Microelectronic pressure sensor

• US 8,878,790 B2
• Filed: 07/10/2008
• Issued: 11/04/2014
• Est. Priority Date: 07/12/2007
• Status: Active Grant

• Current Assignee: Stmicroelectronics France (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SA (STMicroelectronics NV)
• Inventors: Abele, Nicolas
• Primary Examiner(s): Kumar, Srilakshmi K
• Assistant Examiner(s): Abebe, Sosina
• Application Number:
  US12/170,849
• Publication Number:
  US 20090027352A1
• Time in Patent Office: 2,308 Days
• Field of Search: 345/173, 257/254, 257/E29.324
• 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 including;

source and drain regions in the substrate;

a channel between the source and drain region in the substrate;

a mobile gate formed from a first material over the channel, the mobile gate having an upper surface and sidewalls; and

a first cavity that separates the mobile gate from the channel; and

a gate actuator formed from a second non-conductive material that is different from the first material, the gate actuator being formed above the mobile gate, the gate actuator being in contact with the upper surface and sidewalls of the mobile gate, an upper surface of the gate actuator being configured to receive a pressure from a physical object and to move said mobile gate toward the channel in response to the pressure on the upper surface of the gate actuator, the upper surface of the gate actuator being separated from the cavity by the mobile gate, the gate actuator being an elastic material that has a thickness between the upper surface of the mobile gate and the upper surface of the gate actuator, the thickness of the gate actuator being configured to vertically compress in a plurality of locations in response to the pressure, the plurality of locations corresponding to a plurality of locations on the object.

2. A microelectronic pressure sensor according to claim 1 wherein said gate actuator includes a silicone gel in direct contact with the upper surface and the sidewalls of the mobile gate, the upper surface of the gate actuator being a top surface of the silicone gel that is configured to convert the pressure applied by the object to a mechanical movement of the mobile gate.

3. A microelectronic pressure sensor according to claim 2 wherein the gel is configured to adhere to the upper surface of the mobile gate and to the sidewalls of the mobile gate, the gel is also configured to adhere to the substrate to form the first cavity between the substrate and the mobile gate.

4. A microelectronic pressure sensor according to claim 1 wherein said gate actuator comprises a membrane formed on the gate actuator and spaced from the mobile gate by a variable distance, the membrane being configured to distort under application of the pressure and to generate an electrostatic or electromagnetic force that affects 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 that includes a base and sidewalls extending from the base, the base and sidewalls enclosing a second cavity, the substrate being on the base in second cavity, the second cavity being closed by said membrane, wherein said membrane is in contact with the sidewalls and is elastic, conductive and configured to be biased with respect to said mobile gate.

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 configured to measure a position of said mobile gate with 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 configured 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 second cavity opening on said matrix, wherein the gate actuator includes a silicone gel on top of the mobile gates and in mechanical contact with said mobile gates, the upper surface being a top surface of the silicone gel that is configured to convert the pressure applied by the mechanical contact to a mechanical movement of said mobile gates.

12. A microelectronic pressure sensor according to claim 10, further comprising a package supporting said chip, the package comprising a second cavity opening on said matrix, the gate actuator including a membrane that closes the second cavity and is substantially parallel to a surface of said chip.

13. A microelectronic pressure sensor according to claim 1 wherein the gate actuator has interior walls that define sidewalls of the first cavity, the interior walls configured to compress in response to the pressure on the gate actuator.

14. A process, comprising:

measuring contours of a first surface of a body, the measuring including;

moving mobiles gates of MOSFET transistors towards a channel of each transistor in response to pressure locally exercised on an upper surface of a gate actuator by the first surface of the body, the gate actuator being a first material, the first surface being above the upper surface of the gate actuator, the gate actuator being formed above the mobile gates, the mobile gates being a second non-conductive material that is different from the first material, the mobile gates each having an upper surface and sidewalls, the gate actuator being in contact with the upper surface and sidewalls of the mobile gates, the transistors each including a cavity that separates the mobile gate from the channel of the transistor, the upper surface of the gate actuator being separated from the cavity by the mobile gate, the gate actuator being an elastic material that has a thickness between the upper surface of the mobile gate and the upper surface of the gate actuator, the thickness of the gate actuator being configured to vertically compress in a plurality of locations in response to the pressure, the plurality of locations corresponding to a plurality of locations on the body; and

converting the movement of the mobile gates that correspond to the plurality of locations into electrical quantities that correspond to relative distances between the mobile gates and the channels.

15. A process according to claim 14, wherein said body is a finger and the contours to be measured correspond to a fingerprint of the finger.

16. A process according to claim 15, further comprising:

processing the electrical quantities in an electronic chip that includes the transistors; and

extracting the fingerprint from the electrical quantities.

17. A process according to claim 14, wherein the gate actuator is a silicone gel, the upper surface of the gate actuator being a top surface of the silicone gel, said moving includes using the silicone gel to move the mobile gates in response to the pressure exerted by the first surface of body.

18. A process according to claim 14 wherein said moving includes using a membrane to move the gate actuator to move mobile gates in response to the pressure exerted by the first surface of body.

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

forming a MOSFET transistor, the forming of the transistor including;

forming source and drain regions in the substrate;

forming a channel between the source and drain region in the substrate;

forming a mobile gate over the channel from a first material;

forming the mobile gate to have an upper surface and sidewalls; and

forming a cavity that separates the mobile gate from the channel; and

forming a gate actuator from a second non-conductive material that is different from the first material, the gate actuator being above the mobile gate, the gate actuator being in contact with the upper surface and sidewalls of the mobile gate, an upper surface of the gate actuator configured to receive a pressure from an object and to move said mobile gate towards the channel in response to a pressure on the upper surface of the gate actuator, the upper surface of the gate actuator being separated from the cavity by the mobile gate, the gate actuator being an elastic material that has a thickness between the upper surface of the mobile gate and the upper surface of the gate actuator, the thickness of the gate actuator being configured to vertically compress in a plurality of locations in response to the pressure, the plurality of locations corresponding to a plurality of locations on the object.

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

covering said MOSFET transistor and the gate actuator with an elastic membrane, the membrane being substantially tight, positioned parallel to said substrate, and being electrically conductive.

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

22. A process according to claim 19 wherein forming the gate actuator includes covering said MOSFET transistor with a gel having a Young modulus less than 400 Mpa.

23. 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, the pressure sensors positioned between the matrix and the substrate, each microelectronic pressure sensor including;

a MOSFET transistor including;

source and drain regions in the substrate;

a channel between the source and drain region in the substrate;

a mobile gate of a first material formed over the channel, the mobile gate having an upper surface and sidewalls; and

a cavity that separates the mobile gate from the channel; and

a gate actuator formed of a second non-conductive material that is different from the first material, the gate actuator being formed above the mobile gate, the gate actuator being in contact with the upper surface and sidewalls of the mobile gate, an upper surface configured to receive a pressure from an object, the gate actuator configured to move the mobile gate towards the channel in response to the pressure on the upper surface, the upper surface of the gate actuator being separated from the cavity by the mobile gate, the gate actuator being an elastic material that has a thickness between the upper surface of the mobile gate and the upper surface of the gate actuator, the thickness of the gate actuator being configured to vertically compress in a plurality of locations in response to the pressure, the plurality of locations corresponding to a plurality of locations on the object.

24. A flat display system according to claim 23 wherein the gate actuator includes a silicone gel in direct contact with the upper surface and the sidewalls of said mobile gate, the upper surface of the gate actuator being a top surface of the silicone gel, the silicone gel being configured to impart a movement of said gate from the pressure applied on the upper surface of the gate actuator.

25. A flat display system according to claim 23 wherein each pixel is realized by a liquid crystal display cell.

26. A flat display system according to claim 23, wherein each pixel is realized by one or more electroluminescent diodes.