MEMS In-Plane Resonators

• US 20120112765A1
• Filed: 08/10/2010
• Published: 05/10/2012
• Est. Priority Date: 08/13/2009
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Sparks, Andrew, Bhagavat, Milind
• Granted Patent: US 8,593,155 B2
• Time in Patent Office: Days
• US Class Current: 324/633
• CPC Class Codes: G01N 2291/014 Resonance or resonant frequency
• CPC Class Codes: G01N 2291/0256 Adsorption, desorption, surface mass change, e.g. on biosensors
• CPC Class Codes: G01N 2291/0422 Shear waves, transverse waves, horizontally polarised waves
• 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 2009/02511 Vertical, i.e. perpendicular to the substrate plane
• CPC Class Codes: H03H 9/1057 for microelectro-mechanical devices
• CPC Class Codes: H03H 9/2463 Clamped-clamped beam resonators

Abstract

MEMS in-plane resonators include a substrate wafer, at least one resonant mass supported by the substrate wafer and configured to resonate substantially in-plane, and at least one transducer coupled to the at least one resonant mass for at least one of driving and sensing in-plane movement of the at least one resonant mass, wherein at least part of one surface of the resonant mass is configured for exposure to an external environment and wherein the at least one transducer is isolated from the external environment. Such MEMS in-plane resonators may be fabricated using conventional surface micromachining techniques and high-volume wafer fabrication processes and may be configured for liquid applications (e.g., viscometry, densitometry, chemical/biological sensing), gas sensing (e.g., where a polymer film is added to the sensor surface, further degrading the damping performance), or other applications.

Claims

1. A MEMS sensor comprising:

a substrate wafer;

at least one resonant mass supported by the substrate wafer and configured to resonate substantially in-plane; and

at least one transducer coupled to the at least one resonant mass for at least one of driving and sensing in-plane movement of the at least one resonant mass, wherein at least part of one surface of the resonant mass is configured for exposure to an external environment and wherein the at least one transducer is isolated from the external environment.

2. A MEMS sensor according to claim 1, wherein the at least one transducer is at least partially contained within an isolated cavity formed at least in part by the at least one resonant mass and the substrate wafer.

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

4. A MEMS sensor according to claim 3, further comprising a hermetic seal at an interface between the resonator cap and the substrate wafer.

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 at least part of a top side of the resonant mass is configured for exposure to the external environment and wherein a bottom side of the resonant mass includes at least one protrusion configured to interoperate with the at least one transducer for at least one of driving and sensing in-plane movement of the resonant mass.

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 at least one resonant mass is movably coupled by a suspension.

10. A MEMS sensor according to claim 9, wherein the suspension includes at least one of:

a spring;

a spring having a top side notch filled with an elastic material; and

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 surface of at least one resonant mass 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 surface of at least one resonant mass 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 at least one 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, wherein the at least one resonant mass includes a plurality of resonant masses.

19. A MEMS sensor according to claim 18, wherein at least one of:

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

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

the resonant masses are mechanically coupled.

20. A MEMS sensor according to claim 1, further comprising at least one transducer coupled to the at least one resonant mass for at least one of driving and sensing out-of-plane movements of the at least one resonant mass.

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

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

23. Apparatus according to claim 22, 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;

at least two sensors are mechanically coupled; and

at least two sensors are electrically coupled.

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

forming at least one resonant mass supported by a substrate wafer and configured to resonate substantially in-plane; and

forming at least one transducer coupled to the at least one resonant mass for at least one of driving and sensing in-plane movement of the at least one resonant mass, wherein at least one surface the resonant mass is configured for exposure to an external environment and wherein the at least one transducer is isolated from the external environment.