MEMS Capacitive Bending and Axial Strain Sensor

• US 20070256502A1
• Filed: 10/25/2006
• Published: 11/08/2007
• Est. Priority Date: 10/26/2005
• Status: Active Grant

• Current Assignee: Globus Medical, Inc.
• Original Assignee: Orthodata, Inc.
• Inventors: Walsh, Kevin, Crain, Mark, Voor, Michael, Aebersold, Julia
• Granted Patent: US 7,509,870 B2
• Time in Patent Office: Days
• US Class Current: 73/794
• CPC Class Codes: G01L 1/148 using semiconductive material, e.g. silicon

Abstract

A three-dimensional micro-electro-mechanical-systems (MEMS) capacitive bending and axial strain sensor capacitor is described. Two independent comb structures, incorporating suspended polysilicon interdigitated fingers, are fabricated simultaneously on a substrate that can displace independently of each other while attached to a substrate undergoing bending or axial deformation. A change in spacing between the interdigitated fingers will output a change in capacitance of the sensor and is the primary mode of operation of the device. On the bottom and to the end of each comb structure, a glass pad is attached to the comb structure to allow for ample surface area for affixing the sensor to a substrate. During fabrication, tethers are used to connect each comb structure to maintain equal spacing between the fingers before attachment to the substrate. After attachment, the tethers are broken to allow independent movement of each comb structure.

Claims

1. A micro electromechanical system (MEMS) capacitive bending and axial strain sensor comprising:

two simultaneously fabricated independent comb structures capable of independent movement with non-conductive glass attached to each comb structure.

2. The MEMS capacitive bending and axial strain sensor as recited in claim 1, wherein the comb structures are interdigitated fingers with a vertical dimension that exceeds the width of the interdigitated fingers.

3. The MEMS capacitive bending and axial strain sensor as recited in claim 1 consists of the following materials:

silicon, silicon-dioxide and glass.

4. The MEMS capacitive bending and axial strain sensor as recited in claim 1 makes an electrical connection at the end of each comb structure using conductive material.

5. The MEMS capacitive bending and axial strain sensor as recited in claim 1 consists of two independent movable comb structures that are elevated above the substrate.

6. The MEMS capacitive bending and axial strain sensor as recited in claim 1 wherein each comb structure is attached to glass, which is affixed to the substrate.

7. The MEMS capacitive bending and axial strain sensor as recited in claim 1 wherein each comb structure is electrically isolated from the co-planar substrate via the glass.

8. The MEMS capacitive bending and axial strain sensor as recited in claim 1 wherein the sidewalls of the interdigitated fingers form the two plates of each capacitor.

9. The MEMS capacitive bending and axial strain sensor as recited in claim 1 wherein a dielectric medium separates each interdigitated finger.

10. The MEMS variable capacitive bending and deformation sensor as recited in claim 1 wherein each comb structure is electrically isolated from each other.

11. The MEMS capacitive bending and axial strain sensor as recited in claim 1 wherein the number of interdigitated fingers for each comb structure can vary in number to achieve a desired capacitance for any particular application.

12. The MEMS capacitive bending and axial strain sensor as recited in claim 1 wherein the length of the interdigitated fingers for each comb structure and the length of the comb structure can be any dimension to achieve a desired capacitance.

13. The MEMS capacitive bending and axial strain sensor as recited in claim 1 wherein the tethers are used to maintain alignment of the interdigitated fingers of the comb structures before the sensor is applied to the substrate.

14. The MEMS capacitive bending and axial strain sensor as recited in claim 1, wherein the tethers incorporated in the sensor design are broken or released after the sensor is applied to the substrate to allow independent movement of each comb structure.

15. The MEMS capacitive bending and axial strain sensor as recited in claim 1, wherein the glass attached to the bottom of each comb structure will increase displacement of the comb structures giving an increase in sensitivity.