PATENT DOCUMENT

Publication Number: US-10639867-B2
Application Number: US-201715711851-A
Country: US
Kind Code: B2

Title: Sapphire and glass laminates with a gradient layer

Abstract:
A sapphire sheet is laminated to a glass sheet with a gradient layer that transitions from a composition of predominantly Al2O3 at the sapphire sheet to a composition of predominantly SiO2 at the glass sheet. The gradient layer chemically bonds to both the sapphire sheet and the glass sheet and has no distinct interfaces.

Claims:
What is claimed is: 
     
       1. An electronic device including a transparent cover glass, the electronic device comprising:
 a housing; 
 a display positioned within the housing; 
 a cover glass disposed over the display and attached to the housing, the cover glass comprising:
 a sapphire sheet; 
 a glass sheet; and 
 a gradient layer disposed between the sapphire sheet and the glass sheet and that transitions from a composition that is predominantly Al 2 O 3  at the sapphire sheet to a composition that is predominantly SiO 2  at the glass sheet, and wherein the gradient layer includes a first region including nanocrystalline Al 2 O 3  positioned proximate the sapphire sheet and a second region including amorphous Al 2 O 3  positioned between the nanocrystalline Al 2 O 3  and the glass sheet. 
 
 
     
     
       2. The electronic device of  claim 1  wherein the gradient layer gradually transitions from a composition that is predominantly Al 2 O 3  at the sapphire sheet to a composition that is predominantly SiO 2  at the glass sheet. 
     
     
       3. The electronic device of  claim 1  wherein the gradient layer is between 25 and 300 nanometers thick. 
     
     
       4. A glass and sapphire laminate comprising:
 a sapphire sheet; 
 a glass sheet; and 
 a gradient layer disposed between the sapphire sheet and the glass sheet and that transitions from a composition that is predominantly Al 2 O 3  at the sapphire sheet to a composition that is predominantly SiO 2  at the glass sheet, and wherein the gradient layer includes a first region including nanocrystalline Al 2 O 3  positioned proximate the sapphire sheet and a second region including amorphous Al 2 O 3  positioned between the nanocrystalline Al 2 O 3  and the glass sheet. 
 
     
     
       5. The laminate of  claim 4  wherein the Al 2 O 3  nanocrystals have a crystalline orientation that matches a crystalline orientation of the sapphire sheet. 
     
     
       6. The laminate of  claim 4  wherein the Al 2 O 3  nanocrystals have a crystalline orientation that is different from a crystalline orientation of the sapphire sheet. 
     
     
       7. The laminate of  claim 4  wherein when moving in a direction away from the sapphire sheet, the gradient layer transitions from the layer of Al 2 O 3  nanocrystals to a mixture of Al 2 O 3  nanocrystals and amorphous Al 2 O 3 . 
     
     
       8. The laminate of  claim 7  wherein when moving in a direction away from the sapphire sheet, the gradient layer transitions from the mixture of Al 2 O 3  nanocrystals and amorphous Al 2 O 3  to predominantly amorphous SiO 2 . 
     
     
       9. The laminate of  claim 4  wherein the gradient layer gradually changes in chemical composition from predominantly Al 2 O 3  to predominantly SiO 2 . 
     
     
       10. The laminate of  claim 4  wherein the gradient layer is between 25 and 300 nanometers thick. 
     
     
       11. The laminate of  claim 4  wherein the sapphire sheet is between 5 and 100 microns thick. 
     
     
       12. The laminate of  claim 4  wherein the glass sheet is between 100 and 1000 microns thick. 
     
     
       13. The laminate of  claim 4  wherein the gradient layer is a first gradient layer and the laminate further comprises a second gradient layer that is disposed on the sapphire sheet on a side opposite of the first gradient layer. 
     
     
       14. A method of bonding a sapphire sheet to a glass sheet, the method comprising:
 depositing a gradient layer on a first surface of the sapphire sheet, wherein the gradient layer is predominantly composed of Al 2 O 3  at the sapphire sheet and transitions to predominantly SiO 2  at an outer surface of the gradient layer; 
 annealing the sapphire sheet and the gradient layer at a temperature sufficient to chemically bond the gradient layer to the sapphire sheet; 
 disposing a glass sheet on the outer surface of the gradient layer; and 
 annealing the glass sheet, the gradient layer and the sapphire sheet at a temperature sufficient to chemically bond the glass sheet to the gradient layer, and 
 wherein the gradient layer includes a first region including nanocrystalline Al 2 O 3  positioned proximate the sapphire sheet and a second region including amorphous Al 2 O 3  positioned between the nanocrystalline Al 2 O 3  and the glass sheet. 
 
     
     
       15. The method of  claim 14  wherein the gradient layer is deposited as an amorphous layer having a substantially linear gradient that varies from predominantly Al 2 O 3  at the sapphire sheet to predominantly SiO 2  at an outer surface of the gradient layer. 
     
     
       16. The method of  claim 14  wherein the sapphire sheet is annealed at a temperature above a softening point of the glass sheet. 
     
     
       17. The method of  claim 14  wherein annealing the sapphire sheet and the gradient layer causes a layer of Al 2 O 3  nanocrystals to form at an interface between the gradient layer and the sapphire sheet. 
     
     
       18. The method of  claim 14  wherein the gradient layer is also deposited on a second surface of the sapphire sheet that is opposite the first surface.

Description:
CROSS-REFERENCES TO OTHER APPLICATIONS 
     This application claims priority to U.S. provisional patent application Ser. No. 62/399,089, for “SAPPHIRE AND GLASS LAMINATES WITH A GRADIENT LAYER” filed on Sep. 23, 2016 which is hereby incorporated by reference in entirety for all purposes. 
    
    
     FIELD 
     The described embodiments relate generally to electronic devices that employ a transparent cover glass disposed over a display screen. The transparent cover glass forms an exterior portion of the enclosure of the electronic device and protects the display screen from damage. More particularly, the present embodiments relate to a cover glass formed from a sapphire sheet laminated to a glass sheet with a gradient layer that transitions from a composition of predominantly Al 2 O 3  at the sapphire sheet to a composition of predominantly SiO 2  at the glass sheet. 
     BACKGROUND 
     Many portable electronic devices, such as smart phones and tablet computers, include a touch sensitive display. The display typically includes part of a stack of components that includes a display screen, a touch sensitive layer overlaying the display screen and an outer monolithic transparent glass sheet, often referred to as a “cover glass,” that protects the display and touch sensitive layer. As the cover glass is a portion of the outer enclosure of the electronic device, the cover glass needs to be strong and resistant to scratches and other damage that can occur if the portable electronic device is dropped or if the display region undergoes an impact event. 
     The cover glass used for many portable electronic devices is typically made of a chemically-strengthened glass that provides improved fracture resistance to certain drop and impact events as compared to standard glass. The strengthened glass is, however, inherently softer than some other material options, which can lead to scratches formed on the surface of the glass that are detrimental to both user perception and to the reliability of the cover glass, as the scratches can reduce the fracture strength of the glass. 
     SUMMARY 
     Embodiments of the present disclosure pertain to a cover glass that can be used in an electronic device, such as a smart phone or tablet computer. In some embodiments a sapphire sheet is bonded to an underlying and thicker glass sheet using a gradient layer disposed between the sapphire and glass. The resulting cover glass can include a sapphire outer surface that has increased hardness, stiffness, and/or impact resistance as compared to the inner glass portion of the cover glass. 
     Some embodiments relate to a gradient layer that that is deposited on one side of the sapphire sheet and transitions from a composition of predominantly Al 2 O 3  at the sapphire sheet to a composition of predominantly SiO 2  at the opposite surface. A first annealing process can be used to nucleate nanocrystals at the sapphire sheet interface and chemically bond the gradient layer to the sapphire sheet. The glass sheet can be placed on the predominantly SiO 2  opposite surface of the gradient layer and a second, lower temperature annealing process can be used to bond the gradient layer to the glass sheet. After the annealing processes, the sapphire-glass laminate is a monolithic structure in which the gradient layer gradually changes from Al 2 O 3  to SiO 2  with no distinct interfaces. The sapphire-glass laminate can exhibit excellent optical properties and improved reliability as compared to traditional cover glass designs. 
     In some embodiments an electronic device including a transparent cover glass comprises a housing, a display positioned within the housing and a cover glass disposed over the display and attached to the housing. The cover glass comprises a sapphire sheet, a glass sheet and a gradient layer disposed between the sapphire sheet and the glass sheet. The gradient layer transitions from a composition that is predominantly Al 2 O 3  at the sapphire sheet to a composition that is predominantly SiO 2  at the glass sheet. 
     In various embodiments the gradient layer gradually transitions from a composition that is predominantly Al 2 O 3  at the sapphire sheet to a composition that is predominantly SiO 2  at the glass sheet. In some embodiments the gradient layer includes a layer of Al 2 O 3  nanocrystals disposed at an interface between the sapphire sheet and the gradient layer. In various embodiments the gradient layer is between 25 and 300 nanometers thick. 
     In some embodiments a glass and sapphire laminate comprises a sapphire sheet, a glass sheet and a gradient layer disposed between the sapphire sheet and the glass sheet. The gradient layer transitions from a composition that is predominantly Al 2 O 3  at the sapphire sheet to a composition that is predominantly SiO 2  at the glass sheet. In various embodiments the gradient layer includes a layer of Al 2 O 3  nanocrystals disposed at an interface between the sapphire sheet and the gradient layer. 
     In some embodiments the Al 2 O 3  nanocrystals have a crystalline orientation that matches a crystalline orientation of the sapphire sheet. In various embodiments the Al 2 O 3  nanocrystals have a crystalline orientation that is different from a crystalline orientation of the sapphire sheet. In some embodiments when moving in a direction away from the sapphire sheet, the gradient layer transitions from the layer of Al 2 O 3  nanocrystals to a mixture of Al 2 O 3  nanocrystals and amorphous Al 2 O 3 . In various embodiments when moving in a direction away from the sapphire sheet, the gradient layer transitions from the mixture of Al 2 O 3  nanocrystals and amorphous Al 2 O 3  to predominantly amorphous SiO 2 . 
     In some embodiments the gradient layer gradually changes in chemical composition from predominantly Al 2 O 3  to predominantly SiO 2 . In various embodiments the gradient layer is between 25 and 300 nanometers thick. In some embodiments the sapphire sheet is between 5 and 100 microns thick. In some embodiments the glass sheet is between 100 and 1000 microns thick. In various embodiments the gradient layer is a first gradient layer and the laminate further comprises a second gradient layer that is disposed on the sapphire sheet on a side opposite of the first gradient layer. 
     In some embodiments a method of bonding a sapphire sheet to a glass sheet comprises depositing a gradient layer on a first surface of the sapphire sheet, wherein the gradient layer is predominantly composed of Al 2 O 3  at the sapphire sheet and transitions to predominantly SiO 2  at an outer surface of the gradient layer. The method further comprises annealing the sapphire sheet and the gradient layer at a temperature sufficient to chemically bond the gradient layer to the sapphire sheet and disposing a glass sheet on the outer surface of the gradient layer. The glass sheet, the gradient layer and the sapphire sheet are annealed at a temperature sufficient to chemically bond the glass sheet to the gradient layer. 
     In some embodiments the gradient layer is deposited as an amorphous layer having a substantially linear gradient that varies from predominantly Al 2 O 3  at the sapphire sheet to predominantly SiO 2  at an outer surface of the gradient layer. In various embodiments the sapphire sheet is annealed at a temperature above a softening point of the glass sheet. In some embodiments annealing the sapphire sheet and the gradient layer causes a layer of Al 2 O 3  nanocrystals to form at an interface between the gradient layer and the sapphire sheet. In various embodiments the gradient layer is also deposited on a second surface of the sapphire sheet that is opposite the first surface. 
     To better understand the nature and advantages of the present disclosure, reference should be made to the following description and the accompanying figures. It is to be understood, however, that each of the figures is provided for the purpose of illustration only and is not intended as a definition of the limits of the scope of the present disclosure. Also, as a general rule, and unless it is evident to the contrary from the description, where elements in different figures use identical reference numbers, the elements are generally either identical or at least similar in function or purpose. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a simplified perspective view of an electronic device  100  that can include a cover glass according to embodiments of the disclosure; 
         FIG. 2  is a simplified perspective view of the cover glass illustrated in  FIG. 1 ; 
         FIGS. 3A and 3B  are simplified cross-sectional views of the cover glass illustrated in  FIGS. 1 and 2 , according to some embodiments of the disclosure; 
         FIG. 4  illustrates steps associated with a method of bonding a sapphire sheet to a glass sheet according embodiments of the disclosure; 
         FIGS. 5A-5E  illustrate simplified cross-sectional views of a sapphire sheet being bonded to a glass sheet according to the method described in  FIG. 4 ; 
         FIG. 6  illustrates steps associated with a method of bonding a sapphire sheet to a glass sheet using laser annealing according embodiments of the disclosure; 
         FIGS. 7A-7E  illustrate simplified cross-sectional views of a sapphire sheet being bonded to a glass sheet according to the method described in  FIG. 6 ; 
         FIG. 8  illustrates an example composition profile of a laminated cover glass according to embodiments of the disclosure; 
         FIG. 9  illustrates steps associated with a method of bonding a sapphire sheet having a gradient layer on both sides to a glass sheet according embodiments of the disclosure; and 
         FIGS. 10A-10D  illustrate simplified cross-sectional views of a sapphire sheet being bonded to a glass sheet according to the method described in  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION 
     Some embodiments of the present disclosure relate to a cover glass that can be used in an electronic device, such as a smart phone or tablet computer. While the present disclosure can be useful for a wide variety of configurations, some embodiments of the disclosure are particularly useful for a cover glass made from a laminate of glass and sapphire sheets bonded together with a gradient layer that transitions from a composition of predominantly Al 2 O 3  at the sapphire sheet to a composition of predominantly SiO 2  at the glass sheet. The laminate of glass and sapphire can exhibit improved optical properties and reliability as compared to traditional cover glass configurations. 
     For example, in some embodiments a gradient layer is deposited on one surface of a sapphire sheet. The gradient layer is amorphous and transitions from a composition of predominantly Al 2 O 3  at the sapphire sheet to a composition of predominantly SiO 2  at the opposite surface. A first annealing process is performed that chemically bonds the gradient layer to the sapphire sheet and forms Al 2 O 3  nanocrystals at the sapphire surface. The glass sheet is then placed on the opposite surface, that is predominantly SiO 2 , of the gradient layer and a lower temperature second annealing step is performed to chemically bond the glass sheet to the gradient layer. 
     In order to better appreciate the features and aspects of laminated sapphire and glass cover glass for electronic devices according to the present disclosure, further context for the disclosure is provided in the following section by discussing one particular implementation of an electronic device according to embodiments of the present disclosure. These embodiments are for example only and other embodiments can be employed in other electronic devices such as, but not limited to computers, watches, media players and other devices. 
       FIG. 1  depicts a simplified perspective view of an electronic device  100  that can include a cover glass according to embodiments of the disclosure. As shown in  FIG. 1 , electronic device  100 , which in this example is a smart phone, includes a cover glass  105  attached to a housing  110  and positioned at least partially over display  117 . Cover glass  105  and housing  110  combine to provide an enclosure that houses the various electronic components of electronic device  100  including a processor, communication circuitry, display  117 , camera and battery, among other components (not all shown in  FIG. 1 ). Cover glass  105  is transparent and includes a central area  115  that corresponds to display  117 , and outside the central display area includes a small cut out  120  for a receiver and an area for an input button  125  near the top and bottom of electronic device  100 , respectively. In some embodiments cover glass  105  provides protection for display  117  and can also form a continuous transparent surface of the enclosure for electronic device  100 . 
       FIG. 2  is a simplified perspective view of the cover glass illustrated in  FIG. 1 . As shown in  FIG. 2 , cover glass  105  is removed from housing  110  (see  FIG. 1 ). While not visible in  FIG. 2 , in some embodiments cover glass  105  can include one or more thin sapphire sheets bonded to an underlying base layer (sheet) of glass with a gradient layer as discussed in more detail below. 
       FIG. 3A  is a simplified partial cross-sectional view of the cover glass illustrated in  FIGS. 1 and 2 , according to embodiments of the disclosure. As shown in  FIG. 3A , cover glass  105  can include a relatively thin sapphire sheet  310  adhered to a thicker glass sheet  320  using a gradient layer  330 . 
     Sapphire sheet  310  can form an outer surface  335  of cover glass  105  when the cover glass is incorporated into an electronic device, such as electronic device  100  illustrated in  FIG. 1 . Since sapphire sheet  310  is considerably harder than glass or strengthened glass that is typically used as a cover glass, cover glass  105  is more resistant to scratching and damage than traditional cover glass. Further, since gradient layer  330  is used to bond sapphire sheet  310  to glass sheet  320 , cover glass  105  is reliable (e.g., does not delaminate) and has a relatively low amount of internal reflection, as described in more detail below. 
     In some embodiments, gradient layer  330  is a layer that gradually changes in composition from predominantly Al 2 O 3  at a first interface  370  (between sapphire sheet  310  and gradient layer  330 ) to predominantly SiO 2  at a second interface  380  (between glass sheet  320  and gradient layer  330 ). The gradual change in composition allows gradient layer  330  to chemically bond to both sapphire sheet  310  and glass sheet  320  forming a reliable and solid composite structure. Further, since gradient layer  330  has no distinct interfaces and gradually changes in composition, it exhibits less internal reflection than there would be if sapphire sheet  310  were directly bonded to glass sheet  320 . Therefore, gradient layer  330  provides a reliable interface between sapphire sheet  310  and glass sheet  320 , with a low amount of internal reflection. 
     In some embodiments, as shown in  FIG. 3B , one or more annealing processes can be employed to form an aluminum rich nano-crystalline Al 2 O 3  layer  340  within gradient layer  330  to increase the strength of the bond between sapphire sheet  310  and glass sheet  320 , as described in more detail below. 
     In some embodiments, glass sheet  320  can be a transparent glass sheet that can be made from any glass material, including chemically strengthened glass. In one embodiment glass sheet  320  is made from silicon dioxide (SiO 2 ). In another embodiment glass sheet  320  is made from “blue glass” that blocks at least a portion of the infra-red spectrum. Any other type of glass can be used including glass having one or more coatings applied to it that limit reflection and/or transmission of certain wavelengths of light. While embodiments of the disclosure are not limited to any particular thickness of glass sheet  320 , in some embodiments the glass sheet is between 100 to 1000 microns thick, while in other embodiments the glass sheet is between 300 to 800 microns thick and in further embodiments the glass sheet is between 400 to 700 microns thick. 
     In some embodiments, sapphire sheet  310  is a layer of crystalline Al 2 O 3  and can have one or more coatings applied to it that limit reflection and/or transmission of certain wavelengths of light. While embodiments of the disclosure are not limited to any particular thickness of sapphire sheet  310 , in some embodiments the sapphire sheet is between 5 to 100 microns thick, while in other embodiments the sapphire sheet is between 10 to 80 microns thick and in further embodiments the sapphire sheet is between 20 to 70 microns thick. 
       FIG. 4  illustrates steps associated with a method of bonding a sapphire sheet to a glass sheet according embodiments of the disclosure.  FIGS. 5A-5E  illustrate simplified cross-sectional views of a sapphire sheet being bonded to a glass sheet according to the method described in  FIG. 4 . As shown in  FIG. 4 , method  400  includes forming a sapphire sheet (step  405 ) using any appropriate manufacturing technique. Referring to  FIG. 5A , sapphire sheet  505  is provided. In some embodiments sapphire sheet  505  is between 5 to 100 microns thick, while in other embodiments the sapphire sheet is between 10 to 80 microns thick and in further embodiments the sapphire sheet is between 20 to 70 microns thick. 
     Ian step  410  an Al 2 O 3  to SiO 2  gradient layer  510  (see  FIG. 5B ) is deposited on sapphire sheet  505 . Gradient layer  510  is formed on one surface of sapphire sheet  505 . In some embodiments gradient layer  510  can be deposited using a physical vapor deposition (PVD) sputtering process in which separate silicon and aluminum targets are positioned within the PVD chamber and the PVD process is controlled such that the deposited gradient layer  510  has a substantially linear gradient that varies from a relatively high concentration of Al 2 O 3  and a relatively low concentration of SiO 2  at the surface of sapphire sheet  505  to a relatively low concentration of Al 2 O 3  and relatively high concentration of SiO 2  at an outer surface  507  of the gradient layer. In other embodiments the composition of gradient layer  510  is not substantially linear and can have any composition profile. Other deposition techniques than PVD can be used to form gradient layer  510  and are within the scope of this disclosure. 
     In some embodiments, gradient layer  510  can be an amorphous layer deposited, for example, to between 25 to 300 nanometers thick, while in other embodiments it can be between 50 to 200 nanometers thick and in further embodiments between 50 to 100 nanometers thick. In various embodiments in which it is desirable to minimize internal reflection within the composite cover glass, the thickness of gradient layer  510  can be selected to be above 50 microns. In various embodiments the thickness of gradient layer  510  can be selected to be above 100 microns to achieve a further reduction in internal reflection within the composite cover glass. 
     In step  415  a first annealing treatment on sapphire sheet  505  with Al 2 O 3  to SiO 2  gradient layer  510  is performed. The first annealing treatment is performed at a temperature sufficient to chemically bond gradient layer  510  to sapphire sheet  505  can be above a temperature that glass sheet  530  (which is not subjected to the high temperature anneal) would melt. In some embodiments the first annealing treatment is performed in an inert or non-inert atmosphere at a final annealing temperature greater than 1000° C. In another embodiment the final annealing temperature of the first annealing treatment can be above 1200° C. In one embodiment the first annealing treatment temperature ramps to the final annealing temperature in four to six hours, is held at the final annealing temperature for approximately two hours, then ramps back to the ambient temperature over approximately 16 hours. In other embodiments different temperatures and ramp profiles can be used, including laser annealing, as described in more detail below. 
     As shown in  FIG. 5C , in some embodiments, the first annealing treatment causes a layer of nano-crystals  520  of Al 2 O 3  to form on an inner layer  525  of sapphire sheet  505 . More specifically, during the relatively high temperatures in the first annealing treatment, nano-crystals nucleate on the crystalline lattice of sapphire sheet  505 . In some embodiments the nano-crystals have the same crystalline orientation as sapphire sheet  505  while in other embodiments the nano-crystals can have a different orientation than the sapphire sheet. The nano-crystals nucleate out of gradient layer  510  and grow during the first annealing treatment. The amount and size of the nano-crystals that are formed can be controlled by controlling the time and temperature profile of the first annealing treatment. 
     In step  420 , which can be performed independent of steps  405  to  415 , method  400  includes forming a glass sheet  530  using any appropriate manufacturing technique. In some embodiments glass sheet  530  is provided that is between 100 to 1000 microns thick, while in other embodiments the glass sheet is between 300 to 800 microns thick and in further embodiments the glass sheet is between 400 to 700 microns thick. In various embodiments glass sheet  530  is made from silicon dioxide and can be chemically strengthened and/or configured to block infra-red light. 
     In step  425 , glass sheet  530  is aligned with and placed on top of gradient layer  510 , as illustrated in  FIG. 5D . 
     In step  430  a second annealing treatment is performed at a lower temperature than the first annealing treatment described in step  415 . In some embodiments the second annealing treatment is performed in an ambient atmosphere and at a final annealing temperature of approximately 125° C. As shown in  FIG. 5E , in some embodiments, the second annealing treatment causes gradient layer  510 , which is rich in SiO 2  at the interface between the gradient layer and glass sheet  530 , to chemically bond to glass sheet  530 . In some embodiments pressure can be applied between sapphire sheet  505  and glass sheet  530  during the second annealing treatment to ensure the surfaces are intimately bonded. 
       FIG. 6  illustrates steps associated with a method of bonding a sapphire sheet to a glass sheet using a laser annealing process according embodiments of the disclosure.  FIGS. 7A-7E  illustrate simplified cross-sectional views of a sapphire sheet being bonded to a glass sheet according to the method described in  FIG. 6 . As described in  FIG. 6 , a gradient layer is deposited on the glass sheet instead of on the sapphire sheet as discussed above. 
     As shown in  FIG. 6 , method  600  includes forming glass sheet (step  605 ) using any appropriate manufacturing technique. Referring to  FIG. 7A , glass sheet  705  is provided that can be between 100 to 1000 microns thick, while in other embodiments the glass sheet is between 300 to 800 microns thick and in further embodiments the glass sheet is between 400 to 700 microns thick. In various embodiments glass sheet  705  is made from silicon dioxide and can be chemically strengthened and/or configured to block infra-red light. 
     In step  610  a SiO 2  to Al 2 O 3  gradient layer  710  (see  FIG. 7B ) is deposited on one side of glass sheet  705 . In some embodiments gradient layer  710  is an amorphous layer deposited using the same type of PVD sputtering process described above with respect to  FIG. 4  except that gradient layer  710  varies from a very high concentration of SiO 2  and very low concentration of Al 2 O 3  to a very low concentration of SiO 2  and high concentration of Al 2 O 3  at the outer surface of the gradient layer. More specifically, in this embodiment gradient layer  710  starts with SiO 2  instead of Al 2 O 3  so the SiO 2  can form a bond with glass sheet  705 . In some embodiments the composition of gradient of layer  710  can be linear while in other embodiments it can be non-linear. 
     In some embodiments, gradient layer  710  can be an amorphous layer deposited, for example, to between 25 to 300 nanometers thick, while in other embodiments it can be between 50 to 200 nanometers thick and in further embodiments between 50 to 100 nanometers thick. In various embodiments in which it is desirable to minimize internal reflection within the composite cover glass, the thickness of gradient layer  710  can be selected to be above 50 microns. In some embodiments the thickness of gradient layer  710  can be selected to be above 100 microns to achieve a further reduction in internal reflection within the composite cover glass. 
     In step  615  a sapphire sheet of Al 2 O 3  is formed using any appropriate manufacturing technique. Referring to  FIG. 7C , sapphire sheet  715  is provided. In some embodiments sapphire sheet  715  is between 5 to 100 microns thick, while in other embodiments the sapphire sheet is between 10 to 80 microns thick and in further embodiments the sapphire sheet is between 20 to 70 microns thick. 
     In step  620  sapphire sheet  715  is aligned with glass sheet  705  and placed in direct contact with gradient layer  710  (see  FIG. 7C ). 
     In step  625  a first annealing treatment is performed on sapphire sheet  715  and gradient layer  710 . In some embodiments the first annealing treatment is performed in an ambient atmosphere using a laser that is transmitted through sapphire sheet  715  and focused at or near interface  707  between the sapphire sheet and gradient layer  710  to heat the interface to a temperature that is sufficient to cause atomic level bonding between the sapphire sheet and the Al 2 O 3 -rich portion of the gradient layer without substantially softening glass sheet  705 . In one embodiment the laser is configured to heat up the interface to a temperature of greater than 1000° C. while in other embodiments it can heat up the interface to a temperature of greater than 1200° C. 
     As shown in  FIG. 7D , in some embodiments, first annealing treatment performed in step  625  causes a layer of nano-crystals  720  of Al 2 O 3  to form on an inner layer  725  of sapphire sheet  715 . More specifically, during the relatively high temperatures generated during the first annealing treatment, nano-crystals nucleate on the crystalline lattice of sapphire sheet  715 . In some embodiments the nano-crystals have the same crystalline orientation as sapphire sheet  715  while in other embodiments the nano-crystals can have a different orientation than the sapphire sheet. The nano-crystals nucleate out of gradient layer  710  and grow during the first annealing treatment. The amount and size of the nano-crystals that are formed can be controlled by controlling the time and temperature profile of the first annealing treatment performed in step  625 . 
     In step  630  a second annealing treatment on the materials is performed at a lower temperature than the first annealing treatment performed in step  625 . In some embodiments the second annealing treatment can be performed in an ambient atmosphere and at a final annealing temperature of approximately 125° C. In some embodiments the second annealing treatment can be performed in an oven or using a laser at a final annealing temperature that is below a softening point of glass sheet  705 . In one example, the second annealing treatment performed in step  630  heats the interface between glass sheet  705  and gradient layer  710  to a temperature of approximately 125° C. As shown in  FIG. 7E , in some embodiments, the second annealing treatment causes the SiO 2 -rich portion of gradient layer  710  to bond to glass sheet  705 . In various embodiments pressure can be applied between sapphire sheet  715  and glass sheet  705  during the second annealing treatment to ensure the surfaces are intimately bonded. 
     In each of the methods  400  and  600  for bonding a sapphire sheet to a glass sheet described above, the composition profiles of Al 2 O 3  and SiO 2  within the gradient layer can change considerably from an as-deposited composition profile as initially formed to a final composition profile after the one or more annealing treatments, as described in more detail below. 
       FIG. 8  illustrates one example of a final composition profile  800  of a completed laminated cover glass formed according to embodiments of the disclosure, including either method  400  or method  600 . As shown in  FIG. 8 , in some embodiments a final composition profile  800  of gradient layer  330  can change throughout its thickness in a non-linear manner. The various portions of final composition profile  800  are referred to below using reference numbers depicted in  FIG. 3 , and to facilitate the description of final composition profile  800  reference is sometimes made simultaneously to  FIGS. 3 and 8 . 
     Final composition profile  800  illustrates sapphire sheet  310  on the right and glass sheet  320  on the left. Starting at sapphire sheet  310 , the composition of the sapphire sheet is reasonably constant showing stable atomic percentages of oxygen and aluminum. Progressing towards first interface  370  (between sapphire sheet  310  and gradient layer  330 ), the atomic percentage of silicon starts to gradually increase due to the diffusion of silicon into the sapphire sheet from the gradient layer. Progressing through first interface  370  and into gradient layer  330  an aluminum-rich nano-crystalline Al 2 O 3  layer  340  can include nano-crystals of Al 2 O 3  that have been formed at the sapphire surface. In some embodiments the nano-crystals can have the same crystalline orientation as that of sapphire sheet  310 , while in other embodiments they can have a different crystalline orientation. As shown in  FIG. 8 , the composition in aluminum-rich nano-crystalline Al 2 O 3  layer  340  can be primarily aluminum and oxygen and can be approximately 20 nanometers thick. 
     Moving further towards glass sheet  320 , aluminum-rich nano-crystalline Al 2 O 3  layer  340  can transition to a silicon-rich nano-crystalline and amorphous layer  350 . More specifically, in some embodiments, at first interface  370 , primarily nano-crystalline Al 2 O 3  exists and moving towards glass sheet  320  the composition of gradient layer  330  transitions to amorphous Al 2 O 3 . In one example the composition of silicon-rich nano-crystalline and amorphous layer  350  can be a mixture of oxygen, silicon and aluminum and can be between 10 to 50 nanometers thick. 
     Moving further towards glass sheet  320 , in some embodiments silicon-rich nano-crystalline and amorphous layer  350  can transition to amorphous silicon dioxide such that it is predominantly silicon dioxide at the surface of glass sheet  320 . In various embodiments, as silicon-rich nano-crystalline and amorphous layer  350  transitions to glass sheet  320 , the percent composition of aluminum reduces and diminishes to near zero at second interface  380  (between glass sheet  320  and gradient layer  330 ). Moving further towards glass sheet  320  the composition is predominantly silicon and oxygen within glass sheet  320 , with trace amounts of aluminum that have diffused into the glass sheet from gradient layer  330 . 
     The layer thicknesses and chemical compositions illustrated in  FIG. 8  are for example only and other thicknesses and compositions are within the scope of this disclosure. 
       FIG. 9  illustrates steps associated with a method of bonding a sapphire sheet having a gradient layer on both sides to a glass sheet according embodiments of the disclosure.  FIGS. 10A-10D  illustrate simplified cross-sectional views of a sapphire sheet being bonded to a glass sheet according to the method described in  FIG. 9 . As described in  FIG. 9 , a gradient layer is deposited on both sides of the sapphire sheet, instead of only on one side of the sapphire sheet as discussed in the embodiments described above in  FIGS. 5A-8 . Depositing a gradient layer on both sides of the sapphire sheet can reduce bowing of the sapphire sheet, as described in more detail below. 
     As illustrated in  FIG. 9 , in step  905  a sapphire sheet of Al 2 O 3  is formed using any appropriate manufacturing technique. Referring to  FIG. 10A , sapphire sheet  1015  is provided. In some embodiments sapphire sheet  1015  is between 5 to 100 microns thick, while in other embodiments the sapphire sheet is between 10 to 80 microns thick and in further embodiments the sapphire sheet is between 20 to 70 microns thick. 
     In step  910  a first Al 2 O 3  to SiO 2  gradient layer  1010   a  (see  FIG. 10B ) is deposited on a first side  1040  of sapphire sheet  1015  and a second Al 2 O 3  to SiO 2  gradient layer  1010   b  is deposited on a second side  1045  of the sapphire sheet. In some embodiments first and second gradient layers  1010   a ,  1010   b , respectively, are amorphous layers deposited using the same type of PVD sputtering process described above with respect to  FIG. 4 . In some embodiments the gradient layers can be deposited simultaneously while in other embodiments they can be deposited sequentially. In this example, first and second gradient layers  1010   a ,  1010   b , respectively, start with Al 2 O 3  at the sapphire surface so the Al 2 O 3  can form a bond with sapphire sheet  1015 . In some embodiments the composition of first and second gradient layers  1010   a ,  1010   b , respectively, can be linear while in other embodiments it can be non-linear. The deposition first and second gradient layers  1010   a ,  1010   b , respectively, on either side of sapphire sheet  1015  can “balance” the stresses in the sapphire sheet and reduce bowing of the sapphire sheet as compared to embodiments that have a gradient layer coated on only one side, such as the example illustrated in  FIG. 4 . 
     In step  915  a first annealing treatment on sapphire sheet  1015  with first and second gradient layers  1010   a ,  1010   b , respectively, is performed. The first annealing treatment is performed at a temperature sufficient to chemically bond first and second gradient layers  1010   a ,  1010   b , respectively, to sapphire sheet  1015 . In some embodiments the first annealing treatment is performed in an inert or non-inert atmosphere at a final annealing temperature greater than 1000° C. In another embodiment the final annealing temperature of the first annealing treatment can be above 1200° C. In one embodiment the first annealing treatment temperature ramps to the final annealing temperature in four to six hours, is held at the final annealing temperature for approximately two hours, then ramps back to the ambient temperature over approximately 16 hours. In other embodiments different temperatures and ramp profiles can be used including using laser annealing. 
     As shown in  FIG. 10C , in some embodiments, the first annealing treatment causes first and second layers of nano-crystals  1020   a ,  1020   b , respectively, of Al 2 O 3  to form on first and second sides  1040 ,  1045 , respectively of sapphire sheet  1015 . More specifically, during the relatively high temperatures in the first annealing treatment, nano-crystals nucleate on the crystalline lattice on both sides of sapphire sheet  1015 . In some embodiments the nano-crystals have the same crystalline orientation as sapphire sheet  1015  while in other embodiments the nano-crystals can have a different orientation than the sapphire sheet. The nano-crystals nucleate out of first and second gradient layers  1010   a ,  1010   b , respectively, and grow during the first annealing treatment. The amount and size of the nano-crystals that are formed can be controlled by controlling the time and temperature profile of the first annealing treatment. 
     In step  920 , which can be performed independent of steps  905  to  915 , method  400  includes forming a glass sheet  1030  using any appropriate manufacturing technique. In some embodiments a glass sheet  1030  is provided that is between 100 to 1000 microns thick, while in other embodiments the glass sheet is between 300 to 800 microns thick and in further embodiments the glass sheet is between 400 to 700 microns thick. In various embodiments glass sheet  1030  is made from silicon dioxide and can be chemically strengthened and/or configured to block infra-red light. 
     In step  925 , glass sheet  1030  is aligned with and placed on top of first gradient layer  1010   a , as illustrated in  FIG. 10D . 
     In step  930  a second annealing treatment is performed at a lower temperature than the first annealing treatment described in step  915 . In some embodiments the second annealing treatment is performed in an ambient atmosphere and at a final annealing temperature of approximately 125° C. As shown in  FIG. 10D , in some embodiments, the second annealing treatment causes first gradient layer  1010   a , which is rich in SiO 2  at the interface between the gradient layer and glass sheet  1030 , to chemically bond to the glass sheet. In some embodiments pressure can be applied between sapphire sheet  1015  and glass sheet  1030  during the second annealing treatment to ensure the surfaces are intimately bonded. 
     As discussed above, the deposition first and second gradient layers  1010   a ,  1010   b , respectively, on either side of sapphire sheet  1015  can reduce bowing of the sapphire sheet as compared to embodiments that have a gradient layer coated on only one side. Further, the reduced bowing can enable improved adhesion and lamination to glass sheet  1030  (see  FIG. 10D ) and can also reduce bowing in the completed laminated structure, illustrated in  FIG. 10D . 
     In embodiments where a reduced surface reelection is desired, second gradient layer  1010   b  can exhibit a surface reelection of approximately 4 percent or less as compared to sapphire sheet  1015  that exhibits a surface reflection of approximately 8 percent. 
     In some embodiments where the improved scratch resistant properties of the sapphire sheet are desired on the outer surface of the electronic device, second gradient layer  1010   b  can be polished off after lamination to glass sheet  1030 . In various embodiments a different type of coating can be applied on second side  1045  of sapphire sheet  1015  in place of second gradient layer  1010   b . For example, in one embodiment a diamond like carbon coating can be applied on second side  1045 . In some embodiments the different coating can offer improved scratch resistance (e.g., better than second gradient layer  1010   b ) and can also reduce bowing as described above. In various embodiments the different coating can be selected to have an appropriate coefficient of thermal expansion and/or modulus to counterbalance first gradient layer  1010   a  and can also offer improved scratch resistant properties over second gradient layer  1010   b.    
     Other variations and embodiments are within the scope of this disclosure. For example, in another embodiment a sapphire sheet can be bonded to either side of a glass sheet. That is, a first sapphire sheet can be bonded to a first side of a glass sheet and a second sapphire sheet can be bonded to a second side of glass sheet to balance stresses within the glass sheet. 
     Although electronic device  100  (see  FIG. 1 ) is described and illustrated as one particular electronic device, embodiments of the disclosure are suitable for use with a multiplicity of electronic devices. For example, any device that receives or transmits audio, video or data signals can be used with embodiments of the disclosure. In some instances, embodiments of the disclosure are particularly well suited for use with portable electronic media devices because of their use of transparent display screens. As used herein, an electronic media device includes any device with at least one electronic component that can be used to present human-perceivable media. Such devices can include, for example, portable music players (e.g., MP3 devices and Apple&#39;s iPod devices), portable video players (e.g., portable DVD players), cellular telephones (e.g., smart telephones such as Apple&#39;s iPhone devices), video cameras, digital still cameras, projection systems (e.g., holographic projection systems), gaming systems, PDAs, as well as tablet (e.g., Apple&#39;s iPad devices), laptop or other mobile computers. Some of these devices can be configured to provide audio, video or other data or sensory output. 
     For simplicity, various internal components, such as the control circuitry, graphics circuitry, bus, memory, storage device and other components of electronic device  100  (see  FIG. 1 ) are not shown in the figures. 
     In the foregoing specification, embodiments of the disclosure have been described with reference to numerous specific details that can vary from implementation to implementation. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. The sole and exclusive indicator of the scope of the disclosure, and what is intended by the applicants to be the scope of the disclosure, is the literal and equivalent scope of the set of claims that issue from this application, in the specific form in which such claims issue, including any subsequent correction. The specific details of particular embodiments can be combined in any suitable manner without departing from the spirit and scope of embodiments of the disclosure. 
     Additionally, spatially relative terms, such as “bottom or “top” and the like can be used to describe an element and/or feature&#39;s relationship to another element(s) and/or feature(s) as, for example, illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use and/or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as a “bottom” surface can then be oriented “above” other elements or features. The device can be otherwise oriented (e.g., rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

Metadata:
Filing Date: 20170921
Publication Date: 20200505
Grant Date: 20200505
Priority Date: 20160923
Inventors: NGUYEN, Que Anh S.
MEMERING, DALE N.
JONES, CHRISTOPHER D.
ROGERS, MATTHEW
Assignee: APPLE INC
CPC Classifications: [{"code": "B32B17/06", "inventive": true, "first": false, "tree": "[]"}, {"code": "C30B29/20", "inventive": true, "first": false, "tree": "[]"}, {"code": "B32B7/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "B32B2457/208", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/0488", "inventive": true, "first": false, "tree": "[]"}, {"code": "B32B9/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "C03C3/125", "inventive": true, "first": false, "tree": "[]"}, {"code": "B32B5/145", "inventive": true, "first": false, "tree": "[]"}, {"code": "B32B15/20", "inventive": true, "first": true, "tree": "[]"}, {"code": "B32B17/06", "inventive": true, "first": false, "tree": "[]"}, {"code": "B32B15/20", "inventive": true, "first": true, "tree": "[]"}, {"code": "B32B5/145", "inventive": true, "first": false, "tree": "[]"}, {"code": "C03C3/125", "inventive": true, "first": false, "tree": "[]"}, {"code": "C30B29/20", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0488", "inventive": true, "first": false, "tree": "[]"}, {"code": "B32B9/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "B32B17/06", "inventive": true, "first": false, "tree": "[]"}, {"code": "B32B2457/208", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B7/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "B32B7/022", "inventive": true, "first": true, "tree": "[]"}, {"code": "B32B2307/704", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B2457/208", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B2307/584", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B9/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "B32B9/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "B32B2571/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B2307/412", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B2307/732", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B2255/20", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B2250/02", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 61687524