Piezoelectric thin-film resonator, filter using the same, and duplexer using the same

1. A piezoelectric thin film resonator comprising:

a substrate;

a lower electrode formed on the substrate;

a piezoelectric film formed on the lower electrode; and

an upper electrode formed on the piezoelectric film, the lower electrode and the upper electrode opposing each other through the piezoelectric film to form an opposing region, the opposing region including a space at a boundary of the opposing region, wherein the space extending from an inner side to an outer side of the opposing region is formed in or on the piezoelectric film, and

the space is formed by removing a part of the piezoelectric film including removing the part of an upper surface or a lower surface of the piezoelectric film to straddle an edge of the upper electrode.

2. The piezoelectric thin film resonator according to claim 1 , wherein a cavity is formed under the opposing region and an area of the cavity opposing to the opposing region is larger than an area of the opposing region opposing to the cavity.

3. The piezoelectric thin film resonator according to claim 1 , wherein the piezoelectric thin film resonator resonates in a thickness extensional mode.

4. A filter configured to include at least one piezoelectric thin film resonator according to claim 1 .

5. A duplexer configured to include at least one piezoelectric thin film resonator according to claim 1 .

6. A transmission device configured to include at least one piezoelectric thin film resonator according to claim 1 .

7. A piezoelectric thin film resonator comprising:

a substrate;

a lower electrode formed on the substrate;

a piezoelectric film formed on the lower electrode; and

an upper electrode formed on the piezoelectric film, the lower electrode and the upper electrode opposing each other through the piezoelectric film to form an opposing region, the opposing region including a space at a boundary of the opposing region, wherein the space extending from an inner side to an outer side of the opposing region is formed in or on the piezoelectric film, and

the space is formed by removing a part of the piezoelectric film including removing the part of an upper surface or a lower surface of the piezoelectric film to straddle an edge of the lower electrode.

8. A piezoelectric thin film resonator comprising:

a substrate;

a lower electrode formed on the substrate;

a piezoelectric film formed on the lower electrode; and

an upper electrode formed on the piezoelectric film, the lower electrode and the upper electrode opposing each other through the piezoelectric film to form an opposing region, the opposing region including a space at a boundary of the opposing region, wherein the space extending from an inner side to an outer side of the opposing region is formed in or on the piezoelectric film, and the space is provided between the upper electrode and the upper surface of the piezoelectric film or between the lower electrode and the lower surface of the piezoelectric film.

9. A piezoelectric thin film resonator comprising:

a substrate;

a lower electrode formed on the substrate;

a piezoelectric film formed on the lower electrode; and

an upper electrode formed on the piezoelectric film, the lower electrode and the upper electrode opposing each other through the piezoelectric film to form an opposing region, the opposing region including a space at a boundary of the opposing region, wherein the space extending from an inner side to an outer side of the opposing region is formed in or on the piezoelectric film, and

the space is filled with an insulating material.

10. A piezoelectric thin film resonator comprising:

a substrate;

a lower electrode formed on the substrate;

a piezoelectric film formed on the lower electrode; and

an upper electrode formed on the piezoelectric film, the lower electrode and the upper electrode opposing each other through the piezoelectric film to form an opposing region, the opposing region including an insulator of a different acoustic impedance from a acoustic impedance of the piezoelectric film at a boundary of the opposing region, wherein the insulator extending from an inner side to an outer side of the opposing region is formed so as to pass through the piezoelectric film.

11. The piezoelectric thin film resonator according to claim 10 , wherein the acoustic impedance of the insulator is smaller than the acoustic impedance of the piezoelectric film.

12. The piezoelectric thin film resonator according to claim 10 , wherein the insulator is made of silicon oxide.

13. The piezoelectric thin film resonator according to claim 10 , wherein a cavity is formed under the opposing region and an area of the cavity opposing to the opposing region is larger than an area of the opposing region opposing to the cavity.

14. The piezoelectric thin film resonator according to claim 10 , wherein the piezoelectric thin film resonator resonates in a thickness extensional mode.

15. A piezoelectric thin film resonator comprising:

a substrate;

a lower electrode formed on the substrate;

a piezoelectric film formed on the lower electrode; and

an upper electrode formed on the piezoelectric film, the lower electrode and the upper electrode opposing each other through the piezoelectric film to form an opposing region, the opposing region including a space at a boundary of the opposing region, wherein the space extending from an inner side to an outer side of the opposing region is formed so as to pass through the piezoelectric film and the upper electrode includes a portion which extends to the outer of the opposing region and opposes to an edge of the lower electrode.

16. The piezoelectric thin film resonator according to claim 15 , wherein a cavity is formed under the opposing region and an area of the cavity opposing to the opposing region is larger than an area of the opposing region opposing to the cavity.

17. The piezoelectric thin film resonator according to claim 15 , wherein the piezoelectric thin film resonator resonates in a thickness extensional mode.