Scanning capacitive semiconductor fingerprint detector

• US 6,317,508 B1
• Filed: 01/13/1998
• Issued: 11/13/2001
• Est. Priority Date: 01/13/1998
• Status: Expired due to Term

• Current Assignee: Apple Inc.
• Original Assignee: STMicroelectronics Incorporated (STMicroelectronics NV)
• Inventors: Kramer, Alan, Brady, James
• Primary Examiner(s): Bella, Matthew C.
• Assistant Examiner(s): CHAWAN, SHEELA C
• Application Number:
  US09/006,670
• Time in Patent Office: 1,400 Days
• Field of Search: 382/124, 382/126, 382/312, 235/439, 235/445, 235/446, 235/447, 235/451
• US Class Current: 382/124
• CPC Class Codes: G06V 40/1306 non-optical, e.g. ultrasonic or capacitive sensing

Abstract

A scanning fingerprint detection system that includes an array of capacitive sensing elements. The array has a first dimension greater than the width of a fingerprint and a second dimension less than the length of a fingerprint. Each of the capacitive sensing elements has a size less than the width of a fingerprint ridge. Circuitry is provided for scanning the array to capture an image of a portion of fingerprint and for assembling the captured images into a fingerprint image as a fingerprint is moved over the array.

Claims

1. A scanning fingerprint detection system, which comprises:

a sensing array having a first dimension and a second dimension;

said first dimension extending at least the width of a fingerprint;

said second dimension extending less than the length of a fingerprint;

said sensing array formed of a plurality of elements;

wherein each of said elements is a capacitive sensing cell and having a size less than the width of a ridge of a fingerprint;

means for scanning said sensing array to capture successive images of successive portions of the fingerprint formed as the fingerprint is moved across the sensing array in a direction parallel to the second dimension; and

means for assembling the captured successive images into a complete fingerprint image.

2. The scanning fingerprint detection system as claimed in claim 1, wherein a capacitive sensing cell comprises:

a first conductor positioned on a substrate and defining a first plate of said capacitive sensing cell;

a second conductor positioned on said substrate and defining a second plate of said capacitive sensing cell, said first and second conductors being spaced apart from each other;

a reference voltage source providing an input voltage; and

,

an amplifier having an input and output, said input being coupled to said reference voltage and said first conductor, and said output being coupled to said second conductor.

3. The scanning fingerprint detection system as claimed in claim 2, wherein said amplifier includes an inverting amplifier.

4. The scanning fingerprint detection system as claimed in claim 2, including a protective coating deposited over said first and second conductor.

5. The scanning fingerprint detection system as claimed in claim 2, including an input capacitor coupled between said reference voltage source and said input of said amplifier.

6. The scanning fingerprint detection system as claimed in claim 2, including a switch connected between said input and said output of said amplifier.

7. The scanning fingerprint detection system as claimed in claim 1, wherein a capacitive sensing cell comprises:

a first conductor supported by a semiconductor substrate and defining a first plate of said capacitive sensing cell;

a second conductor supported by said semiconductor substrate and defining a second plate of said capacitive sensing cell, said first and second conductors being spaced apart from each other;

a reference voltage source providing an input voltage;

an inverting amplifier having an input and output, said input being coupled to said reference voltage and said first conductor plate, and said output being coupled to said second conductor plate;

an input capacitor connected between said reference voltage source and said input of said inverting amplifier; and

a switch connected between said input and said output of said inverting amplifier.

8. The scanning fingerprint detection system as claimed in claim 7, wherein said first dimension is about one-half inch and said second dimension is about one-tenth inch.

9. A scanning fingerprint detection system, which comprises:

a sensing array having a first dimension and a second dimension;

said first dimension extending at least the width of a fingerprint, wherein said first dimension is about one-half inch;

said second dimension extending less than the length of a fingerprint, wherein said second dimension is about one-tenth inch;

said sensing array formed of a plurality of elements;

wherein each of said elements is a capacitive sensing cell and having a size less than the width of a ridge of a fingerprint, wherein each capacitive sensing cell comprises;

a first conductor positioned on a substrate and defining a first plate of said capacitive sensing element;

a second conductor positioned on said substrate and defining a second plate of said capacitive sensing element, said first and second conductors being spaced apart from each other;

a reference voltage source providing an input voltage; and

,

an amplifier having an input and output, said input being coupled to said reference voltage and said first conductor, and said output being coupled to said second conductor.

10. A fingerprint detection system comprising:

an insulating layer supported by a semiconductor substrate, said insulating layer having an upper surface;

a capacitive sensor disposed on said upper surface, said sensor extending in a plane parallel to and above said upper surface of said insulating layer, said sensor generating electrical signals based on a fingerprint sensed as the fingerprint is moved along and parallel to said plane;

image generating circuitry electrically connected to said capacitive sensor for receiving the electrical signals and assembling an image corresponding to a complete fingerprint that is successively sensed by said capacitive sensor during movement of the fingerprint thereover; and

wherein said sensor has a first dimension parallel to said plane and a second dimension parallel to said plane, said first dimension being substantially longer than said second dimension, and wherein the fingerprint is moved in a direction generally parallel to said second dimension.

11. The fingerprint detection system as claimed in claim 10, wherein said first dimension is about ½

inch and said second dimension is about {fraction (1/10)} inch.

12. The fingerprint detection system as claimed in claim 10, wherein said capacitive sensor comprises an array of sensing elements.