FINGERPRINT SENSING DEVICE WITH HETEROGENEOUS COATING STRUCTURE COMPRISING A MOLD

• US 20160354801A1
• Filed: 04/26/2016
• Published: 12/08/2016
• Est. Priority Date: 06/08/2015
• Status: Active Grant

• Current Assignee: Fingerprint Cards AB
• Original Assignee: Fingerprint Cards AB
• Inventors: LUNDAHL, Karl
• Granted Patent: US 9,842,243 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G06F 18/00 Pattern recognition
• CPC Class Codes: G06V 40/1329 Protecting the fingerprint sensor against damage caused by the finger

Abstract

The invention relates to a fingerprint sensing device comprising a sensing chip comprising an array of capacitive sensing elements. The sensing device comprises a coating material arranged in a layer on top of the array of sensing elements, the coating material comprising a plurality of cavities filled with a mold material; wherein locations of the cavities correspond to locations of the sensing elements, such that a cross-section area of a cavity covers at least a portion of an area of a corresponding sensing element; and wherein a dielectric constant of the mold material is higher than a dielectric constant of the coating material. The invention also relates to a method for manufacturing such a device.

Claims

1. A method for manufacturing a fingerprint sensing device, said method comprising;

providing a sensing chip comprising an array of sensing elements, said sensing elements being configured to be connected to readout circuitry for detecting a capacitive coupling between each of said sensing elements and a finger placed on a sensing surface of said sensing device;

depositing a layer of a coating material covering said array of conductive sensing elements;

forming a plurality of cavities in said coating material, wherein locations of said cavities correspond to locations of said sensing elements such that a cross-section area of a cavity covers at least a portion of an area of a corresponding sensing element, wherein forming said cavities comprises forming openings between adjacent cavities so that a liquid mold can flow between adjacent cavities; and

filling said cavities with a mold material, said mold material having a dielectric constant higher than a dielectric constant of said coating material.

2. The method according to claim 1, wherein said step of filling said cavities with a mold material comprises compression molding.

3. The method according to claim 2, wherein said step of compression molding comprises:

dispensing granulated mold particles on said layer of coating and in said cavities;

heating said granulated mold particles; and

applying a pressure to said granulated mold particles.

4. The method according to claim 1, wherein said coating layer is deposited by spin coating or by spray coating.

5. The method according to claim 1, wherein a dielectric constant of said mold material is in the range of 5 to 100.

6. The method according to claim 1, wherein a dielectric constant of said coating material is in the range of 2 to 5.

7. The method according to claim 1, wherein a ratio between said dielectric constant of said mold and said dielectric constant of said coating material is equal to or larger than 2:

1.

8. The method according to claim 1, wherein said mold material comprises filler particles having a dielectric constant higher than an average dielectric constant of said mold material.

9. The method according to claim 8, wherein said filler particles comprise a ferroelectric material.

10. The method according to claim 8, wherein said openings are larger than a maximum size of said filler particles in said mold material.

11. The method according to claim 1, wherein said coating material is a photoresist and wherein forming a plurality of cavities in said coating material comprises patterning said layer of coating material by photolithography.

12. The method according to claim 1, further comprising plasma cleaning of said coating material prior to the step of providing said mold material.

13. The method according to any claim 1, further comprising:

depositing an adhesive on said mold material; and

attaching a protective plate to said fingerprint sensing device by means of said adhesive.

14. A fingerprint sensing device comprising:

a sensing chip comprising an array of sensing elements, said sensing elements being configured to be connected to readout circuitry for detecting a capacitive coupling between each of said sensing elements and a finger placed on a sensing surface of said sensing device;

a coating material arranged in a layer on top of said array of sensing elements, said coating material comprising a plurality of cavities filled with a mold material, wherein said mold material is deposited by compression molding;

wherein locations of said cavities correspond to locations of said sensing elements, such that a cross-section area of a cavity covers at least a portion of an area of a corresponding sensing element, said cavities comprising openings between adjacent cavities so that a liquid mold can flow between adjacent cavities during compression molding; and

wherein a dielectric constant of said mold material is higher than a dielectric constant of said coating material.

15. The device according to claim 14, wherein a ratio between said dielectric constant of said mold and said dielectric constant of said coating material is equal to or larger than 2:

1.

16. The device according to claim 14, wherein said mold material comprises filler particles having a dielectric constant higher than an average dielectric constant of said mold material.

17. The device according to claim 16, wherein said filler particles comprise a ferroelectric material.

18. The device according to claim 16, wherein said openings are larger than a maximum size of said filler particles in said mold material.

19. The device according to any claim 14, further comprising:

a protective plate attached to said fingerprint sensing device by means of an adhesive.

20. A fingerprint sensing device comprising:

a sensing chip comprising an array of sensing elements, said sensing elements being configured to be connected to readout circuitry for detecting a capacitive coupling between each of said sensing elements and a finger placed on a sensing surface of said sensing device;

a coating material arranged in a layer on top of said array of sensing elements, said coating material comprising a plurality of trenches filled with a mold material, wherein locations of said trenches correspond to areas between adjacent sensing elements;

wherein said mold material is deposited by compression molding; and

wherein a dielectric constant of said mold material is lower than a dielectric constant of said coating material.