Baw filters having different center frequencies on a single substrate and a method for providing same

Abstract

A method of fabricating a plurality of bulk acoustic wave (BAW) resonators on a single substrate, and the corresponding product, the BAW resonators having substantially different resonant frequencies, the method including the steps of: providing a substrate having an upper facing surface; depositing an isolation structure on the upper facing surface of the substrate; depositing a first metallic layer on the isolation structure, the first metallic layer serving as a bottom electrode; and depositing piezolayer material on the bottom electrode so as to have thicknesses corresponding to each of the different resonant frequencies, each different thickness located in a location where a resonator having a resonant frequency corresponding to the thickness is to be located. In one of several embodiments, the step of depositing piezolayer material on the bottom electrode itself includes the steps of: depositing piezolayer material to a thickness corresponding to the lowest frequency resonator; providing hard mask material over areas where the lowest frequency resonators are to be located; and removing the piezolayer material down to the thickness of the next higher frequency resonators. In some applications of the method, the isolation structure is an acoustic mirror, and the method further includes the step of providing the acoustic mirror, interposed between the substrate and the bottom electrode, according to a design that imparts to the acoustic mirror a desired reflection coefficient over a predetermined range of frequency including the substantially different resonant frequencies.