Acoustic mirror type thin film bulk acoustic resonator, and filter, duplexer and communication apparatus comprising the same

A filter comprising two or more thin film bulk acoustic resonators which are connected in a ladder form, wherein

• at least one of the thin film bulk acoustic resonators comprises:
• a substrate;
• an acoustic mirror layer provided on the substrate, including a plurality of impedance layers alternately having a high acoustic impedance and a low acoustic impedance;
• and
• a piezoelectric thin film vibrator provided on the acoustic mirror layer, including a lower electrode, a piezoelectric thin film and an upper electrode,
• wherein the sum of a thickness of the lower electrode and a thickness of the upper electrode is 5% or more and 60% or less of a whole thickness of the piezoelectric thin film vibrator, and the thickness of the lower electrode is larger than the thickness of the upper electrode.

A duplexer comprising a transmission filter and a reception filter, wherein

• at least one of the transmission filter and the reception filter comprises two or more thin film bulk acoustic resonators which are connected in a ladder form, and
• at least one of the thin film bulk acoustic resonators comprises:
• a substrate;
• an acoustic mirror layer provided on the substrate, including a plurality of impedance layers alternately having a high acoustic impedance and a low acoustic impedance;
• and
• a piezoelectric thin film vibrator provided on the acoustic mirror layer, including a lower electrode, a piezoelectric thin film and an upper electrode,
• wherein the sum of a thickness of the lower electrode and a thickness of the upper electrode is 5% or more and 60% or less of a whole thickness of the piezoelectric thin film vibrator, and the thickness of the lower electrode is larger than the thickness of the upper electrode.

A communication apparatus comprising at least one thin film bulk acoustic resonator, wherein

• the at least one thin film bulk acoustic resonators comprises:
• a substrate;
• an acoustic mirror layer provided on the substrate, including a plurality of impedance layers alternately having a high acoustic impedance and a low acoustic impedance;
• and
• a piezoelectric thin film vibrator provided on the acoustic mirror layer, including a lower electrode, a piezoelectric thin film and an upper electrode,
• wherein the sum of a thickness of the lower electrode and a thickness of the upper electrode is 5% or more and 60% or less of a whole thickness of the piezoelectric thin film vibrator, and the thickness of the lower electrode is larger than the thickness of the upper electrode.