PATENT DOCUMENT

Publication Number: US-9623628-B2
Application Number: US-201313738200-A
Country: US
Kind Code: B2

Title: Sapphire component with residual compressive stress

Abstract:
A method comprises shaping an aluminum oxide ceramic material into a component for an electronic device. The component has first and second major surfaces. A selected region of one or both of the first and second major surfaces is heated to an annealing temperature. The selected region is then cooled below the annealing temperature, so that residual compressive stress is generated in the selected region.

Claims:
I claim: 
     
       1. A method comprising:
 shaping a sapphire material into a sapphire component for an electronic device, the sapphire component having first and second major surfaces; 
 heating a selected region of one or both of the first and second major surfaces of the sapphire component to an annealing temperature that alters a chemical or physical property of the selected region, the annealing temperature being above 700° C. and below 2030° C.; and 
 quenching the selected region of the sapphire component below the annealing temperature by introducing a fluid to the selected region that cools the selected region at a higher rate as compared to a non-quenched cooling rate, such that residual compressive stress is generated in the selected region of the sapphire component; wherein: 
 the selected region of the sapphire component having the generated residual compressive stress comprises a depth less than a thickness of the sapphire component; and 
 the sapphire component further comprises an untreated region positioned adjacent the selected region on the first major surface of the sapphire component. 
 
     
     
       2. The method of  claim 1 , further comprising assembling the sapphire component into the electronic device. 
     
     
       3. The method of  claim 1 , wherein shaping the sapphire material comprises forming the sapphire component with a substantially single crystal plane orientation between the first and second major surfaces. 
     
     
       4. The method of  claim 3 , wherein the selected region of the sapphire component is prone to impact when assembled into the electronic device. 
     
     
       5. The method of  claim 4 , wherein the sapphire component forms a cover glass for the electronic device, and the selected region of the sapphire component comprises a corner portion of the cover glass, when the sapphire component is assembled into the electronic device. 
     
     
       6. The method of  claim 5 , wherein the selected region of the sapphire component excludes a central portion of the cover glass, when the sapphire component is assembled into the electronic device. 
     
     
       7. The method of  claim 6 , wherein the selected region of the sapphire component comprises at least a portion of each of the first and second major surfaces. 
     
     
       8. The method of  claim 1 , wherein the selected region of the sapphire component excludes one of the first and second major surfaces. 
     
     
       9. The method of  claim 1 , further comprising defining a failure pattern in the sapphire component, based on the residual compressive stress generated in the selected region. 
     
     
       10. The method of  claim 1 , wherein heating the selected region of the sapphire component comprises laser heating one or both of the first and second major surfaces, in the selected region. 
     
     
       11. The method of  claim 10 , wherein cooling the selected region of the sapphire component comprises directing a jet of cooling fluid onto one or both of the first and second major surfaces, in the selected region. 
     
     
       12. The method of  claim 11 , wherein a substantially single crystal plane orientation is maintained between the first and second major surfaces of the sapphire component, throughout heating and cooling of the selected region. 
     
     
       13. The method of  claim 12 , wherein the sapphire component further comprises an inner portion positioned between the first and second major surfaces of the sapphire component, the inner portion comprising the substantially single crystal plane orientation. 
     
     
       14. The method of  claim 10  further comprising depositing a surface coating over one or both of the first and second major surfaces of the selected region of the sapphire component prior to the laser heating one or both of the first and second major surfaces of the selected region of the sapphire component. 
     
     
       15. The method of  claim 14 , wherein the laser heating of one or both of the first and second major surfaces of the selected region further comprises:
 removing the deposited surface coating from one or both of the first and second major surfaces of the selected region. 
 
     
     
       16. The method of  claim 1 , wherein the depth of the selected region of the sapphire component is within a range of approximately 1% of the thickness of the sapphire component and 10% of the thickness of the sapphire component. 
     
     
       17. The method of  claim 1 , wherein the quenching of the selected region of the sapphire component comprises cooling the selected region of the sapphire component such that the selected region of the sapphire component maintains a substantially single crystal plane orientation. 
     
     
       18. A method comprising:
 shaping a sapphire material into a sapphire component for an electronic device, the sapphire component having first and second major surfaces; 
 heating the sapphire material to an annealing temperature that is within a range of between 700° C. to 2030° C.; and 
 forming a residual compressive stress in a selected region of the sapphire component by quenching the selected region of the sapphire component using a fluid that cools the selected region below the annealing temperature at an accelerated cooling rate that is greater than an unquenched cooling rate without the fluid, the selected region of the sapphire component having greater residual compressive stress than an untreated region of the sapphire component in which the residual compressive stress is not induced; wherein: 
 the selected region of the sapphire component comprises a depth less than a thickness of the sapphire component; and 
 the untreated region of the sapphire component is positioned below the selected region, within the sapphire component. 
 
     
     
       19. The method of  claim 18 , wherein the selected region of the sapphire component comprises an aperture for an audio device. 
     
     
       20. The method of  claim 18 , wherein the sapphire component is positioned adjacent a display of the electronic device. 
     
     
       21. The method of  claim 20 , wherein the first major surface of the sapphire component is positioned adjacent the display and oriented toward an interior of the electronic device. 
     
     
       22. The method of  claim 20 , wherein the second major surface of the sapphire component is positioned opposite the display and oriented toward an exterior of the device. 
     
     
       23. The method of  claim 20 , wherein the display is visible through the sapphire component. 
     
     
       24. A method comprising:
 heating a selected region of at least one surface of a sapphire component for an electronic device to an annealing temperature that is less than 2030° C. and greater than 700° C., the selected region exhibiting a material toughness distinct from an untreated region of the sapphire component based on the annealing temperature altering a chemical or physical property of the selected region; 
 quenching the selected region of the sapphire component below the annealing temperature such that a differential cooling rate is generated between the selected region and the untreated region of the sapphire component that is not subject to the quenching; and 
 creating a residual compressive stress in the selected region of the sapphire component, the generated residual compressive stress created in the selected region of the sapphire component comprises a depth less than a thickness of the sapphire component; wherein 
 the selected region of the sapphire component is substantially surrounded by the untreated region of the sapphire component. 
 
     
     
       25. The method of  claim 24 , wherein the untreated region of the sapphire component comprises a compressive stress less than the residual compressive stress created in the selected region of the sapphire component. 
     
     
       26. The method of  claim 24 , wherein the untreated region is formed on:
 the at least one surface of the sapphire component comprising the selected region; and 
 on at least one distinct surface, distinct from the at least one surface of the sapphire component comprising the selected region. 
 
     
     
       27. The method of  claim 24 , wherein the creating of the residual compressive stress in the selected region of the sapphire component further comprises creating the residual compressive stress in the selected region comprising at least a portion of a second surface of the sapphire component, the second surface distinct from the first surface.

Description:
TECHNICAL FIELD 
     This subject matter of this disclosure relates generally to display and cover glass components for electronic devices, including, but not limited to, mobile phones and other personal digital devices. In particular, the disclosure relates to display and cover glass components suitable for use in smartphones, mobile and cellular devices, tablet computers, personal computers, personal digital assistants, media players, and other electronic devices, in both portable and stationary applications. 
     BACKGROUND 
     Electronic devices generally include a variety of different display and cover components, including front and back glasses (or cover glasses), display windows, touch screens, track pads, camera lenses and covers, and other internal and external components for which optical properties, strength and durability are design issues. In use, these components are subject to a wide range of environmental and operational effects, including shock, impact, scratching, and temperature and pressure extremes. 
     These effects raise a number of design and engineering considerations, particularly for cover glass and display components in which performance and operational range are limited by environmental factors. These considerations include stress and strain resistance, machinability, temperature stability, and other properties such as electrical resistance, thermal conductivity, and magnetic permeability. As a result, there is a need for improved cover glass and display components that address these considerations without suffering the limitations of the prior art, while providing impact and shock resistance across a broad range of environmental and operational conditions. 
     SUMMARY 
     This disclosure relates to cover glasses, displays, and other components for electronic devices, methods of making the components, and electronic devices incorporating the components. In various examples and embodiments, an aluminum oxide ceramic or sapphire material is shaped into a component for assembly into an electronic device. A selected region of the component is heated to an annealing temperature, then cooled below the annealing temperature to generate residual compressive stress in the selected region, for example along one or both major surfaces. 
     The sapphire component may be formed with a substantially single crystal plane orientation, extending between the first and second major surfaces. The selected region may be prone to impact when the sapphire component is assembled into the electronic device, for example an edge or corner portion of a cover glass component. The selected region may also exclude a central portion of the cover glass, for example a central portion that is less prone to impact, as compared to the edge or corner portion. 
     The selected region of the sapphire component may also include at least a portion of each of the first and second major surfaces, or the selected region may exclude one of the first and second major surfaces. A failure pattern may also be defined, based on the residual compressive stress generated in the selected region of the sapphire or ceramic component. 
     Heating the selected region of the component may be performed by laser heating of one or both of the major surfaces, and cooling may be performed by directing a jet of cooling fluid onto the major surface(s), in the selected region. The substantially single crystal plane orientation of the sapphire component can be maintained between the first and second major surfaces, throughout the heating and cooling steps. 
     In additional examples and embodiments, a cover glass component for an electronic device may include a substantially single crystal aluminum oxide material defined between first and second major surfaces. Residual compressive stress may be induced in a first portion of the cover glass component, so that the component has greater residual compressive stress in the first portion, in which the residual stress is induced, as compared to other portions, in which the residual compressive stress is not induced. 
     When assembled into an electronic device, the first portion of the cover glass component may be more prone to impact than the second portion. For example, the first portion may include a corner region of the cover glass component, and the second portion may include a center region. The first portion may also be adjacent an edge of the cover glass component, and the second portion may be spaced from the edge by the first portion. 
     In further examples and embodiments, a mobile device may include a display in combination with the cover glass component. Alternatively, a mobile electronic device may include an aluminum oxide ceramic or sapphire cover glass component with a first major surface adjacent a display and a second major surface opposite the display; that is, with the first and second major surfaces oriented toward the interior and exterior of the device, respectively. Residual compressive stress may be induced in a selected region of the cover glass component, so that the selected region has greater residual compressive stress than other regions, in which the residual compressive stress is not induced. 
     The selected region of the cover glass component may include a corner region of one or both of the first and second major surfaces, and the other region may include a central portion, in which the residual compressive stress is not induced. The selected region may also be more prone to impact when the mobile electronic device is dropped, as compared to any region in which the residual compressive stress is not induced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an electronic device in a communications embodiment, showing the front cover glass. 
         FIG. 2A  is a rear perspective view of the device, showing the back cover glass. 
         FIG. 2B  is an alternate view of the electronic device, with the back cover glass in a different configuration. 
         FIG. 3  is a front perspective view of the electronic device, in a media player or tablet computer embodiment. 
         FIG. 4  is a block diagram illustrating internal and external features of the device. 
         FIG. 5A  is a cross-sectional view of the device. 
         FIG. 5B  is a cross-sectional view of a cover glass or other component for the device, illustrating a method for generating residual compressive stress. 
         FIG. 5C  is a cross-sectional view of the component, illustrating an alternate method for generating residual compressive stress. 
         FIG. 6  is perspective view of the electronic device, showing a representative residual compressive stress pattern. 
         FIG. 7  is block diagram illustrating a method for forming a cover glass component for an electronic device, with residual compressive stress. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a perspective view of electronic device  10 , in a communications embodiment. As shown in  FIG. 1 , device  10  includes front cover or cover glass  12 A with display window  14  and housing assembly  16 , as configured, for example, in a mobile phone or smartphone application. Alternatively, device  10  may be configured as a media player, digital assistant, tablet computer, personal computer, computer display, or other electronic device, in either portable or stationary form.  FIGS. 2A and 2B  are rear perspective views of device  10 , showing alternate configurations for back glass  12 B and housing  16 . 
     In the particular example of  FIG. 1 , front cover glass  12 A and rear cover glass  12 B are coupled to top and bottom housing components  16 A and  16 B of housing assembly  16  via a bezel or frame assembly  18 . One or both of front and rear cover glass components  12 A and  12 B may also incorporate an aluminum oxide, sapphire crystal, or sapphire glass material, with residual compressive stress to provide impact resistance, durability, and improved stress and strain performance, as described below. 
     Display window  14  is typically configured for viewing a touch screen or other display component through cover glass  12 A, for example as defined between border regions  15 . Depending on configuration, display window  14  may also accommodate interactive control features, for example internal or external touch screen or touch-sensitive display components, with capacitive or resistive coupling across the front surface of cover glass  12 A. 
     Cover glasses  12 A and  12 B may also include apertures to accommodate additional control and accessory features, including, but not limited to, a home button or other control device  20 , and one or more audio (e.g., speaker or microphone) features  22 , sensors or cameras  24 A and  24 B, and lighting or indicator features  26  (e.g., a flash unit or light emitting diode). Depending on design, additional glass or sapphire based components may also be provided for control and accessory features  20 ,  22 ,  24 A,  24 B and  26 , for example a separate cover glass element  12 C for camera  24 B, as provided in back cover glass  12 B. 
     Housing  16  and frame  18  are typically formed of metal, composites, and durable polymer materials, including metals and metal alloys such as aluminum and stainless steel, durable plastics, and carbon-based or fiber/matrix composites. Housing  16  and frame  18  may either be provided in substantially unitary form or as discrete components, for example with one or more top, bottom, side and back housing sections  16 A,  16 B,  16 C, and  16 D in combination with a unitary or multi-part bezel or frame assembly  18 . 
     Cover glasses  12 A and  12 B, housing  16  and frame  18  can also be configured to accommodate additional accessory features, including, but not limited to, speaker or microphone apertures  28 , connector apertures  30  for power, audio, and data communications, mechanical fasteners  32 , and access ports  34 , e.g., for a subscriber identity module or SIM card, a flash memory device, or other internal component of electronic device  10 . 
       FIG. 2A  is a rear perspective view of electronic device  10 , showing back glass  12 B in the form or two or more discrete inlay or inset components  12 D. Housing  16  is also provided in a multi-part configuration, for example with bottom housing  16 A, top housing  16 B, and side housing sections  16 C. 
     Depending on configuration, side housings  16 C may be coupled across middle plate  16 D to form the back surface of device  10 , between back glass insets  12 D, as shown in  FIG. 2A , and housing components  16 A,  16 B, and  16 C may be provided in either beveled or unbeveled form. A separate cover glass element  12 C may also be provided for back camera  24 B, as described above. 
       FIG. 2B  is a perspective view of electronic device  10 , showing back glass  12 B in a unitary configuration, with two-part housing assembly  16 A (bottom) and  16 B (top). As shown in  FIGS. 2A and 2B , unitary and multi-piece back glass components  12 B and  12 D may be variously configured to accommodate a range of different accessories, including microphones and other audio features  22 , back camera or other sensor features  24 B, and a flash unit or other lighting/indicator feature  26 . Device  10  may also accommodate additional control features, for example volume buttons  20 A and  20 B, ringer/mute switch  20 C, and hold button  20 D, as provided in any combination of cover glass components  12 A- 12 D and housing components  16 A- 16 D. 
       FIG. 3  is a front perspective view of electronic device  10  in an alternate embodiment, for example a media player, tablet computer, pad computer, or other computing device, or a computer monitor or display. As shown in  FIG. 3 , front glass  12 A is configured to accommodate display window  14  and accessory features including a hold button or other control device  20 . Housing assembly  16  may have a substantially unitary configuration; for example housing  16  may be formed together with the back cover of device  10 . 
     As illustrated in  FIG. 3 , the various horizontal and vertical orientations of device  10  are arbitrary, and designations of the front, back, top, bottom, and side components may be interchanged without loss of generality. Housing assembly  16  can also be coupled to front glass  12 A with a substantially internal frame  18  or bezel member  18 A, or via in internal groove in unitary housing  16 , for example via an adhesive coupling. One or both of housing  16  and frame or bezel components  18  and  18 A can be also formed of a plastic or other durable polymer material, rather than metal, or using a combination of metal, plastic polymer, and composite materials. 
       FIG. 4  is a block diagram illustrating various internal and external components of electronic device  10 , including microprocessor/controller  42 , display  43 , an accelerometer or other motion sensor  44 , and additional accessories and control features  20 ,  22 ,  24 , and  26 . Device  10  encompasses a range of different portable and stationary electronic applications, as described in  FIGS. 1, 2A, 2B, and 3 , above, as well as hybrid devices including smartphones with media player capabilities, game players, remote global positioning and telecommunications devices, and laptop, desktop, notebook, handheld and ultraportable computer devices and displays. 
     As shown in  FIG. 4 , controller  42  is electronically coupled to display  43 , an accelerometer or other motion sensor  44 , control devices  20 , and accessory features  22 ,  24 , and  26 . Various hard-wired and wireless communication connections  46  may be provided to support one or more external accessories  47 , host devices  48 , and/or networks  49 . 
     Controller  42  includes microprocessor (pp) and memory components configured to execute a combination of operating system and application firmware and software, in order to control device  10  and provide various functionality including, but not limited to, voice communications, voice control, media playback and development, internet browsing, email, messaging, gaming, security, transactions, navigation, and personal assistant functions. Controller  42  may also include a communications interface or other input-output ( 10 ) device configured to support connections  46  to one or more external accessories  47 , host devices  48 , and network systems  49 , including hard-wired, wireless, audio, visual, infrared (IR), and radio frequency (RF) communications. 
     Display  43  is viewable through front or rear cover glass  12 , within display window  14 . Cover glass  12  may also accommodate various different control features  20 , audio components  22 , camera and sensor features  24 , and lighting or indicator features  26 , including, but not limited to, button and switch control features  20 A- 20 D, speaker and microphone features  22 , front and rear camera or sensor features  24 A and  24 B, and LED flash or lighting/indicator features  26 , as described above. 
     Cover glass  12  comprises one or more of front cover glass  12 A, back cover glass  12 B, lens cover or inset components  12 C and  12 D, or other components for electronic device  10 , as described above. Cover glass  12  is formed of a substantially single-crystal aluminum oxide, sapphire, or sapphire glass material, and provided with residual compressive stress to improve strength, durability, and stress and strain resistance, as described below. 
     As used herein, the terms “glass” and “cover glass” are not limited to amorphous forms such as silica glass, but also encompass sapphire, sapphire glass, and other aluminum oxide ceramics, in either substantially single-crystal or polycrystalline form. The terms “sapphire” and “sapphire glass” encompass α-Al 2 O 3  and other aluminum oxide materials with varying degrees of trace elements and impurities, including sapphire, corundum, ruby, and ion impregnated or doped aluminum oxide ceramics and sapphire materials. 
     These definitions reflect usage in the art, in which cover glasses, front glasses, back glasses, glass inlays, glass insets, glass inserts, and other “glass” components may be provided in the form of silica glass, lead crystal, quartz, and other amorphous or polycrystalline forms. The definitions also reflect usage in this disclosure, where cover glasses and other “glass” components may be formed of aluminum oxide ceramics and sapphire materials, in either substantially single-crystal or polycrystalline (e.g., fused polycrystalline) form. 
     The term “substantially single crystal” encompasses both identically single-crystal and substantially single-crystal forms of sapphire material, as distinguished from amorphous and polycrystalline forms. The term “substantially single crystal” does not does not necessarily imply a fault-free construction, and may include some degree of inclusions and lamellar twinning, including crystal plane orientations in which such localized faults, inclusions, and lamellar twinning are present, but in which the same or substantially similar crystal plane orientation is expressed or extant across the structure the component, or as defined between the first and second (e.g., interior and exterior) major surfaces of the component. 
       FIG. 5A  is a cross-sectional view of electronic device  10 , for example as taken along line A-A of  FIG. 3 , or for any of the other devices  10  as shown in  FIGS. 1, 2A, 2B and 4 . In this particular configuration, device  10  comprises front glass  12 A, back glass  12 B, and housing (or housing assembly)  16 , with internal components including controller  42 , display  43  and a battery or other power source  50 . 
     As shown in  FIG. 5A , front glass  12 A and back glass  12 B are coupled to sides  16 C of housing  16 , for example via mechanical attachment to frame  18 . Controller  42 , display  43  and battery  50  are disposed within the interior of device  10 , with front glass  12 A located in front of (or above) display  10 , and back glass  12 B located behind (or below) display  43 . 
     Display window  14  is defined as a substantially transparent feature in front glass  12 A, in order to observe the viewable area of display  43 . Substantially opaque side or border portions  15  may also be provided, in order to define the boundaries of transparent display window  14 . Back glass  12 B may also include one or more transparent display windows  14 , for example to accommodate an additional back-side display or indicator, or a camera or other sensor internal to electronic device  10 . Alternatively, one or both of back glass  12 A and  12 B may be substantially opaque. 
     One or both of front glass  12 A and back glass  12 B are formed of an aluminum oxide material to increase durability and improve stress and strain resistance, for example a substantially single-crystal or fused polycrystalline sapphire material, or a layered sapphire material, with thicknesses ranging from about 0.2 mm or less to about 1.0 mm or more. The sapphire material may also be provided with residual compressive stress in selected regions  52 , as described below, in order to reduce the risk of damage in the event or a drop or impact event. 
       FIG. 5B  is a schematic diagram illustrating compressive stress in sapphire or ceramic component  12 , for example a front or rear cover glass  12 A or  12 B, as shown in  FIG. 5A , or a lens cover  12 C, inset  12 D, or another sapphire, sapphire glass or ceramic component for electronic device  10 , as described above. As shown in  FIG. 5B , component  12  is formed of a substantially single crystal or polycrystalline sapphire material in inner region  54 , as defined between opposing major surfaces  56 A and  56 B. One or both of major (e.g., inner and outer) surfaces  56 A and  56 B may be provided with selected regions  52  of compressive residual stress, in order to improve impact and shock resistance. 
     Residual compressive stress regions  52  are typically generated after shaping sapphire component  12  into the desired form for use in electronic device  10 . Heating, cooling, tempering, quenching, and toughening may be utilized to generate the residual compressive stress, or a combination of such methods. Tempering and toughening, for example, are accomplished by heating sapphire material  54  to an annealing temperature, either in air or using a high temperature vacuum furnace apparatus  58 , and then rapidly cooling or quenching one or both surfaces  56 A and  56 B to produce region(s)  52  of compressive stress. 
     The annealing temperature for sapphire component  12  is generally above the range of 500 C-700 C used for toughening amorphous silica glass, for example above about 1200 C, or above about 1500 C. The annealing temperature may also be selected in a range below the melting point of sapphire material  54 , for example about 1800 C to about 2000 C, as compared to a melting point of about 2030 C to about 2050 C, or in a lower range of about 1900 C to about 1950 C, to an upper range or about 2000 C to about 2020 C. 
     Cooling may be achieved in a relatively rapid process, for example using jets J of air or other fluid to cool one or both major surfaces  56 A and  56 B of sapphire component  12 , or by quenching. As the selected surfaces of sapphire component  12  are cooled, regions  52  of the sapphire material may contract or deform, relative to interior regions  54 , which cool more slowly, and remain closer to the annealing temperature for a longer period of time. As a result, an internal stress distribution is generated within sapphire component  12 , producing residual compressive stress in selected surface regions  52 . The compressive stress is retained as sapphire component  12  cools to room temperature, and across the typical operational range when assembled into a particular electronic device  10 , as shown in  FIG. 5A . 
       FIG. 5C  is an alternate cross-sectional view of sapphire component  12 , illustrating the formation of residual compressive stress in selected regions  52  by alternate methods, for example via laser heating or laser strengthening. In laser processes, one or more (e.g., infrared or other high power) laser beams L may be utilized to rapidly heat one or both major surfaces  56 A and  56 B of sapphire component  12 . This results in regions  52  of residual compressive stress when the sapphire material cools and contracts. Cooling may be accomplished either by conduction, radiation, and convention, or by application of one or more cooling jets J. 
     In laser processes, a surface coating (C) (see,  FIG. 5C ) may be applied to one or both of first and second major surface  56 A and  56 B, in order to increase surface energy absorption. Surface coating (C) is typically destroyed during the laser heating process, or removed by cleaning. Laser beams L may also be applied either in a continuous beam operation or in a pulsed mode, for example to modulate the power input, or to generate mechanical shock waves in compressive stress regions  52 . 
     Generally, regions  52  of residual compressive stress are stronger and more resistant to breakage and other damage, as compared to other untreated regions  60 , which are not subject to the same heating and cooling processes. In particular, compressive stress regions  52  may provide sapphire component  12  with a higher failure loading, for example in excess of 1,000 MPa or more, or about 2,000-3,000 MPa, as determined in a notched beam test or other procedure. 
     The heating and cooling processes can also be controlled to generate compressive stress regions  52  with relatively greater or less depth, as compared to thickness T of sapphire component  12 , between opposing major surfaces  56 A and  56 B. In the jet-cooled or quenched processes of  FIG. 5B , for example, the relative depth and other characteristic of residual compressive stress regions  52  are determined by the thermal properties of cooling jets J, including composition, density, and flow rate. In the laser processes of  FIG. 5C , the depth and other characteristics of compressive stress regions  52  are determined by laser frequency, intensity and pulse rate, with or without the application of cooling jets J. 
     This contrasts with diffusion hardening processes in amorphous glass materials, and ion beam assisted deposition (or ion implantation) methods in sapphire, in which the treatment depth is determined by the transport of ions or diffusive materials through major surfaces  56 A or  56 B of component  12 . In some ion implantation methods, for example, the treatment thickness may be limited to a subsurface layer no deeper than about 200-300 nm, or less. 
     These processes also contrast with traditional glass tempering, in which heat is applied to major surfaces  56 A and  56 B through convection heating, and which are only applicable to parts with significant thickness T, in order to properly create compressive stress layers  52 . In the laser heating and jet cooling methods of  FIGS. 5B and 5C , however, compressive stress regions or layers  52  may be generated with a broader range of depths or thicknesses t, as appropriate to sapphire component thicknesses T ranging from about 0.3 mm or less up to about 1-2 mm or more. 
     By controlling the heating time and/or laser profile, subsurface regions of sapphire component  12  can also be locally or globally heated, and then cooled or quenched to generate compressive stress regions  52  with thicknesses t ranging from about 100-200 nm up to 1 μm or more, while the crystal plane orientation of sapphire component  12  is substantially preserved. One or more laser beams L can also be used to locally or globally generate high temperature on one or both surfaces  56 A and  56 B of sapphire component  12 , before an immediate quench or cooling step using cooing jets or fluid J is applied, generating compressive stress regions  52  with depth or thickness t of up to 0.1 mm or more, or up to 1-10 percent or more of component thickness T. 
     Compressive stress regions  52  may also exhibit different fracture patterns and other properties, as compared to untreated regions  60 , and the heating and cooling processes may be selectively applied to specific regions of sapphire component  12 , generating compressive stress regions  52  in areas that are prone to fracture, when assembled into a particular electronic device  10 . Sapphire component  12  can also be provided with a customized compressive stress layer  52 , for example with varying depth t and surface coverage, in order to provide a defined fracture pattern for extremely high loading conditions, where failure is unavoidable. 
       FIG. 6  is perspective view of electronic device  10 , showing representative residual compressive stress patterns or regions  52 , as defined, e.g., in front cover glass  12 A. As shown in  FIG. 6 , residual compressive stress region  52  (dashed line) may extend substantially about the periphery of cover glass  12 A, including corner regions  52 A that are prone to mechanical shock or impact when assembled into electronic device  10 , as compared to untreated (central or interior) region  60 , for example when device  10  is dropped on a hard surface. 
     Depending upon application, residual compressive stress region  52  may include one or more apertures, for example apertures for a control device  20  or audio device  22 , in order to reduce the probability of failure when the aperture is subject to impact, stress or strain. Residual compressive stress region  52  may also include one or more edge regions  52 B of cover glass component  12 , for example a side or end region  52 B extending between corner regions  52 A. Alternatively, residual compressive stress region  52  may be defined in one or more corner regions  52 A, only, without edge regions  52 B, or in any combination of corner regions  52 A and side or end regions  52 B, and on either or both of the interior and exterior surfaces. 
     In additional embodiments, the stress pattern may be reversed, with residual compressive stress region  52  provided in a central portion of cover glass  12 A, and untreated region  60  disposed in a corner, side, or peripheral portion. Compressive stress region  52  may also extend over substantially the entire surface area of cover glass  12 A, on either or both major surfaces, including one or more apertures for control features  20 , audio devices  22 , and other accessories. 
       FIG. 7  is block diagram illustrating method  70  for forming a cover glass or other sapphire component for an electronic device, with residual compressive stress. As shown in  FIG. 7 , method  70  comprises one or more of forming a sapphire material (step  71 ), shaping a sapphire component from the sapphire material (step  72 ), heating a selected portion of the component (step  73 ) to an annealing temperature, and cooling the component (step  74 ) to generate residual compressive stress (step  75 ). Depending upon application, the component may then be assembled into an electronic device (step  76 ). 
     Forming the sapphire material (step  71 ) may comprise sintering and fusing aluminum oxide (alumina; Al 2 O 3  or α-Al 2 O 3 ), for example in an inert atmosphere, in order to produce a substantially single crystal sapphire, ruby or corundum boule. Typical synthesis processes include, but are not limited to, Verneuil processes, Czochralski processes, and flux methods. Alternatively, a polycrystalline or laminated sapphire material may be utilized. 
     Shaping the component (step  72 ) comprises cutting, drilling, milling or machining the sapphire material (e.g., using industrial diamond tools) to form the selected component, for example a cover glass, lens cover, inset, or other sapphire component  12 A,  12 B,  12 C, or  12 D, as described above. Generally, the sapphire component is defined between first and second major surfaces, for example opposing interior and exterior surfaces, and in some configurations the sapphire material may be laminated. 
     Depending on application, one or more apertures may also be formed in the component (step  77 ), in order to accommodate audio devices or other control and accessory features. For example, the component may be provided with one or more apertures to accommodate any of control devices  20  and  20 A- 20 D, microphones or speakers  22 , cameras or sensors  24 ,  24 A, and  24 B, and lighting or indicator features  26 . 
     Heat treatment (step  73 ) comprises heating a selected portion of the sapphire component to an annealing temperature. The annealing temperature is typically selected below the melting point of about 2030 C-2050 C, for example about 1800 C-2000 C. Alternatively, a lower temperature annealing or tempering range is utilized, for example above about 1200 C or above about 1500 C. 
     Heat treatment may be performed using a using a high-temperature furnace or other apparatus, for example in a vacuum environment, or in air. Alternatively, heat treatment (step  73 ) may be performed with a laser apparatus, for example using a pulsed infrared laser, or another high intensity laser apparatus. 
     Cooling (step  74 ) may be performed by quenching or applying air jets or other cooling fluid to the heated surfaces of the sapphire component. Alternatively, cooling may be achieved via any combination of conduction, radiation, and convection, without active quenching or jet cooling. 
     Cooling generates residual compressive stress (step  75 ) in the selected (heated and cooled) regions of the sapphire component. Generally, the residual compressive stress may be generated after machining and other forming steps, so that the residual compressive stress is greater in the treated regions of the finished part, as compared to any untreated regions. 
     Assembly (step  76 ) comprises assembling the sapphire component into an electronic device, for example a mobile phone, smartphone, computing device, or other mobile or stationary electronic device  10 , as described above. The treated regions may be selected (step  78 ) based on characteristics of the component when assembled into such an electronic device, for example corner or edge regions that are relatively more prone to impact, as compared to any untreated region, such as the central portion of a display or cover glass component. 
     Alternatively, substantially the entire surface area of the component may be provided with residual compressive stress. The compressive stress pattern(s) may also be provided on either one or both of the major surfaces of the component, with either uniform or varying treatment depth. Based on these parameters, the compressive stress regions may be selected to reduce the risk of damage due to shock or impact or to provide a predefined failure geometry, or to provide both functions. 
     While this invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof, without departing from the spirit and scope of the invention. In addition, modifications may be made to adapt the teachings of the invention to particular situations and materials, without departing from the essential scope thereof. Thus, the invention is not limited to the particular examples that are disclosed herein, but encompasses all embodiments falling within the scope of the appended claims.

Metadata:
Filing Date: 20130110
Publication Date: 20170418
Grant Date: 20170418
Priority Date: 20130110
Inventors: KWONG KELVIN
Assignee: APPLE INC
CPC Classifications: [{"code": "B32B3/266", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04M1/0266", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04M1/185", "inventive": false, "first": false, "tree": "[]"}, {"code": "Y10T29/49826", "inventive": false, "first": false, "tree": "[]"}, {"code": "C04B41/0036", "inventive": true, "first": false, "tree": "[]"}, {"code": "C30B33/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "C04B41/0081", "inventive": true, "first": false, "tree": "[]"}, {"code": "C30B29/20", "inventive": true, "first": false, "tree": "[]"}, {"code": "B32B7/02", "inventive": true, "first": true, "tree": "[]"}, {"code": "Y10T428/24992", "inventive": false, "first": false, "tree": "[]"}, {"code": "Y10T428/24331", "inventive": false, "first": false, "tree": "[]"}, {"code": "C04B41/0081", "inventive": true, "first": true, "tree": "[]"}, {"code": "C30B33/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "B32B3/266", "inventive": true, "first": false, "tree": "[]"}, {"code": "C04B41/0081", "inventive": true, "first": true, "tree": "[]"}, {"code": "Y10T29/49826", "inventive": false, "first": false, "tree": "[]"}, {"code": "C30B29/20", "inventive": true, "first": false, "tree": "[]"}, {"code": "Y10T428/24331", "inventive": false, "first": false, "tree": "[]"}, {"code": "C30B33/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "Y10T29/49826", "inventive": false, "first": false, "tree": "[]"}, {"code": "Y10T428/24331", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04M1/0266", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04M1/0266", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04M1/185", "inventive": false, "first": false, "tree": "[]"}, {"code": "Y10T428/24992", "inventive": false, "first": false, "tree": "[]"}, {"code": "Y10T428/24992", "inventive": false, "first": false, "tree": "[]"}, {"code": "C04B41/0036", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04M1/185", "inventive": false, "first": false, "tree": "[]"}, {"code": "C30B29/20", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 49989500