WO2014126777A1

WO2014126777A1 - A mobile electronic device comprising a multilayer sapphire cover plate having layers with different orientations

Info

Publication number: WO2014126777A1
Application number: PCT/US2014/015075
Authority: WO
Inventors: John Q. DUMM
Original assignee: Gt Crystal Systems, Llc
Priority date: 2013-02-15
Filing date: 2014-02-06
Publication date: 2014-08-21

Abstract

An electronic device comprising a cover plate is disclosed. The cover plate comprises one or more sapphire layers having different orientations, such as crystal orientation or surface orientation.

Description

A MOBILE ELECTRONIC DEVICE COMPRISING A MULTILAYER SAPPHIRE COVER PLATE HAVING LAYERS WITH DIFFERENT ORIENTATIONS

BACKGROUND OF THE INVENTION

CROSS-REFERENCE TO RELATED APPLICATION

The subject invention claims the benefit of priority from U.S. Provisional Patent Application Serial No. 61/765,183, filed February 15, 2013, the disclosure of which is herein incorporated by reference in its entirety.

1. Field of the Invention.

[0001] The present invention relates to a mobile electronic device comprising a sapphire cover plate, particularly a cover plate comprising two or more layers of sapphire having different orientations.

2. Description of the Related Art.

[0002] There are many types of mobile electronic devices currently available which include a display window assembly that is at least partially transparent. These include, for example, handheld electronic devices such media players, mobile telephones (cell phones), personal data assistants (PDAs), pagers, tablets, and laptop computers and notebooks. The display screen assembly may include multiple component layers, such as, for example, a visual display layer such as a liquid crystal display (LCD), a touch sensitive layer for user input, and at least one outer cover layer used to protect the visual display. Each of these layers are typically laminated or bonded together.

[0003] Many of the mobile electronic devices used today are subjected to excessive mechanical and/or chemical damage, particularly from careless handling and/or dropping, from contact of the screen with items such as keys in a user's pocket or purse, or from frequent touch screen usage. For example, the touch screen surface and interfaces of smartphones and PDAs can become damaged by abrasions that scratch and pit the physical user interface, and these imperfections can act as stress concentration sites making the screen and/or underlying components more susceptible to fracture in the event of mechanical or other shock. Additionally, oil from the use's skin or other debris can coat the surface and may further facilitate the degradation of the device. Such abrasion and chemical action can cause a reduction in the visual clarity of the underlying electronic display components, thus potentially impeding the use and enjoyment of the device and limiting its lifetime.

[0004] Various methods and materials have been used in order to increase the durability of the display windows of mobile electronic devices. For example, polymeric coatings or layers can be applied to the touch screen surface in order to provide a barrier against degradation. However, such layers can interfere with the visual clarity of the underlying electronic display as well as interfere with the touch screen sensitivity. Furthermore, as the coating materials are often also soft, they can themselves become easily damaged, requiring periodic replacement or limiting the lifetime of the device.

[0005] Another common approach is to use more highly chemically and scratch resistant materials as the outer surface of the display window. For example, touch sensitive screens of some mobile devices may include a layer of chemically-strengthened alkali aluminosilicate glass with potassium ions replacing sodium ions for enhanced hardness, such as the material referred to as Gorilla® glass available from Corning. However, even this type of glass can be scratched by many harder materials, including metal keys, sand, and pebbles, and, further, as a glass, is prone to brittle failure and shattering. Sapphire has also been suggested and used as a material for either the outer layer of the display assembly or as a separate protective sheet to be applied over the display window. However, sapphire is relatively expensive, particularly at the currently available thicknesses.

[0006] Thus, while materials are available which can enable the display of a mobile electronic device to be relatively resistant to damage, there remains a need in the industry for materials and methods for providing improved mechanical toughness and scratch resistance without reducing transmittance.

SUMMARY OF THE INVENTION [0007] The present invention relates to an electronic device comprising a cover plate having at least one transparent display region. The cover plate comprises two or more glass layers having a different orientation. In one embodiment, the two sapphire layers have a different crystalline orientation. In another embodiment, the two sapphire layers have a different surface orientation, such as a different orientation of surface artifacts. The electronic device may further comprise at least one display element having a display surface, and the cover plate can be either affixed to the display surface or removably positioned on top of the display surface as a protective layer. Preferably, the sapphire layer is the front surface of the cover plate.

[0008] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide further explanation of the present invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG 1 and FIG 2 are exploded perspective views of specific embodiments of the electronic device of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention relates to an electronic device comprising a cover plate having specifically oriented multiple layers.

[0011] The electronic device of the present invention comprises a cover plate having at least one transparent display region through which an image can be displayed, such as from a display element upon which the cover plate is placed. Non-transparent regions may also be present, particularly as decorative elements such as borders or as elements to delineate various functional sections of the display. The electronic device can be any known in the art comprising a display or display element, such as mobile or portable electronic devices including, but not limited to, electronic media players for music and/or video, such as an mp3 player, mobile telephones (cell phones), personal data assistants (PDAs), pagers, laptop computers, or electronic notebooks or tablets. The display element of the device may include multiple component layers, including, for example, a visual display layer such as an LCD and a touch sensitive layer as part of a touch screen application. The cover plate can be affixed to the display surface of the display element of the device or it can be a separate protective layer that can be placed or positioned over or on top of the display element and later removed if desired.

[0012] The cover plate of the electronic device of the present invention comprises two or more sapphire layers. Thus, the cover plate is a multilayer composite of sapphire layers, comprising, for example, 2-10 layers, such as 2-5 layers or 2-3 layers. Preferably, the sapphire layer is the exterior layer of the cover plate and of the electronic device, although an antireflective and/or oleophobic coating may also be applied, typically having a thickness of from about 0.001 microns to about 1.5 microns. The sapphire layers may be combined using any technique known in the art. For example, the layers may be permanently or temporarily affixed to each other using an adhesive, such as a transparent adhesive or adhesive layer. Examples of suitable adhesives include, but are not limited to, polymers or combinations of polymers such as poly (propylene carbonate) (PC), poly (ethylene carbonate) (PEC), or poly(butylenes carbonate) (PBC). Electrostatic adhesion may also be used.

[0013] The thickness of the sapphire layer can be the same or different and can vary depending on, for example, the type and size of the electronic device, cost, and the desired properties of the cover plate. For example, for cost reasons, thinner layers are preferred, but a layer that is too thin may have reduced mechanical strength. For the present invention, the thickness of the sapphire layers can be less than about 3 mm, such as from about 0.01 mm to about 3 mm, including less than about 2 mm, such as less than about 1 mm, less than about 0.5 mm, or less than about 0.1 mm. In addition, the sapphire layers may be ultrathin sapphire layers, such as can be prepared from a sapphire donor using an ion implantation method, having a thickness of less than 50 microns, including, for example, less than 30 microns, less than 25 microns, less than 20 microns, or even less than 15 microns. Preferably, the ultrathin sapphire layers are free-standing and are therefore able to be handled independently of a carrier layer. In addition, the overall thickness of the cover plate of the electronic device of the present invention can also vary depending on a variety of factors, including, for example, the number of layers and the desired size and weight of the electronic device. In general, the cover plate has a thickness that is less than about 5 mm and preferably has a thickness of from about 0.3 mm to about 3.0 mm, more preferably between about 0.4 mm to about 2.5 mm, even more preferably from about 0.5 mm to about 2.0 mm, and most preferably between about 0.5 mm and about 1.0 mm.

[0014] In the present invention, at least two of the sapphire layers of the cover plate have different orientations. Thus, the cover plate comprises at least one sapphire layer oriented in one direction and at least one other sapphire layer oriented in a different direction. Preferably the layers having different orientations are in direct contact with each other. For example, the cover plate can comprise two adjacent sapphire layers having different orientations. Pairs of differently oriented layers can be stacked together, with the same or different sets of orientations. As another example, the cover plate may comprise three adjacent sapphire layers, wherein the first and third layers have the same orientation but wherein the second layer has a different orientation, thereby forming a sandwich structure. Also, the cover plate may comprise three layers, each having different orientations. Other combinations of layers and orientations are also possible, given the benefit of this disclosure.

[0015] In one embodiment, the sapphire layers are oriented based on their crystallinity. As is known in the art, sapphire may include one of several different crystalline axes, such as the c-axis, the m-axis, or the a-axis, and the properties of a sapphire sheet vary depending on this crystal orientation. For this first embodiment, the cover plate of the present invention comprises a first sapphire layer and a second sapphire layer, each having a different crystalline orientation. For example, the first sapphire layer of the cover plate may have a c- axis orientation and the second sapphire layer may have an m-axis orientation, or vice-versa. As a further example, the orientation of the first sapphire layer may be along the c-axis and the orientation of the second sapphire layer may be along the a-axis, or vice-versa. Other combinations of orientations are also possible.

[0016] In another embodiment, the sapphire layers are oriented based on their surface properties. Typically, the surface and subsurface of a sapphire layer include various surface artifacts which are often oriented in a specific direction based on the tooling and fixturing used in the manufacturing process. For example, sapphire layers are typically prepared by cutting or slicing, which can induce surface features oriented in the direction of the cutting. In addition, these rough surfaces may be further processed by grinding or polishing in order to improve their optical properties. During the cutting and polishing processes, locally stressed regions of material can be produced in the surface or subsurface of the layer, which are oriented in the direction of polishing. These locally stressed regions of subsurface material may be allowed to remain in a sapphire layer if the cost to remove them by further polishing is not justified by a proportional improvement in the mechanical, optical or other relevant properties of the finished product. The properties of a sapphire layer can vary depending on the orientation of these surface or subsurface features. For this additional embodiment of the present invention, the cover plate comprises a first sapphire layer and a second sapphire layer, each having different orientations of these surface artifacts. For this embodiment of the present invention, the first sapphire layer can have locally stressed regions resulting from polishing, oriented in one direction and the second sapphire layer can have similar regions oriented in a different direction.

[0017] For both embodiments, the degree of orientation mismatching can vary depending, for example, on the misoriented feature and the magnitude of the effect of that feature on the desired performance property. In general, one layer may be positioned in the cover plate such that it has an orientation that is between 5° and 90° different from the orientation of the second layer, including between about 20° and about 90° different. Having the two orientations perpendicular to each other may be preferred in some cases. For example, for the embodiment in which the sapphire layers are oriented according to their crystalline orientation, since the c-axis and the m-axis of sapphire are perpendicular to each other, a first sapphire layer having a c-axis orientation may be combined with a second sapphire layer having an m-axis orientation, and the two layers would have orientations that differ by 90°. Likewise, since the a-axis of sapphire is perpendicular, to the c-axis, a sapphire layer oriented in the c-direction would be 90° different from a sapphire layer oriented in the a-direction. As another example, since the a-axis is 30° from the m-axis in sapphire, a cover plate of the present invention may comprise a first sapphire layer having an a-axis orientation and a second sapphire layer having an m-axis orientation, and these layers would have a 30° difference in orientation. Furthermore, two sapphire layers having c-axis orientations may be combined, wherein the c-axis of one layer is rotated relative to the c-axis of the other layer.

[0018] Specific embodiments of the electronic device of the present invention are shown schematically in FIG 1 and FIG 2. In particular, FIG 1 shows cover plate 100 comprising first sapphire layer 110, having crystalline orientation 115 on top of second sapphire layer 120, having crystalline orientation 125. The two sapphire layers are positioned over display element 130, having a display surface that produces an image seen by a user, and the crystal orientations of the layers are different. In this specific example, first sapphire layer 110 is oriented along the m-axis, and second sapphire layer 120 is oriented along the c- axis, as shown by the crystal axes alongside each layer. As shown, the specific orientations of each layer are aligned, but each orientation is different and, as a result, first sapphire layer 110 is oriented 90° from second sapphire layer 120. Additional sapphire layers may also be included, having the same or different orientations as desired.

[0019] Similarly, FIG 2 shows cover plate 200 comprising first sapphire layer 210, having surface orientation 215, on top of second sapphire layer 220, having surface orientation 225. In this specific example, the surface orientations are surface or subsurface artifacts produced by polishing. Cover plate 200 is positioned over display element 230. The surface orientations of the two layers differ and, as shown, are oriented 90° away from each other, although other angles are also possible.

[0020] A cover plate for an electronic device comprising sapphire layers having different orientations, such as different crystalline or surface orientations, would be expected to have improved overall performance properties compared to a cover plate comprising sapphire layers having the same orientation. In particular, improvements in mechanical properties, such as strength or bending, would be expected, although it is believed that any property that is dependent on orientation can also be improved. Improvements would be particularly evident the thinner the sapphire layers. For example, it has been shown that, at room temperature, the flexural strength of sapphire is 50% higher when stress is applied along the m-axis compared to the c-axis. Thus, electronic devices with cover plates comprising sapphire oriented along the c-axis would be more prone to cracking if stressed in that direction, such as from careless handling and/or dropping, from contact with sharp items such as keys, or from frequent touch screen usage. Multiple layers of sapphire of this same orientation, while an improvement, would still be prone to fracture along this direction. However, a cover plate comprising two sapphire layers - one oriented along the c-axis in combination with another oriented along the m-axis - would have improved strength since the strongest orientation of one layer would lie in same direction as the weakest orientation of the other, and vice-versa. Overlapping layers in this way would impart an average increase in strength for the cover plate, reducing the likelihood of cracking and failure and increasing the service life of the electronic device. Furthermore, alternating orientations ensures high flexural strength along both axes, thereby accommodating any stress applied or resolved along either axis. In the same way, a cover plate having sapphire layers with different surface orientations, such as locally stressed regions of material which can act as sites for fracture, would also be expected to have improved overall properties.

[0021] Furthermore, improvements in performance would be expected without deteriorating other desirable properties of the cover plate for the electronic device, such as clarity or touch sensitivity. Thus, the sapphire layers preferably further have desirable mechanical, physical, and/or optical properties. For example, at room temperature, the layer of sapphire preferably has a flexural strength of at least about 700 MPA, including between about 800 and 1000 MPa, a fracture toughness (i.e., the ability of the material containing a crack or scratch to resist fracture) of greater than 1 MPa, including between about 2 and 5 MPa, a Knoop hardness of greater than about 15 GPa, including between about 17 and about 20 GPa, and/or a Vickers hardness of greater about 1000 kg/m, including between about 2000 and 3000 kg/m. The modulus, such as the Young's modulus, is also preferably between about 300-400 GPa, but can vary depending on the desired properties of the cover plate (such as touch sensitivity).

[0022] The sapphire layers of the cover plate can be prepared using any method known in the art. For example, the sapphire layers can be sawn or cut from a larger bulk sapphire crystal that has been prepared in a crystal growth apparatus, which is a high- temperature furnace capable of heating and melting solid feedstock, such as alumina, in a crucible at temperatures generally greater than about 1000°C, including greater than about 2000°C, and subsequently promoting resolidification of the resulting melted feedstock material to form a crystalline material, such as a sapphire boule. Preferably, the sapphire body is prepared in a heat exchanger method crystal growth furnace, in which a crucible comprising alumina feedstock and at least one single crystal sapphire seed is heated above its melting point to melt the feedstock without substantial melting of the seed, and the heat is then removed from the crucible using a heat exchanger, such as a helium-cooled heat exchanger, provided in thermal communication with the bottom of the crucible and positioned under the seed. This method has been shown to produce large, high quality sapphire bodies, sometimes referred to as boules, from which the sapphire layers can be removed.

[0023] The foregoing description of preferred embodiments of the present invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications and variations are possible in light of the above teachings, or may be acquired from practice of the invention. The embodiments were chosen and described in order to explain the principles of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto, and their equivalents.

[0024] What is claimed is:

Claims

1. An electronic device comprising a cover plate having at least one transparent display region, the cover plate comprising two or more sapphire layers, wherein at least two sapphire layers have different orientations.

2. The electronic device of claim 1, wherein the cover plate comprises a first sapphire layer having and a second sapphire layer, each having a crystalline orientation, and wherein the crystalline orientation of the first sapphire layer is different than the crystalline orientation of the second sapphire layer.

3. The electronic device of claim 2, wherein the first sapphire layer has a c-axis orientation and the second sapphire layer has an m-axis orientation.

4. The electronic device of claim 2, wherein the first sapphire layer has a c-axis orientation and the second sapphire layer has an a-axis orientation.

5. The electronic device of claim 1, wherein the cover plate comprises a first sapphire layer and a second sapphire layer, each having a surface orientation, and wherein the surface orientation of the first sapphire layer is different than the surface orientation of the second sapphire layer.

6. The electronic device of claim 5, wherein the first surface orientation and the second surface orientation are oriented surface artifacts.

7. The electronic device of claim 6, wherein the surface artifacts are locally stressed regions produced by polishing.

8. The electronic device of claim 1, wherein the two sapphire layers are adjacent to each other.

9. The electronic device of claim 1, wherein the two sapphire layers differ in thickness.

10. The electronic device of claim 1, wherein the two sapphire layers are substantially similar in thickness.

11. The electronic device of claim 1, wherein at least one of the two sapphire layers has a thickness of less than about 2 mm.

12. The electronic device of claim 1, wherein at least one of the two sapphire layers has a thickness of less than about 1 mm.

13. The electronic device of claim 1, wherein at least one of the sapphire layers has a thickness of less than 0.5 mm.

14. The electronic device of claim 1, wherein at least one of the two sapphire layers has a thickness of less than about 50 microns.

15. The electronic device of claim 1, wherein the cover plate has thickness between about 0.3 and 3.0.

16. The electronic device of claim 1, wherein the cover plate has thickness between about 0.4 and 2.5.

17. The electronic device of claim 1, wherein the cover plate has thickness between about 0.5 and 1.0.

18. The electronic device of claim 1, wherein the cover plate is two free standing sapphire layers adhered together.

19. The electronic device of claim 1, wherein the electronic device further comprises at least one display element having a display surface and wherein the cover plate is affixed to the display surface.

20. The electronic device of claim 1, wherein the electronic device further comprises at least one display element having a display surface and wherein the cover plate is a protective layer removably positioned on top of the display surface.

21. The electronic device of claim 1, wherein the cover plate further comprises an exterior anti-reflective layer.

22. The electronic device, of claim 1, wherein the electronic device is an electronic media player, a mobile telephone, a personal data assistant, a pager, a tablet, a laptop computer, or an electronic notebook

23. The electronic device of claim 1, wherein the sapphire layer comprises single crystal sapphire prepared in a crystal growth furnace.

24. The electronic device of claim 30, where the crystal growth furnace is a heat exchanger method furnace.