Capacitive gap force sensor with multi-layer fill

1. An electronic device, comprising:

a capacitive gap force sensor, comprising:

a first electrode;

a second electrode spaced apart from the first electrode;

a first layer of dielectric material positioned between the first electrode and the second electrode; and

a second layer of conductive material positioned between the first layer and the second electrode; and

a housing having a force input surface; wherein,

the first layer has a first compression resistance less than a second compression resistance of the second layer;

an effective capacitive sensing gap is defined between the first electrode and the second layer;

the capacitive gap force sensor is positioned near or against an interior surface of the housing, under the force input surface; and

the first layer is configured to compress or deform and alter the effective capacitive sensing gap when a force is received on the force input surface.

2. The electronic device of claim 1 , wherein the first layer and the second layer are part of a multi-layer fill that spans an entirety of a space between the first electrode and the second electrode.

3. The electronic device of claim 1 , wherein the first layer comprises a polymer foam.

4. The electronic device of claim 1 , wherein each of the first layer and the second layer comprises a polymer foam.

5. The electronic device of claim 1 , wherein the housing comprises acrylonitrile butadiene styrene (ABS).

6. The electronic device of claim 5 , wherein a first stiffness of the first electrode and a second stiffness of the first layer are at least an order of magnitude less stiff than a third stiffness of the force input surface.

7. The electronic device of claim 1 , wherein the capacitive gap force sensor defines an air gap between one of:

the first electrode and the first layer; or

the first layer and the second layer.

8. The electronic device of claim 1 , further comprising:

a capacitive force sensing circuit coupled to at least one of the first electrode or the second electrode.

9. A capacitive gap force sensor, comprising:

a first electrode;

a second electrode spaced apart from the first electrode;

a first layer of dielectric material positioned between the first electrode and the second electrode; and

a second layer of conductive material positioned between the first layer and the second electrode; wherein,

the first layer has a first compression resistance less than a second compression resistance of the second layer;

an effective capacitive sensing gap is defined between the first electrode and the second layer; and

the first layer is configured to compress or deform and alter the effective capacitive sensing gap when a force is received at the first electrode or the second electrode.

10. The capacitive gap force sensor of claim 9 , wherein each of the first layer and the second layer comprises a hydrophobic material.

11. The capacitive gap force sensor of claim 9 , wherein each of the first layer and the second layer comprises a closed cell foam.

12. The capacitive gap force sensor of claim 9 , wherein the second layer comprises an open cell foam.

13. The capacitive gap force sensor of claim 9 , further comprising:

an adhesive attaching the first layer to the second layer.

14. The capacitive gap force sensor of claim 9 , wherein the second layer comprises a polymer foam at least partially coated with a metal.

15. A method of constructing a capacitive gap force sensor, comprising:

constructing a stack of materials, the constructing including,

attaching a first electrode to a first surface of a first layer of dielectric material;

attaching a second electrode to a first surface of a second layer of conductive material; and

attaching a second surface of the first layer to a second surface of the second layer;

compressing the stack of materials; and

structurally modifying the second layer, after compressing the stack of materials; wherein,

the second surface of the first layer is opposite the first surface of the first layer;

the second surface of the second layer is opposite the first surface of the second layer; and

the stack of materials defines an effective capacitive sensing gap between the first electrode and the second layer of conductive material;

after constructing the stack of materials, the first layer has a first compression resistance greater than a second compression resistance of the second layer; and

the structural modification of the second layer transitions the second compression resistance to a compression resistance greater than the first compression resistance.

16. The method of claim 15 , wherein structurally modifying the second layer comprises:

heating the second layer.

17. The method of claim 15 , wherein structurally modifying the second layer comprises:

exposing the second layer to a predetermined wavelength or wavelengths of light.

18. The method of claim 15 , wherein structurally modifying the second layer comprises:

exposing the second layer to oxygen or removing oxygen from an environment of the second layer.

19. The method of claim 15 , wherein structurally modifying the second layer comprises:

chemically treating the second layer.

20. The method of claim 15 further comprising:

positioning the stack of materials within an electronic device; wherein,

the compressing occurs at least partially during the positioning.

21. The method of claim 15 , further comprising:

positioning the stack of materials within an electronic device; wherein,

the compressing occurs at least partially after the positioning.