Amplitude detecting micromechanical resonating beam magnetometer

Abstract

A highly sensitive magnetometer is demonstrated using a resonant amplitude detection method in an integrated vacuum encapsulated resonant microbeam which has a very high quality factor (Q). The magnetic field is efficiently converted to mechanical vibrations of the high Q microbeam by using the Lorentz force between a beam current and the applied magnetic field. The mechanical vibration causes an optical modulation during the transmission of the light through the layers of the resonator. The modulated light produces an electronic output signal at an embedded photodiode just below the microbeam. The optical detection of the beam vibration allows a simple resonator structure and good output signal isolation from the input current leading to a less noisy output. Measured Q-values of the fabricated devices are above 50,000 with die yield exceeding 90%. Measured magnetic sensitivities near 55,000 V/ATesla are much higher than those reported for Hall effect devices.