Acoustic mirror with improved reflection

• US 20050068124A1
• Filed: 12/06/2002
• Published: 03/31/2005
• Est. Priority Date: 12/11/2001
• Status: Active Grant

• Current Assignee: Snaptrack Incorporated (Qualcomm, Inc.)
• Original Assignee: Epcos AG (TDK Corporation)
• Inventors: Stoemmer, Ralph
• Granted Patent: US 7,230,509 B2
• Time in Patent Office: Days
• US Class Current: 333/189
• CPC Class Codes: H03H 9/02149 of ageing changes of characteristics, e.g. electro-acousto-migration
• CPC Class Codes: H03H 9/175 Acoustic mirrors
• CPC Class Codes: H03H 9/585 Stacked Crystal Filters [SCF]
• CPC Class Codes: H03H 9/589 Acoustic mirrors

Abstract

For a BAW resonator or a stacked-crystal filter, an acoustic mirror is proposed that has at least one layer pair of λ/4 or 3λ/4 layers, where each layer pair has a first layer with lower acoustic impedance and a second layer with higher acoustic impedance relative to it and where a low-k dielectric is selected as the material with lower acoustic impedance.

Claims

1. An acoustic mirror comprising:

constituent layers comprising substantially odd multiples of λ

/4, the constituent layers comprising a first impedance layer and a second impedance layer,

the first impedance layer comprising a first material having a first acoustic impedance and a first dielectric constant, the first material being produced using benzocyclobutene,

the second impedance layer comprising a second material having a second acoustic impedance and a second dielectric constant, the second material comprising at least one of aluminum nitride, gallium nitride, zinc oxide, tungsten, and molybdenum,

the second acoustic impedance being higher than the first acoustic impedance, and

the first dielectric constant being lower than the second dielectric constant.

2. The acoustic mirror of claim 1, wherein the acoustic mirror is on a top layer of a bulk acoustic wave resonator BAW resonator or a stacked-crystal filter, the acoustic mirror comprising an initial layer of the first material followed by a layer of the second material deposited on the layer of the first material.

4. The acoustic mirror of claim 1, wherein the first material has a density of at least 2.4 g/cm², an elastic constant with a value of less than 10 Gpa, and a dielectric constant of less than 3.

9. The acoustic mirror of claim 1, wherein the first material has nanopores.

10. The acoustic mirror of claim 1, wherein the constituent layers comprise a single pair of layers that are substantially λ

/4, the first material comprises at least a polymerized benzocyclobutene, and the second material comprises at least one of aluminum nitride, gallium nitride, and zinc oxide.

19. The acoustic mirror of claim 1, wherein the constituent layers are substantially λ

/4 or substantially 3λ

/4.

3. (canceled)

5-8. -8. (canceled)

11. A bulk acoustic wave (BAW) resonator comprising:

a substrate;

a first impedance layer above the substrate, the first impedance layer comprising a substantially odd multiple of λ

/4, the first impedance layer comprising a first material having a first acoustic impedance and a first dielectric constant;

a second impedance layer above the first impedance layer relative to the substrate, the second impedance layer comprising a substantially odd multiple of λ

/4, the second impedance layer comprising a second material having a second acoustic impedance and a second dielectric constant, the second acoustic impedance being higher than the first acoustic impedance, and the first dielectric constant being lower than the second dielectric constant;

electrode layers that are above the second impedance layer relative to the substrate, the electrode layers comprising at least one of Al, W, Mo, Cu, and Au; and

a piezoelectric layer between the electrode layers, the piezoelectric layer comprising at least one of zinc oxide, aluminum nitride, gallium nitride, and other piezoelectric materials.

14. A reactance filter comprising multiple BAW reasonators of claim 11 connected in serial and parallel relationships.

15. The reactance filter of claim 14, wherein the BAW resonators are connected in a lattice structure.

16. A duplexer comprising a first and second BAW resonators according to claim 11.

17. The duplexer of claim 16, wherein the first and second BAW resonators are over a common acoustic mirror.

18. The duplexer of claim 17, wherein the common acoustic mirror is formed over a substrate under the first and second BAW resonators.

20. The BAW resonator of claim 11, wherein each substantially odd multiple of λ

/4 comprises either λ

/4 or 3λ

/4.

12. A stacked-crystal filter comprising:

a substrate;

a first impedance layer above the substrate, the first impedance layer comprising a substantially odd multiple of λ

/4, the first impedance layer comprising a first material having a first acoustic impedance and a first dielectric constant;

a second impedance layer above the first impedance layer relative to the substrate, the second impedance layer comprising a substantially odd multiple of λ

/4, the second impedance layer comprising a second material having a second acoustic impedance and a second dielectric constant, the second acoustic impedance being higher than the first acoustic impedance and the first dielectric constant being lower than the second dielectric constant;

electrode layers that are above the second impedance layer relative to the substrate, the electrode layers comprising at least one of Al, W, Cu, and Au; and

plural piezoelectric layers between the electrode layers, the plural piezoelectric layers comprising at least one of zinc oxide, aluminum nitride, gallium nitride, and other piezoelectric materials.

13. The stacked-crystal filter of claim 12, wherein the electrode layers comprise a first electrode and a second electrode, the second electrode being split into two partial electrodes;

and

wherein the stacked-crystal filter further comprises at least one additional layer located between the two partial electrodes, the at least one additional layer comprising a layer that is substantially λ

/4 and that has a dielectric constant that is less than the second dielectric constant.

21. The stacked-crystal filter of claim 12, wherein each substantially odd multiple of λ

/4 comprises either λ

/4 or 3λ

/4.