PATENT DOCUMENT

Publication Number: US-10401535-B2
Application Number: US-201715617706-A
Country: US
Kind Code: B2

Title: Electronic devices having transparent crystalline structures with antireflection coatings

Abstract:
A graded index antireflection layer may be formed on a transparent crystalline member such as a sapphire member. The graded index layer may include aluminum oxide and silicon oxide. The graded index layer may extend from a first surface at the transparent member to a second surface. The fraction of aluminum oxide in the graded index layer may be at a maximum at the first surface so that the index of refraction of the graded index layer at the first surface matches the index of refraction of the transparent member and may be at a minimum at the second surface so the index of refraction of the graded index layer is minimized at the second surface. The graded index layer may be annealed to form aluminum oxide nanocrystals in the graded index layer and to form a polycrystalline aluminum oxide adhesion layer at the first surface.

Claims:
What is claimed is: 
     
       1. An electronic device, comprising:
 a housing; 
 a component in the housing; 
 a transparent crystalline member that overlaps the component, wherein the transparent crystalline member has a first index of refraction; and 
 a graded index antireflection layer formed from first and second materials on the transparent crystalline member, wherein the graded index antireflection layer has a first surface that faces the transparent crystalline member and that has the first index of refraction and an opposing second surface having a second index of refraction, wherein the graded index antireflection layer has more of the first material than the second material at the first surface and has more of the second material than the first material at the second surface, and wherein the first and second materials include nanocrystals. 
 
     
     
       2. The electronic device defined in  claim 1  wherein the first material comprises aluminum oxide nanocrystals. 
     
     
       3. The electronic device defined in  claim 2  wherein the nanocrystals have diameters of less than 10 nm. 
     
     
       4. The electronic device defined in  claim 2  wherein the graded index antireflection layer comprises a polycrystalline aluminum oxide layer that serves as an adhesion layer for the graded index antireflection layer. 
     
     
       5. The electronic device defined in  claim 1  further comprising a layer of plasmonic metal nanoparticles on the graded index antireflection layer. 
     
     
       6. The electronic device defined in  claim 1  further comprising color-adjusting dopant in the graded index antireflection layer. 
     
     
       7. The electronic device defined in  claim 1  wherein the component comprises a camera, wherein the transparent crystalline member comprises a camera window, wherein the transparent crystalline member comprises aluminum oxide, and wherein the graded index antireflection layer has a polycrystalline layer at an interface between the graded index antireflection layer and the transparent crystalline member. 
     
     
       8. The electronic device defined in  claim 1  wherein the component comprises:
 a display, wherein the transparent crystalline member comprises a transparent display cover layer that overlaps the display; and 
 an oleophobic coating on second surface of the graded index antireflection layer. 
 
     
     
       9. The electronic device defined in  claim 8  wherein the graded index antireflection layer has a polycrystalline layer at an interface between the graded index antireflection layer and the transparent crystalline member. 
     
     
       10. The electronic device defined in  claim 9  wherein the oleophobic coating comprises a polymer layer. 
     
     
       11. The electronic device defined in  claim 10  wherein the polymer layer comprises a fluoropolymer layer. 
     
     
       12. The electronic device defined in  claim 11  wherein the transparent crystalline member comprises a sapphire layer. 
     
     
       13. Apparatus, comprising:
 a transparent sapphire member having an index of refraction; 
 an oleophobic coating; and 
 a graded index layer on the transparent sapphire member, wherein the graded index layer extends between the transparent sapphire member and the oleophobic coating, wherein the graded index layer has a first index of refraction at the transparent sapphire member that matches the index of refraction of the transparent sapphire member and has a second index of refraction at the oleophobic coating that is less than the index of refraction of the transparent sapphire member, wherein the graded index layer has a polycrystalline layer at the transparent sapphire member, wherein the graded index layer comprises first and second materials, wherein the first material is different from the second material, and wherein the graded index layer has more of the first material than the second material at the transparent sapphire member and has more of the second material than the first material at the oleophobic coating. 
 
     
     
       14. The apparatus defined in  claim 13  further comprising aluminum oxide crystal particles in the graded index layer. 
     
     
       15. The apparatus defined in  claim 14  wherein the first material is aluminum oxide and the second material is silicon oxide. 
     
     
       16. The apparatus defined in  claim 15  wherein the oleophobic coating comprises a fluoropolymer. 
     
     
       17. The apparatus defined in  claim 16  further comprising:
 an electronic device housing; and 
 a display in the electronic device housing, wherein the transparent sapphire member covers the display. 
 
     
     
       18. The apparatus defined in  claim 16  further comprising:
 a camera; and 
 an electronic device housing, wherein the transparent sapphire layer is mounted in the electronic device housing overlapping the camera and serves as a camera window for the camera. 
 
     
     
       19. A method, comprising:
 depositing a graded index layer having opposing first and second surfaces on a sapphire member with the first surface facing the sapphire member, wherein the graded index layer comprises a composition of aluminum oxide and silicon oxide that smoothly changes throughout the graded index layer, and wherein the graded index layer has more aluminum oxide than silicon oxide at the first surface and has more silicon oxide than aluminum oxide at the second surface; and 
 annealing the deposited graded index layer to form nanocrystals of aluminum oxide in the graded index layer. 
 
     
     
       20. The method defined in  claim 19  wherein annealing the deposited graded index layer comprises heating the deposited graded index layer to a temperature of greater than 1100° C. to form a polycrystalline layer of aluminum oxide at an interface between the graded index layer and the sapphire member.

Description:
This application claims the benefit of provisional patent application No. 62/366,391, filed Jul. 25, 2016, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     This relates generally to antireflection coatings, and, more particularly, to antireflection coatings for transparent structures in electronic devices. 
     Electronic devices such as cellular telephones, computers, watches, and other devices contain transparent members such as display cover layers and camera windows. Transparent members such as these may be prone to undesired light reflections. Light reflections in display cover layers can obscure images that are being presented on a display. Light reflections in camera windows can create undesired image artifacts. 
     Light reflections such as these arise because there is an index of refraction difference between the material from which a transparent member is formed and surrounding air. To help reduce reflections, transparent members may be provided with antireflection coatings formed from a stack of alternating high-index-of-refraction and low-index-of-refraction dielectric layers. These antireflection coatings may be sensitive to angular orientation during operation and may be prone to delamination if scratched. 
     It would therefore be desirable to be able to provide improved antireflection coatings for transparent members in electronic devices. 
     SUMMARY 
     An electronic device may be provided with a transparent member such as a display cover layer or a camera window. The transparent member may be formed from a crystalline material such as sapphire. A graded index layer may be formed on the transparent member and may serve as an antireflection coating. 
     The graded index layer may include varying proportions of aluminum oxide and silicon oxide. The graded index layer may extend from a first surface at the transparent member to a second surface. The fraction of aluminum oxide in the graded index layer may be at a maximum at the first surface so that the index of refraction of the graded index layer at the first surface matches the index of refraction of the transparent member and may be at a minimum at the second surface so the index of refraction of the graded index layer is minimized to suppress reflections at the second surface. 
     The graded index layer may be annealed to form aluminum oxide nanocrystals in the graded index layer and to form a polycrystalline aluminum oxide adhesion layer at the first surface. The nanocrystals help harden the graded index layer. The adhesion layer helps prevent delamination of the graded index layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device of the type that may include transparent members with antireflection coatings in accordance with an embodiment. 
         FIG. 2  is a cross-sectional side view of an illustrative electronic device window such as a camera window that may be provided with an antireflection coating in accordance with an embodiment. 
         FIG. 3  is a diagram of illustrative equipment and operations involved in forming a transparent member with an antireflection coating in accordance with an embodiment. 
         FIG. 4  is a diagram of an illustrative antireflection layer on a transparent member and a graph showing how the composition of the antireflection layer can be gradually varied as a function of position within the layer in accordance with an embodiment. 
         FIG. 5  is a flow chart of illustrative steps involved in forming an antireflection layer in accordance with an embodiment. 
         FIG. 6  is a diagram of illustrative equipment and operations involved in forming a colored layer with embedded plasmonic nanoparticles in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices and other items may be provided with transparent structures such as sapphire and other transparent crystalline materials. Antireflection coatings may be formed on the transparent structures to reduce light reflections. Illustrative configurations in which antireflection coatings are provided on transparent members for electronic devices such as transparent layers in displays and windows for cameras and other light-based devices may sometimes be described herein as an example. In general, however, antireflection coatings may be formed on any suitable transparent members. 
     An illustrative electronic device of the type that may be provided with transparent members having antireflection coatings is shown in  FIG. 1 . Electronic device  10  may be a computing device such as 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 wristwatch device (e.g., a watch with a wrist strap), a pendant device, a headphone or earpiece device, a device embedded in eyeglasses or other equipment worn on a user&#39;s head, 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. In the illustrative configuration of  FIG. 1 , device  10  is a portable device such as a cellular telephone, media player, tablet computer, wrist device, or other portable computing device. Other configurations may be used for device  10  if desired. The example of  FIG. 1  is merely illustrative. 
     In the example of  FIG. 1 , device  10  includes a display such as display  14  mounted in housing  12 . Housing  12 , which may sometimes be referred to as an enclosure or case, may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, titanium, gold, 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.). 
     Display  14  may be a touch screen display that incorporates a layer of conductive capacitive touch sensor electrodes or other touch sensor components (e.g., resistive touch sensor components, acoustic touch sensor components, force-based touch sensor components, light-based touch sensor components, etc.) or may be a display that is not touch-sensitive. Capacitive touch screen electrodes may be formed from an array of indium tin oxide pads or other transparent conductive structures. 
     Display  14  may include an array of pixels formed from liquid crystal display (LCD) components, an array of electrophoretic pixels, an array of plasma pixels, an array of organic light-emitting diode pixels or other light-emitting diodes, an array of electrowetting pixels, or pixels based on other display technologies. 
     Display  14  may include one or more layers of transparent material. For example, the outermost layer of display  14 , which may sometimes be referred to as a display cover layer, may be formed from a hard transparent material help protect display  14  from damage. Illustrative configurations in which a display cover layer and other transparent members in device  10  (e.g., windows for cameras and other light-based devices) are formed from a hard transparent crystalline material such as sapphire (sometimes referred to as corundum or crystalline aluminum oxide) may be described herein as an example. Sapphire makes a satisfactory material for display cover layers and windows due to its hardness (9 Mohs). In general, however, these transparent members may be formed from any suitable material. 
     A display cover layer for display  14  may planar or curved and may have a rectangular outline, a circular outline, or outlines of other shapes. If desired, openings may be formed in the display cover layer. For example, an opening may be formed in the display cover layer to accommodate a button, a speaker port, or other component. Openings may be formed in housing  12  to form communications ports (e.g., an audio jack port, a digital data port, etc.), to form openings for buttons, or to form audio ports (e.g., openings for speakers and/or microphones). 
     Antireflection coatings may be formed on display cover layers to reduce reflections and thereby help users view images on display  14 . Antireflection coatings may also be formed on transparent windows in device  10 . A cross-sectional side view of an illustrative window in a portion of device  10  is shown in  FIG. 2 . As shown in  FIG. 2 , device  10  may have housing  12 . Light-based component  18  may be mounted in alignment with opening  20  in housing  12 . Opening  20  may be circular, may be rectangular, may have an oval shape, may have a triangular shape, may have other shapes with straight and/or curved edges, or may have other suitable shapes (outlines when viewed from above). Window  16  may be mounted in opening  20  of housing  12  so that window  16  overlaps component  18 . A gasket, bezel, adhesive, screws, or other fastening mechanisms may be used in attaching window  16  to housing  12 . Surface  22  of window  16  may lie flush with surface  24  of housing  12 , may be recessed below surface  24 , or may, as shown in  FIG. 2 , be proud of surface  24  (i.e., surface  22  may lie in a plane that is some distance away from surface  24  in direction  26 ). Surface  24  may form the rear face of housing  12  or other suitable portion of housing  12 . 
     Light-based device  18  may be based on one or more components that emit light (e.g., a light-emitting diode, a laser, a lamp, etc.) and/or one or more components that detect light (e.g., an image sensor that captures digital images through a lens, a proximity sensor detector that measures infrared light from an infrared emitter that has reflected off of external objects adjacent to device  10 , an ambient light sensor that measures the intensity and/or color of ambient light, or other light producing and/or light measuring circuitry). With one illustrative configuration, window  16  is a circular window and device  18  includes a rectangular image sensor and a lens that is interposed between the circular window and the rectangular image sensor. Other types of light-based devices may be aligned with windows such as illustrative window  16  of  FIG. 2 . The configuration of  FIG. 2  is merely illustrative. 
     Transparent members for device  10  such as a display cover glass in display  14  or window  16  may be formed from a durable material such as sapphire or other hard crystalline materials. Hard materials (particularly materials such as sapphire with a Mohs hardness of 9 or more, but also materials that are softer such as materials with a hardness of 8 Mohs or more or other suitable hard materials) will tend to resist scratches when the transparent members are subject to wear from normal use. Illustrative configurations in which the transparent members for device  10  (e.g., display cover layers for displays such as display  14 , windows such as window  16  of  FIG. 2 , etc.) are formed from sapphire (i.e., crystalline aluminum oxide) are sometimes be described herein as an example. In general, these transparent structures may be formed from any suitable materials. 
     Sapphire has a relatively large refractive index (1.8), which causes sapphire structures to reflect light. Light reflections can make it difficult to view images on display  14  and can interfere with image capture operations and other operations using windows  16 . To suppress light reflections, transparent sapphire members may be provided with antireflection coatings. The antireflection coatings may be configured to resist scratching. 
       FIG. 3  is a diagram of illustrative equipment and operations that may be used to provide a sapphire member with an antireflection coating that resists scratching. As shown in  FIG. 3 , deposition tool  32  may be used to deposit thin-film layer  34  on sapphire member  30  (or other suitable crystalline substrate). Sapphire member  30  may be a planar layer of material or other suitable sapphire structure. Deposition tool  32  may be a sputtering tool, an evaporator, other physical vapor deposition equipment, a chemical vapor deposition tool, or other equipment for depositing layer  34 . The thickness of layer  34  may be about 100 nm, less than 150 nm, more than 50 nm, or other suitable thickness. Layer  34  may be an inorganic dielectric layer formed from materials such as aluminum oxide and silicon oxide and/or other inorganic dielectric materials. 
     To form an antireflection coating, the index of refraction of layer  34  may be varied continuously (i.e., layer  34  may be a gradient-index layer, sometimes referred to as a graded index layer). For example, layer  34  may be formed from aluminum oxide and silicon oxide in proportions that vary as a function of distance between the surfaces of layer  34 . At boundary  36  between layer  34  and member  30  (i.e., at an interface formed at a first surface of layer  34 ), layer  34  may be composed of entirely (or nearly entirely) aluminum oxide (Al 2 O 3 ) so that the index of refraction of layer  34  matches the index of refraction of member  30 . At surface  38  of layer  34  (i.e., at a second surface of layer  34  such as at an interface between layer  34  and air or at an interface between layer  34  and an overlapping coating), layer  34  may be formed entirely (or nearly entirely) of silicon oxide (SiO 2 ), thereby minimizing the index of refraction of layer  34  at the second surface. To provide layer  34  with a desired gradient-index profile, the ratio of aluminum oxide to silicon oxide can be varied as a function of distance above interface  36  (i.e., the amount of silicon oxide that is present in layer  34  can be gradually increased while the amount of aluminum oxide that is present in layer  34  can be gradually decreased). The index of refraction of aluminum oxide is about 1.8 and the index of refraction of silicon oxide is about 1.5. By forming a gradient-index layer such as layer  34 , reflections of light from member  30  can be reduced. 
     To enhance the adhesion and strength of layer  34 , member  30  and layer  34  may be annealed using annealing tool  40 . Annealing tool  40  may be a furnace or other tool that can heat member  30  and layer  34  to an elevated temperature such as 1200° C., more than 1100° C., less than 1500° C., or other suitable temperature. The temperature to which member  30  and layer  34  are heated during annealing is preferably below the melting point of member  30  (i.e., 1600° C.) but sufficiently high to cause crystals of aluminum oxide to segregate from amorphous materials in layer  34 . Member  30  and layer  34  may be annealed for 2 hours, more than 30 minutes, less than 4 hours, or other suitable annealing time. 
     During annealing, a portion of layer  34  near interface  36  with member  30  (i.e., a first surface of layer  34 ) may crystallize, thereby forming a polycrystalline layer such as layer  34 B (e.g., a polycrystalline aluminum oxide layer). Layer  34  may be 5-20 nm thick, may be more than 5 nm thick, may be less than 20 nm thick, or may have any other suitable thickness. Due to densification of layer  34  and diffusion that takes place during annealing, the annealing process may cause the thickness of layer  34  to be reduced from about 100 nm (or more than 50 nm or less than 150 nm) to about 80 nm (or more than 30 nm, or less than 130 nm) during annealing. Polycrystalline layer  34 B may contain crystalline grains of aluminum oxide of about 3-6 nm in size (diameter), more than 2 nm in size, less than 10 nm in size, etc. Polycrystalline layer  34 B may serve as an adhesion layer that helps secure portion  34 A of layer  34  to member  30  (e.g., by reducing the risk of delamination of layer  34  at interface  36 ). 
     Annealing with tool  40  may also cause isolated crystals  46  of aluminum oxide to form in portion  34 A of layer  34 . These crystals, which may sometimes be referred to as nanoparticles or nanocrystals may be less than 10 nm in size or other suitable size and may help harden and strengthen layer  34 . The nanocrystals in layer  34  and the crystalline aluminum oxide of member  30  may have the same crystal orientation. 
     Following annealing, deposition tool  42  may be used to deposit one or more layers such as layer  44  on layer  34 . Layer  44  may be an oleophobic layer that helps prevent smudging on layer  34 . Deposition tool  42  may include physical vapor deposition equipment, chemical vapor deposition equipment, equipment for printing or spraying material onto layer  34 , or other suitable equipment for depositing layer  44  on layer  34 . For example, tool  42  may be an evaporator and layer  44  may be an evaporated oleophobic layer formed from a polymer such as a fluoropolymer. 
       FIG. 4  is a diagram showing layers that may be formed on member  30  using equipment of the type shown in  FIG. 3 . As shown in  FIG. 4 , layer  34  may extend from a first surface at interface  36  with member  30  to a second surface on which layer  44  is formed. Following annealing, polycrystalline aluminum oxide layer  34 B may be formed at interface  36  between layer  34  and member  30  (i.e., at the first surface of layer  34 ). Layer  34 B may serve as an adhesion layer that helps to secure layer  34  to member  30 . 
     The graph on the right side of  FIG. 4  shows illustrative concentrations of aluminum oxide (curve  48 ) and silicon oxide (curve  50 ) in layer  34  as a function of distance X through layer  34 . As shown by curve  48 , the relative fraction of aluminum oxide in layer  34  decreases as a function of increasing distance X from interface  36  while, as shown by curve  50 , the relative fraction of silicon oxide in layer  34  increases by a corresponding amount as a function of increasing distance X. 
     At interface  36 , layer  34  is composed of 100% aluminum oxide and 0% silicon oxide, so that the index of refraction of layer  34  matches the index of refraction of member  30  and reflections at interface  36  are minimized. At upper surface  38  of layer  34 , layer  34  is composed of 100% silicon oxide and 0% aluminum oxide. Because layer  34  is formed from silicon oxide (index of 1.5) at surface  38  instead of aluminum oxide at surface  38  (index 1.8), reflections at surface  38  are reduced. Because layer  34  is formed of aluminum oxide at interface  36 , layer  34  is formed from the same material as member  30  at interface  36 , which helps ensure that layer  34  adheres to member  30 . Reflections within layer  34  due to abrupt changes in the index of refraction of layer  34  are avoided by smoothly altering the composition of layer  34  and therefore the refractive index of layer  34  as a function of distance X. 
     The index of refraction of layer  34 A may be graded throughout the entirety of layer  34 A or, if desired, may be graded only through lower portion  34 A- 2  of layer  34 A (i.e., upper portion  34 A- 1  of layer  34 A may be formed from pure silicon oxide). The inclusion of silicon oxide in portion  34 A- 2  may help in adhering oleophobic layer  44  to layer  34  and/or may help render the surface of layer  34  oleophobic (e.g., so that layer  44  can be omitted). 
     During the annealing process in which layer  34  is annealed using annealing tool  40  ( FIG. 3 ), aluminum oxide nanocrystals such as crystals  46  may form in layer  34 A. Crystals  46  may have a size (diameter) of about 7.5 nm, more than 5 nm, less than 10 nm, or other suitable size. The presence of particulates (segregates) such as nanocrystals  46  may help harden and thereby strengthen layer  34 . The hardness of layer  34  and the adhesion of layer  34  may help make layer  34  resistant to damage from scratches. 
     The color of layer  34  and, if desired, the reflectivity of layer  34 , may be modified by depositing one or more additional layers of material on layer  34 . For example, one or more thin-film dielectric layers such as high refractive index materials (e.g., niobium oxide, titanium oxide, etc.) alternated with one or more low refractive index materials (e.g., silicon oxide) may be formed on surface  38  below oleophobic coating layer  44  or in place of coating layer  44 . These layers may form a thin-film filter that serves as a thin-film antireflection layer and/or that serves as a color adjustment layer that adjusts the appearance of layer  34 . For example, thin-film inorganic dielectric layers such as these (e.g., two to three layers, more than two layers, or other suitable number of layers) may be used to convert layer  34  from a reddish color to a bluish color. The thicknesses of the thin-film layers (which are typically on the order of a wavelength of light or less) may be selected based on the desired color properties of the layers, the desired antireflection properties of the layers, the number of layers that are present, and the index of refraction for each thin-film layer. In some situations, it may be desirable to minimize the thickness of any additional layers such as these on surface  38  under coating  44 , because the graded index material of layer  34  is able to serve as an antireflection layer and the inclusion of a large number of additional layers may create delamination vulnerabilities. Accordingly, it may be desirable to use additional layers such as these in relatively small numbers (e.g., 2-3 layers). Configurations in which more dielectric layers are added on top of layer  34  may also be used, if desired. 
       FIG. 5  is a flow chart of illustrative operations involved in forming an antireflection coating from an annealed graded index layer on a crystalline substrate such as a sapphire member. 
     At step  54 , a graded index layer such as layer  34  may be deposited on transparent crystalline member  30 . Member  30  may be formed from aluminum oxide (sapphire) or other material. Layer  34  may be formed from aluminum oxide and silicon oxide or other materials. The ratio of aluminum oxide to silicon oxide may vary continuously to form an antireflection coating as described in connection with  FIG. 4 . 
     At step  56 , layer  34  may be annealed. The annealing process may form polycrystalline aluminum oxide adhesion layer  34 B and nanocrystals  46  in layer  34 A. 
     At step  58 , an optional thin-film filter formed from thin-film dielectric layers (e.g., alternating high index and low index materials) may be formed on layer  34  to help reduce reflections, adjust the color of layer  34 , etc. 
     At step  60 , layer  34  may be coated with an optional oleophobic coating or other coating layer  44  (e.g., a fluoropolymer). The surface of layer  34  may also be rendered oleophobic by forming a layer of silicon oxide at the top of layer  34  and/or on top of any additional thin-film filter layers on layer  34 . 
     If desired, the appearance of layer  34  can be adjusted by forming a layer of plasmonic nanoparticles (i.e., plasmonic metal nanoparticles) on surface  38 . The plasmonic nanoparticles may, for example, change the apparent color of layer  34 . Dopant can also be added to layer  34  to adjust the color of layer  34 . 
     Illustrative equipment and operations for forming a layer with an adjustable color (e.g., a coating layer with plasmonic metal nanoparticles) are shown in  FIG. 6 . As shown in  FIG. 6 , a transparent member such as substrate layer  62  (e.g., member  30  and coating  34  or other suitable substrate materials) may be coated with layer  66  using deposition tool  64 . Deposition tool  64  may be a physical vapor deposition tool (e.g., a sputtering tool), a chemical vapor deposition tool, or other equipment for forming layer  66  on substrate  62 . For example, deposition tool  64  may be a sputtering tool that can sputter metal and/or inorganic dielectric onto substrate  62 . 
     Layer  66  may be a pure metal layer (elemental metal or a metal alloy) or may be formed of cosputtered metal and dielectric. The metal of layer  66  may be, for example, gold, chromium, iron, or other metals. Dielectric for layer  66  may be, for example, an inorganic dielectric such as silicon oxide, zirconium oxide, or other inorganic dielectric material. 
     After layer  66  has been deposited on substrate  62 , substrate  62  and layer  66  may be annealed using annealing tool  68 . Annealing tool  68  may, for example, raise the temperature of layer  62  to a sufficiently high temperature (e.g., more than 1000° C., more than 1200° C., more than 1400° C., less than 1600° C., etc.) for a sufficiently long period of time (e.g., more than 1 h, more than 2 h, less than 3 h, etc.) to cause metal nanoparticles  70  to form within layer  66  (e.g., by causing a pure metal layer to pool into nanoparticles of metal and/or by causing metal that is embedded within the cosputtered dielectric of layer  66  to segregate thereby form nanoparticles of metal. Nanoparticles  70  may have diameters of less than 10 nm, more than 5 nm, less than 15 nm, or other suitable size. 
     Nanoparticles  70  may be sufficiently small to exhibit plasmonic resonances (i.e., nanoparticles  70  may be plasmonic nanoparticles). The plasmonic resonances may impart a color cast to layer  66 . For example, layer  66  may appear red, blue, or may have other colors due to the presence of plasmonic nanoparticles  70 . Layer  66  may have any suitable thickness (e.g., 10 nm or more, 50 nm or more, 100 nm or more, fewer than 70 nm, etc. If desired colored layers such as illustrative layer  66  of  FIG. 6  may be incorporated into structures of the type shown in  FIG. 4  (e.g., a layer of plasmonic metal nanoparticles may be formed under layer  44  or may be formed on layer  34  in place of layer  44 ) to help adjust the apparent color of layer  34  and member  30 . If desired, annealing operations used to form plasmonic nanoparticles may be combined with annealing operations used to anneal layer  34 . 
     In addition to adjusting the color of layer  34  using metal plasmonic nanoparticles, dopants may be added to a layer such as layer  34  to adjust the color of layer  34 . Zirconia dopant may be added by incorporating zirconium into layer  34  prior to annealing so that zirconia forms when layer  34  is annealed, or dopant may be incorporated into layer  34  by diffusion (e.g., by applying a dopent in a film such as layer  66  of  FIG. 6  followed by annealing with tool  68 ), by ion-implantation, or using other suitable doping techniques. Color-adjusting dopants may be any suitable elements or compounds that impart a color to layer  34 . Color-adjusting dopant may be distributed evenly throughout layer  34  or other thin-film layer(s) on member  30  or other substrate layer and/or dopant may be added to the upper surface of layer  34  or other portion of layer  34 . 
     Although sometimes illustrated in the context of sapphire members with graded index coatings of aluminum oxide and silicon oxide, other transparent crystalline materials may serve as transparent members in device  10  and may be coated with other types of graded index material. For example, infrared-transparent materials such as crystalline silicon and crystalline germanium may be used as window materials for infrared light-based devices. 
     The foregoing is merely illustrative and various modifications can be made to the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20170608
Publication Date: 20190903
Grant Date: 20190903
Priority Date: 20160725
Inventors: ROGERS, MATTHEW S.
MATSUYUKI, NAOTO
NGUYEN, Que Anh S.
Assignee: APPLE INC
CPC Classifications: [{"code": "G02B1/113", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B1/02", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B1/02", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B1/02", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B1/113", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B1/113", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 60987992