MEMS DEVICES EXHIBITING LINEAR CHARACTERISTICS

• US 20120204643A1
• Filed: 02/10/2012
• Published: 08/16/2012
• Est. Priority Date: 02/11/2011
• Status: Active Grant

• Current Assignee: Indiana University, Purdue Research Foundation (The Trustees of Purdue University (d/b/a Purdue University))
• Original Assignee: Purdue Research Foundation (The Trustees of Purdue University (d/b/a Purdue University))
• Inventors: CLARK, JASON VAUGHN
• Granted Patent: US 8,966,990 B2
• Time in Patent Office: Days
• US Class Current: 73/514.32
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: H01G 5/16 using variation of distance between electrodes

Abstract

A micro electro mechanical system device has a first subassembly having sensor element including a coupler, and a second subassembly including a comb drive. The comb drive having stator plates and rotor plates and the coupler configured to displace the rotor plates relative to the stator plates providing a variable capacitance dependent on the displacement of the rotor plate.

Claims

1. A microfabricated variable capacitor, comprising:

a stator including a plurality of electrically conductive plates each spaced apart from one another, each said pair of adjacent plates forming a channel therebetween, each of said plates being in a first common electrical communication;

a rotor including central hub and first and second arms extending in cantilever manner from opposite sides of said hub, a first plurality of electrically conductive blades being coupled to said first arm and a second plurality of electrically conductive blades being coupled to said second arm, each of said first plurality and said second plurality of blades being in a second common electrical communication; and

wherein said hub is suspended from said stator by first and second springs, such that each of said blades is received within a corresponding one of said channels and a portion of each said blade coacts with an adjacent said plate to store electrical charge, and the capacitance between the first electrical communication and the second electrical communication varies as said first and second springs bias the rotor to different positions relative to said stator.

2. The capacitor of claim 1 which further comprises means for varying the position of said rotor relative to said stator.

3. The capacitor of claim 2 wherein said means includes coupling said capacitor to a moving object, and the relative motion is related to the inertia of said rotor.

4. The capacitor of claim 3 wherein said capacitor is part of an accelerometer.

5. The capacitor of claim 1 wherein said means includes a flexible object, said stator is coupled to one portion of the object, said rotor is coupled to another portion of the object, and the one portion moves relative to the other portion.

15. The capacitor of claim 1 wherein each said first and second spring have a first spring constant corresponding to movement of said blades parallel to said plates, and a second spring constant corresponding to movement of said blades toward said plates, and the second spring constant is greater than the first spring constant.

6. A microfabricated variable capacitor, comprising:

a stator having a width and including a plurality of electrically conductive plates each spaced apart from one another, each said plate having a top, a bottom, and a midsection therebetween, each said pair of adjacent plates forming a channel between opposing midsections, each of said plates being in a first common electrical communication;

a rotor having a length and including a plurality of electrically conductive blades, each said blade having a top, a bottom, and a midsection therebetween, said rotor being suspended relative to said stator such that each of said blades is received within a corresponding one of said channels and the midsection of each said blade includes an area that overlaps with an area of an adjacent said plate, each of said blades being in a second common electrical communication; and

a suspension system for flexibly coupling said rotor relative to said stator, said system flexibly coupling to said stator at a location about midway across the width, said system flexibly coupling to said rotor at a location about midway along the length;

wherein the capacitance between the first electrical communication and the second electrical communication varies in correspondence to different overlapping areas.

7. The capacitor of claim 6 wherein said suspension system includes a first cantilever support extending from one end of said stator to said rotor and a second cantilever support extending from the opposite end of said stator to said rotor.

8. The capacitor of claim 6 wherein said first cantilever extends from the one end with approximately clamped boundary conditions and said second cantilever extends from the other end with approximately clamped boundary conditions.

9. The capacitor of claim 6 wherein said suspension system couples to said rotor such that such said rotor is mass balanced in two dimensions relative to said stator.

10. The capacitor of claim 6 wherein said rotor includes a centrally located hub, and said blades are cantileveredly supported from said hub.

11. The capacitor of claim 10 which further comprises a cantilever arm supporting said blades, one end of said arm being coupled to said hub, each said blade extending from said arm in a direction that is generally transverse to the direction from the hub to the free end of said arm.

12. The capacitor of claim 6 wherein said plates are planar and said blades are planar.

13. The capacitor of claim 6 wherein said plates are circular about an axis and said blades are circular about the same axis.

14. The method of claim 23 which further comprises microfabricating the rotor, the stator, and the diaphragm.

16. A micro electro mechanical system sensor, comprising:

a comb drive having a stator portion with a plurality of stator plates each spaced apart from one another and a rotor portion including a plurality of rotor plates spaced apart from one another, the rotor portion being elastically suspended from said stator portion, the plurality of stator plates and the plurality of rotor plates forming a capacitor having a capacitance that varies with the position of the rotor portion relative to the stator portion;

a membrane suspended proximate the comb drive, the membrane having a stub in physical contact with the rotor portion of the comb drive, the stub biasing the rotor portion to a first position having a first comb drive capacitance; and

wherein a movement of the membrane causes the stub to bias the rotor portion to a second position having a second comb capacitance.

17. The micro electro mechanical system sensor of claim 16 wherein the stator plates and the rotor plates are parallel.

18. The micro electro mechanical system sensor of claim 16 further comprising a packaging defining a pressure port and an otherwise fluid impervious environment.

19. The micro electro mechanical system sensor of claim 16 wherein the stator plates and the rotor plates are arcuate elements positioned at spaced distances from a common center.

20. The micro electro mechanical system sensor of claim 19 wherein the stub contacts the common center.