Frequency-based magnetic field sensing using Lorentz force axial strain modulation in a double-ended tuning fork

Abstract

This paper presents a frequency-based silicon micromechanical resonant magnetic field sensor with a high quality factor by using a double-ended tuning fork (DETF). The sensing mechanism is based on the detection of resonant frequency shift of the DETF resonator due to the exertion of a Lorentz force generated under the presence of a magnetic field. By designing the strain-sensitive resonator as a DETF, we are able to achieve a quality factor (Q) of over 100,000 for the anti-phase mode. An analytical and finite element (FE) model describing the sensitivity of the magnetic field sensor is presented. Good agreement between the FE model and measurements is obtained, which are close to the analytical model estimates. Through more careful choice of the device physical dimensions, we show that the current sensitivity of 215.74ppm/T can be improved tenfold. Given this level of field sensitivity, we envisage that magnetic noise floor levels in the μT range are achievable using the device concepts described in this paper.