Temperature compensating transparent force sensor

• US 9,665,200 B2
• Filed: 06/03/2015
• Issued: 05/30/2017
• Est. Priority Date: 01/13/2014
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Huppi, Brian Q., Filiz, Sinan, Pedder, James E., Ogata, Charley T., Patel, Dhaval Chandrakant, Choi, Shin John, Butler, Christopher J., Grunthaner, Martin P., Smith, John Stephen
• Primary Examiner(s): OLSON, JASON C
• Application Number:
  US14/729,172
• Publication Number:
  US 20160139717A1
• Time in Patent Office: 727 Days
• Field of Search: 345173
• 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, which may be used as input to an electronic device. The optically transparent force sensor may be configured to compensate for variations in temperature using two or more force-sensitive components that are formed from materials having different temperature- and strain-dependent responses.

Claims

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

a first transparent force-sensitive component having a first temperature-dependent response and a first strain-dependent response;

a second transparent force-sensitive component having a second temperature-dependent response and a second strain-dependent response;

a sensor circuit operatively coupled to the first and second transparent force-sensitive components, configured to detect a change in an electrical property of the first and second transparent force-sensitive components, and output a force estimate that compensates for a variation in temperature using the first and second temperature-dependent responses of the first and second transparent force-sensitive components;

wherein

a strain ratio between the first strain-dependent response and the second strain-dependent response is different than a temperature ratio between the first temperature-dependent response and the second temperature-dependent response.

2. The force sensor of claim 1, wherein

the sensor circuit is configured to compensate for the variation in temperature using the first strain-dependent response and the first temperature-dependent response of the first transparent force-sensitive component and the second strain-dependent response and the second temperature-dependent response of the second transparent force-sensitive component.

3. The force sensor of claim 1, wherein

the first strain-dependent response is represented by a first strain relationship that is a linear relationship between a first strain experienced by the first transparent force-sensitive component and a first resistance exhibited by the first transparent force-sensitive component;

the second strain-dependent response is represented by a second strain relationship that is a linear relationship between a second strain experienced by the second transparent force-sensitive component and a second resistance exhibited by the second transparent force-sensitive component;

the first temperature-dependent response is represented by a first temperature relationship that is a linear relationship between the first temperature and the first resistance; and

the second temperature-dependent response is represented by a second temperature relationship that is a linear relationship between the second temperature and the second resistance.

4. The force sensor of claim 1, wherein

the surface of the device is a cover disposed over a display of the device, and

the force estimate corresponds to the force of a touch on the surface of the cover.

5. The force sensor of claim 1, wherein the first transparent force-sensitive component is formed from an indium tin oxide (ITO) material and the second transparent force-sensitive component is formed from a polyethyleneioxythiophene (PEDOT) material.

6. The force sensor of claim 1, wherein the first transparent force-sensitive component is formed from a first type of polyethyleneioxythiophene (PEDOT) material having the first temperature-dependent response and the second transparent force-sensitive component is formed from a second type of PEDOT material having the second temperature-dependent response, wherein the first and second temperature-dependent responses are different.

7. An electronic device having a transparent force sensor, the device comprising:

an enclosure;

a display disposed within the enclosure;

a cover disposed above the display and forming a portion of an outer surface or the device;

a first array of transparent force-sensitive components disposed below the cover and having a first temperature-dependent response and a first strain-dependent response;

a second array of transparent force-sensitive components disposed below the first array and having a second temperature-dependent response and a second strain-dependent response;

a sensor circuit operatively coupled to the first and second array, configured to detect a change in an electrical property of components of the first and second arrays, and output a force estimate that compensates for a variation in temperature using the first and second temperature-dependent responses of the first and second transparent force-sensitive components;

wherein

a strain ratio between the first and second strain-dependent responses is different than a temperature ratio between the first and second temperature-dependent responses.

8. The electronic device of claim 7, wherein the display is disposed between the cover and the first array of transparent force-sensitive components.

9. The electronic device of claim 7, wherein the display is disposed below the first array of transparent force-sensitive components.

10. The electronic device of claim 7, further comprising:

a third array of transparent force-sensitive components disposed between the first array and the second array and having the first temperature-dependent response.

11. The electronic device of claim 7, further comprising:

a third array of transparent force-sensitive components disposed between the first array and the second array and having the first temperature-dependent response; and

a fourth array of transparent force-sensitive components disposed between the third array and the second array and having the second temperature-dependent response.

12. The electronic device of claim 7, further comprising:

a pressure-sensitive adhesive layer disposed between the first array and the cover, wherein the pressure-sensitive adhesive layer has an elasticity of approximately 1 MPa.

13. An electronic device having a transparent force sensor, the device comprising:

an enclosure;

a display disposed within the enclosure;

a cover disposed above the display and forming a portion of an outer surface or the device;

a first array of transparent force-sensitive components disposed below the cover and including components having a first and second temperature-dependent response and a first and second strain-dependent response, respectively;

a second array of transparent force-sensitive components disposed below the first array and including components having the first and second temperature-dependent response and the first and second strain-dependent response, respectively; and

a sensor circuit operatively coupled to the first and second array, configured to detect a change in an electrical property of components, and output a force estimate that compensates for a variation in temperature using the first and second temperature-dependent responses;

wherein

a strain ratio between the first and second strain-dependent responses is different than a temperature ratio between the first and second temperature-dependent responses.

14. The electronic device of claim 13, wherein the first array of transparent force-components includes alternating structures formed from an indium tin oxide material and a polyethyleneioxythiophene (PEDOT) material.

15. The electronic device of claim 13, wherein the first array of transparent force-components includes alternating structures formed from a first type of polyethyleneioxythiophene (PEDOT) material having the first temperature-dependent response and a second type of PEDOT material having the second temperature-dependent response.

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

a transparent force-sensitive component including an array of pixel elements;

a primary pixel of the array of pixel elements;

at least one reference pixel of the array of pixel elements, wherein the at least on reference pixel is separated from the primary pixel by at least one other pixel element;

a sensor circuit configured to form an electrical bridge circuit across the primary pixel and the at least one reference pixel to detect a change in resistance of the primary pixel.

17. The transparent force sensor of claim 16, wherein the at least one reference pixel and the primary pixel are subjected to similar thermal conditions and are subjected to different strain conditions when the force is applied to the surface of the device.

18. The transparent force sensor of claim 16, wherein the at least one reference pixel is formed on a different layer than the primary pixel.