Stacked lateral overlap transducer (slot) based three-axis accelerometer

• US 20110265568A1
• Filed: 12/30/2010
• Published: 11/03/2011
• Est. Priority Date: 04/30/2010
• Status: Active Grant

• Current Assignee: Snaptrack Incorporated (Qualcomm, Inc.)
• Original Assignee: Qualcomm MEMS Technologies Incorporated (Qualcomm, Inc.)
• Inventors: Burns, David William, Shenoy, Ravindra Vaman, Stephanou, Philip Jason
• Granted Patent: US 9,032,796 B2
• Time in Patent Office: Days
• US Class Current: 73/514.32
• CPC Class Codes: G01C 19/5712 the devices involving a micromechanical structure
• CPC Class Codes: G01C 19/5719 using planar vibrating masses driven in a translation vibration along an axis
• CPC Class Codes: G01C 19/5747 each sensing mass being connected to a driving mass, e.g. driving frames
• CPC Class Codes: G01C 19/5769 Manufacturing; Mounting; Housings
• CPC Class Codes: G01C 25/00 Manufacturing, calibrating, cleaning, or repairing instruments or devices referred to in the other groups of this subclass testing, calibrating or compensating compasses G01C17/38
• 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
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/73265 Layer and wire connectors
• CPC Class Codes: H01L 2224/92247 the second connecting process involving a wire connector
• CPC Class Codes: H01L 2924/00012 Relevant to the scope of the group, the symbol of which is combined with the symbol of this group
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H01L 2924/181 Encapsulation
• CPC Class Codes: H01L 2924/19107 off-chip wires
• CPC Class Codes: H10N 30/03 Assembling devices that include piezoelectric or electrostrictive parts
• CPC Class Codes: H10N 30/071 Mounting of piezoelectric or electrostrictive parts together with semiconductor elements, or other circuit elements, on a common substrate
• CPC Class Codes: H10N 30/072 by laminating or bonding of piezoelectric or electrostrictive bodies
• CPC Class Codes: Y10T 29/42 Piezoelectric device making
• CPC Class Codes: Y10T 29/49002 : Electrical device making
• CPC Class Codes: Y10T 29/49005 : Acoustic transducer
• CPC Class Codes: Y10T 29/49155 : Manufacturing circuit on or in base

Abstract

This disclosure provides systems, methods and apparatus, including computer programs encoded on computer storage media, for making and using accelerometers. Some such accelerometers include a substrate, a first plurality of electrodes, a second plurality of electrodes, a first anchor attached to the substrate, a frame and a proof mass. The substrate may extend substantially in a first plane. The proof mass may be attached to the frame, may extend substantially in a second plane and may be substantially constrained for motion along first and second axes. The frame may be attached to the first anchor, may extend substantially in a second plane and may be substantially constrained for motion along the second axis. A lateral movement of the proof mass in response to an applied lateral acceleration along the first or second axes may result in a change in capacitance at the first or second plurality of electrodes.

Claims

1. An accelerometer, comprising:

a substrate extending substantially in a first plane;

a first plurality of electrodes formed substantially along a first axis on the substrate;

a second plurality of electrodes formed substantially along a second axis on the substrate;

a first anchor attached to the substrate;

a frame attached to the first anchor and extending substantially in a second plane, the frame being substantially constrained for motion along the second axis; and

a proof mass attached to the frame and extending substantially in the second plane, the proof mass having a first plurality of slots extending along the first axis and a second plurality of slots extending along the second axis, the proof mass being substantially constrained for motion along the first axis and along the second axis,

wherein a lateral movement of the proof mass in response to an applied lateral acceleration along the first axis results in a first change in capacitance at the second plurality of electrodes, and

wherein a lateral movement of the proof mass in response to an applied lateral acceleration along the second axis results in a second change in capacitance at the first plurality of electrodes.

2. The accelerometer of claim 1, further comprising first flexures that couple the proof mass to the frame, the first flexures allowing the proof mass to move along the first axis without causing the frame to move along the first axis.

3. The accelerometer of claim 1, further comprising second flexures that couple the frame to the first anchor, the second flexures allowing the proof mass and the frame to move together along the second axis.

4. The accelerometer of claim 1, wherein the frame surrounds the first anchor and the proof mass surrounds the frame.

5. The accelerometer of claim 1, wherein one or more slots extend completely through the proof mass.

6. The accelerometer of claim 1, wherein one or more slots extend only partially through the proof mass.

7. The accelerometer of claim 1, wherein the frame includes a third plurality of slots extending along the first axis.

8. The accelerometer of claim 1, wherein at least one of the proof mass and the frame is formed, at least in part, from metal.

9. The accelerometer of claim 1, wherein the frame includes a first portion coupled to the first anchor, the first portion having stress isolation slits proximate the first anchor.

10. The accelerometer of claim 1, further comprising:

an appended mass coupled to the proof mass; and

a third electrode and a fourth electrode on the substrate,

wherein a capacitance between the appended mass and the third and fourth electrodes change in response to a normal acceleration applied to the proof mass.

11. The accelerometer of claim 1, further including:

a second anchor formed on the substrate;

a flexure attached to the second anchor, the flexure and the second anchor forming a pivot;

a third electrode formed on the substrate;

a fourth electrode formed on the substrate;

a second proof mass having a first side proximate the third electrode and a second side proximate the fourth electrode, the second proof mass disposed adjacent the pivot, the second proof mass being coupled to and configured for rotation about the pivot, the rotation resulting in a third change in capacitance at the third electrode and a fourth change in capacitance at the fourth electrode.

12. The accelerometer of claim 11, wherein a center of mass of the proof mass is substantially offset from the pivot.

13. The accelerometer of claim 11, wherein the second proof mass includes a first portion coupled to the second anchor, the first portion having stress isolation slits proximate the second anchor.

14. The accelerometer of claim 13, wherein the second proof mass includes a second portion coupled to the first portion via torsional flexures.

15. The accelerometer of claim 14, wherein the torsional flexures are substantially perpendicular to the stress isolation slits.

16. An accelerometer, comprising:

substrate means extending substantially in a first plane;

first electrode means formed substantially along a first axis on the substrate;

second electrode means formed substantially along a second axis on the substrate;

first anchor means attached to the substrate means;

frame means attached to the first anchor means and extending substantially in a second plane, the frame means being substantially constrained for motion along the second axis; and

proof mass means attached to the frame means and extending substantially in the second plane, the proof mass means being substantially constrained for motion along the first axis and along the second axis,

wherein a lateral movement of the proof mass means in response to an applied lateral acceleration along the first axis results in a first change in capacitance at the second electrode means, and

wherein a lateral movement of the proof mass means in response to an applied lateral acceleration along the second axis results in a second change in capacitance at the first electrode means.

17. The accelerometer of claim 16, further comprising first flexure means for allowing the proof mass means to move along the first axis without causing the frame means to move along the first axis.

18. The accelerometer of claim 16, further comprising second flexure means for allowing the proof mass means and the frame means to move together along the second axis.

19. A method of fabricating an accelerometer, comprising:

forming the following on a substrate that extends substantially in a first plane;

a first plurality of electrodes substantially along a first axis;

a second plurality of electrodes substantially along a second axis; and

a first anchor;

forming a frame and a proof mass that extend substantially in a second plane, wherein the process of forming the proof mass includes;

forming a first plurality of slots in the proof mass that extend substantially along the first axis; and

forming a second plurality of slots in the proof mass that extend substantially along the second axis, and

wherein the process of forming the frame involves;

forming first flexures that are configured for attaching the proof mass to the frame and for allowing the proof mass to move substantially along the first axis without causing the frame to move along the first axis, and

forming second flexures that are configured for attaching the frame to the first anchor, for substantially constraining the frame for motion along the second axis and for allowing the proof mass and the frame to move together along the second axis.

20. The method of claim 19, wherein the process of forming the first and second plurality of electrodes on the substrate includes depositing the first and second plurality of electrodes on the substrate.

21. The method of claim 19, wherein the process of forming the proof mass involves an electroplating process.

22. The method of claim 19, wherein the process of forming the frame involves forming the frame around the first anchor.

23. The method of claim 19, wherein the process of forming the proof mass involves forming the proof mass around the frame.

24. The method of claim 19, wherein the process of forming the proof mass involves forming one or more slots at least partially through the proof mass.

25. The method of claim 19, wherein the process of forming the frame involves forming a third plurality of slots in the frame and extending along the first axis.

26. The method of claim 19, wherein the process of forming the frame involves:

forming a first portion coupled to the first anchor; and

forming stress isolation slits in the first portion proximate the first anchor.

27. The method of claim 21, further comprising:

partially forming features of a plurality of accelerometers on the substrate; and

dividing the substrate into sub-panels after the structures are partially formed,

wherein the electroplating process is performed using the sub-panels.

28. The method of claim 27, wherein partially forming the features involves deposition processes, patterning processes and etching processes.