Abstract:
Systems and method for creating crystalline parts having a desired primary and secondary crystallographic orientations are provided. One embodiment may take the form of a method of manufacturing a part having a crystalline structure. The method includes melting aluminum oxide and drawing the melted aluminum oxide up a slit. Additionally, the method includes orienting the seed crystal relative to a growth apparatus such that a crystalline structure grows having a desired primary plane and a desired secondary plane orientation. Moreover, the method includes pulling the crystal as it forms to create a ribbon shaped crystalline structure and cutting a part from the crystalline structure.

Description:
TECHNICAL FIELD 
       [0001]    The present application is directed to the manufacture of crystalline structures and, more particularly, to orienting planes of crystalline structures during growth of the crystal. 
       BACKGROUND 
       [0002]    Corundum is a crystalline form of aluminum oxide and is found in various different colors, all of which are generally commonly referred to as sapphire except for red corundum which is commonly known as ruby and pinkish-orange corundum which is known as padparadscha. Transparent forms of corundum are considered precious stones or gems. Generally, corundum is extraordinarily hard with pure corundum defined to have 9.0 Mohs and, as such, is capable of scratching nearly all other minerals. 
         [0003]    As may be appreciated, due to certain characteristics of corundum, including its hardness and transparent characteristics, among others, it may be useful in a variety of different applications. However, the same characteristics that are beneficial for particular applications commonly increase both the cost and difficulty in processing and preparing the sapphire for those applications. As such, beyond costs associated with it being a precious stone, the costs of preparing the corundum for particular uses is often prohibitive. For example, the sapphire&#39;s hardness makes cutting and polishing the material both difficult and time consuming when conventional processing techniques are implemented. Further, conventional processing tools such as cutters experience relatively rapid wear when used on corundum. 
       SUMMARY 
       [0004]    Systems and method for creating crystalline parts having a desired primary and secondary crystallographic orientations are provided. One embodiment may take the form of a method of manufacturing a part having a crystalline structure. The method includes melting aluminum oxide and drawing the melted aluminum oxide up a slit. Additionally, the method includes orienting the seed crystal relative to a growth apparatus such that a crystalline structure grows having a desired primary plane and a desired secondary plane orientation. Moreover, the method includes pulling the crystal as it forms to create a ribbon shaped crystalline structure and cutting a part from the crystalline structure. 
         [0005]    Another embodiment may take the form of a method of manufacturing sapphire parts. The method includes growing a sapphire boule and slicing the sapphire boule to create a sapphire wafer having a desired primary crystallographic orientation. The method also includes cutting a sapphire part from the wafer. The sapphire part is cut to have a desired secondary crystallographic orientation. 
         [0006]    Yet another embodiment may take the form of a system for creating sapphire parts having a desired primary and secondary crystallographic orientations. The system includes a crucible configured to melt aluminum oxide and a slit extending downward into the crucible configured to draw melted aluminum oxide through capillary action. The system also includes a die positioned at the top of the crucible and over the slit to shape a sapphire crystal as it is formed and a mechanism for holding an oriented seed crystal relative to the die so that the seed crystal contacts the melted aluminum oxide, the mechanism further configured to pull a sapphire ribbon from the die. 
         [0007]    While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following Detailed Description. As will be realized, the embodiments are capable of modifications in various aspects, all without departing from the spirit and scope of the embodiments. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  illustrates a first example process for sapphire growth. 
           [0009]      FIG. 2  illustrates a second example process for sapphire growth. 
           [0010]      FIG. 3  illustrates a third example process for sapphire growth. 
           [0011]      FIG. 4A  illustrates a sapphire ribbon having selected primary and secondary crystallographic orientations. 
           [0012]      FIG. 4B  illustrates a sapphire part having selected primary and secondary crystallographic orientations cut from the sapphire ribbon of  FIG. 4A . 
           [0013]      FIG. 5A  illustrates another sapphire ribbon having selected primary and secondary orientations with the secondary orientation having an angle relative to at least one edge of the ribbon. 
           [0014]      FIG. 5B  illustrates another sapphire part having selected primary and secondary crystallographic orientations with the secondary crystallographic orientation having an offset angle relative to at least one edge of the sapphire part. 
           [0015]      FIG. 6  illustrates a sapphire wafer with a desired primary crystallographic orientation and orienting cuts from the wafer based on a secondary orientation. 
           [0016]      FIG. 7  is a flowchart illustrating an example method of creating sapphire parts having a desired primary and secondary crystallographic orientation. 
           [0017]      FIG. 8  is a flowchart illustrating another example method of creating sapphire parts having a desired primary and secondary crystallographic orientation. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    For sapphire to be used as an enclosure material in electronic devices, high and consistent strength is desired in order to ensure reliability and avoid fracture in use event like a drop. Whereas glass and metals tend to be isotropic in their properties, meaning that their implementation does not need to take into account the orientation of the part and material relative to the product, sapphire is anisotropic due to its crystal structure. 
         [0019]    The anisotropic nature may be utilized to take advantage of differences in the properties between planes for specific applications. Specifically, when implementing sapphire as an enclosure material, such as for a cover glass for a smart phone, or tablet computer, the orientation of the part surface with respect to a specific crystal plane may be defined, as well as the orientation of the edges of the part with respect to other crystallographic planes. For example, a high strength part for a given implementation may be defined as having a primary crystallographic orientation of A Plane (relative to a primary part surface) with a secondary crystallographic orientation of 45° off from the C Plane (relative to a long edge of the part). By fine tuning the orientation of the sapphire part, the alignment of low energy fracture planes with the highest stress directions of the part during loading may be avoided. Further, the fracture plane can instead be aligned so that they experience low stress. In testing, statistically significant strength improvements over other secondary orientations have been seen and much more uniform strength is expected over parts with a given primary orientation and random secondary orientations. 
         [0020]    Another reason to control the secondary orientation of the sapphire part is for optical reasons. Since liquid crystal displays utilize polarizers, the birefringence of the sapphire can impact the appearance of the display when view through polarized sunglasses. As such the secondary orientation may be selected to help avoid the sapphire having an impact on the appearance of the display. 
         [0021]    As such, certain embodiments may take the form of a method that includes specifying the primary and secondary orientations of the crystal prior to growth of the crystal to help increase the yield of the grown crystal. For example, in an edge-defined film-fed growth (EFG) process, the seed crystal may be oriented relative to the growth die such that the surface of the EFG ribbon results has an A-plane crystallographic orientation, while the edges of the ribbon may be oriented at some angle, such as 45°, to the M-plane so that utilization of the grown ribbon would be maximized. This optimization applies to most growth methods. It should be appreciated that various different combinations of crystallographic orientations may be implemented. As such, each of various possible combinations of different primary and secondary crystallographic orientations of the A-plane, C-plane, M-plane and R-plane may be created. 
         [0022]    Generally, the process of growing sapphire starts with alumina powder that is subjected to a densification process to form densified alumina (or crackle). The alumina is melted and a seed crystal is inserted into the molten alumina. The molten alumina is then cooled with precisely controlled temperatures and the crystal is formed on the seed. Additional processing steps such as cutting and polishing the formed crystal may be performed, as well as annealing steps to help “heal” the crystalline structure that may have formed during growth or subsequent processing, as mentioned above. 
         [0023]    Some common growth methods include Kyropoulos, Verneuil, Czochralski, flux, hydrothermal, vertical horizontal gradient freezing (“VHGF”), Stepanov (i.e., EFG), and Bridgman (i.e., horizontal moving growth). The Kyropoulos, Verneuil, Czochralski, flux, and hydrothermal processes generate a sapphire boule, whereas the EFG, VHGF and horizontal moving growth processes generate sapphire members having continuous cross-sections. It should be appreciated that although specific examples described herein may refer to a particular process for sapphire growth the examples are not intended to be limiting. As such, the present techniques, systems and methods may be used in conjunction with each of the various sapphire growth processes. 
         [0024]    Turning to the drawings and referring initially to  FIG. 1A , a system  100  for performing the Kyropoulos process is illustrated by a cross-sectional view of a crucible  102 . The crucible  102  holds the alumina melt  104  and a seed crystal  106  is inserted into the crucible  102  with a support rod  108 . Crystallization of the molten alumina  104  occurs on the seed crystal  106  following the orientation of the seed crystal. The seed, crystal, therefore is oriented in a manner to help optimize yield of the crystal according to a desired primary plane orientation as well as an orientation of the secondary plane, as discussed in greater detail below. 
         [0025]    A system  110  for growing sapphire according to the EFG process is illustrated in  FIG. 2  with a cross-sectional view of another crucible  112 . Again, the crucible  112  holds the alumina melt  114 . The crucible  112  may be heated by heating elements  118  which surround the crucible. The molten alumina  114  is drawn up a melt supply slit of a die  116  which may take the form of two close, parallel plates which draw the molten alumina up through capillary action. A die tip  117  may be positioned at or near a boundary formed by the crucible and the die  116 . The die tip  117  or top geometry of the plates determine the output geometry of the sapphire as it is formed. 
         [0026]    A mechanism  115  for holding the seed crystal  119  may be provided. In some embodiments, the mechanism  115  may be configured to reorient the seed crystal, for example by rotating the orientation of the seed crystal  119  relative to the die. The mechanism  115  may bring the seed crystal  119  into contact with the molten alumina which propagates crystalline growth and sapphire  120  may then draw the crystal upwardly out of the crucible  112 . The sapphire is formed in the shape of the die  117  and the sapphire crystalline structure follows the existing orientation of the seed. In some embodiments, the die may be configured to approximate the size and shape of the part being created. For example, the die may be 5-10 percent larger than the cross-section of the part being formed. The orientation of the crystal is selected to achieve a desired primary plane orientation and a desired secondary orientation of the crystal. 
         [0027]    A system  122  for growing sapphire according to the VHGF process is illustrated in  FIG. 3 , with a cross-sectional view of a chamber  124 . The chamber  124  surrounds an alumina charged crucible  126  into which a seed crystal is positioned at the bottom of the crucible. A heat sink  128  and heater  130  are each coupled to crucible  126  and an insulator  132  is provided within the chamber around the heater and crucible. The heater  130  melts the alumina in the crucible and the melted alumina is subsequently cooled by the heat sink  128  to form crystal in the shape of the crucible and following the orientation of the seed crystal. The seed crystal is positioned within the crucible so that the primary and secondary plane orientations provided for a high yield of the grown crystal. Once the crystal is cooled, the crucible  126  is cracked off and the crystal may be further processed (e.g., sliced, diced, polished, etc.). 
         [0028]      FIG. 4A  illustrates a sapphire ribbon  140  grown in accordance with one of the above-described growth processes. For example, the sapphire ribbon may have been grown in accordance with the EFG process. A seed crystal for the EFG growth process was oriented to yield a ribbon having a designated primary surface plane orientation, as well as an orientation for at least one edge. In particular, seed crystal was oriented so that the primary surface  142  primary surface has an A-plane crystallographic orientation. Additionally, long side  146  of the grown crystal  140  may have a C-plane crystallographic orientation. Further, a third surface (e.g., the short edge  148  of the ribbon  140 ) may have a desired crystallographic orientation, such as an M-plane crystallographic orientation. 
         [0029]    The orientation of the seed crystal during the growth process allows for a high yield of the grown crystal for a specific part. In particular, the dashed line  144  in  FIG. 4A  illustrates the cut line for a desired part. Specifically, the part may take the form of a cover glass  152  (illustrated in  FIG. 4B ) for an electronic device such as a smart phone, tablet computing device, and so forth. A portion  150  of the ribbon  150  that remains unused after cutting is minimized by specifically orienting the seed crystal to grow crystal with the desired crystallographic orientation. The high yield helps to reduce waste, thereby achieving efficiencies that help reduce costs. 
         [0030]    It should be appreciated that the selection of the primary and secondary (or more) crystallographic orientations through orientation of the seed crystal may achieve orientations that are offset from the surface of the part. For example, a secondary crystallographic orientation may be offset by a desired angle to help avoid aligning low energy fracture planes with the highest stress directions of the part. Rather, the low energy fracture planes can instead be aligned with the directions of lowest stress. 
         [0031]    Turning to  FIGS. 5A and 5B , the offset of the secondary crystallographic orientation is illustrated. Specifically, another sapphire ribbon  160  (e.g., grown through the EFG process) is illustrated having a primary crystallographic orientation providing a top surface  162  with an A-plane orientation. Additionally, a long side  164  of the ribbon  160  has a crystallographic orientation of an offset C-plane. That is, the C-plane crystallographic orientation is offset an angle  166  from the long side  162 . 
         [0032]    The offset angle  166  may be selected based on empirical data gathered that relates to low energy fracture planes. In particular, upon finding low energy fracture planes, the orientation of the crystallographic orientation may be adjusted to avoid the low energy fracture plane being exposed or particularly vulnerable along the long edge  164 . In some embodiments, the offset angle  166  may be between approximately 5 and 85°. More specifically, the offset angle  166  may be between approximately 35° and 55°, such as approximately 45°. 
         [0033]    As with the prior example, orienting the seed crystal before growth of the ribbon  160  results high yield sapphire production. That is the part  168  may constitute a large portion of the grown sapphire after it is cut from the ribbon  160 . The part  168  has the desired primary and secondary crystallographic orientations. It should further be appreciated, that at least a third crystallographic orientation may be desirable and may be selected based on the seed crystal orientation. Specifically, an offset angle  167  relative to a short side of the part  168  may be selected. 
         [0034]    In some embodiments, the offset angle  167  may be related to the offset angle  166  relative to the long side (e.g., because the offset angle is of the same crystallographic plane as that of the long side). In other embodiment, an offset angle relative to the short side may be related to a crystallographic orientation of a plane different from that of the long side. For example, rather than an offset of the C-plane relative to the short side, an offset relative to the M-plane may be set. 
         [0035]    Orientation of the seed crystal prior to the growth of the crystal to achieve high yield of the crystal may be utilized in growth processes other than those that produce crystal ribbons or other flat crystal structures. In particular, the seed crystal for growth processes that yield crystal boule may be oriented to achieve high yields. Generally, the boule may be sliced into wafers that have a desired primary crystallographic orientation (such as an A-plane surface). Further, the wafer may be cut into discrete parts that achieve a desired secondary orientation. As shown in  FIG. 6 , a wafer  170  may have a surface with an A-plane crystallographic orientation. Parts  172  may be cut from the wafer  170  to achieve a desired secondary crystallographic orientation. For example, a long side and a short side of a part cut from the wafer may have desired offset angles  174 ,  176  from a C-plane. 
         [0036]    Both the planes of crystallographic orientation, as well as the offset angles relative to the part, may be selected based at least in part upon the orientation of the seed crystal and the way the part is cut from the crystal. The crystallographic orientation and offset angles may provide specific characteristics that are desirable for the part. In particular, the crystallographic orientation may provide a desired strength to the part and or optical effects. 
         [0037]      FIG. 7  is a flowchart illustrating an example method  200  of producing a sapphire part in accordance with an example embodiment. Initially, aluminum oxide is heated and melted in a crucible (Block  202 ). A seed crystal is oriented to yield a desired crystallographic orientation in the grown crystal (Block  204 ). The seed crystal brought into contact with the melted aluminum oxide (Block  206 ) to propagate crystal growth having a desired crystallographic orientation. The crystal is cooled and removed from the crucible (Block  208 ). The crystal is sliced into wafers having a desired primary crystallographic orientation (Block  210 ) and parts are cut from the wafers to achieve a desired secondary crystallographic orientation (Block  212 ). 
         [0038]      FIG. 8  illustrates a method  220  for generating a sapphire part. The method includes heating and melting aluminum oxide (Block  222 ). The melted alumina is drawn up a slit (Block  224 ) by capillary action and into a shaping die. A seed crystal is oriented to produce a desired primary and secondary crystallographic orientation (Block  226 ). Sapphire crystal is drawn through the die (Block  228 ) having the desired primary and secondary crystallographic orientation. The crystal is cooled (Block  230 ) and one or more sapphire parts are cut from the sapphire crystal (Block  232 ). 
         [0039]    It should be appreciated that alternative embodiments may include more or fewer steps and, additionally, that the processes of polishing, grinding and/or annealing may be part of the method  200  although not addressed herein. 
         [0040]    Although the foregoing discussion has presented specific embodiments, persons skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the embodiments. For example, crystallographic orientations that provide for planes other than those mentioned above by way of example may be implemented. Accordingly, the specific embodiments described herein should be understood as examples and not limiting the scope thereof.