Patent ID: 6496085
Filing Date: 2002-12-17
Classification: H03H,Y10T

Abstract:
A method of fabricating a multi-resonator bulk acoustic wave (BAW) filter having a plurality of layers of materials serving as an acoustic mirror for a plurality of resonator sections, each resonator section including at least a top electrode and a bottom electrode sandwiching a piezolayer, the method comprising the steps of:a) choosing dielectric materials for some of the layers of materials serving as the acoustic mirror and metallic materials for the others of the layers; and b) providing at least one of the metallic layers via a fabrication procedure in which the metallic layer is patterned into distinct portions by an etching process that removes enough of the metallic layer between where different resonator sections are to be placed as to provide electrical isolation between the portions of the layer beneath the different resonator sections; wherein step (b) comprises the steps of: i) depositing consecutively the different layers of the acoustic mirror, beginning with a metallic layer and continuing up to but not necessarily including the layer that is to be nearest the resonator, so that the dielectric layers alternate with the metallic layers; ii) etching through each of the at least one metallic layer, so as to leave on the substrate a pillbox-type structure of the at least one metallic layer, thereby providing at least one patterned metallic layer; and iii) depositing as a filler a dielectric material to replace the material removed by etching, the depositing being sufficient in depth to allow polishing the filler down to the top of the last deposited at least one patterned metallic layer; thereby providing a multi-resonator BAW filter with reduced capacitive coupling between resonators, compared to the capacitive coupling present in a multi-resonator BAW filter fashioned in a similar manner except excluding the step of etching to pattern at least one metallic layer of the similarly fashioned acoustic mirror.