Single proof mass, 3 axis MEMS transducer

• US 6,936,492 B2
• Filed: 12/10/2004
• Issued: 08/30/2005
• Est. Priority Date: 07/08/2003
• Status: Expired due to Fees

• Current Assignee: North Star Innovations Inc. (Wi-LAN Inc.)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: McNeil, Andrew C., Li, Gary, Koury, Jr., Daniel N.
• Primary Examiner(s): CHAPMAN JR, JOHN E
• Application Number:
  US11/009,109
• Publication Number:
  US 20050097957A1
• Time in Patent Office: 263 Days
• Field of Search: 735/143.2, 361/280, 438/50, 438/52
• US Class Current: 438/50
• 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
• CPC Class Codes: G01P 2015/0831 the mass being of the paddle type having the pivot axis between the longitudinal ends of the mass, e.g. see-saw configuration

Abstract

A transducer is provided herein which comprises an unbalanced proof mass (51), and which is adapted to sense acceleration in at least two mutually orthogonal directions. The proof mass (51) has first (65) and second (67) opposing sides that are of unequal mass.

Claims

1. A method for making a transducer, comprising:

providing a substrate;

depositing a first conductive layer on said substrate;

patterning said first conductive layer to define first and second capacitive structures therein;

depositing a sacrificial layer over said first conductive layer;

depositing a second conductive layer over the sacrificial layer; and

patterning the second conductive layer to define a proof mass and sense fingers therein such that the center of mass of the proof mass is asymmetrically disposed relative to said first and second capacitive structures.

2. The method of claim 1, further comprising the step of removing at least a portion of the sacrificial layer to obtain release of the proof mass.

3. The method of claim 1, wherein said first and second conductive layers comprise polysilicon.

4. The method of claim 1, wherein the transducer is an accelerometer adapted to sense acceleration in a direction perpendicular to the substrate by measuring the capacitances between the proof mass and the first and second capacitive structures.

5. The method of claim 1, wherein the first and second capacitive structures are plates.

6. The method of claim 1, wherein said proof mass comprises a first set of sense fingers whose longitudinal axes are parallel to a first axis, and a second set of sense fingers whose longitudinal axes are parallel to a second axis.

7. The method of claim 1, wherein said proof mass comprises a plurality of compliant structures that support the proof mass above the first and second capacitive structures.

8. The method of claim 1, wherein said proof mass comprises a plurality of fixed fingers, and wherein each sense finger is disposed between a pair of fixed fingers.

9. The method of claim 1, wherein said proof mass comprises:

a first set of sense fingers whose longitudinal axes are parallel to a first axis, and a second set of sense fingers whose longitudinal axes are parallel to a second axis;

a plurality of compliant structures that support the proof mass above the first and second capacitive structures; and

a plurality of fixed fingers;

wherein each sense finger is disposed between a pair of fixed fingers, and wherein the first and second sets of sense fingers, the plurality of compliant structures, and the plurality of fixed fingers are disposed in an arrangement that has at least one plane of mirror symmetry.

10. The method of claim 9, wherein the first and second sets of sense fingers, the plurality of compliant structures, and the plurality of fixed fingers are formed in the second conductive layer, and wherein the arrangement has at least two planes of mirror symmetry about a plane orthogonal to a major surface of the second conductive layer.

11. The method of claim 10, wherein the arrangement has at least a four-fold rotational axis of symmetry around an axis orthogonal to a major surface of the second conductive layer.

12. The method of claim 1, wherein the proof mass is asymmetrically disposed relative to said first and second plates.

13. The method of claim 1, further comprising the step of depositing a material on a surface of the proof mass such that the center of mass of the proof mass is asymmetrically disposed relative to said first and second plates.

14. The method of claim 13, wherein the material comprises a metal.