MEMS Sensors with Closed Nodal Anchors for Operation in an In-Plane Contour Mode

• US 20120195797A1
• Filed: 01/31/2011
• Published: 08/02/2012
• Est. Priority Date: 01/31/2011
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Sparks, Andrew, Sawyer, William D.
• Granted Patent: US 9,039,976 B2
• Time in Patent Office: Days
• US Class Current: 422/69
• CPC Class Codes: G01N 2291/02818 Density, viscosity
• CPC Class Codes: G01N 2291/0427 Flexural waves, plate waves, e.g. Lamb waves, tuning fork, cantilever
• CPC Class Codes: G01N 29/022 Fluid sensors based on microsensors, e.g. quartz crystal-microbalance [QCM], surface acoustic wave [SAW] devices, tuning forks, cantilevers, flexural plate wave [FPW] devices microdevices per se B81B
• CPC Class Codes: G01N 29/036 by measuring frequency or resonance of acoustic waves
• CPC Class Codes: H03H 2009/02503 Breath-like, e.g. Lam? mode, wine-glass mode
• CPC Class Codes: H03H 9/1057 for microelectro-mechanical devices
• CPC Class Codes: Y10T 29/49007 Indicating transducer

Abstract

A MEMS sensor includes at least one closed nodal anchor along a predetermined closed nodal path on at least one surface of a resonant mass. The resonant mass may be configured to resonate substantially in an in-plane contour mode. Drive and/or sense electrodes may be disposed within a cavity formed at least in part by the resonant mass, the closed nodal anchor, and a substrate.

Claims

1. A MEMS sensor comprising:

a substrate;

a resonant mass configured to resonate in an in-plane contour mode;

a first closed nodal anchor connecting the resonant mass to the substrate along a first predetermined closed nodal path on a first surface of the resonant mass; and

at least one transducer in communication with the first resonant mass for at least one of driving and sensing in-plane movement of the resonant mass, wherein at least a portion of the first surface of the resonant mass is configured for exposure to an external environment.

2. A MEMS sensor according to claim 1, wherein the at least one transducer is at least partially contained within a cavity formed at least in part by the resonant mass, the substrate, and the first closed nodal anchor.

3. A MEMS sensor according to claim 1, further comprising:

a second closed nodal anchor connecting the resonant mass to the substrate along a second predetermined closed nodal path on a second surface of the resonant mass opposite the first surface.

4. A MEMS sensor according to claim 2, wherein the resonant mass is part of a cap that is attached to a substrate wafer to form thereby an isolated cavity within which the at least one transducer is at least partially contained.

5. A MEMS sensor according to claim 1, wherein the resonant mass is movably coupled to the at least one transducer via an elastic material, and wherein portions of the at least one transducer that would otherwise be exposed to the external environment are covered with at least one material to isolate those portions from the external environment.

6. A MEMS sensor according to claim 1, wherein the at least one transducer includes at least one drive transducer and at least one sense transducer, wherein the at least one drive transducer is operatively coupled to a side edge of the resonant mass and the at least one sense transducer is operatively coupled to a bottom surface of the resonant mass, the transducers isolated from the external environment.

7. A MEMS sensor according to claim 1, further comprising:

a set of shield structures on the substrate wafer.

8. A MEMS sensor according to claim 1, further comprising circuitry configured to apply a predetermined electrical potential to at least one outer conductive surface exposed to the external environment.

9. A MEMS sensor according to claim 1, wherein the resonant mass is movably coupled by a suspension.

10. A MEMS sensor according to claim 9, wherein the suspension includes an elastic plug.

11. A MEMS sensor according to claim 2, wherein the cavity is partially or completely evacuated.

12. A MEMS sensor according to claim 1, wherein the at least one transducer includes one of:

a capacitively-coupled transducer; and

a piezoelectrically-coupled transducer.

13. A MEMS sensor according to claim 1, wherein the portion of the first surface configured for exposure to the external environment is at least partially covered by a material meant to interact with a specific type of target in the external environment, such interaction changing the moving mass of the resonant mass so as to change the resonance frequency of the resonant mass, the sensor further including circuitry configured to detect a change in resonance frequency resulting from such interaction.

14. A MEMS sensor according to claim 13, wherein the material includes one of:

an adhesive material to which the target adheres;

a chemically or electrochemically active material;

a hydrophilic material;

a receptor material to which a specific target binds; and

a material that dissolves or dissipates in the presence of the target so as to decrease the moving mass of the resonator and consequently increase the resonance frequency of the resonator.

15. A MEMS sensor according to claim 1, wherein the portion of the first surface configured for exposure to the external environment is at least partially covered by a material meant to reduce interactions with the external environment.

16. A MEMS sensor according to claim 1, further comprising circuitry configured to sense an electrical potential caused by interaction with the external environment.

17. A MEMS sensor according to claim 1, wherein the resonant mass includes raised and/or recessed features patterned or otherwise formed on of from the top surface of the resonant mass.

18. A MEMS sensor according to claim 1, further comprising at least one of a microfluidic network and sensors.

23. Apparatus comprising an array of a plurality of MEMS sensors according to claim 1.

24. Apparatus according to claim 23, wherein at least one of:

at least two sensors are of the same mechanical design;

at least two sensors are of different mechanical designs;

at least two sensors have the same functional coating;

at least two sensors have different functional coatings; and

at least two sensors are electrically coupled.

19. A MEMS sensor comprising:

a substrate;

a plurality of resonant masses, each resonant mass configured to resonate in an in-plane contour mode and including a first closed nodal anchor connecting the resonant mass to the substrate along a first predetermined closed nodal path on a first surface of the resonant mass; and

a plurality of transducers in communication with the resonant masses for at least one of driving and sensing in-plane movement of the resonant masses, wherein at least a portion of the first surface of each resonant mass is configured for exposure to an external environment.

20. A MEMS sensor according to claim 19, wherein the plurality of transducers are at least partially contained within a cavity formed at least in part by the resonant masses, the substrate, and the first closed nodal anchors.

21. A MEMS sensor according to claim 19, wherein each resonant mass further comprises a second closed nodal anchor connecting the resonant mass to the substrate along a second predetermined closed nodal path on a second surface of the resonant mass opposite the first surface.

22. A MEMS sensor according to claim 19, wherein at least one of:

the portions of the first surfaces configured for exposure to the external environment are at least partially coated with the same material;

the portions of the first surfaces configured for exposure to the external environment are at least partially coated with different materials; and

the resonant masses are mechanically coupled.

25. A method of fabricating a MEMS in-plane resonator comprising:

forming a resonant mass supported by a substrate and configured to resonate substantially in an in-plane contour mode;

forming a first closed nodal anchor connecting the resonant mass to the substrate along a first predetermined closed nodal path on a first surface of the resonant mass; and

forming at least one transducer in communication with the first resonant mass for at least one of driving and sensing in-plane movement of the resonant mass, wherein at least a portion of the first surface of the resonant mass is configured for exposure to an external environment.