MEMS MOTION SENSOR AND METHOD OF MANUFACTURING

• US 20150260519A1
• Filed: 02/13/2015
• Published: 09/17/2015
• Est. Priority Date: 08/02/2013
• Status: Active Grant

• Current Assignee: Motion Engine inc
• Original Assignee: Motion Engine inc
• Inventors: Boysel, Robert Mark, Ross, Louis
• Granted Patent: US 11,852,481 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01C 19/56 Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces
• CPC Class Codes: G01C 19/5712 the devices involving a micromechanical structure
• CPC Class Codes: G01C 19/5755 the devices having a single sensing mass
• 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: H01L 2224/94 at wafer-level, i.e. with connecting carried out on a wafer comprising a plurality of undiced individual devices

Abstract

A MEMS motion sensor and its manufacturing method are provided. The sensor includes a MEMS wafer including a proof mass and flexible springs suspending the proof mass and enabling the proof mass to move relative to an outer frame along mutually orthogonal x, y and z axes. The sensor includes top and bottom cap wafers including top and bottom cap electrodes forming capacitors with the proof mass, the electrodes being configured to detect a motion of the proof mass. Electrical contacts are provided on the top cap wafer, some of which are connected to the respective top cap electrodes, while others are connected to the respective bottom cap electrodes by way of insulated conducting pathways, extending along the z axis from one of the respective bottom cap electrodes and upward successively through the bottom cap wafer, the outer frame of the MEMS wafer and the top cap wafer.

Claims

1. A MEMS motion sensor comprising:

an electrically conductive MEMS wafer having a first side and a second side[s] and including an outer frame, a proof mass and flexible springs suspending the proof mass relative to the outer frame and enabling the proof mass to move relative to the outer frame along mutually orthogonal x, y and z axes;

an electrically conductive top cap wafer and an electrically conductive bottom cap wafer respectively bonded to the first side and the second side of the MEMS wafer such that the top cap wafer, the bottom cap wafer and the outer frame of the MEMS wafer define a cavity for housing the proof mass;

a plurality of top cap wafer electrodes and a plurality of bottom cap wafer electrodes that are respectively positioned with the top cap wafer and the bottom cap wafer, the electrodes forming capacitors with the proof mass that are operative to detect a motion of the proof mass; and

a first set of electrical contacts connected to the plurality of top cap wafer electrodes, and a second set of electrical contacts being conductively connected to the bottom cap wafer electrodes with insulated conducting pathways that extend upwardly through the bottom cap wafer, the outer frame of the MEMS wafer and the top cap wafer.

2. The MEMS motion sensor according to claim 1, wherein the proof mass and flexible springs form a resonant structure having resonant frequencies f_x, f_y and f_z for motion along the x, y and z axes, respectively.

3. The MEMS motion sensor according to claim 2, comprising electrode assemblies, each including at least one pair of said top cap electrodes, or at least one pair of said bottom cap electrodes or a combination of said top cap electrodes and bottom cap electrodes, said electrode assemblies comprising:

a first electrode assembly configured to detect a rocking motion of the proof mass about the y axis, indicative of an acceleration of the proof mass along the x axis;

a second electrode assembly configured to detect a rocking motion of the proof mass about the x axis, indicative of an acceleration of the proof mass along the y axis; and

a third electrode assembly configured to detect a translational motion of the proof mass along the z axis, indicative of an acceleration of the proof mass along the z axis.

4. The MEMS motion sensor according to claim 3, wherein one of the electrode assemblies is connectable to a drive circuit configured to vibrate the proof mass at a drive frequency along the z axis, and two other of the electrode assemblies are configured to detect Coriolis-induced oscillations of the proof mass along the x and y axes, indicative of an angular motion of the proof mass about the y and x axes, respectively.

5. The MEMS motion sensor according to claim 4, wherein the drive frequency corresponds to the resonant frequency f_z.

6. The MEMS motion sensor according to claim 4, wherein the resonant frequency f_z is substantially identical to each of the respective resonant frequencies f_x, f_y, in order to provide matched resonance conditions.

7. The MEMS motion sensor according to claim 4, wherein a relative difference between any two of the resonant frequencies f_z, f_x, f_y is no more than 10%.

8. The MEMS motion sensor according to claim 4, wherein the drive frequency is lower than at least one of the respective resonant frequencies f_x and f_y.

9. The MEMS motion sensor according to claim 4, wherein the drive frequency is 10-40% lower than each of the respective resonant frequencies f_x and f_y.

10. The MEMS motion sensor according to claim 3, wherein one of the electrode assemblies is configured to vibrate the proof mass at a drive frequency along a corresponding one of the x and y axes, respectively, and another one of the electrode assemblies is configured to detect Coriolis-induced oscillations of the proof mass along the other one of the x and y axes, indicative of an angular motion of the proof mass about the z axis.

11. The MEMS motion sensor according to claim 10, wherein the drive frequency along the corresponding one of the x and y axes corresponds to a respective one of the resonant frequencies f_x and f_y.

12. The MEMS motion sensor according to claim 3, wherein the resonant structure is shaped, sized and configured such that each of the resonant frequencies f_x, f_y and f_z is substantially higher than sensing frequencies at which the electrode assemblies are configurable with a sensing circuit to detect the motion of the proof mass in response to accelerations of the proof mass along to the x, y and z axes, respectively.

13. The MEMS motion sensor according to claim 1, wherein the resonant structure is shaped, sized and configured with each of the resonant frequencies f_x, f_y and f_z being substantially different.

14. The MEMS motion sensor according to claim 13, wherein the resonant structure is shaped, sized and configured with the resonant frequencies f_x, f_y and f_z having mutually non-overlapping 3 dB-bandwidths.

15. The MEMS motion sensor according to claim 1, wherein said top and bottom cap electrodes comprise a pair of said top and bottom electrodes, aligned with the z axis, the electrodes being centered relative to the proof mass.

16. The MEMS motion sensor according to claim 1, wherein said top and bottom cap electrodes comprise two pairs of said top and bottom electrodes disposed along the x axis on each side of the y axis.

17. The MEMS motion sensor according to claim 1, wherein said top and bottom cap electrodes comprise two pairs of said top and bottom electrodes disposed along the y axis on each side of the x axis.

18. The MEMS motion sensor according to claim 1, wherein the proof mass is shaped as a convex polygonal prism.

19. The MEMS motion sensor according to claim 1, wherein the proof mass is shaped as a regular convex polygonal prism.

20. The MEMS motion sensor according to claim 1, wherein the proof mass is shaped as an octagonal prism.

21. The MEMS motion sensor according to claim 1, wherein the flexible springs comprise four flexible springs.

22. The MEMS motion sensor according to claim 1, wherein the top and bottom cap wafers have respective thicknesses, the top and bottom electrodes extending through the entire thicknesses of the top and bottom cap wafers, respectively.

23. The MEMS motion sensor according to claim 1, wherein the top cap wafer, the MEMS wafer and the bottom cap wafer comprise a silicon semiconductor.

24. The MEMS motion sensor according to claim 1, wherein the MEMS wafer is a silicon on-insulator (SOI) wafer with an insulating layer separating a device layer from a handle layer.

25. The MEMS motion sensor according to claim 24, wherein the proof mass is patterned in both the device and handle layers.

26. The MEMS motion sensor according to 1, wherein top and bottom electrodes are delimited by insulated channels.

27. The MEMS motion sensor according to claim 1, wherein the bottom cap wafer is provided with an electrical contact, the MEMS motion sensor comprising an additional insulated conducting pathway extending through the bottom cap wafer, through the frame of the MEMS wafer, and through the top cap wafer along the z axis and optionally in an x-y plane, between one of the electrical contacts of the top cap wafer to one of the electrical contacts of the bottom cap wafer, thereby forming a conductive feedthrough.

28. A method for manufacturing a MEMS motion sensor, the method comprising the steps of:

a) providing top and bottom cap wafers having respective inner and outer sides;

forming insulated conducting cap wafer channels;

patterning trenches and filling the trenches to form electrodes on the inner sides of said cap wafers, some of the insulated conducting cap wafer channels being electrically connected to the respective electrodes;

b) providing a MEMS wafer having first and second sides, and patterning portions of a proof mass, of flexible springs, of an outer frame with insulated conducting MEMS wafer channels, in one of the first and second sides;

c) bonding the side of the MEMS wafer patterned in step b) to the inner side of the top or bottom cap wafer by aligning the insulated conducting cap wafer channels with the corresponding portions of the insulated conducting MEMS channels, and by aligning the electrodes relative to the proof mass and the springs;

d) patterning the remaining portions of the proof mass, the flexible springs, the outer frame with the insulated conducting MEMS wafer channels on the other side of the MEMS wafer;

e) bonding the side of the MEMS wafer patterned in step d) to the inner side of the other top or bottom cap wafer, by aligning the electrodes of the top cap wafer with the electrodes of the bottom cap wafer and by aligning the insulated conducting cap wafer channels of said other cap wafer with the remaining portions of the insulated conducting MEMS channels, creating insulated conducting pathways, with some of said insulated conducting pathways extending from the electrodes of the bottom cap wafer, through the outer frame of the MEMS wafer and through the top cap wafer, and enclosing the proof mass suspended relative to the outer frame by the flexible springs within a cavity formed by the top and bottom cap wafers and by the outer frame of the MEMS wafer; and

f) removing a portion of the outer sides of the top and bottom cap wafers to expose and isolate the insulated conducting pathways and the electrodes in the top and bottom cap wafers.

29. A method for operating a motion sensor comprising:

operating a motion sensor including a proof mass in a cavity, the cavity defined by a conductive top cap wafer having an inner top cap side bonded to a first side of a conductive MEMS wafer that includes the proof mass suspended from flexible springs and an outer frame, the cavity being further defined by a conductive bottom cap wafer having an inner bottom cap side bonded to a second side of the MEMS wafer, the top cap wafer having a first set of top cap electrical contacts and a second set of top cap electrical contacts, the first set of electrical contacts being connected to top cap wafer electrodes and the second set of electrical contacts being connected to bottom cap wafer electrodes; and

conducting electrical signals between the bottom cap wafer through the outer frame to electrical contacts on the top cap wafer with insulated conducting pathways that extend from the bottom cap wafer through the outer frame and the top cap wafer, the insulated conducting pathways being in conductive contact with corresponding electrical contacts on the top cap wafer.

30. The method of claim 29 further comprising driving the proof mass at a drive frequency with a drive circuit and sensing motion of the proof mass with a sensing circuit.