Piezoelectric thin film resonator and filter
A piezoelectric thin film resonator includes: a substrate; a lower electrode and an upper electrode located on the substrate; a piezoelectric film, at least a part of the piezoelectric film being sandwiched between the upper electrode and the lower electrode, the piezoelectric film including a discontinuous portion in which the piezoelectric film discontinues in at least a part of a region surrounding a center region that includes a center of a resonance region where the upper electrode and the lower electrode face each other across the at least a part of the piezoelectric film.
1. A piezoelectric thin film resonator comprising:
a substrate;
a lower electrode and an upper electrode located on the substrate; and
a piezoelectric film, at least a part of the piezoelectric film being sandwiched between the upper electrode and the lower electrode, the piezoelectric film including a discontinuous portion in which the piezoelectric film discontinues in at least a part of a region surrounding a center region that includes a center of a resonance region where the upper electrode and the lower electrode face each other across the at least a part of the piezoelectric film,
wherein the discontinuous portion is located from a tip of the lower electrode and is not located in a region other than the tip of the lower electrode among the region surrounding the center region,
wherein an air gap is located under the lower electrode, and
wherein the discontinuous portion is located in a region in which an edge portion of the lower electrode substantially coincides with an edge portion of the air gap.
2. The piezoelectric thin film resonator according to claim 1 , a cross-section of the discontinuous portion has a triangle shape or a trapezoidal shape having a width increasing toward the lower side.
3. The piezoelectric thin film resonator according to claim 1 , further comprising:
an insertion film that is inserted in the piezoelectric film, is located in at least a part of an outer peripheral region within the resonance region, and is not located in the center region of the resonance region.
4. The piezoelectric thin film resonator according to claim 3 , wherein
the discontinuous portion is located in the piezoelectric film located on or under the insertion film.
5. The piezoelectric thin film resonator according to claim 3 , wherein
an acoustic impedance of the insertion film is less than an acoustic impedance of the piezoelectric film.
6. The piezoelectric thin film resonator according to claim 1 , wherein
the discontinuous portion is a crack or an air gap located in the piezoelectric film.
7. A filter comprising:
the piezoelectric thin film resonator as set forth in claim 1 .
8. The piezoelectric thin film resonator according to claim 1 , wherein the discontinuous portion is located in an extraction region in which the upper electrode is extracted from the resonance region and is not located in a region other than the extraction region among the region surrounding the center region.
9. A piezoelectric thin film resonator, comprising:
a substrate;
a lower electrode and an upper electrode located on the substrate;
a piezoelectric film, at least a part of the piezoelectric film being sandwiched between the upper electrode and the lower electrode, the piezoelectric film including a discontinuous portion in which the piezoelectric film discontinues in at least a part of a region surrounding a center region that includes a center of a resonance region where the upper electrode and the lower electrode face each other across the at least a part of the piezoelectric film; and
an insertion film that is inserted in the piezoelectric film, is located in at least a part of an outer peripheral region within the resonance region, and is not located in the center region of the resonance region,
wherein the discontinuous portion is located in the piezoelectric film located under the insertion film, and is not located in the piezoelectric film located on the insertion film.
10. The piezoelectric thin film resonator according to claim 9 , wherein
an air gap or an acoustic mirror that includes the resonance region and is larger than the resonance region in planar view is located under the lower electrode, and
the discontinuous portion is located in an edge portion of the resonance region, further out than the edge portion of the resonance region and further in than an edge portion of the air gap or an edge portion of the acoustic mirror, or in the edge portion of the air gap or the edge portion of the acoustic mirror.
11. The piezoelectric thin film resonator according to claim 9 , wherein
the discontinuous portion is located from a tip of the lower electrode.
12. The piezoelectric thin film resonator according to claim 9 , wherein
an air gap is located under the lower electrode, and
the discontinuous portion is located in a region in which an edge portion of the lower electrode substantially coincides with an edge portion of the air gap.
13. A piezoelectric thin film resonator, comprising:
a substrate;
a lower electrode and an upper electrode located on the substrate;
a piezoelectric film, at least a part of the piezoelectric film being sandwiched between the upper electrode and the lower electrode, the piezoelectric film including a discontinuous portion in which the piezoelectric film discontinues in at least a part of a region surrounding a center region that includes a center of a resonance region where the upper electrode and the lower electrode face each other across the at least a part of the piezoelectric film; and
an insertion film that is inserted in the piezoelectric film, is located in at least a part of an outer peripheral region within the resonance region, and is not located in the center region of the resonance region,
wherein the discontinuous portion is located in the piezoelectric film located on the insertion film, and is not located in the piezoelectric film located under the insertion film.