PATENT DOCUMENT

Publication Number: US-11399442-B2
Application Number: US-201916403425-A
Country: US
Kind Code: B2

Title: Colored coatings for electronic devices

Abstract:
An electronic device may have transparent housing structures such as walls formed of glass or sapphire. Housing structures such as transparent housing structures may have a colored coating. The colored coating may include an absorptive layer and a metal layer. The coating may exhibit a color that can be adjusted by adjusting the thickness of the thin absorptive layer. A colored layer such as a layer of colored polymer may be incorporated into the colored coating to further adjust the color of the coating. The colored coating may be formed on an inner or outer housing structure surface. The surface may have a texture to provide the coating with a matte appearance. When formed on an outer surface, a diamond-like carbon layer may protect the colored coating. When formed on an inner surface, a passivation layer may be used to prevent oxidation of the metal layer.

Claims:
What is claimed is: 
     
       1. An electronic device, comprising:
 a housing structure formed of a transparent material, wherein the transparent material is transparent to visible light;
 a display coupled to the housing structure; and 
 a colored coating on an inner surface of the housing structure, wherein the colored coating includes a metal layer and includes an amorphous semiconductor layer that is formed on the inner surface between the metal layer and the housing structure. 
 
 
     
     
       2. The electronic device defined in  claim 1  wherein the amorphous semiconductor layer comprises an amorphous silicon layer. 
     
     
       3. The electronic device defined in  claim 2  wherein the metal layer is formed on the amorphous silicon layer and wherein the metal layer comprises a metal layer selected from the group consisting of: a pure aluminum layer, an aluminum silicon alloy layer, a tin layer, a titanium layer, and a metal layer with gaps. 
     
     
       4. The electronic device defined in  claim 3  wherein the amorphous silicon layer has a thickness of less than 120 nm. 
     
     
       5. The electronic device defined in  claim 2  further comprising a passivation layer on the metal layer, wherein the metal layer is between the passivation layer and the amorphous silicon layer. 
     
     
       6. The electronic device defined in  claim 1  wherein the transparent material comprises a transparent material selected from the group consisting of: glass and sapphire. 
     
     
       7. The electronic device defined in  claim 1  wherein the housing structure comprises a rear housing wall and wherein the metal layer is patterned to form gaps that block eddy currents. 
     
     
       8. The electronic device defined in  claim 1  wherein the housing structure comprises a housing wall with an outer surface opposing the inner surface and wherein the inner surface is textured and has a surface roughness of 25 nm to 400 nm. 
     
     
       9. An electronic device, comprising:
 a housing structure formed of a transparent material, wherein the transparent material is transparent to visible light;
 a display coupled to the housing structure; and 
 a colored coating on an inner surface of the housing structure, wherein the colored coating includes a metal layer, an amorphous silicon layer between the metal layer and the housing structure, and a colored polymer layer. 
 
 
     
     
       10. The electronic device defined in  claim 9  wherein the colored polymer layer comprises dye. 
     
     
       11. The electronic device defined in  claim 9  wherein the colored polymer layer is formed on the inner surface between the amorphous silicon layer and the housing structure. 
     
     
       12. The electronic device defined in  claim 9  wherein the colored polymer layer is formed on the metal layer and wherein the metal layer is between the colored polymer layer and the amorphous silicon layer. 
     
     
       13. The electronic device defined in  claim 9  wherein the transparent material comprises a transparent material selected from the group consisting of: glass and sapphire. 
     
     
       14. An electronic device, comprising:
 a transparent housing wall, wherein the transparent housing wall is transparent to visible light; 
 a display coupled to the transparent housing wall; and 
 a colored coating on the transparent housing wall that includes a metal alloy layer and an amorphous silicon layer. 
 
     
     
       15. The electronic device defined in  claim 14  wherein the transparent housing wall has inner and outer surfaces, wherein the colored coating is on the inner surface, and wherein the metal alloy layer is between the amorphous silicon layer and the transparent housing wall. 
     
     
       16. The electronic device defined in  claim 15  wherein the metal alloy layer comprises TiAlN. 
     
     
       17. The electronic device defined in  claim 16  wherein the colored coating further comprises a mirror coating on the amorphous silicon layer. 
     
     
       18. The electronic device defined in  claim 17  wherein the mirror coating includes a first layer and a second layer, wherein the first layer is between the second layer and the amorphous silicon layer, and wherein the first layer comprises silicon oxide. 
     
     
       19. The electronic device defined in  claim 18  wherein the second layer comprises amorphous silicon. 
     
     
       20. The electronic device defined in  claim 14  wherein the transparent housing wall comprises a rear housing wall and wherein the colored coating comprises a mirror coating on the amorphous silicon layer that is formed from a stack of thin-film layers.

Description:
This application claims the benefit of provisional patent application No. 62/693,872, filed Jul. 3, 2018, which is hereby incorporated by reference herein in its entirety. 
    
    
     FIELD 
     This relates generally to electronic devices, and, more particularly, to colored coatings for electronic devices. 
     BACKGROUND 
     Electronic devices such as cellular telephones, computers, watches, and other devices may contain housing structures formed of glass and other materials. For example, an electronic device may have a rear housing wall that is covered with a layer of glass. 
     If care is not taken, housing structures may have an undesired appearance. For example, a coating layer on a housing may have an unattractive color or may have an appearance that changes more than desired as a function of viewing angle. 
     SUMMARY 
     An electronic device may include electrical components and other components mounted within a housing. The housing may have transparent housing structures such as walls formed of glass or sapphire. 
     Housing structures such as transparent housing structures may have a colored coating. The colored coating may cover a housing wall or may be patterned to form a logo or trim. 
     The colored coating may include a thin absorptive layer and a metal layer configured so that the coating exhibits a desired color. Adjustments to the colored coating such as adjustments to the thickness of the thin absorptive layer may be used to alter the color of the coating. If desired, a colored layer such as a layer of colored polymer may be incorporated into the colored coating to further adjust the color of the coating. 
     The colored coating may be formed on an inner or outer housing structure surface. The surface may have a texture to provide the coating with a matte appearance. When formed on an outer surface, a transparent diamond-like carbon layer may be included in the colored coating to protect the colored coating from scratches. When formed on an inner surface, a passivation layer may be included on the inner side of the colored coating to prevent oxidation of the metal layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device of the type that may include a coating in accordance with an embodiment. 
         FIG. 2  is a cross-sectional side view of an illustrative electronic device in accordance with an embodiment. 
         FIG. 3  is a cross-sectional side view of an illustrative housing structure with a coating in accordance with an embodiment. 
         FIG. 4  is a graph in which light reflection has been plotted as a function of wavelength for structures associated with the coating of  FIG. 3  in accordance with an embodiment. 
         FIG. 5  is a side view of an illustrative housing structure with a coating in accordance with an embodiment. 
         FIG. 6  is a graph in which light reflection has been plotted as a function of wavelength for structures associated with the coating of  FIG. 5  in accordance with an embodiment. 
         FIG. 7  is a diagram of an illustrative housing structure with a textured surface covered with a coating in accordance with an embodiment. 
         FIG. 8  is a side view of an illustrative housing structure with a radio-frequency transparent colored coating containing a metal alloy layer in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices and other items may be provided with structures that have coatings. The structures may be formed from glass, polymer, crystalline material such as sapphire, metal, and/or other materials. In some arrangements, the structures may form a rear housing wall, sidewall, or other housing structures. The housing structures may, if desired, be transparent housing structures such as layers of glass or sapphire. Coatings can be formed on the inner or outer surfaces of housing structures. For example, an inner surface of a transparent rear housing wall may be provided with a logo-shaped coating or a blanket coating that covers the entire wall. In some configurations, edge portions of a protective display cover layer that overlaps a layer of pixels in a display may be provided with a coating. 
     A coating may be colored to impart a desired color to a portion of a device. The color that is provided by the coating may be a non-neutral color such as red, yellow, blue, green, rose gold, champagne, or other non-neutral color. The coating may, if desired, exhibit desirable properties such as color invariance over a wide range of viewing angles (e.g., exhibiting less than 5% or less than 10% change in color coordinate values over viewing angles ranging +/−40° from the surface normal of a coated surface), the ability to form the coating from a relatively small number of layers of material (e.g., 2 or 3 layers, 2-4 layers, etc.), the ability to cover a wide range of different color options, high reliability, good manufacturability, and/or low cost. 
     An illustrative electronic device of the type that may include a structure that is coated with a colored coating layer 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, goggles, a helmet or other equipment worn on a user&#39;s head (e.g., a head-mounted display), 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 a housing. The housing may include housing structures such as housing sidewalls  12  and other structures for supporting display  14 . 
     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. If desired, display  14  may use a microelectromechanical systems pixel array. 
     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 rigid polymer or a hard transparent material such as glass or sapphire to help protect more sensitive portions of display  14  from damage. Other portions of device  10  such as housing structures on the sidewall or rear wall of device  10  may also be formed from transparent material (e.g., glass, sapphire, polymer, etc.). 
       FIG. 2  is a cross-sectional side view of an illustrative device such as device  10  of  FIG. 1 . As shown in  FIG. 2 , the housing for device  10  may include housing structures such as housing sidewalls  12  on the sides of device  10  and rear housing wall  24  on a rear face of device  10  (as an example). Sidewalls  12  and/or rear housing wall  24  may be formed from metal, glass, sapphire or other crystalline material, polymer, fiber composite materials, and/or other materials. As an example, some or all of sidewalls  12  may be formed from metal and some or all of rear housing wall  24  may be formed from transparent material such as glass or sapphire. Other configurations may be used, if desired. 
     As shown in  FIG. 2 , display  14  may include display cover layer  16  (e.g., a layer of glass, sapphire, or clear polymer) and display layer  18  (e.g., a display layer that includes an array of pixels to present images for a user on the front face of device  10 ). Display layer  18 , which may sometimes be referred to as a pixel array layer, may be a liquid crystal display structure, an organic light-emitting diode display structure (e.g., a flexible organic light-emitting diode display layer), or other suitable display. During operation, display layer  18  may present images that are viewable through transparent portions of display cover layer  16 . In some arrangements, edge portions of display cover layer  16  may bend downwards to form portions of sidewall  12  and/or edge portions of rear wall  24  may bend upwards to form portions of sidewall  12 . 
     Internal components in device  10  such as components  22  (e.g., electrical components such as integrated circuits, sensors, etc.) may be mounted on one or more substrates such as printed circuit  20  in the interior of device  10 . 
     To hide internal components such as components  22  from view, inactive border areas in layer  16  and portions of other transparent structures (e.g., a transparent rear housing layer such as rear housing wall  24  on the rear face of device  10  and/or transparent housing sidewall structures) may be covered with coatings (e.g., opaque coatings). Coating layers may be formed on the inner and/or outer surfaces of these housing structures. For example, a coating may be formed on some or all of the inner surface of sidewall  12 , the inner surface of rear housing wall  24 , and/or the inner surface of border portions of display cover layer  16 . Arrangements in which the coating is formed on some or all of the outer surfaces of these structures may also be used. 
     In some arrangements, a coating may be used primarily to block light (e.g., to hide internal device structures from view). In other arrangements, a patterned coating may be used to form text, logos, trim, and/or other decorative patterns. Black coatings may sometimes be used to form opaque masking layers. Coatings for structures in device  10  may also have non-neutral colors (e.g., blue, red, yellow, gold, rose gold, red-violet, pink, etc.). 
     A colored coating for device  10  may from metal (e.g., aluminum, gold, and/or other highly reflective metals), absorptive materials (e.g., amorphous semiconductor layers such as layers of amorphous silicon or amorphous germanium), colored polymers and/or other dielectrics, and/or other materials. Materials for the coatings may include organic materials such as polymer layers and/or inorganic materials such as oxide layers, nitride layers, and/or other inorganic dielectric materials. Polymer may include dye, pigment, or other colorants to impart a desired color to the polymer. In some arrangements, a coating may include a transparent (optical) diamond-like carbon layer (e.g., a hard amorphous carbon layer). A transparent diamond-like carbon layer may, for example, be used as a protective outer layer in a coating. The visible light transmission of the diamond-like carbon layer in this type of arrangement may be at least 90%, at least 95%, at least 99%, at least 99.8%, or less than 99.99% (as examples). The relative amounts of sp3 bonds, sp2 bonds, and hydrogen content in the diamond-like carbon layer may be adjusted during deposition to ensure that the diamond-like carbon layer has a desired hardness for resisting scratches while maintaining a desired optical transparency so that underlying color coating layers are visible to the user. 
       FIG. 3  is a cross-sectional side view of an illustrative coating layer. In the example of  FIG. 3 , coating  32  has been formed on an inner surface of layer  30 . Layer  30 , which may sometimes be referred to as a substrate layer, may be a transparent layer of glass, sapphire, or polymer (as examples). In device  10 , layer  30  may serve as a housing structure (e.g., some or all of sidewall  12  and/or rear housing wall  24 ) and/or may be a peripheral border portion of display cover layer  16  (a housing structure of glass, polymer, sapphire, or other suitable material that is formed near the edge of the array of pixels displaying images for a user of device  10 ). 
     Coating layer  32  may include layers  34  and  36 . Layer  36  may be a reflective layer formed from a material such as metal. For example, layer  36  may be an aluminum layer. The thickness of layer  36  may be at least 30 nm, 30-50 nm, at least 50 nm, at least 20 nm, less than 70 nm, or other suitable thickness. 
     Layer  34  may be an absorptive layer (e.g., a layer that absorbs at least some of the light passing through layer  34 ). Absorptive layer  34  may be interposed between viewer  26  and layer  36 . For example, in arrangements in which coating  32  is formed on the inner surface of a layer such as layer  30 , layer  34  may be interposed between layer  30  and layer  36 . Layer  34  may, if desired, be formed directly on the inner surface of layer  30 . Absorptive layer  34  may be formed form an absorptive material such as amorphous silicon that absorbs visible light. The index of refraction of amorphous silicon is relatively high (e.g., the refractive index of amorphous silicon in the visible light range is 4-4.5), which tends to refract off-axis light towards the surface normal of layer  34 . As a result, coating  32  will tend to have an appearance that is relatively invariant to changes in viewing angle. Layer  34  may have a thickness h of at least 15 nm, at least 20 nm, 20-80 nm, at least 40 nm, less than 70 nm, less than 80 nm, less than 100 nm, less than 120 nm, or other suitable thickness. The thickness h of layer  34  is preferably much less (e.g., at least 5 times less, at least 15 times less, at least 25 times less, or more) than the wavelength of visible light (e.g., about 500 nm) divided by 4*n, where n is the refractive index of amorphous silicon. 
     As shown in  FIG. 3 , optional passivation layer  38  may be formed on the innermost surface of layer  36  (e.g., in scenarios in which layer  30 ′ is not present). Passivation layer  38  may be formed from any suitable material that helps protect layer  34 . For example, passivation layer  38  may be formed from amorphous silicon and may help prevent aluminum or other metal in layer  36  from oxidizing when contacted by the atmosphere. 
     As illustrated by optional substrate layer  30 ′, coating  32  may, if desired, be formed on an outer surface of device  10  (e.g., in an arrangement in which substrate layer  30  is not present and coating  32  covers the outer surface of a housing structure or other layer  30 ′). In this type of arrangement, a diamond-like carbon layer may be formed on the outer surface of coating  32  in the position shown by layer  30  of  FIG. 3 . The diamond-like carbon layer may help prevent damage to coating  32  from scratches. 
       FIG. 4  is a graph in which light reflectivity R has been plotted as a function of wavelength λ for layer  36  and coating  32 . Layer  36  may be, for example, a metal layer such as an aluminum layer and may be characterized by a relatively broadband reflection spectrum (see, e.g., flat reflectivity curve  40  of  FIG. 4 ). In the presence of silicon layer  34  on layer  36 , coating  32  may exhibit thin-film interference effects (e.g., constructive interference at some wavelengths λ of visible light) so that the absorption of visible light by coating  32  may peak and the reflectivity of visible light may exhibit a valley at a wavelength such as wavelength λc. This is illustrated by curve  42  of  FIG. 4 , which represents the reflectivity spectrum of coating  32  at visible light wavelengths. The position of wavelength λc within the visible spectrum (390 to 700 nm) may be adjusted by selecting the value of thickness h of layer  34 . The color of coating  32  can be tuned in this way (e.g., coatings  32  in which the thickness h of layer  34  is different will have different non-neutral colors). 
     Another illustrative configuration for coating  32  is shown in  FIG. 5 . In the example of  FIG. 5 , coating  32  has been formed on the inner surface of substrate layer  30 . Layer  34  may be an amorphous silicon layer with a thickness h and layer  36  may be a metal layer such as an aluminum layer, as described in connection with  FIG. 3 . Adjustment of coating  32  (e.g., adjustment of thickness h) can be used to adjust the color of coating  32 . Further adjustment of the color of coating  32  can be obtained by incorporating one or more colored dielectric layers into coating  32 . For example, colored layer  44  may be interposed between layer  34  and substrate  30  and/or colored layer  46  may be formed on the innermost surface of layer  36 . 
     Colored layers  44  and  46  may be formed from polymer or other dielectric that includes dye, pigment, or other colorant that provides layers  44  and  46  with desired color casts. The graph of  FIG. 6  in which reflectivity R has been plotted as a function of wavelength λ illustrates a possible reflection spectrum for coating  32 . Silicon layer  34  on metal layer  36  may be characterized by a reflection spectrum such as curve  48  (e.g., a reflection spectrum with a valley at wavelength λ 1 , corresponding to an absorption spectrum peak). Colored coating layer  44  (or colored coating layer  46 , or both colored coating layers  44  and  46 ) may be characterized by a reflection spectrum such as curve  50  (e.g., a reflection spectrum with a valley at wavelength λ 3 , corresponding to an absorption spectrum peak due to the presence of dye, pigment, or other colorant). At wavelengths away from the reflectivity spectrum valleys at λ 1  and λ 3  (e.g., at wavelengths such as wavelength λ 2 , which may correspond to green light, for example), coating  32  will reflect light. As a result, coating  32  may have a color determined by the spectral responses of 1) layers  34  and  36 ) and 2) the colored coating material (e.g., layer  44  and/or layer  46 ). In arrangements in which the colored polymer material is formed on the inner surface of metal layer  36  (as shown by illustrative layer  46 ), ambient light passes through metal layer  36  before reaching layer  46 . Layer  46  can adjust the color of coating  32 , provided that layer  36  is sufficiently thin (e.g., 30-50 nm or less or other suitable thickness) to allow a non-negligible amount of light to pass to and from layer  46 . 
     As illustrated by optional substrate layer  30 ′, coating  32  of  FIG. 5  may, if desired, be formed on an outer surface of device  10  (e.g., in an arrangement in which substrate layer  30  is not present). In this type of arrangement, a transparent diamond-like carbon layer may be formed on the outer surface of coating  32  in the position shown by layer  30  of  FIG. 5  to help protect coating  32  from scratches. 
     In some arrangements, it may be desirable for some or all of the coated structures in device  10  to exhibit a matte appearance. As shown in  FIG. 7 , coating layer  32  may be provided with a matte appearance by texturing the inner surface of substrate  30  (e.g., so that this surface has a root-mean-square surface roughness of at least 25 nm, at least 50 nm, at least 100 nm, less than 400 nm, less than 1600 nm, or other suitable surface roughness. This rough surface texture helps scatter ambient light that is reflecting off of coating  32  and thereby provides coating  32  with a matte appearance. As illustrated by optional substrate layer  30 ′, coating  32  of  FIG. 7  may, if desired, be formed on a textured outer surface of device  10  (e.g., a textured surface of layer  30 ′) in an arrangement in which substrate layer  30  is not present. To help protect coating  32  in this type of arrangement, a protective coating such as a transparent diamond-like carbon layer may be formed on the outer surface of coating  32  (e.g., in the position of layer  30  of  FIG. 7 ). 
     In some arrangements, it may be desirable for the colored coating to exhibit radio-frequency transparency. For example, in systems in which layer  30  forms an electronic device housing wall, it may be desirable to allow wireless power signals and/or radio-frequency antenna signals to be transmitted and/or received through layer  30  and the colored coating on layer  30 . To enhance radio-frequency transparency for wireless communications and/or to support inductive wireless charging, conductive materials (e.g., metal layer  36 ) may be patterned to form isolated islands (e.g., rectangular pads or pads of other shapes such as triangles, hexagons, etc.) on layer  30 . The pads may be tiled in an array with rows and columns or other suitable patterns. A mesh of gaps (e.g., intersecting lines extending horizontally and vertically between rows and columns of pads or other thin elongated gap structures such as illustrative gaps G in  FIG. 7 ) may be present in the patterned layer. These gaps are free of metal or other conductive material in layer  36  and therefore block current flow (e.g., the gaps block eddy currents and prevent electromagnetic signal resonances from occurring). Each pad may have lateral dimensions equal to a fraction of a wavelength for radio-frequency signals of interest (e.g., less than 1/10 of a wavelength, less than ⅕ of a wavelength, at least 1/100 of a wavelength, at least 1/20 of a wavelength, etc.) or may have other suitable shapes and sizes for reducing or eliminating radio-frequency signal interactions as radio-frequency antenna signals and/or wireless power signals pass through layer  30 . 
     In addition to or instead of patterning conductive layer(s) of material to form pads, layer conductivity can be reduced by using low-conductivity alloys. For example, layer  36  may be formed from a reflective alloy such as a metal-silicon alloy (e.g., aluminum silicon), or other metal which has a lower conductivity than pure aluminum. Lower conductivity metals that may be used in forming layer  36  include titanium and tin. The use of a lower conductivity material for forming layer  36  (in alloy form or pure form) may enhance radio-frequency transparency for layer  36  when compared to arrangements in which pure aluminum is used in forming layer  36 . 
     An illustrative configuration in which layer  30  has a coating that is radio-frequency transparent is shown in  FIG. 8 . In the example of  FIG. 8 , radio-frequency transparent coating layers have been formed on the inner surface of substrate layer  30 . In particular, coating  32  has been formed on the inner surface of substrate layer  30 . Layer  36  of coating  32  may be a highly resistive metal alloy layer containing titanium, aluminum, and nitrogen such as a TiAlN layer. Layer  34  may be an amorphous silicon layer. Layer  32  serves as a lossy antireflection coating. The color of layer  32  and therefore the appearance of the structures of  FIG. 8  when viewed in direction  28  by viewer  26  may be tuned by adjusting the thickness of layers  34  and  36 . The color of layer  32  may, if desired, be yellow, blue, red, or other non-neutral color. In general, the thicknesses of layers  34  and  36  may be 10-200 nm, at least 20 nm, at least 50 nm, less than 150 nm, less than 100 nm, or other suitable thickness. As an example, layer  36  may have a thickness of 75 nm and layer  34  may have a thickness of 24 nm. Color shifts due to variations in viewing angle may be negligible. 
     To ensure that coating  32  of  FIG. 8  has sufficient radio-frequency transparency, the sheet resistance of the TiAlN layer may be adjusted (e.g., by adjusting the flow rate of N 2  gas that is present during the deposition process). Increases in N 2  flow rates have been observed to increase sheet resistance. 
     If desired, one or more coating layers may be formed on the inner surface of layer  32  to change the appearance of layer  32 . In the example of  FIG. 8 , a thin-film interference filter that serves as a mirror (mirror coating) has been formed from thin-film stack  64 . Thin-film stack  64  may contain a stack of two or more thin-film layers with different refractive index values (e.g., alternating higher and lower refractive index values). In the example of  FIG. 8 , stack  64  includes a first layer  60  and a second layer  62  with different respective refractive indices. Layer  60  may be, as an example, a silicon oxide layer with a thickness of 85 nm and layer  70  may be, as an example, an amorphous silicon layer with a thickness of 75 nm. Other materials and/or other thicknesses (e.g., thin-film thicknesses of at least 5 nm, at least 20 nm, at least 50 nm, less than 400 nm, less than 200 nm, or less than 100 nm) may be selected for the thin-film layers in stack  64 . The thicknesses of the layers may be selected based on the materials used (and their refractive indices), the number of layers present, and the desired optical properties of the mirror coating (e.g., a desired target reflectivity). 
     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: 20190503
Publication Date: 20220726
Grant Date: 20220726
Priority Date: 20180703
Inventors: BAYAT, Khadijeh
MATSUI, YOSHITAKA
SUGAWARA, Naomi
NOZU, DAISUKE
ZHAO, Xianwei
YUEN, AVERY P.
MELCHER, MARTIN
WILSON, JAMES R.
FAN, DI
Assignee: APPLE INC
CPC Classifications: [{"code": "C03C17/3684", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K5/0243", "inventive": true, "first": false, "tree": "[]"}, {"code": "C03C2217/72", "inventive": false, "first": false, "tree": "[]"}, {"code": "C03C17/3482", "inventive": true, "first": true, "tree": "[]"}, {"code": "C03C2217/72", "inventive": false, "first": false, "tree": "[]"}, {"code": "C03C17/3655", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K9/0009", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K5/069", "inventive": true, "first": true, "tree": "[]"}, {"code": "C03C17/3636", "inventive": true, "first": false, "tree": "[]"}, {"code": "B32B1/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "C03C17/3684", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K9/0009", "inventive": true, "first": false, "tree": "[]"}, {"code": "C03C2217/72", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K5/0243", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K5/069", "inventive": true, "first": true, "tree": "[]"}, {"code": "C03C17/3655", "inventive": true, "first": false, "tree": "[]"}, {"code": "B32B1/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "C03C17/3636", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 69101479