PATENT DOCUMENT

Publication Number: US-11419232-B2
Application Number: US-202016869061-A
Country: US
Kind Code: B2

Title: Doped metal oxide coating having increased color durability

Abstract:
This application relates to a portable electronic device. The portable electronic device includes an enclosure having a metal oxide coating, the metal oxide coating including a metal alloy substrate that is doped with a dopant, and a metal oxide layer overlaying and formed from the metal alloy substrate so that the metal oxide layer includes the dopant.

Claims:
What is claimed is: 
     
       1. A portable electronic device comprising:
 an enclosure, including:
 a metal alloy substrate that includes a dopant; and 
 a metal oxide layer overlaying and formed from the metal alloy substrate, wherein the dopant in the metal alloy substrate is only dispersed in an upper region of the metal alloy substrate, the upper region extending from an external surface and into the metal alloy substrate and comprising less than 50% of a thickness of the metal alloy substrate. 
 
 
     
     
       2. The portable electronic device of  claim 1 , wherein the metal alloy substrate includes at least one of titanium, zirconium or steel. 
     
     
       3. The portable electronic device of  claim 1 , wherein the dopant includes a transition metal or a rare earth element. 
     
     
       4. The portable electronic device of  claim 1 , wherein the the metal oxide layer includes a metal oxide material including the dopant, and the metal oxide material is characterized as having a band gap disposed between a valence band and a conduction band. 
     
     
       5. The portable electronic device of  claim 4 , wherein the metal oxide layer includes an external surface, and when visible light is incident upon the external surface, the metal oxide material including the dopant absorbs photons of the visible light such as to impart the metal oxide layer with a color that corresponds to the band gap. 
     
     
       6. The portable electronic device of  claim 5 , wherein the band gap is between 1.2 eV to 3 eV. 
     
     
       7. An enclosure for a portable electronic device, the enclosure comprising:
 a substrate that includes a metal alloy; and 
 a metal oxide layer overlaying the substrate, wherein the metal oxide layer includes metallic atoms and a dopant so that the metal oxide layer is characterized as having a band gap, wherein the dopant is additionally present only in an upper region of the substrate, and in a uniform distribution, the upper region extending from an external surface and into the substrate and comprising less than 50% of a thickness of the substrate. 
 
     
     
       8. The enclosure of  claim 7 , wherein when visible light is incident upon an external surface of the metal oxide layer, the metal oxide layer absorbs a selected wavelength of the visible light that corresponds to the band gap. 
     
     
       9. The enclosure of  claim 7 , wherein the metal oxide layer is characterized as having a hardness of 1000 Hv or greater. 
     
     
       10. The enclosure of  claim 7 , wherein the metal oxide layer includes between 0.001 wt % to 10 wt % of the dopant. 
     
     
       11. The enclosure of  claim 7 , wherein the dopant is a transition metal or a rare earth element. 
     
     
       12. The enclosure of  claim 7 , wherein the band gap is between 1.2 eV to 3 eV. 
     
     
       13. An enclosure for a portable electronic device, the enclosure comprising:
 a metal substrate; and 
 a metal oxide coating overlaying the metal substrate, the metal oxide coating including a first surface portion and a second surface portion adjacent to the first surface portion, wherein the first surface portion includes a first dopant and the second surface portion includes a second dopant different than the first dopant, wherein the first dopant and the second dopant are additionally present and dispersed only throughout an upper region of the metal alloy substrate, the upper region extending from an external surface into the metal substrate and comprising less than 50% of a thickness of the metal substrate. 
 
     
     
       14. The enclosure of  claim 13 , wherein the metal oxide coating is characterized as having a hardness of 1000 Hv or greater. 
     
     
       15. The enclosure of  claim 13 , wherein the first and second dopants include at least one of a rare earth element or a transition metal. 
     
     
       16. The enclosure of  claim 13 , wherein the metal oxide coating has a uniform thickness. 
     
     
       17. The enclosure of  claim 13 , wherein the metal oxide coating is free of pores. 
     
     
       18. The enclosure of  claim 13 , wherein the first surface portion is characterized as having a first band gap, and the second surface portion is characterized as having a second band gap greater than the first band gap.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This claims priority to U.S. Provisional Patent Application No. 62/902,308, filed 18 Sep. 2019, entitled “DOPED METAL OXIDE COATING HAVING INCREASED COLOR DURABILITY,” the entire disclosure of which is hereby incorporated by reference. 
    
    
     FIELD 
     The described embodiments relate generally to a metal oxide coating that is intentionally doped with a foreign atom or impurities. More particularly, the described embodiments relate to methods for doping the metal oxide coating of an enclosure for a portable electronic device with a foreign atom such as to impart the enclosure with a color. 
     BACKGROUND 
     Enclosures for portable electronic devices may be manufactured from different types of metals, which may be colored with dyes in order to improve their aesthetic appearance. For example, anodized coatings may be colored with various dyes. However, the color of these dyed anodized coatings is susceptible to fading and chipping when the enclosures are subjected to environmental exposure (e.g., UV exposure, saltwater exposure, mechanical damage, etc.). Accordingly, there is a need to provide a most robust manner for coloring these enclosures. 
     SUMMARY 
     This paper describes various embodiments that relate to a metal oxide coating that is intentionally doped with a foreign atom or impurities. More particularly, the described embodiments relate to methods for intentionally doping the metal oxide coating of an enclosure for a portable electronic device with a foreign atom such as to impart the enclosure with a color. 
     According to some embodiments, a portable electronic device is described. The portable electronic device includes an enclosure having a metal alloy substrate that includes a dopant, and a metal oxide layer overlaying and formed from the metal alloy substrate so that the metal oxide layer includes the dopant. 
     According to some embodiments, an enclosure for a portable electronic device is described. The enclosure includes a substrate that includes a metal alloy, and a metal oxide layer overlaying the substrate, where the metal oxide layer includes a dopant so that the metal oxide layer is characterized as having a band gap. 
     According to some embodiments, an enclosure for a portable electronic device is described. The enclosure includes a metal substrate, and a metal oxide coating overlaying the metal substrate, the metal oxide coating including a first surface portion and a second surface portion adjacent to the first surface portion, where the first surface portion includes a first dopant and the second surface portion includes a second dopant different than the first dopant. 
     Other aspects and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the described embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements. 
         FIG. 1  illustrates perspective views of various portable electronic devices having enclosures that may be processed using the techniques described herein, in accordance with some embodiments. 
         FIGS. 2A-2D  illustrate cross-sectional views of a process for forming a doped metal oxide coating, in accordance with some embodiments. 
         FIGS. 3A-3D  illustrate cross-sectional views of a process for forming a doped metal oxide coating, in accordance with some embodiments. 
         FIG. 4  illustrates a cross-sectional view of a doped metal oxide coating, in accordance with some embodiments. 
         FIGS. 5A-5B  illustrate cross-sectional views of a metal substrate having a color, in accordance with some embodiments. 
         FIGS. 6A-6B  illustrate cross-sectional views of a doped metal oxide coating having a color in accordance with a band gap, in accordance with some embodiments. 
         FIGS. 7A-7C  illustrate various exemplary doped metal oxide coatings having different colors, in accordance with some embodiments. 
         FIG. 8  illustrates a method for forming a doped metal oxide coating, in accordance with some embodiments. 
         FIG. 9  illustrates a method for forming a doped metal oxide coating, in accordance with some embodiments. 
         FIG. 10  illustrates a method for forming a doped metal oxide coating, in accordance with some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Representative applications of methods and apparatus according to the present application are described in this section. These examples are being provided solely to add context and aid in the understanding of the described embodiments. It will thus be apparent to one skilled in the art that the described embodiments may be practiced without some or all of these specific details. In other instances, well known process steps have not been described in detail in order to avoid unnecessarily obscuring the described embodiments. Other applications are possible, such that the following examples should not be taken as limiting. 
     In the following detailed description, references are made to the accompanying drawings, which form a part of the description and in which are shown, by way of illustration, specific embodiments in accordance with the described embodiments. Although these embodiments are described in sufficient detail to enable one skilled in the art to practice the described embodiments, it is understood that these examples are not limiting; such that other embodiments may be used, and changes may be made without departing from the spirit and scope of the described embodiments. 
     Enclosures for portable electronic devices may be manufactured from different types of metals, which may be subsequently colored with dyes in order to improve their aesthetic appearance. For example, anodized coatings may be colored with various dyes. However, the majority of the dye of an anodized coating is concentrated towards the upper region. As a result, the color of these dyed anodized coatings is susceptible to fade and chipping when the enclosures are subjected to environmental exposure (e.g., UV exposure, saltwater exposure, dropping, etc.). In another example, physical vapor deposition may be utilized to form a metal oxide layer having different colors. However, the metal oxide layer formed by physical vapor deposition is susceptible to delamination when induced to strain. In another example, light interference coloring may also be undesirable due to the ease of changing the color, such as by adding finger oil to the surface of the anodized coating. Accordingly, there is a need for a more robust way of coloring enclosures. 
     Additionally, the more robust methods for coloring these enclosures cannot affect the ductility and strength of the metals that comprise these enclosures. According to some embodiments described herein, one technique for coloring these enclosures includes doping the metal and/or the metal oxide coating formed thereof with a foreign atom. For example, a metal substrate may be doped with at least one foreign atom, and subsequently oxidized to form a doped metal oxide layer. The doped metal oxide layer has a color that corresponds to a band gap of the metal oxide material of the metal oxide layer. Advantageously, the color of the doped metal oxide layer is not dependent upon a thickness of the doped metal oxide layer—therefore, the color is more vibrant and resistant to chipping, scratching, and UV light exposure relative to conventional coloring techniques. In some instances, the color of the doped metal oxide layer may be referred to as intrinsic coloring because the color is based upon a band gap of the metal oxide material. Furthermore, because the metal substrate and/or metal oxide layer is doped with the foreign atom, instead of micro-alloyed with the foreign atom, the metal substrate and/or metal oxide layer maintains its pre-existing amount of ductility and hardness. 
     As described herein, the term “doping” refers to the substitution of a foreign atom or an external atom into a metal matrix that comprises a crystal lattice of a metal material or a metal oxide material. The foreign atom or the external atom refers to an element (e.g., Zr, Ce, etc.) that may not be included in the underlying metal substrate or metal alloy substrate from which the metal oxide material was formed from. For example, if the underlying metal substrate includes zirconium, then the external atom may not be zirconium. It should be noted that the foreign atom itself is not colored, and the color of the resulting doped metal oxide layer is a result of a change in band gap. 
     Additionally, as used herein, the term “doping” is not to be confused with an alloying element or alloying process. For example, some metal alloys include trace amounts of the alloying element in order to increase hardness or ductility. Thus, the alloying element is used to alter physical, mechanical or chemical properties of the material being alloyed. Additionally, the alloying element is added through a combination of heat and/or pressure. However, unlike the alloying element, the doping element is added at the atomic scale as the doping element substitutes itself for a metal atom present in the crystal lattice that comprises the metal or metal alloy or is integrated into the crystal lattice interstitially. As a result, the doping element does not result in the formation of a new crystalline phase/structure. In contrast, the micro-alloying element leads to the formation of a new crystalline phase/structure. 
     As described herein, doping is used to alter the electrical properties of a metal part (e.g., substrate, oxidized metal substrate, etc.). For example, the metal part has greater electrical potential after being doped with a foreign atom. In some embodiments, a doped metal part may include a band gap that defines a space between the valence band and the conduction band. Below the band gap is a valence band that contains a full complement of valence electrons in the absence of being triggered by energy (e.g., photons of light). Above the band gap is a conduction band. Valence electrons that are excited to this level are available to conduct. In some embodiments, the band gap refers to the energy difference between the two energy levels (represented by the conduction band and the valence band). Valence electrons present in the conduction band have the ability to move throughout the crystal lattice of the material, thereby enabling the material to conduct. Introducing different doping elements into the material results in altering the color of emitted light by the doped material. 
     In some examples, the color of the doped metal oxide layer may be characterized according to CIE L*a*b* color-opponent dimension values. The L* color opponent dimension value is one variable in an L*a*b* color space. In general, L* corresponds to an amount of lightness. L*=0 represents an extreme black while L*=100 represents white. In general, a* indicates amounts of red color and green color in a sample. A negative a* value indicates a green color, while a positive a* value indicates a red color. Accordingly, samples having a positive a* value will indicate that more red than green is present. In general, b* indicates amounts of blue color and yellow color in a sample. A negative b* value indicates a blue color, while a positive b* value indicates yellow color. Accordingly, samples having a positive b* value will indicate more yellow than blue is present. 
     According to some embodiments, a portable electronic device is described. The portable electronic device includes an enclosure having a metal alloy substrate that includes a dopant, and a metal oxide layer overlaying and formed from the metal alloy substrate so that the metal oxide layer includes the dopant. 
     These and other embodiments are discussed below with reference to  FIGS. 1-10 ; however, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanatory purposes only and should not be construed as limiting. 
       FIG. 1  illustrates various portable electronic devices that can be processed using the techniques as described herein. The techniques as described herein can be used to process surfaces of enclosures of the portable electronic devices. In some examples, the enclosures can include at least one of a metal, a metal alloy, a polymer, glass, ceramics, or a thermoplastic. In some examples, the enclosure can include a metal part that is attached to a non-metal part. According to some embodiments, the techniques described herein may be utilized to impart the enclosure with a color that is based on a band gap of a material of the enclosure. 
       FIG. 1  illustrates exemplary portable electronic devices including a smartphone  102 , a tablet computer  104 , a smartwatch  106 , and a portable computer  108  that include enclosures that may be processed using the techniques as described herein. These exemplary portable electronic devices may be capable of using personally identifiable information that is associated with one or more users. It is well understood that the use of personally identifiable information should follow privacy policies and practices that are generally recognized as meeting or exceeding industry or governmental requirements for maintaining the privacy of users. In particular, personally identifiable information data should be managed and handled so as to minimize risks of unintentional or unauthorized access or use, and the nature of authorized use should be clearly indicated to users. 
     Surface(s) of the portable electronic devices  102 ,  104 ,  106 ,  108  described herein may assume any number of desired surface geometries and surface finishes. In some examples, the enclosures may have a three-dimensional structure having a height, width, and depth, and any type of geometry. In particular, the enclosures is characterized as rectangular, polygonal, circular, beveled edges, angular edges, elliptical, etc. 
       FIGS. 2A-2D  illustrate cross-sectional views of a process for forming a doped metal oxide coating, in accordance with some embodiments. In some embodiments, a metal part  200 , that is processed according to the techniques described herein, has a near net shape of a final part, such as the enclosures of the portable electronic devices  102 ,  104 ,  106 , and  108 . 
       FIG. 2A  illustrates a cross-sectional view of a metal part  200  prior to undergoing a process for forming a doped metal oxide coating. In some examples, the metal part  200  is a metal substrate formed of a pure metal or a metal alloy. For example, the metal part  200  may be formed of stainless steel, zirconium alloy or a titanium alloy. Notably, the metal part  200  may be characterized as lacking a band gap or having a narrow band gap less than 1.7 eV. A band gap of about 1.7 eV corresponds to the lowest energy of visible light. In other words, the metal part  200  is characterized as having a black or near black color. In particular, the atoms that comprise the metal material of the metal part  200  are sufficiently close together so that the distinct energy levels of the conduction band and the valence band interact. The low energy level of the valence band overlaps with the high energy level of the conduction band so that the metal part  200  lacks a band gap or has a narrow band gap less than 1.7 eV. In some examples, an external surface  204  of the metal substrate  204  may be polished prior to the doping process in order to increase the luster of the external surface  204 . 
       FIG. 2B  illustrates a cross-sectional view of the metal part  200  that is exposed to a doping process, in accordance with some embodiments. In some embodiments, the metal part  200  is exposed to at least one doping atom  212 . In some examples, the at least one doping atom  212  includes one type of element, and or if the metal part  200  is exposed to multiple doping atoms  212 , then the metal part  200  may be exposed to different types of elements. In particular, the doping atom  212  may include at least one of a rare earth mineral or a transition metal. It should be noted that for purposes of the techniques described herein, only rare earth minerals and transition metals may be used as dopants because rare earth minerals and transition metals have the requisite number of valence electrons to transition from a lower energy level of the valence band to occupy a higher energy level of the conduction band. Therefore, the doping atom  212  may also be referred to as a doping ion due to having a positive charge or a negative charge based upon having an unequal number of electrons and protons. 
     Particular examples of the doping atom  212  that may be incorporated into the metal part  200  include cerium (Ce), dysprosium (Dy), erbium (Er), europium (Eu), gadolinium (Gd), holmium (Ho), lanthanum (La), lutetium (Lu), neodymium (Nd), praseodymium (Pr), promethium (Pm), samarium (Sm), scandium (Sc), terbium (Tb), thulium (Tm), ytterbium (Yb), and yttrium (Y). More preferably, the doping atom  212  may be Ce, Pr, Er, Ni, Co, Fe, Nd, which are capable of imparting the metal part and/or the oxidized metal part with a color in the visible light spectrum (e.g., between ˜380 nm to ˜740 nm). 
     In some examples, the doping process includes an ion implantation process, a thermal diffusion process or a molecular layer doping process. According to some examples, the ion implantation process involves bombarding the external surface  204  of the metal substrate  202  with highly energetic doping elements (e.g., the doping atom  212 ). The ion implantation process provides good control over the dosage and depth of the doping elements directed at the external surface  204 . Moreover, the ion implantation process causes amorphization of the crystal lattice of the material that comprises the metal substrate  202  whereby the doping atom  212  substitutes for some of the metal atoms (e.g., Zr, Ti, etc.) that comprise the crystal lattice. According to some examples, the molecular layer doping process involves diffusing dopant atom  212  into the metal substrate  202 . In contrast to the ion implantation process, the molecular layer doping process is a non-destructive method that does not alter the crystal lattice of the material that comprises the metal substrate  202 . The doping processes described herein are distinct from sintering, whereby powder is pressed together and then sintered to form a color. 
       FIG. 2C  illustrates a cross-sectional view of a doped metal part  220  subsequent to the doping process, in accordance with some embodiments. As a result of the doping process, the external surface  204  is modified to form a doped external surface  222 . By using a controlled doping process (e.g., ion implantation, etc.), at least one doping atom  212  may be uniformly distributed through an upper region (Ru) of the doped metal part  220 . However, in other examples, at least one doping atom  212  may be randomly dispersed throughout the upper region (Ru). According to some embodiments, the upper region (Ru) is defined as a region extending from the external surface  204  and into the metal substrate  202  that is less than 50% of a thickness of the metal substrate  202 , less than 35% of a thickness of the metal substrate  202 , or less than 25% of a thickness of the metal substrate  202 . 
     As illustrated in  FIG. 2C , the doped metal part  220  is exposed to an oxidation process. The oxidation process involves exposing the doped metal part  220  to oxygen atoms ( 02 )  224  such as to form a doped metal oxide layer that overlays the metal substrate  202 . In some examples, the oxidation process includes applying heat and/or vacuum pressure to the doped metal part  220 . 
     In some embodiments, as a result of doping the metal substrate  202  with at least one doping atom  212 , the material of the metal substrate  202  undergoes a change in electrical properties (i.e., changing the band gap). However, the doped metal substrate (non-oxidized) does not have a band gap; therefore, the doped metal substrate has a metallic color. Indeed, the non-oxidized, doped metal substrate will appear silver due to the metal reflecting substantially all visible wavelengths of light. Indeed, in order to attain a non-metallic, non-black, visible color, the doped metal substrate may be sintered, as described in more detail with reference to  FIG. 8 . 
       FIG. 2D  illustrates a cross-sectional view of a doped oxidized part  230  subsequent to an oxidation process, in accordance with some embodiments. The doped oxidized part  230  includes a doped metal oxide layer  232 . The doped oxidized part  230  includes metal oxide material  234 . However, the atomic composition of the metal oxide material  234  is modified by incorporating the doping atoms  212  therein. In some examples, the doped metal oxide layer  232  includes between about 0.001 wt % to about 10 wt % of the doping atoms  212 . In some examples, the doping atoms  212  of the doped oxidized part  230  will not be in particle form. In some embodiments, the doped oxidized part  230  has a uniform distribution of the doping atoms  212  within the metal oxide material  234 . 
     Some conventional metal oxide materials may be characterized as an electrical insulator due to having a material with a band gap between the valence and conduction bands that is too wide for valence electrons to surmount. However, the doping process described herein (with reference to  FIG. 2B ) reduces the band gap between the valence and conduction bands such that the band gap is between 1.7 eV to 3.0 eV and is characterized as having a non-metallic, non-black color (e.g., purple, blue, etc.). It should be noted that the color of the doped oxidized part  230  are not dependent upon the thickness of the doped metal oxide layer  232 . 
     Additionally, in some embodiments, the metal substrate  202  does not include aluminum. As a result, the metal oxide coating  230  is characterized as being free of pores. This is in contrast to anodized aluminum coatings having generally columnar pores. 
       FIGS. 3A-3D  illustrate a cross-sectional view of a process for forming a doped metal oxide coating, in accordance with some embodiments.  FIG. 3A  illustrates a cross-sectional view of a metal part  300  prior to a doping process. The metal part  300  includes a metal substrate  302  having an external surface  304 . 
     As illustrated in  FIG. 3B , the metal part  300  is subjected to an oxidation process. In particular, the oxidation process involves exposing the metal substrate  302  to oxygen ions  312 . In some examples, the metal substrate  302  is subjected to a controlled oxidation process in order to grow a metal oxide layer in a controlled manner. Beneficially, growing the metal oxide layer in a controlled manner ensures that the metal oxide layer has a uniform thickness. According to some embodiments, the metal oxide layer is characterized as an electrical insulator due to having a material with a band gap between the valence and conduction bands that is too wide for valence electrons to surmount. Accordingly, a doping process described herein (with reference to  FIG. 3D ) is required to reduce the band gap between the valence and conduction bands such as to impart the doped metal oxide layer with a non-metallic color (e.g., purple, blue, red, etc.). 
       FIG. 3C  illustrates a cross-sectional view of an oxidized part  320  subsequent to the oxidation process, in accordance with some embodiments. As illustrated in  FIG. 3C , the oxidized part  320  includes a metal oxide layer  324  that overlays the metal substrate  302 . The metal oxide layer  324  includes metal oxide material  326 . In some examples, the metal oxide material  326  includes ZrO 2  or TiO 2 . In some examples, the metal oxide layer  324  may be formed by an anodization process or a passivation process. For example, if the metal oxide layer  324  is formed by a passivation process, then the metal oxide layer  324  may be referred to as a passivation oxide layer or a native oxide layer. However, it should be noted that the passivation process is an uncontrolled, naturally-occurring oxidation process. In contrast, the anodization process is a controlled electrochemical process that utilizes an anodizing voltage (e.g., between 15 V to 21 V). Beneficially, if the metal substrate  302  is subjected to a controlled anodization process, the metal oxide layer  324  grows in a more controlled manner. As a result, the metal oxide layer  324  subsequent to an anodization process has a uniform thickness whereas the metal oxide layer  324  formed by a passivation process has a varied or non-uniform thickness. 
     Beneficially oxidizing the metal material  306  of the metal substrate  302  imparts the oxidized part  320  with an increased amount of hardness, which one of ordinary skill in the art would recognize is more desirable when the oxidized part  320  is utilized to protect operational components carried within the enclosure. In some examples, the oxidized part  320  has a hardness of greater than 1000 Hv. 
       FIG. 3D  illustrates a cross-sectional view of a doped oxidized part  330  subsequent to a doping process, in accordance with some embodiments. As illustrated in  FIG. 3D , the doped oxidized part  330  is exposed to a doping process. The doping process includes depositing doping atom  322  onto the external surface  304  of the oxidized part  320 . In some examples, the doping process includes an ion implantation process or a diffusion process. The doping process alters the electrical properties of the doped oxidized part  330 . In some examples, the doping atoms  312  of the doped oxidized part  330  will not be in particle form. 
     As a result of the doping process, the doping atom  322  is incorporated into the metal oxide material  326  of the metal oxide layer  324 , thereby forming a doped metal oxide layer  332 . By incorporating the doping atom  322  within the metal oxide material  326 , the doping atom  322  (e.g., atoms) will substitute for some of the metal ions present in the metal oxide material  326 . For example, if the metal oxide material  326  is ZrO 2  and includes a crystal lattice of Zr +  atoms, and the doping element is Ce 3+ , then some of the Zr +  atoms will be replaced by Ce 3+ . Incorporating the doping element within the metal oxide material  326  forms a doped metal oxide material  334 . The doped metal oxide material  334  has greater electrical conductivity than the metal oxide material  326  such that the doped metal oxide layer  332  has greater electrical conductivity than the metal oxide layer  324 . According to some examples, the metal oxide material  326  includes between about 0.001 wt % to about 10 wt % of the doping atom  322 . 
     In one example, the metal oxide material  326  includes Zr +  atoms. Each of the Zr +  atoms includes valence electrons. The valence electrons between adjacent Zr +  atoms form bonds that hold the crystal lattice together. By undergoing the doping process, some of the Zr +  atoms are substituted with Ce 3+ . However, the force that holds the valence election Ce 3+  in place is very weak. As a result, the valence electron can move about (orbit) the entire solid structure, this will increase electrical conductivity of the doped structure. As the extra valence electron moves about the doped structure it creates an empty unoccupied quantum state at the valence band that makes it easier for other valence electrons of other Zr +  atoms to occupy due to there being lower energy. 
       FIG. 3D  illustrates uniform distribution of the doping atoms  322  of the doped oxidized part  330 . Additionally, there may also be non-uniform distribution. However, uniform distribution shows controlled doping which may be more desirable. In some embodiments, the doping is a controlled process, whereby the external atoms (i.e., dopants) are substituted into the crystal lattice of the in a controlled manner. As very small amounts of the dopants (in the parts-per-million range) can dramatically affect the electrical conductivity, careful measures may be implemented to ensure uniform spatial distribution of the dopants. For example, as a result of the controlled doping process, the doped metal oxide layer  332  may have a uniform distribution of the doping atom  322  through the crystal lattice of the metal oxide material  326  to ensure a uniform appearance of color throughout the surface area of the doped oxidized part  330 . Generating a uniform appearance of color throughout millions of may be especially desirable and of importance for a manufacturer that produces on the scale of several thousands of enclosures for consumer electronic devices on a daily basis. 
     According to some embodiments, the doped oxidized part  230  of  FIG. 2D  and the doped oxidized part  330  of  FIG. 3D  may be characterized as having a non-metallic, visible color when visible light is incident upon an external surface of the doped metal oxide layer—e.g., the doped metal oxide layer  232 . Referring to the doped oxidized part  230 , when visible light is incident upon the doped external surface  222 , photons of the visible light ray are absorbed by the doped metal oxide layer  232 . When photons of the visible light ray strike the doped external surface  222 , valence electrons that are present in the valence band may be excited to a higher energy level, which corresponds to the conduction band. In other words, the photons of the visible light ray have an amount of energy that is sufficient to excite valence electrons to a higher energy level in order to occupy a higher energy state in the conduction band. 
     The doped metal oxide material  234  is capable of absorbing an amount of energy (represented as a wavelength of light) from the photons of the visible light ray. In turn, an amount of energy (represented as a wavelength of light) of the visible light ray is absorbed by the doped metal oxide material  234 . Any amount of energy which is greater than the amount of energy absorbed by the doped metal oxide material  234  is, in turn, reflected by the doped metal oxide material  234  as a reflected light ray. As will be described with reference to  FIGS. 5A-5B and 6A-6B , the color of the doped oxidized part  230  corresponds to the amount of energy (represented as a wavelength of light) that is absorbed by the doped metal oxide material  234 . 
     It should be noted that the doped oxidized part  230  imparts a color at the molecular level. In other words, the color of the doped oxidized part  230  is not correlated to the thickness of the doped metal oxide layer  232 . To demonstrate this concept, even if the doped metal oxide layer  232  were separated from the remainder of the doped oxidized part  230  (i.e., the metal substrate  202 ), the doped metal oxide layer  232  would retain substantially the same color. In contrast, anodized coatings that are formed by anodizing a metal alloy substrate without doping the metal oxide material and/or the metal alloy substrate are capable of imparting a thin film interference effect. The thin film interference effect is dependent upon a refractive index of the anodized layer. For example, the color of the anodized layer is a function of the thickness of the anodized layer. 
       FIG. 4  illustrates a cross-sectional view of a doped oxidized part  400 , in accordance with some embodiments. The doped oxidized part  400  includes a metal substrate  402  that includes an external surface  404 . The external surface  404  includes a first surface portion  406  and a second surface portion  408 . The first surface portion  406  is doped with a first doping element  416  and the second surface portion  408  is doped with a second doping element  418 . In some embodiments, the first and second surface portions  406 ,  408  may be exposed to different respective doping processes. For example, the first surface portion  406  is masked while the second surface portion  408  is exposed to a second doping process. The second doping process includes exposing the second surface portion  408  to the second doping element  428 . Subsequently, the second surface portion  408  is masked while the first surface portion  406  is exposed to a first doping process. The first doping process includes exposing the first surface portion  406  to the first doping element  426 . 
     Thereafter, the first and second surface portions  406 ,  408  that have been doped may be oxidized to form a first doped metal oxide layer  416  and a second doped metal oxide layer  418 . In some examples, the first and second doped metal oxide layers  416 ,  418  may have uniform or non-uniform thicknesses. As a result of the first and second doped metal oxide layers  416 ,  418  being doped with different elements, these metal oxide layers will exhibit different colors that correspond to their respective band gap. However, despite generating different colors, the amount of the first and second doping elements  426 ,  428  is generally insufficient to alter the mechanical properties of the first and second metal oxide layers  416 ,  418 . Furthermore, the first and second metal oxide layers may be generally translucent such that the underlying textures of the first and second surface portions are visible therethrough. 
       FIGS. 5A-5B  illustrate cross-sectional views of a metal substrate having a color, in accordance with some embodiments.  FIG. 5A  illustrates a cross-sectional view of the metal part  200 , as previously described with reference to  FIG. 2A . The metal part  200  includes a metal substrate  202  that is without a doping element—e.g., the doping atom  212 . Since the metal substrate  202  is without a doping element, the metal substrate  202  may be without a band gap between a valence band (Vb) and a conduction band (Cb), as illustrated in  FIG. 5B . 
       FIG. 5B  illustrates a band gap structure  500  that corresponds to the metal part  200 . In some examples, the valence band (Vb) will overlap with the conduction band (Cb) such that there is no band gap. As a result, any visible light ray that is incident upon the external surface  204  of the metal substrate  202  will cause generally all visible light wavelengths to be absorbed by the metal material of the metal substrate  202 . In turn, the metal part  200  will appear black or near black. 
     In order to alter the electronic structure of the metal part  200  such as to impart a non-black color, it may be necessary to dope the metal substrate  202  and/or a metal oxide layer derived from the metal substrate  202  with a doping element—e.g., the doping atom  212 . 
       FIGS. 6A-6B  illustrate cross-sectional views of a doped metal oxide coating having a color in accordance with a band gap, in accordance with some embodiments.  FIG. 6A  illustrates a cross-sectional view of the doped oxidized part  230 , as previously described with reference to  FIG. 2D . The doped oxidized part  230  includes a doped metal oxide layer  232  that overlays a metal substrate  202 . In contrast to the metal part  200 , the doped oxidized part  230  has been doped with a doping element—e.g., the doping atom  212 . 
       FIG. 6B  illustrates a band gap structure  600  that corresponds to the doped oxidized part  230 . In contrast to the band gap structure  500  of the metal part  200 , the band gap structure  600  has a band gap that separates the conduction band (Cb) from the valence band (Vb). When visible light rays are incident upon the external surface  204  of the doped metal oxide layer  232 , energy associated with the visible light rays excites valence electrons that are present in the valence band. The amount of energy associated with the visible light rays is sufficient to excite the valence electrons to reach the next energy level—i.e., the conduction band. The amount of energy sufficient to excite the valence electrons corresponds to the band gap. In turn, the excited valence electrons leave behind unoccupied quantum states in the valence band. In some examples, the doped oxidized part  230  will exhibit a band gap greater than about 1.70 eV and less than about 3.0 eV. As a result, the doped oxidized part  230  will have a color that correspond to the band gap, as will be described in greater detail with reference to  FIGS. 7A-7C . In other words, the color of light that is reflected or transmitted by the doped oxidized part  230  corresponds to the band gap. 
       FIGS. 7A-7C  illustrate various exemplary doped metal oxide coatings having different colors, in accordance with some embodiments. 
       FIG. 7A  illustrates a band gap structure  700 -A of a doped metal oxide coating where the band gap between the valence band (Vb) and the conduction band (Cb) is 1.2 eV. The doped metal oxide coating includes metal oxide material that is doped with one or more foreign atoms. As a result, when visible light is incident upon an external surface of the doped metal oxide coating, the doped metal oxide coating will absorb all energy greater than 1.2 eV. In this particular instance, all visible wavelengths of light have an energy greater than 1.2 eV; therefore, the doped metal oxide coating will absorb generally all visible wavelengths of light and appear black or near black. In some examples, the color of the doped metal oxide coating that corresponds to the band gap structure  700 -A is characterized as having an L* value of less than 40. As generally understood, L*=0 represents an extreme black while L*=100 represents white. 
       FIG. 7B  illustrates a band gap structure  700 -B of a doped metal oxide coating where the band gap between the valence band (Vb) and the conduction band (Cb) is 1.8 eV. When visible light is incident upon an external surface of the doped metal oxide coating, the doped metal oxide coating will absorb all energy greater than 1.8 eV. In this particular instance, light having a red color has an energy that is less than 1.8 eV. Therefore, the doped metal oxide coating will absorb substantially all visible light except for light having a red color. Accordingly, the doped metal oxide coating will appear red. In some examples, the color of the doped metal oxide coating that corresponds to the band gap structure  700 -B is characterized as having a positive value of greater than 0 and less than 5. 
       FIG. 7C  illustrates a band gap structure  700 -C of a doped metal oxide coating where the band gap between the valence band (Vb) and the conduction band (Cb) is 2.5 eV. When visible light is incident upon an external surface of the doped metal oxide coating, the doped metal oxide coating will absorb all energy greater than 2.5 eV. In this particular instance, light having red, orange, yellow, and green colors have an energy that is less than 2.5 eV. Therefore, the doped metal oxide coating will absorb substantially all visible light except for light having red, orange, yellow, and green colors. Accordingly, the doped metal oxide coating will appear a red/orange/yellow/green mixture. In some examples, the color of the doped metal oxide coating that corresponds to the band gap structure  700 -C is characterized as having a positive b* value of greater than 0 and less than 5. 
     It should be noted from these examples that a greater amount of energy is required to excite valence electrons from the valence band to the conduction band in order to impart a blue or purple color. As described herein, the dopant of the metal oxide coating may include Ce, Dy, Er, Eu, Gd, Ho, La, Lu, Nd, Pr, Pm, Sm, Sc, Tb, Tm, Yb, and Y. Notably, in the examples described herein, it may be possible to infer the specific type of dopant included in a doped metal oxide coating based upon the color of the doped metal oxide coating. 
     In some examples, a metal oxide coating doped with Er is characterized as having a peach or pink color that is defined as an a* value greater than 0, and a b* value less than 25. 
     In some examples, a metal oxide coating having Pr is characterized as having a yellow color that is defined as a b* value greater than 0. 
     In some examples, a metal oxide coating doped with Nd is characterized as having a purple color that is defined as a negative b* value that is less than 0. 
     In some examples, a metal oxide coating doped with Ni is characterized as having a green color that is defined as a negative a* value that is less than 0. 
     In some examples, a metal oxide coating doped with Co is characterized as having a dark blue color that is defined as a negative b* value that is less than 0. 
       FIG. 8  illustrates a method  800  for forming a doped metal oxide coating, in accordance with some embodiments. In some embodiments, the method  800  may be implemented in conjunction with a closed feedback loop that is implemented by an optical detection system and/or a controlled oxidation system. 
     As illustrated in  FIG. 8 , the method  800  begins at step  802 , which involves forming a metal substrate—e.g., the metal substrate  202 . The metal substrate  202  includes a pure metal or a metal alloy. In some examples, the metal substrate  202  includes a metal composition having a minimal and/or no band gap; therefore, the metal substrate  202  has a black or substantially black color. As described herein, a substantially black color refers to an L* value that is less than 30. As a result, the metal substrate  202  should be doped to impart a non-black color. 
     At step  804 , the metal substrate  202  is doped with at least one external element or doping atom—e.g., the doping atom  212  in conjunction with a doping process. The doping process may include exposing the metal substrate  202  to ion implantation, a molecular layer doping process, a thermal diffusion process, and the like. 
     In some embodiments, the metal substrate  202  may be doped with multiple, different types of external elements. For example, if the metal substrate is titanium, then the external elements may include neodymium and praseodymium. In some embodiments, the metal substrate is doped with a first amount of the neodymium and a second amount of praseodymium, where the second amount is different from the first amount. As a result of the doping process, the metal substrate  202  is doped to form a doped metal part—e.g., the doped metal part  220 . The doped metal part  220  includes a crystal lattice, where some of the metal atoms (e.g., titanium) are substituted with the one or more doping atoms. For example, some of titanium atoms may be substituted with at least one of neodymium or praseodymium. In some examples, where the metal substrate  202  is subjected to ion implantation, the ion implantation process amorphizes the crystal lattice to such an extent that damage to the crystal lattice may occur. 
     As a result of doping the metal substrate  202  with the at least one doping atom  212 , the material of the metal substrate  202  undergoes a change in electrical properties (i.e., changing the band gap). However, the doping process in itself may be insufficient to result in a change of color. 
     At step  806 , the metal substrate  202  may be optionally processed. In one example, the doped metal substrate may be sintered such as to be imparted with a non-black, visible color (e.g., red, etc.). In some examples, the sintering process includes compressing a solid mass of material onto a surface of the doped metal substrate with heat or pressure. It should be noted that an oxidation step does not usually follow the sintering process. 
     In another example, the doped metal substrate may be repaired by exposing the doped metal part  220  to an annealing process. The annealing process is performed to repair any damage caused by the doping process. For example, diffusion or movement of the doping atoms  212  may cause the doping atoms  212  to diffuse deeper into the crystal lattice. The annealing process may include exposing the doped metal part  220  to a high temperature. 
     At step  808 , the doped metal part  220  may be oxidized to form a doped oxidized part  230 . In particular, the doped metal part  220  is exposed to oxygen atoms—e.g., the oxygen atoms  222 . In some embodiments, the doped metal part  220  is oxidized in a controlled manner such that the resulting doped metal oxide layer  232  has a uniform or substantially uniform thickness. The doped metal oxide layer  232  includes a doped metal oxide material (e.g., titanium dioxide) having a crystal lattice, where some of the titanium atoms remain substituted with at least one of neodymium or praseodymium. In some embodiments, the doped metal part  220  is also oxidized in a controlled manner such as to more precisely control the thickness and/or color of the doped oxidized part  230 . The doped metal oxide layer  232  includes doped metal oxide material  234 . 
     At step  810 , an optical detection system may be utilized to monitor the color of the doped metal oxide layer  232 . In some embodiments, the optical detection system may determine whether the color of the doped oxidized part  230  satisfies predetermined value and/or range. For example, the optical detection system may determine at least one of whether the L* value of the doped metal oxide layer  232  satisfies a predetermined L* value, the a* value of the doped metal oxide layer  232  satisfies a predetermined a* value or the b* value of the doped metal oxide layer  232  satisfies a predetermined b* value. 
     At step  812 , if the optical detection system determines that the doped metal oxide layer  232  has a color that does not satisfy any one of the predetermined L*, a* or b* values, then an oxidation parameter (e.g., voltage, anodizing solution, doping elements, concentration of dopants, etc.) may be adjusted in order to cause the doped oxidized part  230  to satisfy any one of the predetermined L*, a* or b* values. 
     Alternatively, at step  814 , if the optical detection system determines that the doped metal oxide layer  232  has a color that satisfies any one of the predetermined L*, a* or b* values, then the doped oxidized part  230  may be subjected to an annealing process. As a result, the annealing process may further tune the color of the doped oxidized part  230 , such as increasing the saturation of the color. The annealing process may also restore some of the metal oxide material subsequent to the doping process. 
       FIG. 9  illustrates a method  900  for forming a doped metal oxide coating, in accordance with some embodiments. In some embodiments, the method  900  may be implemented in conjunction with a closed feedback loop that is implemented by an optical detection system and/or a controlled oxidation system. 
     As illustrated in  FIG. 9 , the method  900  begins at step  902 , which involves forming a metal substrate—e.g., the metal substrate  302 . The metal substrate  302  includes a pure metal or a metal alloy. In some examples, the metal substrate  302  includes a metal composition having a minimal and/or no band gap; therefore, the metal substrate  302  has a black or substantially black color. 
     At step  904 , the metal substrate  302  may be oxidized to form an oxidized part  320 . In particular, the metal substrate  302  is exposed to oxygen atoms—e.g., the oxygen atoms  312 . In some embodiments, the metal substrate  302  is oxidized in a controlled manner such that the resulting metal oxide layer  324  of the oxidized part  320  has a uniform or substantially uniform thickness. The metal oxide layer  324  includes metal oxide material  326  (e.g., zirconium oxide) having a crystal lattice. 
     At step  906 , the metal oxide layer  324  is doped with at least one external element or doping atom—e.g., the doping atom  322  in conjunction with a doping process to form a doped metal oxide layer  332 . The doping process may include exposing the oxidized part  320  to ion implantation, a molecular layer doping process, a thermal diffusion process, and the like. In some embodiments, the metal substrate  202  may be doped with multiple, different types of external elements. 
     As a result of the doping process, the oxidized part  320  is doped to form a doped oxidized part  330 . The doped oxidized part  330  includes a crystal lattice of doped metal oxide material  334 , where some of the metal atoms (e.g., titanium) are substituted with the one or more doping atoms  322 . For example, some of the zirconium atoms may be substituted with the doping atoms  322 . 
     At step  908 , an optical detection system may be utilized to monitor the color of the doped metal oxide layer  332 . In some embodiments, the optical detection system may determine whether the color of the doped oxidized part  330  satisfies predetermined value and/or range. For example, the optical detection system may determine at least one of whether the L* value of the doped metal oxide layer  332  satisfies a predetermined L* value, the a* value of the doped metal oxide layer  332  satisfies a predetermined a* value or the b* value of the doped metal oxide layer  332  satisfies a predetermined b* value. 
     At step  910 , if the optical detection system determines that the doped metal oxide layer  332  has a color that does not satisfy any one of the predetermined L*, a* or b* values, then an oxidation parameter (e.g., voltage, anodizing solution, doping elements, concentration of dopants, etc.) may be adjusted in order to cause the doped oxidized part  330  to satisfy any one of the predetermined L*, a* or b* values. 
     Alternatively, at step  912 , if the optical detection system determines that the doped metal oxide layer  332  has a color that satisfies any one of the predetermined L*, a* or b* values, then the doped oxidized part  330  may be subjected to an annealing process. In some examples, the annealing process may further create oxygen vacancies in the doped metal oxide material  334 . As a result, the annealing process may further tune the color of the doped oxidized part  330 , such as increasing the saturation of the color. The annealing process may also restore some of the metal oxide material subsequent to the doping process. Additionally, the annealing process may also precipitate additional phases in the doped metal oxide layer  332  such as inter-metallic compounds, silicates, or spin-off phases, which are detectable due to increased light absorption leading to more saturated colors. In some examples, where the oxidized part  320  is subjected to ion implantation, the ion implantation process amorphizes the crystal lattice to such an extent that damage to the crystal lattice may occur. 
       FIG. 10  illustrates a method  1000  for forming a doped metal oxide coating, in accordance with some embodiments. As illustrated in  FIG. 10 , the method  1000  begins at step  1002 , which involves forming a metal substrate—e.g., the metal substrate  402 . The metal substrate  402  includes a pure metal or a metal alloy. 
     At step  1004 , a second surface portion  408  of an external surface  404  of the metal substrate  402  may be masked while leaving a first surface portion  406  of the external surface  404  of the metal substrate  402  exposed to a first doping process. At step  1006 , the first surface portion  406  is doped with a first type of doping element  426  in conjunction with a first doping process. 
     At step  1008 , the first surface portion  416  of the metal substrate  402  is masked off while leaving the second surface portion  408  exposed to a second doping process. At step  1010 , the second surface portion  408  is doped with a second type of doping element  428  that is different from the first type of doping element  426 . In some examples, the first and second doping processes may include different types of doping elements and/or different concentrations of the doping elements. 
     At step  1012 , the first and second surface portions  406 ,  408  of the doped metal substrate may be oxidized to form first and second doped metal oxide layers  416 ,  418  that overlays the first and second surface portions  406 ,  408 , respectively. In some embodiments, the first and second surface portions  406 ,  408  that were doped are oxidized in a controlled manner such that the first and second doped metal oxide layers  416 ,  418  have a uniform or substantially uniform thickness. In some embodiments, the first doped metal oxide layer  416  includes the first type of doping element  416  and the second doped metal oxide layer  418  includes the second type of doping element  418 . 
     At step  1014 , the first and second doped metal oxide layers  416 ,  418  may be subjected to an annealing process. As a result, the annealing process may further tune the color of the doped oxidized part  400 , such as increasing the saturation of the color. The annealing process may also restore some of the metal oxide material subsequent to the doping process. 
     Any ranges cited herein are inclusive. The terms “substantially”, “generally,” and “about” used herein are used to describe and account for small fluctuations. For example, they can refer to less than or equal to ±5%, such as less than or equal to ±2%, such as less than or equal to ±1%, such as less than or equal to ±0.5%, such as less than or equal to ±0.1%. 
     The various aspects, embodiments, implementations or features of the described embodiments can be used separately or in any combination. Various aspects of the described embodiments can be implemented by software, hardware or a combination of hardware and software. The described embodiments can also be embodied as computer readable code on a nontransitory computer readable medium. The non-transitory computer readable medium is any data storage device that can store data which can thereafter be read by a computer system. Examples of the non-transitory computer readable medium include read-only memory, random-access memory, CD-ROMs, HDDs, DVDs, magnetic tape, and optical data storage devices. The nontransitory computer readable medium can also be distributed over network-coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. 
     The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of specific embodiments are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the described embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.

Metadata:
Filing Date: 20200507
Publication Date: 20220816
Grant Date: 20220816
Priority Date: 20190918
Inventors: LI, HOISHUN
FEINBERG, ZECHARIAH D.
WANIUK, Theodore A.
Assignee: APPLE INC
CPC Classifications: [{"code": "C22C14/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "C23C8/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "C22C16/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K5/04", "inventive": true, "first": true, "tree": "[]"}, {"code": "C23C14/0015", "inventive": true, "first": false, "tree": "[]"}, {"code": "C22C38/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "C22C14/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "C23C14/5806", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C14/5853", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C8/80", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C14/48", "inventive": true, "first": true, "tree": "[]"}, {"code": "C23C14/08", "inventive": true, "first": false, "tree": "[]"}, {"code": "C22C38/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "C22C16/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "C23C8/36", "inventive": true, "first": false, "tree": "[]"}, {"code": "C22C14/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "C22C16/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "C23C14/08", "inventive": true, "first": false, "tree": "[]"}, {"code": "C22C38/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K5/04", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 74869126