PATENT DOCUMENT

Publication Number: US-9239496-B2
Application Number: US-201313861231-A
Country: US
Kind Code: B2

Title: Display with column spacer structures for enhanced light leakage and pooling resistance

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. The column spacer structures may be formed from polymer structures such as photoresist pillars and may include 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. Column spacer structures may include main spacer structures, subspacer structures, and intermediate thickness spacer structures to enhance pooling mura and light leakage performance.

Claims:
What is claimed is: 
     
       1. A display, comprising:
 a color filter layer; 
 a thin-film transistor layer; 
 a layer of liquid crystal material between the color filter layer and the thin-film transistor layer; and 
 a plurality of column spacer structures between the color filter layer and the thin-film transistor layer, wherein the column spacer structures include first column spacer structures of a first thickness, second column spacer structures of a second thickness, and third column spacers of a third thickness that is between the first and second thicknesses, and wherein a density of the third column spacers in the display is less than a density of the second column spacers in the display. 
 
     
     
       2. The display defined in  claim 1  wherein the column spacer structures include fourth column spacer structures of a fourth thickness that is between the first and third thicknesses. 
     
     
       3. The display defined in  claim 2  wherein at least some of the column spacer structures include photoresist pillars and metal pads. 
     
     
       4. A display, comprising:
 a first display layer; 
 a second display layer; and 
 a layer of liquid material between the first and second display layers, wherein the first and second display layers are separated by a distance; and 
 spacer structures between the first and second display layers that include first spacer structures of a first thickness, second spacer structures of a second thickness, and third spacers of a third thickness that is between the first and second thicknesses, wherein the first thickness is equal to the distance, and wherein the second spacer structures cover a greater area of the display than the third spacers. 
 
     
     
       5. The display defined in  claim 4  wherein the spacer structures include polymer structures and metal pads. 
     
     
       6. The display defined in  claim 5  wherein the polymer structures comprise first polymer structures in the first spacer structures, second polymer structures in the second spacer structures, and third polymer structures in the third spacer structures and wherein the first, second, and third polymer structures have equal thicknesses. 
     
     
       7. A display, comprising:
 a color filter layer having a lower surface; 
 a thin-film transistor layer having an upper surface; 
 a liquid crystal layer between the lower surface and the upper surface; and 
 a plurality of column spacers between the color filter layer and the thin-film transistor layer, wherein first and second column spacers of the plurality of column spacers have respective first and second metal pads, and wherein the first and second metal pads have different thicknesses. 
 
     
     
       8. The display defined in  claim 7  wherein the plurality of column spacers comprises a main column spacer, a subspacer column spacer, and an intermediate column spacer, wherein the first metal pad is associated with the main column spacer and has a first thickness, and wherein the second metal pad is associated with the intermediate column spacer and has a second thickness that is less than the first thickness. 
     
     
       9. The display defined in  claim 8  wherein no metal pads are positioned beneath the subspacer column spacer. 
     
     
       10. The display defined in  claim 9  wherein the first and second metal pads are located on the upper surface of the thin-film transistor layer. 
     
     
       11. The display defined in  claim 9  wherein the first or second metal pad is located on the lower surface of the color filter layer. 
     
     
       12. The display defined in  claim 9  wherein the plurality of column spacers comprises an additional intermediate column spacer that has a third metal pad with a third thickness, wherein the third thickness is less than the first thickness, and wherein the third thickness is different than the second thickness. 
     
     
       13. The display defined in  claim 12  wherein the main column spacer is formed on the lower surface of the color filter layer. 
     
     
       14. The display defined in  claim 12  wherein the subspacer column spacer is formed on the lower surface of the color filter layer. 
     
     
       15. The display defined in  claim 14  wherein the intermediate column spacer is formed on the lower surface of the color filter layer. 
     
     
       16. The display defined in  claim 14  wherein the second metal pad is formed on the lower surface of the color filter layer, and wherein the intermediate column spacer is formed on the second metal pad. 
     
     
       17. The display defined in  claim 14  wherein the main column spacer, intermediate column spacer, and the subspacer column spacer all have the same thickness. 
     
     
       18. The display defined in  claim 7  wherein the plurality of column spacers comprises main column spacers, subspacer column spacers, and intermediate column spacers, wherein the main column spacers are associated with main metal pads that have a first thickness, and wherein the intermediate column spacers are associated with intermediate metal pads that have a second thickness that is less than the first thickness. 
     
     
       19. The display defined in  claim 18  wherein the density of the intermediate metal pads is less than the density of the main metal pads.

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. 
     There are typically two types of column spacers in a liquid crystal display. A relatively sparse set of main column spacers extends between the color filter layer and the thin-film transistor layer. The thickness of the column spacers and their associated landing pads establishes the amount of separation between the color filter layer and the thin-film transistor layer. Another set of column spacers, referred to as subspacers, has structures that extend only partway between the color filter layer and the thin-film transistor layer. Subspacers are used to prevent the thin-film transistor layer and column spacer from contacting one another. The subspacers do not extend all the way between the color filter layer and thin-film transistor layer to accommodate deformation of the color filter layer relative to the thin-film transistor upon a drop in ambient temperature for the display. 
     There are tradeoffs involved when determining an appropriate number column spacers to use in a given display. If too few of the main column spacers are provided, there will be insufficient support for the display. This will make the display susceptible to an undesirable visual effect called pooling mura. If too many of the main column spacers are provided, the display will become overly stiff. This will make the display prone to stress-induced birefringence when deformed, leading to undesired light leakage effects. With existing column spacer designs, it can be challenging to identify an acceptable tradeoff between pooling and light leakage. Displays are often sensitive to manufacturing variations and may exhibit more pooling and light leakage effects than desired. 
     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. 
     Column spacer structures may include main spacer structures, subspacer structures, and one or more different types of intermediate thickness spacer structures. The use of the intermediate thickness spacer structures may simultaneously improve pooling mura performance and light leakage performance. 
     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 cross-sectional side view of a portion of a display with a main column spacer that is supported by a pad on a color filter layer in accordance with an embodiment of the present invention. 
         FIG. 8  is a cross-sectional side view of a portion of a display with a main column spacer that extends between a pad on a color filter layer and a pad on a thin-film transistor layer in accordance with an embodiment of the present invention. 
         FIG. 9  is a cross-sectional side view of a portion of a display with a column spacer formed on a color filter layer and separated from a thin-film transistor layer by a gap in accordance with an embodiment of the present invention. 
         FIG. 10  is a cross-sectional side view of a portion of an illustrative display having column spacer structures of different thicknesses in accordance with an embodiment of the present invention. 
         FIG. 11  is a graph in which pooling and light leakage performance values have been plotted as a function of main column spacer density in accordance with an embodiment of the present invention. 
         FIG. 12  is a table of illustrative column spacer characteristics that may be used in a column spacer arrangement in accordance with an embodiment of the present invention. 
         FIG. 13  is a cross-sectional side view of a portion of a display having main column spacer structures, subspacer structures, and intermediate column spacer structures using pads of different thicknesses on the surface of a thin-film transistor layer in accordance with an embodiment of the present invention. 
         FIG. 14  is a cross-sectional side view of a portion of a display having main column spacer structures, subspacer structures, and intermediate column spacer structures using pads of different thicknesses on the surface of a thin-film transistor layer and on the surface of a color filter layer in accordance with an embodiment of the present invention. 
         FIG. 15  is a cross-sectional side view of a portion of a display having main column spacer structures, subspacer structures, and two different types of intermediate column spacer structures with respective first and second intermediate column spacer thicknesses 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). 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 . 
       FIGS. 6 ,  7 ,  8 , and  9  are cross-sectional side views of a portion of display  14  in arrangements with different respective column spacer structures (sometimes referred to as column spacers). The arrangements of  FIG. 6 ,  7 ,  8 , or  9 , other column spacer structures, and combinations of two or more of these configurations may be used in forming column spacer structures for display  14 . 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 . 
     If desired, column spacer structures  100  may be formed in display  14  using a configuration in which a pad (e.g., metal pad  104 ) is formed on lower surface  114  of color filter layer  56 , as shown in  FIG. 7 . Column spacer  102  may be formed on top of pad  104 . The total thickness of column spacer structures  100  in this scenario is made up of the thickness of pad  104  plus the thickness of column spacer  102 . As with the illustrative configuration of  FIG. 6 , column spacer structures  100  of  FIG. 7  may extend from lower surface  114  of color filter  56  to upper surface  116  of thin-film transistor layer  58  or may extend from surface  114  to position  108  so that a gap such as gap  110  is formed between the lower surface of column spacer structures  100  and upper surface  116  of thin-film transistor layer. 
     In the illustrative arrangement of  FIG. 8 , pads such as metal pads have been formed above and below column spacer  102 . In particular, metal pad  104 - 1  has been formed on surface  114  of color filter layer  56  and metal pad  104 - 2  has been formed on surface  116  of thin-film transistor layer  58 . In this type of configuration, column spacer structures  100  may include a column spacer such as column spacer  102  that extends between metal pads  104 - 1  and  104 - 2  or a column spacer that extends from pad  104 - 1  to surface  108  to create gap  110  between the column spacer and the upper surface of pad  104 - 2 . 
     As shown in  FIG. 9 , column spacer structures  100  may include a column spacer such as column spacer  102  that is formed directly on surface  114  of color filter layer  56 . Mating landing pads need not be provided on surface  116  of thin-film transistor layer  58 . Gap  110  may separate the lower surface of column spacer  102  from upper surface  116  of thin-film transistor layer  58 . 
       FIG. 10  is a cross-sectional side view of a portion of display  14  in a configuration in which there are three different types of column spacer structures between color filter layer  56  and thin-film transistor layer  58 . As shown in  FIG. 10 , 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  separated by a grid of opaque masking lines such as masking lines  126 . Color filter elements  124  may be formed from colored polymers (e.g., red, blue, and green photoresist elements). Covering layers  128  may be clear material (e.g., 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 A,  100 B, and  100 C may be formed by depositing column spacers on surface  114  of color filter layer  56  such as column spacers  102 A,  102 B, and  102 C. 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, numerous column spacer structures such as column spacer structures  100 B, and numerous column spacer structures such as column spacer structures  100 C and structures  100 A,  100 B, and  100 C are generally distributed uniformly across the surface of display  14 . The portion of display  14  shown in  FIG. 10  in which there is a single one of each of these types of column spacer structures is merely illustrative. 
     Column spacers  102 A,  102 B, and  102 C have different thicknesses (sometimes referred to as heights). For example, column spacer  102 A of  FIG. 10  may have a thickness (height) H 1 , column spacer  102 B of  FIG. 10  may have a thickness (height) H 2 , and column spacer  102 C of  FIG. 10  may have a thickness (height) H 3 . The values of H 1 , H 2 , and H 3  may all be different (as an example). 
     Column spacer structures  100 A (and column spacers  102 A) may sometimes be referred to as main column spacer structures (or main column spacers). As shown in  FIG. 10 , 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. 10 , column subspacer structures  100 B are free of metal pads such 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 toward 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 . 
     Column spacer structures  100 C form a gap ΔH′ that is intermediate in size between the size of gap ΔH associated with subspacer column spacer structures  100 B and the zero gap size associated with main column spacer structures  100 A. The thickness of column spacer structures  100 C also lies between the thickness of main column spacer structures  100 A and the thickness of subspacer column spacer structures  100 B. Column spacer structures  100 C may therefore sometimes be referred to as intermediate column spacer structures, intermediate thickness column spacer structures, or transitional column spacer structures. 
     Intermediate column spacer structures  100 C are thicker than subspacer structures  100 B (e.g., intermediate column spacers  102  are thicker than subspacer column spacers  102 B) and therefore provide more support for the layers of display  14  than subspacer column spacers  100 B. This can help display  14  resist undesired pooling mura. As shown in  FIG. 10 , intermediate column spacer structures  100 C may have intermediate thickness column spacers  102 C of thickness H 3  that are separated from surface  116  of thin-film transistor layer  158  by gap ΔH′ (which is different than ΔH). 
     There are generally tradeoffs to be considered between light leakage performance and pooling performance in a display such as display  14  of  FIG. 10 .  FIG. 11  is a graph in which pooling performance has been plotted on the left-hand vertical axis as a function of main column spacer concentration and in which light leakage performance has been plotted on the right-hand vertical axis as a function of main column spacer concentration. 
     Pooling mura curve  140  illustrates how pooling performance tends to degrade as the concentration of main column spacers in a display decreases. This is because the column spacer structures in a display help to prevent layers  56  and  58  from coming into contact with each other. By providing a sufficient number of main column spacers, pooling performance can be improved, as indicated by the downward slope of curve  140  in of  FIG. 11 . 
     Light leakage curve  142  illustrates how stress-induced birefringence and therefore light leakage tends to become worse as the number of main column spacers in a display increases. For a given deformation in the planarity of display  14 , stress tends to rise in proportion to the stiffness of the display. Displays with fewer main column spacers are more flexible than displays with more column spacers. As a result, displays with fewer main column spacers develop less stress when deformed and produce correspondingly less stress-induced birefringence and light leakage (undesired localized brightening of the display). This behavior is reflected by the upwards slope of curve  142 . When fewer main column spacers are present (near the left-hand side of curve  142  in  FIG. 11 ), light leakage performance is better. When more main column spacers are present (near the right-hand side of curve  142  in  FIG. 11 ), light leakage performance is worse. 
     The inclusion of intermediate thickness column spacer structures such as column spacer structures  100 C that have thicknesses greater than that of subspacer structures  100 B enhances pooling mura performance by providing additional structural support for the layers of display  14  during temperature changes and other forces that exert bending pressure on layers such as color filter layer  56  without causing excessive stiffness of the type that may result by increasing the number of main column spacers  102 A in display  14 . The benefit of including intermediate thickness column spacer structures such as column spacer structures  100 C of  FIG. 10  into display  14  is illustrated by dashed curve  144 . 
     As illustrated by arrows  146 , curve  144  represents an improvement over curve  140  resulting from the inclusion of intermediate column spacers. When trading off light leakage performance against pooling mura performance in a display without intermediate column spacer structures  100 C, a display might be configured to use the number of main column spacers associated with point  148  of the graph of  FIG. 11 . When trading off light leakage performance against pooling mura performance in a display with intermediate column spacer structures  100 C, in contrast, a display might be configured to use the number of main column spacers associated with point  150  of the graph of  FIG. 11 . When display  14  is configured in accordance with point  150 , both pooling mura performance and light leakage performance can be improved relative to a display configured in accordance with point  148 . 
       FIG. 12  is a table showing illustrative numbers (in percentages) of main column spacer density, intermediate column spacer density, and subspacer column spacer density that may be used in display  14 . The table of  FIG. 12  also shows illustrative thicknesses for column spacers  102 A,  102 B, and  102 C and shows illustrative gap sizes Δ (zero for the main column spacers, non-zero for the intermediate column spacers and subspacers). 
     If desired, column spacer structures can use upper and/or lower pads (e.g., metal pads) and/or column spacers of different thicknesses to achieve desired overall thicknesses for the column spacer structures. Consider, as an example, the arrangement of  FIG. 13 . In this configuration, main column spacer structures  100 A are formed from main column spacers  102 A on surface  114  of color filter layer  56  and landing pad  104  on surface  116  of thin-film transistor layer  58 . Subspacer column spacer structures  100 B are formed from subspacer  102 B on surface  114  of color filter layer  56 . Intermediate column spacer structures  100 C of  FIG. 13  are formed from intermediate column spacer  102 C and pad  104 C on surface  116  of thin-film transistor layer  58 . The thickness of spacers  102 A,  102 B, and  102 C may, if desired, all be equal (H 1 ). 
     In the example of  FIG. 13 , two types of pads are being used—pads such as pad  104 A serve as part of the main column spacer structures for display  14  and pads such as pad  104 C serve as part of the intermediate column spacer structures for display  14 . Other combinations of pads may be used in the column spacer structures if desired (see, e.g.,  FIGS. 6 ,  7 ,  8 , and  10 ). The example of  FIG. 14  in which two different thicknesses of pads on surface  116  of thin-film transistor layer are used in two different types of column spacer structures is merely illustrative. 
       FIG. 14  is a cross-sectional side view of a portion of display  14  in a configuration in which the thickness H 1  of each column spacer is the same and in which pad  104 C has been formed on surface  114  of color filter layer  56 . In general, pads may be formed on surface  114 , on surface  116 , or on a combination of surfaces  114  and  116 . If desired, subspacer column spacer structures  100 B (and/or structures  100 A and/or structures  100 C) may include one or more pads, as described in connection with  FIGS. 6 ,  7 , and  8 . 
     The example of  FIG. 15  involves the use of four different types of column spacer structure. In addition to main column spacer structures  100 A and subspacer column spacer structures  100 B, the column spacer structures of  FIG. 15  include first and second intermediate column spacer structures  100 C- 1  and  100 C- 2 , each with a different respective thickness. In the  FIG. 15  example, main column spacer structures  100 A are formed from main column spacer  102 A and main column spacer pad  104 A and subspacer column spacer structures  100 B are formed from subspacer column spacer  102 B (without a pad). Intermediate column spacer structures  100 C- 1  have been formed without using a pad by using intermediate column spacer  102 C- 1  of thickness H 3 . Intermediate column spacer structures  100 C- 2  are formed from a column spacer  102 C- 2  of thickness H 2 , which is the same as the thickness of subspacer column spacer  102 B and which is different from main column spacer thickness H 1  of main column spacer  102 A. Pad  104 C- 2  and spacer  102 C- 2  contribute to the overall thickness of column spacer structures  100 C- 2 . To provide two different levels of intermediate column support for display  14 , the thickness of intermediate column spacer structures  100 C- 1  is preferably different than the thickness of intermediate column spacer structures  100 C- 2 . 
     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: 20130411
Publication Date: 20160119
Grant Date: 20160119
Priority Date: 20130411
Inventors: GE ZHIBING
CHEN CHENG
DORJGOTOV ENKHAMGALAN
QI JUN
Assignee: APPLE INC
CPC Classifications: [{"code": "G02F2001/13398", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/13394", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F2001/13396", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/13398", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/13394", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/13398", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/13396", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/13394", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/13396", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 50687671