Film bulk acoustic resonator, filter, and fabrication method thereof

• US 20070279155A1
• Filed: 05/30/2007
• Published: 12/06/2007
• Est. Priority Date: 05/30/2006
• Status: Active Grant

• Current Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Original Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Inventors: Sakai, Hiroyuki, Yahata, Kazuhiro, Tsurumi, Naohiro, Uno, Takashi
• Granted Patent: US 7,760,049 B2
• Time in Patent Office: Days
• US Class Current: 333/191
• CPC Class Codes: H03H 2003/025 the resonators or networks comprising an acoustic mirror
• CPC Class Codes: H03H 3/02 for the manufacture of piezoelectric or electrostrictive resonators or networks H03H3/08 takes precedence
• CPC Class Codes: H03H 9/175 Acoustic mirrors
• CPC Class Codes: H03H 9/589 Acoustic mirrors

Abstract

A film bulk acoustic resonator includes a substrate; an acoustic reflector portion formed on the substrate; and an acoustic resonator portion including a lower electrode, a piezoelectric film, and an upper electrode which are sequentially stacked on the acoustic reflector portion, An uppermost layer of the acoustic reflector portion which is in contact with the acoustic resonator portion has a root-mean-square roughness of approximately 1 nm or less.

Claims

1. A film bulk acoustic resonator comprising:

a substrate;

an acoustic reflector portion formed on the substrate; and

an acoustic resonator portion including a lower electrode, a piezoelectric film, and an upper electrode which are sequentially stacked on the acoustic reflector portion,

wherein an uppermost layer of the acoustic reflector portion which is in contact with the acoustic resonator portion has a root-mean-square roughness of approximately 1 nm or less.

2. The film bulk acoustic resonator of claim 1, wherein the uppermost layer of the acoustic reflector portion which is in contact with the acoustic resonator portion is a film formed by spin coating.

3. The film bulk acoustic resonator of claim 1, wherein a material forming the acoustic reflector portion includes an organic solvent or an inorganic solvent for spin coating.

4. The film bulk acoustic resonator of claim 1, wherein

the acoustic reflector portion is a low acoustic impedance layer which is formed of a material having an acoustic impedance value lower than that of the lower electrode which is included in the acoustic resonator portion, and

the low acoustic impedance layer is a film formed by spin coating.

5. The film bulk acoustic resonator of claim 1, wherein the acoustic reflector portion includes a low acoustic impedance layer and a high acoustic impedance layer which are stacked on the substrate, the acoustic impedance of the high acoustic impedance layer being higher than that of the low acoustic impedance layer.

6. The film bulk acoustic resonator of claim 1, wherein the acoustic reflector portion includes low acoustic impedance layers and high acoustic impedance layers which are alternately stacked on the substrate, the acoustic impedance of the high acoustic impedance layers being higher than that of the low acoustic impedance layers.

7. The film bulk acoustic resonator of claim 6, wherein each of the low acoustic impedance layers is a film formed by spin coating.

8. The film bulk acoustic resonator of claim 7, wherein each of the low acoustic impedance layers is formed of a spin-on glass material, a fluorine-based resin material, a silicone-based resin material, or an epoxy-based resin material.

9. The film bulk acoustic resonator of claim 6, wherein each of the high acoustic impedance layers is a film formed by spin coating.

10. The film bulk acoustic resonator of claim 6, wherein each of the high acoustic impedance layers and each of the low acoustic impedance layers are formed of an insulating material.

11. The film bulk acoustic resonator of claim 6, wherein the acoustic reflector portion includes a smoothing layer formed on an uppermost part of the acoustic reflector portion.

12. The film bulk acoustic resonator of claim 11, wherein the smoothing layer serves as one of the low acoustic impedance layers.

13. The film bulk acoustic resonator of claim 11, wherein the smoothing layer is formed by spin coating.

14. The film bulk acoustic resonator of claim 13, wherein the smoothing layer is formed of a spin-on glass material, a fluorine-based resin material, a silicone-based resin material, or an epoxy-based resin material.

15. The film bulk acoustic resonator of claim 6, wherein a plurality of acoustic resonator portions formed on the acoustic reflector portion are apart from each other, and each of the high acoustic impedance layers is divided into a plurality of regions corresponding to each of the acoustic resonator portions.

16. A filter comprising a plurality of film bulk acoustic resonators of claim 1.

17. The filter of claim 16, wherein the plurality of film bulk acoustic resonators includes:

the acoustic reflector portion which includes a plurality of acoustic reflector portions separated each other for electrically-isolation; and

the acoustic resonator portion which includes a plurality of acoustic resonator portions, each of the plurality of acoustic resonator portions being formed on each of the plurality of reflector portions.

18. The filter of claim 16, wherein the plurality of film bulk acoustic resonators includes:

the acoustic reflector portion; and

the acoustic resonator portion which includes a plurality of acoustic resonator portions, the plurality of acoustic resonator portions being formed on the same acoustic reflector portion.

19. A fabrication method of a film bulk acoustic resonator comprising the steps of:

(a) forming an acoustic reflector portion on a substrate; and

(b) forming an acoustic resonator portion by sequentially forming a lower electrode, a piezoelectric film, and an upper electrode on the acoustic reflector portion,

wherein step (a) includes forming an uppermost layer of the acoustic reflector portion which is in contact with the acoustic resonator portion by spin coating such that an upper surface of the layer has a root-mean-square roughness of approximately 1 nm or less.

20. The fabrication method of claim 19, wherein step (a) includes forming a low acoustic impedance layer, an acoustic impedance value of the low acoustic impedance layer being lower than that of the lower electrode.

21. The fabrication method of claim 20, wherein step (a) includes stacking a high acoustic impedance layer and the low acoustic impedance layer, an acoustic impedance value of the high acoustic impedance layer being higher than that of the low acoustic impedance layer.

22. The fabrication method of claim 19, wherein step (a) includes alternately stacking low acoustic impedance layers and high acoustic impedance layers, an acoustic impedance value of the low acoustic impedance layers being lower than that of the lower electrode, and an acoustic impedance value of the high acoustic impedance layers being higher than that of the low acoustic impedance layers.

23. The fabrication method of claim 22, wherein step (a) includes forming a smoothing layer as the uppermost layer of the acoustic reflector portion which is in contact with the acoustic resonator portion.

24. The fabrication method of claim 22, further comprising the steps of:

(c) before step (a), selectively forming a sacrifice layer on the substrate such that the substrate is sectioned by the sacrifice layer into a plurality of regions, the sacrifice layer having a thickness greater than a thickness of the acoustic reflector portion; and

(d) after step (a) and before step (b), removing the sacrifice layer such that the acoustic reflector portion is divided into a plurality of regions,

wherein step (b) includes forming the acoustic resonator portion in each of the regions of the divided acoustic reflector portion.

25. The fabrication method of claim 24, wherein the sacrifice layer is formed such that the distribution of a solution for the spin coating is kept in uniformly when the low acoustic impedance layers and the high acoustic impedance layers are formed by spin coating in step (a).

26. The fabrication method of claim 25, wherein the sacrifice layer is formed in a lattice-like arrangement avoiding a crossing point of the lattice on the substrate.

27. The fabrication method of claim 22, wherein

step (a) includes

(a1) after each one of the low acoustic impedance layers is formed by spin coating, selectively exposing the formed low acoustic impedance layer to light having a first wave length to partially crystallize the low acoustic impedance layer;

(a2) after each one the high acoustic impedance layers is formed by spin coating, selectively exposing the formed high acoustic impedance layer to light having a second wave length to partially crystallize the high acoustic impedance layer; and

(a3) after step (a1) and step (a2) are alternately repeated, removing uncrystallized parts of the partially crystallized low acoustic impedance layer and the partially crystallized high acoustic impedance layer to form the acoustic reflector portion which is divided into a plurality of regions, and

step (b) includes forming the acoustic resonator portion in each of the regions of the divided acoustic reflector portion.

28. The fabrication method of claim 22, wherein

step (a) includes

(a1) alternately stacking the low acoustic impedance layers and the high acoustic impedance layers by spin coating;

(a2) respectively selectively exposing the stacked low acoustic impedance layers and the stacked high acoustic impedance layers to light having a first wave length to crystallize the low acoustic impedance layers and to light having a second wave length to crystallize the high acoustic impedance layers;

(a3) removing uncrystallized parts of the crystallized low acoustic impedance layers and the crystallized high acoustic impedance layers to form the acoustic reflector portion divided into a plurality of regions, and

step (b) includes forming the acoustic resonator portion in each of the regions of the divided acoustic reflector portion.