Electronic Device Having Direction-Dependent Strain Elements

• US 20170285864A1
• Filed: 09/22/2016
• Published: 10/05/2017
• Est. Priority Date: 03/31/2016
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Pedder, James E., Smith, John Stephen, Vosgueritchian, Michael, Garg, Vikram, Filiz, Sinan, Christophy, Miguel C.
• Granted Patent: US 10,209,830 B2
• Time in Patent Office: Days
• CPC Class Codes: G01L 1/18 using properties of piezo-resistive materials, i.e. materials of which the ohmic resistance varies according to changes in magnitude or direction of force applied to the material
• CPC Class Codes: G01L 1/205 using distributed sensing elements
• CPC Class Codes: G01L 1/2281 for temperature variations
• CPC Class Codes: G01L 5/00 Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
• CPC Class Codes: G06F 2203/04103 Manufacturing, i.e. details related to manufacturing processes specially suited for touch sensitive devices
• CPC Class Codes: G06F 2203/04105 Pressure sensors for measuring the pressure or force exerted on the touch surface without providing the touch position
• CPC Class Codes: G06F 3/0412 Digitisers structurally integrated in a display
• CPC Class Codes: G06F 3/04144 using an array of force sensing means position sensing using the local deformation of sensor cells G06F3/0447
• CPC Class Codes: G06F 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment
• CPC Class Codes: G06F 3/044 by capacitive means
• CPC Class Codes: G06F 3/045 using resistive elements, e.g. a single continuous surface or two parallel surfaces put in contact
• CPC Class Codes: H10K 59/40 OLEDs integrated with touch screens

Abstract

A force sensor is disclosed. The force sensor includes a force-sensitive structure that compensates for temperature and other environmental changes through the use of a strain-sensitive element and one or more reference elements. An array of such force-sensitive structures forms a force-sensing layer.

Claims

1. An electronic device, comprising:

an enclosure;

a display positioned at least partially within the enclosure;

a transparent cover positioned over the display; and

an opaque force-sensing layer positioned beneath the display, comprising;

a substrate; and

an array of force-sensitive structures disposed on the substrate, a force-sensitive structure of the array comprising;

a strain-sensitive element configured to produce a first electrical response in response to a deflection of the transparent cover;

a first reference element positioned proximate to the strain-sensitive element and configured to produce a second electrical response in response to the deflection of the transparent cover; and

a second reference element positioned proximate to the strain-sensitive element and configured to produce a third electrical response in response to the deflection of the transparent cover;

wherein a magnitude of each of the second and third electrical responses is smaller than the first electrical response.

2. The electronic device of claim 1, wherein the electronic device further comprises:

force-sensing circuitry operatively coupled to the array of force-sensitive structures and configured to estimate a temperature-compensated strain using the first and second electrical responses of the force-sensitive structure.

3. The electronic device of claim 1, wherein:

the strain-sensitive element is formed from conductive material defining a first set of interconnected traces formed along a first direction;

the first and second reference elements are formed from the conductive material defining a second and third set of interconnected traces formed along a second direction; and

the second direction is transverse to the first direction.

4. The electronic device of claim 1, wherein

the substrate comprises a first substrate layer and a second substrate layer;

a first strain-relief feature is formed into the first substrate layer between the strain-sensitive element and the first reference element; and

a second strain-relief feature is formed into the first substrate layer between the strain-sensitive element and the second reference element.

5. The electronic device of claim 4, wherein the first substrate layer comprises one or more of:

a polyimide sheet, a glass sheet, or a polyethylene terephthalate sheet.

6. The electronic device of claim 1, wherein the opaque force-sensing layer further comprises:

a strain concentrating structure comprising a group of stiffener segments, each stiffener segment coupled to the substrate to define a group of strain concentration regions located between pairs of stiffener segments.

7. The electronic device of claim 6, wherein:

the strain-sensitive element is positioned within one of the group of strain-concentration regions;

the strain-sensitive element is positioned on a first side of the substrate; and

the strain concentrating structure is positioned on a second side of the substrate opposite the first side.

8. The electronic device of claim 1, wherein the first electrical response is a change in resistance of the strain-sensitive element.

9. The electronic device of claim 1, wherein the strain-sensitive element and the first and second reference elements comprise one or more of:

a constantan, a karma, or an isoelastic material.

10. A force-sensing layer for sensing a force applied to an electronic device, the force-sensing layer comprising:

a substrate;

an array of force-sensitive structures arranged on the substrate, each force-sensitive structure comprising;

a strain-sensitive element positioned on the substrate and configured to produce a first change in resistance in response to strain along a direction; and

a reference element positioned on the substrate proximate to the strain-sensitive element and configured to produce a second change in resistance in response to strain along the direction that is smaller than the first change in resistance;

wherein

the strain-sensitive element and the reference element are disposed in an interlocking spiral pattern.

11. The force-sensing layer of claim 10, wherein the electronic device further comprises:

force-sensing circuitry operatively coupled to the strain-sensitive element and the reference element and configured to estimate a temperature-compensated strain using the first and the second changes in resistance.

12. The force-sensing layer of claim 10, wherein the strain-sensitive element and the reference element are formed on a same surface of the substrate.

13. The force-sensing layer of claim 11, wherein:

the strain-sensitive element comprises a first conductive material disposed in a first spiral pattern;

the reference element comprises a second conductive material disposed in a second spiral pattern interlocked with the first spiral pattern; and

the force-sensing circuitry is configured to compensate for strain based on a known relationship between a material property of the first conductive material and the second conductive material.

14. An electronic device, comprising:

a component forming an exterior surface of the electronic device;

a force-sensing layer positioned below the exterior surface and comprising;

a substrate attached to the component and configured to, in response to a deflection in the exterior surface, produce strain along a series of radial paths extending between a middle region of the substrate and a perimeter of the substrate;

an array of force-sensitive structures disposed on the substrate, each force-sensitive structure comprising;

a first strain-sensitive element configured to exhibit a primary sensitivity to strain along a first direction substantially aligned with a respective radial path; and

a second strain-sensitive element positioned adjacent the first strain-sensitive element and configured to exhibit a primary sensitivity to strain along a second direction that is transverse to the first direction;

wherein

in response to the deflection in the exterior surface, the first strain-sensitive element exhibits a first change in resistance and the second strain-sensitive element exhibits a second change in resistance that is smaller than the first change in resistance.

15. The electronic device of claim 14, wherein the electronic device further comprises:

force-sensing circuitry operatively coupled to the first and second strain-sensitive elements and configured to estimate a temperature-compensated strain using the first and second changes in resistance.

16. The electronic device of claim 14, wherein:

the substrate includes a group of strain-relief features formed along the first direction; and

the first strain-sensitive element is positioned between a pair of strain-relief features of the group of strain-relief features.

17. The electronic device of claim 16, wherein the group of strain-relief features includes an array of slits formed into the first side of the substrate.

18. The electronic device of claim 14, wherein:

the first strain-sensitive element is formed on a first surface of the substrate; and

the second strain-sensitive element is formed on a second surface of the substrate opposite the first surface.

19. The electronic device of claim 14, wherein:

the first strain-sensitive element and the second strain-sensitive element are formed on a same surface of the substrate; and

each force-sensitive structure further comprises a third strain-sensitive element positioned on the same surface and adjacent the first strain-sensitive element, and configured to exhibit a primary sensitivity to strain along the second direction.

20. The electronic device of claim 14, wherein:

the electronic device further comprises a display and a transparent cover positioned over the display;

the first strain-sensitive element is positioned between the transparent cover and the display; and

the first and second strain-sensitive elements comprise indium tin oxide.

21. An electronic device, comprising:

a component forming an exterior surface of the electronic device;

a force-sensing layer positioned below the exterior surface and comprising;

a substrate attached to the component and configured to strain in response to a deflection in the exterior surface;

a first force-sensitive structure comprising;

a first strain-sensitive element disposed on a first surface of the substrate and configured to exhibit a first primary sensitivity to the strain along a first direction; and

a second strain-sensitive element disposed on a second surface of the substrate and aligned vertically with the first strain-sensitive element;

a second force-sensitive structure comprising;

a third strain-sensitive element disposed on the first surface of the substrate and configured to exhibit a second primary sensitivity to the strain along a second direction different from the first direction; and

a fourth strain-sensitive element disposed on the second surface of the substrate and aligned vertically with the third strain-sensitive element,

wherein

the first direction is based on a first location of the first strain-sensitive element on the first surface of the substrate; and

the second direction is based on a second location of the third strain-sensitive element on the first surface of the substrate.

22. The electronic device of claim 21, wherein

the strain comprises a series of radial paths extending outward from a location of a deflection of the substrate;

the first direction and the second direction are substantially transverse to respective radial paths; and

in response to the deflection in the exterior surface;

the first strain-sensitive element exhibits a first change in resistance and the second strain-sensitive element exhibits a second change in resistance that is smaller than the first change in resistance; and

the third strain-sensitive element exhibits a third change in resistance and the fourth strain-sensitive element exhibits a fourth change in resistance that is smaller than the third change in resistance.