PATENT DOCUMENT

Publication Number: US-9829740-B2
Application Number: US-201414339263-A
Country: US
Kind Code: B2

Title: Display with reduced color mixing

Abstract:
A display may have a thin-film transistor layer formed from a layer of thin-film transistor circuitry on a substrate, a color filter layer, and a layer of liquid crystal material interposed between the thin-film transistor layer and the color filter layer. The thin-film transistor layer, the liquid crystal layer, and the color filter layer may be sandwiched between upper and lower polarizers. A backlight unit may supply backlight illumination for pixels in the display. The color filter layer may have a black matrix with an array of openings. Color filter elements of different colors may be formed in the openings. The black matrix may have sidewalls that are steep or that are undercut. The profile of the black matrix helps block improperly colored off-axis light and thereby reduces undesired color mixing in the display.

Claims:
What is claimed is: 
     
       1. A display, comprising:
 a substrate having a surface normal; 
 a black matrix on the substrate having an array of openings, wherein the black matrix has a first surface and a second surface interposed between the first surface and the substrate, wherein the black matrix is formed from cross-linked black masking material, and wherein an amount of cross-linking in the black masking material increases along the surface normal from the second surface to the first surface; and 
 color filter elements in the openings, wherein the black matrix has a profile with undercut sidewalls and has overhanging portions, wherein the color filter elements are formed from color filter element material, and wherein at least some of the color filter element material is interposed between the overhanging portions and the substrate. 
 
     
     
       2. The display defined in  claim 1  wherein the black matrix is formed from acrylic. 
     
     
       3. The display defined in  claim 1  wherein the substrate comprises a clear substrate layer and wherein the clear substrate layer, the black matrix, and the color filter elements make up a color filter layer. 
     
     
       4. The display defined in  claim 3  further comprising a thin-film transistor layer having a layer of thin-film transistor circuitry. 
     
     
       5. The display defined in  claim 4  further comprising a layer of liquid crystal material between the color filter layer and the thin-film transistor layer. 
     
     
       6. A display, comprising:
 a substrate having a surface normal; 
 a black matrix on the substrate having an array of openings, wherein the black matrix is formed from black masking material; and 
 color filter elements in the openings, wherein the black matrix has first and second opposing surfaces and a sidewall surface, wherein the first surface is interposed between the second surface and the substrate, wherein the sidewall surface extends from the second surface to the first surface, wherein the sidewall surface is interposed between the second surface and the substrate, wherein at least one of the color filter elements is interposed between the sidewall surface and the substrate, and wherein the black masking material has a density that increases from the first surface of the black matrix to the second surface of the black matrix. 
 
     
     
       7. The display defined in  claim 6  wherein the sidewalls are angled away from the surface normal by less than 25° . 
     
     
       8. The display defined in  claim 7  wherein the black matrix comprises polyimide. 
     
     
       9. The display defined in  claim 7  wherein the substrate comprises transparent material and wherein the substrate, the black matrix, and the color filter elements form a color filter layer. 
     
     
       10. The display defined in  claim 9  wherein the color filter elements include red color filter elements, green color filter elements, and blue color filter elements. 
     
     
       11. The display defined in  claim 10  further comprising a thin-film transistor layer having a layer of thin-film transistor circuitry and a layer of liquid crystal material between the color filter layer and the thin-film transistor layer. 
     
     
       12. The display defined in  claim 11  further comprising:
 an upper polarizer; and 
 a lower polarizer, wherein the color filter layer, the layer of liquid crystal material, and the thin-film transistor layer are interposed between the upper polarizer and the lower polarizer.

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 computers may have displays for presenting information to a user. 
     Liquid crystal displays contain a layer of liquid crystal material. 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 pixel controls the polarization state of the liquid crystal material and thereby adjusts the brightness of the pixel. 
     Substrate layers such as color filter layers and thin-film transistor layers are used in liquid crystal displays. A thin-film transistor layer contains an array of thin-film transistors and associated pixel electrodes that are used in controlling electric fields in the liquid crystal layer. A 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. 
     The color filter layer contains a black masking material that is patterned to form a grid-shaped black matrix. Openings in the black matrix contain color filter elements. Conventional black matrix openings have gently sloped sidewalls, which can give rise to undesired color mixing between adjacent pixels, particularly in high resolution displays in which small amounts of misalignment between the color filter layer and thin-film transistor layer can be difficult to completely eliminate. 
     It would therefore be desirable to provide displays with reduced color mixing. 
     SUMMARY 
     A display may have a thin-film transistor layer formed from a layer of thin-film transistor circuitry on a substrate, a color filter layer, and a layer of liquid crystal material interposed between the thin-film transistor layer and the color filter layer. The thin-film transistor layer, the liquid crystal layer, and the color filter layer may be sandwiched between upper and lower polarizers. A backlight unit may supply backlight illumination for pixels in the display. 
     The color filter layer may have a black matrix with an array of openings. Color filter elements of different colors may be formed in the openings. The openings may be aligned with pixel electrodes in the thin-film transistor layer. 
     The black matrix may have sidewalls that are steep or that are undercut. The steep or undercut profiles of the sidewalls in the black matrix may help block improperly colored off-axis light and thereby reduce undesired color mixing in the display. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device such as a laptop computer with a display in accordance with an embodiment. 
         FIG. 2  is a perspective view of an illustrative electronic device such as a handheld electronic device with a display in accordance with an embodiment. 
         FIG. 3  is a perspective view of an illustrative electronic device such as a tablet computer with a display in accordance with an embodiment. 
         FIG. 4  is a perspective view of an illustrative electronic device such as a computer display with display structures in accordance with an embodiment. 
         FIG. 5  is a cross-sectional side view of an illustrative display in accordance with an embodiment. 
         FIG. 6  is a cross-sectional side view of a portion of a display showing how misalignment of a color filter layer with respect to a thin-film transistor layer has a potential to lead to color mixing. 
         FIG. 7  is a cross-sectional side view of a portion of a color filter layer in a display showing how a black matrix can be provided with steep sidewalls to reduce color mixing in accordance with an embodiment. 
         FIG. 8  is a cross-sectional side view of a portion of a color filter layer in a display showing how the use of a black matrix with undercut sidewalls may help reduce color mixing in accordance with an embodiment. 
         FIG. 9  is a cross-sectional side view of a layer of black masking material such as a polyimide-based black masking material being processed to form a black matrix with steep or undercut sidewalls in accordance with an embodiment. 
         FIG. 10  is a cross-sectional side view of a layer of black masking material such as an acrylic-based black masking material being processed to form a black matrix with steep or undercut sidewalls in accordance with an embodiment. 
         FIG. 11  is a side view of an illustrative photolithographic tool of the type that may be used in fabricating a black matrix for a color filter layer in accordance with an embodiment. 
         FIG. 12  is a side view of an illustrative infrared heating system that may be used to cure layers of material on a color filter substrate in accordance with an embodiment. 
         FIG. 13  is a diagram showing equipment and steps involved in forming a black matrix for a color filter in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices may include displays. The displays may be used to display images to a user. Illustrative electronic devices that may be provided with displays are shown in  FIGS. 1, 2, 3, and 4 . 
     Illustrative electronic device  10  of  FIG. 1  has 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 be 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, a computer that has been integrated into a computer display, or a display for other electronic equipment. With this type of arrangement, housing  12  for device  10  may be mounted on a support structure such as stand  30  or stand  30  may be omitted (e.g., stand  30  can be omitted when mounting device  10  on a wall). 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  may include 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 thin-film transistor 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 user  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  56  may be a thin-film transistor layer that includes an array of thin-film transistors and associated electrodes (display pixel electrodes) for applying electric fields to pixel-sized portions of liquid crystal layer  52  and thereby displaying images on display  14 . Layer  58  may be a color filter layer that includes an array of color filter elements for providing display  14  with the ability to display color images. If desired, upper layer  56  may be a color filter layer and lower layer  58  may be a thin-film transistor layer. Another illustrative configuration involves forming color filter elements and thin-film transistor circuits with associated pixel electrodes on a common substrate. This common substrate may be the upper substrate or may be the lower substrate and may be used in conjunction with an opposing glass or plastic layer (e.g., a layer with or without any color filter elements, thin-film transistors, etc.) to contain liquid crystal layer  52 . Illustrative configurations for display  14  in which layer  56  is a color filter layer and layer  58  is a thin-film transistor layer are sometimes described herein as an example. 
     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 one or more display driver integrated circuits and other display driver circuitry (e.g., thin-film gate drivers, etc.) using a signal path such as a signal path formed from conductive metal traces in a rigid or flexible printed circuit. 
     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. If desired, light sources such as light source  72  may be located along multiple edges of light guide plate  78 . 
     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 a reflective film such as reflector  80 . Reflector  80  may be formed from a reflective material such as a reflective layer of white plastic or other reflective materials. 
     To enhance backlight performance for backlight structures  42 , backlight structures  42  may include optical films  70 . Optical films  70  may include one or more diffuser layers for helping to homogenize backlight  44  and thereby reduce hotspots and one or more prism films (also sometimes referred to as turning films or brightness enhancement films) for collimating backlight  44 . Compensation films for enhancing off-axis viewing may be included in optical films  70  or may be incorporated into other portions of display  14  (e.g., in polarizer layers such as layers  54  and/or  60 ). 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. 
     Some of the layers of display  14  may be formed from structures on clear glass or plastic substrates. For example, color filter layer  56  and thin-film transistor layer  58  may each have a substrate layer on which additional structures are formed. In color filter layer  56 , an array of color filter elements may be formed on the lower surface of a glass substrate. In thin-film transistor layer  58 , a layer of thin-film transistor circuitry may be formed on the upper surface of a glass substrate. 
     Consider, as an example, the portion of display  14  that is shown in  FIG. 6 . As shown in  FIG. 6 , thin-film transistor layer  58  may include a glass or plastic substrate such as substrate  58 - 2 . Thin-film transistor layer  58 - 1  may be formed from a layer of thin-film transistor circuitry on substrate  58 - 2 . Thin-film transistor circuitry  58 - 1  may be formed from polysilicon thin-film transistors, indium gallium zinc oxide thin-film transistors, or other silicon or semiconducting oxide thin-film transistors, metal traces that form signal interconnects, metal traces that form pixel electrodes such as pixel electrodes  90 , and other thin-film circuitry. The thin-film circuitry of layer  58 - 1  may include pixel circuits for controlling voltages on respective pixel electrodes  90 . 
     Each set of pixel electrodes  90  is used to supply a controllable amount of electric field to a respective pixel-sized portion of liquid crystal layer  52 . In the example of  FIG. 6 , there are three pixels: pixel  92 - 1 , pixel  92 - 2 , and pixel  92 - 3 , each with a corresponding set of electrodes  90 . The pixel circuit of each pixel contains a drive transistor that is used in routing signals from a data line onto the electrodes of that pixel. The strength of the signal on the electrodes of each pixel determines the strength of the electric field in the adjacent portion of liquid crystal layer  52  and thereby determines how much the liquid crystals of that pixel are rotated and how much light is transmitted through that pixel of display  14 . 
     Color filter layer  56  includes color filter layer substrate  56 - 3  (e.g., a clear glass or plastic layer). Layers  56 - 2  and  56 - 1  are formed on the inner surface of substrate  56 - 3 . Layer  56 - 2  contains an array of color filter elements  94  separated by black matrix  96 . Layer  56 - 3  may be a clear polymer planarization layer (sometimes referred to as an overcoat) on the inner surface of color filter structures  56 - 2 . 
     Each pixel of display  14  has a respective color. For example, color filter elements  94  may contain red color filter elements such as red color filter element R, green color filter elements such as green color filter element G, and blue color filter elements such as blue color filter element B. Color filter elements  94  may be formed form colored photoimageable polymers or other color filter element material. In the example of  FIG. 6 , red color filter element R is associated with pixel  92 - 1 , green color filter element G is associated with pixel  92 - 2 , and blue color filter element B is associated with pixel  92 - 3 . In pixel  92 - 1  and in pixel  92 - 3 , the voltage on electrodes  90  has been adjusted to make the pixel dark (i.e., liquid crystal material  52 - 1  in pixel  92 - 1  and liquid crystal material  52 - 3  in pixel  92 - 3  have been placed in a non-transmissive “off” state). The voltage on electrodes  90  in pixel  92 - 2  has been adjusted to make pixel  92 - 2  light (i.e., liquid crystal material  52 - 2  in pixel  92 - 2  has been placed in a transmissive “on” state). 
     Backlight  44  traverses liquid crystal layer  52  from bottom to top in the orientation of  FIG. 6 . Backlight  44  that is traveling vertically (i.e., parallel to axis Z) will pass through liquid crystal layer  52  and then through color filter layer  56 , which will impart color to the backlight. In the example of  FIG. 6 , light that passes vertically through liquid crystal material  52 - 1  and liquid crystal material  52 - 3 , which have been placed in an “off” state, will be blocked and will not exit polarizer  54 . Light that passes vertically through liquid crystal material  52 - 2 , which has been placed in an “on” state, will exit polarizer  54  for viewing by a user as part of an image on display  14 . 
     If there is no significant misalignment between color filter layer  56  and thin-film transistor layer  58 , the light that passes through liquid crystal material  52 - 2  will generally pass through green color filter element G and will be properly green in color as expected. Off-axis light (e.g., light that is traveling at an angle with respect to vertical axis Z) also passes through liquid crystal material  52 - 2 . Off-axis light that is oriented at a relatively small angle with respect to axis Z will pass through green color filter element G and will be green in color as desired. Off-axis light that is oriented at larger angles with respect to axis Z will be blocked by black matrix  96 , as illustrated by blocked light ray  98 . Due to the presence of black matrix  96 , off-axis light rays that pass through “on” liquid crystal material  52 - 2  will not pass through adjacent (incorrectly colored) elements such as element R. 
     In some situations, however, such as when manufacturing variations give rise to lateral misalignment between color filter layer  56  and thin-film transistor layer  58 , there is a potential for undesired color mixing effects. Color mixing occurs when the light rays of one pixel pass through an (incorrectly colored) color filter element of an adjacent pixel. In the  FIG. 6  example, dashed line  96 ′ shows where black matrix  96  might be located in the event of misalignment in lateral dimension Y with respect to thin-film transistor layer  58 . In an ideal display, black matrix  96  forms a grid with openings that are aligned exactly above corresponding pixel electrodes  90  for different pixels. Due to the misalignment of black matrix  96 ′, off-axis light rays such as ray  98  will not be blocked by black matrix  96 ′. Rather, ray  98  will pass by left-hand edge  103  of black matrix  96 ′ and will therefore exit the upper surface of display  14  as unblocked light ray  100 . A user will view light ray  100  as part of the image being displayed on display  14 . Because ray  100  is passing through red color filter element R, rather than green filter element G (in this example), color mixing will be present (i.e.,“on” pixel  92 - 2  will appear more red in color than desired). 
     As explained in more detail in  FIG. 7 , color mixing can be influenced by the slope (taper) of the edges (sidewalls) of the black matrix. In the illustrative configuration of  FIG. 7 , color filter layer  56  has been provided with a black matrix layer of two different profile shapes. Solid line  96 BR corresponds to a conventional black matrix profile having edges  100 BR that are oriented at about 40° from surface normal  102  to color filter substrate  56 - 3  (so that edges  100 BR lie at an angle of about 50° with respect to the plane dividing layers  56 - 3  and  56 - 2 ). Dash-and-dotted line  100 N corresponds to a black matrix profile having edges  100 N that are oriented at a steep angle of about 20° with respect to surface normal  102 . 
     Dashed line  100  corresponds to a ray of backlight such as ray  100  of  FIG. 7  that bends in the direction shown by ray  100 ′ upon exiting layer  56  and entering surrounding air. Ray  100 ′ corresponds to light that has spread 60° from surface normal  102  (e.g., the maximum spread desired for light from display  14  in the example of  FIG. 7 ). It may be desirable for a user such as user  48  to be able to view rays such as ray  100 ′ in direction  104  when using display  14 . It is therefore assumed for the example of  FIG. 7  that a viewer may want to view rays such as ray  100 ′. Proper display operation is assured by eliminating color mixing for such rays. 
     To prevent color mixing in the scenario of  FIG. 7 , properly colored rays such as ray  100 ″ that have passed through green color filter G should be allowed to pass to viewer  48  unimpeded, whereas improperly colored rays such as ray  100 ′ should be blocked. Due to the larger index of refraction of layer  56  relative to air  106  above display  14 , ray  100  makes a smaller angle with respect to surface normal  102  than ray  100 ′. In particular, when ray  100 ′ is oriented at an angle of 60° (considered to be the maximum viewing angle for display  14  in this example), ray  100  will be oriented at an angle of 35° with respect to surface normal  102 . 
     Conventional black matrix profiles that involve sidewalls such as sidewall  100 BR that are angled at more than 35° with respect to surface normal  102  will be too shallow to block ray  100  and therefore will not block improperly colored ray  100 ′ at viewer  48 . In contrast, black matrix structures with edges such as edge  100 N that are angled at less than 35° with respect to surface normal  102  (e.g., 20° in the  FIG. 7  example) will block rays  100  and  100 ′. 
     As the example of  FIG. 7  demonstrates, the black matrix in color filter layer  56  preferably has steeply angled sidewalls. The black matrix may, as an example, have a sidewall that is angled at an angle with respect to surface normal  102  that is less than 35°, that is less than 30°, that is less than 25°, that is less than 20°, that is 5-10°, that is 2-20°, that is less than 5°, or that has other suitable values. In configurations in which the black matrix has edge surfaces with steep angles such as these, improperly colored off-axis light rays will be blocked and color mixing will be reduced. 
     As shown in  FIG. 8 , improperly colored light rays such as light rays  100  and  100 ′ of  FIG. 8  can also be blocked by providing the black matrix with a reverse taper (sometimes referred to as narrowing or undercut sidewalls such as sidewalls  100 N′). Sidewalls  100 N′ may, as an example, be angled at an angle A with respect to surface normal  102  that is greater than 0°, greater than 10°, greater than 20° or that has other suitable values. As shown in  FIG. 8 , when black matrix  96 ′ has undercut sidewalls, there is color filter material such as material  94 ′ that lies between extended portions such as overhanging portions  96 E of black matrix  96 ′ and color filter substrate  56 - 3 . Portion  96 E blocks improperly colored off-axis light and therefore reduces color mixing. 
       FIG. 9  shows how black masking material can be processed to form a black matrix structure with steep sidewalls or undercut sidewalls. In the example of  FIG. 9 , black masking material  120  has been deposited on substrate  56 - 3 . Photoimageable polymer  122  (e.g., positive photoresist) has been deposited on layer  120 . Light  124  (e.g., ultraviolet light from a mercury lamp at wavelengths of 300-465 nm or other suitable ultraviolet light) has been used to expose portion  122 ′ of layer  122 . Following development in a developer, the remaining portion of layer  122  (i.e., the portions other than exposed portion  122 ′) are removed. Layer  120  can be cured by applying heat (infrared light) in direction  131  from an oven or other heat source. This makes the upper portions of layer  120  (i.e., the portion of layer  120  at the outermost surface of layer  120  near layer  122 ) denser and more resistant to etching than the lower portions of layer  120  (i.e., the portion of layer  120  at the lower surface of layer  120  bordering layer  56 - 3 ). Layer  120  may be formed from a black masking material such as polyimide that incorporates a black material such as carbon black or other opaque additive. Layer  120  may be etched using a wet etch such as an etchant based on tetramethylammonium (TMA). The TMA etch will etch the less dense (lower) portions of layer  120  more than the more dense (upper) portions of layer  120 , resulting in a black matrix profile having sidewalls such as undercut sidewalls  126  or at least steeply tapered sidewalls  128  of  FIG. 9 . 
     Another illustrative fabrication technique for forming steep or undercut sidewall profiles in the black matrix involves the use of black matrix material based on photosensitive acrylic that incorporates black material (e.g., carbon black or other opaque additive). When patterning a black matrix material such as photosensitive acrylic, a single layer of black masking material  130  may be deposited on substrate  56 - 3 , as shown in  FIG. 10 . Light  132  may expose and crosslink portion  130 ′ of layer  130  to form a black matrix on substrate  56 - 2 . Light  132  may be ultraviolet light (e.g., light from a mercury lamp having wavelengths of 300-465 nm). Photoimageable acrylic layer  130  may be configured to have a low sensitivity at wavelengths of greater than about 400 nm. As a result of the low sensitivity to light at 400 nm or more, most exposure and cross-linking of the polymer of portion  130 ′ will take place at upper regions of portion  130 ′. This is because the absorption depth of light  132  is smaller for shorter wavelengths and larger for longer wavelengths. Following exposure with light  132  to promote cross-linking at the upper surface of portion  130 ′, layer  130  may be etched in a wet etchant such as KOH or NaCO3 or other suitable wet etchant to remove unexposed portions of layer  130  and thereby form the black matrix. Due to the relatively large amount of cross-linking of material  130 ′ at the upper surface of material  130 ′, the resulting black matrix will have undercut sidewalls  134  or at least will have steeply tapered sidewalls such as sidewalls  136 . 
       FIG. 11  is a diagram of an illustrative photolithographic tool of the type that may be used to apply light to the photoimageable polymer layers used in forming the black matrix. As shown in  FIG. 11 , photolithography tool  140  may have ultraviolet light source  142 . Light source  142  may be a mercury lamp or other source of short wavelength light. One or more masks such as masks  144  may be used to pattern the light from source  142  and thereby form patterned light  146  for applying to one or more layers of photoimageable polymer on substrate  56 - 3  such as illustrative layer  148 . Optional lens  149  may help direct the light from source  142  into desired portions of layer  148 . 
       FIG. 12  is an illustrative diagram of a heat source of the type that may be used in curing black matrix polymer on substrate  56 - 3  as described in connection with  FIG. 9 . After depositing one or more layers of polymer on substrate  56 - 3  such as polymer  148 , heat source  150  (e.g., an infrared lamp, an oven, or other source that can heat layer  148  from above rather than below as with a conventional hotplate) may generate infrared radiation  152  (sometimes referred to as infrared light, IR light, or heat) that is applied to polymer  148 . Because infrared light  152  is applied from the outer surface of layer  148 , the outer surface of layer  148  will generally be cured (cross-linked) more than the inner portions of layer  148 , helping to form steep and undercut sidewalls, as described in connection with  FIG. 9 . 
     A diagram of equipment and operations involved in forming a color filter layer having a black matrix with steep or undercut sidewalls is shown in  FIG. 13 . 
     Initially, substrate  56 - 3  is uncoated. Equipment  160  may be used to apply polymer layers (e.g., a layer of black masking material and an optional photoresist layer) and may be used to cure the applied layer(s). Equipment  160  may include polymer deposition equipment such as spray deposition tools, screen printing tool, spin-on deposition tools, or other equipment for depositing liquid polymer layers). Equipment  160  can also include heating equipment for curing the deposited layers (e.g., an infrared lamp or oven of the type described in connection with  FIG. 12 , etc.). 
     Following deposition and curing, polymer  148  (e.g., the black masking layer and, if desired, optional photoresist coating layer) may be exposed to patterned ultraviolet light using photolithography tool  162  (e.g., equipment of the type described in connection with  FIG. 11 ). Exposed areas  164  have the shape of a desired black matrix (e.g., a grid with an array of openings for color filter elements such as a grid with multiple rows and columns of rectangular openings or openings of other shapes). 
     After exposure using tool  162 , development tool  164  may use chemicals (e.g., wet etchants, etc.) to remove unexposed portions of layer  148 , thereby forming black matrix  166 . Black matrix  166  may have steep or undercut sidewalls. Black matrix  166  may be covered with color filter elements and an overcoat layer to form color filter layer  56 . Display  14  may be formed from color filter layer  56 , liquid crystal layer  52 , thin-film transistor layer  58 , and other display layers  46  and backlight  42 . Display  14  may then be installed in housing  12  with other components to form device  10 . 
     The foregoing is merely illustrative and various modifications can be made by those skilled in the art without departing from the scope and spirit of the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20140723
Publication Date: 20171128
Grant Date: 20171128
Priority Date: 20140723
Inventors: LIN SHANG-CHIH
CHEN YUAN
GE ZHIBING
Assignee: APPLE INC
CPC Classifications: [{"code": "G02F1/133516", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133512", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133514", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133514", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133512", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133516", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 55166655