PATENT DOCUMENT

Publication Number: US-11104616-B2
Application Number: US-201615267088-A
Country: US
Kind Code: B2

Title: Ceramic having a residual compressive stress for use in electronic devices

Abstract:
A toughened ceramic component having a residual compressive stress and methods of forming the toughened ceramic component is disclosed. The ceramic component may include an internal portion having a first coefficient of thermal expansion (CTE) and an external portion substantially surrounding the internal portion and forming an exterior surface of the ceramic component. The external portion may have a second CTE that is less than the first CTE. Additionally, the external portion may be in compressive stress.

Claims:
What is claimed is: 
     
       1. An electronic device, comprising:
 a housing having an opening; and 
 a transparent ceramic cover positioned at least partially within the opening and defining an exterior surface of the electronic device, the cover comprising:
 a singular sintered ceramic structure comprising:
 an external portion comprising a perimeter region and a center region, the perimeter region having a first thickness and the center region having a second thickness that is less than the first thickness; 
 an internal portion surrounded by the external portion; and 
 at least one of yttrium, silicon, germanium, or chromium dopant atoms distributed within the singular sintered ceramic structure, the dopant atoms having a first dopant concentration at the external portion and a second, lower dopant concentration at the internal portion, a concentration of dopant atoms decreasing from the first dopant concentration to the second dopant concentration to define a dopant gradient, wherein the external portion has a coefficient of thermal expansion that is different than a coefficient of thermal expansion of the internal portion. 
 
 
 
     
     
       2. The electronic device of  claim 1 , wherein the external portion has a lower coefficient of thermal expansion than the internal portion. 
     
     
       3. The electronic device of  claim 1 , wherein the external portion defines substantially all of a top surface and a bottom surface of the ceramic cover. 
     
     
       4. The electronic device of  claim 1 , wherein:
 a compressive residual stress of the transparent ceramic cover at the first portion is greater than a compressive residual stress of the transparent ceramic cover at the second portion. 
 
     
     
       5. The electronic device of  claim 1 , wherein the singular sintered ceramic structure comprises at least one of: zirconia, alumina (Al 2 O 3 ), silicon carbide, or silicon nitride. 
     
     
       6. The electronic device of  claim 1 , wherein the transparent ceramic cover is positioned over a display of the electronic device.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a nonprovisional patent application of and claims the benefit of U.S. Provisional Patent Application No. 62/234,783, filed Sep. 30, 2015 and titled “Ceramic Having a Residual Compressive Stress for Use in Electronic Devices,” the disclosure of which is hereby incorporated herein by reference in its entirety. 
    
    
     FIELD 
     The disclosure relates generally to ceramic material and more particularly to components formed from toughened ceramic material having a residual compressive stress and methods of forming a residual compressive stress within the ceramic material. 
     BACKGROUND 
     Electronic devices typically include enclosures for protecting the internal components of the device. For example, a conventional electronic device may include a housing for containing the internal components of the electronic device, such as a display. Additionally, the display may be protected by a transparent cover glass. The housing and/or cover glass may prevent damage to the electronic device and its components when the electronic device undergoes an undesirable shock event (e.g., drop). The housing and cover glass may be formed from durable materials that may withstand these undesirable shock events. 
     However, while the durable material may protect the internal components, the enclosures (e.g., housing, cover glass) may be susceptible to damage. For example, when the electronic device is dropped, the housing and/or the cover glass may be scratched, dented, cracked, chipped and may suffer other material or surface defects. Where a material defect, such as a crack or dent, is formed in the enclosure, the material may be weakened and/or may be vulnerable to further damage, especially during subsequent, undesirable shock events. That is, the material defects may weaken the strength of the material, which may in turn reduce the enclosure&#39;s ability to protect the internal components of the electronic device. Additionally, in the instance where the enclosure (e.g., cover glass) is cracked, the crack may grow over time, which renders the electronic device partially or totally in operable. 
     Therefore, it is desirable to form the enclosure and/or the cover glass of the electronic device from a toughened material that both prevents material defects and mitigates or minimizes surface defects that may be formed in or on the enclosure and/or the cover glass. 
     SUMMARY 
     A ceramic component comprising an internal portion having a first coefficient of thermal expansion (CTE), and an external portion substantially surrounding the internal portion and forming an exterior surface of the ceramic component. The external portion has a second CTE less than the first CTE. Additionally, the external portion is in compressive stress. 
     A method for forming a toughened ceramic component. The method comprises applying, to an exterior surface of a ceramic substrate, a material having a first coefficient of thermal expansion (CTE) that is lower than a second CTE of the ceramic substrate, heating the material and the ceramic substrate, and in response to heating the material and the ceramic substrate, diffusing at least a portion of the material into an external portion of the ceramic substrate. The method also comprises cooling the material and the ceramic substrate thereby generating a compressive stress within the external portion of the ceramic substrate. 
     A method for forming a toughened ceramic component. The method comprises forming a preform comprising an internal portion formed from a first ceramic-based material having a first coefficient of thermal expansion (CTE), and an external portion positioned adjacent the internal portion. The external portion formed from a second ceramic-based material having a second CTE lower than the first CTE. The method also comprises sintering the preform to fuse the internal portion and the external portion to form a fused structure, and cooling the fused structure thereby forming a compressive stress within the external portion. 
     A method for forming a toughened ceramic component. The method comprises altering a first thermal expansion characteristic of an external portion of a ceramic preform while leaving a second thermal expansion characteristic of an internal portion of the ceramic preform unaltered. The method also comprises sintering the ceramic preform, cooling the ceramic preform, and forming a compressive stress within the external portion. The external portion of the ceramic preform is positioned adjacent the internal portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which: 
         FIG. 1A  shows a ceramic component. 
         FIG. 1B  shows a side cross-section view of the ceramic component of  FIG. 1A  taken along line  1 B- 1 B having an external portion and an internal portion. 
         FIG. 1C  shows an enlarged portion of the ceramic component of  FIG. 1B . 
         FIG. 2  shows a flow chart of an example process for forming a toughened ceramic component. 
         FIG. 3A  shows a side cross-section view of a portion of a ceramic substrate covered with a dopant material. 
         FIG. 3B  shows an enlarged view of the portion of the ceramic substrate covered with the dopant material of  FIG. 3A . 
         FIG. 3C  shows a side cross-section view of the portion of the ceramic substrate, the dopant material of  FIG. 3A  undergoing a heating process. 
         FIG. 3D  shows an enlarged view of the portion of the ceramic substrate covered with the dopant material of  FIG. 3C . 
         FIG. 3E  shows a side cross-section view of the portion of the ceramic substrate, the dopant material of  FIG. 3A  undergoing a cooling process. 
         FIG. 3F  shows an enlarged view of the portion of the ceramic substrate covered with the dopant material of  FIG. 3E . 
         FIG. 3G  shows a side cross-section view a ceramic component formed from the ceramic substrate of  FIG. 3A . The ceramic component has an external portion and an internal portion. 
         FIG. 4  shows a flow chart of an example process for forming a toughened ceramic component. 
         FIG. 5A  shows a side cross-section view of a portion of a ceramic-based preform formed from undoped ceramic material and doped ceramic material. 
         FIG. 5B  shows an enlarged view of the portion of the ceramic-based preform of  FIG. 5A . 
         FIG. 5C  shows a side cross-section view of the portion of the ceramic-based preform of  FIG. 5A  undergoing a sintering process. 
         FIG. 5D  shows an enlarged view of the portion of the ceramic-based preform of  FIG. 5C . 
         FIG. 5E  shows a side cross-section view of the portion of the ceramic-based preform of  FIG. 5A  undergoing a cooling process. 
         FIG. 5F  shows an enlarged view of the portion of the ceramic-based preform of  FIG. 5E . 
         FIG. 6  shows a flow chart of an example process for forming a toughened ceramic component. 
         FIG. 7A  shows a side cross-section view of a portion of a ceramic material formed with two distinct grain sizes of material. 
         FIG. 7B  shows an enlarged view of the portion of the ceramic material of  FIG. 7A . 
         FIG. 7C  shows a side cross-section view of the portion of the ceramic material of  FIG. 7A  undergoing a first and second sintering process. 
         FIG. 7D  shows an enlarged view of the portion of the ceramic material of  FIG. 7C  undergoing the first sintering process. 
         FIG. 7E  shows an enlarged view of the portion of the ceramic material of  FIG. 7C  undergoing the second sintering process. 
         FIG. 7F  shows a side cross-section view of a ceramic component formed from the ceramic material of  FIG. 7A . The ceramic component has an external portion and an internal portion. 
         FIG. 8  shows a side cross-section view a ceramic component having a selective compressive stress formed therein. 
         FIG. 9  shows a side cross-section view of a ceramic component having a varying thickness external portion and an internal portion. 
         FIG. 10  shows an isometric view of an electronic device that may utilize the ceramic component having an external portion and an internal portion, as discussed, with respect to  FIGS. 1A-9 . 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to representative embodiments illustrated in the accompanying drawings. It should be understood that the following descriptions are not intended to limit the embodiments to one preferred embodiment. To the contrary, it is intended to cover alternatives, modifications, and equivalents as can be included within the spirit and scope of the described embodiments as defined by the appended claims. 
     The following disclosure relates generally to ceramic material and more particularly to components formed from toughened ceramic material having a residual compressive stress and to methods of forming a residual compressive stress within the ceramic material. 
     In a particular embodiment, the toughed ceramic component includes a residual compressive stress formed therein. The compressive stress can be formed on an external portion of the ceramic component, which includes the exterior surface of the component. The compressive stress formed in the ceramic component improves physical characteristics (e.g., toughness, brittleness, and so on) of the ceramic component. Additionally, the compressive stress mitigates and/or prevents the spreading of surface defects (e.g., cracks, splits, breaks, chips and so on) that are formed in the ceramic component. Specifically, the compressive stress formed in the external portion of the ceramic component mitigates and/or prevents the spreading of surface defects formed in on exterior surface and/or within external portion of the ceramic component forming the exterior surface. The improved physical characteristics of the ceramic material are beneficial when the ceramic component is used in electronic devices, specifically handheld or wearable electronic devices that are susceptible to undesirable shock events (e.g., impacts). 
     These and other embodiments are discussed below with reference to  FIGS. 1A-10 . However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these Figures is for explanatory purposes only and should not be construed as limiting. 
       FIG. 1A  shows a toughened ceramic component or structure having a residual compressive stress formed in an external portion. Ceramic component  100  is shown in  FIG. 1A  as a sheet, but may take the form of any preform structure of ceramic material, for example, a wafer. As discussed herein, ceramic component  100  may take the form of a variety of components. In a non-limiting example, and as discussed herein, ceramic component  100  may be a cover positioned over a display of an electronic device (see,  FIG. 10 ). Ceramic component  100  can be a single component that is in a final shape after undergoing the processes discussed herein. 
       FIG. 1B  shows a side cross-section view of toughened ceramic component  100 . Forming the residual compressive stress in external portion  102  of ceramic component  100  improves the strength of the material forming ceramic component  100  when compared to untreated and/or unprocessed ceramic material, which typically is brittle and susceptible to cracking. Additionally, toughened ceramic component  100 ) having a residual compressive stress formed in external portion  102 ) may have improved toughness, brittleness and/or improves protection against damage as compared to a conventional ceramic component  100 . The residual compressive stress formed in external portion  102  also mitigates and/or prevents the spreading of surface defects (e.g., cracks, splits, breaks, chips and so on) that are formed in ceramic component  100  and specifically on an exterior surface  104  and/or within external portion  102 . In a non-limiting example, the external portion  102  having the residual compressive stress prevents surface defects from spreading within external portion  102  and/or spreading to internal portion  106  of ceramic component  100 . 
     The improved physical characteristics for ceramic component  100  are crucial for certain utilizations of ceramic component  100 . As discussed herein, toughened ceramic component  100  may take the form of a variety of components. In non-limiting examples, and as discussed herein, toughened ceramic component  100  may form a cover positioned over a display of an electronic device and/or may form an enclosure or housing for the electronic device. The improved physical characteristics, such as improved strength and crack propagation, allow the electronic device to withstand more day-to-day wear, such as shock or drop events, without becoming damaged, cracked and/or broken. As a result, and according to the example discussed herein, ceramic component  100  can improve the operational life of the electronic device. 
     Ceramic component  100 , as shown in  FIG. 1B , is formed as a single structure or component. As discussed herein, although ceramic component  100  is shown to have external portion  102  and internal portion  106 , each having distinct cross-hatching in  FIG. 1B , it is understood that external portion  102  and internal portion  106  are a single structure. However, in another non-limiting example, external portion  102  and internal portion  106  may be distinct components and/or may be separated from one another. 
     Ceramic component  100  is formed from any suitable crystalline structure or structures. Additionally, ceramic component  100  is formed from any suitable ceramic material(s) that is capable of undergoing the processes discussed herein to form a residual compressive stress in external portion  102  of ceramic component  100 . In non-limiting examples, ceramic component  100  is formed from, but not limited to, zirconia, alumina (Al 2 O 3 ), commonly known as sapphire, silicon carbide, silicon nitride and other crystalline ceramic materials having substantially similar characteristics as the specific materials discussed herein. 
     As shown in  FIG. 1B , external portion  102  of ceramic component  100  substantially surrounds internal portion  106 . Also shown in  FIG. 1B , external portion  102  surrounds all portions of internal portion  106  and forms exterior surface  104  of ceramic component  100 . External portion  102  and internal portion  106  are under and/or experience distinct stresses when forming ceramic component  100 . In a non-limiting example, and as discussed herein, at least a portion of external portion  102  is under a residual compressive stress and at least a portion of internal portion  106  is under a tensile stress. In some embodiments, external portion  102  may not fully surround internal portion  106 , but rather may only be formed adjacent a top and bottom surface, for example. 
     In addition to experiencing distinct stresses, other properties and/or characteristics of external portion  102  and internal portion  106  of ceramic component  100  may be distinct. In a non-limiting example, the coefficient of thermal expansion (CTE) is distinct or different for external portion  102  when compared to the CTE for internal portion  106 . In the non-limiting example, the CTE for external portion  102  is less than the CTE for internal portion  106 . As a result, external portion  102  of ceramic component  100  may expand and/or contract less than internal portion  106  when ceramic component  100  is heated and/or cooled, respectively. As discussed herein, the distinction and/or difference in the CTEs for external portion  102  and internal portion  106  substantially impacts the compressive stress formed in external portion  102  and, when applicable, the tensile stress formed in internal portion  106  of ceramic component  100 . 
     The distinction or difference between the CTEs for external portion  102  and internal portion  106  are a result of a distinction or difference between the material composition and/or properties of external portion  102  and the material composition and/or properties for internal portion  106 . That is, the material composition and/or properties of external portion  102  are distinct or different than the material composition and/or properties for internal portion  106  of ceramic component  100 . In a non-limiting example, and as discussed in detail with respect to  FIG. 1C , internal portion  106  has a pure-ceramic material composition (e.g., zirconia), while external portion  102  has a doped-ceramic material composition (e.g., zirconium(IV) oxide-yttria). External portion  102  and internal portion  106  may still form a unitary structure. For example, the materials can be co-sintered or otherwise process to form a single structure. In some embodiments, there may be no visible seam or other separation between internal portion  106  and external portion  102 . 
       FIG. 1C  shows an enlarged region of ceramic component  100  of  FIG. 1B . Specifically,  FIG. 1C  shows part of external portion  102  and internal portion  106  separated by transition line  108 . In a non-limiting example where external portion  102  and internal portion  106  are formed as a single structure, transition line  108  is merely a reference line that distinguishes the external portion  102  and internal portion  106 . In the non-limiting example, transition line  108  more easily identifies where internal portion  106  having a first CTE and/or material composition ends and where external portion  102  having a second CTE and/or material composition begins. In another non-limiting example where external portion  102  and internal portion  106  are formed as distinct layers or structures, transition line  108  indicates a separation or interface between the layers or materials that form external portion  102  and internal portion  106 . 
     As discussed herein, in some embodiments, external portion  102  and internal portion  106  are parts of a single ceramic component  100  and share a common base material. Both external portion  102  and internal portion  106  include a common ceramic material. As shown in  FIG. 1C , both external portion  102  and internal portion  106  are formed from the same ceramic material, which is shown or indicated by the ceramic material or atoms  110  positioned within external portion  102  and internal portion  106 . In a non-limiting example, ceramic component  100  and, specifically, external portion  102  and internal portion  106  are formed from zirconia material. 
     The term “atoms” refers to the particles of matter that make up the material of ceramic component  100 . Atoms may generally, and indiscriminately, refer to the atoms that make up and/or form the entire material of ceramic component  100  and, specifically, external portion  102  and/or internal portion  106 . In a non-limiting example where ceramic component  100  is formed from zirconia or zirconium dioxide, atoms may be used as a general description and may refer to the atoms of all elements (e.g., zirconium and oxygen) of the zirconia indiscriminately, as well as the zirconia itself. As such, and as described herein, ceramic atoms  110  may be any atoms associated with any of the various elements that form zirconia. In another non-limiting example, ceramic atoms  110  may be multiple atoms of different elements that form the material (e.g., zirconia) of ceramic component  100 . The term “atom,” as used herein, may encompass an ion and/or a molecule of the material, as appropriate. 
     As shown in  FIG. 1C , external portion  102  also includes a distinct atom positioned therein. Specifically, in addition to ceramic atoms  110  forming at least a portion of external portion  102 , external portion  102  also includes a dopant material. The dopant material is shown or indicated in  FIG. 1C  by dopant material or atoms  112  positioned within external portion  102 . As shown in  FIG. 1C , dopant atoms  112  are only formed within external portion  102  and are not formed within internal portion  106 . As such, transition line  108  marks a (possibly invisible) boundary between external portion  102  formed from the doped-ceramic material, and internal portion  106  formed from only the ceramic material. 
     The size, orientation, and/or spacing of dopant atoms  110 ,  112  of ceramic component  100 , as shown in  FIG. 1C , and additional figures discussed herein, are merely exemplary. That is, the atoms depicted in the figures are not limited to the size, orientation and/or spacing as shown. Rather, the atoms are merely sized, oriented and/or spaced as an example and/or for clarifying the material properties of ceramic component  100  and the changes the material forming ceramic component  100  experiences when undergoing the processes discussed herein. 
     The dopant material may be any suitable dopant material having a coefficient of thermal expansion (CTE) that is less than the CTE of the ceramic material (e.g., ceramic atoms  110 ) forming ceramic component  100  and, specifically, external portion  102  of ceramic component  100 . In non-limiting examples, dopant material (e.g., dopant atoms  112 ) included within external portion  102  may include, but is not limited to, yttria or yttrium, silicon, germanium, chromium and other dopant materials that may be implanted within crystalline ceramic materials to lower the CTE of the ceramic material. The lowering of the CTE of external portion  102  (when compared to the CTE of internal portion  106 ) results in a compressive stress being formed in external portion  102  when ceramic component  100  undergoes certain formation processes discussed herein. 
     As a result of embedding dopant atoms  112  within external portion  102 , the material composition and/or properties of external portion  102  differ from the material composition and/or properties of internal portion  106 . In the non-limiting example shown in  FIG. 1C , internal portion  106  is entirely composed of ceramic atoms  110  and, as such, is purely a ceramic material. In the non-limiting example, internal portion  106  is composed of zirconia or zirconium dioxide. Additionally, in the non-limiting example shown in  FIG. 1C , external portion  102  is composed of the base ceramic atoms  110  and dopant atoms  112 . As a result, external portion  102  is a doped ceramic material, for example, zirconium(IV) oxide-yttria. 
     As a result of the different material compositions between external portion  102  (e.g., zirconium(IV) oxide-yttria) and internal portion  106  (e.g., zirconium dioxide), the CTEs for each of external portion  102  and internal portion  106  are also distinct or different, as discussed herein. In the non-limiting example, the external portion  102  formed from zirconium(IV) oxide-yttria has a lower CTE than internal portion formed from zirconia or zirconium dioxide. The difference in CTE and, specifically, external portion  102  having a lower CTE than internal portion  106 , creates a compressive stress within external portion  102  when forming ceramic component  100  using the process discussed in detail below. The compressive stress formed in external portion  102  may improve toughness, reduce brittleness and/or other improve resistance to damage of the ceramic component  100 , as well as mitigate propagation of surface defects (e.g., cracks, splits, breaks, chips and so on) in ceramic component  100 . 
     As shown in  FIG. 1C , a concentration of the dopant atoms  112  varies within external portion  102  of ceramic component  100 . That is, external portion  102  includes a gradient  118  of dopant atoms  112 . In a non-limiting example shown in  FIG. 1C , the concentration of dopant atoms  112  is highest adjacent exterior surface  104  of ceramic component  100 . Additionally, the concentration of dopant atoms  112  is lowest adjacent internal portion  106  and/or transition line  108 . Also shown in the non-limiting example of  FIG. 1C , the concentration of dopant atoms  112  formed in external portion  102  gradually decreases from exterior surface  104  to internal portion  106  and/or transition line  108 . Gradient  118  of dopant atoms  112  formed in external portion  102  is a result of the doping and/or diffusion processes undergone when forming ceramic component  100 , as discussed herein. 
       FIG. 2  depicts an example process for forming a toughened ceramic component. Specifically,  FIG. 2  is a flowchart depicting one example process  200  for forming a toughened ceramic component having a residual compressive stress formed within an external portion to improve physical characteristics (e.g., toughness, brittleness, and so on) of the ceramic component. In some cases, the toughened ceramic component may be utilized in an electronic device, as discussed below with respect to  FIG. 10 . 
     In operation  202 , a material is applied to an exterior surface of a ceramic material or substrate. The material applied to the exterior surface has a coefficient of thermal expansion (CTE) lower than a CTE for the ceramic material or substrate. Additionally, the material applied to the exterior surface is a dopant material. As such, applying the material also can include doping the exterior surface of the ceramic substrate. 
     Applying the material to the exterior surface of the ceramic substrate can be performed by a variety of material application processes. In non-limiting examples, applying the material can be done by any or all of dip coating the ceramic substrate in the material, painting the material on the ceramic substrate, tape casting at least one layer of the material on the ceramic substrate, applying a slurry of the material to the ceramic substrate, and chemical vapor depositing (CVD) the material over the ceramic substrate. 
     In operation  204 , the ceramic substrate is heated. In this operation, the material applied to the exterior surface of the ceramic substrate in operation  202  and the ceramic substrate are heated together. The material and the ceramic substrate are heated to a predetermined temperature and/or for a predetermined time to cause diffusion between the material and the ceramic substrate, as discussed in detail with respect to operation  206 . The predetermined temperature and/or predetermined heating time is dependent on, at least in part, the material composition of the ceramic substrate and the material applied to the exterior surface of the ceramic substrate. The material and the ceramic substrate are heated using any suitable heating process and/or heating system including, but not limited to, a laser, a flash-lamp, and a furnace or an oven. 
     Heating the ceramic substrate typically expands ceramic substrate. As the ceramic substrate is heated to the predetermined temperature to cause diffusion, as discussed herein, the ceramic substrate also expands. The entire ceramic substrate expands evenly during the heating process, as the ceramic substrate is a uniform, ceramic material. 
     In operation  206 , atoms, ions, molecules or other portions of the material applied to the exterior surface are diffused into an external portion of the ceramic substrate. The external portion of the ceramic substrate surrounds an internal portion of the ceramic substrate. Diffusion occurs as a result of heating the material and the ceramic substrate in operation  204 . That is, once the ceramic substrate is heated to the predetermined temperature and/or heated for the predetermined time, some of the material applied to the exterior surface is diffused within the external portion of the ceramic substrate. Diffusion occurs while the material and the ceramic substrate are being heated and/or are maintained at the predetermined temperature. Material is diffused within the external portion of the ceramic substrate, such that the internal portion is substantially free from atoms from the material applied to the exterior surface and/or the material composition of the internal portion remains an undoped, ceramic material. 
     The diffusing operation also occurs in the external portion of the ceramic substrate with atoms of the material. That is, during the diffusion process in operation  206 , atoms from the material applied to the exterior surface of the ceramic substrate replace atoms of the ceramic material of the external portion. The replaced ceramic atoms may diffuse and/or migrate to the material, such that an exchange between the two materials occurs. Where the material is a dopant, the material application and diffusion processes are, collectively, commonly referred to as a doping process. 
     The replacing of the atoms in the external portion of the ceramic substrate also includes exchanging or replacing a first number of the ceramic atoms of the external portion directly adjacent the exterior surface of the ceramic substrate and exchanging or replacing a second number of the ceramic atoms of the external portion directly adjacent the internal portion of the ceramic substrate. The second number of the ceramic atoms may be less than the first number of the ceramic atoms. As a result, a gradient of the material diffused into the external portion is formed within the ceramic substrate. Specifically, the replacing of the atoms in the external portion also includes forming a gradient of the atoms of the material diffused into the external portion. The gradient includes a first concentration of the atoms of the material adjacent the exterior surface and a second concentration of the atoms of the material adjacent the internal portion. The second concentration of the atoms of the material is smaller than the first concentration of the atoms of the material. Additionally, the concentration of the atoms of the material gradually decreases when moving from the exterior surface of the ceramic substrate to the internal portion of the ceramic substrate. 
     The diffusion achieved in operation  206  also includes altering the material composition and/or thermal expansion characteristics for the external portion of the ceramic substrate. That is, diffusing and/or replacing ceramic atoms in the external portion with the atoms of the material applied to the exterior surface substantially alters the material composition and/or the thermal expansion characteristics of the external portion. Prior to diffusing the atoms of the material into the external portion, the external portion and the internal portion of the ceramic substrate both have the same material composition. However, subsequent to performing the diffusion process in operation  206 , the external portion includes both ceramic atoms and atoms of the material. As discussed herein with respect to operation  202 , the material can include a dopant material having a CTE lower than the CTE of the ceramic material forming the ceramic substrate. As a result, the atoms of the material diffused into the external portion cause the external portion to be formed from a doped, ceramic material, with a lower CTE than the undoped, ceramic material forming the internal portion of the ceramic substrate. 
     In operation  208 , the material and the ceramic substrate are cooled. That is, subsequent to the heating in operation  204  and the diffusion in operation  206 , the ceramic substrate heated to the predetermined diffusion temperature is cooled. Both the ceramic substrate, including the external portion and the internal portion, and the material applied to the exterior surface of the ceramic substrate are cooled to lower the temperature of the ceramic substrate. Cooling the ceramic substrate can include gradually and/or naturally cooling the ceramic substrate by removing the ceramic substrate from the heating system and/or heating device. Alternatively, the ceramic substrate can be rapidly cooled by removing the ceramic substrate from the heating system and submerging the ceramic substrate into a cold-liquid bath, or spraying the ceramic substrate with a cold or cooled liquid. 
     Cooling the ceramic substrate also shrinks the ceramic substrate. Specifically, the cooling of the heated ceramic substrate causes the external portion and the internal portion of the ceramic substrate to shrink. Distinct from the heating process where ceramic substrate expands evenly and uniformly, in the cooling process the ceramic substrate shrinks unevenly. The external portion and the internal portion of the ceramic substrate shrink at different rates and/or shrink different amounts or distances. This is a result of the change in the material composition and the change in the CTE for the external portion during the diffusion process in operation  206 . As such, when the heated ceramic substrate cools, the external portion having the lower CTE shrinks less and/or slower than the internal portion having the higher CTE. 
     As a result of cooling the ceramic substrate, a compressive stress is formed or generated within the external portion of the ceramic substrate. The compressive stress is formed within the external portion as a result of the lower CTE for the external portion and because the external portion shrinks less than the internal portion of the ceramic substrate. Specifically, the cooling of the heated ceramic substrate and the resulting shrinkage of the distinct portions of the ceramic substrate forms a compressive stress within the external portion of the ceramic substrate. The compressive stress formed in the external portion of the ceramic substrate improves the strength of the ceramic substrate when compared to untreated and/or unprocessed ceramic materials. Additionally, compressive stress formed in the external portion of the ceramic substrate improves (e.g., increases, decreases) the toughness, brittleness and/or improves protection against damage to the ceramic substrate. Furthermore, the compressive stress formed in the external portion also mitigates and/or prevents the spreading of surface defects (e.g., cracks, splits, breaks, chips and so on) within the ceramic substrate and specifically through external portion and/or within the internal portion of the ceramic substrate. 
     Although not shown, process  200  for forming a toughened ceramic component can include additional processes. In a non-limiting example, the process  200  can also include forming or generating a tensile stress within the internal portion of the ceramic substrate. Similar to the formation of the compressive stress within the external portion, the tensile stress formed within the internal portion of the ceramic substrate is a result of the cooling of the heated ceramic substrate. Specifically, the tensile stress is formed within the internal portion as a result of the higher CTE for the internal portion and because the internal portion shrinks more than the external portion of the ceramic substrate. Additionally, the tensile stress is formed within the internal portion as a result of the external portion shrinking around the internal portion and/or a compressive stress being formed within the external portion, which substantially surrounds the internal portion. 
     In another non-limiting example, the ceramic substrate can undergo a material removal process subsequent to forming the compressive stress within the external portion of the ceramic substrate. For example, after forming the compressive stress within the external portion, the ceramic substrate may still include a layer of the material applied to and/or formed on the exterior surface. As such, a material removal process is performed on the ceramic substrate to remove any of the material applied in operation  202  remaining on the exterior surface. 
     In other non-limiting examples, the process  200  can include performing various material finishing processes on the ceramic substrate prior to applying the material to the exterior surface of the ceramic substrate in operation  202 . One non-limiting example includes sintering the ceramic substrate prior to applying the material to the exterior surface of the ceramic substrate. The ceramic substrate is sintered to ensure the material forming the ceramic substrate is not in a preform or “green body” (e.g., unsintered ceramic item), but rather in a finalized, sintered state, ready to undergo the operations of process  200 . In other non-limiting examples, the ceramic substrate can undergo cutting, grinding, shaping, and/or polishing processes prior to applying the material to the exterior surface of the ceramic substrate. 
       FIGS. 3A-3G  show side and enlarged cross-section views, of a ceramic substrate  320  undergoing the example process  200  for forming a toughened ceramic component  300  (see,  FIG. 3G ) as discussed herein with respect to  FIG. 2 . It is understood that similarly numbered and/or named components may function in a substantially similar fashion. Redundant explanation of these components has been omitted for clarity. 
       FIG. 3A  shows a side cross-section view of ceramic substrate  320 . Ceramic substrate  320  is any suitable ceramic material discussed herein. As shown in  FIG. 3A , the material composition of ceramic substrate  320  is uniform throughout the substrate when performing the initial processes discussed herein for forming ceramic component  300  (see,  FIG. 3G ). Additionally, ceramic substrate  320  is a pre-fired and/or sintered substrate of ceramic material. As a result, and as discussed herein, the processes discussed herein with respect to  FIGS. 3A-3G  are performed on ceramic substrate which is pre-sintered and not in a green body. 
     Additionally shown in  FIG. 3A , a material  322  is applied to exterior surface  304  of ceramic substrate  320 . Specifically, a layer of dopant material  322  is applied to the entire exterior surface  304  of ceramic substrate  320 . The dopant material  322  includes any suitable dopant material discussed herein, such as yttria or yttrium, silicon, germanium, chromium, and so on. Additionally, and as discussed herein, dopant material  322  is made from a material having a coefficient of thermal expansion (CTE) that is less than the CTE of the material forming ceramic substrate  320 . 
     Dopant material  322  can be applied to ceramic substrate  320  using various material application techniques. In a non-limiting example, ceramic substrate  320  can be dipped into a substantially liquid-state of dopant material  322  such that ceramic substrate  320  is dip coated, and/or dopant material  322  covers exterior surface  304  of ceramic substrate  320 . In other non-limiting examples, a layer or layers of dopant material  322  can be painted and/or taped casted on exterior surface  304  of ceramic substrate  320 . In another non-limiting example, a slurry of dopant material  322  can be applied and/or disposed over exterior surface  304  of ceramic substrate  320 . Finally, dopant material  322  can be applied to ceramic substrate  320  using a chemical vapor deposition (CVD) process. The process used to apply dopant material  322  is dependent on, at least in part, the material composition of ceramic substrate  320 , the material composition of dopant material  322 , the desired residual compressive stress to be formed within ceramic substrate  320  when forming toughened ceramic component  300  and so on. 
       FIG. 3B  shows an enlarged portion of ceramic substrate  320  and dopant material  322 , as depicted in  FIG. 3A . As shown in  FIG. 3B , and discussed herein with respect to  FIG. 1C , each of ceramic substrate  320  and dopant material  322  are depicted to include atoms, which represent the particles of matter that make up the material of ceramic substrate  320  and dopant material  322 , respectively. In the non-limiting example, ceramic substrate  320  is made up of ceramic atoms  310 , and dopant material  322  is made of dopant atoms  312 . Each particle or atom of the dopant material is contained within the ceramic material, and no material or atoms have been exchanged. As shown in  FIG. 3B , subsequent to dopant material  322  being applied to exterior surface  304 , the respective atoms (e.g., ceramic atoms  310 , dopant atoms  312 ) for each of ceramic substrate  320  and dopant material  322  is only included within its corresponding material and/or substrate. As a result, ceramic atoms  310  of ceramic substrate  320  have not been exchanged with dopant atoms  312  of dopant material  322 , and vice versa. 
     The processes performed on ceramic substrate  320 , as shown and discussed herein with respect to  FIGS. 3A and 3B , may correspond to operation  202  of the process  200  shown in  FIG. 2 . 
       FIG. 3C  shows a heating device  324  positioned adjacent ceramic substrate  320  and dopant material  322 . Specifically, heating device  324  and ceramic substrate  320  are positioned adjacent and/or proximate one another, such that heating device  324  can provide heat (H) to ceramic substrate  320  and dopant material  322  thereon. Heating device  324  is configured to heat ceramic substrate  320  and dopant material  322  to a predetermined diffusion temperature. In a non-limiting example, heating device  324  is configured as a heat or flash lamp that can be positioned adjacent exterior surface  304  of ceramic substrate  320  and/or dopant material  322  and provides heating means to heat ceramic substrate  320  and dopant material  322 . In other non-limiting examples, heating device  324  can be any suitable heating system or component configured to heat ceramic substrate  320  and dopant material  322  during the processes discussed herein, including a laser, a furnace or an oven, and so on. 
     Turning to  FIG. 3D , the effects of heating ceramic substrate  320  and dopant material  322  are more clearly shown. In the non-limiting example shown in  FIG. 3D , and in conjunction with and/or in response to heating ceramic substrate  320  and dopant material  322 , dopant atoms  312  of dopant material  322  are diffused into ceramic substrate  320 . Specifically, when ceramic substrate  320  and dopant material  322  are heated to the predetermined diffusion temperature, an exchange of atoms  310 ,  312  between ceramic substrate  320  and dopant material  322  occurs. In a non-limiting example shown in  FIG. 3D , dopant atoms  312  of dopant material  322  diffuse into ceramic substrate  320  and/or replace ceramic atoms  310  of ceramic substrate  320 . In addition, ceramic atoms  310  that are replaced by dopant atoms  312  migrate toward and/or into dopant material  322  and take the place of dopant atoms  312  that are diffused into ceramic substrate  320 . 
     A concentration of dopant material  322  and/or dopant atoms  312  varies within ceramic substrate  320 . As shown in  FIG. 3D , ceramic substrate  320  includes gradient  318  of dopant atoms  312 . In a non-limiting example, and as discussed herein with respect to  FIG. 1C , the concentration of dopant atoms  312  is highest adjacent exterior surface  304  of ceramic substrate  320 . Additionally, the concentration of dopant atoms  312  formed in ceramic substrate  320  gradually decreases as dopant atoms  312  diffuse further into ceramic substrate  320  from exterior surface  304 . 
     Additionally, in conjunction with and/or in response to heating ceramic substrate  320  and dopant material  322 , ceramic substrate  320  and dopant material  322  expand. As shown in  FIG. 3D , and with comparison to  FIG. 3B , ceramic atoms  310  of ceramic substrate  320  and dopant atoms  312  of dopant material  322  move and/or spread out, resulting in the expansion of ceramic substrate  320  and dopant material  322 , respectively. In a non-limiting example, ceramic substrate  320  and corresponding ceramic atoms  310  expand more than and/or a greater distance than dopant material  322  and corresponding dopant atoms  312 . The difference in expansion is a result of difference in coefficients of thermal expansion (CTE) for ceramic substrate  320  and dopant material  322 . Specifically, because ceramic substrate  320  has a higher CTE than dopant material  322 , ceramic substrate  320  expands more than dopant material  322  when ceramic substrate  320  and dopant material  322  are heated by heating device  324 . 
     The processes performed on ceramic substrate  320 , as shown and discussed herein with respect to  FIGS. 3C and 3D , may correspond to operations  204  and  206  of the process  200  shown in  FIG. 2 . 
       FIG. 3E  shows ceramic substrate  320  and dopant material  322  subsequent to being cooled. Specifically, after ceramic substrate  320  and dopant material  322  are heated to the predetermined diffusion temperature and diffusion occurs between ceramic substrate  320  and dopant material  322  as discussed herein with respect to  FIGS. 3C and 3D , ceramic substrate  320  and dopant material  322  are cooled. The cooling of ceramic substrate  320  results in the formation of ceramic component  300 . In a non-limiting example shown in  FIG. 3E , ceramic substrate  320  is cooled to form ceramic component  300  (including internal portion  306  and external portion  302 ). 
     Ceramic component  300  and dopant material  322  are cooled to a predetermined temperature, for example room temperature. In a non-limiting example, ceramic component  300  and dopant material  322  can be cooled naturally or organically by removing heat supplied by heating device  324  (see,  FIG. 3C ). Alternatively, ceramic component  300  and dopant material  322  can be rapidly cooled by submerging the materials in a bath of cold liquid, sprayed by cold liquid and the like. 
     The cooling of ceramic component  300  and the formation of internal portion  306  and external portion  302  of ceramic component  300  is a result of the shrinkage and/or contraction of ceramic component  300 . Turning to  FIG. 3F , ceramic component  300  shrinks and/or contracts when cooled after undergoing heating and diffusion processes. The shrinkage and/or contraction of ceramic component  300  is shown with respect to positioning of ceramic atoms  310  and dopant atoms  312 . In a non-limiting example shown in  FIG. 3F , and with comparison to  FIG. 3D , the ceramic atoms  310  and dopant atoms  312  of ceramic component  300  shrink and/or contract from the expanded position during heating and/or diffusion (see,  FIG. 3D ). 
     Ceramic component  300  contracts and/or shrinks a different amount or distance, and/or at a different rate. Specifically, the distinct portions of ceramic component  300 , external portion  302  and internal portion  306 , shrink different amounts or distances and/or at different rates when compared to one another. The shrinkage or contraction amount, distance, and/or rate is dependent on the CTE for each external portion  302  and internal portion  306  of ceramic component  300 . 
     In a non-limiting example shown in  FIG. 3F , internal portion  306  is free of dopant atoms  312  and is completely made up of ceramic atoms  310 . As a result, internal portion  306  has a CTE similar to the ceramic material forming internal portion  306  and ceramic substrate  320  (see,  FIGS. 3A-3D ), discussed herein. With comparison to  FIGS. 3B and 3D , ceramic atoms  310  of internal portion  306  shrink and/or contract back to a substantially similar or identical position within ceramic component  300  as before ceramic substrate  320  was heated (see,  FIG. 3B ). 
     In the non-limiting example shown in  FIG. 3F , external portion  302  includes both ceramic atoms  310  and dopant atoms  312  as a result of the heating and diffusion processes. As previously discussed herein with respect to  FIG. 1C , the diffusion of atoms into external portion  302  of ceramic component  300  forms external portion  302  as a doped-ceramic material. As a result, external portion  302  has a different CTE than the ceramic material forming ceramic substrate  320  and/or internal portion  306  (see,  FIGS. 3A-3D ), discussed herein. The CTE for external portion  302  is different and lower than the CTE of internal portion  306 . The lower CTE for external portion  302  is a result of the CTE for dopant material  322  and dopant atoms  312  diffused into external portion  302  being lower than the CTE of the ceramic material forming internal portion  306  and ceramic atoms  310 . As a result, and with comparison to internal portion  306  of  FIG. 3F , the combination of ceramic atoms  310  and dopant atoms  312  of external portion  302  shrink and/or contract less than the ceramic atoms  310  forming internal portion  306  of ceramic component  300 . 
     Additionally as shown in  FIG. 3F , the shrinkage and/or contraction of the atoms of external portion  302  also varies within external portion  302 . As discussed herein, external portion  302  includes gradient  318  of atoms, where the concentration of dopant atoms  312  and/or ceramic atoms  310  varies. Specifically, the concentration of dopant atoms  312  is highest in portions of external portion  302  formed directly adjacent exterior surface  304  of ceramic component  300 , and the concentration of dopant atoms  312  is lowest in portions of external portion  302  formed directly adjacent internal portion  306 . Because the concentration and/or the presence of dopant atoms  312  within external portion  302  affects the CTE of external portion  302 , the CTE may vary within external portion  302  based on the concentration of dopant atoms  312  formed therein. In a non-limiting example shown in  FIG. 3F , portions of external portion  302  formed directly adjacent exterior surface  304  include high concentrations of dopant atoms  312  and therefore include a lower CTE than portions of external portion  302  formed directly adjacent internal portion  306 , which include low concentrations of dopant atoms  312 . As a result, and as shown in  FIG. 3F , portions of external portion  302  formed directly adjacent exterior surface  304  shrink and/or contract less than portions of external portion  302  formed directly adjacent internal portion  306 . 
     The cooling and the corresponding shrinkage and/or contraction of ceramic component  300  results in the formation of distinct stresses within ceramic component  300 . Specifically, when ceramic component  300  is cooled and previously heated ceramic component  300  shrinks and/or contracts, distinct stresses are formed within and/or are experienced by the various portions (e.g., external portion  302 , internal portion  306 ) of ceramic component  300 . In non-limiting examples, a compressive stress is formed within external portion  302 , and a tensile stress is formed within internal portion  306 . In the non-limiting examples, external portion  302  is under a compressive stress because it shrinks and/or contracts, by comparison, less than internal portion  306 . Additionally, internal portion  306  is under a tensile stress because it shrinks and/or contracts, by comparison, more than external portion  302 . As discussed herein, the amount and/or distance of shrinkage and/or contraction for external portion  302  and internal portion  306  is dependent, at least in part, on the CTE for each portion forming ceramic component  300 . 
     The processes performed on ceramic component  300 , as shown and discussed herein with respect to  FIGS. 3E and 3F , may correspond to operation  208  of the process  200  shown in  FIG. 2 . 
       FIG. 3G  shows finalized ceramic component  300  that is configured to be implemented within an electronic device, as discussed herein. As shown in  FIG. 3G , ceramic component  300  includes external portion  302 , which is under a compressive stress, and internal portion  306 , substantially surrounded by external portion  302 , which is under a tensile stress. Additionally, dopant material  322  (see,  FIG. 3E ) is removed from exterior surface  304  of ceramic component  300  in  FIG. 3G . Dopant material  322  previous applied to exterior surface  304  to form external portion  302  is removed using any suitable material removal technique and/or device. The material removal technique and/or device is dependent on, at least in part, the material composition of dopant material  322  and/or the application technique used to apply dopant material  322  to exterior surface  304  of ceramic component  300 , as discussed herein. In a non-limiting example, dopant material  322  is removed from exterior surface  304  of ceramic component  300  using a polishing process. 
       FIG. 4  depicts another example process for forming a toughened ceramic component. Specifically,  FIG. 4  is a flowchart depicting one example process  400  for forming a toughened ceramic component having a residual compressive stress formed within an external portion to improve physical characteristics (e.g., toughness, brittleness, and so on) of the ceramic component. In some cases, the toughened ceramic component may be utilized in an electronic device, as discussed below with respect to  FIG. 10 . 
     In operation  402 , a ceramic-based preform is formed. The ceramic-based preform is formed as a “green body” preform, which is an unsintered (or partially-sintered) ceramic item. As such, and as discussed herein, the ceramic-based material of the preform is made up of substantially raw material, for example, ceramic powder or bulk material. The ceramic-based preform includes an internal portion formed from a first ceramic-based material having a first coefficient of thermal expansion (CTE) and an external portion substantially surrounding the internal portion. The external portion is formed from a second ceramic-based material having a second CTE lower than the first CTE of the internal portion. The first ceramic-based material forming the internal portion of the preform is an undoped and/or substantially pure ceramic material. The second ceramic-based material forming the external portion of the preform is a doped, ceramic material and/or a ceramic material having additional material particles and/or atoms embedded therein. 
     Dependent on the material composition and/or the material state (e.g., printable material, powder, and so on) of the ceramic-based material, the forming of the preform can be performed in a variety of different manners and/or using a variety of techniques. In a non-limiting example, forming the preform can include a material printing process, where distinct layers of distinct ceramic-based materials are printed on each other. Specifically, an undoped, ceramic material is printed over a first layer of doped ceramic material, and a second layer of doped ceramic material is subsequently printed over and/or around the printed, undoped ceramic material. The second layer of printed, doped ceramic material substantially covers the printed, undoped ceramic material, such that the undoped ceramic material forms the internal portion of the preform, and the combination of the first and second layer of printed, doped ceramic material form the external portion of the preform. 
     In another non-limiting example, the ceramic-based material forming preform includes pre-manufactured sheets and/or rolls of material. In the non-limiting example, the forming of the preform includes performing a material tape-casting process. The tape-casting process used to form the preform includes layering at least one layer of an undoped ceramic material, formed in pre-manufactured sheets and/or rolls, over at least one layer of doped ceramic material, also formed in pre-manufactured sheets and/or rolls. Next, the tape-casting process includes layering at least one distinct layer of doped ceramic material over the undoped ceramic material. The distinct layer of doped ceramic material substantially covers the undoped ceramic material, such that the undoped ceramic material forms the internal portion of the preform, and the doped ceramic material forms the external portion of the preform. 
     In an additional non-limiting example, the ceramic-based material forming the preform includes bulk or powder-based material. In the non-limiting example, the forming of the preform includes layering the powder material and subsequently applying a compressive force to the layered powder material. Specifically, a layer of undoped ceramic material in powder form is positioned over a first layer of the doped ceramic material also in powder form. Next, a second layer of doped ceramic material in powder form is positioned over and/or substantially covers the layer of undoped ceramic material. Finally, a compressive force is applied to the first and second layers of doped ceramic material. The compressive force applied to the first and second layers of doped ceramic material combines and/or amalgamates at least a portion of the first and second layers of doped ceramic material with the undoped ceramic material prior to sintering the preform, as discussed herein. 
     In operation  404 , the preform is sintered. The green body preform formed from raw ceramic-based materials is heated to a predetermined temperature and/or for a predetermined duration to sinter the preform. The predetermined temperature and/or predetermined heating time is dependent on, at least in part, the material composition of the ceramic-based material and the material state (e.g., bulk material, powder, printable material and so on) of the ceramic-based material forming the preform. The preform is heated using any suitable heating process and/or heating system, including, but not limited to, a laser, a flash-lamp, and a furnace or an oven. 
     The preform is sintered to fuse the particles and/or atoms of the ceramic-based material forming the preform. Specifically, when sintering the preform, the particles and/or atoms of the raw material forming the internal portion and the external portion are fused together. Additionally, the particles and/or atoms of the internal portion of the preform are fused to the particles and/or atoms of the external portion of the preform. As a result, the undoped ceramic material forming the internal portion of the preform is fused to the doped ceramic material forming the external portion, and vice versa. 
     The sintering and resulting fusion of the particles and/or atoms of the material forming the preform also results in the formation of a solid-state ceramic component. That is, when the atoms of the material forming internal and exterior portion are fused to one another and each other, the raw material preform formed from ceramic-based materials becomes a solid-state ceramic component. The solid-state ceramic component includes and/or maintains the internal portion and the external portion of the preform. 
     The sintering of the solid-state ceramic component also includes shrinking the ceramic component. Specifically, the sintering of the sintered preform formed from the raw ceramic-based material causes the external portion and the internal portion of the formed ceramic component to shrink. As a result of the different material composition and coefficients of thermal expansion (CTE), each portion of the ceramic component shrinks a different amount or distance and/or at a different rate during the sintering process. As discussed herein, the external portion of the ceramic component is formed from a second ceramic-based material having a lower CTE than the CTE of the first ceramic-based material forming the internal portion. As such, when the ceramic component is sintered, the external portion having the lower CTE shrinks less and/or slower than the internal portion having the higher CTE. 
     In operation  406 , the fused internal portion and external portion are cooled, subsequent to sintering the preform to form the solid-state ceramic component in operation  404 . Cooling the ceramic component can include gradually and/or naturally cooling the ceramic component by removing the ceramic component from the heating system and/or heating device. Alternatively, the ceramic component can be rapidly cooled by removing the ceramic component from the heating system and dunking or submerging the ceramic component into a cold-liquid bath. 
     In a non-limiting example, the distinct portions of the ceramic component continue to shrink in size, until the ceramic component reaches a predetermined temperature. Specifically, external portion and internal portion of the formed ceramic component continue to shrink as the temperature of the ceramic component decreases. When the ceramic component reaches the predetermined, cooled temperature, the external portion and the internal portion may not shrink and/or are in a steady-state of the material. Similar to the sintering process, the amount or distance and/or the rate in which the portions of the ceramic component shrink during the cooling process is dependent on the CTE of each portion. Additionally, the portions of the ceramic component may stop shrinking prior to reaching the predetermined, cooled temperature as a result of the difference in CTE for each portion. As one non-limiting example, external portion can stop shrinking prior to the ceramic component reaching the predetermined, cooled temperature as a result of the external portion having a lower CTE than the internal portion. 
     In another non-limiting example, once the cooling process of operation  406  begins, the shrinking of the ceramic component stops and/or is discontinued. As a result, once the ceramic component is starting to be cooled, the external portion and the internal portion of the ceramic component no longer shrink and/or contract. In the non-limiting example, the shrinking or contracting of the external portion and the internal portion of the ceramic component can be stopped or discontinued near-instantaneously by submerging the ceramic component in a cold-liquid bath to rapidly decrease the temperature of the ceramic component. 
     Cooling the fused internal portion and external portion results in a compressive stress is formed within the external portion of the ceramic component. The compressive stress is formed within the external portion as a result of the lower CTE for the external portion and because the external portion shrinks less than the internal portion of the ceramic component. Specifically, the shrinkage or contraction of the external portion of the ceramic component forms a compressive stress within the external portion of the ceramic component. The compressive stress formed in the external portion of the ceramic component improves the strength of the ceramic component when compared to untreated and/or unprocessed ceramic materials. 
     Although not shown, process  400  for forming a toughened ceramic component can include additional processes. In a non-limiting example, and as discussed herein, the process  400  can also include forming a tensile stress within the internal portion of the ceramic component. Similar to the formation of the compressive stress within the external portion, the tensile stress formed within the internal portion of the ceramic substrate is a result of the cooling of the ceramic component. Specifically, the tensile stress is formed within the internal portion as a result of the higher CTE for the internal portion and because the internal portion shrinks more than the external portion of the ceramic component. Additionally, the tensile stress is formed within the internal portion as a result of the external portion shrinking around the internal portion and/or a compressive stress being formed within the external portion, which substantially surrounds the internal portion. 
     In other non-limiting examples, the process  400  can include performing various material finishing processes on the ceramic component after forming the compressive stress in the external portion as discussed with respect to operation  406 . In non-limiting examples, the ceramic component can undergo cutting, grinding, shaping, and/or polishing processes subsequent to forming the compressive stress in the external portion of the ceramic component. 
       FIGS. 5A-5E  show side and enlarged cross-section views of a ceramic substrate  320  undergoing the example process  400  for forming a toughened ceramic component  500  (see,  FIG. 5E ) as discussed herein with respect to  FIG. 4 . It is understood that similarly numbered and/or named components may function in a substantially similar fashion. Redundant explanation of these components has been omitted for clarity. 
       FIG. 5A  shows a side cross-section view of a portion of a ceramic-based preform  526  (hereafter, “preform  526 ”). Preform  526  is a “green body” preform, which is an unsintered ceramic item. The ceramic-based material of preform  526  is made up of substantially raw material, as discussed herein. As shown in  FIG. 5A , preform  526  includes internal portion  506  and external portion  502  positioned adjacent internal portion  506 . Preform  526  can include external portion  502  positioned on opposite sides of internal portion  506 , as shown in  FIG. 5A , or alternatively, can be formed to external portion  502  substantially surrounding internal portion  506 , as discussed herein. 
     Both internal portion  506  and external portion  502  are formed from ceramic-based materials. As shown in  FIG. 5A , the ceramic-based materials forming external portion  502  are distinct from the ceramic-based materials forming internal portion  506 . A first ceramic-based material  528  is used to form internal portion  506 . First ceramic-based material  528  is an undoped and/or substantially pure ceramic material, similar to the ceramic materials discussed herein, such as zirconia or alumina. A second ceramic-based material  530  is used to form external portion  502 . Second ceramic-based material  530  is a doped ceramic material or a ceramic material including additional material, such as a dopant material, embedded therein. In a non-limiting example, second ceramic-based material  530  forming external portion  502  is formed from yttrium-doped zirconia, or zirconium(IV) oxide-yttria. In addition to being compositionally distinct (e.g., doped), second ceramic-based material  530  also has a distinct coefficient of thermal expansion (CTE) than first ceramic-based material  528 . Specifically, the CTE for second ceramic-based material  530  is lower than the CTE for the first ceramic-based material  528 . As discussed herein, the CTE of second ceramic-based material  530  is lower than the CTE of first ceramic-based material  528  because second ceramic-based material  530  includes both ceramic material and dopant material, as discussed herein. 
     Preform  526  can be formed using a variety of techniques. The techniques used to form preform  526  are dependent on, at least in part, the material composition and/or material state (e.g., printable material, bulk material, powder, and so on) of first ceramic-based material  528  and second ceramic-based material  530 . 
     In a non-limiting example, preform  526  can be formed using a printing process. When forming preform  526  using the printing process, distinct layers of distinct ceramic-based materials, such as first and second ceramic-based material  528 ,  530 , are printed on and/or over each other. In the non-limiting example, a layer of undoped, first ceramic-based material  528  is printed over a first layer of doped, second ceramic-based material  530 . Additionally, a second layer of doped, second ceramic-based material  530  is printed over, around and/or substantially covers the printed layer of the undoped, first ceramic-based material  528 . Although the portion of preform  526  shown in  FIG. 5A  only shows doped, second ceramic-based material  530  forming a top portion and bottom portion, it is understood that the second printed layer of doped, ceramic-based material  530  substantially covers all exposed sides of the layer of undoped, first ceramic-based material  528  and contacts the first layer of doped, second ceramic-based material  530 . As such, and as similarly shown in  FIG. 1B , the layer of printed undoped, first ceramic-based material  528  forms the internal portion  506  of preform  526 , and the combination of the first and second printed layer of doped, second ceramic-based material  530  forms external portion  502  of preform  526 . 
     In another non-limiting example, preform  526  can be formed using a tape-casting process. The tape-casting process includes layering and/or stacking pre-manufactured sheets and/or rolls of ceramic-based materials, such as first and second ceramic-based material  528 ,  530 , on and/or over each other. In the non-limiting example, a layer of undoped, first ceramic-based material  528  is layered or cast over a first layer of doped, second ceramic-based material  530 . Additionally, a second layer of doped, second ceramic-based material  530  is layered or cast over, around and/or substantially covers the cast layer of the undoped, first ceramic-based material  528 . Similar to the non-limiting printing process discussed above, and as similarly shown in  FIG. 1B , the layer of cast undoped, first ceramic-based material  528  forms the internal portion  506  of preform  526 , and the combination of the first and second cast layer of doped, second ceramic-based material  530  forms external portion  502  of preform  526 . 
     In a further non-limiting example, preform  526  can be formed by stacking layers of bulk or powdered ceramic-based material and subsequently applying a compressive force. The ceramic-based materials, such as first and second ceramic-based material  528 ,  530 , are in bulk material and/or powder form. In the non-limiting example, forming preform  526  from bulk material and/or powder-form ceramic-based material includes positioning a layer of powder-form undoped, first ceramic-based material  528  over a first layer of powder-form doped, second ceramic-based material  530 . Next, a second layer of powder-form doped, second ceramic-based material  530  is positioned over the layer of powder-form undoped, first ceramic-based material  528 . Once the second layer of powder-form doped, second ceramic-based material  520  is positioned over first ceramic-based material  528 , a compressive force (F) is applied to the first and second layer of doped, second ceramic-based material  530 . As shown in  FIG. 5A , the compressive force (F) is applied to both sides of preform  526  adjacent first and second layer of doped, second ceramic-based material  530  and is applied in a direction toward powder-form undoped, first ceramic based material  528 . Applying the compressive force (F) combines the distinct powder-form ceramic-based materials to reduce the separation between each of the powders forming the distinct layers of preform  526 . That is, the applied compressive force (F) combines and/or amalgamates at least a portion of the first and second layers of doped, second ceramic-based material  530  with the undoped, first ceramic-based material  528  prior to sintering preform  526 , as discussed herein. The layer of powder-form undoped, first ceramic-based material  528  forms the internal portion  506  of preform  526 , and the combination of the first and second layer of powder-form doped, second ceramic-based material  530  forms external portion  502  of preform  526 . 
     Although single layers of ceramic-based materials  528 ,  530  are shown in  FIG. 5A , it is understood that multiple layers of ceramic-based materials  528 ,  530  may be used to form the various layers and/or portions of preform  526 . That is, internal portion  506  of preform  526  can be formed from a single layer or multiple layers of undoped, first ceramic-based material  528 . Additionally, external portion  502  of preform  526  can be formed from a single layer or multiple layers of doped, second ceramic-based material  530 . 
       FIG. 5B  shows an enlarged portion of preform  526 , as depicted in  FIG. 5A . As shown in  FIG. 5B , and discussed herein, preform  526  is depicted to include atoms, which represent the particles of matter that make up the material of preform  526 . Additionally as discussed herein, preform  526  is a green body, and therefore the ceramic-based material  528 ,  530  forming preform  526  and respective atoms of the ceramic-based material is unsintered. The atoms of ceramic-based material  528 ,  530  are shown in  FIG. 5B  as unsintered using a distinct hash-mark pattern when compared to  FIG. 1C , which depicts sintered ceramic atoms. 
     In the non-limiting example, internal portion  506  is formed from undoped, first ceramic-based material  528 . As shown in  FIG. 5B , and discussed herein, because first ceramic-based material  528  is undoped, internal portion  506  formed from first ceramic-based material  528  is free of dopant atoms  512  of a dopant material. Rather, undoped, first ceramic-based material  528  forming internal portion  506  includes only ceramic atoms  510 . As such, undoped, first ceramic-based material  528  forming internal portion  506  is a pure ceramic material, similar to those ceramic materials discussed herein (e.g., zirconia, alumina, and so on). 
     Also shown in  FIG. 5B , external portion  502  is formed from doped, second ceramic-based material  530 . In the non-limiting example, and discussed herein, second ceramic-based material  530  is doped, and as such, external portion  502  formed from second ceramic-based material  530  includes both dopant atoms  512  of a dopant material and ceramic atoms  510 . The dopant material and/or dopant atoms  512  included within doped, second ceramic-based material  530  forming external portion  502  includes any of the suitable dopant materials discussed herein (e.g., yttrium, silicon, and so on). As such, doped, second ceramic-based material  530  forming external portion  502  is a doped-ceramic material, similar to that ceramic material discussed herein (e.g., zirconium(IV) oxide-yttria). 
     The processes performed to form preform  526 , as shown and discussed herein with respect to  FIGS. 5A and 5B , may correspond to operation  402  of the process  400  shown in  FIG. 4 . 
       FIG. 5C  shows a heating device  524  positioned adjacent preform  526 . Specifically, heating device  524  and preform  526  including internal portion  506  formed from undoped, first ceramic-based material  528  and external portion  502  formed from doped, second ceramic based material  530  are positioned adjacent and/or proximate one another, such that heating device  524  can provide heat (H) to preform  526 . The heat (H) provided to preform  526  by heating device  524  sinters preform  526 . In a non-limiting example, heating device  524  heats preform  526  to a predetermined temperature to sinter preform  526  and transform green body preform  526  into a fully sintered ceramic component  500  (see,  FIGS. 5E and 5F ). Heating device  524  is configured as any suitable heating component or system that is configured to heat preform  526  to the predetermined sintering temperature for preform  526 . 
     Turning to  FIG. 5D , the effects of heating and/or sintering preform  526  are more clearly shown. The non-limiting example shown in  FIG. 5D , shows or depicts preform  526  partially sintered by heating device  524 , as discussed herein. In response to heating or sintering preform  526 , the ceramic-based material forming preform  526  begins to shrink or contract. Specifically, undoped, first ceramic-based material  528  forming internal portion  506  and doped, second ceramic based material  530  forming external portion  502  begin to shrink and/or contract when exposed to the heat from heating device  524  to sinter preform  526 . As shown in  FIG. 5D , and with comparison to  FIG. 5B , external portion  502  formed from doped, second ceramic based material  530  shrinks or contracts when preform  526  is sintered. In the non-limiting example, exterior surface  504  of external portion  502  is positioned below the pre-sintered position  532   a  of exterior surface  504  (see,  FIG. 5B ) prior to preform  526  being sintered. 
     Although both internal portion  506  and external portion  502  of preform  526  shrink or contract during sintering, each portion of preform  526  shrinks and/or contracts different amounts or distances and/or at different rates. As shown in  FIG. 5D , and with comparison to  FIG. 5B , undoped, first ceramic-based material  528  forming internal portion  506  shrinks a greater amount and/or at a greater rate than doped, second ceramic-based material  530  forming external portion  502 . Internal portion  506  of preform  526  shrinks and/or contracts a greater amount or distance than external portion  502  because of the difference in the CTE for the materials forming each portion. In the non-limiting example, internal portion  506  is formed from undoped, first ceramic-based material  528 , which has a higher CTE than the CTE for doped, second ceramic-based material  530  forming external portion  502 . As a result, when preform  526  is sintered, internal portion  506  shrinks and/or contracts a greater amount or distance and/or at a greater rate than external portion  502  having a CTE lower than the CTE for internal portion  506 . 
     Additionally, because undoped, first ceramic-based material  528  forming internal portion  506  has a higher CTE than the CTE for doped, second ceramic-based material  530  forming external portion  502 , internal portion  506  of preform  526  sinters before external portion  502 . That is, undoped, first ceramic-based material  528  made up of ceramic atoms  510  sinter at lower temperatures and/or at a faster rate than doped, second ceramic-based material  530  formed from ceramic atoms  510  and dopant atoms  512 , respectively. As shown in  FIG. 5D , and with comparison to  FIG. 5B , ceramic atoms  510  forming undoped, first ceramic-based material  528  are shown as sintered and do not include hash-markings previously corresponding to unsintered ceramic atoms  510  (see,  FIG. 5B ). Ceramic atoms  510  forming undoped, first ceramic-based material  528  of internal portion  506  are depicted in  FIG. 5D  as ceramic atoms  510  that are sintered, similar to those discussed herein with respect to  FIG. 1C . 
     As shown in  FIG. 5D , and with comparison to ceramic atoms  510  of undoped, first ceramic-based material  528  forming internal portion  506 , ceramic atoms  510  of doped, second ceramic-based material  530  forming external portion  502  remain unsintered (see,  FIG. 5B ). Ceramic atoms  510  of doped, second ceramic-based material  530  forming external portion  502  are unsintered as a result of the lower CTE for doped, second ceramic-based material  530 , and/or because of operational parameters and/or specifics of the sintering process performed on preform  526 . In non-limiting examples where preform  526  is partially sintered, ceramic atoms  510  of doped, second ceramic-based material  530  forming external portion  502  remain unsintered as a result of the temperature of preform  526  not yet reaching the predetermined temperature to sinter doped, second ceramic-based material  530  and/or preform  526  not being exposed to heating device  524  for a long enough duration to sinter doped, second ceramic-based material  530 . 
     The processes performed on preform  526  as shown and discussed herein with respect to  FIGS. 5C and 5D , may correspond to operation  404  of the process  400  shown in  FIG. 4 . 
       FIG. 5E  shows preform  526  (see,  FIG. 5C ) subsequent to being completely sintered and/or cooled. Specifically, preform  526  is heated to the predetermined sintering temperature, such that internal portion  506  and external portion  502  are sintered. Subsequent to sintering preform  526 , ceramic-based preform  526  is cooled. The cooling of preform  526  results in the formation of ceramic component  500 . In a non-limiting example shown in  FIG. 5E , when preform  526  is cooled, ceramic component  500  is formed including internal portion  506  and external portion  502  substantially surrounding internal portion  506 . As such,  FIGS. 5E and 5F  refer to previously discussed preform  526  as ceramic component  500 . 
     Ceramic component  500  is cooled down to a predetermined temperature, for example room temperature. In non-limiting examples discussed herein, ceramic component  500  including internal portion  506  and external portion  502  is cooled naturally or organically by removing heat supplied by heating device  524  (see,  FIG. 5C ), or alternatively, is rapidly cooled by submerging the ceramic component  500  in a bath of cold liquid. 
     Turning to  FIG. 5F , the effects of completely sintering preform  526  (see,  FIGS. 5C and 5D ) and subsequently cooling formed ceramic component  500  are more clearly shown. As shown in  FIG. 5F , and with comparison to  FIG. 5D , all material forming ceramic component  500  is sintered. Specifically, ceramic atoms  510  of doped, second ceramic-based material  530  forming external portion  502  are shown or depicted as being sintered and no longer have similar hash-markings to unsintered ceramic atoms  510  (see,  FIGS. 5B and 5D ). As a result, preform  526  is fully and completely sintered and forms ceramic component  500  having sintered internal portion  506  and sintered external portion  502 . 
     Although shown herein to have a single hash-mark pattern, it is understood that dopant atoms  512  are sintered similar to ceramic atoms  510 . That is, although the hash-mark pattern for dopant atoms  512  does not change like ceramic atoms  510 , it is understood that dopant atoms  512  may also be transformed from unsintered to sintered atoms like ceramic atoms  510 , as discussed herein. In a non-limiting example, dopant atoms  512  are sintered simultaneous to ceramic atoms  510  in doped, ceramic-based materials such as doped, second ceramic-based material  530  forming external portion  502 . As such, when ceramic atoms  510  are described as being sintered, it is understood that dopant atoms  512  are also sintered, and therefore doped, second ceramic-based material  530 , including both dopant atoms  512  and ceramic atoms  510 , is completely sintered. 
     The sintering and subsequent cooling of ceramic component  500  results in further shrinkage and/or contraction of ceramic component  500 . As shown in  FIG. 5F , ceramic component  500  shrinks and/or contracts a greater amount when completely sintered and/or cooled. With comparison to  FIGS. 5B and 5D , the various atoms  510 ,  512  forming undoped, first ceramic-based material  528  and doped, second ceramic-based material  530  continue to shrink and/or contract from the unsintered state (see,  FIG. 5B ) of preform  526  and the partially sintered state (see,  FIG. 5D ) of preform  526 . In the non-limiting example shown in  FIG. 5F , exterior surface  504  of external portion  502  is positioned below the pre-sintered position  532   a  of exterior surface  504  (see,  FIG. 5B ) prior to preform  526  undergoing a sintering process. Exterior surface  504  of external portion  502  is also positioned below the partially-sintered position  532   b  of exterior surface  504  (see,  FIG. 5D ) prior to preform  526  being completely sintered. 
     In a non-limiting example, and as similarly discussed herein with respect to the sintering process shown in  FIG. 5D , ceramic component  500  contracts and/or shrinks a different amount or distance, and/or at a different rate during the cooling process. Specifically, the distinct portions of ceramic component  500 , external portion  502  and internal portion  506 , shrink different amounts or distances and/or at different rates when ceramic component  500  undergoes the cooling process and is cooled to a predetermined, cooled temperature. When ceramic component  500  reaches the predetermined, cooled temperature, external portion  502  and internal portion  506  do not shrink and/or are in a steady-state. Similar to the sintering process, the amount or distance, and/or the rate in which the portions of ceramic component  500  shrink during the cooling process is dependent on the CTE of each portion. In the non-limiting example, internal portion  506  formed from undoped, first ceramic-based material  528  has a higher CTE than the CTE for external portion  502  formed from doped, second ceramic-based material  530 . As a result, and as shown in  FIG. 5F , undoped, ceramic-based material  528  forming internal portion  506  shrinks a greater amount and/or at a faster rate than doped, second ceramic-based material  530  forming external portion  502  during the cooling process. 
     Additionally, and similarly dependent on the difference in the CTE between internal portion  506  and external portion  502  of ceramic component  500 , the portions of ceramic component  500  may stop shrinking or contracting prior to reaching the predetermined, cooled temperature during the cooling process. In a non-limiting example, external portion  502  formed from doped, second ceramic-based material  530  stops shrinking prior to ceramic component  500  reaching the predetermined, cooled temperature. External portion  502  may also stop shrinking and/or contracting while internal portion  506  formed from undoped, first ceramic-based material  528  continues to shrink or contract during the cooling process. The distinction between when external portion  502  and internal portion  506  of ceramic component  500  stop shrinking and/or contracting during the cooling process is a result of external portion  502  having a lower CTE than internal portion  506 . 
     In another non-limiting example, once the cooling process of ceramic component  500  begins, the shrinking of the ceramic component  500  stops and/or is discontinued. As a result, once ceramic component  500  is starting to be cooled, external portion  502  and internal portion  506  of ceramic component  500  no longer shrink and/or contract. In the non-limiting example, the shrinking or contracting of external portion  502  and internal portion  506  can be stopped or discontinued near-instantaneously by submerging ceramic component  500  in a cold-liquid bath to rapidly decrease the temperature of ceramic component  500  to the predetermined, cooled temperature discussed herein. 
     The sintering, cooling and the corresponding shrinkage and/or contraction of ceramic component  500  also results in the formation of distinct stresses within ceramic component  500 . Specifically, when sintered ceramic component  500  is cooled and ceramic component  500  shrinks and/or contracts, distinct stresses are formed within and/or experienced by the various portions (e.g., external portion  502 , internal portion  506 ) of ceramic component  500 . In non-limiting examples, and as discussed herein, a compressive stress is formed within external portion  502 , and a tensile stress is formed within internal portion  506 . 
     The processes performed on preform  526 , as shown and discussed herein with respect to  FIGS. 5E and 5F , may correspond to operations  404  and  406  of the process  400  shown in  FIG. 4 . 
       FIG. 6  depicts an additional example process for forming a toughened ceramic component. Specifically,  FIG. 6  is a flowchart depicting one example process  600  for forming a toughened ceramic component having a residual compressive stress formed within an external portion to improve physical characteristics (e.g., toughness, brittleness, and so on) of the ceramic component. In some cases, the toughened ceramic component may be utilized in an electronic device, as discussed below with respect to  FIG. 10 . 
     In operation  602 , thermal expansion characteristics of an external portion of a ceramic preform are altered. The thermal expansion characteristics of the external portion of the ceramic preform are altered such that they are different or distinct from the thermal expansion characteristics for an internal portion of the ceramic preform substantially surrounded by the external portion. The thermal expansion characteristics of an external portion of a ceramic preform include a coefficient of thermal expansion (CTE), a sintering temperature, and/or a sintering rate. 
     In a non-limiting example, altering the thermal expansion characteristics of the external portion of the ceramic preform includes forming the external portion and the internal portion from a bulk ceramic material, such that ceramic preform is a green body ceramic item, similarly discussed herein with respect to  FIGS. 4-5F . In the non-limiting example where the ceramic preform is formed from a bulk ceramic material, the external portion is formed from a ceramic material having a first grain of a first size, and the internal portion is formed from the ceramic material having a second grain of a second size. The second grain of the ceramic material forming the internal portion of the ceramic preform is larger than the first grain of the ceramic material forming the internal portion. The ceramic material forming each of the internal portion and the external portion are materially and/or compositionally identical, except for the difference in the grain size of the material forming each portion of the ceramic component. 
     Although compositionally identical and/or formed from the same ceramic material, the grain size of the material used to form each portion of the ceramic preform alters the thermal expansion characteristics for the internal portion and/or the external portion of the ceramic preform. Additionally, because the grain size of the ceramic material forming the external portion of the ceramic preform is smaller than the grain size of the ceramic material forming the internal portion, the thermal expansion characteristics for the external portion are distinct and/or different than the thermal expansion characteristics for the internal portion. In a non-limiting example, the smaller grain size of the ceramic material forming the external portion alters, varies and/or increases the coefficient of thermal expansion (CTE) of the external portion when compared to the CTE of the internal portion. As a result, although formed from compositionally the same material, the external portion has a higher CTE than the CTE of the internal portion because of the smaller grain size of the ceramic material forming the external portion. As discussed herein, the external portion shrinks and/or contracts a greater amount than the internal portion during a sintering process as a result of the external portion having a higher CTE. 
     In another non-limiting example, the smaller grain size of the ceramic material forming the external portion of the ceramic preform alters, varies and/or decreases the sintering temperature for the external portion when compared to the sintering temperature of the internal portion. As similarly discussed herein, although formed from compositionally the same material, the external portion has a lower sintering temperature than the sintering temperature for the internal portion because of the smaller grain size of the ceramic material forming the external portion. As a result, and as discussed herein, the external portion shrinks and/or contracts sooner and/or a greater amount than the internal portion during a sintering process as a result of the external portion having a lower sintering temperature than the internal portion. 
     In a further non-limiting example, the smaller grain size of the ceramic material forming the external portion alters, varies and/or increases the sintering rate for the external portion. As a result of the external portion having the higher sintering rate than a sintering rate of the internal portion, the external portion shrinks and/or contracts sooner, more and/or at a greater rate than the internal portion during a sintering process, as discussed herein. 
     Although discussed herein as distinct non-limiting examples, it is understood that the thermal expansion characteristics (e.g., CTE, sintering temperature, and sintering rate) discussed herein are not mutually exclusive. That is, altering one non-limiting example of the thermal expansion characteristics of the external portion to be distinct from the thermal expansion characteristics of the internal portion can also result in the altering of another non-limiting example thermal expansion characteristic. For example, the altering and/or increasing of the CTE for the external portion of the ceramic preform may also lower the sintering temperature and/or increase the sintering rate for the external portion. 
     In operation  604 , the ceramic preform is sintered. The green body ceramic preform including the internal portion and the external portion formed from a ceramic material is heated to sinter the ceramic preform. The sintering of ceramic preform includes heating the ceramic preform to a first sintering temperature and sintering the external portion of the ceramic preform formed from the ceramic material having the first grain smaller than the second grain of the ceramic material forming internal portion. The first sintering temperature corresponds to a predetermined sintering temperature for the altered thermal expansion characteristics of the external portion of the ceramic preform. As discussed herein, the altering of the thermal expansion characteristics of the external portion of the ceramic preform can include increasing the CTE for the external portion, decreasing the sintering temperature, and/or increasing the sintering rate for the external portion. In a non-limiting example, when the ceramic preform is heated to the first sintering temperature and the external portion of the ceramic preform is sintered, the internal portion of the ceramic preform can remain unaffected, unsintered and/or in a green body state. 
     The sintering of the ceramic preform can also include heating the ceramic preform to a second sintering temperature greater than the first sintering temperature and sintering the internal portion of the ceramic preform formed from the ceramic material having the second grain. The second sintering temperature is greater than the first sintering temperature. In addition to sintering the internal portion, heating the ceramic preform to the second sintering temperature greater than the first sintering temperature also results in the continued sintering of the external portion of the ceramic preform. As discussed herein, the preform is heated using any suitable heating process and/or heating system including, but not limited to, a laser, a flash-lamp, and a furnace or an oven. 
     The sintering of the ceramic preform also includes shrinking and/or contracting of the external portion and the internal portion of the ceramic preform. However, because of the altered and/or distinct thermal expansion characteristics between the external portion and the internal portion of the ceramic preform, the portions of the ceramic preform sinter at different temperatures and/or different rates and, therefore, shrink and/or contract at different amounts or distances and/or at different rates. As discussed herein, heating the ceramic preform to the first sintering temperature and sintering the external portion formed from the ceramic material having the first grain smaller than the second grain of the internal portion also results in the shrinkage and/or contraction of the external portion. While the external portion shrinks and/or contracts, the internal portion of the ceramic preform can remain unaffected, unsintered and/or does not contract. Only when the ceramic component is heated to the second sintering temperature does the internal portion of the ceramic preform sinter and, therefore, shrink or contract. Additionally, because of the distinction or differences in the grain sizes of the ceramic material forming the external portion and the internal portion and the altering of the thermal expansion characteristics of the external portion, the external portion shrinks and/or contracts a greater distance than the internal portion of the ceramic preform. 
     As similarly discussed herein with respect to operation  404  in process  400 , the ceramic preform is sintered to fuse the particles and/or atoms of the ceramic material forming the ceramic material. Specifically, the particles and/or atoms of the internal portion of the ceramic preform are fused to each other and to the particles and/or atoms of the external portion of the ceramic preform. Additionally as discussed herein, the sintering and resulting fusion of the particles and/or atoms of the ceramic material forming the ceramic preform also results in the formation of a solid-state ceramic component. The solid-state ceramic component includes and/or maintains the internal portion and the external portion of the ceramic preform. 
     In operation  606 , the sintered ceramic preform including the fused internal portion and external portion are cooled. That is, subsequent to sintering the ceramic preform to form the solid-state ceramic component in operation  604 , the ceramic component, including fused internal and external portions, is cooled. The ceramic component, including the external portion and the internal portion, is cooled to lower the temperature of the ceramic component. As similarly discussed herein with respect to operation  406  of process  400  (see,  FIG. 4 ), cooling the ceramic component can include gradually and/or naturally cooling the ceramic component, or alternatively, rapidly cooling the ceramic component. 
     Additionally, and as discussed herein with respect to operation  406 , the distinct portions of the ceramic component continue to shrink in size, until the ceramic component reaches a predetermined, cooled temperature. Specifically, external portion and internal portion of the formed ceramic component continue to shrink as the temperature of the ceramic component decreases. Similar to the sintering process, the amount or distance, and/or the rate in which the portions of the ceramic component shrink during the cooling process is dependent on the thermal expansion characteristics of each portion. Additionally, the portions of the ceramic component may stop shrinking prior to reaching the predetermined, cooled temperature as a result of the difference in thermal expansion characteristics for each portion. In a non-limiting example, internal portion can stop shrinking prior to the ceramic component reaching the predetermined, cooled temperature as a result of the internal portion having larger grain sizes than the external portion, resulting in a lower CTE, a higher sintering temperature and/or a lower sintering rate than the external portion. 
     In another non-limiting example, once the cooling process of operation  606  begins, the shrinking of the ceramic component stops and/or is discontinued. As a result, once the ceramic component is starting to be cooled, the external portion and the internal portion of the ceramic component no longer shrink and/or contract. 
     In operation  608 , a compressive stress is formed within the external portion of the ceramic component. The compressive stress is formed within the external portion as a result of the external portion shrinking and/or contracting more than the internal portion of the ceramic component as a result of the distinction or difference in the grain sizes of the ceramic material forming each portion and/or the thermal expansion characteristics of each portion of the ceramic component. The compressive stress formed in the external portion of the ceramic component improves the strength, toughness, brittleness and/or improves protection against damage to the ceramic component, as well as mitigates and/or prevents the spreading of surface defects within the ceramic preform, as discussed herein. 
     Although not shown, process  600  for forming a toughened ceramic component can include additional processes. In a non-limiting example, and as similarly discussed herein, the process  600  can also include forming a tensile stress within the internal portion of the ceramic component. The tensile stress is formed within the internal portion as a result of the external portion shrinking around the internal portion and/or a compressive stress being formed within the external portion, which substantially surrounds the internal portion. 
       FIGS. 7A-7F  show side and enlarged cross-section views, respectively, of a ceramic preform  726  undergoing the example process  600  for forming a toughened ceramic component  700  (see,  FIG. 7F ) as discussed herein with respect to  FIG. 6 . It is understood that similarly numbered and/or named components may function in a substantially similar fashion. Redundant explanation of these components has been omitted for clarity. 
       FIG. 7A  shows a side cross-section view of a portion of a ceramic material preform  726  (hereafter, “preform  726 ”). Preform  726  is a “green body” preform, made up of substantially raw material, as discussed herein. 
     As shown in  FIG. 7A , preform  726  includes internal portion  706  and external portion  702  substantially surrounding internal portion  706 . However, distinct from the ceramic substrates and preforms discussed previously (see,  FIGS. 3A-3G and 5A-5F ), both internal portion  706  and external portion  702  of preform  726  are formed from the same ceramic material  734 . Ceramic material  734  is materially and/or compositionally similar or identical in both internal portion  706  and external portion  702 . As shown in  FIG. 7A , internal portion  706  and external portion  702  are separated by a phantom reference line for ease of differentiating the portions, and the distinction between internal portion  706  and external portion  702  of preform  726  is discussed in detail below with respect to  FIG. 7B . Ceramic material  734  forming the entire preform  726  can be a substantially pure ceramic material, similar to the ceramic materials discussed herein, such as zirconia or alumina. Preform  726  can be formed using a variety of techniques similarly discussed herein with respect to the preform of  FIG. 5A . 
       FIG. 7B  shows an enlarged portion of preform  726 , as depicted in  FIG. 7A . As shown in  FIG. 7B , green body preform  726  is depicted to include unsintered material grains or crystals of ceramic material  734  forming preform  726 . Although depicted as being similar to the atoms and/or atoms discussed herein with respect to  FIGS. 1C, 3A-3G and 5A-5F , ceramic material  734  shown in  FIGS. 7B, 7D and 7E , depicts material grains or crystals of ceramic material  734  and how the grains are affected when forming the toughened ceramic component  700 , as discussed herein. 
     Although materially and/or compositionally identical by being formed from ceramic material  734 , external portion  702  is distinct from internal portion  706 . That is, external portion  702  includes altered thermal expansion characteristics that are distinct and/or different from internal portion  706  of preform  726 , even though both external portion  702  and internal portion  706  are formed from ceramic material  734 . The altering of the thermal expansion characteristics of external portion  702  is a result of forming external portion  702  and internal portion  706  from material grains  736 ,  738  of ceramic material  734  having distinct sizes. As shown in  FIG. 7B , external portion  702  is formed from ceramic material  734  having first material grain  736  of a first size, and internal portion  706  is formed from compositionally the same ceramic material  734  having second material grain  738  of a second size. Second grain  738  of ceramic material  734  forming internal portion  706  has a larger grain size than first grain  736  of ceramic material  734  forming external portion  702 . 
     As discussed herein, by forming external portion  702  from ceramic material  734  having first grain  736  smaller than second grain  738  of internal portion  706 , thermal expansion characteristics of external portion  702  are altered and/or distinct from thermal expansion characteristics of internal portion  706 . In a non-limiting example, external portion  702  formed from smaller, first grain  736  has a higher coefficient of thermal expansion (CTE) than the CTE for internal portion formed from larger, second grain  738 . In other non-limiting examples, external portion  702  has a lower sintering temperature and/or a higher sintering rate than the sintering temperature and/or rate of internal portion  706  of preform  726 . As discussed herein, the distinction and/or difference of the thermal expansion characteristics between external portion  702  and internal portion  706  of preform  726  affects the formation of toughened ceramic component  700  (see,  FIG. 7F ), discussed herein. 
     The processes performed to form preform  726  as shown and discussed herein with respect to  FIGS. 7A and 7B , may correspond to operation  602  of the process  600  shown in  FIG. 6 . 
       FIG. 7C  shows a heating device  724  positioned adjacent preform  726 . Specifically, preform  726 , including internal portion  706  formed from ceramic material  734  having first grain  736  (see,  FIGS. 7D and 7E ) and external portion  702  formed from ceramic material  734  having second grain  736 , is positioned adjacent and/or proximate heating device  724 , such that heating device  724  can provide heat (H) to preform  726 . The heat (H) provided to preform  726  by heating device  724  sinters preform  726 , as similarly discussed herein with respect to  FIG. 5C . As discussed in detail herein, heating device  724  can heat preform  726  to a first sintering temperature for sintering external portion  702  of preform  726  (see,  FIG. 7D ) and can heat preform  726  to a second sintering temperature for sintering internal portion  706  (see,  FIG. 7E ). 
     Turning to  FIGS. 7D and 7E , the effects of heating and/or sintering preform  726  are more clearly shown. The non-limiting example shown in  FIG. 7D  shows or depicts preform  726  heated to a first sintering temperature and/or partially sintered. In response to heating preform  726  to the first sintering temperature, external portion  702  of preform  726  is sintered. As shown in  FIG. 7D , and with comparison to  FIG. 7B , first grain  736  of ceramic material  734  forming external portion  702  is sintered (e.g., no hash-markings) when preform  726  is heated to the first sintering temperature. Additionally shown in  FIG. 7D , second grain  738  of ceramic material  734  forming internal portion  706  remains unsintered. 
     Heating preform  726  to the first sintering temperature, as shown in  FIG. 7D , also results in external portion  702  beginning to shrink or contract. Specifically, ceramic material  734  forming external portion  702  begins to shrink and/or contract when heating device  724  heats preform  726  to the first sintering temperature to sinter external portion  702 . As shown in  FIG. 7D , and with comparison to  FIG. 7B , external portion  702  shrinks or contracts when preform  726  is heated to the first sintering temperature. In the non-limiting example, exterior surface  704  of external portion  702  is positioned below the pre-sintered position  732   a  of exterior surface  704  (see,  FIG. 7B ) prior to preform  726  being heated, as shown in  FIG. 7D . Distinct from external portion  702 , and as shown in  FIG. 7D , ceramic material  734  forming internal portion  706  remains in a steady-state and/or does not shrink or contract when preform is heated to the first sintering temperature. 
     The sintering and/or shrinkage of external portion  702  of preform  726  is dependent on the altered thermal expansion characteristics of external portion  702 . As discussed herein, external portion  702  includes different or distinct thermal expansion characteristics when compared to internal portion  706  as a result of the portions of preform  726  being formed from the same ceramic material  734 , but with distinct material grain sizes for each portion. Specifically, thermal expansion characteristics are distinct between internal portion  706  and external portion  702  as a result of external portion  702  being formed from ceramic material  734  having first grain  736  that is smaller than second grain  738  of ceramic material  734  forming internal portion  706 . In non-limiting examples discussed herein, forming external portion  702  from ceramic material  734  having first grain  736  increases the CTE, lowers the sintering temperature and/or increases the sintering rate. As such, and as described above with respect to  FIG. 7D , external portion  702  sinters and/or shrinks or contracts at a first sintering temperature, while internal portion  706  remains in a steady-state and does not sinter and/or shrink or contract. 
     The non-limiting example shown in  FIG. 7E , shows or depicts preform  726  heated to a second sintering temperature and/or completely sintered. The second sintering temperature is higher or greater than the first sintering temperature discussed herein with respect to  FIG. 7D . In response to heating preform  726  to the second sintering temperature, internal portion  706  of preform  726  is now sintered. As shown in  FIG. 7E , and with comparison to  FIGS. 7B and 7D , second grain  738  of ceramic material  734  forming internal portion  706  is sintered (e.g., no hash-markings) when preform  726  is heated to the second sintering temperature. Ceramic material  734  forming external portion  702  remains sintered when preform  726  is heated to the second sintering temperature, as discussed herein with respect to  FIG. 7D . As a result of heating preform  726  to the first sintering temperature (see,  FIG. 7D ) and subsequently heating preform  726  to the second sintering temperature (see,  FIG. 7E ), preform  726  is completely sintered. 
     Heating preform  726  to the second sintering temperature, as shown in  FIG. 7E , results in internal portion  706  beginning to shrink or contract. Specifically, and similar to external portion  702  discussed with respect to  FIG. 7D , ceramic material  734  forming internal portion  706  begins to shrink and/or contract when heating device  724  heats preform  726  to the second sintering temperature to sinter internal portion  706 . Internal portion  706  shrinks or contracts less than external portion  702  when preform  726  is heated to the second sintering temperature to completely sinter preform  726 . As shown in  FIG. 7E , and with comparison to  FIGS. 7B and 7D , second grain  738  of ceramic material  734  forming internal portion  706  shrinks or contracts an amount or distance less that the amount or distance of shrinkage achieved by first grain  736  of ceramic material  734  forming external portion  702 . As discussed herein, the amount or distance of shrinkage is dependent on, at least in part, the thermal expansion characteristics of internal portion  706  and external portion  702 . 
     In addition to beginning to shrink or contract internal portion  706 , external portion  702  continues to shrink or contract when preform  726  is heated to the second sintering temperature. That is, although external portion  702  is already sintered when preform  726  is heated to the second sintering temperature, first grain  736  of ceramic material  734  forming external portion  702  continues to shrink or contract. In the non-limiting example shown in  FIG. 7E , exterior surface  704  of external portion  702  is positioned below the pre-sintered position  732   a  of exterior surface  704  (see,  FIG. 7B ) prior to preform  726  being heated to the first sintering temperature. Exterior surface  704  of external portion  702  is also positioned below the partially-sintered position  732   b  of exterior surface  704  (see,  FIG. 7D ) subsequent to preform  726  being heated to the first sintering temperature, but prior to preform  726  being heated to the second sintering temperature. 
     As discussed herein with respect to external portion  702 , the sintering and/or shrinkage of internal portion  706  of preform  726  is dependent on the altered thermal expansion characteristics of internal portion  706 . The distinct grain sizes of first grain  736  and second grain  738  of ceramic material  734  causes the thermal expansion characteristics to be different or distinct between internal portion  706  and external portion  702 . Additionally, the differences in the thermal expansion characteristics also account for the difference in the amount or rate of shrinkage or contraction between internal portion  706  and external portion  702 . Continuing the examples discussed herein, external portion  702  has a higher CTE, lower sintering temperature and/or higher sintering rate when compared to internal portion  706 . As such, and as described above with respect to  FIGS. 7D and 7E , external portion  702  continues to shrink or contract at a second sintering temperature, while internal portion  706  sinters and/or begins to shrink or contract at the second sintering temperature. Additionally, external portion  702  shrinks or contracts a greater amount or distance than internal portion  706  when preform  726  is heated to the second sintering temperature as a result of the difference in the thermal expansion characteristics between internal portion  706  and external portion  702 . 
     The processes performed on preform  726 , as shown and discussed herein with respect to  FIGS. 7C-7E , may correspond to operation  604  of the process  600  shown in  FIG. 6 . 
       FIG. 7F  shows preform  726  (see,  FIG. 5C ) subsequent to being completely sintered and/or cooled. Specifically, preform  726  is heated to the first and second predetermined sintering temperature, such that internal portion  706  and external portion  702  are sintered. Subsequent to sintering preform  726 , preform  726  is cooled. The cooling of preform  726  results in the formation of ceramic component  700 . In a non-limiting example shown in  FIG. 7F , when preform  726  is cooled, ceramic component  700  is formed including internal portion  706  and external portion  702  substantially surrounding internal portion  706 . As such,  FIG. 7F  refers to previously discussed preform  726  as ceramic component  700 . 
     Although shown with distinct hash-markings similar to those shown in  FIGS. 1B and 3G  for example, it is understood that ceramic component  700  is formed from a single material. Specifically, ceramic component  700  is formed from ceramic material  734  that is compositionally similar in both external portion  702  and internal portion  706 . As discussed herein, the distinction between external portion  702  and internal portion  706  of ceramic component  700  is the material grain size of first grain  736  of external portion  702  and second grain  736  of internal portion  706 . It is understood that the hash-markings for external portion  702  and internal portion  706  shown in  FIG. 7F  are included merely to identify the distinct portions of ceramic component more clearly and do not necessarily represent that external portion  702  and internal portion  706  are formed from distinct materials, as discussed in distinct example embodiments herein. 
     As similarly discussed herein with respect to  FIGS. 5E and 5F , ceramic component  700  is cooled down to a predetermined temperature naturally or organically by removing heat supplied by heating device  724  (see,  FIG. 7C ), or alternatively, is rapidly cooled by submerging the ceramic component  500  in a bath of cold liquid. Additionally, and as discussed herein with respect to  FIGS. 5E and 5F , cooling ceramic component  700  can result in further shrinkage and/or contraction of ceramic component  700 , where internal portion  706  and external portion  702  of ceramic component  700  contract and/or shrink a different amount or distance, and/or at a different rate during the cooling process. This is also similar to the discussion of internal portion  706  and external portion  702  shrinking during the sintering process (see,  FIGS. 7C-7E ). Specifically, external portion  702  may shrink a greater amount or distance and/or at a higher rate during the cooling process when compared to internal portion  706  of ceramic component  700 . As discussed herein, the shrinking or contracting of internal portion  706  and external portion  702  is dependent on, at least in part, the thermal expansion characteristics of each portion. 
     In another non-limiting example, once the cooling process of ceramic component  700  begins, the shrinking of the ceramic component  700  stops and/or is discontinued. As a result, once ceramic component  700  is starting to be cooled, external portion  702  and internal portion  706  of ceramic component  700  no longer shrinks and/or contracts. In the non-limiting example, the positioning of first grain  736  of ceramic material  734  forming external portion  702  and second grain  738  of ceramic material  734  forming internal portion  706  will be similar to that shown in  FIG. 7E , as previously discussed herein. 
     The sintering, cooling and the corresponding shrinkage and/or contraction of ceramic component  700  also results in the formation of distinct stresses within ceramic component  700 , as similarly discussed herein. Specifically, when sintered ceramic component  700  is cooled, and ceramic component  700  shrinks and/or contracts, distinct stresses are formed within and/or experienced by the various portions (e.g., external portion  702 , internal portion  706 ) of ceramic component  700 . In a non-limiting example, and as discussed herein, a compressive stress is formed within external portion  702 , as a result of external portion  702  shrinking and/or contracting more than internal portion  706  due to the differences in thermal expansion characteristics. Additionally, a tensile stress is formed within internal portion  706  as a result of the shrinking or contracting occurring in internal portion  706  and/or the shrinking or contracting of external portion  702  around internal portion  706  of ceramic component  700 . 
     The processes performed on preform  726  and/or ceramic component  700 , as shown and discussed herein with respect to  FIGS. 7E and 7F , may correspond to operations  606  and  608  of the process  600  shown in  FIG. 6 . 
       FIG. 8  shows a side cross-section view of ceramic component  800  having selective compressive stress formed therein. As shown in  FIG. 8 , external portion  802  only forms a portion of exterior surface  804 , and internal portion  806  of ceramic component  800  forms the remaining portion of exterior surface  804 . As discussed herein with respect to  FIGS. 2-7F , external portion  802  provides a residual compressive stress to ceramic component  800 , while internal portion  806  provides a tensile stress. The compressive stress improves the strength, toughness, brittleness and/or improves protection against damage to the ceramic component, as well as mitigates and/or prevents the spreading of surface defects within the ceramic component  800 , as discussed herein. As a result, the formation of selective compressive stress, as shown in  FIG. 8 , is beneficial when ceramic component  800  is utilized in a manner that makes certain or specific portions more susceptible to damage than others. In a non-limiting example discussed herein with respect to  FIG. 10 , ceramic component  800  can form a cover for an electronic device. As a result, it would be beneficial to selectively form compressive stress and/or external portion  802  on or around a border or perimeter of ceramic component  800 , which may be more susceptible to damage when the electronic device utilizing ceramic component  800  is dropped, for example. 
     Forming selective external portion  802  and/or compressive stress on ceramic component  800  is achieved by modifying any of the processes discussed herein. In a non-limiting example where the ceramic substrate forming ceramic component  800  is pre-sintered, the dopant material applied to exterior surface  804  may be selectively applied, such that only a portion of the ceramic substrate undergoes the processes for forming ceramic component  800  having a selective, residual compressive stress (see,  FIGS. 2-3G ). In another non-limiting example where ceramic component  800  is formed from a green body ceramic preform, only a select area of the portion of the preform forming the exterior surface can include doped, ceramic material and/or material having a distinct (e.g., smaller) grain size. In the non-limiting example, when the preform is sintered, the compressive stress will be selectively formed in the select area of the preform, including the doped, ceramic material and/or distinct grain size area. 
       FIG. 9  shows a side cross-section view of a ceramic component  900  having varying thickness external portion  902 . As shown in  FIG. 9 , external portion  902 , which provides a residual compressive stress to ceramic component  900  as discussed herein, includes a portion having a first thickness (T 1 ) and a second thickness (T 2 ), where the first thickness (T 1 ) is greater than the second thickness (T 2 ). As a result of the distinct thicknesses for external portion  902 , the compressive stress formed in ceramic component  900  also varies. In a non-limiting example, the compressive stress formed in ceramic component  900  adjacent external portion  902  having the first thickness (T 1 ) is greater than the compressive stress formed in ceramic component  900  adjacent external portion  902  having the second thickness (T 2 ). Similar to  FIG. 8 , the formation of varying compressive stress, as shown in  FIG. 9 , is beneficial when ceramic component  900  is utilized in a manner that makes certain or specific portions more susceptible to damage than others. In the non-limiting example discussed herein with respect to  FIG. 10 , where ceramic component  900  forms a cover for an electronic device, it would be beneficial to improve or increase the compressive stress on or around a border or perimeter of ceramic component  900  (e.g., first thickness (T 1 )) than the center of ceramic component  900  (e.g., first thickness (T 1 )). This is true when the border or perimeter of ceramic component  900  is more susceptible to damage when the electronic device utilizing ceramic component  900  is dropped, for example. 
     The varying thickness of external portion  902  can be formed in ceramic component  900  by modifying any of the processes discussed herein. In a non-limiting example where the ceramic substrate forming ceramic component  900  is pre-sintered, the dopant material applied to exterior surface  904  may be applied more heavily in a specific area of exterior surface  904 , such that more atoms of the dopant material can be diffused in an selective area of ceramic component  900  (see,  FIGS. 2-3G ). In conjunction with or separate from the increased application of dopant material in a selective area, the dopant material applied to the area desired to have a greater thickness (e.g., first thickness (T 1 )) of external portion  902  can be a different material and/or have a distinct concentration of dopant material different than the remaining dopant material applied to the ceramic substrate forming ceramic component  900 . Additionally, the area desired to have a greater thickness (e.g., first thickness (T 1 )) of external portion  902  can be selectively heated to a higher temperature and/or for a longer period of time, to increase diffusion between the dopant material and the ceramic substrate. 
     In another non-limiting example where ceramic component  900  is formed from a green body ceramic preform, select areas of external portion  902  of the preform forming the exterior surface  904  can include more doped, ceramic material and/or material having a smaller grain size than internal portion  906  and the remaining portion of external portion  902 , respectively. In the non-limiting example, when the preform is sintered, the compressive stress formed in ceramic component  900  by external portion  902  will be greater or larger in the selected area of the preform including the doped, ceramic material and/or smallest grain size. 
       FIG. 10  shows an isometric view of an electronic device  1000 . As discussed herein, electronic device  1000  includes various components that may utilize the ceramic component discussed herein with respect to  FIGS. 1A-9 . As shown in  FIG. 10 , electronic device  1000  is implemented as a mobile phone. Other embodiments can implement electronic device  1000  differently, such as, for example, as a laptop or desktop computer, a tablet computing device, a gaming device, a display, a digital music player, a wearable computing device or display, a health monitoring device, and so on. 
     Electronic device  1000  includes a housing  1002  at least partially surrounding a display module, a cover  1004  substantially covering the display module and one or more buttons  1006  or input devices. Housing  1002  can form an outer surface or partial outer surface and protective case for the internal components of the electronic device  1000  and may at least partially surround the display module positioned within an internal cavity formed by housing  1002 . Housing  1002  can be formed of one or more components operably connected together, such as a front piece and a back piece (not shown). Alternatively, housing  1002  can be formed of a single piece operably connected to the display module. Housing  1002  may be formed from any suitable material that may house and/or may protect the internal components of electronic device  1000 , including the display module. In non-limiting examples, housing  1002  may be formed from glass, sapphire or metal. 
     The display module may be substantially surrounded by housing  1002  and/or may be positioned within an internal cavity formed by housing  1002 . The display module can be implemented with any suitable technology, including, but not limited to, a multi-touch sensing touchscreen that uses liquid crystal display (LCD) technology, light emitting diode (LED) technology, organic light-emitting display (OLED) technology, organic electroluminescence (OEL) technology, or another type of display technology. The display module may be positioned within an internal cavity of housing  1002  and may be substantially protected on almost all sides by housing  1002 . 
     Cover  1004  may be formed integral with and/or may be coupled to housing  1002  to substantially cover and protect the display module. Cover  1004  may cover at least a portion of the front surface of electronic device  1000 . When a user interacts with the display module of electronic device  1000 , the user may touch or contact cover  1004 . Cover  1004  of electronic device  1000  may include the toughened ceramic component discussed herein with respect to  FIGS. 1A-9 , to protect electronic device  1000  and to prevent and/or mitigate damage to cover  1004  during an undesirable shock event (e.g., drop). In a non-limiting example shown in  FIG. 10 , the toughened ceramic component discussed herein (see,  FIGS. 1A-9 ) may form cover  1004  coupled to housing  1002  and positioned over the display module. By utilizing the toughened ceramic component discussed herein to form cover  1004  for electronic device  1000 , cover  1004  may have improved strength, toughness, brittleness and/or improved protection against damage to the ceramic component. 
     Button  1006  can take the form of a home button, which may be a mechanical button, a soft button (e.g., a button that does not physically move but still accepts inputs), an icon or image on a display, and so on. Further, in some embodiments, button  1006  can be integrated as part of cover  1004  of the electronic device  1000 . Button  1006 , like housing  1002 , may be formed from any suitable material that may withstand an undesirable drop event that may occur with electronic device  1000 . In non-limiting examples, button  1006  may be formed from glass, sapphire or metal. 
     The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of the specific embodiments described herein are presented for purposes of illustration and description. They are not targeted to be exhaustive or to limit the embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.

Metadata:
Filing Date: 20160915
Publication Date: 20210831
Grant Date: 20210831
Priority Date: 20150930
Inventors: WILSON, JAMES R.
JONES, CHRISTOPHER D.
Assignee: APPLE INC
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