Temperature compensating transparent force sensor having a compliant layer

• US 9,542,028 B2
• Filed: 12/17/2015
• Issued: 01/10/2017
• Est. Priority Date: 01/13/2014
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Filiz, Sinan, Pedder, James E., Ogata, Charley T., Smith, John Stephen, Patel, Dhaval Chandrakant, Choi, Shin John, Huppi, Brian Q., Butler, Christopher J., Grunthaner, Martin P.
• Primary Examiner(s): Lubit, Ryan A
• Application Number:
  US14/972,917
• Publication Number:
  US 20160103545A1
• Time in Patent Office: 390 Days
• US Class Current: 1/1
• CPC Class Codes: G01L 1/005 by electrical means and not provided for in G01L1/06 - G01L1/22
• CPC Class Codes: G01L 1/16 using properties of piezoelectric devices
• 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 1/20 by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids of piezo-resistive materials G01L1/18; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress
• CPC Class Codes: G01L 1/205 using distributed sensing elements
• 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 2203/04111 Cross over in capacitive digitiser, i.e. details of structures for connecting electrodes of the sensing pattern where the connections cross each other, e.g. bridge structures comprising an insulating layer, or vias through substrate
• 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

Abstract

An optically transparent force sensor that may compensate for environmental effects, including, for example, variations in temperature of the device or the surroundings. In some examples, two force-sensitive layers are separated by a compliant layer. The relative electrical response of the two force-sensitive layers may be used to compute an estimate of the force of a touch that reduces the effect of variations in temperature. In some examples, piezoelectric films having anisotropic strain properties are used to reduce the effects of temperature.

Claims

1. An electronic device comprising:

a touch-sensitive surface;

a force sensor positioned below the touch-sensitive surface and comprising;

a first strain-sensitive element;

a compliant layer disposed below the first strain-sensitive element; and

a second strain-sensitive element below the compliant layer and electrically coupled to the first-strain sensitive element; and

a sensor circuit configured to obtain a differential measurement between a first strain of the first strain-sensitive element and a second strain of the second strain-sensitive element;

wherein

the differential measurement changes in response to a force applied to the touch-sensitive surface; and

the sensor circuit compensates for a difference in temperature between the first and second strain-sensitive elements in response to the differential measurement.

2. The electronic device of claim 1, wherein the compliant layer is configured to conduct heat between the first strain-sensitive element and the second strain-sensitive element.

3. The electronic device of claim 1, wherein

the first strain-sensitive element is a member of a first array of strain-sensitive elements;

and

the second strain-sensitive element is a member of a second array of strain-sensitive elements.

4. The electronic device of claim 3, wherein the first array of strain-sensitive elements is arranged as a grid.

5. The electronic device of claim 3, wherein the first array of strain-sensitive elements is arranged as a line.

6. The electronic device of claim 3, wherein the second array of strain-sensitive elements is arranged in a manner complementary to an arrangement of the first array of strain-sensitive elements.

7. The electronic device of claim 1, wherein the first strain-sensitive element is disposed on a glass substrate.

8. The electronic device of claim 1, wherein the first strain-sensitive element is formed from indium tin oxide.

9. The electronic device of claim 1, wherein the compliant layer comprises an optically clear adhesive.

10. The electronic device of claim 1, wherein at least one of the first or second strain-sensitive elements are optically transparent.

11. An electronic device comprising:

a cover defining a touch-sensitive surface;

a force sensor positioned below the cover and comprising a strain-sensitive element configured to deform in response to a force applied to the touch-sensitive surface; and

a sensor circuit configured to obtain a differential measurement between a strain response of the strain-sensitive element and an electrical response of a resistive element, the resistive element electrically coupled to the strain-sensitive element;

wherein

the resistive element is formed from the same material as the strain-sensitive element; and

the resistive element is thermally coupled to the strain-sensitive element such that the electronic device is configured to reduce a difference in temperature between the resistive element and the strain-sensitive element in response to the differential measurement.

12. The electronic device of claim 11, wherein the strain-sensitive element is a member of an array of strain-sensitive elements disposed on a substrate.

13. The electronic device of claim 12, wherein the array of strain-sensitive elements is arranged in a grid on the substrate.