Microthermistor based fingerprint sensor

• US 6,633,656 B1
• Filed: 06/16/2000
• Issued: 10/14/2003
• Est. Priority Date: 12/24/1999
• Status: Active Grant

• Current Assignee: Institut national d'optique
• Original Assignee: Institut national d'optique
• Inventors: Picard, Francis
• Primary Examiner(s): Mehta, Bhavesh M.
• Assistant Examiner(s): Bayat, Ali
• Application Number:
  US09/595,999
• Time in Patent Office: 1,215 Days
• Field of Search: 382/124, 382/125, 382/126, 382/127, 374/163, 374/178, 340/5.53, 250/338.4, 738/620.46, 257/522
• US Class Current: 382/124
• CPC Class Codes: G01K 17/003 for measuring the power of light beams, e.g. laser beams
• CPC Class Codes: G06V 40/1306 non-optical, e.g. ultrasonic or capacitive sensing

Abstract

The present invention concerns a fingerprint sensor which is small; demonstrates high sensitivity, low power consumption, high data acquisition rate and is insensitive to vibration and pressure. The sensor produces a high contrast fingerprint representation and is not subject to repeated deformation which could potentially reduces its lifetime. The fingerprint sensor has a microthermistor array for converting temperature variation into an electrical signal, the array being composed of a plurality of microthermistors, each of the thermistors being adapted to output an electrical signal proportional to a temperature variation; a read-out integrated circuit operatively connected to the microthermistor array for receiving the electrical signal and converting it into an electronic output signal representative of the ridge and valley structure of a finger; and a substrate for supporting the read-out integrated circuit and the microthermistor array. The invention is based on microthermistor array. The ohmic resistance of these sensors varies strongly with temperature. The parameter directly measured in this case is the temperature-induced resistance variation of each individual microthermistor. Signals from each of the microthermistor part of the array represent the fingerprint pattern.

Claims

1. A fingerprint sensor for transforming the ridge and valley pattern of a finger, hereinafter referred to as a fingerprint, into an electronic output signal, comprising:

(a) a microthermistor array for converting temperature variation into an electrical signal, said array being composed of a plurality of microthermistors, each of said thermistors being adapted to output an electrical signal proportional to a temperature variation;

(b) a read-out integrated circuit operatively connected to said microthermistor array for receiving said electrical signal and converting it into an electronic output signal representative of the ridge and valley structure of a finger; and

(c) a substrate for supporting said read-out integrated circuit and said microthermistor array.

2. A fingerprint sensor according to claim 1, wherein each of said thermistors comprises a pair of spaced apart electrodes, said electrodes being separated by a sensitive layer, each of said electrodes being in electrical contact with said read out circuit;

said sensitive layer being placed on a passivation layer which is in direct contact with said read out circuit, said thermistor further comprising a top passivation layer.

3. A fingerprint sensor according to claim 1, wherein each of said thermistors comprises a pair of spaced apart electrodes, said electrodes being separated by a sensitive layer, each of said electrodes being in contact with said read out layer, said sensitive layer being placed on a passivation layer, said passivation layer being placed on a thermal insulation layer which is in direct contact with said read out circuit, said thermistor further comprising a top passivation layer.

4. A fingerprint sensor according to claim 1, wherein each of said thermistors comprises a pair of spaced apart electrodes, said electrodes being separated by a sensitive layer, each of said electrodes being in contact with said read out layer, said sensitive layer being placed on a passivation layer, said passivation layer being placed on a thermal insulation layer which is in direct contact with said read out circuit, said thermistor further comprising a top passivation layer, wherein said thermal insulation layer is etched away in a rectangular pattern within which said thermistor is located.

5. A fingerprint sensor according to claim 1, wherein adjacent thermistors are centre-to-centre separated by a distance of 50 μ

m or less.

6. A fingerprint sensor according to claim 2, wherein adjacent thermistors are centre-to-centre separated by a distance of 50 μ

m or less.

7. A fingerprint sensor according to claim 3, wherein adjacent thermistors are centre-to-centre separated by a distance of 50 μ

m or less.

8. A fingerprint sensor according to claim 4, wherein adjacent thermistors are centre-to-centre separated by a distance of 50 μ

m or less.

9. A fingerprint sensor according to claim 1, wherein said array of thermistors comprises at least 128×

128 thermistors.

10. A fingerprint sensor according to claim 2, wherein said array of thermistors comprises at least 128×

128 thermistors.

11. A fingerprint sensor according to claim 3, wherein said array of thermistors comprises at least 128×

128 thermistors.

12. A fingerprint sensor according to claim 4, wherein said array of thermistors comprises at least 128×

128 thermistors.

13. A fingerprint sensor according to claim 1, wherein said sensor further comprises a metallic topmost layer, said metallic topmost layer being connected to the ground of said read out circuit.

14. A fingerprint sensor according to claim 2, wherein said sensor further comprises a metallic topmost layer, said metallic topmost layer being connected to the ground of said read out circuit.

15. A fingerprint sensor according to claim 3, wherein said sensor further comprises a metallic topmost layer, said metallic topmost layer being connected to the ground of said read out circuit.

16. A fingerprint sensor according to claim 4, wherein said sensor further comprises a metallic topmost layer, said metallic topmost layer being connected to the ground of said read out circuit.

17. A fingerprint sensor according to claim 1, wherein said sensitive layer is made of VO_x.

18. A fingerprint sensor according to claim 2, wherein said sensitive layer is made of VO_x.

19. A fingerprint sensor according to claim 3, wherein said sensitive layer is made of VO_x.

20. A fingerprint sensor according to claim 4, wherein said sensitive layer is made of VO_x.

21. A fingerprint sensor according to claim 1, wherein said sensor is temperature stabilized.