WO2015149851A1

WO2015149851A1 - Method and system for optical inspection of sapphire element

Info

Publication number: WO2015149851A1
Application number: PCT/EP2014/056644
Authority: WO
Inventors: Stewart DEWEY; Stuart GODFREY
Original assignee: Vertu Corporation Limited
Priority date: 2014-04-03
Filing date: 2014-04-03
Publication date: 2015-10-08
Also published as: CN106461573A

Abstract

A method, system and device for optical inspection of a sapphire element, comprising: providing the sapphire element to a measurement system comprising a light guide and a detecting device, wherein the sapphire element comprising a surface; directing light beams towards the surface of the sapphire element from an angle of inclination with respect to the sapphire element surface, wherein the light beams being provided by the light guide; detecting reflected light beams using the detecting device from the surface of the sapphire element, in response to the light beams directed towards the surface of the sapphire element, to provide a detection signal, wherein the detecting device arranged above of the field of the view of the sapphire element; and processing the detection signal to determine defect information relating to the surface of the sapphire element.

Description

METHOD AND SYSTEM FOR OPTICAL INSPECTION OF SAPPHIRE ELEMENT

TECHNICAL FIELD

The present invention relates generally to optical inspection of optical elements. The invention relates particularly, though not exclusively, to optical inspection of sapphire element.

BACKGROUND ART

Portable apparatuses, such as mobile phones, tablets and personal computers all need optical elements, such as transparent plastics and glass when constructing the product. With increasing consumer awareness of quality and value mobile manufacturers are continuing to use more and more quality materials. With respect to mobile phones and tablets, the last couple of years have seen a market shift from use of plastic screens to more scratch resistant chemical toughened glass (for example Gorilla® Glass).

While Gorilla® Glass is a significant improvement over plastic it can still be scratched by everyday items such as keys or coins in bags and pockets. Also, the glass is easily fractured if the product is dropped. For this reason sapphire, for example, is being considered more and more for use on consumer goods. Sapphire is the second hardest naturally occurring material and can only be scratched by diamonds. Sapphire is also a strong material and has a very high elastic modulus (stiffness). Thus, using sapphire in the construction of mobile apparatuses creates a very stiff product that is less likely to flex during accidental drop or impact. This makes sapphire a very resistant, long lasting material for mobile apparatus usage.

Sapphire is a ceramic material and the absolute strength and toughness of any ceramic is controlled by an area of materials science known as fracture toughness. Fracture toughness is the science that relates defects such as cracks and scratches to the early failure of materials. The simplest way to understand the concept of fracture toughness is to consider what happens when normal glass is scored with a diamond scribe to aid breaking the glass in a controlled way. Perfect, scratch free glass is fairly strong but as soon as a weakness is introduced into the glass (i.e. a scratch or a score) then the glass becomes weak and easily fractures along this defect. The same argument can be applied to sapphire, no matter sapphire being more scratch resistant than glass. It is only when the material is scratch free that the material has its optimum strength and toughness.

Sapphire is more expensive and heavier material than plastic or Gorilla® Glass and at the same time sizes of optical elements, such as display screens, tend to increase. Thus, especially for portable apparatuses an improved solution is needed to provide an optical element made of sapphire that is thinner than known solutions but still meets the strict requirements for portable apparatuses regarding to maximum strength and robustness.

However, the full toughness and strength of sapphire element is achieved when the sapphire material is highly polished and is free from scratches and effects. The detection of microscopic cracks and scratches in sapphire are virtually impossible to see with normal microscope techniques and hence it is difficult to quantify the exact level of scratches on the surface.

Gorilla glass and other chemically toughened glasses (such as Asahi, Dragontrail and others) are typically designed to deal with scratches and defects in a different way compared to sapphire. Gorilla® Glass achieves its toughness through a chemical toughening process which puts the surface layers of the glass into compression. Because the surface of the glass is in compression any cracks and defects do not prorogate to failure. The end result is that Gorilla® Glass can tolerate small scratches in the surface of the material without causing failure.

No such toughening / surface compression process exists for sapphire. Thus, a solution is needed to optically detect defects of a surface of the sapphire element. Only when the sapphire is processed to be completely free from defects are the maximum strength and toughness realized from the sapphire

SUMMARY

According to a first example aspect of the invention there is provided a method for optical inspection of a sapphire element, the method comprising:

providing the sapphire element to a measurement system comprising a light guide and a detecting device, wherein the sapphire element comprising a surface; directing light beams towards the surface of the sapphire element from an angle of inclination with respect to the sapphire element surface, wherein the light beams being provided by the light guide;

detecting reflected light beams using the detecting device from the surface of the sapphire element, in response to the light beams directed towards the surface of the sapphire element, to provide a detection signal, wherein the detecting device arranged above of a field of view of the sapphire element; and processing the detection signal to determine defect information relating to the surface of the sapphire element. In an embodiment, the light guide being arranged to a side of the field of view of the sapphire element.

In an embodiment, the light guide being arranged above the field of view of the sapphire element.

In an embodiment, the defect information comprising at least one of the following: surface scratch information; and

surface shape information.

In an embodiment, the detecting device comprises a microscope.

In an embodiment, the detecting device comprising an objective lens for forming an image based on the reflected light beams. In an embodiment, the detecting device comprising a sensor for forming an image signal based on the reflected light beams. In an embodiment, the light guide comprising at least one of the following:

a prism; and

a light source.

In an embodiment, the light source comprising a dark field light source.

In an embodiment, the light source comprising a circular light source.

In an embodiment, the method further comprising:

providing the sapphire element to a measurement system using a rotatable cradle;

rotating the cradle comprising the sapphire element;

directing light beams towards the surface of the sapphire element from an angle of inclination with respect to the sapphire element surface, wherein the light beams being provided by the light guide;

detecting reflected light beams using the detecting sensor from the surface of the sapphire element, in response to the light beams directed towards the surface of the sapphire element, to provide a detection signal of at least two different rotating moments, wherein the detecting sensor arranged to a top of the sapphire element; and

processing the detection signal of at least two different rotating moments to determine defect information relating to the surface of the sapphire element.

In an embodiment, the angle of inclination being different to 90 degrees. In an embodiment, the detecting device arranged to measure reflected light beams in an optical angle, and the angle of inclination being different to the optical angle. According to a second example aspect of the invention there is provided a system for optical inspection of a sapphire element, the system comprising:

a light guide for directing light beams towards a surface of the sapphire element from an angle of inclination with respect to the sapphire element surface; and

a detecting device for detecting reflected light beams from the surface of the sapphire element, in response to the light beams directed towards the surface of the sapphire element, to provide a detection signal, wherein a detecting device being arranged above a field of view of the sapphire element, wherein the system being configured to process the detection signal to determine defect information relating to the surface of the sapphire element.

In an embodiment, the light guide being arranged to a side of the field of view of the sapphire element.

In an embodiment, the detecting device arranged to receive reflected light beams in an optical angle, and the angle of inclination being different to the optical angle.

In an embodiment, the system comprising:

an objective lens and a sensor for forming an image signal based on the reflected light beams; and

a plurality of prisms arranged around the outside of the objective lens to provide an annulus of light around an optical light path of the detecting device.

In an embodiment, the system comprising:

an objective lens and a sensor for forming an image based on the reflected light beams; and

a plurality of light sources arranged around the outside of the objective lens to provide an annulus of light around an optical light path of the detecting device. In an embodiment, the system comprising:

a rotatable cradle for the sapphire element, the rotatable cradle configured to rotate the sapphire element within the measurement system. In an embodiment, the system comprising:

an eyepiece for forming an image for a user for inspecting the sapphire element.

According to a third example aspect of the invention there is provided a detecting device for optical inspection of a sapphire element, the device comprising:

an objective lens for receiving reflected light beams from the surface of the sapphire element, in response to the light beams directed towards the surface of the sapphire element, wherein the detecting device being arranged above a field of view of the sapphire element.

In an embodiment, the device comprising a sensor for forming an image signal based on the reflected light beams.

In an embodiment, the device comprising a microscope.

In an embodiment, the device comprising an eyepiece for forming an image for a user for inspecting the sapphire element.

According to a fourth example aspect of the invention there is provided an optical element inspected according to the first aspect. According to a fifth example aspect of the invention there is provided an apparatus comprising an optical element of the fourth aspect. In an embodiment, the optical element comprises a display part or a cover part of the apparatus.

In an embodiment, a higher strength axis of a sapphire element is aligned with a higher stress direction of the apparatus.

The apparatus may comprise a portable apparatus, such as a tablet, a smartphone, a mobile phone, a laptop, a digital camera or a personal digital assistant (PDA), for example.

Different non-binding example aspects and embodiments of the present invention have been illustrated in the foregoing. The above embodiments are used merely to explain selected aspects or steps that may be utilized in implementations of the present invention. Some embodiments may be presented only with reference to certain example aspects of the invention. It should be appreciated that corresponding embodiments may apply to other example aspects as well.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described, by way of example only, with reference to the accompanying drawings, in which:

Fig. 1 shows some details of a mobile apparatus in which various embodiments of the invention may be applied;

Fig. 2 shows some details of a mobile apparatus in which various embodiments of the invention may be applied;

Fig. 3 presents a schematic view of a system for detecting defects on a surface of a sapphire element, in which various embodiments of the invention may be applied;

Fig. 4 presents a schematic view of a sapphire crystallographic structure for an optical element, in which various embodiments of the invention may be applied; Fig. 5a presents a schematic side view of a detecting device, such as a microscope, in which various embodiments of the invention may be applied;

Fig. 5b presents a schematic plan view of a detecting device, such as a microscope, in which various embodiments of the invention may be applied;

Fig. 6 shows a flow diagram showing operations, in accordance with an example embodiment of the invention;

Fig. 7 presents an example block diagram of an apparatus in which various embodiments of the invention may be applied;

Fig. 8 shows a schematic view of a sapphire crystal structure, known also as a unit cell, having a plurality of crystal planes, in which various embodiments of the invention may be applied;

Fig 9a shows a micrograph view of a magnified area image of sapphire using a prior known solution, such as bright field inspection; and

Fig 9b shows a micrograph view of a magnified area image of sapphire in which various embodiments of the invention may be applied.

DETAILED DESCRIPTION

In the following description, like numbers denote like elements.

Fig. 1 shows some details of a mobile apparatus 100 in which various embodiments of the invention may be applied.

In an embodiment, the mobile apparatus 100 may comprise a mobile phone, a smart phone, a tablet, a laptop or any other portable apparatus. The apparatus comprises at least one cover part 1 10 for providing protection to the components of the apparatus 100 and creating desired outlook and outer design for the apparatus 100. The cover part 1 10 may comprise several separate cover parts, such as front and rear covers and even a side frame. In Fig. 1 , mainly the front cover is shown. The apparatus 100 further comprises user interface 120, 130 comprising at least one display 120. The display 120 may be a touch-sensitive display for detecting user gestures and providing feedback for the apparatus 100. The apparatus 100 may also comprise a user input device 130, such as a keypad or a touchpad, for example. Furthermore, the apparatus 100 may comprise a camera 140. No matter the described elements 1 10, 120, 130, 140 are shown on the same side of the apparatus 100, they can be located on any side of the apparatus 100. No matter a plurality of apparatus elements 120-140 are illustrated in Fig. 1 , they all need not to be included. For example, only a touch-sensitive display 120 may be included without the need for separate user input device 130. In an embodiment, at least one of the apparatus elements 1 10, 120, 130, 140 comprises an optical element, such as transparent sheet, layer or glass, for example. The cover part 1 10 may comprise an optical element, such as transparent layer coating, to provide good-looking, strong and scratch resistant surface for the apparatus. The display 120 may comprise an optical element, such as a transparent protection layer, to provide strong and scratch-resistant surface for the display but still enable clear visibility for the display 120 from all angles. The user input device may comprise an optical element, similarly as the display, in case of a touchpad, and similarly as the cover part for the keypad frame in case of a traditional keypad. The camera 140 may comprise an optical element, such as protective lens, for example.

In an embodiment, the display 120 may form a permanent part of the cover part 1 10 or, to increase the potential for upgrading the engine throughout the life of the cover part 1 10 it may be a module that can be replaced too. Alternatively, a protective layer of the display 120 may be a part of the cover part 1 10 that layer may be independently exchanged. In further alternative embodiment the protective layer of the display 120 is integrated to the cover part 1 10.

In embodiments of the invention the surface of the optical element, such as sapphire element, may provide an operating face of the device. This gives a design engineer far greater freedom to design a device with a desirable appearance. The operating face may be provided with a user input element 130, for example a key, a touchpad, or an array of such elements. The casing may be a conventional one part casing or a clam shell, or other two or more part arrangement, where the user input elements 130 or keys may be located on a different face to a display 120. Fig. 2 shows some details of a mobile apparatus 100 in which various embodiments of the invention may be applied.

In an embodiment, the cover part 1 10 may also comprise a plurality of cover part elements, located in front and rear covers and in a side frame. In Fig. 2, mainly the rear cover of the apparatus 100 is shown. The apparatus 100 may comprise cover part elements comprising optical elements 210-230. Such optical elements 210- 230 may be configured to provide decorative effects, protective features for underlying elements, or operational features for the apparatus 100, such as speaker or microphone housings. The rear cover of the cover part 1 10 shown in Fig. 2 may also comprise optical elements 210-230, such as display or touchpad, for example. No matter the described elements 210-230 are shown on the same side of the apparatus 100, they can be located on any side of the apparatus 100. No matter a plurality of apparatus elements 210-230 are illustrated in Fig. 2, they all need not to be included.

In an embodiment, at least one of the apparatus elements 210-230 comprises an optical element, such as a sapphire element, for example. The cover part 1 10 may comprise an optical element, such as sapphire layer coating, to provide good- looking, strong and scratch resistant surface for the apparatus.

Sapphire may be used for mobile apparatus optical elements, such as display, cover part element or touch pad, for example. Sapphire has high hardness and strength but its higher refractive index means that more light is reflected from the surface compared to prior known glass or plastic screens.

The present invention discusses both sapphire and alumina. The chemical composition of both is based on AI2O3. For clarifying purposes, sapphire may be understood in this context as a single crystal of alumina and alumina as a polycrystalline form of alumina (PCA).

Fig. 3 presents a schematic view of a system 300 for detecting defects on a surface of a sapphire element 310, in which various embodiments of the invention may be applied.

Controlling and eradicating all grinding and/or polishing scratches is important to reach a maximum strength and toughness from sapphire materials when providing sapphire elements for mobile apparatuses. However, identifying possible defects in a surface of a sapphire element is a particularly difficult problem. This is mainly due to a fact that scratches and cracks possibly weakening the sapphire element are extremely small (under 5 microns) and hence may only be seen with a microscope. However, because sapphire is a transparent material it is virtually impossible to see such scratches using known microscope methods, such as bright field microscopy.

In an embodiment, dark field microscopy is used to allow defects such as scratches and cracks to be easily seen within sapphire element. The dark field microscopy technique may be used as part of the manufacturing process to produce high quality, defect free sapphire elements.

In an embodiment, the dark field microscopy technique may be used at the end of the manufacturing process to confirm that the high quality defect free sapphire elements have been assembled in the final product.

In an embodiment, a sapphire element 310 is optically inspected. A light guide 320, 333, 340 and a detecting device 330 are arranged to the system 300. In an embodiment, at least one light guide 320, 333, 340 is included in the system 300. The system is not limited to the presented positions of light guides but they are presented only as illustrative examples. A light guide 320 may be arranged to a side of the field of the view of the sapphire element. Alternatively a light guide 340, 333 may be arranged above of the field of the view of the sapphire element. The light guide 333 may be integral to the detecting device 330 or a separate light guide 320, 340. The sapphire element 310 comprises a surface 31 1 that is inspected for scratches, for example.

In an embodiment, light beams 321 are directed towards the surface 31 1 of the sapphire element 310 from an angle of inclination (Θ). The angle may be less than 45 degrees with respect to the sapphire element surface 31 1 , for example. The light beams 321 are provided by the light guide 320 arranged to a side of the field of view (FOV) of the sapphire element 310 or by the light guide 333, 340 arranged above of the field of view (FOV) of the sapphire element 310. The light guide 320, 333, 340 may comprise at least one light source or prism, for example.

If the surface 31 1 of the sapphire is perfectly polished then the angle of inclination (O) of the light beam 321 and the angle of reflection 322 will be the same. In this case the reflected light beam 322 does not enter the detection device 330. However, if a scratch is present then this presents a new surface 31 1 that reflects the light beam 323 into the detector 330. The scratches are analogous to tiny mirrors that are angled such that the incident light beam 322 is reflected into the detector 330 and thus detected as a signal.

In an embodiment, reflected light beams 322, 323 are detected using the detecting device 330 from the surface 31 1 of the sapphire element 310, in response to the light beams 321 directed towards the surface 31 1 of the sapphire element 310, to provide a detection signal. The detecting device 330 is arranged above of the field of view (FOV) of the sapphire element 310. The detection signal is processed to determine defect information relating to the surface 31 1 of the sapphire element 310.

The defect information may comprise surface scratch information, crack information, or surface shape information, for example. In an embodiment, the detecting device 330 comprises a microscope. The microscope may comprise an objective lens 331 for forming an image based on the reflected light beams 322, 323.

In an embodiment, light beams may be directed towards the surface 31 1 of the sapphire element 310 from an angle of inclination with respect to the sapphire element surface 31 1 , wherein the light beams being provided by a light guide arranged to another side than the light guide 320 respective of the field of the view (FOV) of the sapphire element 310.

In an embodiment, a light guide 340 may direct light beams 341 towards the surface 31 1 of the sapphire element 310 from an angle of inclination with respect to the sapphire element surface 31 1 or at least from an angle different to 90 degrees, wherein the light beams 341 are provided by a light guide 340 arranged above the field of the view (FOV) of the sapphire element 310. Reflected light beams 342 may be detected by the detecting device 330.

In an embodiment, a light guide 333 may direct light beams towards the surface 31 1 of the sapphire element 310 from an angle of inclination with respect to the sapphire element surface 31 1 or at least from an angle different to 90 degrees, wherein the light beams are provided by a light guide 333 integral to the device 330 and arranged above the field of the view (FOV) of the sapphire element 310. Reflected light beams may be detected by the detecting device 330.

In an embodiment, the light guide 320, 340 may comprise a dark field light source or a circular light source.

In an embodiment, the detecting device 330 comprises the objective lens 331 and a sensor (not shown). At least one light guide 320, 333, 340 is provided by an illumination system that is separate from the detecting device 330. In an embodiment, the detecting device 330 comprises the objective lens 331 , a sensor (not shown) and at least one light guide 320, 333, 340.

In an embodiment, the sapphire element 310 may be provided to a measurement system 300 using a rotatable cradle 350. The cradle 350 comprising the sapphire element 310 may be rotated when measuring the sapphire element 310, directing light beams towards the surface 31 1 of the sapphire element 310 from an angle of inclination with respect to the sapphire element surface, wherein the light beams being provided by the light guide 320, 333, 340 arranged to a side of the field of the view (FOV) of the sapphire element 310 or above the field of the view (FOV) of the sapphire element 310. Reflected light beams 322, 323, 342 may be detected using the detecting device 330 from the surface 31 1 of the sapphire element 310, in response to the light beams directed towards the surface of the sapphire element, to provide a detection signal of at least two different rotating moments, wherein the detecting device 330 arranged above of the field of the view of the sapphire element. The detection signal of at least two different rotating moments may then be processed to determine defect information relating to the surface 31 1 of the sapphire element 310. In an embodiment, dark field microscopy is utilized so that the light 321 that is used to illuminate the sample 310 comes from the side of the sample 310 whereas in normal bright field microscopy the sample is illuminated by light 360 that comes down the optical axis (i.e. perpendicularly to the surface sample 310) of the microscope 330 and providing the bright field 361 for the microscope 330.

In an embodiment, a number of prisms 333 are arranged around the outside of the objective lens 331 . These multiple prisms 333 may effectively create a ring or annulus of light (dark field light illumination) around the optical light path of the lens 331 (of a microscope, for example). The same effect (i.e. an annulus of light) could be achieved by a separate light source that does not involve any prisms 333. A continuous or semi-continuous annulus of light may be created so to illuminate all scratches at all possible angles. The dark field technique works because the scratches act like tiny mirrors in the surface 31 1 of the sapphire 310 so when imagined with dark field illumination 320 (i.e. from the side) the scratches "light up" and become visible. In an embodiment, the detecting device 330 is arranged in optical angle with respect to the field of view of the sapphire element 310. The optical angle corresponds to the angle in which the detecting device is pointed in view of the field of the view. The light beams are directed towards the surface of the sapphire element from an angle of inclination with respect to the sapphire element surface and the angle of inclination is different to the optical angle.

Such solution enables to detect the scratches that control the strength and toughness of the sapphire material. The practical implications of this are that larger and thinner sapphire element can be used on mobile apparatuses more reliably without failures.

This invention would allow sapphire element surface to be accurately examined and hence produced to a very high standard which in turn allows sapphire to be used in a mobile apparatus with more design freedom. This would ultimately make the product thinner, lighter and more robust.

In an embodiment, the detecting systems comprises of an eyepiece 332 for forming an image so that inspections can be performed manually using the human eye.

In an embodiment, depending upon the geometry of the sapphire element 310 or the geometry of a specific defect, different light sources 320, 333, 340 at different angles of illumination might be used to make the scratch visible by dark field illumination.

Fig. 4 presents a schematic view 400 of a sapphire crystallographic structure 410 for an optical element 420, in which various embodiments of the invention may be applied. The optical element 420 may comprise a sapphire element optically inspected.

The optical element 420 may be a display element, for example. The optical element 420 is developed by growing the sapphire crystallographic structure 410. The growing may be arranged in desired planes after detecting the planes and axes of the sapphire single crystal, for example.

In an embodiment, the desired dimensions of the optical element 420 comprise a length L over a first axis and a width W over a second axis, as shown in Fig. 4.

In an embodiment, orientation of the sapphire unit cell 410 may be selected so that the plane of the optical element 420 corresponds to certain planes of the sapphire cell.

Fig. 5a presents a schematic side view of a detecting device 500, such as a microscope, in which various embodiments of the invention may be applied. The microscope may be a dark field microscope, for example. In an embodiment, an objective lens 510 is comprised by the detecting device 500. Optical axis 520 of the lens 510 is selected appropriate for inspecting a sapphire element in question. A sensor 521 may be configured to provide an image signal based on the reflected beams travelling through the lens 510. The image signal may be provided to the user via an eyepiece 332 of Fig. 3, for example.

In an embodiment, at least one prism 530 may be mounted in the detecting device 500 objective to create dark field light beams 540 using the light beams 550 of a circular light source. In an embodiment, the detecting device 500 comprises the objective lens 510 and the sensor 521 . At least one light guide 530, is provided by an illumination system that is separate from the detecting device 330. In an embodiment, the detecting device 500 comprises the objective lens 510, the sensor 521 and at least one light guide 530.

Fig. 5b presents a schematic plan view of a detecting device 500, such as a microscope, in which various embodiments of the invention may be applied.

In an embodiment, an objective lens 510 is comprised by the detecting device 500 to form an image. Light beams may be directed towards the surface of the sapphire element inspected by the device 500, wherein the light beams are provided to a side of a field of the view of the sapphire element. Reflected light beams are detected using the detecting sensor from the surface of the sapphire element, in response to the light beams directed towards the surface of the sapphire element, to provide a detection signal, such as an image. The detecting device is arranged above of the sapphire element. The detection signal may then be processed to determine defect information relating to the surface of the sapphire element.

In an embodiment, a circular light source 560 is used to evenly illuminate the optically detected sapphire with a dark field light beams 540 guided using the prism 530, for example.

Fig. 6 shows operations in a portable apparatus in accordance with an example embodiment of the invention.

In step 600, a method for optical inspection of a sapphire element is started. In step 610, the sapphire element is provided to a measurement system comprising a light guide and a detecting device, wherein the sapphire element comprising a surface. In step 620, light beams are directed towards the surface of the sapphire element from an angle of inclination with respect to the sapphire element surface, wherein the light beams being provided by the light guide arranged to a side of a field of the view of the sapphire element. In step 620, a plurality of light beams from different angles may be used. In step 630, reflected light beams are detected using the detecting device from the surface of the sapphire element, in response to the light beams directed towards the surface of the sapphire element, to provide a detection signal, wherein the detecting device arranged above of the field of the view of the sapphire element. In step 640, the detection signal is processed to determine defect information relating to the surface of the sapphire element. In step 650, the method ends.

Fig. 7 presents an example block diagram of a portable apparatus 100 in which various embodiments of the invention may be applied. The portable apparatus 100 may be a user equipment (UE), user device or apparatus, such as a mobile terminal, a smart phone, a personal digital assistant (PDA), a MP3 player, a laptop, a tablet or other electronic device.

The general structure of the mobile apparatus 100 comprises a user interface 740, a communication interface 750, a processor 710, and a memory 720 coupled to the processor 710. The apparatus 100 further comprises software 730 stored in the memory 720 and operable to be loaded into and executed in the processor 710. The software 730 may comprise one or more software modules and can be in the form of a computer program product. The apparatus 100 further comprises an optical element 760. The optical element may comprise a sapphire element being optically inspected. The optical element 760 may be inspected with different criteria depending on the usage of the element 760 within the apparatus 100. Thus requirements for the optical element 760 used as a display layer may be different to the optical element 760 used as a cover part, for example. The optical element 760 may also be integrated to another element of the apparatus 100, for example to the user interface 740.

The processor 710 may be, e.g. a central processing unit (CPU), a microprocessor, a digital signal processor (DSP), a graphics processing unit, or the like. Fig. 7 shows one processor 710, but the apparatus 100 may comprise a plurality of processors.

The memory 720 may be for example a non-volatile or a volatile memory, such as a read-only memory (ROM), a programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), a random-access memory (RAM), a flash memory, a data disk, an optical storage, a magnetic storage, a smart card, or the like. The apparatus 100 may comprise a plurality of memories. The memory 720 may be constructed as a part of the apparatus 100 or it may be inserted into a slot, port, or the like of the apparatus 100 by a user. The memory 720 may serve the sole purpose of storing data, or it may be constructed as a part of an apparatus serving other purposes, such as processing data.

The user interface 740 may comprise circuitry for receiving input from a user of the apparatus 100, e.g., via a keyboard, graphical user interface shown on the display of the user apparatus 100, speech recognition circuitry, or an accessory device, such as a headset, and for providing output to the user via, e.g., a graphical user interface or a loudspeaker. The display of the user interface 740 may comprise a touch-sensitive display. The optical element 760 may be integrated to the user interface 740, such as a display, a keyboard, or a touchpad. The optical element may also be integrated to a cover part of the apparatus 100.

The optical element 760 may also be comprised by the camera, for providing a protective sheet for the camera optics. The optical element 760 may also provide a protective sheet for multiple elements of the apparatus 100. In an example embodiment, an optical element 760 is configured to provide a protective sheet for the display of the apparatus 100. The optical element may even cover at least a part of the front, rear or side surface of the apparatus 100 cover. The communication interface module 750 implements at least part of radio transmission. The communication interface module 750 may comprise, e.g., a wireless interface module. The wireless interface may comprise such as near field communication (NFC), a WLAN, Bluetooth, infrared (IR), radio frequency identification (RF ID), GSM/GPRS, CDMA, WCDMA, or LTE (Long Term Evolution) radio module. The communication interface module 750 may be integrated into the user apparatus 100, or into an adapter, card or the like that may be inserted into a suitable slot or port of the apparatus 100. The communication interface module 750 may support one radio interface technology or a plurality of technologies. The apparatus 100 may comprise a plurality of communication interface modules 750.

A skilled person appreciates that in addition to the elements shown in Fig. 7, the apparatus 100 may comprise other elements.

Fig. 8 shows a schematic view of a sapphire crystal structure 800, known also as a unit cell, having a plurality of crystal planes 810-840, in which various embodiments of the invention may be applied.

Sapphire is a single crystal material, i.e. it is grown as a continuous large single crystal without grain boundaries. Such a single crystal may be grown before cutting to a desired size and shape for an optical element. The sapphire single crystal, i.e., AI2O3, is used for usage of wider range, because it has higher hardness and toughness. The single crystal of sapphire may be pulled, growing a seed crystal in contact with the surface of the molten alumina to produce the single crystal into a larger single crystal, so as to generally work the single crystal into the desired shape.

In an embodiment, the sapphire crystal is either cut or grown so that a specific plane within the crystal is parallel to the sheet orientation of the sapphire. Hence sapphire may be referred to as A-plane or C-plane sapphire, for example. Thus for A-plane sapphire the A-plane is parallel to a screen direction of the optical element.

Sapphire single crystal is an anisotropic material. This means that the material has different mechanical properties (strength, hardness, optical properties etc.) depending on the direction of the crystal. In simplest terms, A-plane sapphire is generally the strongest plane whilst C-plane has the best optical properties.

In the crystal structure of a sapphire, as shown in Fig. 8, the sapphire crystal is a hexagonal system, wherein C-axis forms a central axis being vertical and normal to C-plane 820. Due to the symmetry of the sapphire crystal structure the A-plane has numerous A-axes in Fig. 8, for example axis a1 to a3 that are to be extended in three directions perpendicular to C-axis. Respectively, A-plane 810 is shown in Fig. 8. M-plane 830 is perpendicular to C-plane 820 and A-plane 810. R-plane 840 is oblique at a constant angle to C-axis.

No matter only four planes 810-840 is shown, the crystal cell may comprise other planes. Furthermore, due to crystal symmetry, there may be several identical planes for each major plane. For example, the unit cell 800 may comprise three A- planes 810, three R-planes 840, one C-plane 820 and three M-planes 830, for example.

The C-axis is typically angled approximately 57.6 degrees with respect to the R- axis. The R-axis is typically angled with respect to the M-axis by approximately 32.4 degrees. The planes and axes of the sapphire can be analyzed for example with X-ray or electron diffraction and can be determined about the actual sapphire single crystal.

In an embodiment, measurements of the sapphire crystal have revealed that A- plane is generally the strongest plane regarding to mechanical stress. However, the integration of sapphire to an optical element of a portable apparatus may be taken even further by controlling anisotropy (sometimes referred to as minor planes) such that the sapphire is orientated within the optical element of the apparatus for maximum strength and hence reliability.

In an embodiment, the crystal planes and directions in hexagonal systems may be indexed using Miller indices, wherein crystallographically equivalent planes have indices which appear dissimilar. To overcome this Miller-Bravais indexing system may be used, where a fourth index is introduced to the three of the Miller system.

A plane is then specified using four indices (hkil), where h, k, i and I are integers. The third index is always the negative of the sum of the first two and can be determined from the Miller system. A direction is specified as [uvtw] where u, v, t and w are integers. The values of u, v and t are adjusted so that their sum is zero. The direction index cannot be written down from the equivalent Miller index.

When looking at Fig. 8 and using the Miller-Bravais indices for defining the planes, following mapping could be used:

- C-plane 820 corresponds to {0 0 0 1 } of the Miller-Bravais indices;

- R-plane 840 corresponds to { 1 0 1 2} of the Miller-Bravais indices; - A-plane 810 corresponds to {1 1 2 0} of the Miller-Bravais indices; and

- M-plane 830 corresponds to {1 0 1 0} of the Miller-Bravais indices.

Referring to Fig. 4, A-plane of the sapphire cell 410 is shown. The length L in this embodiment is greater than the width W, as can be seen from Fig. 4. The sapphire crystallographic structure is configured so that a main plane of the sapphire cell 410 is set to be parallel to the surface plane of the optical element 420 and two minor planes are set to be parallel to the first and second axes (W and L).

In an embodiment, the optical element 420 of an apparatus has a length L in a direction of a first axis and a width W in a direction of a second axis, wherein the length L is greater than or equal to the width W. The optical element 420 is developed and comprising a sapphire crystallographic structure 410 having a plurality of crystal planes with corresponding normal axes represented as C-axis, A-axis and M-axis, for example. A first crystal plane axis is configured to be perpendicular to the first axis L and the second axis W. A second crystal plane axis is configured to be parallel to the first axis L and a third crystal plane axis is configured to be parallel to the second axis W.

In an embodiment, a sapphire crystallographic structure has a plurality of crystal planes, wherein three major planes maybe be represented by three orthogonal axis, wherein a first crystal plane axis is configured to be perpendicular to the second crystal plane axis and the third crystal plane axis is configured to be perpendicular to the first crystal plane axis and the second crystal plane axis.

The plurality of crystal planes comprise at least:

A-plane with A-axis configured to be a normal axis of the A-plane;

C-plane with C-axis configured to be a normal axis of the C-plane, the C- axis being perpendicular to the A-axis; and

M-plane with M-axis configured to be a normal axis of the M-plane, the M- axis being perpendicular to the A-axis and the C-axis.

In an embodiment, the plurality of crystal planes comprises:

A-plane with A-axis configured to be a normal axis of the A-plane, the A- axis being perpendicular to the C-axis and perpendicular to the M-axis; and

C-plane with C-axis configured to be a normal axis of the C-plane, the C- axis being perpendicular to the A-axis and perpendicular to the M-axis; and

M-plane with M-axis configured to be a normal axis of the M-plane, the M- axis being perpendicular to the A-axis and perpendicular to the C-axis.

In an embodiment, the first crystal plane axis is the A-axis perpendicular to the W- axis and the L-axis, the second crystal plane axis is the M-axis parallel to the L- axis and the third crystal plane axis is the C-axis parallel to the W-axis.

Configuring the sapphire crystal 410 planes so that A-plane is parallel to the surface plane of the optical element 420, such as flat display screen, provides improved strength for the optical element 420. Even further strength for the optical element is achieved by aligning the M-axis of the M-plane parallel to a longer side L of the optical element 420 and the C-axis of the C-plane parallel to a shorter side of the optical element 420. Fig 9a shows a micrograph view of a magnified area image 900 of sapphire using a prior known solution, such as bright field inspection. The area image 900 may be 100x magnified area of the sapphire. As can be seen from Fig. 9a, there are no scratches visible in the image 900, such as a bright field image. Fig 9b shows a micrograph view of a magnified area image 910 of sapphire in which various embodiments of the invention may be applied. The area image 910 may be 100x magnified area of the sapphire and correspond to the same area as the area for image 900 in Fig. 9a. The area image 910 may also correspond to the image created from the field of view (FOV) of Fig. 3.

Lots of scratches are visible in the area image 910 and the difference in the two images 900 and 910 for the same area of sapphire is considerable. The image 900 captured using the prior known solution (such as bright field) is featureless without any visible scratches, whereas the solution utilizing embodiments of the invention shows up many scratches within the image 910.

Various embodiments have been presented. It should be appreciated that in this document, words comprise, include and contain are each used as open-ended expressions with no intended exclusivity.

The foregoing description has provided by way of non-limiting examples of particular implementations and embodiments of the invention a full and informative description of the best mode presently contemplated by the inventors for carrying out the invention. It is however clear to a person skilled in the art that the invention is not restricted to details of the embodiments presented above, but that it can be implemented in other embodiments using equivalent means or in different combinations of embodiments without deviating from the characteristics of the invention.

Furthermore, some of the features of the above-disclosed embodiments of this invention may be used to advantage without the corresponding use of other features. As such, the foregoing description shall be considered as merely illustrative of the principles of the present invention, and not in limitation thereof. Hence, the scope of the invention is only restricted by the appended patent claims.

Claims

Claims:

1 . A method for optical inspection of a sapphire element, the method comprising:

detecting reflected light beams using the detecting device from the surface of the sapphire element, in response to the light beams directed towards the surface of the sapphire element, to provide a detection signal, wherein the detecting device arranged above of a field of view of the sapphire element; and processing the detection signal to determine defect information relating to the surface of the sapphire element.

2. The method of claim 1 , wherein the light guide being arranged to a side of the field of view of the sapphire element.

3. The method of claim 1 , wherein the light guide being arranged above the field of view of the sapphire element.

4. The method of any of claims 1 to 3, wherein the defect information comprising at least one of the following:

surface scratch information; and

surface shape information.

5. The method of any of claims 1 to 4, wherein the detecting device comprises a microscope.

6. The method of any of claims 1 to 5, wherein the detecting device comprising an objective lens for forming an image based on the reflected light beams.

7. The method of any of claims 1 to 6, wherein the detecting device comprising a sensor for forming an image signal based on the reflected light beams.

8. The method of any of claims 1 to 7, wherein the light guide comprising at least one of the following:

a prism; and

a light source.

9. The method of claim 8, wherein the light source comprising a dark field light source.

10. The method of claim 9, wherein the light source comprising a circular light source.

1 1 . The method of any of claims 1 to 10, further comprising:

rotating the cradle comprising the sapphire element;

12. The method of any of claims 1 to 1 1 , wherein the angle of inclination being different to 90 degrees.

13. The method of any of claims 1 to 12, wherein the detecting device arranged to measure reflected light beams in an optical angle, and the angle of inclination being different to the optical angle.

14. A system for optical inspection of a sapphire element, the system comprising:

a detecting device for detecting reflected light beams from the surface of the sapphire element, in response to the light beams directed towards the surface of the sapphire element, to provide a detection signal, wherein a detecting device being arranged above a field of the view of the sapphire element, wherein the system being configured to process the detection signal to determine defect information relating to the surface of the sapphire element.

15. The system of claim 14, wherein the light guide being arranged to a side of the field of view of the sapphire element.

16. The system of claim 14, wherein the light guide being arranged above the field of view of the sapphire element.

17. The system of any of claims 14 to 16 for optical inspection of a sapphire element, wherein the detecting device arranged to receive reflected light beams in an optical angle, and the angle of inclination being different to the optical angle.

18. The system of any of claims 14 to 17 for optical inspection of a sapphire element, wherein the system comprising:

19. The system of any of claims 14 to 17 for optical inspection of a sapphire element, wherein the system comprising:

a plurality of light sources arranged around the outside of the objective lens to provide an annulus of light around an optical light path of the detecting device.

20. The system of any of claims 14 to 19 for optical inspection of a sapphire element, the system comprising:

a rotatable cradle for the sapphire element, the rotatable cradle configured to rotate the sapphire element within the measurement system.

21 . The system of any of claims 14 to 20 for optical inspection of a sapphire element, the system comprising:

22. A detecting device for optical inspection of a sapphire element, the device comprising:

23. The detecting device of claim 22 for optical inspection of a sapphire element, the device comprising:

an objective lens for forming an image based on the reflected light beams.

24. The detecting device of claim 22 or 23 for optical inspection of a sapphire element, the device comprising: a sensor for forming an image signal based on the reflected light beams.

25. The detecting device of any of claims 22 to 24 for optical inspection of a sapphire element, the device comprising a microscope.

26. The detecting device of any of claims 22 to 25 for optical inspection of a sapphire element, the device comprising an eyepiece for forming an image for a user for inspecting the sapphire element.