Highly sensitive MEMS magnetic field sensors with integrated powder-based permanent magnets

Magnetic field sensors provide a convenient way for electrical current sensing without invading the electrical circuit. MEMS sensors are especially attractive due to miniaturization and precision in high volume fabrication. In this work MEMS magnetic field sensors based on piezoelectric resonators excited by the interaction of integrated permanent magnets are studied. Sensors are fabricated utilizing recent advances in fabrication processes to fully integrate volumetric permanent magnets in MEMS structures. The fabricated sensors show exceptionally high sensitivities of 34.6-43.4 kV/T in resonance at frequencies of 2.2 kHz and 3.6 kHz. The chosen fabrication process results in resonators of high quality factor of 1700-1900 operated in ambient air. The limit of detection of the sensors is with 7.2 pT/Hz0.5-8.5 pT/Hz0.5 the lowest reported so far for resonant magnetic field sensors fabricated with fully back end of line compatible MEMS processes. A better performance of cantilever structures excited by torque in a homogeneous magnetic field rather than excitation by force in a magnetic field gradient is predicted for cantilever lengths shorter than times the distance between sensor and conductor.