A miniature vibrating cantilever magnetometer

This paper presents the preliminary work to demonstrate the feasibility of a miniature resonator based magnetometer. This magnetometer consists of a thin film of ferromagnetic material sputtered on a cantilever with a magnetic moment aligned along the length of the cantilever. As the resonator vibrates under a magnetic field, the magnetostatic interaction induces a torque on the cantilever that stiffens its spring constant thus shifting its resonance frequency. This principle of operation using a cobalt-nickel thin film and a quartz tuning fork allows developing a miniature (0.1mm²), low power (1mW), low cost, and precise (10nT) magnetometer, that machining technology is compatible with micromachined inertial MEMS sensor technology. It is targeted to be included in miniature IMUS with accelerometers and gyroscopes for guidance and navigation applications. First a theoretical model is presented to obtain analytical expressions of the scale factor and resolution of the sensor. Then the cobalt-nickel sputtering method is shown as well as the characterization of its magnetic moment under magnetic field for different film thicknesses and magnetization methods. The realized miniature quartz tuning forks on which are sputtered the magnetic thin films are presented and characterized, especially in terms of supplementary mechanical damping due to the thin film. Finally, sputtered resonators are connected to electronic oscillators to build magnetometer prototypes that are measured in terms of scale factor and resolution.