Support Structure for Bulk Acoustic Wave Resonator

A bulk acoustic resonator prepared by a process comprising the steps of:

• forming, on a substrate, a layer of sacrificial material;
• forming, in a perimeter around the sacrificial material, a cavity frame;
• forming, over the sacrificial material and the cavity frame, planarizing material, wherein the planarizing material forms a perimeter around the cavity frame;
• removing a portion of the planarizing material to form a planarized layer that includes the sacrificial material, the cavity frame, and the planarizing material, wherein, for an upper surface of the planarized layer that is opposite a lower surface of the planarized layer that is coupled to the substrate, a sacrificial material upper surface of the sacrificial material is substantially level with a cavity frame upper surface of the cavity frame and a planarization material upper surface of the planarization material;
• forming, over the planarized layer, a first electrode (bottom electrode);
• forming, over the first electrode, a piezoelectric film element;
• forming, over the piezoelectric film element, a second electrode (top electrode);
• and
• removing at least a portion of the sacrificial material to form a cavity.