MICROELECTRONIC PRESSURE SENSOR

• US 20090027352A1
• Filed: 07/10/2008
• Published: 01/29/2009
• Est. Priority Date: 07/12/2007
• Status: Active Grant

• Current Assignee: Stmicroelectronics France (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SA (STMicroelectronics NV)
• Inventors: Abele, M. Nicolas
• Granted Patent: US 8,878,790 B2
• Time in Patent Office: Days
• US Class Current: 345/173
• 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: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details

Abstract

A microelectronic pressure sensor comprises a MOSFET transistor adapted with a mobile gate and a cavity between the mobile gate and a substrate. The sensor includes a gate actuator configured to move mobile gate in response to a pressure being exercised. A fingerprint recognition system includes a matrix of such sensors.

Claims

1. A microelectronic pressure sensor, comprising:

a substrate;

a MOSFET transistor having a mobile gate and a cavity between said mobile gate and the substrate; and

a gate actuator structured to move said mobile gate in response to a pressure.

2. A microelectronic pressure sensor according to claim 1 wherein said gate actuator comprises a silicon gel in mechanical contact with said mobile gate and able to convert a pressure applied on an exterior surface of said gel to a mechanical movement of said gate by said mechanical contact.

3. A microelectronic pressure sensor according to claim 2 wherein said gel has a Young Modulus less than 400 MPa, said gel adhering to the mobile gate and laying on the substrate outside of said cavity.

4. A microelectronic pressure sensor according to claim 1 wherein said gate actuator comprises a membrane spaced a variable distance from the mobile gate and structured to be distorted under application of a pressure and generate an electrostatic or electromagnetic force taking effect on said mobile gate, the force varying in accordance with the distance from said membrane to said mobile gate.

5. A microelectronic pressure sensor according to claim 4, further comprising a support having a cavity in which the sensor is located, the support having a top part closed by said membrane, wherein said membrane is elastic, conductive and structured to be biased with respect to said mobile gates.

6. A microelectronic pressure sensor according to claim 1 wherein said MOSFET transistor is a N channel transistor and the substrate is a P type monocrystalline silicon substrate.

7. A microelectronic pressure sensor according to claim 1, further comprising measuring means for measuring the position of said mobile gate using a mathematical model of electrical characteristics of the MOSFET transistor, said model having parameters set in accordance with the position of said mobile gate, said measuring means being structured to capture an electrical working point of said transistor and determine the position of the gate from the model parameters and from the capture of the working point.

8. A microelectronic pressure sensor according to claim 7 wherein the transistor is one of a matrix of MOSFET transistors having mobile gates.

9. A microelectronic pressure sensor according to claim 8, wherein said matrix includes about 200 MOSFET transistors evenly spaced apart from each other.

10. A microelectronic pressure sensor according to claim 8 wherein the matrix is located in a first region of an integrated chip, said chip further comprising a second region including electronic circuits configured to determine a relative position of every mobile gate with respect to the substrate, to process said position and to interface with circuits located outside of said chip.

11. A microelectronic pressure sensor according to claim 10, further comprising a package supporting said chip, the package comprising a cavity opening on said matrix, wherein the gate actuator includes a silicon gel in mechanical contact with said mobile gates and able to convert a pressure applied on an exterior surface of said silicon gel to a mechanical movement of said mobile gates by said mechanical contact.

12. A microelectronic pressure sensor according to claim 10, further comprising a package supporting said chip, the package comprising a cavity opening on said matrix and having a top part, wherein the gate actuator includes a membrane which closes the top part and is substantially parallel to a surface of said chip.

13. A process, comprising:

measuring relief of a surface of a body, the measuring including;

moving mobiles gates of MOSFET transistors in response to pressure which is locally exercised on a surface of a gate actuator by the surface of the body; and

converting the movement of the mobile gates into electrical quantities corresponding to relative distances between the mobile gates and a substrate.

14. A process according to claim 13, wherein said body is a finger and the relief to be measured corresponds to a fingerprint of the finger.

15. A process according to claim 14, wherein the MOSFET transistors are part of an electronic chip that processes the electrical quantities and extracts the fingerprint based on the electrical quantities.

16. A process according to claim 13, wherein said moving includes using a silicon gel to move the mobile gates in response to the pressure exerted by the surface of body.

17. A process according to claim 13 wherein said moving includes using a membrane to move the mobile gates in response to the pressure exerted by the surface of body.

18. A process for manufacturing a microelectronic pressure sensor, comprising:

providing a substrate;

forming a MOSFET transistor having a mobile gate and a cavity between said mobile gate and the substrate; and

forming a gate actuator structured to move said mobile gate in response to a pressure.

19. A process according to claim 18 wherein forming the gate actuator includes:

covering said MOSFET transistor with an elastic membrane, which is substantially tight, parallel to said substrate, electrically conductive, and spaced apart from the mobile gate.

20. A process according to claim 18, further comprising coupling the membrane and mobile gate with a voltage source configured to bias said membrane with respect to said mobile gate.

21. A process according to claim 18 wherein forming the gate actuator includes covering said MOSFET transistor with a gel having a Young modulus less than 400 Mpa.

22. A flat display system, comprising:

a matrix arranged in rows and columns and including pixels at crossings of the rows and columns, respectively; and

an arrangement of microelectronic pressure sensors formed on a substrate, each microelectronic pressure sensor including;

a MOSFET transistor with a mobile gate and a cavity between said mobile gate and the substrate, and

a gate actuator structured to move the mobile gate in response to the application of a pressure.

23. A flat display system according to claim 22 wherein the gate actuator includes a silicon gel in contact with said mobile gate and capable of imparting a movement of said gate from a pressure applied on an exterior surface of said gel by said contact.

24. A flat display system according to claim 22 wherein each pixel is realized by a liquid crystal display cell.

25. A flat display system according to claim 22, wherein each pixel is realized by one or more electroluminescent diodes.