Microelectromechanical sensors based on magnetoresistance have been proposed. Like other microelectromechanical sensors, these would be used to measure physical quantities that can be made to manifest themselves in small mechanical displacements. Potential applications for microelectromechanical sensors include accelerometers, magnetometers, bolometers, pressure sensors, seismometers, Golay cells, and microphones. Potential markets include the aerospace, biomedical, semiconductor, automotive, and defense industries.

The Magnetoresistive Device would be used to measure the local strength of the magnetic field of the film. Because the magnetic-field strength would depend on the distance from the film, the measurement would indicate the displacement of the cantilever from the equilibrium position.
Similar microelectromechanical sensors based on quantum-mechanical tunneling of electrons at movable tips of diaphragms, cantilevers, and other flexible members have been developed, and have been reported in a number of previous articles in NASA Tech Briefs. The fabrication and electrical characterization of the tunneling-based sensors have proven to be difficult. Operation has proven to be difficult in that tunneling tips must be kept spaced about 1 nm apart; tips often crash together, with consequent damage, leading to rejection of parts.

The proposed sensors are expected to be less problematic, because they would be manufactured and operated by use of techniques that have become well established in the data-storage (computer-disk) industry. In a typical sensor of proposed type, a magnetoresistive device mounted on a diaphragm or near the free end of a cantilever in a magnetic-field gradient (see figure) would be used to measure the field strength and thus, indirectly, the distance from the source of the magnetic field. This distance would, in turn, be indicative of the displacement of the diaphragm or cantilever from an equilibrium distance. The magnetic field would be provided by a hard magnetic thin film attached to the relatively stationary portion of the device structure, facing the magnetoresistive device. The strength and gradient of the magnetic field would depend partly on the thickness of the film and partly on the distances between magnetic domains in the film.

Unlike in a tunneling-based sensor, it would not be necessary to maintain a distance of about 1 nm or less between tunneling tips; instead, the film thickness and thus the magnetic-field strength could be increased to enable the use of a greater equilibrium distance between the magnetoresistive device and the film, making the proposed sensor less vulnerable to damage. Also, inasmuch as techniques for measuring magnetic fields are well established in the data-recording industry, magnetic-field changes corresponding to subnanometer displacements could be measured accurately.

This work was done by John D. Olivas and Bruce Lairson of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp  under the Physical Sciences category.

This invention is owned by NASA, and a patent application has been filed. Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to

the Patent Counsel
NASA Management Office–JPL; (818) 354-4770.

Refer to NPO-20146.

This Brief includes a Technical Support Package (TSP).
Microelectromechanical Sensors Based on Magnetoresistance

(reference NPO-20146) is currently available for download from the TSP library.

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