Piezoelectric thin film resonator, filter, and multiplexer
A piezoelectric thin film resonator includes: a piezoelectric film located on a substrate; lower and upper electrodes facing each other across a part of the piezoelectric film; and an insertion film located between the lower and upper electrodes, located in a part of an outer peripheral region within a resonance region where the lower and upper electrodes face each other across the piezoelectric film, and not located in a center region of the resonance region, a first width in the resonance region of the insertion film in a first region, where the upper electrode is extracted from the resonance region, being greater than a third width in the resonance region in a third region other than a second region, where the lower electrode is extracted from the resonance region, and the first region, a second width in the resonance region in a second region being the third width or greater.
1. A piezoelectric thin film resonator comprising:
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; and
an insertion film that is located between the lower electrode and the upper electrode, is located in at least a part of a region surrounding a center region of a resonance region defined by a region where the lower electrode and the upper electrode face each other across the piezoelectric film, overlaps with an outer circumference of the resonance region, is located along the outer circumference, and is not located in a center region of the resonance region, a first width in the resonance region of the insertion film in a first region being greater than a third width in the resonance region in a third region, a second width in the resonance region in a second region being equal to or greater than the third width, the first region being defined by a region where the upper electrode being extracted from the resonance region, the third region being a region other than the second region and the first region, the second region being defined by a region where the lower electrode being extracted from the resonance region, the first width in the first region being a width perpendicular to the outer circumference, being greater than 0 and being substantially uniform, the second width in the second region being a width perpendicular to the outer circumference, being greater than 0 and being substantially uniform, the third width in the third region being a width perpendicular to the outer circumference, being greater than 0 and being substantially uniform.
2. The piezoelectric thin film resonator according to claim 1 , wherein
the second width is greater than the third width.
3. The piezoelectric thin film resonator according to claim 1 , wherein
the first width is greater than the second width.
4. The piezoelectric thin film resonator according to claim 1 , further comprising:
an additional film located on the upper electrode in the first region.
5. The piezoelectric thin film resonator according to claim 4 , wherein
the additional film overlaps with a part of the resonance region in plan view.
6. The piezoelectric thin film resonator according to claim 1 , wherein
an end face of the lower electrode is inclined so that a lower surface of the lower electrode is larger than an upper surface of the lower electrode.
7. The piezoelectric thin film resonator according to claim 1 , wherein
the insertion film has Young's modulus less than Young's modulus of the piezoelectric film.
8. The piezoelectric thin film resonator according to claim 1 , wherein
an air layer is located under the lower electrode in the resonance region.
9. The piezoelectric thin film resonator according to claim 1 , wherein
an acoustic mirror reflecting an acoustic wave propagating through the piezoelectric film is located under the lower electrode in the resonance region.
10. The piezoelectric thin film resonator according to claim 1 , wherein
an angle between an end face of the upper electrode and a lower surface of the upper electrode in the second region is greater than an angle between an end face of the lower electrode and a lower surface of the lower electrode in the first region.
11. The piezoelectric thin film resonator according to claim 1 , wherein
the lower electrode is located from inside the resonance region to outside the resonance region in the third region,
the piezoelectric film includes a lower piezoelectric film and an upper piezoelectric film located on the lower piezoelectric film,
the insertion film is located between the lower piezoelectric film and the upper piezoelectric film,
an end face of the upper piezoelectric film substantially coincides with an end face of the upper electrode in the second region and the third region in plan view, and
an end face of the lower piezoelectric film is located further out than the end face of the upper piezoelectric film and overlaps with the lower electrode in the second region and the third region in plan view.
12. The piezoelectric thin film resonator according to claim 2 , further comprising an additional film only located on the upper electrode in the first region among the resonance region.
13. 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; and
an insertion film that is located between the lower electrode and the upper electrode, is located in at least a part of a region surrounding a center region of a resonance region defined by a region where the lower electrode and the upper electrode face each other across the piezoelectric film, overlaps with an outer circumference of the resonance region, is located along the outer circumference, and is not located in a center region of the resonance region, a first width in the resonance region of the insertion film in a first region being greater than a third width in the resonance region in a third region, a second width in the resonance region in a second region being equal to or greater than the third width, the first region being defined by a region where the upper electrode being extracted from the resonance region, the third region being a region other than the second region and the first region, the second region being defined by a region where the lower electrode being extracted from the resonance region, the first width in the first region being a width perpendicular to the outer circumference, being greater than 0 and being substantially uniform, the second width in the second region being a width perpendicular to the outer circumference, being greater than 0 and being substantially uniform, the third width in the third region being a width perpendicular to the outer circumference, being greater than 0 and being substantially uniform.
14. A multiplexer comprising:
a filter including a piezoelectric thin film resonator, wherein
the 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; and
an insertion film that is located between the lower electrode and the upper electrode, is located in at least a part of a region surrounding a center region of a resonance region defined by a region where the lower electrode and the upper electrode face each other across the piezoelectric film, overlaps with an outer circumference of the resonance region, is located along the outer circumference, and is not located in a center region of the resonance region, a first width in the resonance region of the insertion film in a first region being greater than a third width in the resonance region in a third region, a second width in the resonance region in a second region being equal to or greater than the third width, the first region being defined by a region where the upper electrode being extracted from the resonance region, the third region being a region other than the second region and the first region, the second region being defined by a region where the lower electrode being extracted from the resonance region, the first width in the first region being a width perpendicular to the outer circumference, being greater than 0 and being substantially uniform, the second width in the second region being a width perpendicular to the outer circumference, being greater than 0 and being substantially uniform, the third width in the third region being a width perpendicular to the outer circumference, being greater than 0 and being substantially uniform.