material. 
 
     
     
       15. The method defined in  claim 14  wherein forming the plurality of column spacers comprises forming pillars of photoresist. 
     
     
       16. The method defined in  claim 14  further comprising:
 depositing and patterning an opaque masking material on the color filter substrate. 
 
     
     
       17. The method defined in  claim 14  further comprising:
 depositing a transparent overcoat material over the red, green, and blue color filter elements.

Description:
This application claims the benefit of provisional patent application No. 61/925,999, filed Jan. 10, 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 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. 
     There are tradeoffs involved in designing an appropriate column spacer arrangement for a display. If the column spacers do not provide sufficient support for a display, the display may be susceptible to an undesirable visual effect called pooling mura. On the other hand, column spacer designs that cause a display to become overly rigid will make the display prone to stress-induced birefringence when deformed, leading to undesired light leakage effects. 
     In order to provide sufficient support for a display, care must be taken to ensure that the column spacers are deposited on a flat surface. In a typical configuration, an array of red, green, and blue color filter elements are deposited on an inner surface of a color filter substrate. An array of column spacers is then formed over the array of color filter elements. Because the color filter elements have varying heights with respect to the inner surface of the color filter substrate, a transparent planarization layer is formed over the color filter array prior to forming the column spacer array. 
     The varying step height between red, green, and blue color filter elements requires a thick transparent overcoat layer in order to form a planar surface over the color filter array. This type of thick overcoat layer can cause display colors to appear washed out to a user. 
     It would therefore be desirable to be able to provide a display with an improved column spacer configuration. 
     SUMMARY 
     A display may have a color filter layer with opposing upper and lower surfaces and a thin-film transistor layer with opposing upper and lower surfaces. A layer of liquid crystal material may be located between the lower surface of the color filter layer and the upper surface of the thin-film transistor layer. 
     Column spacer structures may be formed between the color filter layer and the thin-film transistor layer to maintain a desired separation between the color filter layer and the thin-film transistor layer. The column spacer structures may be formed from polymer structures such as photoresist pillars and may include pads such as metal pads. The metal pads may be formed on the upper surface of the thin-film transistor layer or the lower surface of the color filter layer. The photoresist pillars may be formed on a surface in the display such as the lower surface of the color filter layer. 
     The color filter layer may include a color filter array having rows of red, green, and blue color filter elements formed on a color filter substrate. Each color filter element may overlap a corresponding light-transmitting region through which light exits the display. There may be multiple rows of light-transmitting regions corresponding to respective rows of display pixels. The rows of light-transmitting regions may be separated from each other by column spacer regions on which column spacers may be formed. 
     Blue color filter material that forms blue color filter elements in the color filter layer may also be used to form a planar surface over red and green color filter elements in the column spacer regions. Using the blue color filter material to planarize the surface on which column spacers are formed ensures that the column spacers are able to provide sufficient support for the display without requiring an additional planarization layer. 
     The blue color filter material may include lines of blue color filter material interposed between adjacent rows of light-transmitting regions. A column spacer may be formed on a portion of the blue color filter material that overlaps a boundary between two adjacent color filter elements. The lines of blue color filter material may be wider in portions that overlap a boundary between two color filter elements than in portions that do not overlap a boundary. 
     A grid of opaque masking material having an array of openings may be formed on the color filter substrate. Each opening may correspond to an associated light-transmitting region and may overlap a corresponding color filter element. Lines of opaque masking material in the grid may overlap the lines of blue color filter material on which column spacers are formed. 
     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device such as a laptop computer with a display in accordance with an embodiment of the present invention. 
         FIG. 2  is a perspective view of an illustrative electronic device such as a handheld electronic device with a display in accordance with an embodiment of the present invention. 
         FIG. 3  is a perspective view of an illustrative electronic device such as a tablet computer with a display in accordance with an embodiment of the present invention. 
         FIG. 4  is a perspective view of an illustrative electronic device such as a computer display with display structures in accordance with an embodiment of the present invention. 
         FIG. 5  is a cross-sectional side view of an illustrative display in accordance with an embodiment of the present invention. 
         FIG. 6  is a cross-sectional side view of a portion of a display with a main column spacer that is supported by a landing pad on a thin-film transistor layer in accordance with an embodiment of the present invention. 
         FIG. 7  is a bottom view of an illustrative color filter layer showing how column spacers may be formed on a planar surface of blue color filter material in accordance with an embodiment of the present invention. 
         FIG. 8  is a cross-sectional side view of a portion of a display with an array of column spacers formed on a planar surface of blue color filter material in accordance with an embodiment of the present invention. 
         FIG. 9  is a perspective view of a portion of a color filter array in which lines of blue color filter material form a planar surface to accommodate column spacers in between rows of light-transmitting regions in accordance with an embodiment of the present invention. 
         FIG. 10  is a bottom view of an illustrative color filter layer showing how column spacers may be formed on a planar surface of blue color filter material that extends onto an adjacent color filter material in accordance with an embodiment of the present invention. 
         FIG. 11  is a bottom view of an illustrative color filter layer showing how column spacers may be formed on planar surfaces of blue color filter material that extend onto two adjacent color filter materials in accordance with an embodiment of the present invention. 
         FIG. 12  is a perspective view of a portion of a color filter array in which blue color filter material that extends onto an adjacent color filter material forms a planar surface to accommodate column spacers in between rows of light-transmitting regions in accordance with an embodiment of the present invention. 
         FIG. 13  is a flow chart of illustrative steps involved in forming a color filter array of the type shown in  FIG. 9  in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices may include displays. The displays may be used to display images to a user. Illustrative electronic devices that may be provided with displays are shown in  FIGS. 1, 2, 3, and 4 . 
       FIG. 1  shows how electronic device  10  may have the shape of a laptop computer having upper housing  12 A and lower housing  12 B with components such as keyboard  16  and touchpad  18 . Device  10  may have hinge structures  20  that allow upper housing  12 A to rotate in directions  22  about rotational axis  24  relative to lower housing  12 B. Display  14  may be mounted in upper housing  12 A. Upper housing  12 A, which may sometimes referred to as a display housing or lid, may be placed in a closed position by rotating upper housing  12 A towards lower housing  12 B about rotational axis  24 . 
       FIG. 2  shows how electronic device  10  may be a handheld device such as a cellular telephone, music player, gaming device, navigation unit, or other compact device. In this type of configuration for device  10 , housing  12  may have opposing front and rear surfaces. Display  14  may be mounted on a front face of housing  12 . Display  14  may, if desired, have openings for components such as button  26 . Openings may also be formed in display  14  to accommodate a speaker port (see, e.g., speaker port  28  of  FIG. 2 ). 
       FIG. 3  shows how electronic device  10  may be a tablet computer. In electronic device  10  of  FIG. 3 , housing  12  may have opposing planar front and rear surfaces. Display  14  may be mounted on the front surface of housing  12 . As shown in  FIG. 3 , display  14  may have an opening to accommodate button  26  (as an example). 
       FIG. 4  shows how electronic device  10  may be a computer display or a computer that has been integrated into a computer display. With this type of arrangement, housing  12  for device  10  may be mounted on a support structure such as stand  27 . Display  14  may be mounted on a front face of housing  12 . 
     The illustrative configurations for device  10  that are shown in  FIGS. 1, 2, 3, and 4  are merely illustrative. In general, electronic device  10  may be a laptop computer, a computer monitor containing an embedded computer, a tablet computer, a cellular telephone, a media player, or other handheld or portable electronic device, a smaller device such as a wrist-watch device, a pendant device, a headphone or earpiece device, or other wearable or miniature device, a television, a computer display that does not contain an embedded computer, a gaming device, a navigation device, an embedded system such as a system in which electronic equipment with a display is mounted in a kiosk or automobile, equipment that implements the functionality of two or more of these devices, or other electronic equipment. 
     Housing  12  of device  10 , which is sometimes referred to as a case, may be formed of materials such as plastic, glass, ceramics, carbon-fiber composites and other fiber-based composites, metal (e.g., machined aluminum, stainless steel, or other metals), other materials, or a combination of these materials. Device  10  may be formed using a unibody construction in which most or all of housing  12  is formed from a single structural element (e.g., a piece of machined metal or a piece of molded plastic) or may be formed from multiple housing structures (e.g., outer housing structures that have been mounted to internal frame elements or other internal housing structures). 
     Display  14  may be a touch sensitive display that includes a touch sensor or may be insensitive to touch. Touch sensors for display  14  may be formed from an array of capacitive touch sensor electrodes, a resistive touch array, touch sensor structures based on acoustic touch, optical touch, or force-based touch technologies, or other suitable touch sensor components. 
     Display  14  for device  10  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. 
     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 or photo spacers). The column spacer structures may be formed from column structures (e.g., cylindrical posts) and/or planar structures such as metal pads on the surfaces of color filter layer  56  and/or thin-film transistor layer  58 . 
       FIG. 6  is a cross-sectional side view of a portion of display  14  showing an illustrative column spacer arrangement. In the example of  FIG. 6 , column spacer structures  100  extend between lower (innermost) surface  114  of color filter layer  56  and upper (outermost) surface  116  of thin-film transistor layer  58 . 
     Column spacer structures  100  of  FIG. 6  include column spacer  102  and landing pad  104 . Column spacer structures such as column spacer  102  and other column spacers in display  14  may be formed from photoresist, other polymers, or non-polymer materials. Photolithographic fabrication techniques may be used to pattern column spacers on layers such as color filter layer  56 . Landing pad  104  may be formed from an organic or inorganic material. As an example, landing pad  104  may be formed from metal. Both the thickness (vertical height in dimension Z) of landing pad  104  on surface  116  of thin-film transistor layer  58  and the thickness of column spacer  102  contribute to the total thickness of column spacer structures  100 . If desired, column spacer  102  may extend only to position  108  so that a gap such as gap  110  may be formed between the lower surface of column spacer  102  of column spacer structures  100  and upper surface  106  of pad  104 . 
       FIG. 7  is a bottom view of color filter layer  56  showing an illustrative arrangement for column spacers  102 . Color filter layer  56  may include a color filter array such as color filter element array  122 . Color filter array  122  may include an array of color filter elements such as color filter elements  124 . Color filter elements  124  may, for example, include red color filter elements  124 R, green color filter elements  124 G, and blue color filter elements  124 B. Color filter elements  124  may be formed from colored polymers or resins (e.g., red, green, and blue photoresist material). 
     Each color filter element  124  may overlap a corresponding pixel region  140 . Pixel regions  140  (i.e., regions  140  within dotted lines  146 ) may each correspond to (i.e., may overlap) a given display pixel in display  14 . Each pixel region  140  may transmit light in the Z direction to the exterior of the display. In other words, display light that is transmitted by liquid crystal layer  52  ( FIG. 5 ) may exit the display via pixel regions  140  and color filter elements  124 . Color filter elements  124  may impart color to the light that is transmitted through pixel regions  140 . For example, light that is transmitted through pixel regions  140 R may be red light, light that is transmitted through pixel regions  140 G may be green light, and light that is transmitted through pixel regions  140 B may be blue light. 
     A grid of opaque masking material (sometimes referred to as a black matrix) may be formed under color filter elements  124 . The black matrix may include a grid of crisscrossing lines. Pixel regions  140  of color filter layer  56  may be free of opaque masking material, whereas some or all of the portions outside of pixel regions  140  may include a layer of opaque masking material. The grid of opaque masking material may be used to hide from view control lines and thin-film transistor circuitry on thin-film transistor layer  58  ( FIG. 5 ). The opaque masking material may also be used to separate color filter elements  124  to prevent color mixing and light leakage. 
     As shown in  FIG. 7 , column spacers  102  may be located on portions of color filter layer  56  that lie outside of pixel regions  140  such as column spacer regions  142 . In the illustrative example of  FIG. 7 , column spacers  102  are disposed in rows that run parallel to rows of pixels regions  140  (e.g., parallel to the X axis of  FIG. 7 ). Each row of column spacers  102  may be interposed between an adjacent pair of rows of pixel regions  140 . 
     There may be any suitable number of rows of column spacers  102  on color filter layer  56 . For example, there may be one row of column spacers  102  for every row of pixel regions  140 , for every two rows of pixel regions  140 , for every three rows of pixel regions  140 , etc. Each row of column spacers  102  may include one column spacer for every pixel region  140 , for every two pixel regions  140 , for every three pixel regions  140 , etc. 
     To ensure that column spacers  102  are formed on a flat surface without requiring a thick overcoat layer, the last color filter material to be deposited on color filter layer  56  may also be used to planarize the surface of color filter layer  56 . For example, after red color filter material is deposited and patterned to form red color filter elements  124 R, and after green color filter material is deposited and patterned to form green color filter elements  124 G, blue color filter material may be deposited and patterned to form blue color filter elements  124 B and to form single-color rows in region  142  in between rows of pixel regions  140 . 
     In the illustrative example of  FIG. 7 , blue color filter material (indicated by the shaded regions of  FIG. 7 ) covers the surface of color filter layer  56  except in regions over color filter elements  124 R and  124 G that overlap pixel regions  140 . This is, however, merely illustrative. If desired, blue color filter material may be located only in blue pixel regions  140 B and in regions  142  that lie between rows of pixel regions  140 . 
     By using the blue color filter material as a planarization layer, rather than using a fourth transparent material as a planarization layer, the height of the planarization layer relative to the surface of the color filter substrate may be reduced, thereby minimizing display color wash-out that can result from a thick planarization layer. 
       FIG. 8  is cross-sectional side view of a portion of display  14 , showing a cross-section of color filter layer  56  of  FIG. 7  taken along line  144  and viewed in direction  148 . As shown in  FIG. 8 , there may be different types of column spacer structures between color filter layer  56  and thin-film transistor layer  58 . Color filter layer  56  may include substrate  120  and color filter element array  122 . Substrate  120  may be formed from a transparent planar member such as a clear layer of glass or plastic. Color filter array  122  may be formed on the lower surface of substrate  120 . Color filter array  122  may contain an array of color filter elements  124  and a grid of opaque masking lines such as masking lines  126 . 
     An optional covering layer such as overcoat layer  128  may be formed over color filter array  122 . Overcoat layer  128  may be formed from clear material (e.g., transparent polymer material). Thin-film transistor layer  58  may be formed from a layer of thin-film transistor circuitry  125  (e.g., transistors formed from thin film layers, electrodes, patterned signal lines, capacitors, and other display pixel array circuitry). Thin-film transistor circuitry  125  may be formed on thin-film transistor substrate  127 . Substrate  127  may be a layer of clear glass, plastic, or other material. Coatings (e.g., polymer coating layers) may be formed on the surfaces of color filter layer  56  and thin-film transistor layer  58  (e.g., coatings that cover pad structures on these surfaces). 
     Column spacer structures  100  may be formed by depositing column spacers on surface  114  of color filter layer  56  such as column spacers  102 A and  102 B. One or more masks (e.g., binary masks, halftone masks, and/or grayscale masks) may be used in forming photoresist pillars (column spacers) of different thicknesses. Landing pads such as landing pad  104  and other pad structures may overlap column spacers such as column spacer  102 A and may be used to prevent scratches in the surfaces of the display layers and/or to make desired thickness adjustments in the column spacer structures. Metal or other materials may be used in forming pads. 
     In display  14 , there are generally numerous column spacer structures such as column spacer structures  100 A and numerous column spacer structures such as column spacer structures  100 B, and structures  100 A and  100 B are generally distributed uniformly across the surface of display  14 . 
     Column spacers  102 A and  102 B have different thicknesses (sometimes referred to as heights). For example, column spacer  102 A of  FIG. 8  may have a thickness (height) H 1 , and column spacer  102 B of  FIG. 8  may have a thickness (height) H 2 . The values of H 1  and H 2  may be different (as an example). 
     Column spacer structures  100 A may sometimes be referred to as main column spacer structures (or main column spacers). As shown in  FIG. 8 , main column spacer structures  100 A extend between lower surface  114  of color filter layer  56  and upper surface  116  of thin-film transistor layer  58 , so that there is no gap in the column spacer structures. The main column spacer structures  100 A therefore define the separation distance between color filter layer  56  and thin-film transistor layer  58  in which liquid crystal material  52  is placed. 
     Column spacer structures  100 B do not extend all the way between surface  114  on color filter layer  56  and surface  116  on thin-film transistor layer  58  and are therefore sometimes referred to as subspacers. As shown in  FIG. 8 , column subspacer structures  100 B are free of metal pads such as pad  104 . There is a gap ΔH between subspacer column spacer  102 B and upper surface  116  of thin-film transistor layer  58 . In conditions in which the temperature of liquid crystal material  52  ( FIG. 5 ) changes, color filter layer  56  may deform towards thin-film transistor layer  58 . Color filter layer  56  may also be deformed towards thin-film transistor layer  58  when pressure is applied to color filter layer  56 . In situations such as these, gap ΔH temporarily disappears because the lower surface of column spacer  102 B comes into contact with surface  116  of thin-film transistor layer. The presence of column spacer structures  100 B is therefore used to arrest motion of color filter layer  56  to prevent color filter layer  56  and thin-film transistor layer  58  from contacting one another during use of display  14 . 
     The use of main spacers such as main column spacer structures  100 A and subspacers such as column subspacer structures  100 B is merely illustrative. If desired, column spacer structures  100  may also include intermediate subspacers having a thickness or height between H 1  of main column spacers  102  and H 2  of subspacers  102 B. In general, display  14  may include an array of column spacers having any suitable combination of heights. Some column spacers structures may include landing pads such as landing pad  104  while other column spacer structures may include a gap such as gap ΔH between the column spacer and the upper surface of thin-film transistor layer  58 . 
     Color filter array  122  may include red color filter elements  124 R, green color filter elements  124 G, and blue color filter elements  124 B. As shown in  FIG. 8 , blue color filter material  124 B (indicated by the shaded area of  FIG. 8 ) may cover red and green color filter elements in region  142  ( FIG. 7 ) to form a layer of blue color filter material having a planar surface on which column spacers  102  may be formed. The planar surface of blue color filter material  124 B may be located between rows of light-transmitting pixel regions  140  ( FIG. 7 ). 
     If desired, transparent overcoat layer  128  may be deposited over color filter array  122 . Because the surface of blue color filter material  124 B on which column spacers  102  are formed is already planar, the thickness of overcoat layer  128  may be minimized. 
       FIG. 9  is a perspective view of a portion of color filter array  122 . As shown in  FIG. 9 , opaque masking material  126  may have an array of openings, each corresponding to a respective pixel region  140  through which light is transmitted. Light may travel in direction Z through a respective one of color filter elements  124 R,  124 G, and  124 B before passing through pixel regions  140  to exit the display. 
     In regions  142  between rows of pixel regions  140 , lines of opaque masking material  126  may be used to hide control lines and thin-film transistor circuitry on thin-film transistor layer  58  ( FIG. 8 ) from view. Because light is not transmitted through the opaque masking material in regions  142 , regions  142  provide acceptable locations on which to form column spacers  102 . 
     To provide a planar surface for column spacers  102  in regions  142  without requiring a thick overcoat layer (e.g., without requiring overcoat layer  128  of  FIG. 8  to be excessively thick), blue color filter material  124 B may be deposited over red color filter material  124 R and green color filter material  124 G in regions  142  to form a flat surface (e.g., a surface that is parallel or substantially parallel to the surface of color filter substrate  120  of  FIG. 8 ). 
     If desired, the lines of blue color filter material  124 B that are formed over red and green color filter material in regions  142  (i.e., the lines of blue color filter material that are connected between blue color filter elements) may have varying widths in order to accommodate column spacers  102 . For example, as shown in  FIG. 9 , regions of blue material  124 B on which column spacers  102  are located may have a width W 2  that is larger than the width W 1  of regions without column spacers  102 . 
     If desired, column spacers  102  may have a tapered shape. For example, base surface  102 B of column spacer  102  that rests on color filter material  124  may be larger than opposing tip surface  102 T of column spacer  102  (i.e., the width or diameter of column spacer  102  may be larger at the base than at the tip). This is, however, merely illustrative. If desired, tip surface  102 T may be larger than base surface  102 B (i.e., the width or diameter or column spacer  102  may be larger at the tip than at the base), or column spacers  102  may have uniform width or uniform diameter from base  102 B to tip  102 T. 
     As shown in  FIG. 9 , column spacers  102  may be formed in locations that overlap a boundary or interface between two color filter elements (e.g., column spacers  102  may have one portion overlapping a first color filter element and a second portion overlapping a second color filter element). Forming column spacer  102  over a boundary between two adjacent color filter elements may ensure that the widened portions of blue color filter material do not overlap light-transmitting regions  140 . 
     The examples of  FIGS. 7, 8, and 9  in which blue color filter material  124 B forms a solid contiguous line in region  142  is merely illustrative. If desired, blue color filter material  124 B may extend only partially onto an adjacent color filter in region  142 . This type of arrangement is shown in  FIG. 10 . 
       FIG. 10  is a bottom view of color filter layer  56  showing an illustrative arrangement for column spacers  102 . As shown in  FIG. 10 , red color filter material  124 R, green color filter material  124 G, and blue color filter material  124 B form continuous vertical strips (extending parallel to the y-axis of  FIG. 10 ) that each cover a corresponding column of display pixel regions  140 . As with the example of  FIGS. 7, 8, and 9 , column spacers such as column spacer  102  are formed on portions of color filter layer  56  that lie outside of pixel regions  140  such as column spacer regions  142 . 
     To ensure that column spacers  102  are formed on a flat surface without requiring a thick overcoat layer, the last color filter material to be deposited on color filter layer  56  may also be used to planarize the surface of color filter layer  56 . For example, after red color filter material is deposited and patterned to form red color filter elements  124 R, and after green color filter material is deposited and patterned to form green color filter elements  124 G, blue color filter material may be deposited and patterned to form blue color filter elements  124 B and to form extended color filter portion  124 P in region  142  between rows of pixel regions  140 . Column spacer  102  may be formed on extended portion  124 P of blue color filter material  124 B. 
     Protruding portion  124 P of color filter material  124 B may be formed by expanding the width of color filter material  124 B in region  142 . For example, color filter material  124 B may have a width W 3  in regions  150  where color filter material  124 B overlaps pixel region  140 B, whereas in regions  142  (between rows of pixel regions  140 ), color filter material  124 B has a width W 4  that is larger than width W 3 . 
     As shown in  FIG. 10 , protruding portion  124 P of color filter material  124 B may overlap the color filter material of an adjacent column of color filter material. For example, protruding portion  124 P may overlap an adjacent column of red color filter material  124 R or an adjacent column of green color filter material  124 G. If desired, protruding portion  124 P may extend only partially onto the adjacent color filter. For example, as shown in  FIG. 10 , a first portion of red color filter material  124 R in region  142  is covered by protruding portion  124 P, while a second portion of red color filter material  124 R in region  142  remains uncovered by blue color filter material and separates protruding portion  124 P from the adjacent green color filter material  124 G. 
     By using the blue color filter material as a planarization layer, rather than using a fourth transparent material as a planarization layer, the height of the planarization layer relative to the surface of the color filter substrate may be reduced, thereby minimizing display color wash-out that can result from a thick planarization layer. 
     The example of  FIG. 10  in which the column of blue color filter material  124 B includes extending portion  124 P extending from one side of color filter material  124 P is merely illustrative. If desired, protruding portions may extend from both sides of a column of color filter material. This type of arrangement is illustrated in  FIG. 11 . 
       FIG. 11  is a bottom view of color filter layer  56  showing an illustrative arrangement for column spacers  102 . As shown in  FIG. 11 , red color filter material  124 R, green color filter material  124 G, and blue color filter material  124 B form continuous vertical strips (extending parallel to the y-axis of  FIG. 11 ) that each cover a corresponding column of display pixel regions  140 . As with the example of  FIGS. 7, 8, 9, and 10 , column spacers such as column spacer  102  are formed on portions of color filter layer  56  that lie outside of pixel regions  140  such as column spacer regions  142 . 
     To ensure that column spacers  102  are formed on a flat surface without requiring a thick overcoat layer, the last color filter material to be deposited on color filter layer  56  may also be used to planarize the surface of color filter layer  56 . For example, after red color filter material is deposited and patterned to form red color filter elements  124 R, and after green color filter material is deposited and patterned to form green color filter elements  124 G, blue color filter material may be deposited and patterned to form blue color filter elements  124 B and to form extended color filter portions  124 P′ and  124 P″ in region  142  between rows of pixel regions  140 . A first column spacer  102  may be formed on extended portion  124 P′ and a second column spacer  102  may be formed on extended portion  124 P″. 
     Protruding portions  124 P′ and  124 P″ of color filter material  124 B may be formed by expanding the width of color filter material  124 B in region  142 . For example, color filter material  124 B may have a width W 3  in regions  150  where color filter material  124 B overlaps pixel region  140 B, whereas in regions  142  (between rows of pixel regions  140 ), color filter material  124 B has a width W 5  that is larger than width W 3 . 
     As shown in  FIG. 11 , protruding portions  124 P′ and  124 P″ of color filter material  124 B may each overlap the color filter material of an adjacent column of color filter material. For example, protruding portion  124 P′ may overlap an adjacent column of green color filter material  124 G on one side of color filter material  124 B, while protruding portion  124 P″ may overlap an adjacent column of red color filter material  124 R on an opposing side of color filter material  124 B. 
     By using the blue color filter material as a planarization layer, rather than using a fourth transparent material as a planarization layer, the height of the planarization layer relative to the surface of the color filter substrate may be reduced, thereby minimizing display color wash-out that can result from a thick planarization layer. 
       FIG. 12  is a perspective view of a portion of color filter array  122  with a column spacer arrangement of the type shown in  FIGS. 10 and 11 . As shown in  FIG. 12 , opaque masking material  126  may have an array of openings, each corresponding to a respective pixel region  140  through which light is transmitted. Light may travel in direction Z through a respective one of color filter elements  124 R,  124 G, and  124 B before passing through pixel regions  140  to exit the display. 
     In regions  142  between rows of pixel regions  140 , lines of opaque masking material  126  may be used to hide control lines and thin-film transistor circuitry on thin-film transistor layer  58  ( FIG. 8 ) from view. Because light is not transmitted through the opaque masking material in regions  142 , regions  142  provide acceptable locations on which to form column spacers  102 . 
     To provide a planar surface for column spacers  102  in regions  142  without requiring a thick overcoat layer (e.g., without requiring overcoat layer  128  of  FIG. 8  to be excessively thick), blue color filter material  124 B may have protruding portion  124 P that extends onto an adjacent color filter and that forms a flat surface on which column spacer  102  can be formed (e.g., a surface that is parallel or substantially parallel to the surface of color filter substrate  120  of  FIG. 8 ). 
     As shown in  FIG. 12 , column spacers  102  may be formed in locations that overlap a boundary or interface between two color filter elements (e.g., column spacers  102  may have one portion overlapping a first color filter element and a second portion overlapping a second color filter element). Forming column spacer  102  over a boundary between two adjacent color filter elements may ensure that the widened portions of blue color filter material do not overlap light-transmitting regions  140 . 
       FIG. 13  is a flow chart of illustrative steps involved in forming a color filter array and column spacer array on a color filter layer. 
     At step  200 , a layer of opaque masking material may be deposited and patterned on a color filter substrate such as color filter substrate  120  of  FIG. 8 . This may include, for example, using photolithographic fabrication techniques to form a grid of crisscrossing opaque lines having openings through which display light may exit display  14 . The grid of crisscrossing lines may, for example, be formed from black photoresist material and may sometimes be referred to as a black matrix. 
     At step  202 , a layer of red color filter material may be deposited and patterned on the color filter substrate. This may include depositing a layer of red photoresist over the black matrix and subsequently patterning the layer of red photoresist using photolithography techniques to form an array of red color filter elements. Each red color element may cover a respective one of the openings in the black matrix formed in step  200 . 
     At step  204 , a layer of green color filter material may be deposited and patterned on the color filter substrate. This may include depositing a layer of green photoresist over the black matrix and the red color filter elements. The layer of green photoresist may subsequently be patterned using photolithography techniques to form an array of green color filter elements. Each green color element may cover a respective one of the openings in the black matrix formed in step  200 . 
     At step  206 , a layer of blue color filter material may be deposited and patterned on the color filter substrate. This may include depositing a layer of blue photoresist over the black matrix, the red color filter elements, and the green color filter elements. The layer of blue photoresist may subsequently be patterned using photolithography techniques to form an array of blue color filter elements. Each blue color element may cover a respective one of the openings in the black matrix formed in step  200 . During the depositing step, the blue color filter material may be deposited to form a planar surface over portions of red and green color filter material. During the patterning step, portions of the blue color filter material may be patterned to form single-color rows of blue color filter material in between rows of red, green, and blue color filter elements. The rows of blue color filter material may, for example, be located in regions  142  of  FIG. 7 . The rows of blue color filter material may form a planar surface and may, if desired, have varying widths (e.g., as shown in  FIG. 9 ) to accommodate column spacers  102 . 
     At step  208 , column spacers  102  may be deposited on the rows of blue color filter material in regions  142  formed in step  206 . This may include, for example, using photolithographic fabrication techniques to form an array of photoresist pillars. If desired, column spacers may be formed form other polymers or may be formed from non-polymers. 
     If desired, a transparent overcoat layer may be formed over the red, green, and blue color filter material prior to forming photoresist pillars in step  208 . Because the surface of the color filter array in column spacer regions  142  is already planarized by blue color filter material in step  206 , the thickness of the transparent overcoat layer may be minimized. 
     The examples of  FIGS. 7-10  in which blue color filter material is used to planarize the surface of color filter array  122  is merely illustrative. If desired, any other suitable color filter material may be used to planarize the surface of color filter array  122  in region  142 . For example, red color filter material  124 R may be used to form red color filter elements and may be deposited over green and blue color filter material to form a planar surface of red color filter material in column spacer regions  142 . If desired, green color filter material may be used to form green color filter elements and may be deposited over red and blue color filter material to form a planar surface of green color filter material in column spacer regions  142 . 
     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: 20140829
Publication Date: 20170404
Grant Date: 20170404
Priority Date: 20140110
Inventors: CHOI SANG UN
GE ZHIBING
LIN SHANG-CHIH
OSAWA HIROSHI
WANG TON-YONG
XU MING
Assignee: APPLE INC
CPC Classifications: [{"code": "G02F1/133516", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F2001/133519", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F2001/13398", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133512", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133514", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B5/201", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/13394", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133512", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/13398", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133514", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133519", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133512", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133516", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/13394", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133519", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/13398", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B5/201", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/13394", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133516", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B5/201", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133512", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133514", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133516", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B5/201", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/13394", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 53521262