Micromachined devices with anti-levitation devices

• US 6,481,284 B2
• Filed: 12/17/2001
• Issued: 11/19/2002
• Est. Priority Date: 09/02/1997
• Status: Expired due to Term

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Geen, John A., Carow, Donald W.
• Primary Examiner(s): CHAPMAN JR, JOHN E
• Application Number:
  US10/022,688
• Publication Number:
  US 20020046603A1
• Time in Patent Office: 337 Days
• Field of Search: 735/041.2, 735/041.3, 735/041.4, 735/041.5, 735/041.6, 735/040.4
• US Class Current: 73/504.12
• CPC Class Codes: G01C 19/5719 using planar vibrating masses driven in a translation vibration along an axis

Abstract

A micromachined device has first and second sets of interdigitating fingers movable on a plane parallel to a substrate. A first group of conductive members is formed on the substrate and is at the same DC voltage as a first group of fingers. A second group of conductive members is formed on the substrate and is electrically coupled to the second group of fingers. The conductive members help to prevent one group of fingers from levitating with respect to others.

Claims

1. A micromachined device comprising:

a substrate;

a first body suspended over the substrate in a plane parallel to the substrate and movable in the plane and relative to the substrate;

a first plurality of fingers extending in parallel away from the first body and coplanar with the first body;

a second plurality of fingers parallel to the first plurality of fingers and interdigitating with the first plurality of fingers;

a first conductive member on the substrate under a first group of the first plurality of fingers and the second plurality of fingers, the first conductive member held at the same voltage as the second plurality of fingers; and

a second conductive member on the substrate under a second group of the first plurality of fingers and the second plurality of fingers, the second conductive member held at the same DC voltage as the first plurality of fingers.

2. The device of claim 1, wherein the first and second pluralities of fingers include drive fingers for dithering the first body in a first direction.

3. The device of claim 1, wherein the first conductive member is coupled to the second plurality of fingers.

4. The device of claim 3, wherein the first plurality of fingers have a net downward force over the first conductive members and the second plurality of fingers have a net upward force over the second conductive members, the forces canceling to keep the first body in the plane.

5. The device of claim 1, wherein the first body is movable in the plane along a dither axis, the device further comprising a second body suspended over the substrate, the first and second bodies being coplanar in a first plane parallel to the substrate, the second body coupled to the first body such that the second body is substantially inhibited from moving relative to the substrate along the dither axis.

6. The device of claim 5, wherein the first body surrounds the second body.

7. The device of claim 5, wherein the second body surrounds the first body.

8. The device of claim 5, wherein the second body is movable in the plane in a sensing direction perpendicular to the dither axis, the second body having fingers, the device further comprising stationary fingers that form a differential capacitor in the plane to sense movement in the sensing direction.

9. The device of claim 1, wherein the first body has a perimeter portion defining and surrounding an aperture.

10. The device of claim 9, wherein the first plurality of fingers extends inwardly from the first body into the aperture.

11. The device of claim 9, wherein the first body has at least one cross-piece extending from one part of the perimeter portion to another part of the perimeter portion to define a plurality of apertures.

12. The device of claim 11, wherein the first plurality of fingers extends inwardly from the cross-piece into at least two apertures.

13. The device of claim 1, further comprising a package, wherein the device is packaged under ambient conditions.

14. A micromachined device comprising:

a substrate;

a first body over the substrate;

a second body suspended over the substrate in a plane parallel to the substrate and movable in the plane and relative to the substrate and to the first body;

a first conductive member on the substrate under a portion of the first and second body and held at a voltage; and

a second conductive member formed on the substrate under a second portion of the first and second body and electrically coupled to the first body.

15. The device of claim 14, further comprising a third conductive member on the substrate and under a third portion of the first and second body and held at the voltage.

16. The device of claim 15, further comprising a fourth conductive member on the substrate and under a fourth portion of the first and second body and electrically coupled to the second body.

17. The device of claim 16, wherein the first, second, third, and fourth conductive members are arranged in a row, with each spaced from the other.

18. A micromachined device comprising:

a substrate;

a first body suspended over the substrate and movable relative to the substrate;

a first plurality of fingers extending away from the first body;

a second plurality of fingers interdigitating with the first plurality of fingers;

a first conductive layer on the substrate under the first plurality of fingers and the second plurality of fingers, the first conductive layer held at the same voltage as the second plurality of fingers; and

a second conductive layer on the substrate under the first plurality of fingers and the second plurality of fingers, the second conductive layer held at the same voltage as the first plurality of fingers.

19. The device of claim 18, further comprising a third conductive layer spaced from the first conductive layer and held at the same voltage as the second plurality of fingers, and a fourth conductive layer spaced from the second conductive layer and held at the same voltage as the first plurality of fingers.

20. The device of claim 19, wherein the first through fourth conductive layers are arranged in a line under the fingers in the order of first, second, third and fourth layers.