Ultra-sensitive magnetoresistive displacement sensing device

US6507187B1 · kind B1 · utility

Assignee

• The United States of America as represented by the Administrator of the National Aeronautics and Space Administration · US

Inventors

• John D. Olivas · Houston, US
• Bruce Lairson · Los Altos, US
• Rajeshuni Ramesham · Pasadena, US

Key dates

• Filing date: Aug 24, 1999
• Grant date: Jan 14, 2003
• Expiry date: Aug 24, 2019

Classification

• Technology area (CPC G): Physics
• CPC primary: G01P15/105
• WIPO field: Measurement
• WIPO sector: Instruments

Abstract

An ultrasensitive displacement sensing device for use in accelerometers, pressure gauges, temperature transducers, and the like, comprises a sputter deposited, multilayer, magnetoresistive field sensor with a variable electrical resistance based on an imposed magnetic field. The device detects displacement by sensing changes in the local magnetic field about the magnetoresistive field sensor caused by the displacement of a hard magnetic film on a movable microstructure. The microstructure, which may be a cantilever, membrane, bridge, or other microelement, moves under the influence of an acceleration a known displacement predicted by the configuration and materials selected, and the resulting change in the electrical resistance of the MR sensor can be used to calculate the displacement. Using a micromachining approach, very thin silicon and silicon nitride membranes are fabricated in one preferred embodiment by means of anisotropic etching of silicon wafers. Other approaches include reactive ion etching of silicon on insulator (SOI), or Low Pressure Chemical Vapor Deposition of silicon nitride films over silicon substrates. The device is found to be improved with the use of giant m…