COMBINED MAGNETOMETER ACCELEROMETER MEMS DEVICES AND METHODS

• US 20160139173A1
• Filed: 11/17/2015
• Published: 05/19/2016
• Est. Priority Date: 11/17/2014
• Status: Active Grant

• Current Assignee: McGill University
• Original Assignee: Frederic Nabki, Mourad El-Gamal
• Inventors: Elsayed, Mohannad, El-Gamal, Mourad, Cicek, Paul-Vahe, Nabki, Frederic
• Granted Patent: US 10,197,590 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: B81B 2201/0221 Variable capacitors
• CPC Class Codes: B81B 2201/0235 Accelerometers
• CPC Class Codes: B81B 2201/0292 Sensors not provided for in B81B2201/0207 - B81B2201/0285
• CPC Class Codes: B81B 2203/0109 Bridges
• CPC Class Codes: B81B 2203/0307 Anchors
• CPC Class Codes: B81B 3/0021 Transducers for transforming electrical into mechanical energy or vice versa dynamo-electric machines H02K99/00; electrostatic machines H02N1/00; piezoelectric devices H10N30/00
• CPC Class Codes: B81B 7/008 MEMS characterised by an electronic circuit specially adapted for controlling or driving the same B81B7/0087 takes precedence; arrangements for starting, regulating, braking, or otherwise controlling an actuator H02N; control arrangements or circuits for visual indicators G09G3/00
• CPC Class Codes: B81C 1/00015 for manufacturing microsystems
• CPC Class Codes: B81C 2203/0735 Post-CMOS, i.e. forming the micromechanical structure after the CMOS circuit
• CPC Class Codes: B81C 2203/0771 Stacking the electronic processing unit and the micromechanical structure
• 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
• CPC Class Codes: G01R 33/0286 comprising microelectromechanical systems [MEMS] MEMS devices in general B81B

Abstract

Considerations for selecting capacitive sensors include accuracy, repeatability, long-term stability, ease of calibration, resistance to chemical and physical contaminants, size, packaging, integration options with other sensors and/or electronics, and cost effectiveness. It is beneficial if such sensors are amenable to above-IC integration with associated control/readout circuitry for reduced parasitics and reduced footprint through area sharing. The inventors have established a combined Lorentz force based magnetometer and accelerometer MEMS sensor exploiting a low temperature, above-IC-compatible fabrication process operating without requiring vacuum packaging. By switching an electrical current between two perpendicular directions on the device structure a 2D in-plane magnetic field measurement can be achieved whilst concurrently, the device serves as a 1D accelerometer for out-of-plane acceleration, by switching the current off and by monitoring the structure'"'"'s capacitive change in response to acceleration. The design can thus separate magnetic and inertial force measurements, utilizing a single compact device.

Claims

1. A microelectromechanical (MEMS) device comprising:

a structural member;

a plurality of supports suspending the structural member above a bottom electrode; and

a plurality of top electrical contacts, each top electrical contact associated with a support;

wherein

the structural member acts as a current carrying element for a magnetometer; and

the structural member acts as a proof mass for an accelerometer supporting concurrent use as a magnetometer and an accelerometer with the same structural MEMS element.

2. The MEMS device according to claim 1, wherein

the plurality of top electrical contacts provide for:

an electrical current to be driven along a first axis within the plane of the structural member; and

an electrical current to be driven along a second axis within the plane of the structural member perpendicular to the first axis; and

the bottom electrode allows for capacitance of a capacitor formed between the bottom electrode and suspended structural member.

3. The MEMS device according to claim 1, wherein

the plurality of top electrical contacts provide for:

a first electrical current to be driven along a first axis within the plane of the structural member via the plurality of top electrical contacts such that displacement of the structural element as a result of a Lorentz force due to any magnetic field along a second axis within the plane of the structural member perpendicular to the first axis can be detected via the bottom electrode; and

a second electrical current to be driven along the second axis via the plurality of top electrical contacts such that displacement of the structural element as a result of a Lorentz force due to any magnetic field along the first axis can be detected via the bottom electrode;

wherein

the bottom electrode provides for the capacitance determinations if either the first electrical current and second electrical current and for capacitance determination when neither of the first electrical current and second electrical current are being driven to determine any motion to inertial force along a third axis mutually perpendicular to both the first axis and the second axis.

4. The MEMS device according to claim 1, wherein

at least one of electrical control and electrical drive signals to the MEMS device are varied according to a predetermined sequence in order to provide a series of measurements allowing at least one of magnetic field and acceleration data to be generated and the effect of acceleration on the magnetic field measurements to be removed.

5. The MEMS device according to claim 1 wherein,

the MEMS device operates as a magnetometer in at least one of a single dimension, two dimensions, and three dimensions.

6. The MEMS device according to claim 1 wherein,

the MEMS device operates as an accelerometer in at least one of a single dimension, two dimensions, and three dimensions.

7. A microelectromechanical (MEMS) device comprising:

a lower electrode on a substrate having a first electrical contact; and

a diaphragm suspended above the substrate and lower electrode and supported by four beams each ending in a discrete electrical contact with a first pair of beams along a first edge of the diaphragm and a second pair of beams along a second opposite side edge of the diaphragm;

wherein

the first and second pairs of beams allow the diaphragm to move relative to the substrate during at least one of;

a first mode of operation absent applying a current to any of the four beams wherein capacitance variations between the diaphragm and lower electrode are determined arising from acceleration of the MEMS device perpendicular to the diaphragm;

a second mode of operation comprising applying a current to the first pair of beams wherein capacitance variations between the diaphragm and lower electrode are determined arising from at least one of acceleration of the MEMS device perpendicular to the diaphragm and a magnetic field in the plane of the diaphragm in first direction; and

a third mode of operation comprising applying a current to a first beam of the first pair of beams and a second beam of the second pair of beams wherein first beam of the first pair of beams and the second beam of the second pair of beams are disposed on the same side of the diaphragm and capacitance variations between the diaphragm and lower electrode are determined arising from at least one of acceleration of the MEMS device perpendicular to the diaphragm and a magnetic field in the plane of the diaphragm in a second direction.

8. The MEMS device according to claim 7, wherein

the manufacturing process for the MEMS device limits the maximum temperature of a CMOS electronic circuit formed within a substrate upon which the MEMS device is manufactured to one of 200°

C., 250°

C., 300°

C., and 350°

C.; and

the structural MEMS element is formed from a material selected from the group comprising silicon, silicon dioxide, silicon nitride, silicon oxynitride, carbon, aluminum oxide, silicon carbide and a ceramic.

9. The MEMS device according to claim 7, wherein

the MEMS device is at least one of fabricated above a Complementary Metal Oxide Semiconductor (CMOS) electronic circuit and fabricated upon a substrate with integrated CMOS electronics after the CMOS electronics has been fabricated.