MICRO-ELECTRO-MECHANICAL-SYSTEM TEMPERATURE SENSOR

• US 20120076172A1
• Filed: 09/28/2010
• Published: 03/29/2012
• Est. Priority Date: 09/28/2010
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Gill, Jason P., Harmon, David L., Sullivan, Timothy D.
• Granted Patent: US 8,480,302 B2
• Time in Patent Office: Days
• US Class Current: 374/188
• CPC Class Codes: G01K 5/52 with electrical conversion means for final indication

Abstract

The present invention provides a micro-electro-mechanical-system (MEMS) temperature sensor that employs a suspended spiral comprising a material with a positive coefficient of thermal expansion. The thermal expansion of the suspended spiral is guided to by a set of guideposts to provide a linear movement of the free end of the suspended spiral, which is converted to an electrical signal by a set of conductive rotor azimuthal fins that are interdigitated with a set of conductive stator azimuthal fins by measuring the amount of capacitive coupling therebetween. Real time temperature may thus be measured through the in-situ measurement of the capacitive coupling. Optionally, the MEMS temperature sensor may have a ratchet and a pawl to enable ex-situ measurement.

Claims

1. A micro-electro-mechanical-structure (MEMS) temperature sensor comprising:

a suspended spiral comprising a material having a positive thermal expansion coefficient, wherein a central end of said suspended spiral is fixed to a substrate and a peripheral end of said suspended spiral moves upon thermal expansion;

an actuator configured to be azimuthally rotated about a pivot point by said peripheral end of said suspended spiral and including a set of at least one conductive rotor azimuthal fin; and

a set of at least one conductive stator azimuthal fin that is fixed to said substrate, wherein capacitance between said set of at least one conductive rotor azimuthal fin and said set of at least one conductive stator azimuthal fin varies with an azimuthal rotation of said actuator.

2. The MEMS temperature sensor of claim 1, further comprising at least one guide post that guides said peripheral end of said suspended spiral to provide a linear movement of said peripheral end.

3. The MEMS temperature sensor of claim 1, further comprising:

a first conductive pad electrically connected to said at least one conductive rotor azimuthal fin; and

a second conductive pad electrically connected to said at least one conductive stator azimuthal fin.

4. The MEMS temperature sensor of claim 3, wherein a radial arm of said actuator and said set of at least one conductive rotor azimuthal fin are of integral and unitary construction, and wherein said pivot point is located in a pivot structure that is fixed to said substrate.

5. The MEMS temperature sensor of claim 1, wherein said set of at least one conductive rotor azimuthal fin and said set of at least one conductive stator azimuthal fin are interdigitated, and wherein all of said at least one conductive rotor azimuthal fin and said at least one conductive stator azimuthal fin have a same center of curvature.

6. The MEMS temperature sensor of claim 1, wherein said capacitance between said set of at least one conductive rotor azimuthal fin and said set of at least one conductive stator azimuthal fin increases with an increase in a rotational angle of said actuator.

7. The MEMS temperature sensor of claim 1, wherein said capacitance between said set of at least one conductive rotor azimuthal fin and said set of at least one conductive stator azimuthal fin decreases with an increase in a rotational angle of said actuator.

8. The MEMS temperature sensor of claim 1, further comprising:

a ratchet located on an azimuthal fin attached to a radial arm of said actuator and comprising a set of asymmetrical teeth; and

a pawl configured to allow a unidirectional motion of said ratchet and to stop said ratchet from moving in an opposite direction.

9. The MEMS temperature sensor of claim 7, further comprising:

a pawl post attached to an end of said pawl and fixed to said substrate;

a ratchet reset electrode located in proximity to said pawl; and

another conductive pad resistively connected to said ratchet reset electrode.

10. The MEMS temperature sensor of claim 1, further comprising at least one suspension support spring attached to said actuator to reduce sagging of said actuator.

11. The MEMS temperature sensor of claim 1, further comprising an enclosure including a set of enclosure sidewalls, said substrate, and a top cover overlying said suspended spiral, said actuator, and said set of at least one conductive stator azimuthal fin.

12. The MEMS temperature sensor of claim 1, further comprising a capture cup located at an end portion of an azimuthal fin which is attached to a radial arm of said actuator, wherein a concave surface of said capture cup confines a lateral movement of said peripheral end of said suspended spiral.

13. The MEMS temperature sensor of claim 1, wherein said pivot point is located in a pivot structure including a vertical stack of a lower pivot structure comprising a first conductive material and an upper pivot structure comprising a second conductive material, wherein said pivot structure is fixed to said substrate, and wherein said suspended spiral, said set of at least one conductive rotor azimuthal fin, and said set of at least one conductive stator azimuthal fin comprise said second conductive material.

14. The MEMS temperature sensor of claim 13, wherein said second conductive material comprises a doped polysilicon, a doped silicon-containing semiconductor alloy, or a metallic material.

15. The MEMS temperature sensor of claim 14, further comprising a silicon nitride layer underlying said suspended spiral and vertically separated from said spiral.

16. A method of forming a micro-electro-mechanical-structure (MEMS) temperature sensor comprising:

forming a first dielectric material layer on a substrate;

depositing and patterning a first conductive material layer to form first conductive material portions;

depositing a second dielectric material layer over said first conductive material portions;

depositing and patterning a second conductive material layer to form second conductive material portions, wherein a first subset of said second conductive material portions vertically abut one of said first conductive material portions, and wherein a second subset of said second conductive material portions does not overlie said first conductive material portions; and

etching said second dielectric material layer selective to said first and second conductive material portions, wherein said second subset of said second conductive material portions include a suspended spiral, an actuator configured to be azimuthally rotated about a pivot point by a peripheral end of said suspended spiral, and a variable capacitor of which the capacitance varies with a movement of said actuator.

17. The method of claim 16, wherein said suspended spiral comprises a material having a positive thermal expansion coefficient, wherein a central end of said suspended spiral is fixed to said substrate and said peripheral end of said suspended spiral moves upon thermal expansion.

18. The method of claim 17, wherein said variable capacitor includes:

a set of at least one conductive rotor azimuthal fin attached to a radial arm of said actuator; and

a set of at least one conductive stator azimuthal fin that is fixed to said substrate, wherein capacitance between said set of at least one conductive rotor azimuthal fin and said set of at least one conductive stator azimuthal fin varies with an azimuthal rotation of said actuator.

19. The method of claim 16, further comprising:

depositing a third dielectric material layer on said second conductive material portions;

depositing an encapsulating material layer on said third dielectric material layer; and

etching said third dielectric material layer selective to said first and second conductive material portions.

20. The method of claim 19, wherein said second and third dielectric material layer comprises silicon oxide, and wherein said second conductive material layer comprises a doped polysilicon, a doped silicon-containing semiconductor alloy, or a metallic material.