Piezoelectric thin film resonator and filter
A piezoelectric thin film resonator includes: a substrate; a piezoelectric film located on the substrate; a lower electrode and an upper electrode located to sandwich the piezoelectric film; a load film formed from patterns in a resonance region in which the lower electrode and the upper electrode face each other across the piezoelectric film, wherein the patterns are formed so as to surround a center of the resonance region and intersect with a pathway extending from the center to an outer periphery of the resonance region.
1. A piezoelectric thin film resonator comprising:
a substrate;
a piezoelectric film located on the substrate;
a lower electrode and an upper electrode located to sandwich the piezoelectric film;
a load film formed of a plurality of separate patterns in a resonance region in which the lower electrode and the upper electrode face each other across the piezoelectric film, the resonance region being defined by a region in a plan view where all of the lower electrode, the upper electrode, and the piezoelectric film overlap with each other,
wherein each of the plurality of separate patterns is formed so as to surround a center of the resonance region, and each of the plurality of separate patterns is disposed to intersect with a same virtual straight line extending from the center of the resonance region to an outside of the resonance region.
2. The piezoelectric thin film resonator according to claim 1 , wherein
each of the plurality of separate patterns is a closed round or rectangular loop surrounding the center.
3. The piezoelectric thin film resonator according to claim 2 , wherein
each of the plurality of separate patterns has an approximately homothetic shape to an outer shape of the resonance region.
4. The piezoelectric thin film resonator according claim 1 , wherein
the plurality of separate patterns intersect with the same virtual straight line at fixed intervals.
5. The piezoelectric thin film resonator according to claim 1 , wherein
the resonance region is symmetric with respect to the center.
6. The piezoelectric thin film resonator according to claim 1 , wherein
the load film is formed on the upper electrode.
7. The piezoelectric thin film resonator according to claim 1 , wherein
an air-space is formed between the substrate and the lower electrode in the resonance region.
8. The piezoelectric thin film resonator according to claim 1 , further comprising:
an acoustic reflection film that reflects an acoustic wave propagating through the piezoelectric film under the lower electrode in the resonance region.
9. A filter comprising:
the piezoelectric thin film resonator according to claim 1 .
10. The filter according to claim 9 , further comprising:
one or more series resonators and one or more parallel resonators,
wherein at least one of the series resonators is the piezoelectric thin film resonator.