Thin-film piezoelectric resonator and filter circuit

A thin-film piezoelectric resonator comprising:

• a substrate having a cavity which penetrates through from the principal surface to the bottom surface thereof;
• a lower electrode provided on the principal surface of the substrate so as to cover the cavity;
• a piezoelectric film provided on the lower electrode so as to be located above the cavity;
• and
• an upper electrode provided on the piezoelectric film, including;
• a main portion which overlaps a part of the cavity in a plan view,
• a protruding portion, which is connected to the main portion, a part of which overlaps the cavity and the remaining part thereof does not overlap the cavity but overlaps the lower electrode,
• an extension portion provided at the opposite side of the main portion from the protruding portion, and
• a connecting portion, which connects the main portion and the extension portion, provided so that at least a part thereof does not overlap the cavity but overlaps the lower electrode,
• the length of the protruding portion in a direction perpendicular to a direction of connecting to the main portion being substantially the same as the length of the connecting portion in a direction perpendicular to a direction of connecting to the main portion.