MEMS Micro-Wire Magnetic Field Detection Method at CERN

Abstract

This paper reports a novel construction of a micromachined MEMS magnetometer characterized by static magnetic fields of CERN’s reference dipole with a custom made capacitive read-out. The magnetic flux density is characterized via the vibration modes of the MEMS structure, which are sensed capacitively. The device consists of a single-crystal silicon clamped-free plate (cantilever) carrying a thin conductor. The cantilever and the thin film metal electrodes are separated by a small gap, forming a vibrating plate capacitor. Movements of the cantilever are read out conveniently by electronic circuits. A static magnetic field generates a force density acting on the conductor that alternates according to the frequency of the current. When the electrical current is known, the deflection amplitude of the cantilever is a measure of the component of the magnetic flux density that points perpendicular to the current. The highest vibration amplitudes are expected, in the vicinity of resonance frequencies of the micromachined structure. At ambient pressure, the prototype sensor has a measured resonance frequency of 3.8 kHz for the fundamental mode and 20 kHz for the first antisymmetric mode. In experiments, the magnetic flux of the dipole has been characterized between 0.1 and 1 T, with a relative uncertainty of $3\times 10^{-4}$ .