MULTI-MASS MEMS MOTION SENSOR

• US 20170108336A1
• Filed: 01/12/2015
• Published: 04/20/2017
• Est. Priority Date: 06/02/2014
• Status: Active Grant

• Current Assignee: Motion Engine inc
• Original Assignee: Motion Engine inc
• Inventors: Boysel, Robert Mark, Ross, Louis
• Granted Patent: US 11,674,803 B2
• Time in Patent Office: Days
• CPC Class Codes: B81B 2201/0235 Accelerometers
• 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 19/5733 Structural details or topology
• 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 2015/084 the mass being suspended at more than one of its sides, e.g. membrane-type suspension, so as to permit multi-axis movement of the mass

Abstract

A micro-electro-mechanical system (MEMS) motion sensor is provided that includes a MEMS wafer having a frame structure, a plurality of proof masses suspended to the frame structure, movable in three dimensions, and enclosed in one or more cavities. The MEMS sensor includes top and bottom cap wafers bonded to the MEMS wafer and top and bottom electrodes provided in the top and bottom cap wafers, forming capacitors with the plurality of proof masses, and being together configured to detect motions of the plurality of proof masses. The MEMS sensor further includes first electrical contacts provided on the top cap wafer and electrically connected to the top electrodes, and a second electrical contacts provided on the top cap wafer and electrically connected to the bottom electrodes by way of vertically extending insulated conducting pathways. A method for measuring acceleration and angular rate along three mutually orthogonal axes is also provided.

Claims

1. A micro-electro-mechanical system (MEMS) motion sensor (10) comprising:

a MEMS wafer (16) having opposed top and bottom sides (161, 162) and comprising a frame structure (50), a plurality of proof masses (17a to 17e), and a plurality of spring assemblies (27a to 27e) each suspending a corresponding one of the proof masses (17a to 17e) from the frame structure (50) and enabling the corresponding one of the proof masses (17a to 17e) to move along mutually orthogonal first, second and third axes;

top and bottom cap wafers (12, 14) respectively bonded to the top and bottom sides (161, 162) of the MEMS wafer (16), the top cap, bottom cap and MEMS wafers (12, 14, 16) being electrically conductive, the top cap wafer (12), bottom cap wafer (14) and frame structure (50) together defining one or more cavities (31) each enclosing one or more of the plurality of proof masses (17a to 17e), each proof mass (17a to 17e) being enclosed in one of the one or more cavities (31);

top and bottom electrodes (13, 15) respectively provided in the top and bottom cap wafers (12, 14) and forming capacitors with the plurality of proof masses (17a to 17e), the top and bottom electrodes (13, 15) being together configured to detect motions of the plurality of proof masses (17a to 17e); and

first and second sets of electrical contacts (42a, 42b) provided on the top cap wafer (12), the first set of electrical contacts (42a) being electrically connected to the top electrodes (13), and the second set of electrical contacts (42b) being electrically connected to the bottom electrodes (15) by way of insulated conducting pathways (33) extending successively through the bottom cap wafer (14), the frame structure (50) of the MEMS wafer (16) and the top cap wafer (12).

2. The MEMS motion sensor (10) according to claim 1, wherein the MEMS motion sensor (10) is configured as a six-degree-of-freedom (6-DOF) motion sensor (10) enabling three-axis linear acceleration and angular rate measurements.

3. The MEMS motion sensor (10) according to claim 2, wherein the top and bottom electrodes (13, 15) form a plurality of electrode assemblies (181 to 188) each electrode assembly (181 to 188) including at least one pair of the top and/or bottom electrodes (13, 15), the plurality of electrode assemblies (181 to 188) comprising:

a first sensing electrode assembly (181) associated with one or more of the plurality of proof masses (17a to 17e) and configured to detect a translational motion of the one or more proof masses (17a to 17e) associated with the first sensing electrode assembly (181) along the first axis, the translational motion being indicative of a linear acceleration along the first axis;

a second sensing electrode assembly (182) associated with one or more of the plurality of proof masses (17a to 17e) and configured to detect a rotation of the one or more proof masses (17a to 17e) associated with the second sensing electrode assembly (182) about the third axis, the rotation about the third axis being indicative of a linear acceleration along the second axis;

a third sensing electrode assembly (183) associated with one or more of the plurality of proof masses (17a to 17e) and configured to detect a rotation of the one or more proof masses (17a to 17e) associated with the third sensing electrode assembly (183) about the second axis, the rotation about the second axis being indicative of a linear acceleration along the third axis;

a first driving electrode assembly (187) associated with and configured to drive a motion of one or more associated ones of the plurality of proof masses (17a to 17e) along the first axis at an out-of-plane drive frequency;

a fourth sensing electrode assembly (184) associated with the one or more proof masses (17a to 17e) associated with the first driving electrode assembly (187) and configured to sense a Coriolis-induced, rocking motion of the one or more proof masses (17a to 17e) associated with the first driving electrode assembly (187) along the third axis, the Coriolis-induced, rocking motion along the third axis being indicative of an angular rate about the second axis;

a fifth sensing electrode assembly (185) associated with the one or more proof masses (17a to 17e) associated with the first driving electrode assembly (187) and configured to sense a Coriolis-induced, rocking motion of the one or more proof masses (17a to 17e) associated with the first driving electrode assembly (187) along the second axis, the Coriolis-induced, rocking motion along the second axis being indicative of an angular rate about the third axis;

a second driving electrode assembly (188) associated with and configured to drive a rocking motion of one or more associated ones of the proof masses (17a to 17e) along one of the second and third axes at an in-plane drive frequency; and

a sixth sensing electrode assembly (186) associated with the one or more proof masses (17a to 17e) associated with the second driving electrode assembly (188) and configured to sense a Coriolis-induced, rocking motion of the one or more proof masses (17a to 17e) associated with the second driving electrode assembly (188) along the other one of the second and third axes, the Coriolis-induced, rocking motion along the other one of the second and third axes being indicative of an angular rate about the first axis.

4. The MEMS motion sensor (10) according to claim 3, wherein the out-of-plane and in-plane drive frequencies each range from 1 to 100 kilohertz, and wherein each of the first, second and third sensing electrode assemblies are configured to sense the motion of the one or more proof masses (17a to 17e) associated therewith at an acceleration sensing frequency that is less than between about 30 percent and 50 percent of both the out-of-plane and in-plane drive frequencies.

5. The MEMS motion sensor (10) according to claim 3 or 4, wherein the cavity 31 of each mass associated with at least one of the first and second driving electrode assemblies (187, 188) is a hermetically sealed vacuum cavity.

6. The MEMS motion sensor (10) according to any one of claims 3 to 5, wherein the plurality of proof masses (17a to 17e) consists of two proof masses (17a, 17b) configured as follows:

a first proof mass (17a) associated with the first driving electrode assembly (187) and the first, second, third, fourth and fifth sensing electrode assemblies (181 to 185); and

a second proof mass (17b) associated with the second driving electrode assembly (188) and the sixth sensing electrode assembly (186).

7. The MEMS motion sensor (10) according to any one of claims 3 to 5, wherein the plurality of proof masses (17a to 17e) consists of three proof masses (17a to 17c) configured as follows:

a first proof mass (17a) associated with the first driving electrode assembly (187) and the fourth and fifth sensing electrode assemblies (184, 185);

a second proof mass (17b) associated with the second driving electrode assembly (188) and the sixth sensing electrode assembly (186); and

a third proof mass (17c) associated with the first, second and third sensing electrode assemblies (181 to 183).

8. The MEMS motion sensor (10) according to any one of claims 3 to 5, wherein the plurality of proof masses (17a to 17e) consists of four proof masses (17a to 17d) configured as follows:

first and second proof masses (17a, 17b) both associated with the first driving electrode assembly (187) and the fourth and fifth sensing electrode assemblies (184, 185); and

third and fourth proof masses (17c, 17d) both associated with the second driving electrode assembly (188) and the sixth sensing electrode assembly (186), at least one of the four proof masses (17a to 17d) being further associated with the first, second and third sensing electrode assemblies (181 to 183).

9. The MEMS motion sensor (10) according to any one of claims 3 to 5, wherein the plurality of proof masses (17a to 17e) consists of five proof masses (17a to 17e) configured as follows:

first and second proof masses (17a, 17b) both associated with the first driving electrode assembly (187) and the fourth and fifth sensing electrode assemblies (184, 185); and

third and fourth proof masses (17c, 17d) both associated with the second driving electrode assembly (188) and the sixth sensing electrode assembly (186); and

a fifth proof mass (17e) associated with the first, second and third sensing electrode assemblies (181 to 183).

10. The MEMS motion sensor (10) according to claim 9, wherein the five proof masses (17a to 17e) are arranged in a common plane encompassing the second and third axes, the fifth proof mass (17e) being located centrally and surrounded by the first, second, third and fourth proof masses (17a to 17d).

11. The MEMS motion sensor (10) according to claim 9 or 10, wherein the first driving electrode assembly (187) is configured to drive the first proof mass (17a) 180 degrees out-of-phase relative to the second proof mass (17b), and wherein the second driving electrode assembly (188) is configured to drive the third proof (17c) mass 180 degrees out-of-phase relative to the fourth proof mass (17d).

12. The MEMS motion sensor (10) according to any one of claims 9 to 11, wherein:

the fourth sensing electrode assembly (184) is configured to form first and second capacitors with the first and second proof masses (17a, 17b), respectively, and to measure a difference between a capacitance of the first capacitor and a capacitance of the second capacitor, said difference being indicative of an angular rate of the first and second proof masses (17a, 17b) about the second axis;

the fifth sensing electrode assembly (185) is configured to form third and fourth capacitors with the first and second proof masses (17a, 17b), respectively, and to measure a difference between a capacitance of the third capacitor and a capacitance of the fourth capacitor, said difference being indicative of an angular rate of the first and second proof masses (17a, 17b) about the third axis; and

the sixth sensing electrode assembly (186) is configured to form fifth and sixth capacitors with the third and fourth proof masses (17c, 17d), respectively, and to measure a difference between a capacitance of the fifth capacitor and a capacitance of the sixth capacitor, said difference being indicative of an angular rate of the third and fourth proof masses (17c, 17d) about the first axis.

13. The MEMS motion sensor (10) according to any one of claims 9 to 12, wherein:

the first driving electrode assembly (187) comprises;

a pair of top driving electrodes (13e, 13f), one (13e) of which being located above a central region (171) of the first proof mass (17a) and the other (13f) being located above a central region (171) of the second proof mass (17b); and

a pair of bottom driving electrodes (15e, 15f), one (15e) of which being located below the central region (171) of the first proof mass (17a) and the other (15f) being located below the central region (171) of the second proof mass (17b);

the fourth sensing electrode assembly (184) comprises;

a first pair of top sensing electrodes (13g, 13h) disposed along a line parallel to the third axis, on opposite sides of the top driving electrode (13e) located above the central region (171) of the first proof mass (17a);

a second pair of top sensing electrodes (13i, 13j) disposed along a line parallel to the third axis, on opposite sides of the top driving electrode (13f) located above the central region (171) of the second proof mass (17b);

a first pair of bottom sensing electrodes (15g, 15h) disposed along a line parallel to the third axis, on opposite sides of the bottom driving electrode (15e) located below the central region (171) of the first proof mass (17a); and

a second pair of bottom sensing electrodes (15i, 15j) disposed along a line parallel to the third axis, on opposite sides of the bottom driving electrode (15f) located below the central region (171) of the second proof mass (17b); and

the fifth sensing electrode assembly (185) comprises;

a first pair of top sensing electrodes (13k, 13l) disposed along a line parallel to the second axis, on opposite sides of the top driving electrode (13e) located above the central region (171) of the first proof mass (17a);

a second pair of top sensing electrodes (13m, 13n), disposed along a line parallel to the second axis, on opposite sides of the top driving electrode located (13f) above the central region (171) of the second proof mass (17b);

a first pair of bottom sensing electrodes (15k, 15l) disposed along a line parallel to the second axis, on opposite sides of the bottom driving electrode (15e) located below the central region (171) of the first proof mass (17a); and

a second pair of bottom sensing electrodes (15m, 15n) disposed along a line parallel to the second axis, on opposite sides of the bottom driving electrode (15f) located below the central region (171) of the second proof mass (17b).

14. The MEMS motion sensor (10) according to any one of claims 9 to 13, wherein:

the second driving electrode assembly (188) comprises;

a first pair of top driving electrodes (13o, 13p) disposed along a line parallel to the one of the second and third axes, above and laterally offset with respect to a central region (171) of the third proof mass (17c);

a second pair of top driving electrodes (13q, 13r) disposed along a line parallel to the one of the second and third axes, above and laterally offset with respect to a central region (171) of the fourth proof mass (17d);

a first pair of bottom driving electrodes (15o, 15p) disposed along a line parallel to the one of the second and third axes, below and laterally offset with respect to the central region (171) of the third proof mass (17c); and

a second pair of bottom driving electrodes (15q, 15r) disposed along a line parallel to the one of the second and third axes, below and laterally offset with respect to the central region (171) of the fourth proof mass (17d); and

the sixth sensing electrode assembly (186) comprises;

a first pair of top sensing electrodes (13s, 13t) disposed along a line parallel to the other one of the second and third axes, above and laterally offset with respect to a central region (171) of the third proof mass (17c);

a second pair of top sensing electrodes (13u, 13v) disposed along a line parallel to the other one of the second and third axes, above and offset with respect to a central region (171) of the fourth proof mass (17d);

a first pair of bottom sensing electrodes (15s, 15t) disposed along a line parallel to the other one of the second and third axes, below and laterally offset with respect to a central region (171) of the third proof mass (17c); and

a second pair of bottom sensing electrodes (15u, 15v) disposed along a line parallel to the other one of the second and third axes, below and offset with respect to a central region (171) of the fourth proof mass (17d).

15. The MEMS motion sensor (10) according to any one of claims 1 to 14, wherein each proof mass (17a to 17e) and corresponding spring assembly (27a to 27e) form a resonant structure (54) configured to provided matched or near-matched resonance conditions for angular rate measurements.

16. The MEMS motion sensor (10) according to any one of claims 1 to 15, wherein the top cap wafer (12), bottom cap wafer (14) and MEMS wafer (16) are each made of a silicon-based semiconductor.

17. The MEMS motion sensor (10) according to claim 16, wherein the MEMS wafer (16) is a silicon-on-insulator (SOI) wafer including a device layer (20), a handle layer (22) under and spaced from the device layer (20), and an insulating layer (24) sandwiched between the device and handle layers (20, 22).

18. The MEMS motion sensor (10) according to any one of claims 1 to 17, wherein:

the proof masses (17a to 17e) each have a thickness and a polygonal cross-section respectively along and perpendicular to the first axis; and

the spring assemblies (27a to 27e) each comprise flexible springs (270) mechanically connecting the corresponding proof mass to the frame structure (50), the flexible springs (270) each having a thickness along the first axis that is significantly less than the thickness of the corresponding proof mass (17a to 17e).

19. The MEMS motion sensor (10) according to claim 18, wherein the thickness of each of the plurality of proof masses (17a to 17e) ranges from 10 to 1000 micrometers.

20. A MEMS motion sensor system architecture comprising:

a MEMS motion sensor (10) according to any one of claims 1 to 20; and

an integrated circuit (IC) wafer (77) bonded to the top cap wafer (12) of the MEMS motion sensor (10), the IC wafer (77) having circuitry electrically connected to the MEMS motion sensor (10).

21. The MEMS motion sensor system architecture according to claim 20, wherein the circuitry of the IC wafer (77) is electrically connected to the first and second sets of electrical contacts (42a, 42b) of the MEMS motion sensor (10) for routing signals to and from the top and bottom electrodes (13, 15).

22. A method of measuring acceleration and angular rate along mutually orthogonal first, second and third axes, the method comprising:

(a) providing a MEMS motion sensor (10) comprising a MEMS wafer (16) having opposed top and bottom sides (161, 162) and comprising a frame structure (50), a plurality of proof masses (17a to 17e), and a plurality of spring assemblies (27a to 27e) each suspending a corresponding one of the proof masses (17a to 17e) from the frame structure (50) and enabling the corresponding one of the proof masses (17a to 17e) to move along the first, second and third axes, and top and bottom cap wafers (12, 14) respectively bonded to the top and bottom sides (161, 162) of the MEMS wafer (16), the top cap, bottom cap and MEMS wafer (12, 14, 16) being electrically conductive, the top cap wafer (12), bottom cap wafer (14) and frame structure (50) together defining one or more cavities (31) each enclosing one or more of the plurality of proof masses (17a to 17e), each proof mass (17a to 17e) being enclosed in one of the one or more cavities (31);

(b) vibrating one or more of the proof masses (17a to 17e) along the first axis at an out-of-plane drive frequency;

(c) sensing Coriolis-induced, rocking motions along the third and second axes of the one or more proof masses (17a to 17e) driven along the first axis, in response to an angular rate about the second and third axes, respectively;

(d) vibrating one or more of the proof masses (17a to 17e) in a rocking motion along one of the second and third axes at an in-plane drive frequency;

(e) sensing a Coriolis-induced, rocking motion along the other one of the second and third axes of the one or more proof masses (17a to 17e) driven along the one of the second and third axes, in response to an angular rate about the first axis; and

(f) sensing a translational motion along the first axis, a rotation about the second axis, and a rotation about the third axis of one of the proof masses (17a to 17e), indicative of linear accelerations along the first, third and second axes, respectively.

23. The method according to claim 22, wherein the plurality of proof masses consists of five proof masses (17a to 17e), and wherein:

step (b) comprises vibrating first and second ones of the five proof masses (17a to 17e) along the first axis at the out-of-plane drive frequency;

step (c) comprises sensing Coriolis-induced, rocking motions along the third and second axes of the first and second proof masses (17a, 17b), in response to an angular rate of the first and second proof masses (17a, 17b) about the second and third axes, respectively;

step (d) comprises vibrating third and fourth ones of the five proof masses (17a to 17e) in a rocking motion along the one of the second and third axes at the in-plane drive frequency;

step (e) comprises sensing a Coriolis-induced, rocking motion along the other one of the second and third axes of the third and fourth proof masses (17c, 17d), in response to an angular rate of the third and fourth proof masses (17c, 17d) about the first axis; and

step (f) comprises sensing a translational motion along the first axis, a rotation about the second axis, and a rotation about the third axis of a fifth one of the five proof masses (17a to 17e), indicative of linear accelerations along the first, third and second axes of the fifth proof mass (17e), respectively.

24. The method according to claim 23, wherein step (b) comprises vibrating the first and second proof masses (17a, 17b) 180 degrees out-of-phase with each other

25. The method according to claim 24, wherein step (c) comprises:

forming first and third capacitors with the first proof mass (17a), and second and fourth capacitors with the second proof mass (17b);

measuring a difference between a capacitance of the first capacitor and a capacitance of the second capacitor, said difference being indicative of the angular rate of the first and second proof masses (17a, 17b) about the second axis; and

measuring a difference between a capacitance of the third capacitor and a capacitance of the fourth capacitor, said difference being indicative of the angular rate of the first and second proof masses (17a, 17b) about the third axis.

26. The method according to any one of claims 23 to 25, wherein step (d) comprises vibrating the third and fourth proof masses (17c, 17d) 180 degrees out-of-phase with each other.

27. The method according to claim 26, wherein step (e) comprises:

forming fifth and sixth capacitors respectively with the third and fourth proof masses (17c, 17d);

measuring a difference between a capacitance of the fifth capacitor and a capacitance of the sixth capacitor, said difference being indicative of the angular rate of the third and fourth proof masses (17c, 17d) about the first axis.

28. The method according to any one of claims 23 to 27, wherein step (f) comprises sensing the translational motion along the first axis, the rotation about the second axis, and the rotation about the third axis of the fifth proof mass (17e) at respective acceleration sensing frequencies that are each less than between 30 percent and 50 percent of both the out-of-plane and in-plane drive frequencies.