Internally shock caged serpentine flexure for micro-machined accelerometer

• US 7,024,933 B2
• Filed: 04/08/2005
• Issued: 04/11/2006
• Est. Priority Date: 12/15/2003
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Malametz, David L.
• Primary Examiner(s): CHAPMAN JR, JOHN E
• Application Number:
  US11/102,222
• Publication Number:
  US 20050183503A1
• Time in Patent Office: 368 Days
• Field of Search: 735/143.2, 735/143.6, 735/143.8, 735/041.2, 735/041.4
• US Class Current: 73/514.32
• CPC Class Codes: B81B 2201/0235 Accelerometers
• CPC Class Codes: B81B 2203/0163 Spring holders
• CPC Class Codes: B81B 3/0051 For defining the movement, i.e. structures that guide or limit the movement of an element mechanical arrangements for preventing or damping vibration or shock H01H3/60
• CPC Class Codes: B81B 7/0016 Protection against shocks or vibrations, e.g. vibration damping
• CPC Class Codes: G01P 15/08 with conversion into electric or magnetic values
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 15/18 in two or more dimensions
• CPC Class Codes: G01P 2015/082 for two degrees of freedom of movement of a single mass

Abstract

An apparatus and method for sensing accelerations and other forces. The apparatus having a capacitance pick-off force sensor having a proof mass that is suspended relative to a relatively stationary frame by a plurality of serpentine suspension members having internal caging. The device provides easily implemented fabrication modification for trading-off between input range and pick-off sensitivity by altering etching periods of the serpentine suspension members. The input range and pick-off sensitivity can be traded-off by enlarging or reducing the quantity of elongated flexure fingers forming the serpentine suspension member. Different ones of the elongated flexure fingers are optionally formed with different thicknesses, whereby the serpentine suspension member exhibits a spring rate that progressively increases as it is compressed by in-plane motion of the proof mass relative to the relatively stationary frame.

Claims

1. A micro-machined electromechanical sensor (MEMS) device, comprising:

a substantially planar proof mass suspended for in-plane motion from a relatively stationary frame by pluralities of first and second pairs of spaced-apart resiliently flexible elongated flexure members, wherein;

each of the first pairs of elongated flexure members are interconnected at respective first ends, and adjacent pairs of the elongated flexure members are interconnected at respective second ends of adjacent elongated flexure members with respective second ends of first and last flexure members being interconnected between a first end of the proof mass and the frame, and

each of the second pairs of elongated flexure members are interconnected at respective first ends, and adjacent pairs of the elongated flexure members are interconnected at respective second ends of adjacent elongated flexure members with respective second ends of first and last flexure members being interconnected between a second end of the proof mass and the frame;

a promontory mass formed between adjacent second pairs of the elongated flexure members on one end of a relatively short crosswise member interconnecting the respective first ends of one of the first pairs of the elongated flexure members; and

one or more comb-type capacitive pickoff sensors formed between the proof mass and the frame and structured for changing capacitance as a function of a movement of the proof mass relative to the frame.

2. The device of claim 1, further comprising a promontory mass positioned between the frame and the relatively short crosswise member interconnecting the respective first ends of one of the first and second pairs of the elongated flexure members.

3. The device of claim 2 wherein the promontory mass is positioned at one end of the relatively short interconnecting member and extends a part of the distance between the relatively short interconnecting member and the frame.

4. The device of claim 2 wherein the promontory mass is positioned on the frame and extends a part of the distance between the relatively short interconnecting member and the frame.

5. The device of claim 1, further comprising a promontory mass positioned between one of the first and second ends of the proof mass and the relatively short crosswise member interconnecting the respective first ends of one of the first and second pairs of the elongated flexure members.

6. The device of claim 5 wherein the promontory mass is positioned at one end of the relatively short interconnecting member and extends a part of the distance between the relatively short interconnecting member and the proof mass.

7. The device of claim 5 wherein the promontory mass is positioned on the proof mass and extends a part of the distance between the relatively short interconnecting member and the proof mass.

8. The device of claim 1 wherein a spring rate of one or more of the flexures progressively changes between the proof mass and the frame.

9. A micro-machined electromechanical sensor (MEMS) device, comprising:

a substantially planar proof mass suspended for in-plane motion from a relatively stationary frame by pluralities of first and second pairs of spaced-apart resiliently flexible elongated flexure members, wherein;

each of the first pairs of elongated flexure members are interconnected at respective first ends, and adjacent pairs of the elongated flexure members are interconnected at respective second ends of adjacent elongated flexure members with respective second ends of first and last flexure members being interconnected between a first end of the proof mass and the frame,

each of the second pairs of elongated flexure members are interconnected at respective first ends, and adjacent pairs of the elongated flexure members are interconnected at respective second ends of adjacent elongated flexure members with respective second ends of first and last flexure members being interconnected between a second end of the proof mass and the frame, and

a spring rate associated with one of the elongated flexure members is different from a spring rate associated with a different one of the elongated flexure members;

a promontory mass formed between adjacent second pairs of the elongated flexure members on one end of a relatively short crosswise member interconnecting the respective first ends of a pair one of the first pairs of the elongated flexure members; and

one or more comb-type capacitive pickoff sensors formed between the proof mass and the frame and structured for changing capacitance as a function of a movement of the proof mass relative to the frame.

10. The device of claim 9 wherein the proof mass, frame and flexure members are formed between substantially parallel and planar spaced-apart surfaces of a silicon substrate.

11. The device of claim 9, further comprising a promontory mass positioned between the frame and the relatively short crosswise member interconnecting the respective first ends of one of the first and second pairs of the elongated flexure members.

12. The device of claim 9, further comprising a promontory mass positioned between one of the first and second ends of the proof mass and the relatively short crosswise member interconnecting the respective first ends of one of the first and second pairs of the elongated flexure members.

13. A micro-machined electromechanical sensor (MEMS) device, comprising:

a silicon substrate having substantially parallel and planar spaced-apart surfaces;

a proof mass formed in the substrate;

a frame formed in the substrate surrounding the proof mass;

a plurality of capacitive pickoff sensors formed between the proof mass and the frame and structured for changing capacitance as a function of an in-plane movement of the proof mass relative to the frame;

a plurality of serpentine flexures formed in balanced configuration between the proof mass and the frame and structured for enabling the in-plane movement of the proof mass relative to the frame, one or more of the serpentine flexures comprising a plurality of substantially parallel and spaced-apart resiliently flexible elongated flexure members that are arranged substantially crosswise to a direction of the in-plane movement of the proof mass relative to the frame and are interconnected at opposite ends of alternate pairs of the elongated flexure members;

a plurality of relatively short interconnecting members arranged crosswise to the longitudinal axes of the elongated flexure members and interconnecting opposite ends of alternate pairs of the elongated flexure members in a serpentine configuration; and

a promontory mass formed between the serpentine flexures, the promontory mass being positioned at one end of one or more of the relatively short interconnecting members and being sized to span a part of the distance between adjacent elongated flexure members.

14. The device of claim 13 wherein a spring rate of one or more of the serpentine flexures progressively changes between the proof mass and the frame.

15. A micro-machined electromechanical sensor (MEMS) device having a serpentine flexure, the device comprising:

a relatively stationary frame formed in a substrate having substantially parallel and planar spaced-apart surfaces;

a moveable proof mass that is formed in the substrate; and

a plurality of serpentine flexures suspending the proof mass from the frame, one or more of the serpentine flexures comprising;

a plurality of elongated flexure members each formed in the substrate between the spaced-apart surfaces thereof,

a relatively short interconnecting member arranged crosswise to the longitudinal axes of the elongated flexure members and interconnecting opposite ends of alternate pairs of the elongated flexure members in a serpentine configuration, and

a small mass formed as an extension formed on one end of one or more of the interconnecting members and extending a part of a distance between adjacent elongated flexure members.

16. The device of claim 15, further comprising a small mass extending a part of a distance between one of the frame and the proof mass and one of elongated flexure members that is adjacent thereto.

17. The device of claim 15, further comprising a plurality of capacitive pickoff sensors formed between the proof mass and the frame.

18. A micro-machined electromechanical sensor (MEMS) device having a serpentine flexure, the device comprising:

a relatively stationary frame formed in a substrate having substantially parallel and planar spaced-apart surfaces;

a moveable proof mass that is formed in the substrate; and

a plurality of serpentine flexures suspending the proof mass from the frame, one or more of the serpentine flexures comprising;

a plurality of elongated flexure members each formed in the substrate between the spaced-apart surfaces thereof,

a relatively short interconnecting member arranged crosswise to the longitudinal axes of the elongated flexure members and interconnecting opposite ends of alternate pairs of the elongated flexure members in a serpentine configuration, and

a small mass formed as an extension formed on each of two opposite ends of one or more of the interconnecting members and extending a part of a distance between adjacent elongated flexure members.

19. A micro-machined electromechanical sensor (MEMS) device having a serpentine flexure, the device comprising:

a relatively stationary frame formed in a substrate having substantially parallel and planar spaced-apart surfaces;

a moveable proof mass that is formed in the substrate; and

a plurality of serpentine flexures suspending the proof mass from the frame, one or more of the serpentine flexures comprising;

a plurality of elongated flexure members each formed in the substrate between the spaced-apart surfaces thereof wherein a spring rate of one or more of the serpentine flexures progressively changes between the proof mass and the frame, and

a small mass extending a part of a distance between adjacent elongated flexure members.

20. The device of claim 19 wherein one or more of the plurality of elongated flexure members is thicker than one or more others of the elongated flexure members.