MEMS Magnetic Sensor with Bridge-Type Resonator and Magnetostrictive Thin Film

Abstract

This paper reports on fabrication and characterization of resonant-type mechanical MEMS magnetic sensors using magnetostrictive FePd sputtered film. The sensor has a thin Si resonator bridge with a PZT piezoelectric thin film element for excitation. The resonator is pulled by other bridges with the FePd film when magnetic flux is applied. The sensor was fabricated from an SOI wafer by sol-gel PZT deposition, FePd sputtering, and Si etching processes. The completed sensor showed a resonant peak with a Q factor of 229 at 26.39 kHz. When magnetic flux was applied along the microbridges, resonant frequency drastically decreased due to relaxation of initial deflection of the resonant bridge. Magnetic flux can be detected by resonant frequency change with a sensing resolution of 0.2 G per 0.1 Hz. When excitation frequency was fixed at slightly below the resonant frequency, amplitude of the bridge vibration slightly decreased with increasing magnetic flux in low magnetic flux region. High sensitive sensing of magnetic flux was difficult by the amplitude change. It was found that the magnetic sensor showed large thermal drift.