Electronic device having a biometric input system including a composite cover element

1. An electronic device comprising:

an enclosure;

a display positioned within the enclosure; and

a biometric button assembly positioned along a side of the display and comprising:

a carrier structure configured to translate in response to a user press input;

a switch assembly configured to detect a translation of the carrier structure in response to the user press input;

a biometric sensing component coupled to the carrier structure and comprising an array of sensing elements configured to sense a fingerprint in response to the user press input; and

a dielectric coating at least partially encapsulating the array of sensing elements of the biometric sensing component, defining an input surface for the biometric button assembly, and formed from a composite material comprising:

oxide particles having a mean particle size greater than or equal to 50 nm and less than 1 micrometer; and

a binder comprising a thermoset polymer material.

2. The electronic device of claim 1 , wherein:

the enclosure includes a housing and a cover defining a transparent window over the display;

at least a portion of the biometric button assembly is positioned in an opening in the housing;

each of the sensing elements of the array of sensing elements is a field sensing element; and

the dielectric coating has:

a thickness greater than 5 micrometers and less than or equal to 200 micrometers over an outer surface of the biometric sensing component; and

an oxide particle loading that falls within a range from 80% to 90% by weight.

3. The electronic device of claim 2 , wherein:

the outer surface and at least a portion of a side surface of the biometric sensing component protrudes from the opening; and

the dielectric coating encapsulates the outer surface and the portion of the side surface of the biometric sensing component.

4. The electronic device of claim 2 , wherein:

the biometric button assembly further comprises a circuit layer conductively coupled to the biometric sensing component;

the biometric sensing component is mounted to an outward-facing surface of the circuit layer;

the biometric button assembly further comprises a circuit component mounted to an inward-facing surface of the circuit layer and conductively coupled to the biometric sensing component through the circuit layer; and

a molding compound, different from the composite material, at least partially encapsulates the circuit component and the inward-facing surface of the circuit layer.

5. The electronic device of claim 4 , wherein:

a connector conductively couples the outer surface of the biometric sensing component to the inward-facing surface of the circuit layer;

the dielectric coating at least partially encapsulates the connector and the outward-facing surface of the circuit layer; and

the thickness of the coating ranges from 90 micrometers to 200 micrometers.

6. The electronic device of claim 4 , wherein:

the dielectric coating defines an outer face of the biometric button assembly; and

the outer face defines an elongated shape.

7. The electronic device of claim 1 , wherein the switch assembly includes a dome switch.

8. An electronic device comprising:

an enclosure defining an opening;

a bio-authentication button assembly positioned at least partially within the opening and comprising:

a capacitive sensing component defining a component surface; and

a cap defining a touch input surface and disposed over the component surface, the cap formed from a composite material comprising:

dielectric particles having a mean particle size greater than or equal to 50 nm and less than or equal to 500 nm; and

a binder comprising a dielectric polymer material; and

a processor positioned within the enclosure, operatively coupled to the capacitive sensing component, and configured to authenticate a user based on an output of the capacitive sensing component.

9. The electronic device of claim 8 , wherein:

the touch input surface of the cap defines an elongated shape; and

the bio-authentication button assembly further comprises:

a conductive carrier structure coupled to the capacitive sensing component; and

a force sensor configured to detect a force applied to the touch input surface.

10. The electronic device of claim 9 , wherein:

the touch input surface of the cap is proud of the opening; and

the composite material has a Young's modulus ranging from 15 GPa to 20 GPa.

11. The electronic device of claim 9 , wherein a portion of the conductive carrier structure extends along a side surface of the capacitive sensing component.

12. The electronic device of claim 8 , wherein:

the bio-authentication button assembly further comprises a circuit layer;

an inward-facing surface of the capacitive sensing component is conductively coupled to the circuit layer; and

the cap has a thickness ranging from 40 micrometers to 120 micrometers over an outward-facing surface of the capacitive sensing component opposite to the inward-facing surface.

13. The electronic device of claim 8 , wherein:

the enclosure includes a housing and an at least partially transparent cover coupled to the housing and positioned over a display; and

the opening is defined by a hole that extends through the housing.

14. The electronic device of claim 13 , wherein:

an exterior surface of the housing defines a recessed portion; and

the recessed portion defines a perimeter of the opening.

15. An electronic device comprising:

a housing defining an opening along a side surface of the electronic device;

a touch-sensitive biometric button assembly extending partially through the opening and comprising:

a biometric sensing component including a sensing layer; and

an exterior package layer defining an input surface of the touch-sensitive biometric button assembly, at least partially encapsulating an outward-facing surface of the biometric sensing component, and formed from a dielectric material comprising:

80% to 95% by weight of oxide particles having a mean particle size greater than or equal to 50 nm and less than or equal to 500 nm; and

5% to 20% by weight of a binder comprising a thermoset polymer material; and

a switch assembly positioned inward of the touch-sensitive biometric button assembly and configured to detect a user press input.

16. The electronic device of claim 15 , wherein:

the touch-sensitive biometric button assembly further includes a carrier structure; and

the switch assembly includes:

an electromechanical switch; and

a compressible assembly coupled to the carrier structure and configured to compress in response to the user press input.

17. The electronic device of claim 15 , wherein the sensing layer includes an array of field sensing elements.

18. The electronic device of claim 15 , wherein the touch-sensitive biometric button assembly further includes:

a circuit layer; and

an interior package layer formed of a molding compound different from the dielectric material and at least partially encapsulating the circuit layer.

19. The electronic device of claim 18 , wherein an inward-facing surface of the biometric sensing component defines a substrate for the circuit layer.

20. The electronic device of claim 15 , wherein:

the oxide particles are silica particles; and

the thermoset polymer material is an epoxy-based polymer material.