BULK ACOUSTIC WAVE RESONATOR

• US 20110037539A1
• Filed: 04/24/2009
• Published: 02/17/2011
• Est. Priority Date: 04/29/2008
• Status: Active Grant

• Current Assignee: Qorvo US, Inc. (Qorvo, Inc.)
• Original Assignee: NXP B.V. (NXP Semiconductors NV)
• Inventors: Spaan, Erik, Lobeek, Jan-Willem, Jansman, Andreras B. M., Strijbos, Rensinus C.
• Granted Patent: US 8,487,719 B2
• Time in Patent Office: Days
• US Class Current: 333/187
• CPC Class Codes: H03H 9/02118 of lateral leakage between adjacent resonators
• CPC Class Codes: H03H 9/175 Acoustic mirrors
• CPC Class Codes: Y10T 29/42 Piezoelectric device making
• CPC Class Codes: Y10T 29/49005 Acoustic transducer

Abstract

A resonator comprises a bottom electrode layer (12), a top electrode layer (10) which defines a resonator body; and a piezoelectric layer (14) sandwiched between the top and bottom electrode layers. An external region (152) is provided around the outside of the periphery of the resonator body. The cutoff frequency of a first resonance mode of the external region (152) is matched to the cutoff frequency of a second, different, resonance mode of the resonator body. The invention provides a deliberate change (typically increase) in the cutoff frequency the resonance modes in the external region, so that one of the modes has a cutoff frequency close to the cutoff frequency of the fundamental mode of the resonator body.

Claims

1. A resonator comprising:

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,

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 top electrode comprises a frame region of greater mass per surface area around the periphery of the resonator body and an inner region within the frame region.

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

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

5. 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 as a layer in the resonator body region.

6. A resonator as claimed in claim 1 wherein the resonator body has an area of 2500 μ

m² to 90000 μ

m².

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

m.

8. A resonator as claimed in claim 1, wherein the external region extends to a distance of 30 μ

m or less.

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

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

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

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

13. A filter as claimed in claim 11, comprising thinned or removed layers at the locations where a bottom or top electrode interconnect contacts the respective electrode.

14. 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; 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.

15. A method as claimed in claim 14, further comprising forming a frame region of greater mass per surface area around the periphery of the top electrode.

16. A method as claimed in claim 15, wherein the external region is processed so that the cutoff frequency of the first resonance mode is increased to the larger than the anti-resonance frequency of the resonator body.

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

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

/or

removing the bottom electrode (12) in the external region; and

/or

adapting a thickness of a lower layer in the external region (152) between the bottom electrode (12) and the piezoelectric layer (14); and

/or

at least partially etching away a first layer in the external region (152) and depositing a lighter material layer.