Fingerprint sensor having enhanced ESD protection and associated methods

• US 20030215116A1
• Filed: 05/17/2002
• Published: 11/20/2003
• Est. Priority Date: 05/17/2002
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: AuthenTec Incorporated (Apple Inc.)
• Inventors: Salatino, Matthew M., Brandt, Robert Scott, Setlak, Dale Raymond, Sherlock, Peter Eric, Gebauer, David Carl
• Granted Patent: US 7,076,089 B2
• Time in Patent Office: Days
• US Class Current: 382/124
• CPC Class Codes: G06V 40/1329 Protecting the fingerprint sensor against damage caused by the finger
• CPC Class Codes: H01L 23/60 Protection against electrostatic charges or discharges, e.g. Faraday shields
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00

Abstract

A fingerprint sensor may include a plurality of electrostatic discharge (ESD) electrodes carried by a dielectric layer of a fingerprint sensing portion. The fingerprint sensing portion is for sensing a fingerprint of a user. The fingerprint sensing portion may include the dielectric layer, and, in some embodiments, may also include an array of sensing electrodes also carried by the dielectric layer. Accordingly, each ESD electrode may be interposed between adjacent sensing electrodes. The ESD electrodes attract ESD events and dissipate the energy therein to avoid damaging adjacent sensing electrodes and/or portions of the dielectric layer. The fingerprint sensor may also include an electrically conductive layer connected to the ESD electrodes, which may provide a convenient ground plane, for example, for removing ESD energy from the fingerprint sensor. The electrically conductive layer may extend beneath the sensing electrodes.

Claims

1. A fingerprint sensor comprising:

a fingerprint sensing portion for sensing a fingerprint of a user positioned adjacent thereto, said fingerprint sensing portion comprising a dielectric layer and an array of sensing electrodes carried thereby;

a plurality of electrostatic discharge (ESD) electrodes also carried by said dielectric layer for ESD protection of said fingerprint sensing portion, each ESD electrode interposed between adjacent sensing electrodes; and

an electrically conductive layer adjacent said dielectric layer and connected to said plurality of ESD electrodes, said electrically conductive layer extending beneath said sensing electrodes.

2. A fingerprint sensor according to claim 1 wherein said plurality of ESD electrodes are arranged in spaced apart relation in a regular pattern across said fingerprint sensing portion.

3. A fingerprint sensor according to claim 1 wherein said ESD electrodes are exposed at an upper surface of said dielectric layer.

4. A fingerprint sensor according to claim 1 wherein said sensing electrodes are embedded in said dielectric layer.

5. A fingerprint sensor according to claim 1 wherein outermost ones of said sensing electrodes define an available sensing area;

and wherein said ESD electrodes occupy less than about ten percent of the available sensing area.

6. A fingerprint sensor according to claim 1 wherein each of said array of sensing electrodes is of a same size;

and wherein said array of sensing electrodes are arranged in a regular grid pattern with predetermined locations within the grid pattern being unoccupied by sensing electrodes and instead occupied by respective ESD electrodes.

7. A fingerprint sensor according to claim 6 wherein each of said ESD electrodes has a smaller size than the size of said sensing electrodes so as to define an enlarged spacing between each ESD electrode and adjacent sensing electrodes.

8. A fingerprint sensor according to claim 1 wherein each sensing electrode has a generally rectangular shape;

and wherein sensing electrodes adjacent each ESD electrode have cut-off corner portions to provide spacing for each ESD electrode.

9. A fingerprint sensor according to claim 1 wherein said dielectric layer comprises a first dielectric layer, and further comprising:

a second dielectric layer adjacent said electrically conductive layer and opposite said first dielectric layer; and

a semiconductor substrate adjacent said second dielectric layer and having active semiconductor devices formed therein.

10. A fingerprint sensor according to claim 1 wherein each ESD electrode comprises a vertically conducting portion extending through said dielectric layer, and an enlarged top portion connected thereto.

11. A fingerprint sensor according to claim 10 wherein said enlarged top portion comprises gold.

12. A fingerprint sensor according to claim 1 wherein said fingerprint sensing portion further comprises an electrically conductive guard ring surrounding each sensing electrode.

13. A fingerprint sensor according to claim 1 further comprising a package surrounding said fingerprint sensing portion and having an opening therein to expose an upper surface of said fingerprint sensing portion.

14. A fingerprint sensor according to claim 1 further comprising at least one respective isolation element connecting each of said ESD electrodes to said electrically conductive layer.

15. A fingerprint sensor according to claim 14 wherein said isolation elements comprise at least one of a diode, a Zener diode, a resistor, and a transistor.

16. A fingerprint sensor comprising:

a fingerprint sensing portion for sensing a fingerprint of a user positioned adjacent thereto, said fingerprint sensing portion comprising a dielectric layer and an array of sensing electrodes carried thereby, said array of sensing electrodes being of a same size and shape; and

a plurality of electrostatic discharge (ESD) electrodes also carried by said dielectric layer for ESD protection of said fingerprint sensing portion, each ESD electrode interposed between adjacent sensing electrodes;

said array of sensing electrodes being arranged in a regular grid pattern with predetermined locations within the grid pattern being unoccupied by sensing electrodes and instead occupied by respective ESD electrodes.

17. A fingerprint sensor according to claim 16 wherein said ESD electrodes are exposed at an upper surface of said dielectric layer.

18. A fingerprint sensor according to claim 16 wherein said sensing electrodes are embedded in said dielectric layer.

19. A fingerprint sensor according to claim 16 wherein outermost ones of said sensing electrodes define an available sensing area;

and wherein said ESD electrodes occupy less than about ten percent of the available sensing area.

20. A fingerprint sensor according to claim 16 wherein each of said ESD electrodes has a smaller size than the size of said sensing electrodes so as to define an enlarged spacing between each ESD electrode and adjacent sensing electrodes.

21. A fingerprint sensor according to claim 16 wherein said fingerprint sensing portion further comprises a semiconductor substrate adjacent said dielectric layer and having active semiconductor devices formed therein.

22. A fingerprint sensor according to claim 16 wherein each ESD electrode comprises a vertically conducting portion extending through said dielectric layer, and an enlarged top portion connected thereto.

23. A fingerprint sensor according to claim 16 further comprising an electrically conductive layer adjacent said dielectric layer and connected to said plurality of ESD electrodes, said electrically conductive layer extending beneath said sensing electrodes.

24. A fingerprint sensor according to claim 23 further comprising at least one respective isolation element connecting each of said ESD electrodes to said electrically conductive layer.

25. A fingerprint sensor according to claim 24 wherein said isolation elements comprise at least one of a diode, a Zener diode, a resistor, and a transistor.

26. A fingerprint sensor according to claim 16 wherein said ESD electrodes have a substantially similar shape as said sensing electrodes.

27. A fingerprint sensor comprising:

a fingerprint sensing portion for sensing a fingerprint of a user positioned adjacent thereto, said fingerprint sensing portion comprising a dielectric layer and an array of sensing electrodes carried thereby;

a plurality of electrostatic discharge (ESD) electrodes also carried by said dielectric layer for ESD protection of said fingerprint sensing portion, each ESD electrode interposed between adjacent sensing electrodes, and said plurality of ESD electrodes being arranged in spaced apart relation in a regular pattern across said fingerprint sensing portion; and

at least one respective isolation device connecting each of said ESD electrodes to a voltage reference.

28. A fingerprint sensor according to claim 27 wherein said ESD electrodes are exposed at an upper surface of said dielectric layer.

29. A fingerprint sensor according to claim 27 wherein said sensing electrodes are embedded in said dielectric layer.

30. A fingerprint sensor according to claim 27 wherein outermost ones of said sensing electrodes define an available sensing area;

and wherein said ESD electrodes occupy less than about ten percent of the available sensing area.

31. A fingerprint sensor according to claim 27 wherein each of said array of sensing electrodes is of a same size;

and wherein said array of sensing electrodes are arranged in a regular grid pattern with predetermined locations within the grid pattern being unoccupied by sensing electrodes and instead occupied by respective ESD electrodes.

32. A fingerprint sensor according to claim 31 wherein each of said ESD electrodes has a smaller size than the size of said sensing electrodes so as to define an enlarged spacing between each ESD electrode and adjacent sensing electrodes.

33. A fingerprint sensor according to claim 27 wherein each sensing electrode has a generally rectangular shape;

and wherein sensing electrodes adjacent each ESD electrode have cut-off corner portions to provide spacing for each ESD electrode.

34. A fingerprint sensor according to claim 27 wherein said fingerprint sensing portion further comprises a semiconductor substrate adjacent said dielectric layer and having active semiconductor devices formed therein.

35. A fingerprint sensor according to claim 27 wherein each ESD electrode comprises a vertically conducting portion extending through said dielectric layer, and an enlarged top portion connected thereto.

36. A fingerprint sensor according to claim 27 further comprising an electrically conductive layer adjacent said dielectric layer and connecting each of said isolation elements to the voltage reference, said electrically conductive layer extending beneath said sensing electrodes.

37. A fingerprint sensor according to claim 27 wherein said isolation elements comprise at least one of a diode, a Zener diode, a resistor, and a transistor.

38. A fingerprint sensor according to claim 27 wherein the voltage reference comprises ground.

39. A method for making a fingerprint sensor comprising:

forming an electrically conductive layer;

forming a fingerprint sensing portion adjacent the electrically conductive layer for sensing a fingerprint of a user positioned adjacent thereto, the fingerprint sensing portion comprising a dielectric layer and an array of sensing electrodes carried thereby, the electrically conductive layer extending beneath the field sensing electrodes; and

forming a plurality of electrostatic discharge (ESD) electrodes interposed between adjacent sensing electrodes and carried by the dielectric layer for ESD protection of the fingerprint sensing portion, each ESD electrode being connected to the electrically conductive layer.

40. A method according to claim 39 wherein forming the plurality of ESD electrodes comprises arranging the plurality of ESD electrodes in spaced apart relation in a regular pattern across the fingerprint sensing portion.

41. A method according to claim 39 wherein forming the plurality of ESD electrodes comprises exposing the ESD electrodes at an upper surface of the dielectric layer.

42. A method according to claim 39 wherein forming the fingerprint sensing portion comprises embedding the sensing electrodes in the dielectric layer.

43. A method according to claim 39 wherein outermost ones of the sensing electrodes define an available sensing area;

and wherein the ESD electrodes occupy less than about ten percent of an available sensing area of the array of the sensing electrodes.

44. A method according to claim 39 wherein each of the array of sensing electrodes is of a same size;

wherein forming the fingerprint sensing portion comprises arranging the array of sensing electrodes in a regular grid pattern with predetermined locations within the grid pattern being unoccupied by sensing electrodes; and

wherein forming the ESD electrodes comprises positioning the ESD electrodes in the predetermined locations.

45. A method according to claim 39 wherein each sensing electrode has a generally rectangular shape;

and wherein sensing electrodes adjacent each ESD electrode have cut-off corner portions to provide spacing for each ESD electrode.

46. A method according to claim 39 wherein each ESD electrode comprises a vertically conducting portion extending through the dielectric layer, and an enlarged top portion connected thereto.

47. A method according to claim 39 further comprising forming at least one respective isolation element connecting each of the ESD electrodes to the electrically conductive layer.

48. A method according to claim 47 wherein the isolation elements comprise at least one of a diode, a Zener diode, a resistor, and a transistor.