Piezoelectric thin film resonator, filter, and multiplexer

A filter comprising:

• a piezoelectric thin film resonator including:
• a substrate;
• a piezoelectric film located on the substrate;
• a lower electrode and an upper electrode facing each other across at least a part of the piezoelectric film;
• a first insertion layer located between the lower electrode and the upper electrode and located in at least a part of an outer peripheral region within a resonance region in which the lower electrode and the upper electrode face each other across the piezoelectric film, the first insertion layer being not located in a center region of the resonance region;
• and
• a second insertion layer located between the lower electrode and the upper electrode and located in at least a part of the outer peripheral region within the resonance region, the second insertion layer being not located in the center region of the resonance region, a position of an edge of the second insertion layer in the resonance region being different from a position of an edge of the first insertion film in the resonance region.

A multiplexer comprising:

• a filter including a piezoelectric thin film resonator, wherein
• the piezoelectric thin film resonator includes:
• a substrate;
• a piezoelectric film located on the substrate;
• a lower electrode and an upper electrode facing each other across at least a part of the piezoelectric film;
• a first insertion layer located between the lower electrode and the upper electrode and located in at least a part of an outer peripheral region within a resonance region in which the lower electrode and the upper electrode face each other across the piezoelectric film, the first insertion layer being not located in a center region of the resonance region;
• and
• a second insertion layer located between the lower electrode and the upper electrode and located in at least a part of the outer peripheral region within the resonance region, the second insertion layer being not located in the center region of the resonance region, a position of an edge of the second insertion layer in the resonance region being different from a position of an edge of the first insertion film in the resonance region.