Fingerprint sensing device with heterogeneous coating structure comprising a mold

1. 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.

2. The device 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.

3. The device 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.

4. The device according to claim 3 , wherein said filler particles comprise a ferroelectric material.

5. The device according to claim 3 , wherein said openings are larger than a maximum size of said filler particles in said mold material.

6. The device according to any claim 1 , further comprising: a protective plate attached to said fingerprint sensing device by means of an adhesive.

7. 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 and wherein forming said cavities comprises forming openings between adjacent cavities so that a liquid mold can flow between adjacent cavities during compression molding; and

filling said cavities with a mold material, wherein said step of filling said cavities with the mold material comprises compression molding and wherein a dielectric constant of said mold material is higher than a dielectric constant of said coating material.

8. The method according to claim 7 , 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.

9. The method according to claim 7 , wherein said layer of coating material is deposited by spin coating or by spray coating.

10. The method according to claim 7 , wherein the dielectric constant of said mold material is in the range of 5 to 100.

11. The method according to claim 7 , wherein the dielectric constant of said coating material is in the range of 2 to 5.

12. The method according to claim 7 , 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.

13. The method according to claim 7 , wherein said mold material comprises filler particles having a dielectric constant higher than an average dielectric constant of said mold material.

14. The method according to claim 13 , wherein said filler particles comprise a ferroelectric material.

15. The method according to claim 13 , wherein said openings are larger than a maximum size of said filler particles in said mold material.

16. The method according to claim 7 , 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.

17. The method according to claim 7 , further comprising plasma cleaning of said coating material prior to the step of providing said mold material.

18. The method according to claim 7 , further comprising:

depositing an adhesive on said mold material; and

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