Magnetostrictive-based Quartz MEMS RF Sensors

AT-cut shear-mode UHF quartz MEMS resonators have been found to be highly sensitive to magnetic signals when magnetostrictive films are deposited on the top electrode surface. The induced voltages across the resonator plates due to applied external magnetic signals have been computed within a COMSOL 3D finite-element model. Optimal orientations of the internal magnetization and polarization of the external H fields relative to the quartz crystalline axes were determined. Self-consistent coupled strains induced in the magnetostrictive film from both the piezoelectric plate deformations and the external magnetic field were included. The theory of magnetostriction and the characterization of magnetostrictive curve of thin-film Ni (nickel) deposited on quartz resonator with the Ni film magnetized either prior or after deposition were discussed. The magnetostriction curve is an important determinant of the induced voltage across the quartz plate in external H fields. Both the responses of the AT-cut resonator without Ni coating and with Ni coating were simulated in this paper. The experimentally observed response of a 355-MHz AT-cut resonator to the electric component of external RF wave was reported. The electric response of magnetostrictive Ni coated AT-cut resonator dominated the magnetic response. The sensitivity of electric response was calculated to be 320 mV/Oe.