Dynamically balanced capacitive pick-off accelerometer

• US 7,146,856 B2
• Filed: 06/07/2004
• Issued: 12/12/2006
• Est. Priority Date: 06/07/2004
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Malametz, David L.
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): Hanley, John C
• Application Number:
  US10/863,047
• Publication Number:
  US 20050268719A1
• Time in Patent Office: 918 Days
• Field of Search: 7351417-51418, 735/142.3, 735/143.2, 735/143.6, 735/143.7
• US Class Current: 73/514.32
• 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 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 by a flexure in close proximity to the substrate surface;

the 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, and a substantially flexible portion between the inflexible portion and the sensing element where it is attached between 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 respectively positioned on the substrate surface on opposite sides of the flexure, a portion of the first and second electrodes forming respective first and second capacitors with the first and second sensing portions of the sensing element, each electrode having a geometric centerline substantially parallel to the geometric centerline of the flexure, wherein the geometric centerlines of the metal electrodes are symmetrically positioned from the dynamic centerline of the flexure.

2. The sensor device of claim 1 wherein the dynamic centerline of the flexible portion of the flexure is determined by the position of the flexible portion with the sensing element deflected from the undeflected state.

3. The sensor device of claim 2 wherein the position of the dynamic centerline is determined when the sensing element is deflected less than a maximum deflection thereof.

4. The sensor device of claim 2 wherein the flexure suspending the sensing element is attached to the sensing element at a position intermediate of the first and second sensing portions of the sensing element.

11. The sensor device of claim 1 wherein the geometric centerline of the flexure is defined when the sensing element is deflected from the neutral position by less than a maximum deflection of the sensing element.

12. The sensor device of claim 1 wherein the sensor device is a capacitive acceleration sensor.

5. 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 by a pair of flexures;

the pair of flexures being connected to 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 sensing element, wherein the inflexible portions of 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 when the flexible portions are moved away from the geometric centerline due to movement of the sensing element; and

first and second metal electrodes positioned, respectively, on the surface of the substrate on opposite sides of the flexure, each electrode having a portion thereof forming a capacitor, respectively, with the first and second sensing portions of the movable sensing element, the portions of the first and second metal electrodes forming capacitors each having a geometric centerline substantially parallel to the geometric centerline of the flexures, where the geometric centerlines of the electrode portions are symmetrically spaced from the flexure dynamic centerline.

6. The sensor device of claim 5 wherein the position of the flexure dynamic centerline is determined by the position of the flexible portion of the flexures when the sensing element is deflected from a neutral position.

7. The sensor device of claim 6 wherein the deflection of the sensing element from a neutral position is less than a maximum deflection of the sensing element.

8. The sensor device of claim 6 wherein the deflection of the sensing element from a neutral position comprises a maximum deflection of the sensing element relative to the substrate surface.

9. The sensor device of claim 5 wherein the flexures are attached to the sensing element between a longer and a shorter portion of the sensing element.

10. 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 in a neutral position of the sensing element, the movable sensing element having first and second sensing portions;

a flexure positioned between the first and second sensing portions of the movable acceleration sensing element and suspending the sensing element from a stationary attachment point with respect to the substrate, the flexure having a geometric centerline in the neutral position of the sensing element, and a dynamic centerline offset from the geometric centerline by an offset distance, when the sensing element is moved away from its neutral position;

first and second electrodes respectively positioned on the surface of the substrate on opposite sides of the geometric centerline of the flexure, a portion of each first and second electrode being covered, respectively, by the first and second sensing portions of the sensing element, whereby a plurality of capacitors is formed by the electrodes on the surface of the substrate and the respective sensing portions of the sensing element, and wherein each electrode has a geometric centerline substantially parallel to the geometric centerline of the flexure, the respective first and second covered portions of the electrodes being respectively positioned in an asymmetrical relationship with respect to the geometric centerline of the flexure in which the geometric centerline of one electrode is positioned a distance of twice the offset distance farther from the geometric centerline of the flexure than the geometric centerline of the other electrode.