FINGERPRINT SENSING DEVICE AND METHOD FOR MANUFACTURING A FINGERPRINT SENSING DEVICE

• US 20170351895A1
• Filed: 03/21/2017
• Published: 12/07/2017
• Est. Priority Date: 06/01/2016
• Status: Active Grant

• Current Assignee: Fingerprint Cards IP AB
• Original Assignee: Fingerprint Cards AB
• Inventors: Lundahl, Karl, Hgglund, Robert, Hjalmarson, Emil, Sundblad, Rolf, Jansson, Christer
• Granted Patent: US 9,977,945 B2
• Time in Patent Office: Days
• CPC Class Codes: G06F 2203/0338 Fingerprint track pad, i.e. fingerprint sensor used as pointing device tracking the fingertip image
• CPC Class Codes: G06F 2203/04103 Manufacturing, i.e. details related to manufacturing processes specially suited for touch sensitive devices
• CPC Class Codes: G06F 3/0412 Digitisers structurally integrated in a display
• CPC Class Codes: G06V 40/1306 non-optical, e.g. ultrasonic or capacitive sensing
• CPC Class Codes: G06V 40/1365 Matching; Classification

Abstract

There is provided a capacitive fingerprint sensing device for sensing a fingerprint pattern of a finger, said capacitive fingerprint sensing device comprising: a protective top layer to be touched by said finger; a first metal layer comprising a two-dimensional array of sensing structures arranged underneath said top layer; a second metal layer, arranged underneath said first metal layer, comprising a plurality of conductive structures a dielectric layer arranged between the first and second metal layers to electrically insulate the first metal layer from the second metal layer, the dielectric layer comprising a low-k material; and readout circuitry arranged underneath said second metal layer and coupled to each of the electrically conductive sensing structures by means of via connections to receive a sensing signal indicative of a distance between said finger and said sensing structure. There is also provided a method for manufacturing such a device.

Claims

1. A capacitive fingerprint sensing device for sensing a fingerprint pattern of a finger, said capacitive fingerprint sensing device comprising:

a protective top layer to be touched by said finger;

a first metal layer comprising a two-dimensional array of sensing structures arranged underneath said protective top layer;

a second metal layer, arranged underneath said first metal layer, comprising a plurality of conductive structures;

a dielectric layer arranged between the first and second metal layers to electrically insulate the first metal layer from the second metal layer, the dielectric layer comprising a low-k material configured to reduce a capacitive coupling between the first and second metal layer, thereby reducing capacitive crosstalk between the sensing structures and the conductive structures; and

readout circuitry arranged underneath said second metal layer and coupled to each of the electrically conductive sensing structures by means of via connections to receive a sensing signal indicative of a distance between said finger and said sensing structure.

2. The sensing device according to claim 1, wherein the dielectric layer comprises an organic polymer.

3. The sensing device according to claim 1, wherein the dielectric layer has thickness of at least 3 μ

m.

4. The sensing device according to claim 1, wherein the dielectric constant k of the low-k material dielectric layer is in the range of 1<

k<

3.9.

5. The sensing device according to claim 1, wherein the dielectric layer is Polybenzobisoxazole (PBO), Polyimide or Benzocyclobutene (BCB).

6. The sensing device according to claim 1, wherein the dielectric layer is provided in the form of a dry film.

7. The sensing device according to claim 1, comprising a metal structure of said second metal layer arranged directly below a sensing structure of the first metal layer and having an area smaller than the area of the sensing structure.

8. The sensing device according to claim 7, wherein a thickness and a dielectric constant of the dielectric layer is selected based on a desired capacitance between a sensing structure of the first layer and the underlying metal structure of the second metal layer.

9. A method for manufacturing a fingerprint sensing device, the method comprising;

providing a substrate comprising a plurality of metal structures arranged in a metal layer on the surface of the substrate and fingerprint readout circuitry located within the substrate;

providing a low-k dielectric layer covering the substrate;

forming via connection openings in the dielectric layer;

depositing a top metal layer on the dielectric layer forming via connections such that each sensing structure is connected to corresponding readout circuitry by means of said via connections; and

patterning the top metal layer to form a two dimensional array of sensing structures, wherein the low-k layer is configured to reduce a capacitive coupling between the first and second metal layer, thereby reducing capacitive crosstalk between the sensing structures and the conductive structures.

10. The method according to claim 9, wherein the dielectric layer is deposited using spin coating or spray coating.

11. The method according to claim 9, wherein the dielectric layer is deposited using dry film lamination.

12. The method according to claim 9, wherein the dielectric layer comprises an organic polymer.

13. The method according to claim 9, wherein the metal layer is deposited using sputtering.

14. The method according to claim 9, further comprising electrodeposition of metal to form the top metal layer.

15. The method according to claim 9, wherein the openings in the dielectric layer are formed using photolithography or direct laser structuring.