Granted Patent B2

US 8,487,719 · App. 12/989,488 · Granted Jul 16, 2013

Abstract

Claims (27)

1. A resonator comprising:

a bottom electrode layer;

a top electrode layer which defines a resonator body, the top electrode layer comprising a top electrode comprising a frame region of greater mass per surface area around the periphery of the resonator body and an inner region within the frame region; and

a piezoelectric layer sandwiched between the top and bottom electrode layers to form a stack;

wherein an external region is provided around the outside of the periphery of the resonator body,

such that the cutoff frequency of a first resonance mode of the external region is matched to the cutoff frequency of a second, different, resonance mode of the resonator body.

2. A resonator as claimed in claim 1 , wherein the external region has a lower number of layers than the resonator body region.

3. A resonator as claimed in claim 1 , wherein the external region has a lower thickness than the resonator body region.

4. A resonator as claimed in claim 1 , wherein the external region comprises a layer with a higher weight or acoustic wave velocity than a layer at the same position within the stack in the resonator body region.

5. A resonator as claimed in claim 1 wherein the resonator body has an area of 2500 μm 2 to 90000 μm 2 .

6. A resonator as claimed in claim 1 , wherein the frame region extends inwardly of the periphery by between about 2 and about 6 μm.

7. A resonator as claimed in claim 1 , wherein the external region extends to a distance of 30 μm or less.

8. A resonator as claimed in claim 1 wherein the matching is to within about 10%.

9. A resonator as claimed in claim 8 , wherein the cutoff frequency of the first resonance mode is larger than the anti-resonance frequency of the resonator body.

10. A filter comprising a resonator as claimed in claim 1 .

11. A filter as claimed in claim 10 , wherein the external region does not contain top electrode nor bottom electrode along a significant part of the resonator body edge.

12. A filter as claimed in claim 10 , comprising thinned or removed layers at the locations where a bottom or top electrode interconnect contacts the respective electrode.

13. A method of producing a resonator, comprising:

forming a bottom electrode layer, a top electrode layer which defines a resonator body and a piezoelectric layer sandwiched between the top and bottom electrode layers;

forming a frame region of greater mass per surface area around the periphery of the top electrode; and

processing an external region around the outside of the periphery of the resonator body such that a cutoff frequency of a first resonance mode of the external region is matched to the cutoff frequency of a second, different, resonance mode of the resonator body.

14. A method as claimed in claim 13 , wherein the external region is processed so that the cutoff frequency of the first resonance mode is increased to be larger than the anti-resonance frequency of the resonator body.

15. A method as claimed in claim 13 , wherein processing the external region comprises:

thinning or removing the top piezoelectric layer from the external region; and/or

removing the bottom electrode in the external region; and/or

adapting a thickness of a lower layer in the external region between the bottom electrode and the piezoelectric layer and/or

at least partially etching away a first layer in the external region and depositing a lighter material layer.

Assignments (13)