Method for fabricating single crystal piezoelectric RF resonators and filters with improved cavity definition

A method of fabricating an FBAR filter device comprising an array of resonators, each resonator comprising a single crystal piezoelectric film sandwiched between a first metal electrode and a second metal electrode, wherein the first metal electrode is supported by a support membrane over an air cavity, the air cavity embedded in a silicon dioxide layer over a silicon handle, with through-silicon via holes through the silicon handle and into the air cavity, said air cavity in the silicon dioxide layer having side walls defined by perimeter trenches that are resistant to a silicon dioxide etchant, comprising stages of:

• A. fabricating the support membrane over a silicon dioxide box on the silicon handle, having through support membrane filled barriers that traverse the silicon dioxide layer, and wherein the support membrane is coated with at least a first bonding layer of the first metal electrode coupled to the support membrane by a first adhesion layer;
• B. fabricating a piezoelectric film coupled to a detachable carrier substrate and coated with at least a second bonding layer of the first metal electrode coupled to the piezoelectric film by a second adhesion layer;
• C. bonding the support membrane to the piezoelectric film by bonding the the first and second bonding layers together to sandwich the first metal electrode between the piezoelectric film and the support membrane and creating a bonded structure having a support membrane side of the support membrane and a piezoelectric layer side of the piezoelectric film;
• D. fabricating an array of filters by processing the piezoelectric film coupled to the support membrane from the piezoelectric layer side by removing the detachable carrier substrate, trimming the piezoelectric film, the first metal electrode and an exposed surface of the support membrane, surrounding the piezoelectric film with a passivation material and coating with the second metal electrode, and building up base sections of seal rings and contact stacks;
• E. fabricating an array of lids having an outer surface and an inner surface, with external terminations on the outer surface and upper sections of the seal rings and contact stacks on the inner surface, such that the external terminations are coupled to the contact stacks by through lid vias, and fabricating upper sections of the seal rings and contact stacks for coupling to the base sections of the seal rings and contact stacks by another bonding layer;
• F. attaching the array of filters to the array of lids by coupling the base sections of the seal rings and contact stacks to the upper sections of the seal rings and contact stacks with the another bonding layer;
• G. thinning the silicon handle, drilling holes through the thinned silicon handle to the silicon dioxide layer, and etching away silicon dioxide of the silicon dioxide layer;
• and
• H. dicing the array of filters into individual filters.