TRANSPARENT FORCE SENSOR WITH STRAIN RELIEF

• US 20150242037A1
• Filed: 11/21/2014
• Published: 08/27/2015
• Est. Priority Date: 01/13/2014
• Status: Abandoned Application

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Pedder, James E., Smith, John Stephen
• Application Number:
  US14/550,845
• Publication Number:
  US 20150242037A1
• Time in Patent Office: Days
• US Class Current: 1/1
• 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: G06F 2203/04105 Pressure sensors for measuring the pressure or force exerted on the touch surface without providing the touch position

Abstract

A transparent force sensor for detecting an applied force on a surface of a device. The transparent force sensor includes a transparent force-sensitive film having an array of strain-relief features oriented along a first direction. The transparent force-sensitive film is formed from a transparent piezoelectric material that exhibits a substantially reduced net charge when strained along a primary direction. The force sensor also includes a display element disposed on one side of the transparent force-sensitive film.

Claims

1. A transparent force sensor for detecting a force of a touch on a surface of a device, the transparent force sensor comprising:

a transparent force-sensitive film having an array of slit features oriented along a first direction, wherein the transparent force-sensitive film is formed from a piezoelectric material that exhibits a substantially reduced net charge when strained along a primary direction.

2. The transparent force sensor of claim 1, further comprising a display element disposed on one side of the transparent force-sensitive film.

3. The transparent force sensor of claim 1, wherein the piezoelectric material exhibits a strain-direction dependent charge polarity.

4. The transparent force sensor of claim 1, wherein the piezoelectric material exhibits a positive charge when bent upward along a first strain direction and exhibits a negative charge when bent upward along a second strain direction that is substantially perpendicular to the first strain direction.

5. The transparent force sensor of claim 1, wherein the piezoelectric material is a poly-L-lactide (PLLA) or poly-D-lactide (PDLA) polymer film material.

6. The transparent force sensor of claim 1, further comprising:

a first electrode disposed above the transparent force-sensitive film;

a second electrode disposed below the transparent force-sensitive film; and

sense circuitry electrically coupled to the first and second electrodes, wherein the sense circuitry is configured to detect a change in an electrical property of the transparent force-sensitive film due to the force on the device.

7. The transparent force sensor of claim 6, wherein the electrical property is an electrical charge.

8. A transparent force sensor for detecting a force applied to a device, the transparent force sensor comprising:

a cover forming a portion of an exterior surface of the device;

a transparent force-sensitive film disposed below the cover and having an array of strain-relief features oriented along a first direction, wherein the transparent force-sensitive film is formed from a piezoelectric material that exhibits a substantially reduced net charge when strained along a primary direction, and

a display element disposed below the transparent force-sensitive film.

9. The transparent force sensor of claim 8, wherein the strain-relief features are slit features oriented along the first direction.

10. The transparent force sensor of claim 8, wherein the strain-relief features are recessed channel features oriented along the first direction.

11. The transparent force sensor of claim 8, wherein the strain-relief features are perforated features that are arranged along the first direction.

12. A transparent force sensor for detecting a force of a touch on a device, the transparent force sensor comprising:

a first transparent force-sensitive film having an array of slit features oriented along a first direction, wherein the transparent force-sensitive film is formed from a piezoelectric material that exhibits a substantially reduced net charge when strained along a first primary direction; and

a second transparent force-sensitive film having an array of slit features oriented along a second direction, wherein the second transparent force-sensitive film is formed from a piezoelectric material that exhibits a substantially reduced net charge when strained along a second primary direction.

13. The transparent force sensor of claim 12, wherein the first direction is substantially perpendicular to the second direction.

14. The transparent force sensor of claim 12, wherein the first primary direction is substantially perpendicular to the second primary direction.

15. The transparent force sensor of claim 12, wherein the first direction is approximately 45 degrees from the first primary direction and the second direction is approximately 45 degrees from the second primary direction.

16. The transparent force sensor of claim 12, further comprising:

a cover disposed above the first transparent force-sensitive film; and

a display element disposed below the second transparent force-sensitive film, wherein the second transparent force-sensitive film is disposed below the first transparent force-sensitive film.

17. The transparent force sensor of claim 12, further comprising:

a top electrode disposed above the first transparent force-sensitive film;

a middle electrode disposed below the first transparent force-sensitive film;

a bottom electrode disposed below the second transparent force-sensitive film; and

sense circuitry electrically coupled to the top, middle, and bottom electrodes, wherein the sense circuitry is configured to detect a change in an electrical property of the first and second transparent force-sensitive films due to the force on the device.

18. The transparent force sensor of claim 17, wherein the first transparent force-sensitive film is configured to produce a charge when strained perpendicular to the first direction, and the second transparent force-sensitive film is configured to produce a charge when strained perpendicular to the second direction.

19. The transparent force sensor of claim 17, wherein the sense circuitry is configured to measure a magnitude of the touch.

20. The transparent force sensor of claim 17, further comprising:

a first optically-clear adhesive disposed between the top electrode and the first transparent force-sensitive film; and

a second optically-clear adhesive disposed between the middle electrode and the first transparent force-sensitive film.