PATENT DOCUMENT

Publication Number: US-11402669-B2
Application Number: US-201916268338-A
Country: US
Kind Code: B2

Title: Housing surface with tactile friction features

Abstract:
A glass component of an electronic device housing may define a textured surface having micro-scale tactile friction features that provide a specified friction between a user&#39;s finger and the glass component. More specifically, the tactile friction features may reduce a contact surface area that is in contact with the user&#39;s finger in order to produce a reduced or specified coefficient of friction.

Claims:
What is claimed is: 
     
       1. An electronic device comprising:
 an enclosure defining an internal volume and having a glass structure at least partially defining a touch-sensitive exterior surface of the electronic device, the touch-sensitive exterior surface comprising:
 a base surface defining a first planar region having a first area; and 
 a set of tactile friction features distributed along the touch-sensitive exterior surface and extending from the base surface to define:
 a plurality of substantially flat tops, the plurality of substantially flat tops defining a second planar region having a second area less than the first area; 
 a micro-scale average width; and 
 a height defined by an offset between the second planar region and the first planar region, the height less than the micro-scale average width; and 
 
 
 a touch sensor positioned below the glass structure and configured to detect a touch gesture along the touch-sensitive exterior surface, the set of tactile friction features providing a frictional resistance to the touch gesture. 
 
     
     
       2. The electronic device of  claim 1 , wherein:
 each tactile friction feature of the set of tactile friction features has a circular contour defining a diameter ranging from 1 micron to 20 microns; and 
 the height is less than or equal to 5 microns. 
 
     
     
       3. The electronic device of  claim 1 , wherein:
 the electronic device further comprises a display positioned under the glass structure; 
 the glass structure comprises:
 a first region positioned over a visible portion of the display; and 
 a second region at least partially surrounding the first region and not positioned over the visible portion of the display; 
 
 the set of tactile friction features is a first set of tactile friction features positioned along the first region; 
 the electronic device further comprises a second set of tactile friction features positioned along the second region; and 
 a first pitch between tactile friction features of the first set of tactile friction features is greater than a second pitch between tactile friction features of the second set of tactile friction features. 
 
     
     
       4. The electronic device of  claim 3 , wherein:
 the first pitch is measured as an average distance between centers of adjacent tactile friction features; and 
 the first pitch is between 5 and 600 microns. 
 
     
     
       5. The electronic device of  claim 1 , wherein:
 the touch gesture is provided by a user&#39;s finger in contact with the touch-sensitive exterior surface; and 
 the set of tactile friction features prevents the user&#39;s finger from contacting the base surface. 
 
     
     
       6. An electronic device comprising:
 a display; 
 a touch sensor positioned over the display; and 
 an enclosure comprising a glass structure enclosing the display and defining an exterior surface of the electronic device, a touch-sensitive region of the exterior surface of the electronic device positioned over the touch sensor and defining a substantially planar base surface and a set of glass tactile friction features extending from the substantially planar base surface, each glass tactile friction feature of the set of glass tactile friction features including:
 a base having a micro-scale width; 
 a top; 
 a sidewall extending from the base to the top; and 
 a height between the base and the top, the height being less than or equal to the micro-scale width, 
 
 wherein: 
 the tops of multiple glass tactile friction features of the set of glass tactile friction features are substantially flat; and 
 the set of glass tactile friction features are configured to provide a frictional resistance to a touch applied to the touch-sensitive region. 
 
     
     
       7. The electronic device of  claim 6 , wherein:
 the set of glass tactile friction features is substantially evenly distributed over the touch-sensitive region; 
 and 
 the frictional resistance is due, at least in part, to contact between a user&#39;s finger and the tops of the multiple glass tactile friction features of the set of glass tactile friction features. 
 
     
     
       8. The electronic device of  claim 6 , wherein the substantially planar base surface includes an interstitial region that defines a substantially random spacing between the bases of adjacent pairs of the set of glass tactile friction features. 
     
     
       9. The electronic device of  claim 7 , wherein:
 the touch includes a gesture; and 
 the user&#39;s finger does not touch the substantially planar base surface when performing the gesture. 
 
     
     
       10. The electronic device of  claim 8 , wherein an average spacing between adjacent bases along the substantially planar base surface is less than an average width of micro-scale widths of the bases. 
     
     
       11. The electronic device of  claim 6 , wherein an average height of the set of glass tactile friction features ranges from 50 nm to 2 μm. 
     
     
       12. The electronic device of  claim 6 , wherein:
 the sidewall defines a conical portion and an oblique internal taper angle of each glass tactile friction feature. 
 
     
     
       13. The electronic device of  claim 12 , wherein:
 the set of glass tactile friction features is a first set of glass tactile friction features having a first height; 
 the exterior surface of the electronic device has a second set of glass tactile friction features that is interspersed with the first set of glass tactile friction features; and 
 the first height of the first set of glass tactile friction features is greater than a second height of the second set of glass tactile friction features. 
 
     
     
       14. The electronic device of  claim 6 , wherein the enclosure further comprises an oleophobic coating including a fluorinated material bonded to the set of glass tactile friction features. 
     
     
       15. An electronic device comprising:
 a display; 
 a touch sensor; and 
 an enclosure at least partially surrounding the display and including a glass structure defining a touch-sensitive input region positioned over the touch sensor, the touch-sensitive input region defining:
 a substantially flat base surface; and 
 a set of tactile friction features extending outward from the substantially flat base surface and defining:
 a plurality of substantially flat top surfaces having an average width ranging from 1 to 20 microns and at least partly providing a frictional resistance to the touch-sensitive input region; 
 an average height less than or equal to the average width; and 
 adjacent pairs of tactile friction features of the set of tactile friction features having circular bases separated by an interstitial region of the substantially flat base surface. 
 
 
 
     
     
       16. The electronic device of  claim 15 , wherein:
 the glass structure is positioned over both the display and the touch sensor; 
 the glass structure includes a display window region; 
 the set of tactile friction features is distributed along the display window region; and 
 the touch sensor is configured to detect a touch on the glass structure along the display window region. 
 
     
     
       17. The electronic device of  claim 15 , wherein:
 the interstitial region defines an average spacing between adjacent tactile friction features; and 
 a ratio of the average height to the average spacing of the set of tactile friction features ranges from 0.005 to 10. 
 
     
     
       18. The electronic device of  claim 17 , wherein each tactile friction feature of the set of tactile friction features has a circular contour and each of the plurality of substantially flat top surfaces is offset from the substantially flat base surface by a distance of less than or equal to 2 microns. 
     
     
       19. The electronic device of  claim 15 , wherein:
 the set of tactile friction features has a uniform width; and 
 the uniform width is smaller than a pixel size of the display. 
 
     
     
       20. The electronic device of  claim 15 , wherein the set of tactile friction features is configured to allow finger contact with top surfaces of an adjacent pair of tactile friction features without contacting the interstitial region of the substantially flat base surface.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a non-provisional patent application of and claims the benefit of U.S. Provisional Patent Application No. 62/663,943 filed Apr. 27, 2018 and titled “Glass Surface with Tactile Friction Features,” the disclosure of which is hereby incorporated by reference in its entirety. 
    
    
     FIELD 
     The described embodiments relate generally to electronic devices. More particularly, the present embodiments relate to surfaces of enclosures, input structures, and the like made from glass and having projections, depressions, or other structural features that provide tactile friction to an object touching the surface. 
     BACKGROUND 
     Electronic devices may be designed for a variety of uses. Many modern electronic devices are configured to be held in the hand of a user and many devices include touch-sensitive surfaces that receive a user touch. For some devices, a surface texture or material property of the housing may provide a suitable grip for hand-held applications. It may also be desirable that touch-sensitive surfaces provide a low friction interface to facilitate touch input. Some traditional devices provide a tactile feel by using a particular material or textured coating that extends along the exterior surfaces of the device. However, some textured coatings and materials are subject to wear over time and may not be sufficiently transparent for use in conjunction with a display of a device. The systems and techniques described herein may overcome some or all of these limitations with traditional techniques by forming a tactile surface directly into a surface of a glass component. 
     SUMMARY 
     Aspects described herein relate to tactile features formed along an exterior surface of an electronic device housing. In embodiments described herein, the tactile features may be perceptible by touch, but not individually perceptible by sight. The tactile features may provide a different level of friction with a touching object than a smooth housing surface and may therefore be referred to as “tactile friction features.” 
     In embodiments, the electronic device housing may comprise a structure and an external surface of the electronic device housing may be defined, at least in part, by the structure. For example, the structure may be a cover glass, an input structure, a housing, and so on. The structure may define a set of tactile friction features. Each tactile friction feature may include a base, a tip or top, and a sidewall extending from the base to the tip or top. The structure may further define a base surface and the set of tactile friction features may extend outward from the base surface. In embodiments, the structure is a glass structure or comprises a glass layer which defines the base surface and the set of tactile friction features. 
     In further embodiments, the tactile friction features may provide a lower level of friction than a smooth housing surface. For example, when the shape and spacing of the glass tactile friction features prevent an object from touching the base surface, a lower level of friction may result. In additional embodiments, the tactile friction features may provide a higher level of friction than a smooth housing surface. 
     In aspects described herein, the tactile friction features further comprise a coating bonded to surfaces of the glass tactile friction features. For example, the tactile friction features may comprise an oleophobic coating bonded to the glass tactile friction features. The coating may be thin relative to dimensions of the glass tactile friction features. 
     Certain embodiments described herein take the form of an electronic device comprising an enclosure defining an internal volume and having a glass structure at least partially defining a touch-sensitive exterior surface of electronic device. The touch-sensitive exterior surface comprises: a base surface defining a first planar region having a first area and a set of tactile friction features distributed along the touch-sensitive exterior surface and extending above the base surface to define a second planar region having a second area less than the first area. The electronic device further comprises a touch sensor positioned below the glass structure and configured to detect a touch along the touch-sensitive exterior surface. 
     In further embodiments, the electronic device further comprises a display positioned under the glass structure. The glass structure comprises: a first region positioned over a visible portion of a display; and a second region at least partially surrounding the first region and not positioned over the visible portion of the display. In addition, the set of tactile friction features is a first set of tactile friction features positioned along the first region. The electronic device further comprises a second set of tactile friction features along the second region. A first pitch between tactile friction features of the first set of tactile friction features is different than a second pitch between tactile friction features of the second set of tactile friction features. In certain embodiments, the pitch of the first set of tactile friction features is an average distance between centers of adjacent tactile friction features. By the way of example, the pitch is greater than 1 micron and less than 1 mm, such as between 150 and 600 microns. The glass structure may be a cover glass and the cover glass may define, at least in part, the first set and the second set of the tactile friction features. 
     In further embodiments, an electronic device comprises a display and a touch sensor positioned over the display. The electronic device further comprises an enclosure comprising a glass structure enclosing the display and defining an exterior surface of the electronic device, the exterior surface of the electronic device having a set of glass tactile friction features. Each glass tactile friction feature of the set of glass tactile friction features includes a base having a micro-scale width, a top, a sidewall extending from the base to the top, and a height between the base and the top, the height being less than or equal to the width. 
     In additional embodiments, an electronic device comprises a display; and an enclosure at least partially surrounding the display and including a structure. The structure defines: a base surface and a set of tactile friction features extending outward from the base surface, adjacent pairs of the tactile friction features having circular bases separated by an interstitial region of the base surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like elements. The elements of the drawings are not necessarily to scale relative to each other. Identical reference numerals have been used, where possible, to designate identical features that are common to the figures. 
         FIG. 1A  shows a finger touching and moving across a glass surface. 
         FIG. 1B  is a cross-section view of a portion of the finger and glass surface of  FIG. 1A . 
         FIG. 1C  is a detail view of a portion of the finger and glass surface of  FIG. 1B . 
         FIG. 1D  is a detail view of a portion of the finger and glass surface of  FIG. 1C . 
         FIG. 2  illustrates a sample electronic device incorporating a cover that has tactile friction features. 
         FIG. 3  is a detail view of a portion of section  3 - 3  of  FIG. 2 , illustrating the tactile friction features on a glass cover at a greatly exaggerated scale. 
         FIG. 4  is a cross-section view taken along line  4 - 4  of  FIG. 3 , showing the tactile friction features. 
         FIG. 5  is a first cross-section view of a finger contacting tactile friction features formed on a glass surface. 
         FIG. 6  is a second cross-section view of a finger contacting tactile friction features formed on a glass surface. 
         FIG. 7A  shows a first sample distribution of tactile friction features on a glass surface. 
         FIG. 7B  shows a second sample distribution of tactile friction features on a glass surface. 
         FIG. 8  is a cross-section view of tapered tactile friction features at an exaggerated scale. 
         FIG. 9A  is a cross-section view of a finger moving across tactile friction features at a first speed. 
         FIG. 9B  is cross-section view of a finger moving across tactile friction features at a second speed less than the first speed of  FIG. 9A . 
         FIG. 10A  is a first cross-section view of a finger contacting tapered tactile friction features formed on a glass surface. 
         FIG. 10B  is a second cross-section view of a finger contacting tapered tactile friction features formed on a glass surface. 
         FIG. 11A  is a cross-section view of a finger moving across a set of sloped tactile friction features in a first direction. 
         FIG. 11B  is a cross-section view of finger moving across the set of sloped tactile friction features in a second direction. 
         FIG. 12  shows a cross-section of a glass structure having tactile friction features with a peaked upper surface 
         FIG. 13  shows a cross-section of a glass structure having tactile friction features with a rounded upper surface. 
         FIG. 14  shows a cross-section of an example glass structure having tactile friction features with a concave surface. 
         FIG. 15  illustrates a cross-section of another example glass structure having tactile friction features with a concave surface. 
         FIG. 16  is a block diagram of a sample electronic device that can incorporate a glass structure having tactile friction features. 
     
    
    
     The use of cross-hatching or shading in the accompanying figures is generally provided to clarify the boundaries between adjacent elements and also to facilitate legibility of the figures. Accordingly, neither the presence nor the absence of cross-hatching or shading conveys or indicates any preference or requirement for particular materials, material properties, element proportions, element dimensions, commonalities of similarly illustrated elements, or any other characteristic, attribute, or property for any element illustrated in the accompanying figures. 
     Additionally, it should be understood that the proportions and dimensions (either relative or absolute) of the various features and elements (and collections and groupings thereof) and the boundaries, separations, and positional relationships presented there between, are provided in the accompanying figures merely to facilitate an understanding of the various embodiments described herein and, accordingly, may not necessarily be presented or illustrated to scale, and are not intended to indicate any preference or requirement for an illustrated embodiment to the exclusion of embodiments described with reference thereto. 
     DETAILED DESCRIPTION 
     Reference will now be made in detail to representative embodiments illustrated in the accompanying drawings. It should be understood that the following descriptions are not intended to limit the embodiments to one preferred embodiment. To the contrary, it is intended to cover alternatives, modifications, and equivalents as can be included within the spirit and scope of the described embodiments as defined by the appended claims. 
     The following disclosure generally relates to housing surfaces that include tactile features. In embodiments, a glass surface (e.g., a base surface) of the housing has protrusions or depressions (“tactile features”) that provide a different coefficient of friction with a touching object than a smooth glass surface does, and so provides a different feel than does a glass surface lacking such tactile features. Tactile features that change a coefficient of friction for a finger or other object in contact with the tactile feature, as compared to a glass surface that is substantially smooth or otherwise lacks such features, are called “tactile friction features” in this document. Further, it should be understood that references to “friction” in this document are to kinetic friction, unless otherwise stated. 
     Generally, a surface feels “smooth” or “sticky” to the touch at least in part due to the friction between a user&#39;s skin and the object. The lower the friction, the smoother the object feels. Likewise, the higher the friction, the stickier the object feels (for example, the more easily it is gripped). Similarly, the lower the coefficient of friction between a surface and an object in contact with that surface, the less energy is required to move the object along the surface. Accordingly, the coefficient of friction between a user&#39;s skin and a surface affects not only the feel of the surface but the effort (e.g., amount of energy) required to move along the surface. 
     It may be useful to provide a surface, such as a glass surface, with a particular feel by ensuring the coefficient of friction between typical human skin and the surface falls within a particular range. A touch screen of an electronic device may be both tactilely pleasant and relatively easy to use (e.g., requiring low energy to move along) if it is smooth. By contrast, a glass enclosure for the same electronic device may be easier to hold if it is sticky or otherwise “grippy.” As yet another example, a single enclosure surface or glass surface might have two different coefficients of friction—and thus two different “feels” in separate areas. This may be useful to differentiate an input region of the enclosure surface or glass surface from a non-input region, as one non-limiting example. In embodiments, the dynamic coefficient of friction, the static coefficient of friction, or a combination thereof is tailored to provide a desired “feel” to the electronic device. 
     Without being bound to a particular theory, a surface&#39;s coefficient of friction with respect to a moving body (e.g., dynamic coefficient of friction) may be described as being a combination of two different effects that may be generally referred to as mechanical friction and intermolecular adhesion. The term “mechanical friction” may be used to refer to the interaction of physical structures (asperities) on two surfaces moving with respect to one another. Thus, when a fingerprint ridge, bump, or other portion of skin contacts a projection or protrusion on a surface while the finger is moving over the surface, mechanical friction results. Skin asperities can be ridges, bumps, temporary or permanent deformations of the epidermis, and so on. Surface asperities include projections, protrusions, depressions, and other structures that render a surface uneven or otherwise discontinuous. It should be appreciated that many asperities on a surface may be invisible to the naked eye. Additionally, skin asperities may be temporary, as when skin deforms in response to an external force (like that of a protrusion pressing into the skin). 
     The term “intermolecular adhesion,” as used herein, may be used to refer to frictional effects due to the attraction of nearby molecules to one another, as well as the attraction of molecules to nearby atoms or ions. Van der Waals forces are an example of intermolecular adhesion. Generally, intermolecular adhesion varies directly with the contact area of two surfaces. Thus, as contact area increases, intermolecular adhesion increases. As contact area decreases, intermolecular adhesion decreases. Generally, intermolecular friction can be as much as five times as strong as mechanical friction. Thus, in many embodiments intermolecular adhesion provides a much greater portion of overall friction than does mechanical friction. Accordingly, controlling the contact area between two surfaces directly influences friction between the surfaces, and thus whether the surface feels smooth or sticky/grippy. 
     By including tactile friction features protruding from a housing surface (or, in some embodiments, recessed into the housing surface), the contact area between skin and the housing surface can be controlled. This can permit control of the coefficient of friction and thus the feel of the housing surface to a person touching it. In embodiments, the contact area is different than a surface area of the glass enclosure. In further embodiments, the contact area of the tactile friction features is different from the contact area of a corresponding flat surface. For example, the contact area of the tactile friction features may be less than the contact area of a corresponding flat surface. Typically, the tactile friction features are provided along an exterior or outer surface of the electronic device. In embodiments, the housing surface is a glass surface. 
     As discussed with respect to  FIGS. 3-15 , one or more physical characteristics (height, radius, width, length, shape, separation distance, and so on) of the tactile friction features can affect whether the surface feels smooth or sticky/grippy. In addition, the presence of a surface coating (e.g., an oleophobic coating) can further affect the feel of the surface. These and other embodiments are discussed below with reference to  FIGS. 1A-16 . However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanatory purposes only and should not be construed as limiting. 
       FIG. 1A  illustrates a finger  100  moving along a glass surface  110  of glass structure  105 . The movement of the finger  100  may correspond to a touch input on a touch-sensitive surface of a device. The touch input may include gesture input that involves movement of the finger  100  while applying light pressure to the glass surface  110 . Touch input may also correspond to taps, momentary touches, twisting finger input, and other types of touch input that can be performed using a finger. While the following examples are provided with respect to finger-touch input, similar principles may be applied for stylus input or input using another type of object. 
     The glass surface  110  may define a portion of an electronic device enclosure. For example, the glass structure  105  may be a cover glass, an input structure, a housing, component of an enclosure, and so on. In embodiments, the enclosure may include both a front and a rear cover glass. In additional embodiments, the glass structure  105  may form part or all of a housing or enclosure. In further embodiments, the glass structure  105  may a single monolithic component (e.g. a single piece of glass) which defines a back cover and a housing or a front cover, a back cover, and a housing. In some cases, the glass structure  105  may define substantially the entire front surface of a device as well as a portion of a surrounding sidewall or side of the device. The glass structure  105  may also define substantially the entire rear surface of the device as well as a portion of a surrounding sidewall or side of the device. Likewise, the glass structure  105  may define front, rear, and sides of a device. 
     Generally, as the finger  100  moves along the glass surface  110 , its motion is opposed by friction between the finger  100  and the glass surface  110 . The higher the coefficient of friction, the more energy is required to move the finger  100  and the rougher (or stickier, or more easily gripped) the glass surface  110  feels. 
       FIG. 1B  illustrates a cross-section view of a portion of the finger  100 , glass surface  110 , and glass structure  105  of  FIG. 1A . As shown, the finger&#39;s fingerprint ridges  120  contact the glass surface  110  while fingerprint valleys  130  do not. As the contact area between the finger  100  and glass surface  110  increases, the coefficient of friction increases as does the friction itself. 
       FIG. 1C  is a close-up view of a fingerprint ridge  120  contacting the glass surface  110 . In this magnified view asperities  150  in the glass surface  110  of glass structure  105  are visible, such as ridges and peaks. The finger&#39;s skin catches on these asperities  150  and the skin deforms. This gives rise to mechanical friction, as discussed above. Asperities  150  of  FIG. 1C  define local high points of the glass surface. The glass surface of  FIG. 1C  can be viewed as having adjacent peaks connected by a valley which defines a (local) low point of the glass surface. The roughness of such a glass surface may be measured from a mean line, with the high and low points typically being respectively located above and below the mean line. 
       FIG. 1D  is a close-up view of a portion of the finger  100  contacting an asperity  150  on the surface  110  of glass structure  105 . Here, the close-up view illustrates the individual molecules  160  of the skin of finger  100 , the individual atoms  170  of glass surface  110 , and the bonds  180  created between them by intermolecular adhesion. It should be appreciated that intermolecular adhesion occurs only where the skin molecules  160  contact the glass atoms  170  (or are in very close proximity). As previously mentioned, increasing the contact area between skin and glass increases the intermolecular adhesion between the two and thus the coefficient of friction. 
       FIG. 2  shows a sample electronic device  200 . In some embodiments, the electronic device  200  may be a mobile telephone, a notebook computing device (e.g., a notebook), a tablet computing device (e.g., a tablet), a portable media player, a wearable device, or another type of portable electronic device. The electronic device  200  may also be a desktop computer system, computer component, input device, appliance, or virtually any other type of electronic product or device component. 
     As shown in  FIG. 2 , electronic device  200  has an enclosure  220  including a cover  205  (example glass structure). The cover  205  may be affixed to a housing  260  to form an exterior of the electronic device  200 . The cover  205  may define a front surface  210  and the housing  260  may define a side surface  212  of the electronic device. 
     In aspects of the following disclosure, the cover may be described as a cover glass. However, more generally the cover may be formed from multiple layers that include glass sheets, polymer sheets, and/or various coatings and layers. Typical covers herein are thin, typically less than 5 mm in thickness, and more typically less than 3 mm in thickness. In some aspects, the cover can be from about 0.1 mm to 2 mm in thickness, and more typically from 0.15 mm to 1 mm in thickness. 
     While some of the following embodiments are described with respect to a cover  205 , the same or similar principles may be applied to any component that defines a portion of an external surface of a device. For example, another example glass component may define a portion or all of an internal cavity of the electronic device  200  that is configured to receive the various electronic components of the electronic device  200 . In some cases, the glass component (in this case the cover  205 ) may define an entire or substantially an entire front surface of the electronic device  200 , as well as one or more sides or sidewalls of the electronic device  200 . Similarly, the glass component may define an entire or substantially an entire rear surface of the electronic device  200 , as well as one or more sides or sidewalls of the electronic device  200 . Further, the glass component may be a monolithic component that defines the front surface, rear surface, and one or more side surfaces of the electronic device  200 . 
     In some embodiments, the enclosure may at least partially surround a display and the cover may be positioned over the display. The display may be configured to produce a graphical output that is viewable through the cover  205 . The cover  205  may define a transparent window region or window portion through which the graphical output may be viewed. The tactile friction features, as described herein, may be distributed along the transparent window region or window portion of the cover  205 . 
     In embodiments, the electronic device comprises a touch sensor configured to detect a touch or touch input along a region of the exterior surface of the electronic device. The region of the exterior surface is thus touch-sensitive. In some instances, a touch-sensitive layer or touch sensor (e.g., a capacitive touch sensor) is positioned below the cover  205  and, in some cases, positioned between the cover  205  and the display. The cover  205  is configured to allow the touch sensor to detect the touch or touch input along the region of the exterior surface of the cover  205 . By the way of example, a glass structure (such as a cover) may define a display window region and the touch sensor may be configured to detect a touch or touch input along the display window region. 
     As described herein, the tactile friction features may be configured to produce a specific tactile effect or friction with a user&#39;s finger to facilitate smooth gesture or other touch input along a touch-sensitive region of the cover  205 . For example, the tactile friction features may be configured to provide a specific frictional resistance to a touch gesture. The friction features may also be configured to provide sufficient transparency to allow graphical output from the display to be viewed through the cover  205  without significantly altering the visual quality of the graphical output. 
     A variety of electronic device components may be positioned within the enclosure  220 . For example, the electronic device may comprise one or more of a display, a processing unit, memory, an input/output device, a power source, a network communication interface, a camera, and a sensor. Components of a sample electronic device are discussed in more detail below with respect to  FIG. 16 . 
     Generally, the cover  205  and/or enclosure  220 , as well as the input structure  230 , may all comprise glass having tactile friction features. In some embodiments, a single element (e.g., the cover  205 , enclosure  220 , input structure  230 , housing  260  or other portions of the electronic device  200 ) may have different sets of tactile friction features in different regions. 
     For example, a first set of tactile friction features with a first physical characteristic (height, radius, width, length, shape, separation distance, and so on) may be formed in a first region  240  of the cover  205  corresponding to a display area. A second set of tactile friction features with a second, different physical characteristic may be formed in and defined by a second region  250  of the cover glass that corresponds to a non-display area. 
     Given the change in physical characteristic, the contact area between the finger and the tactile friction features will vary between the two regions  240 ,  250 . Thus, a user touching the cover glass in the display area  240  will have a first sensation controlled by the first coefficient of friction. The same user touching the cover  205  in the non-display area  250  will feel a second sensation since the coefficient of friction will be different. Further, the difference in physical characteristic (which results in a difference in contact area) may be visually undetectable or invisible to the human eye. Thus, even though the cover  205  may be visually continuous such that the first and second regions  240 ,  250  are visually indistinguishable, the feel of the two regions may be very different to a user. This may provide a tactile indication of where the display region  240  ends and the non-display region  250  begins, even if the device is powered off. Some embodiments may pattern or change physical characteristics of tactile friction features in input regions and non-input regions to likewise provide physical feedback to a user, indicating where inputs may be accepted by an electronic device  200 . 
     In additional embodiments, a first set of tactile friction features with a first physical characteristic may be formed on cover  205  while a second set of tactile friction features with a second physical characteristic may be formed on another part of enclosure  220 . For example, the first set of tactile friction features may be formed to give a smooth feel to cover  205  while a second set of tactile friction feature may be formed to give a sticky/grippy feel to a rear cover glass and/or to housing  260 . 
       FIG. 3  shows a detail view of a portion of section  3 - 3  of a cover glass  305  which is an example of cover  205  shown in  FIG. 2 . It should be appreciated that the scale of  FIG. 3  is greatly exaggerated as compared to the scale of  FIG. 2 , in order to illustrate certain features. As shown in  FIG. 3 , multiple tactile friction features  300   a ,  300   b ,  300   c ,  300   d ,  300   e ,  300   f ,  300   g  (collectively referred to with number “300”) are present on or in the cover glass  305 . The tactile friction features may be distributed along a particular region of the cover glass and/or along a particular touch-sensitive surface of the electronic device. The cover glass  305  defines a base surface  310  which surrounds each of the tactile friction features  300   a ,  300   b ,  300   c ,  300   d ,  300   e ,  300   f ,  300   g.    
     The tactile friction features  300  are randomly spaced apart from one another but have an average “pitch” (e.g., separation distance)  320 . As referred to herein, the pitch is the distance between the centers of two adjacent tactile friction features  300 . In some cases adjacent tactile friction features may abut one another or even merge into one another, as do tactile friction features  300   f  and  300   g . In other cases, the separation distance between two tactile friction features may be much greater than the average pitch  320 , as is the case with tactile friction features  300   d  and  300   g . Across a sufficiently large region or part of a glass structure, however, the pitch will have an average value. In embodiments, the average pitch is micro-scale, having a size from 1 micron to less than 1 mm. In embodiments, the average pitch is from 5 to 600 microns, from 10 to 100 microns, or from 5 to 50 microns. The tactile friction features  300  may be substantially evenly distributed along a region of the cover even though the spacing between any two adjacent tactile friction features may vary. 
     In additional embodiments, an average width (or diameter) of the tactile friction features is also micro-scale. In embodiments, the average width of the set of tactile friction features ranges from 1 micron to 50 microns, from 1 micron to 20 microns, from 2 microns to 50 microns, or from 5 microns to 25 microns. Further, the average width of the tactile friction features may be less than the average pitch. 
     As shown in  FIG. 3 , each of the friction features  300   a - 300   e  define a circular contour and a circular shape as viewed from above. The contour and shape of a friction feature as viewed from above may be defined by a top  324  of the friction feature. Friction features  300   f  and  300   g , which contact each other, each define a shape which is a segment of a circle and a contour in the form of a circular arc. In embodiments, the bases of at least some of the friction features (e.g., friction features  300   a - 300   e ) also define a circular contour and may be described as circular bases. 
     Varying the average pitch  320  can affect the coefficient of friction between a user&#39;s skin and the cover glass, such as when the user&#39;s finger applies a touch gesture to the electronic device. If adjacent tactile friction features contact each other, then the pitch between the features is determined by the half widths of the adjacent tactile friction features. As the average pitch  320  approaches zero, then the tactile friction features  300  substantially overlap and the cover glass would be substantially flat on the macro scale, although asperities too small for the human eye to see would still exist. As the pitch  320  increases, skin moving across the cover glass comes into contact with less and less area and so the coefficient of friction between the user&#39;s finger and the cover glass can decrease. This is discussed in more detail below with respect to  FIG. 5 . 
     When the pitch becomes sufficiently large, however, the tactile friction features  300  are spaced so far apart that skin can sag or drop down between adjacent features to the point that the skin contacts the base surface  310  of the glass. This can have the effect of increasing contact area between the skin and the cover glass, which in turn increases the coefficient of friction. Thus, depending on the particular geometries of the tactile friction features  300 , increasing pitch  320  beyond a threshold can increase friction between the cover glass (or other article) and skin, rather than decrease it. In embodiments where a relatively low coefficient of friction is desired, the tactile friction features  300  may be configured to prevent a user&#39;s finger from touching the base surface when performing a touch gesture. 
     In embodiments, the coefficient of friction depends on the height of the tactile friction features  300  as well as the pitch. The average height of the tactile friction features may be micro-scale or nano-scale (having a size from 1 nm to less than 1 micron). In embodiments, the average height of the tactile friction features is less than or equal to 10 microns, less than or equal to 5 microns, less than or equal to 2 microns, or less than or equal to 1 micron. In further embodiments, the average height of the tactile friction features is from 100 nm to 10 microns, from 200 nm to 2 microns, from 200 nm to 1 micron, or from 500 nm to 5 microns. 
     For a cylindrical tactile friction feature  300  having a radius of approximately 2.5 microns and a height of 0.25-0.5 microns, a pitch  320  greater than about 600 microns can cause the coefficient of fiction between a typical human finger and the cover glass to increase. The pitch may be as low as 1-10 nanometers in some embodiments, such as embodiments formed through non-imprinting processes, but is typically between 5 and 600 microns. For a tactile friction feature  300  having a constant radius of 2.5 microns and a height of 0.5 microns, a pitch of approximately 15-20 microns may be used to reduce the coefficient of friction. Decreases in pitch below about 15 microns or above about 20 microns may cause increases in the coefficient of friction, in such an embodiment. 
     The foregoing values presume the finger exerts approximately 50 grams of force on the glass. It should be appreciated that the force exerted by a user on the glass will also alter the coefficient of friction between glass and skin. 
     As shown in  FIG. 3 , at least some of the adjacent tactile friction features are spaced apart from one another. The space between a pair of adjacent tactile friction features may be referred to as a channel or as an interstitial region (e.g., interstitial region  302  in  FIG. 4 ). The interstitial region may be defined by the pair of adjacent tactile friction features and a portion of the base surface  310  (e.g., interstitial region  314  of the base surface  310  in  FIG. 4 ). One measure of the spacing between a pair of adjacent friction features is the minimum spacing between edges of a pair of adjacent friction features (or edge to edge spacing). This spacing may be referred to as a channel spacing or as an interstitial region width. Generally, a channel or interstitial aspect ratio may be defined as the tactile friction feature height divided by the spacing between adjacent tactile friction features (e.g., pitch minus tactile friction feature diameter for the tactile friction features  300 ). Similarly, an average channel or interstitial aspect ratio may be defined by the average tactile friction feature height defined by the average spacing between adjacent tactile friction features. For a human finger exerting about 50 g normal force on a set of tactile friction features, an average channel aspect ratio of about 0.01 to about 0.08 yields relatively low friction. 
     It should be appreciated that the pitch  320  or channel aspect ratio at which friction begins increasing may vary for different people and even for the same person at different times, as the water content, elasticity, thickness, and other physical characteristics of skin change. Accordingly, the foregoing values are illustrative and may vary in different embodiments. 
       FIG. 4  is a cross-sectional view taken along line  4 - 4  of  FIG. 3 , illustrating two tactile friction features  300   a ,  300   b  extending upward from a base surface  310  of the cover glass  305 . In embodiments, tactile friction features provided on an enclosure extend outward from the base surface  310  (e.g., above the base surface and away from the interior of the enclosure). As shown in  FIGS. 3 and 4 , the tactile friction features  300   a ,  300   b  are generally cylindrical with a substantially vertical sidewall  326 . In embodiments, the tactile friction features comprise glass tactile friction features and the composition of the glass tactile friction features is substantially the same as that of the cover glass. 
     As shown in  FIG. 4 , the tactile friction features (e.g.,  300   b ) have a base  322  located along base surface  310 . The tactile friction features also have a top  324  located at a height H above base surface  310 . In embodiments, the surface defined by top  324  (i.e., the top surface) is flat or flat to within a specified tolerance. Sidewall  326  extends from base  322  to top  324 . A set of tactile friction features may have an average height. In embodiments, a set of the tactile friction features has a substantially uniform height, so that the heights of individual tactile friction features in the set are substantially the same. In embodiments, the heights of individual tactile friction features may be uniform to within a specified amount of variation, such as +/−10%, +/−5%, or +/−2%. 
     In embodiments, the base surface  310  defines a first region and the tops  324  of the tactile friction features  300   b  define a second region. The first region and the second region may each be planar to within a specified tolerance, and may therefore be referred to as a first planar region and a second planar region. For example, the specified tolerance may be 1 micron, 500 nm, 250 nm, 100 nm, 50 nm, 10 nm, or 5 nm. The second planar region may be offset from the first planar region by the (average) height of the tactile friction features. The first planar region may have a first area and the second planar region may have a second area. In embodiments, the second area is less than the first area. As shown in  FIG. 3 , the second region defined by the tops  324  of the tactile friction features and the first region defined by the base surface  310  need not be contiguous. 
     As shown in  FIG. 4 , the interstitial region  314  of the base surface  310  may be substantially flat or planar between tactile friction features  300   a ,  300   b . Generally, the tactile friction features have a width W; for the cylindrical tactile friction features  300   a ,  300   b  the width is a diameter. A set of tactile friction features may have an average width. In embodiments, a set of the tactile friction features has a substantially uniform width, so that the widths of the individual tactile friction features in the set are substantially the same. In embodiments, the widths of individual tactile friction features may be uniform to within a specified amount of variation, such as +/−10%, +/−5%, or +/−2%. In embodiments, the average width of the tactile friction features may be less than, equal to, or greater than the average height of the tactile friction features. In additional embodiments, the tactile friction features may be described by an aspect ratio defined as the height divided by the width. 
     As was discussed with respect to  FIG. 3 , tactile friction features  300   a  and  300   b  are spaced apart by a pitch. As shown in  FIG. 4 , channel or interstitial region  302  is the space between a pair of adjacent tactile friction features. Typically the channels or interstitial regions  302  are not aligned along a given direction across a large portion of the glass surface in order to avoid anisotropy in the coefficient of friction (e.g., to avoid a “tramlining” effect). In embodiments, the tactile friction features are not arranged in a regular array, such as square or a hexagonal array, across a large portion the glass surface. Instead, the positions of the tactile friction features may be randomized. 
     In addition, tactile friction features  300   a  and  300   b  are separated by a distance X between sidewalls of the adjacent tactile friction features (also termed “channel spacing” or “interstitial region width,” e.g., pitch minus tactile friction feature width). For tactile friction features having a substantially vertical sidewall, the distance X is substantially the same at the top  324  and the base  322  of the sidewall  326 . The channel aspect ratio of the channel or interstitial region  302  defined between tactile friction features  300   a ,  300   b  is therefore H/X. When the spacing between tactile friction features varies, a set of the tactile friction features may have an average channel spacing (an average of the distances X) and the channel aspect ratio may be a ratio of the average height to the average channel spacing. For example, a channel aspect ratio to produce a smooth effect may be from 0.01 or greater, while a channel aspect ratio to produce a grippier effect may be less than 0.01. 
     It should be appreciated, however, that the tactile friction features  300  may have any suitable shape, angle, or orientation of the sidewall, and/or number of sidewalls. For example, the tactile friction features  300  may be conical, ovoid, arched, have a curved upper surface, rectangular, polygonal, a frustum of a shape such as a cone, and so on. Likewise, the sidewall(s) may be curved, rounded, multi-faceted, and the like. In addition, at least some of the bases and/or the tops of the tactile friction features  300  may define a contour which is generally circular, oval, or polygonal.  FIGS. 7-15  show additional examples of tactile friction feature shapes. In embodiments, the description of physical characteristics such as height, width, and separation distance of the tactile friction features of  FIGS. 3 and 4  may also apply to the tactile friction features of  FIGS. 5-15 . 
       FIG. 5  is a cross-sectional view showing skin of a finger  100  in contact with multiple tactile friction features  500   a ,  500   b  of glass structure  505 . As illustrated, the tactile friction features  500   a ,  500   b  are of sufficient height, width, and pitch that they prevent the finger  100  from touching the base surface  510  of the glass. Accordingly, the contact area between the finger  100  and glass structure  505  is limited to the surface area of the touched tactile friction features. As this is less area than would be contacted if the glass lacked the tactile friction features  500 , it can be appreciated that the glass structure  505  would feel smooth, slippery, or the like to the touch. Tactile friction features producing a smooth effect may be provided, for example, on a cover glass or other input component of an enclosure. In embodiments, a ratio of the average height to the average channel spacing between features to produce a smooth effect is from 0.01 to 10, 0.01 to 2, or 0.05 to 5. 
     In contrast,  FIG. 6  illustrates a glass structure  605  having tactile friction features  600   a ,  600   b  that are too small and/or spaced apart by too great a pitch to prevent skin of finger  100  from touching the base surface  610  of the glass structure  605 . For example, the channel aspect ratio does not prevent the skin from touching the base surface. Thus, while the coefficient of friction between the finger  100  and the glass structure  605  may be reduced somewhat by the tactile friction features  600   a ,  600   b , this embodiment will feel stickier than the embodiment shown in  FIG. 5 . The embodiment shown in  FIG. 6  illustrates an example where the pitch is large enough that the coefficient of friction, while not as large as if the tactile friction features  600   a ,  600   b  were absent, nonetheless is greater than if the features were closer together. 
     In additional embodiments, the pitch may be large enough that the coefficient of friction is larger than if the tactile friction features  600  were absent. Tactile friction features to enhance stickiness may be provided, for example, on a peripheral surface of an enclosure, a rear cover glass, or other such component of an enclosure. In embodiments, a ratio of the average height to the average channel spacing between features to enhance stickiness is from 1×10 −5  to less than 1×10 −2 , 1×10 −5  to 1×10 −3 , or from 1×10 4  to 1×10 −2 . 
       FIGS. 7A and 7B  illustrate tactile friction features having the same shape and size, but having different pitches between them. For example, in  FIG. 7A  tactile friction features  700   a  may be arranged at a distance represented by pitch P 1 . As with prior embodiments, the tactile friction features  700   a  prevent the skin of the finger  100  from contacting the base surface  710   a  of the glass structure  705   a  also referred to herein as a channel or interstitial region. 
       FIG. 7B  is a cross-section of a glass structure  705   b  having tactile friction features  700   b  separated by a larger pitch P 2 . Although the skin of the finger  100  is closer to the base surface  710   b  of the glass structure  705   b  than in the embodiment of  FIG. 7A , it nonetheless does not touch the base surface  710   b . Given the lower density of tactile friction features in the embodiment of  FIG. 7B  as compared to  FIG. 7A , the glass structure  705   b  of  FIG. 7B  may feel smoother or slipperier than the cover glass as shown in  FIG. 7A . By contrast, the glass structure  705   a  shown in  FIG. 7A  may be more consistent in maintaining its coefficient of friction, and thus its feel, under a greater force than the glass structure  705   b  illustrated in  FIG. 7B . It should thus be appreciated that increasing pitch between tactile friction features (or channel aspect ratio) may reduce friction with a finger or other object under a first input force, but may result in higher friction if the input force exceeds a threshold. As with other embodiments discussed herein, the value of that threshold is dependent on the physical characteristics of the tactile friction features, the user&#39;s skin, and so on 
       FIG. 8  is a cross-sectional view illustrating two tactile friction features  800  extending upward from a base surface  810  of a glass structure  805 . In embodiments, tactile friction features provided on an enclosure extend outward from the base surface  810  (e.g., away from the interior of the enclosure). As shown in  FIG. 8 , the tactile friction features  800  are generally tapered and include a conical portion  830  (also referred to as conical feature structure). In embodiments, the tactile friction features and the glass structure comprise the same glass material as the glass structure. 
     As shown in  FIG. 8 , the tactile friction features  800  have a base  822  located along base surface  810  and having a base width W. Tactile friction features  800  also have a tip  824  (also referred to as a “top”) located at a height H above base surface  810 . Tactile friction features  800  taper from base  822  to tip  824 . Sidewall  826  extends from base  822  to tip  824  at a slope. At least a portion of sidewall  826  defines the conical portion  830  of tactile friction features  800 . As shown in  FIG. 8 , the conical portion  830  may have the general shape of the frustum of a cone. In embodiments, base  822  defines a circular contour. 
     The sidewall  826  is obliquely angled with respect to a longitudinal axis  828  of the tactile friction feature  800 . The sidewall  826  further defines an internal taper angle θ of conical portion  830  which is twice the angle between the sidewall  826  and the longitudinal axis  828 . In embodiments, the internal taper angle θ is oblique, acute, right, or obtuse. The internal taper angle θ may be from 60 degrees and to 180 degrees, from 60 degrees to 120 degrees, or from 110 degrees to 170 degrees. 
     A set of tactile friction features may have an average height. In embodiments, a set of the tactile friction features has a substantially uniform height, so that the heights of individual tactile friction features in the set are substantially the same. In embodiments, the average height of the tactile friction features is from 100 nm to 10 microns, from 200 nm to 2 microns, or from 500 nm to 5 microns. 
     As shown in  FIG. 8 , base surface  810  may be substantially flat between tactile friction features  800 . Therefore, the cover may have a substantially uniform thickness between the tactile friction features. In embodiments, the thickness of the cover may be uniform to within a specified amount of variation, such as +/−10%, +/−5%, or +/−2%. 
     The tactile friction features  800  have a base width W. For generally conical tactile friction features the base width may be a diameter. A set of tactile friction features may have an average base width. In embodiments, a set of the tactile friction features has a substantially uniform base width, so that the base widths of the individual tactile friction features in the set are substantially the same. In embodiments, the base widths of individual tactile friction features may be uniform to within a specified amount of variation, such as +/−10%, +/−5%, or +/−2%. In embodiments, the average base width of the set of tactile friction features is from 1 micron to 50 microns, from 2 microns to 50 microns, or from 5 microns to 25 microns. In embodiments, the average base width of the tactile friction features may be less than, equal to, or greater than the average height of the tactile friction features. 
     The tip  824  of tactile friction features  800  is generally smaller than the base  822 . In embodiments, the tip  824  is rounded and may be characterized by a tip radius. In alternative embodiments, the tip  824  may be flat, so that the tactile friction feature has the form of a frustum of a cone. 
     As illustrated in  FIG. 8 , the tactile friction features  800  and the base surface  810  together define an interstitial region or channel  802 . Typically the interstitial regions or channels  802  are not aligned along a given direction across a large portion of the glass surface in order to avoid anisotropy in the coefficient of friction (e.g., to avoid a “tramlining” effect). In embodiments, the tactile friction features are not arranged in a regular array, such as square or a hexagonal array, across a large portion the glass surface. 
     In embodiments, the tactile friction features  800  are separated by a distance X between bases of the adjacent tactile friction features (e.g., pitch minus tactile friction feature base diameter). For tapered tactile friction features having a sloped sidewall, the distance between the tips of  824  is greater than the distance X between the bases  822 . In embodiments, the distance between the tips may be the pitch minus twice the tip radius R. When the tip radius R is small, the distance between the tips may be approximately equal to the pitch. In embodiments, the average spacing between adjacent bases may be less than, equal to, or greater than the average width of the bases. In embodiments, the average pitch is from 5 to 600 microns, from 10 to 100 microns, or from 5 to 50 microns. 
     In embodiments, the aspect ratio of the interstitial region or channel between tactile friction features  800  may be measured as the distance between the bases divided by the height of the tactile friction features. When the spacing between tactile friction features varies, a set of the tactile friction features may have an average channel spacing (or interstitial region width) and the channel aspect ratio may be a ratio of the average height to the average channel spacing. In embodiments, a ratio of the average height to the average channel spacing between features to produce a smooth effect is from 0.01 to 10, 0.01 to 2, or 0.05 to 5. 
     In embodiments, the coefficient of friction of the tactile friction features may depend on the speed at which an object, such as a finger, moves across the tactile friction features.  FIG. 9A  schematically shows a finger  100  moving at a first speed across tactile friction features  900  while  FIG. 9B  schematically shows the finger  100  moving at a second speed, lower than the first speed, across the tactile friction features  900 . As shown in  FIGS. 9A and 9B , at higher speeds the finger has a lesser extent of deformation into the channel or interstitial region between the tactile friction features, decreasing the extent of interlocking and the coefficient of friction between the finger and the tactile friction features. In embodiments, the tactile friction features of  FIGS. 9A and 9B  have dimensions similar to those described for the tactile friction features of  FIG. 8 . 
       FIG. 9A  shows a finger  100  moving across a set of tactile friction features  900 . The finger  100  is moving at a speed at which it does not substantially deform into the interstitial region or channel  902 . In embodiments, the channel aspect ratio of the tactile friction features  900  is such that the contact area and the coefficient of friction between the finger  100  and the tactile friction features  900  is lower than that of a flat glass surface, as previously described with respect to  FIG. 5 . 
       FIG. 9B  shows a finger  100  moving across the same set of tactile friction features  900  at a speed where the finger  100  substantially deforms into interstitial region or channel  902 . Therefore, the contact area and the coefficient of friction between the finger  100  and the tactile friction features  900  is greater than for the finger movement illustrated in  FIG. 9A . However, the finger does not deform to the extent that it contacts the glass surface  910 . 
       FIG. 10A  is a cross-sectional view of a finger  100  contacting tactile friction features  1000   a ,  1000   b  of a glass structure  1005 . Here, the glass structure  1005  includes both large tactile friction features  1000   a  and small tactile friction features  1000   b  that are interspersed with the large tactile friction features  1000   a . Generally, large (e.g., taller) tactile friction features  1000   a  are separated from one another by small tactile friction features  1000   b , although in some embodiments the spacing, orientation, and the like of large and small features may be substantially random. The tactile friction features  1000   a ,  1000   b  extend from base surface  1010 . In embodiments, the large tactile friction features  1000   a  may have a first average height and the small tactile friction features  1000   b  may have a second average height smaller than the first average height. In additional embodiments, a first set of glass tactile friction features may have a first average height and a second set of glass tactile friction features may have a second average height smaller than the first average height. 
     When the user&#39;s finger  100  exerts a first force against the glass structure  1005 , the finger contacts the large tactile friction features  1000   a  but may not contact the smaller tactile friction features  1000   b . Further, the channel aspect ratio and/or spacing (e.g., pitch) between the large tactile friction features  1000   a  is sufficient to prevent the skin from touching the base surface  1010  of the glass structure  1005 . 
     As the user increases his or her input force, however, the skin deforms around the large tactile friction features  1000   a  and contacts the small tactile friction features  1000   b , as shown in  FIG. 10B . Here, the input force exerted by the user&#39;s finger  100  is greater than in  FIG. 10A . For example, the user may exert 100 grams of force instead of 50 grams of force, although it should be understood these values are examples and not limiting. 
     Given the greater input force exerted by the user&#39;s finger  100 , the finger deforms around the large tactile friction features  1000   a . Put another way, the large tactile friction features  1000   a  press into the user&#39;s finger. The skin of the finger  100  is still prevented from touching the base surface  1010  of the glass structure  1005  by the small tactile friction features  1000   b . The small tactile friction features  1000   b  thus may provide additional support to prevent contact between the finger  100  and the base surface  1010  of the glass when an input force increases beyond a threshold. Accordingly, in some embodiments tactile friction features of varying sizes, shaped, dimensions, or other physical characteristics may be used in a single region of a glass structure  1005 . 
       FIGS. 11A and 11B  illustrate cross-sections of a glass structure  1105  having tactile friction features  1100   a ,  1100   b  with a sloped or angled upper surface (e.g., contact surface). For example, the tactile friction feature  1100   a  has a sloped upper surface  1120   a  that meets a sidewall  1140   a  at a sharp angle defining a peak  1130   a , as shown in  FIGS. 11A-11B . As the finger  100  moves right across the tactile friction feature  1100   a  (shown in  FIG. 11A ), it engages the sloped upper surface  1120   a  and slides across the peak  1130   a . The peak  1130   a  deforms the finger  100  to some relatively minor, gentle degree. 
     By contrast, as the finger moves left across the tactile friction features  1100   a ,  1100   b  (shown in  FIG. 11B ), it is pushed into the vertical sidewall of each such feature (e.g.,  1140   a ). This causes the peak (e.g.,  1130   a ) to press into the finger  100 , deforming the skin of the finger to a much greater degree than in the example of  FIG. 11A . This results both in greater mechanical friction and a greater contact area between finger  100  and glass structure  1105 . The increased contact area (as compared to the motion shown in  FIG. 11A ) likewise increases intermolecular adhesions between the finger  100  and glass structure  1105 . Accordingly, overall friction is greater when the finger moves to the left across the tactile friction features  1100  than when it moves to the right. 
       FIGS. 11A and 11B  illustrate that tactile friction features can be configured to provide different coefficients of friction, and thus different feelings or perceptions of a surface, depending on a direction of motion of an object across that surface. The tactile friction features are keyed so that the surface feels smooth in a first direction but sticky or grippy in a second direction. Accordingly, the tactile friction features can be anisotropic in some embodiments. 
       FIG. 12  illustrates a cross-section of a glass structure  1205  having tactile friction features  1200  with an upper surface (e.g., contact surface) that defines a peak that is centrally located. The tactile friction features  1200  extend upward from a base surface  1210  of a glass structure  1205 . In embodiments, tactile friction features provided on an enclosure extend outward from the base surface  1210  (e.g., away from the interior of the enclosure). 
     As shown in  FIG. 12 , the tactile friction features  1200  have a base  1222  located along the base surface  1210  and having a base width W. The tactile friction features  1200  also have a tip  1224  located at a height H above base surface  1210 . Tactile friction features  1200  have a first sidewall portion  1226   a  and a second sidewall portion  1226   b . The first sidewall portion  1226   a  is obliquely angled with respect to a longitudinal axis  1228  of tactile friction feature  1200 . The first sidewall portion  1226   a  further defines an internal taper angle θ of conical portion  1230  which is twice the angle between the sidewall and the longitudinal axis  1228 . In embodiments, the internal taper angle is oblique, acute, right, or obtuse. The internal taper angle θ may be from 60 degrees and to 180 degrees, from 60 degrees to 120 degrees, or from 110 degrees to 170 degrees. The first sidewall portion  1226   a  extends from the tip to join the second sidewall portion  1226   b . The second sidewall portion  1226   b  extends outward from the base surface  1210  and may be substantially vertical (e.g., parallel to the longitudinal axis  1228  of tactile friction feature  1200 ). As shown in  FIG. 12 , base surface  1210  may be substantially flat between tactile friction features  1200 . 
     The set of tactile friction features may have an average height. In embodiments, a set of the tactile friction features has a substantially uniform height, so that the heights of individual tactile friction features in the set are substantially the same. The average height may be as described for  FIG. 8 . 
     The tactile friction features  1200  have a base width W. When the second sidewall portion  1226   b  defines a generally cylindrical portion of a tactile friction feature  1200  the base width may be a diameter. A set of tactile friction features may have an average base width. In embodiments, a set of the tactile friction features has a substantially uniform base width, so that the base widths of the individual tactile friction features in the set are substantially the same. The average base width may be as described for  FIG. 8 . 
     In embodiments, the tactile friction features  1200  are separated by a distance X between bases of the adjacent tactile friction features (e.g., pitch minus tactile friction feature base diameter). In embodiments, the channel aspect ratio of the interstitial region or channel  1202  between tactile friction features  1200  may be measured as the distance between the bases or as the distance between the tips divided by the height of the tactile friction features. When the spacing between tactile friction features varies, a set of the tactile friction features may have an average channel spacing and the channel aspect ratio may be a ratio of the average height to the average channel spacing. The ratio of the average height to the average channel spacing between features may be as described for  FIG. 8 . 
       FIG. 13  illustrates a cross-section of a glass structure  1305  having tactile friction features  1300  with a rounded upper surface (e.g., contact surface). The tactile friction features  1300  extend upward from a base surface  1310  of a glass structure  1305 . In embodiments, tactile friction features provided on an enclosure extend outward from the base surface  1310  (e.g., away from the interior of the enclosure). An interstitial region or channel  1302  is defined between adjacent tactile friction features  1300 . 
     As shown in  FIG. 13 , the tactile friction features  1300  have a base  1322  located along the base surface  1310  and having a base width W. The tactile friction features  1300  also have a tip  1324  located at a height H above base surface  1310 . Tactile friction features  1300  have a first sidewall portion  1326   a  and a second sidewall portion  1326   b . The first sidewall portion  1326   a  defines a concave surface, also referred to as a rounded upper surface of the tactile friction feature  1300 . The first sidewall portion  1326   a  extends from the tip to join the second sidewall portion  1326   b . The second sidewall portion  1326   b  extends outward from the base surface  1310  and may be substantially vertical (e.g., parallel to the longitudinal axis of tactile friction feature  1300 ). As shown in  FIG. 13 , base surface  1310  may be substantially flat between tactile friction features  1300 . The heights, widths, and channel aspect ratios of the tactile friction features may be as described for  FIG. 12 . 
       FIG. 14  illustrates a cross-section of a glass structure  1405  having tactile friction features  1400  with a concave surface. The tactile friction features  1400  extend upward from a base surface  1410  of a glass structure  1405 . In embodiments, tactile friction features provided on an enclosure extend outward from the base surface  1410  (e.g., away from the interior of the enclosure). An interstitial region or channel  1402  is defined between adjacent tactile friction features  1400  even though the bases of adjacent tactile friction features  1400  may contact one another. 
     As shown in  FIG. 14 , the tactile friction features  1400  have a base  1422  located along the base surface  1410  and having a base width W. The tactile friction features  1400  also have a tip  1424  located at a height H above base surface  1410 . Tactile friction features  1400  have a side surface  1426  which extends between the tip  1424  and the base  1422 . The side surface  1426  defines a concave surface having a radius of curvature R. As shown in  FIG. 14 , base surface  1410  may be substantially flat between tactile friction features  1400 . The heights and widths of the tactile friction features may be as described for  FIG. 12  and the tactile friction features may be described by an aspect ratio defined as the height divided by the base width. 
       FIG. 15  illustrates a cross-section of another example glass structure  1505  having tactile friction features  1500  with a concave side surface. The tactile friction features  1500  extend upward from a base surface  1510  of the glass structure  1505 . In embodiments, tactile friction features provided on an enclosure extend outward from the base surface  1510  (e.g., away from the interior of the enclosure). An interstitial region or channel  1502  is defined between adjacent tactile friction features  1500 . 
     As shown in  FIG. 15 , the tactile friction features  1500  have a base  1522  located along the base surface  1510  and having a base width W. The tactile friction features  1500  also have a tip  1524  located at a height H above base surface  1510 . Tactile friction features  1500  have a side surface  1526  which extends between the tip  1524  and the base  1522 . The side surface  1526  may define a concave curve having a radius of curvature R; the radius of curvature R of the tactile friction features shown in  FIG. 15  is less than that of the tactile friction features of  FIG. 14 . As shown in  FIG. 15 , base surface  1510  may be substantially flat between tactile friction features  1500 . The heights, widths, and channel aspect ratios of the tactile friction features may be as described for  FIG. 12 . 
     As previously mentioned, tactile friction features may be incorporated into a cover glass or other surface above a display of an electronic device. In some embodiments the shape, size, pitch or other physical characteristic of the tactile friction features, or aspect ratio of channels, may be selected to reduce or eliminate optical distortion. As one non-limiting example, stepped edges, sharp angles, and the like between exterior surfaces of a tactile friction feature and/or a base surface may be avoided in order to reduce or prevent diffraction, sparkling effects, or the like when a display is active. In some embodiments, tactile friction features may be positioned between pixels of a display but not directly over display pixels, again to reduce or minimize optical aberrations when the display is operating. In additional embodiments, a width of the tactile friction features is different from a pixel size of the display. For example, the width of the tactile friction features may be greater than the pixel size of the display or smaller than the pixel size of the display. In still other embodiments physical characteristics of the tactile friction features may be configured to match a harmonic wavelength of light passing through them in order to avoid or reduce optical aberrations. 
     In embodiments, the tactile friction features may provide additional optical effects. In further embodiments, a surface with the tactile friction features may have a reflectance or transmittance which differs from that of a corresponding surface without the tactile friction features. For example, the surface with the tactile friction features may have a lower reflectance and/or a lesser amount of specular reflection than the corresponding surface. 
     In additional embodiments, the tactile friction features may provide an anti-glare effect. For example, the tactile friction features may provide an anti-glare effect by increasing scattering of light from the tactile friction features as compared to a surface without the tactile friction features. In embodiments, the anti-glare effect provided by the tactile friction features does not unduly reduce the distinctness of image (DOI). As examples, tactile friction features having a conical, semi-conical, or pyramidal shape may be used to provide an anti-glare effect. 
     Further, the tactile friction features may provide an anti-reflective effect by reducing the amount of reflected light as compared to a corresponding surface without the tactile friction features. Similarly, the tactile friction features increase the amount of transmitted light (e.g. visible light) as compared to the corresponding surface. In embodiments, the anti-reflective effect provided by the tactile friction features does not unduly darken the appearance of the glass structure. For example, the anti-reflective effect may depend, at least in part, on the percentage of the base surface covered by the tactile friction features. In embodiments, the greater amount of coverage of the base surface by the tactile friction features produces a greater reduction in the reflectivity of the glass structure. As an example, the percentage coverage of the base surface may range from 5% to 50%. 
     Further, the ratio of the average diameter of the tactile friction features to the average pitch may be used as a measure of the coverage of the base surface by the tactile friction features. In embodiments, the ratio of the average base diameter of cone-shaped tactile friction features to the average pitch may be less than one, less than 0.75, less than 0.5, less than 0.25, less than 0.1, or from 0.05 to 0.5 to limit the anti-reflective effect. In further embodiments, if the height and the spacing of tapered tactile friction features are less than wavelengths of visible light (e.g., less than one micron) the tactile friction feature may function as graded refractive index (GRIN) structure and produce an anti-reflective effect thereby. 
     The tactile friction features discussed herein may be formed in any of a variety of ways, including by lithography in combination with chemical etching, laser ablation, mechanical removal of material, and so on. Any suitable method of manufacture is contemplated and embraced by the embodiments described herein. In embodiments, the composition of the tactile friction features (excluding any surface coating) is substantially the same as that of the base surface and/or the underlying cover. 
     By the way of example, a process for forming the glass tactile friction features may include an operation of forming or applying a mask on the surface of a glass structure. The mask has a pattern configured to produce the desired shape and arrangement of the glass tactile friction features during a subsequent etching step. An operation of forming a mask may include applying a layer of a resist material to the surface of the glass structure and then forming a pattern in the resist material, such as a pattern of apertures or a pattern including different thicknesses of the resist material. 
     In some aspects, the mask is formed by imprint lithography, such as nano-imprint lithography. In embodiments, the mask is formed by pressing a patterned tool into a softened polymeric resist material to form a thickness pattern in the resist material. For example, the thickness pattern may have thinner regions corresponding to the interstitial regions and thicker regions corresponding to the locations of the glass tactile friction features. When the glass tactile friction features have a generally conical or rounded shape, the thickness of the thicker regions typically varies accordingly. The tool may be patterned by a variety of methods including, but not limited to, micro-machining, laser direct writing, grayscale lithography, or an imprinting process. The resist material may be softened by heating it to a temperature above a glass transition temperature and below a temperature at which undue flow of the resist material occurs. 
     In further aspects, the mask is formed by photolithography, in which case the resist material may be a positive or negative photoresist. Suitable photolithography techniques include, but are not limited to, binary photolithography techniques and 3-D photolithography techniques (e.g., multiple-step, direct-write, and grayscale mask photolithography). 
     An operation of applying a mask may include applying a patterned hard mask to the surface of the glass structure. For example, a hard mask may be formed of or include a metal, silicon, silicon nitride, or a polymer with an etch resistant layer on the backside (the side facing away from the enclosure to be coated). 
     A process for forming the glass tactile friction features typically includes an etching operation after the operation of forming or applying the mask on the surface. For example, when the mask defines gaps or apertures, the etching operation may include etching away a portion of the glass structure through gaps or apertures in the mask. When the mask defines thicker and thinner portions of the resist material, the etching operation may include etching the thinner portions of the mask to create gaps or apertures in the mask (resist material) prior to etching away a portion of the glass structure. For example, the portion of the glass structure to be etched may be removed using a dry etching technique. Dry etching techniques include, but are not limited to reactive ion etching. 
     Although embodiments have generally been described with respect to a glass structure or surface, it should be appreciated that tactile friction features may be formed on or from any suitable substrate, including metal, ceramic, glass ceramic, plastic, combinations of materials, and so on. Accordingly, examples discussing glass tactile friction features and processes for making glass tactile friction features are illustrative and not limiting. 
     In addition, any of the tactile friction features, glass surfaces, or combinations thereof described herein may be coated with a material to provide resistance to oils and other deposits. In this case, the coating may also at least partially define the touch-sensitive surface of the electronic device. For example, the material may comprise a fluorinated material, such as a fluorinated oligomer or polymer, to impart oleophobic and/or hydrophobic properties. For example, the contact angle of an oil on the coating may be greater than or equal to about 65 degrees or about 70 degrees. As an additional example, the contact angle of water on the coating may be greater than or equal to 90 degrees. The fluorinated material may comprise a linear (non-branched) fluorinated molecule such as a linear fluorinated oligomer or a linear fluorinated polymer. 
     For example, a coating comprising a fluorinated material may be applied to both the tactile friction features and the base surface. In embodiments, the layer of the fluorinated material is from 5 nm to 20 nm or from 10 nm to 50 nm. The layer of the fluorinated material may be bonded directly to the tactile friction features or may be bonded to an intermediate adhesion layer. The layer of the fluorinated material may be thin relative to the dimensions of the tactile friction features. 
     As an additional example, an adhesion layer may be applied to both the tactile friction features and the base surface and then a coating comprising the fluorinated material applied to the adhesion layer. The adhesion layer may comprises an inorganic material, may comprise a silicon oxide, such as silicon dioxide, or may consist essentially of silicon dioxide. In additional embodiments, the thickness of the adhesion layer is 10 nm or less, such as from 1 nm to 10 nm or from 1 nm to 5 nm. 
     In embodiments, the glass structure is chemically strengthened by ion exchange. As an example, ions present in the glass are exchanged for larger ions in an ion-exchange bath to form a compressive stress layer extending from a surface of the glass structure. In embodiments, the compressive stress layer extends at least partially into the tactile friction features. Generally, the ion-exchange operation precedes application of a coating of fluorinated material to the tactile friction features. 
     Ion-exchangeable glasses include, but are not limited to, soda lime glasses, aluminosilicate glasses, and aluminoborosilicate glasses. For example, an ion-exchangeable glass may include monovalent or divalent ions such as alkali metal ions (e.g., Li + , Na + , or K + ) or alkaline earth ions (e.g., Ca 2+  or Mg 2+ ) which may be exchanged for other alkali metal or alkaline earth ions. For example, if the glass structure comprises sodium ions, the sodium ions may be exchanged for potassium ions. Similarly, if the glass structure comprises lithium ions, the lithium ions may be exchanged for sodium ions and/or potassium ions. 
       FIG. 16  is an illustrative block diagram of an electronic device  1650  as described herein (e.g., electronic device  200  of  FIG. 2 , for example). The electronic device can include a display  1616 , one or more processing units  1600 , memory  1602 , one or more input/output (I/O) devices  1604  such as a button assembly  1606 , a power source  1608 , and a network communication interface  1610 . 
     The display  1616  may provide an image or graphical output (e.g., computer-generated image data) for the electronic device. The display may also provide an input surface for one or more input devices, such as, for example, a touch sensing device and/or a fingerprint sensor. The display  1616  may be substantially any size and may be positioned substantially anywhere on the electronic device. The display  1616  can be implemented with any suitable technology, including, but not limited to liquid crystal display (LCD) technology, light emitting diode (LED) technology, organic light-emitting display (OLED) technology, organic electroluminescence (OEL) technology, or another type of display technology. The display  1616  provides a graphical output, for example associated with an operating system, user interface, and/or applications of the electronic device  1650 . In some embodiments, the display  1616  is configured as a touch-sensitive (e.g., single-touch, multi-touch) and/or force-sensitive display to receive inputs from a user. In some embodiments, the touch-sensitive display includes one or more sensors (e.g., capacitive touch sensors, ultrasonic sensors, or other touch sensors) positioned above, below, or integrated with the display. In various embodiments, a graphical output of the display  1616  is responsive to inputs provided to the electronic device  1650 . 
     It should be appreciated that the display  1616  may include, or be covered by, a cover glass incorporating tactile friction features as described herein. 
     The processing unit  1600  can control some or all of the operations of the electronic device. The processing unit  1600  can communicate, either directly or indirectly, with substantially all of the components of the electronic device. For example, a system bus or signal line or other communication mechanisms (e.g., electronic connectors) can provide communication between the processing unit(s)  1600 , the memory  1602 , the I/O device(s)  1604 , the power source  1608 , and/or the network communication interface  1610 . The one or more processing units  1600  can be implemented as any electronic device capable of processing, receiving, or transmitting data or instructions. For example, the processing unit(s)  1600  can each be a microprocessor, a central processing unit, an application-specific integrated circuit, a field-programmable gate array, a digital signal processor, an analog circuit, a digital circuit, or combination of such devices. The processor may be a single-thread or multi-thread processor. The processor may be a single-core or multi-core processor. 
     Accordingly, as described herein, the phrase “processing unit” or, more generally, “processor” refers to a hardware-implemented data processing unit or circuit physically structured to execute specific transformations of data including data operations represented as code and/or instructions included in a program that can be stored within and accessed from a memory. The term is meant to encompass a single processor or processing unit, multiple processors, multiple processing units, analog or digital circuits, or other suitably configured computing element or combination of elements. 
     The memory  1602  can store electronic data that can be used by the electronic device. For example, a memory can store electrical data or content such as, for example, audio and video files, documents and applications, device settings and user preferences, timing signals, signals received from the one or more sensors, one or more pattern recognition algorithms, data structures or databases, and so on. The memory  1602  can be configured as any type of memory. By way of example only, the memory can be implemented as random access memory, read-only memory, flash memory, removable memory, or other types of storage elements, or combinations of such devices. 
     The one or more I/O devices  1604  can transmit and/or receive data to and from a user or another electronic device. The I/O device (s)  1604  can include any components discussed herein to provide tactile outputs, including input structures, tactile features, and the like. The I/O device(s)  1604  can further include a display, a touch or force sensing input surface such as a trackpad, one or more buttons, one or more microphones or speakers, one or more ports such as a microphone port, one or more accelerometers for tap sensing, one or more optical sensors for proximity sensing, and/or a keyboard. The I/O devices  1604  may include a surface configured for contact by a user or an object; such surface may incorporate tactile friction features as discussed herein. As one example, a button assembly  1606  may include a cap or other surface formed from glass, ceramic, plastic, or any other suitable material. That cap or surface may have tactile friction features. 
     The power source  1608  can be implemented with any device capable of providing energy to the electronic device. For example, the power source  1608  can be one or more batteries or rechargeable batteries, or a connection cable that connects the electronic device to another power source such as a wall outlet. 
     The network communication interface  1610  can facilitate transmission of data to or from other electronic devices. For example, a network communication interface can transmit electronic signals via a wireless and/or wired network connection. Examples of wireless and wired network connections include, but are not limited to, cellular, Wi-Fi, Bluetooth, IR, and Ethernet. 
     It should be noted that  FIG. 16  is for illustrative purposes only. In other examples, an electronic device may include fewer or more components than those shown in  FIG. 16 . Additionally or alternatively, the electronic device can be included in a system and one or more components shown in  FIG. 16  are separate from the electronic device but included in the system. For example, an electronic device may be operatively connected to, or in communication with a separate display. As another example, one or more applications can be stored in a memory separate from the electronic device. The processing unit in the electronic device can be operatively connected to and in communication with the separate display and/or memory. 
     As used herein, the terms “about”, “approximately,” “substantially,” and “substantially equal to” are used to account for relatively small variations, such as a variation of +/−10%, +/−5%, or +/−2%. 
     The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of the specific embodiments described herein are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.

Metadata:
Filing Date: 20190205
Publication Date: 20220802
Grant Date: 20220802
Priority Date: 20180427
Inventors: POOLE, Joseph C.
PREST, CHRISTOPHER D.
NEKIMKEN, KYLE J.
SCHNEIDER, SAMUEL O.
Assignee: APPLE INC
CPC Classifications: [{"code": "G06F3/043", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F2201/56", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F2203/04809", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/044", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/0072", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/0072", "inventive": true, "first": true, "tree": "[]"}, {"code": "C03C2217/76", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/041", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/041", "inventive": true, "first": false, "tree": "[]"}, {"code": "B82Y30/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "B82Y30/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F2203/04809", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/041", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F2201/56", "inventive": false, "first": false, "tree": "[]"}, {"code": "C03C2217/76", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/0072", "inventive": true, "first": true, "tree": "[]"}, {"code": "B82Y30/00", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 68290692