Nano-gap piezoelectric resonators for RF mechanical magnetic field modulation

Novel piezoelectric MEMS resonators with integrated magnetic flux guides have been developed to mechanically generate RF (30-60 MHz) magnetic fields from static magnetic fields. Submicron gaps between aluminum nitride (AlN) resonators covered with a thin film nickel iron (NiFe) magnetic shielding alloy allow a static magnetic field supplied below the resonator to leak into the space above. When the resonator plate moves, the flux intensity (B) in the surrounding area changes, and the magnetic field will vary with the frequency of the resonator. Design requirements of the resonator stack included high frequency operation and shielding alloy with a high permeability in thin film form.;To provide the magnetic flux guide, thermally evaporated thin film NiFe (10 to 20 was developed with a saturation flux density of 0.5 T, coercivity of 500 A/m and a high relative permeability of 3.7 x 103. The stoichiometry of 80% Ni and 20% Fe was chosen for high permeability and low magnetostriction effects and the magnetic properties achieved allow for a large range of static magnetic fields to be applied and for the film to shield the space above the resonators properly.;The aluminum nitride resonators developed for high frequency operation resonate in a contour mode to increase and decrease the gap surrounding the resonator. The 200 to 350 nm gaps are formed using a polysilicon sidewall deposition as a sacrificial spacer. Low temperature oxide is deposited and polished, using chemical mechanical polishing (CMP), to fill the space around the patterned aluminum nitride. The magnetic shielding alloy is incorporated without any additional lithographic steps and is deposited on released structures after a xenon difluoride etch removes both the polysilicon sidewall spacer and the silicon below the resonator.;Resonators with frequencies up to 60 MHz have been fabricated and tested with an atomic and magnetic force microscope (MFM). Dynamic MFM measurements show a shift in the magnetic field when the resonator is actuated. With a novel fabrication process, the development of thin film NiFe for magnetic shielding and evaluation of the resonators, this thesis represents an important step in the fundamental development of mechanical generation of RF magnetic fields.