Dynamically balanced capacitive pick-off accelerometer

• US 20050268719A1
• Filed: 06/07/2004
• Published: 12/08/2005
• Est. Priority Date: 06/07/2004
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Malametz, David L.
• Granted Patent: US 7,146,856 B2
• Time in Patent Office: Days
• US Class Current: 73/514.320
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: H01G 5/18 due to change in inclination, e.g. by flexing, by spiral wrapping
• CPC Class Codes: H01G 5/40 Structural combinations of variable capacitors with other electric elements not covered by this subclass, the structure mainly consisting of a capacitor, e.g. RC combinations

Abstract

A Micro Electro-Mechanical System (MEMS) acceleration sensing device formed of a silicon substrate having a substantially planar surface; a pendulous sensing element having a substantially planar surface suspended in close proximity to the substrate planar surface; a flexure suspending the sensing element for motion relative to the substrate planar surface, the flexure having a both static geometric centerline and a dynamic centerline that is offset from the static geometric centerline; and a metal electrode positioned on the substrate surface for forming a capacitor with the pendulous sensing element, the metal electrode being positioned as a function of the dynamic centerline of the flexure.

Claims

1. A sensor device, comprising:

a stationary substrate;

a movable acceleration sensing element spaced away from the stationary substrate and substantially parallel with a surface thereof;

a flexure positioned between first and second sensing portions of the movable acceleration sensing element and the suspending sensing element relative to a stationary attachment point, the flexure having a substantially inflexible portion adjacent to the attachment point between the attachment point and the sensing element, and a substantially flexible portion between the inflexible portion and the sensing element;

one or more electrodes positioned on the surface of the substrate on each of opposite first and second sides of a geometric centerline of the flexure, a portion of each electrode opposite from the sensing element being in an asymmetrical relationship with the geometric centerline of the flexure, the asymmetrical relationship being an offset distance of a dynamic centerline of the flexure from the geometric centerline; and

a plurality of capacitors formed by the electrodes on the surface of the substrate and an opposing surface of the sensing element.

2. The sensor device of claim 1 wherein the asymmetrical relationship further comprises:

one or more electrodes on the first side of the geometric centerline of the flexure being offset away from the geometric centerline by the offset distance, and

the one or more electrodes positioned on second side of the geometric centerline of the flexure being offset toward the geometric centerline by the offset distance.

3. The sensor device of claim 1 wherein the offset distance is a distance between a geometric axis of the flexure in an undeflected condition, and a centerline of the flexible portion of the flexure.

4. The sensor device of claim 3 wherein the centerline of the flexible portion of the flexure is determined with the sensing element deflected from a neutral position.

5. The sensor device of claim 3 wherein the sensing element is deflected from a neutral position less than a maximum deflection of the sensing element.

6. The sensor device of claim 3 wherein the sensor device is a capacitive pick-off sensor constructed as an acceleration sensor having the flexure.

7. (canceled)

8. A Micro Electro-Mechanical System (MEMS) sensor device comprising:

a silicon substrate having a substantially planar surface;

a movable sensing element having a substantially planar surface forming first and second sensing portions suspended in close proximity to the substrate surface;

a flexure suspending the sensing element for motion relative to the substrate surface about a stationary attachment point, the flexure having a substantially inflexible portion adjacent to the attachment point between the attachment point and the sensing element, and a substantially flexible portion between the inflexible portion and the first and second sensing portions of the sensing element, wherein

a static geometric centerline is defined by a geometric axis of the flexure in an undeflected state and a dynamic centerline is defined by a centerline of the flexible portion of the flexure that is offset from the static geometric centerline; and

first and second metal electrodes positioned on the substrate surface and a portion of the first and second electrodes forming respective first and second capacitors with the first and second sensing portions of the pendulous sensing element, the portions of the metal electrodes forming the first and second capacitors being symmetrically positioned on opposite first and second sides of the dynamic centerline of the flexure.

9. The sensor device of claim 8 wherein the dynamic centerline of the flexible portion of the flexure is determined with the pendulous sensing element deflected relative to the substrate surface.

11. The sensor device of claim 9 wherein the pendulous sensing element is deflected less than a maximum deflection thereof.

12. The sensor device of claim 9 wherein the flexure suspending the sensing element is positioned intermediate of the first and second sensing portions of the sensing element.

10. (canceled)

13. (canceled)

14. A Micro Electro-Mechanical System (MEMS) capacitive pick-off acceleration sensor device comprising:

a silicon substrate having a substantially planar surface;

a pair of spaced apart attachment points spaced in close proximity above the substrate surface;

a movable sensing element of substantially constant cross-section and having a substantially planar surface suspended adjacent to the attachment points in close proximity to the substrate surface;

a pair of flexures integral with the sensing element between first and second sensing portions thereof and suspending the sensing element from the attachment points for motion relative to the substrate surface, each of the flexures further comprising a substantially inflexible portion adjacent to one of the attachment points and a substantially flexible portion between the inflexible portion and the first and second sensing portions of the sensing element wherein the flexures define a geometric centerline thereof and the flexible portions of the flexures define a dynamic centerline that is spaced away from the geometric centerline; and

first and second metal electrodes formed on the surface of the substrate and having portions thereof symmetrically positioned on each of opposite first and second sides of the flexure dynamic centerline to form respective capacitors with the first and second sensing portions of the pendulous sensing element.

16. The sensor device of claim 14 wherein the flexure dynamic centerline is determined having the sensing element deflected from a neutral position.

17. The sensor device of claim 16 wherein the deflection of the sensing element from a neutral position is less than a maximum deflection.

18. The sensor device of claim 17 wherein the deflection of the sensing element from a neutral position further comprises a maximum deflection of the sensing element relative to the substrate surface.

19. The sensor device of claim 14 wherein the flexures are offset between a longer and a shorter portion of the pendulous sensing element.

15. (canceled)

20. (canceled)