PATENT DOCUMENT

Publication Number: US-8755010-B2
Application Number: US-201113299289-A
Country: US
Kind Code: B2

Title: Displays with multilayer masks and color filters

Abstract:
An electronic device may have a display such as a liquid crystal display. The display may have multiple layers of material such as a color filter layer and a thin-film transistor layer. An opaque masking layer may be formed on a display layer such as the color filter layer. In an inactive portion of the display, the opaque masking layer may form a rectangular ring that serves as a border region surrounding a rectangular active portion of the display. In the active portion of the display, the opaque masking layer may be patterned to from an opaque matrix that separates color filter elements in an array of color filter elements. The opaque masking layer and color filter elements may be formed from polymers such as photoresist. The opaque masking layer may include a black pigment such as carbon black. Color filter elements and opaque masking material may include multiple sublayers.

Claims:
What is claimed is: 
     
       1. A display, comprising:
 a thin-film transistor layer; 
 a color filter substrate layer; 
 a layer of liquid crystal material interposed between the thin-film transistor layer and the color filter substrate layer; 
 a first pigmented layer on the color filter substrate layer; and 
 a second pigmented layer on the color filter substrate layer, wherein the first pigmented layer is interposed between the second pigmented layer and the color filter substrate layer, the first and second pigmented layers have different respective pigment concentrations , and the first and second pigmented layers comprise black mask layers with different respective first and second concentrations of black pigment. 
 
     
     
       2. The display defined in  claim 1  wherein the first and second pigmented layers are patterned to form an opaque border region that covers a peripheral inactive area in the display. 
     
     
       3. The display defined in  claim 2  wherein the black pigment in the first and second pigmented layers comprise carbon black. 
     
     
       4. The display defined in  claim 1  further comprising an array of color filter elements on the color filter substrate, wherein the first and second pigmented layers are patterned to form a black matrix having openings in which the color filter elements are formed. 
     
     
       5. The display defined in  claim 4  further comprising a layer of color filter element material that is interposed between the first and second pigmented layers in the black matrix. 
     
     
       6. The display defined in  claim 5  wherein the first pigmented layer comprises black matrix lines of a first width and wherein the second pigmented layer comprises black matrix lines of a second width that is greater than the first width, wherein the black matrix lines of the first width overlap with the black matrix lines of the second width. 
     
     
       7. The display defined in  claim 1  wherein the first and second pigmented layers further include at least one layer of color filter material. 
     
     
       8. The display defined in  claim 1  wherein the first pigmented layer further comprises color filter material and wherein the second pigmented layer further comprises color filter material. 
     
     
       9. The display defined in  claim 8  wherein the first and second pigmented layers are configured to form at least some color filter elements in an array of color filter elements in an active portion of the display. 
     
     
       10. The display defined in  claim 9  wherein the first and second pigmented layers include pigment selected from the group consisting of: green pigment, blue pigment, and red pigment. 
     
     
       11. A display, comprising:
 a thin-film transistor layer; 
 a color filter substrate layer; 
 a layer of liquid crystal material interposed between the thin-film transistor layer and the color filter substrate layer; 
 a first pigmented layer on the color filter substrate layer; and 
 a second pigmented layer on the color filter substrate layer, wherein the first pigmented layer is interposed between the second pigmented layer and the color filter substrate layer, the first and second pigmented layers have different respective pigment concentrations, the first pigmented layer comprises color filter material, and the second color filter material comprises black pigmented material. 
 
     
     
       12. The display defined in  claim 11  wherein the first and second pigmented layers are patterned to form an opaque masking region surrounding a peripheral active display region in the display. 
     
     
       13. The display defined in  claim 11  wherein the first and second pigmented layers are patterned to form at least one black matrix structure in a color filter array. 
     
     
       14. A display, comprising:
 a plurality of display layers through which light passes that forms an image for a viewer; and 
 a black masking layer on a surface of one of the plurality of display layers, wherein the black masking layer comprises a first black masking sublayer having a first concentration of black pigment and a second black masking sublayer on the first black masking sublayer, wherein the second black masking sublayer has a second concentration of black pigment that is different than the first concentration of black pigment. 
 
     
     
       15. The display defined in  claim 14  wherein the first and second black masking sublayers comprise photoresist and wherein the black pigment comprises carbon black. 
     
     
       16. The display defined in  claim 15  wherein a portion of the black masking layer is patterned to form a black matrix, the display further comprising a color filter array with elements that are separated by portions of the black matrix. 
     
     
       17. The display defined in  claim 16  wherein the color filter array comprises at least one color filter element formed from multiple layers of material having different respective colored pigment concentrations. 
     
     
       18. The display defined in  claim 16  wherein the color filter array comprises at least one color filter element formed exclusively from a single layer of color filter material. 
     
     
       19. A liquid crystal display comprising:
 a thin-film transistor layer having thin-film transistors on a thin-film substrate layer; 
 a color filter layer having a color filter substrate layer; 
 a layer of liquid crystal material between the thin-film transistor layer and the color filter layer, wherein the color filter layer comprises an opaque masking layer, the opaque masking layer comprises a first layer of photoresist with a first concentration of pigment and a second layer of photoresist that covers the first layer of photoresist and that has a second concentration of pigment that is different from the first concentration of pigment, and the first and second layers of photoresist comprise black mask layers. 
 
     
     
       20. The liquid crystal display defined in  claim 19  wherein the opaque masking layer is interposed between the color filter layer substrate and the thin-film transistor substrate layer and wherein the first layer of photoresist has a thickness and pigment concentration configured to reduce light reflections from the opaque masking layer. 
     
     
       21. The liquid crystal display defined in  claim 20  wherein the second layer of photoresist has a carbon black concentration of at least 70%.

Description:
BACKGROUND 
     This relates generally to electronic devices and, more particularly, to electronic devices with displays. 
     Electronic devices such as computers and cellular telephones may have displays. In a typical display such as a liquid crystal display, an array of display pixels is used to display images for a user. Each display pixel may contain an electrode that is used to apply an adjustable electric field to a portion of a liquid crystal layer. The magnitude of the electric field in each pixel controls how much light is allowed to pass through the display to the user. 
     To provide a display such as a liquid crystal display with the ability to display color images, an array of color filter elements may be aligned with the array of display pixels. A color filter array may contain color filter elements such as red, blue, and green color filter elements that are separated from each other by a patterned black masking layer. Portions of the black masking layer may also be used around the periphery of the color filter array. A typical black masking layer is formed from a resin that has been colored with a black pigment such as carbon black. 
     To enhance device aesthetics and to improve the visibility of information on a display, it may be desirable to reduce reflections from components in the display. Unwanted reflections may make black portions of the display such as portions of a black masking layer appear lighter than desired. Reflections from structures in the vicinity of the display pixels in a display may make it difficult for a viewer to see images on the display. With traditional display designs, it can be challenging to reduce reflections, because the structures in the display are prone to reflections. For example, although black masking layers formed from resins that incorporate carbon black are black in color, such layers may give rise to undesired reflections when used in an electronic device display. 
     It would therefore be desirable to be able to provide electronic devices with improved displays such as electronic devices with minimized display reflections. 
     SUMMARY 
     An electronic device may have a display such as a liquid crystal display. The display may have multiple layers of material such as a color filter layer and a thin-film transistor layer. A layer of liquid crystal material may be interposed between the color filter layer and the thin-film transistor layer. 
     An opaque masking layer may be formed on a display layer such as the color filter layer. The display may have a central active area such as a rectangular active area. Display pixels in the active area may present images to a user of the electronic device. The active area may be surrounded by an inactive area. For example, the active area may be surrounded by an inactive area that has the shape of a rectangular ring. 
     In the inactive portion of the display, the opaque masking layer may form a rectangular border that surrounds the active area. In the active area, the opaque masking layer may be patterned to form a black matrix. Color filter elements such as red, blue, and green color filter elements may be formed within openings in the black matrix. 
     The opaque masking layer and color filter elements may be formed from pigmented materials such as pigmented layers of photoresist. The opaque masking layer may include a black pigment such as carbon black. The color filter elements may include colored pigments such as red, blue, and green pigments. 
     Reflections may be reduced within the display by forming the opaque masking area and color filter elements from multiple sublayers. The sublayers may have different thicknesses and pigment concentrations. If desired, opaque masking layer material or color filter element material may be formed that has a smoothly varying pigment concentration. 
     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 diagram of an illustrative electronic device with a display such as a portable computer in accordance with an embodiment of the present invention. 
         FIG. 2  is a diagram of an illustrative electronic device with a display such as a cellular telephone or other handheld device in accordance with an embodiment of the present invention. 
         FIG. 3  is a diagram of an illustrative electronic device with a display such as a tablet computer in accordance with an embodiment of the present invention. 
         FIG. 4  is a diagram of an illustrative electronic device with a display such as a computer monitor with a built-in computer 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 cross-sectional side view of a portion of a display including multiple layers of material configured to minimize reflections in accordance with an embodiment of the present invention. 
         FIG. 7  is a graph illustrating how reflectance may be influenced by factors such as layer thickness and composition in a multi-layer display structure of the type shown in  FIG. 6  in accordance with an embodiment of the present invention. 
         FIGS. 8 ,  9 ,  10 ,  11 , and  12  are cross-sectional side views of black masking layer structures being fabricated to reduce reflections in accordance with an embodiment of the present invention. 
         FIG. 13  is a cross-sectional side view of black masking layer and color filter element structures that have been fabricated to reduce reflections in accordance with an embodiment of the present invention. 
         FIGS. 14 ,  15 ,  16 , and  17  are cross-sectional side views of illustrative display structures showing how a patterned black masking layer may be implemented using a layer of color filter material and a layer of opaque material such as black mask material in accordance with an embodiment of the present invention. 
         FIGS. 18 ,  19 ,  20 ,  21 , and  22  are cross-sectional side views of illustrative display structures showing how patterned black masking layer and color filter element structures may be implemented using multiple layers of material including a layer of color filter material in accordance with an embodiment of the present invention. 
         FIGS. 23 ,  24 , and  25  are cross-sectional side views of black masking layer and color filter layer structures showing how multiple layers of patterned black masking material may be used to reduce color washout in a configuration in which reflections are being reduced by minimizing black masking layer pigment concentrations in accordance with an embodiment of the present invention. 
         FIG. 26  is a cross-sectional side view of a portion of a multi-layer display structure of the type shown in  FIG. 25  in which the width of the lines in the lower black masking layer in a black matrix has been enlarged to enhance alignment tolerance in accordance with an embodiment of the present invention. 
         FIG. 27  is a cross-sectional side view of illustrative display structures for a display showing how pigment may be distributed in a graded fashion throughout the thickness of a layer to reduce reflections in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     An illustrative electronic device of the type that may be provided with a display is shown in  FIG. 1 . Electronic device  10  may be a computer such as a computer that is integrated into a display such as a computer monitor, a laptop computer, a tablet computer, a somewhat smaller portable device such as a wrist-watch device, pendant device, or other wearable or miniature device, a cellular telephone, a media player, a tablet computer, a gaming device, a navigation device, a computer monitor, a television, or other electronic equipment. 
     As shown in  FIG. 1 , device  10  may include a display such as display  14 . Display  14  may be a touch screen that incorporates capacitive touch electrodes or other touch sensor components or may be a display that is not touch sensitive. Display  14  may include image pixels formed from liquid crystal display (LCD) components or other suitable display pixel structures. Arrangements in which display  18  is formed using liquid crystal display pixels are sometimes described herein as an example. This is, however, merely illustrative. Any suitable type of display technology may be used in forming display  14  if desired. 
     Device  10  may have a housing such as housing  12 . Housing  12 , which may sometimes be referred to as a case, may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, etc.), other suitable materials, or a combination of any two or more of these materials. 
     Housing  12  may be formed using a unibody configuration in which some or all of housing  12  is machined or molded as a single structure or may be formed using multiple structures (e.g., an internal frame structure, one or more structures that form exterior housing surfaces, etc.). 
     As shown in  FIG. 1 , housing  12  may have multiple parts. For example, housing  12  may have upper portion  12 A and lower portion  12 B. Upper portion  12 A may be coupled to lower portion  12 B using a hinge that allows portion  12 A to rotate about rotational axis  16  relative to portion  12 B. A keyboard such as keyboard  18  and a touch pad such as touch pad  20  may be mounted in housing portion  12 B. 
     Display  14  may have an active area such as active area AA and an inactive area such as area IA. Active area AA may be, for example, a rectangular region in the center of display  14  in which display pixels are actively used to display images for a user of device  10 . Inactive area IA may be devoid of active display pixels. In the example of  FIG. 1 , inactive area IA has the shape of a rectangular ring, surrounding the periphery of active area AA of display  14 . Circuitry and other components may sometimes be formed in inactive area IA. To hide the circuitry and other components from view by a user of device  10 , inactive area IA may sometimes be provided with an opaque mask. The opaque mask can be formed from an opaque material such as a black material or may be formed from opaque masking materials of other colors. Configurations in which the opaque masking material in display  14  has a black appearance are sometimes described herein as an example. This is, however, merely illustrative. Opaque masking layers in device  10  may have any suitable colors. 
     In the example of  FIG. 2 , device  10  has been implemented using a housing that is sufficiently small to fit within a user&#39;s hand (i.e., device  10  of  FIG. 2  may be a handheld electronic device such as a cellular telephone). As show in  FIG. 2 , device  10  may include a display such as display  14  mounted on the front of housing  12 . Display  14  may be substantially filled with active display pixels or may have an inactive portion such as inactive portion IA that surrounds an active portion such as active portion AA. Display  14  may have openings (e.g., openings in inactive region IA or active region AA of display  14 ) such as an opening to accommodate button  22  and an opening to accommodate speaker port  24 . 
       FIG. 3  is a perspective view of electronic device  10  in a configuration in which electronic device  10  has been implemented in the form of a tablet computer. As shown in  FIG. 3 , display  14  may be mounted on the upper (front) surface of housing  12 . An opening may be formed in display  14  to accommodate button  22  (e.g., in inactive region IA surrounding active region AA). 
       FIG. 4  is a perspective view of electronic device  10  in a configuration in which electronic device  10  has been implemented in the form of a computer integrated into a computer monitor. As shown in  FIG. 4 , display  14  may be mounted on the front surface of housing  12 . Stand  26  may be used to support housing  12 . Display  14  may include an inactive region such as inactive region IA that surrounds active region AA. 
     If desired, display  14  may be configured so as to minimize or eliminate the size of inactive region IA along one or more edges of active region AA. Configurations in which inactive region IA extends along all four edges of a rectangular active region AA are described herein as an example. 
     Display  14  may be, for example, a liquid crystal display such as display  14  of  FIG. 5 . Display  14  may include an array of pixels. Each pixel may be used to control the light intensity associated with a portion of the display in active area AA. 
     Display  14  may have a layer of liquid crystal material such as liquid crystal material  36  that is sandwiched between a pair of polarizers such as upper polarizer  52  and lower polarizer  30 . An array of electrodes may be controlled by the thin-film transistor circuitry in a thin-film transistor layer in display  14 . As shown in  FIG. 5 , for example, display  14  may have an array of electrodes and associated thin-film transistor circuits such as thin-film transistor circuitry  34  on thin-transistor substrate layer  32  (e.g., a glass substrate). Thin-film transistor circuitry  34  may include thin-film transistor circuitry such as amorphous silicon transistor circuitry or polysilicon transistor circuitry. Thin film transistor circuitry  34  may also include interconnect lines to connect electrodes formed from conductive materials such as indium tin oxide and metal to thin-film structures such as thin-film transistors. 
     The electrodes in thin-film transistor circuitry  34  may be used to produce electric fields that control the orientation of liquid crystals in liquid crystal layer  36 . Backlight unit  28  may be used to produce backlight  54  for display  14 . Backlight  54  may pass through display  14  in vertical direction Z. This provides illumination for display  14  so that a user such as viewer  56  who is observing display  14  in direction  58  may clearly observe images that are produced by the display pixels in active area AA. By controlling the orientation of the liquid crystals in layer  36 , the polarization of backlight  54  may be controlled. In combination with the presence of polarizer layers  30  and  52 , the ability to control the polarization of the light passing through individual pixels of liquid crystal material  36  provides display  14  with the ability to display images for viewer  56 . 
     Backlight unit  28  may include a light source such as a light-emitting diode array for producing backlight  54 . Polarizers such as polarizer  30  and polarizer  52  may be formed from thin polymer films. For example, polarizer  52  may be formed from polymer film  48  and an associated adhesive layer such as optically clear adhesive layer  46 . 
     If desired, display  14  may be provided with layers for reducing fingerprints (e.g., a smudge-resistant coating in a touch-sensitive display), anti-scratch coatings, an antireflection coating such as antireflection coating  50  of  FIG. 5 , a layer for reducing the impact of static electricity such as indium tin oxide electrostatic discharge protection layer  44  of  FIG. 5 , or other layers of material. The display layers that are used in the illustrative configuration of  FIG. 5  are merely illustrative. 
     Display  14  may include a display layer such as color filter layer  38 . Color filter layer  38  may include a color filter layer substrate such as substrate  66 . Substrate  66  and the substrate for thin-film transistor layer  32  may be formed from clear layers of material such as glass or plastic. 
     Color filter layer  38  may include an array of color filter elements  42  formed on substrate  66 . Color filter elements  42  may include, for example, red elements R, green elements G, and blue elements B. The array of color filter elements in color filter layer  38  may be used to provide display  14  with the ability to display color images. Each of display pixels P in thin-film transistor layer  34  may be provided with a respective overlapping color filter element  42 . 
     Adjacent color filter elements  42  may be separated by interposed portions of opaque masking material  40 . Opaque masking material may be formed from a dark substance such as a polymer that contains a black pigment and is therefore sometimes referred to as a black mask, black masking layer, black pigmented layer, or black masking material. Illustrative polymeric materials for forming black masking layer  40  include acrylic-based and polyimide-based photoresists. An illustrative black pigment that may be used for black masking layer  40  is amorphous carbon (e.g., carbon black). 
     In active region AA, black mask  40  may be formed from a grid of relatively thin lines (sometimes referred to as a black matrix). The black matrix may have a pattern of openings such as an array of rectangular holes for receiving color filter elements. In inactive region IA, black masking material may be used in forming a peripheral black mask that serves as a black border for display  14 . The black mask in inactive area IA may have a rectangular ring shape that surrounds a central rectangular active area AA (as an example). 
     Light such as ambient light  75  may reflect from the interfaces of the layers in display  14 , leading to the potential for undesired reflections. Light reflections at the surface of display  14  may be minimized using an antireflection layer such as layer  50 . To minimize internal light reflections, structures such black masking layer  40  and/or color filter elements  40  may be formed using multiple layers of material. 
     As shown in  FIG. 5 , color filter elements  42  and black masking layer  40  may form layer  62  on the lower surface of substrate  66 . The layers of material that lie above layer  66  (layers  60  of  FIG. 5 ) and the layers of material that lie below layer  62  (layers  64  of  FIG. 5 ) may be modeled as infinitely thick material layers having an index of refraction of 1.5 (e.g., an index of refraction substantially equal to the index of refraction for glass). 
     This optical model of the layers of material in display  14  is shown in  FIG. 6 . As shown in  FIG. 6 , ambient light  75  may be reflected from display  14 , leading to the potential for undesired reflected light  75 R. Some of reflected light  75 R may be produced by the materials of layer  60 . For example, the air interface at the upper surface of layer  60  can give rise to reflections due to the index mismatch between the air and the glass-like materials of layer  60 . 
     The materials of layer  62  may also contribute to reflections. The materials of layer  62  include black masking material  40  and color filter elements  42 . The black masking material in layer  62  and the color filter material in layer  62  may each be characterized by an index of refraction having a real component and an imaginary component. In the black masking regions of layer  62 , the imaginary component of the index of refraction is responsible for producing desirable attenuation in the intensity of white light transmitted through layer  62 . In the color filter elements, the imaginary index of refraction is associated with attenuating out-of-band light (e.g., the attenuation of red and blue light in a green color filter element). 
     It can be difficult or impossible to index match a single homogenous layer of material  62  to adjacent layers in display  14  due to the presence of non-zero imaginary index-of-refraction components in layer  62 . By using two or more sublayers in layer  62 , however, a combination of sublayers may be provided in layer  62  that has the overall effect of minimizing reflections. In the example of  FIG. 6 , layer  62  has been provided with two sublayers (upper layer  62 A of thickness d 1  and lower layer  62 B of thickness d 2 ). In general, portions of layer  62  may have any suitable number of sublayers (e.g., one or more, two or more, three or more, etc.). The thicknesses of each of the sublayers and the index of refraction of each sublayer may be configured so that reflections due to the interface produced by layer  62  can be reduced. 
       FIG. 7  is a graph showing how the multilayer thin-film interference equations for the stack-up of  FIG. 6  may be solved to produce desirable reductions in reflection. In the scenario represented by the graph of  FIG. 7 , it has been assumed that black masking layer  40  is to be implemented using a two-layer configuration having upper and lower sublayers. The lower sublayer has been formed from a material that has a large amount of carbon black to maximize its opacity. In the  FIG. 7  example, the lower sublayer of black masking material  40  has been provided with an  80 % carbon black concentration (i.e., the fraction of carbon black in the lower layer has been set to 0.8). This represents an illustrative maximum achievable carbon black concentration. Other concentrations may be used if desired (e.g., the lower sublayer may have a carbon black concentration of at least 60%, at least 70%, at least 80%, or other suitable concentration). Because the carbon black concentration in the lower black mask layer of this example is relatively large, the lower black mask layer may sometimes be referred to as the main black mask layer in black mask layer  40 . The upper layer, whose carbon black concentration and thickness may be chosen to minimize reflections while satisfying other constraints such as manufacturing constraints, may sometimes be referred to as the buffer layer in black mask layer  40 . 
     In the graph of  FIG. 7 , the thickness of the main layer of black masking material (d 2 ) has been plotted on the horizontal axis. The concentration of carbon black that is to be used in the upper layer is plotted on the vertical axis. It was assumed that black masking layer  40  should be sufficiently opaque to reduce the transmittance through layer  40  to a value of 10 −5.3 . Lines  103  correspond to different amounts of black mask reflectivity (e.g., 10 −2 , 10 −2.5 , etc.). Lines  105  correspond to different total thickness (d 1 +d 2 ) for black masking layer  40 . It was assumed that the index of refraction for the buffer layer could be modeled as a homogenous mixture in accordance with equation 1.
 
 n   bm =( n   1   2   x+n   2   2 (1− x )) 1/2   (1)
 
In equation 1, n 1  represents the index of refraction of carbon black (which has a real index component of 1.95 and an imaginary index component of 0.79), n 2  represents the index of refraction of the clear photoresist resin into which the carbon black is incorporated to form the black masking material, x is the fraction of carbon black, and n bm  is the resulting black masking material index of refraction.
 
     Point  101  represents an illustrative satisfactory configuration for black mask layer  40 . When the attributes corresponding to point  101  on the graph of  FIG. 7  are used for layer  40 , layer  40  will be characterized by minimized reflectivity while having a total thickness (d 1 +d 2 ) that is not too thick (thicknesses above 2 microns may produce manufacturing difficulties). Layer  40  will also have a configuration that is not too sensitive to variations in thicknesses d 1  and d 2  (as is the case for points near the right-hand side of the graph) and will exhibit a satisfactory balance between the d 1  and d 2  thickness values. As shown in  FIG. 7 , point  101  corresponds to a black mask buffer layer having a carbon black concentration of about 0.15, a d 2  value of 0.6 microns, and a total thickness (d 1 +d 2 ) of 1.6 microns. If desired, empirical measurements may be used to refine the selection of d 1 , d 2 , and the carbon black concentrations for the main and buffer black mask layers. 
     Moreover, this modeling (and, if desired, empirical refinement) approach may be applied to other combinations of materials in layer  62 . For example, satisfactory thicknesses and pigment concentrations may be identified for structures having three or more layers of material, for structures including multiple layers of color filter material, and for structures including combinations of one or more layers of black masking material and one or more layers of color filter material. Color filter material for elements  42  may be formed by combining red, green, and blue pigments of various concentrations with polymeric material such as acrylic-based or polyimide-based photoresist. During modeling and/or empirical measurements, satisfactory thicknesses for the color filter materials and black mask materials and satisfactory pigment concentrations can be identified to minimize contributions to reflected light  75 R from opaque mask regions  40  and color filter elements  42  of layer  62 . 
     An illustrative process for forming a double-layer black mask is shown in  FIGS. 8 ,  9 ,  10 ,  11 , and  12 . 
     As shown in  FIG. 8 , a layer of material for black mask layer  40 A may be deposited on the underside of substrate  66  (e.g., by using a slot coating technique in which a squeegee applies a layer of material of a desired thickness or other suitable techniques). The initial thickness of layer  40 A may be d 1 ′. 
     A soft bake operation may be used to drive out solvents from layer  40 A, resulting in a thinner thickness d 1  for layer  40 A, as shown in  FIG. 9 . 
     After the soft bake operation, an additional layer of black mask material (coating  40 B) may be formed on layer  40 A (e.g., by slot coating). As shown in  FIG. 10 , layer  40 B may have a thickness of d 2 ′. Following application of an elevated “soft bake” temperature, solvent may be driven out of layer  40 B so that layer  40 B has a thinner thickness of d 2 , as shown in  FIG. 11 . 
     Following a hard bake to cure the photoresist material from which black mask layers  40 A and  40 B are formed and following photolithographic patterning (e.g., resist exposure and development), black mask layer  40  may have the appearance shown in  FIG. 12 . In inactive region IA, layers  40 A and  40 B may form a black border mask for display  14 . In active region AA, holes in black mask layer  40  (e.g., an array of rectangular holes in a black matrix portion of layer  40 ) may be filled with color filter elements  42  to serve as a color filter array for display  14 . 
     As shown in  FIG. 13 , the amount of incoming light that is reflected from color filter elements  42  may be minimized by using the same approach used for the black mask region (as described in connection with  FIG. 7 ) for forming the color filter elements. In the  FIG. 13  example, each color filter element  42  has been formed from a respective first color filter element layer  42 A and a respective second color filter element layer  42 B. If desired, only some colors of color filter element may be provided with multiple layers while one or more other colors of color filter elements are formed from solid color filter material (i.e., structures that are formed exclusively from a single color pigmented material). Color filter elements  42  may also formed from three or more layers of color filter material if desired. In general, each of the sublayers in a color filter element may have a potentially different thickness and color pigment concentration. The thicknesses and pigment concentrations of the layers may be configured to reduce reflections while satisfying design constraints such as layer thickness limits, desired amounts of color filtering, etc. 
       FIGS. 14 ,  15 ,  16 , and  17  illustrate how color filter material (e.g., photoresist that incorporates colored pigment such as red, blue, or green pigment instead of exclusively black pigment) may be used in forming black mask structures. In the example of  FIGS. 14 ,  15 ,  16 , and  17 , blue color filter material has been used to help form black mask regions  40 . Color filter materials of different colors (e.g., red, blue, etc.) may be used if desired. 
     Initially, a layer of blue color filter material may be deposited and patterned on substrate  66 , as shown in  FIG. 14 . The blue color filter material may portions such as portions  70  and  72 . 
     Following the formation of the blue color filter layer, a layer of green color filter element material such as green pigmented material  76  may be deposited and patterned, as shown in  FIG. 15 . 
       FIG. 16  illustrates how a layer of red color filter element material such as red pigmented material  78  may then be deposited and patterned to form red color filter elements. 
     As shown in  FIG. 17 , black pigmented material  80  (e.g., photoresist containing carbon black) may be deposited and patterned on top of the structures of  FIG. 16 . In active region AA, some of black pigmented material  80  will separate adjacent color filter elements and will serve as a grid-shaped black mask layer  40  (black matrix) for display  14 . In inactive region IA, the portion of blue filter material  70  that is covered by black pigmented material  80  will form a portion of black masking layer  40  that can serve as an opaque border for display  14 . Because multiple layers of material (i.e., layers  70  and  80 ) are used, the pigment concentrations and thicknesses of layers  70  and  80  may be selected to minimize black mask reflections in the inactive border region, as described in connection with  FIG. 7 . Portion  70 ′ of blue layer  80  may remain uncovered by black pigmented material  80  (in the  FIG. 17  example) and may therefore serve as a blue color filter element in the color filter array of active region AA. 
       FIGS. 18 ,  19 ,  20 ,  21 , and  22  illustrate how the black mask structures in active area AA may be formed using a layer of color filter material (i.e., color pigmented material) in addition to black pigmented material. 
     As shown in  FIG. 18 , a patterned layer of blue color filter material  82  (or color filter material of other colors) may initially be formed on substrate layer  66 . 
       FIG. 19  shows how a layer of green color filter material  84  may be deposited and patterned on the structures of  FIG. 18 . 
       FIG. 20  shows how a layer of red color filter material  86  may be deposited and patterned on the structures of  FIG. 19 . 
     Additional blue color filter material  88  may then be deposited and pattered, producing the structures of  FIG. 21 . 
     The structures of  FIG. 21  may be covered with a patterned layer of black pigmented material  90  (e.g., photoresist containing carbon black). In inactive region IA, black pigmented material  90  overlaps blue color filter material  82  and produces a region of black masking layer  40  (i.e., a black border structure) with a reduced reflectivity. In active area AA, black pigmented material  90  may likewise overlap blue color filter material  82  and may produce a grid-shape pattern of black masking material (i.e., a black matrix) with a reduced reflectivity. Red color filter elements  42  in active area AA may be formed from a single layer of red color filter material (material  86 ). Green color filter elements  42  in active area AA may be formed from a single layer of green color filter material (material  84 ). Blue color filter elements  42  in active area AA may be formed by initial blue layer  82  and additional blue layer  88 . 
       FIGS. 23 ,  24 , and  25  show how an illustrative color filter layer may be produced that has multiple layers of black pigmented material with interposed color filter material. This type of arrangement may have a relatively thick overall thickness (e.g., 1-5 microns, 3-4 microns, or other suitable thickness), allowing reflectivity to be minimized by using materials that are characterized by relatively low values for their imaginary index of refraction component. 
     Initially, black pigmented material  92  may be deposited and patterned on substrate  66 , as shown in  FIG. 23 . 
     The structures of  FIG. 23  may then be covered with an array of color filter elements  42  formed from red, blue, and green pigmented color filter material  94 . 
       FIG. 25  shows how an additional layer of black pigmented material  96  may be deposited and patterned on of the structures of  FIG. 23 . In the color filter layer of  FIG. 25 , black mask  40  in inactive region IA may be formed from initial black pigmented layer  92  and additional black pigmented layer  96  and an interposed portion of blue color filter element layer  94 . Uncovered portions of blue pigmented layer  94  in active region AA may form blue color filter elements  42 . Red and green color filter elements and blue color filter elements  42  may be separated by a grid-shaped pattern of black masking lines  40  (black matrix lines) each of which may be formed by a line of black pigmented material  92 , an overlapping line of black pigmented material  96 , and an interposed portion of color filter layer  94 . 
     There is a potential for color washout in display  14  to arise during off-angle viewing, particularly in situations in which the thickness of layers  92 ,  96 , and  94  is relatively large. Consider, for example, a scenario in which display  14  is displaying a red pixel for viewer  56 . 
     In this situation, liquid crystal material  104  under a red color filter element will be “on” and transmitting light. If viewer  56  observes display  14  along off-axis direction  102 , viewer  56  may erroneously observe pixel  104  through a portion of an adjacent green color filter element. Light propagating along axis  102  (light that has the potential to appear erroneously green rather than red in this example) may miss edge  98  of initial black pigmented line  92 . Due to the presence of edge portion  100  of additional black pigmented layer  96 , however, this light will be blocked by additional black pigmented layer  96 . The use of a double-black-pigmented-layer structure to form black mask  40  in active area AA may therefore reduce color washout in display  14  to acceptable levels, even when thick layers of material are used to help reduce reflections. 
     To improve alignment tolerances for the portions of grid-shaped black masking layer  40  in active area AA, it may be desirable to form the lines in the lower (more internal) layer of black pigmented material with a larger width than the lines in the upper (more external) layer of black pigmented. This type of arrangement is shown in  FIG. 26 . As shown in  FIG. 26 , the portion of black pigmented layer  92  between adjacent green and red color filter elements in layer  94 , respectively, may be characterized by a width W 1  that is smaller than the width W 2  of the corresponding portion of black pigmented layer  96 . By forming black mask patterns in active area AA that include lines  92  that are narrower than lines  96 , the tolerance of display  14  to misalignment between lines  92  and  96  may be enhanced. 
     If desired, one or more layers in layer  62  (e.g., one or more black masking layers and/or one or more layers of color filter material) may be provided with a pigment concentration that varies continuously. Use of a pigment concentration that varies smoothly within a layer as a function of distance through the layer may help to reduce light reflections in the black mask structures and/or color filter structures in display  14  without requiring the use of multiple distinct layers of material. 
       FIG. 27  is a cross sectional side view of a portion of display  14  showing how the concentration of pigment (% pigment) in layer  62  may vary as a function of dimension T (i.e., as a function of vertical distance through layer  62 ). Layer  62  may have opposing first and second surfaces. Surface  62 - 1  may be located adjacent to substrate  66 . Surface  62 - 2  may be, for example, the innermost surface of layer  62  and may be located adjacent to a display layer, air, or other structures in display  14 . At surface  62 - 1 , layer  62  may have a pigment concentration of P 1 . As shown by curve  118 , the pigment concentration in layer  62  may increase smoothly as a function of increasing distance T (i.e., distance away from surface  62 - 1 ) and may have a pigment concentration value of P 2  at surface  62 - 2 . The pigment in layer  62  may be a black pigment such as carbon black (e.g., in portions of layer  62  that are serving as black mask regions) or may be colored pigment (e.g., in portions of layer  62  that are serving as color filter elements). Examples of pigments that may be used in layer  62  include black pigment, red pigment, blue pigment, and/or green pigment. Pigments such as these may be incorporated into a layer such as layer  62  that is formed from a polymer such as and acrylic-based or polyimide-based photoresist. If desired, layer  62  may be formed using a combination of sublayers such as one or more sublayers with a fixed pigment concentration and one or more sublayers with a pigment concentration that varies continuously as a function of distanced through the thickness of the sublayer. 
     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: 20111117
Publication Date: 20140617
Grant Date: 20140617
Priority Date: 20111117
Inventors: YANG YOUNG CHEOL
CHEN CHENG
XU MING
GE ZHIBING
CHU CHIA-CHING
GU MINGXIA
PARK YOUNG-BAE
LIU WEIMIN
DORJGOTOV ENKHAMGALAN
ZHONG JOHN Z.
YOUNGS LYNN R.
Assignee: APPLE INC
CPC Classifications: [{"code": "G02F1/133514", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F2202/023", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F2201/52", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133512", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F2201/52", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B5/201", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133502", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F2202/023", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B5/201", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133502", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133514", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133512", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 47003221