Piezoelectric thin film resonator, filter, and communication apparatus

A piezoelectric thin film resonator comprising:

• a substrate having a flat surface;
• a lower electrode formed on the flat surface;
• a piezoelectric film formed on the substrate and the lower electrode;
• and
• an upper electrode formed on the piezoelectric film and having a main portion and an extended portion connected to the main portion, the main portion opposing the lower electrode and an opening disposed between the substrate and the lower electrode, the extended portion having a portion which opposes the opening and the substrate.

A filter comprising:

• a piezoelectric thin film resonator including:
• a substrate;
• a lower electrode formed on the substrate;
• a piezoelectric film formed on the substrate and the lower electrode;
• and
• an upper electrode formed on the piezoelectric film and having a main portion and an extended portion connected to the main portion, the main portion opposing the lower electrode and an opening disposed between the substrate and the lower electrode, the extended portion having a portion which opposes the opening and the substrate.

A communication module comprising:

• a filter including:
• a piezoelectric thin film resonator including:
• a substrate;
• a lower electrode formed on the substrate;
• a piezoelectric film formed on the substrate and the lower electrode;
• and
• an upper electrode formed on the piezoelectric film and having a main portion and an extended portion connected to the main portion, the main portion opposing the lower electrode and an opening disposed between the substrate and the lower electrode, the extended portion having a portion which opposes the opening and the substrate.

A communication apparatus comprising:

• a filter including:
• a piezoelectric thin film resonator including:
• a substrate;
• a lower electrode formed on the substrate;
• a piezoelectric film formed on the substrate and the lower electrode;
• and
• an upper electrode formed on the piezoelectric film and having a main portion and an extended portion connected to the main portion, the main portion opposing the lower electrode and an opening disposed between the substrate and the lower electrode, the extended portion having a portion which opposes the opening and the substrate.