Enhanced fingerprint detection

• US 20010025532A1
• Filed: 12/29/2000
• Published: 10/04/2001
• Est. Priority Date: 12/30/1999
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: STMicroelectronics Incorporated (STMicroelectronics NV)
• Inventors: Kramer, Alan
• Granted Patent: US 6,512,381 B2
• Time in Patent Office: Days
• US Class Current: 73/862.68
• CPC Class Codes: A61B 5/1172 using fingerprinting
• CPC Class Codes: G01B 7/287 using a plurality of fixed, simultaneously operating transducers G01B7/293 takes precedence
• CPC Class Codes: G06V 40/1306 non-optical, e.g. ultrasonic or capacitive sensing

Abstract

An enhanced fingerprint sensing circuit in which a voltage change is applied to the body during sensing. When the person'"'"'s fingerprint is being sensed, the person'"'"'s body is in contact with an electrical terminal. When the sensing occurs, the voltage on the electrical terminal changes, which changes the voltage on the person'"'"'s body. The pattern of the fingerprint performs two functions in the sensing circuit. In addition to being a plate of a capacitor whose distance is being sensed, it is now a source of input charge as well. The electrical effect on the cell of a voltage change on a person'"'"'s finger is different at a ridge than at a valley in the fingerprint sensing circuit. Thus, the input capacitance to the sensing circuit is variable, depending upon whether a ridge or a valley is present. The sensing circuit also detects a change in its own capacitance based on the presence of a ridge or a valley. In summary, the person'"'"'s body acts as the input capacitor to provide a variable charge transfer for the input capacitance and at the same time performs the function of being a variable sensing capacitor value for the capacitive sensor. The fingerprint sensor is thus very sensitive and can detect a person'"'"'s fingerprint even if a protective layer, such as plastic, wax paper or the like is over the sensor. In addition, if the person is wearing a thin glove, such as a latex glove, the fingerprint patterns can still be sensed.

Claims

1. A fingerprint detection apparatus comprising:

a capacitive sensor cell for sensing a fingerprint pattern;

a voltage output terminal adapted to be coupled to the body of a person whose fingerprint pattern in being detected;

a switch for selectively providing a first voltage potential and a second voltage potential to the voltage output terminal sequentially while the fingerprint pattern is being detected.

2. The fingerprint detection apparatus according to

claim 1

wherein the voltage output terminal is a conductive metal strip positioned adjacent the capacitive sensor cell.

3. The fingerprint detection apparatus according to

claim 1

further including:

a substrate composed of silicon;

an integrated circuit formed in said substrate; and

a dielectric layer as a top layer of the integrated circuit, the top surface of the dielectric layer being exposed for receiving a fingerprint pattern, the capacitive sensor cell being formed as part of the integrated circuit.

4. The fingerprint detection apparatus according to

claim 3

wherein the voltage output terminal includes a first set of a metal strips located in a top surface of the dielectric layer.

5. The fingerprint detection apparatus according to

claim 3

further including:

first set of metal strips located at the top surface of the dielectric layer;

a second set of metal strips located at the top surface of the dielectric layer;

a control circuit for selecting either the first set of metal strips to be the voltage output terminal or the second set to be the voltage output terminal and the other set to be coupled to a ground voltage potential.

6. The fingerprint detection apparatus according to

claim 1

further including:

a ground terminal positioned adjacent the capacitive sensor cell for coupling a finger placed thereon to ground during sensing of the fingerprint pattern.

7. The fingerprint detection apparatus according to

claim 1

wherein said capacitive sensor cell includes a single plate of a capacitor and the finger, if present, provides a second plate of a capacitor for the cell.

8. The fingerprint detection apparatus according to

claim 1

wherein said capacitive sensor cell includes a two plates of a capacitor and the finger, if present, provides a third plate of a capacitor for the cell.

9. The fingerprint detection apparatus according to

claim 8

further including an inverting amplifier having an input coupled to one plate of the capacitor and an output coupled to the other plate of the capacitor.

10. The fingerprint detection apparatus according to

claim 9

further including:

an input compensation capacitor having one plate coupled to the input of the inverting amplifier and a second plate coupled to a compensation voltage terminal;

a second switch for selectively providing a third voltage potential and a fourth voltage potential to the compensation voltage output terminal sequentially while the fingerprint pattern is being detected.

11. The fingerprint detection apparatus according to

claim 10

wherein the first switch and the second switch are controlled by the same clock signal such that they switch to the different voltage potentials at the same time.

12. The fingerprint detection apparatus according to

claim 10

wherein the first voltage potential is a low value and the second voltage potential is a high value such that the electrical potential on the body is switched from low to high during sensing.

13. The fingerprint detection apparatus according to

claim 10

wherein the third voltage potential is a high value and the fourth voltage potential is a low value such that the input signal to the inverting amplifier is switched from high to low during sensing.

14. The fingerprint detection apparatus according to

claim 1

wherein the first voltage potential is a low value and the second voltage potential is a high value such that the electrical potential on the body is switched from low to high during sensing.

15. The fingerprint detection apparatus according to

claim 3

further including:

a layer of material over the dielectric layer that is the top layer of the integrated circuit.

16. The fingerprint detection apparatus according to

claim 1

further including:

a finger of a user positioned for having the fingerprint sensed;

a glove on the finger of the user during sensing of the fingerprint.

17. The fingerprint detection apparatus according to

claim 3

further including:

a water tight protective layer enclosing the entire detection apparatus, including the substrate and the dielectric layer.

18. A method of sensing a fingerprint patter comprising:

placing a finger adjacent a fingerprint sensor cell;

coupling the finger to a electrical power supply;

sensing the fingerprint pattern; and

changing the voltage on the finger during sensing of the fingerprint pattern.

19. The method according to

claim 18

further including:

placing a glove on the finger prior to placing the finger adjacent the sensor cell.

20. The method according to

claim 18

further including:

placing a protective layer on the sensor cell prior to placing the finger adjacent the sensor cell.

21. The method according to

claim 20

further including:

periodically removing the protective layer on the sensor cell and placing a different protective layer on the sensor cell to maintain a clean top surface of the sensor cell.

22. The method according to

claim 18

further including:

coupling the fingerprint sensor cell to a variable voltage electrical power supply;

sensing the fingerprint pattern; and

changing the voltage provide by the variable voltage power supply on the sensor cell during sensing of the fingerprint pattern.