Coupled lamb wave resonators filter

• US 7,804,383 B2
• Filed: 08/27/2007
• Issued: 09/28/2010
• Est. Priority Date: 08/28/2006
• Status: Active Grant

• Current Assignee: STMicroelectronics SA (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SA (STMicroelectronics NV)
• Inventors: Dubus, Bertrand, Volatier, Alexandre, Ancey, Pascal
• Primary Examiner(s): Pascal; Robert
• Assistant Examiner(s): Wong; Alan
• Application Number:
  US11/845,268
• Publication Number:
  US 20080048804A1
• Time in Patent Office: 1,128 Days
• Field of Search: 333/189, 333/141, 333/145, 333/147, 333190-192
• US Class Current: 333/189
• CPC Class Codes: H03H 9/02228 Guided bulk acoustic wave devices or Lamb wave devices having interdigital transducers situated in parallel planes on either side of a piezoelectric layer
• CPC Class Codes: Y10T 29/42 Piezoelectric device making

Abstract

A coupled Lamb wave resonator filter includes first and second Lamb wave resonators. The first Lamb wave resonator includes a first resonant layer, and first and second electrodes on opposite sides of the first resonant layer. The second Lamb wave resonator includes a second resonant layer, and third and fourth electrodes on opposite sides of the second resonant layer. One of the sides of the first resonant layer belongs to a plane parallel to a plane corresponding to one of the sides of the second resonant layer. Both planes pass through the third and fourth electrodes of the second Lamb wave resonator. A periodic lattice acoustically couples the first and second resonant layers.

Claims

1. A coupled Lamb wave resonator filter comprising:

at least one first Lamb wave resonator comprising a first resonant layer, and first and second electrodes on opposite sides of said first resonant layer;

at least one second Lamb wave resonator comprising a second resonant layer, and third and fourth electrodes on opposite sides of said second resonant layer;

at least one of the sides of said first resonant layer belonging to a plane parallel to a plane corresponding to one of the sides of said second resonant layer, with both planes passing between said third and fourth electrodes of said second Lamb wave resonator; and

a periodic lattice acoustically coupling said first and second resonant layers.

2. A coupled Lamb wave resonator filter according to claim 1, wherein one of the sides of each of said first and second resonant layers belongs to a first plane, and the other of the sides of each of said first and second resonant layers belongs to a second plane parallel to but distinct from the first plane.

3. A coupled Lamb wave resonator filter according to claim 1, wherein at least one of said first and second resonant layers comprises one of a piezoelectric material and an electrostrictive material.

4. A coupled Lamb wave resonator filter according to claim 1, wherein said first and second electrodes of said first Lamb wave resonator are separated, and are not electrically connected to said third and fourth electrodes of said second Lamb wave resonator.

5. A coupled Lamb wave resonator filter according to claim 1, wherein one of said first and second electrodes of said first Lamb wave resonator is electrically connected to one of said third and fourth electrodes of said second Lamb wave resonator.

6. A coupled Lamb wave resonator filter according to claim 1, wherein a length of at least one of said first, second, third and fourth electrodes is equal to about

$\frac{k}{}$

⁢

λ

c 2 ,

where

$f_c=\frac{c}{{\mathrm{\lambda <br><br>}}_c}$

is a central frequency of an output spectrum from the coupled Lamb wave resonator filter, c is an acoustic propagation speed of Lamb waves, λ

_c is a wavelength corresponding to a required central frequency at the filter output, and k is a non-zero natural integer number.

7. A coupled Lamb wave resonator filter according to claim 1, wherein a length of at least one of said first and second resonant layers is equal to about

$\frac{k}{}$

⁢

λ

c 2 ,

where

$f_c=\frac{c}{{\mathrm{\lambda <br><br>}}_c}$

is a central frequency of an output spectrum from the coupled Lamb wave resonator filter, c is an acoustic propagation speed of Lamb waves, λ

_c is a wavelength corresponding to a required central frequency at the filter output, and k is a non-zero natural integer number.

8. A coupled Lamb wave resonator filter according to claim 1, wherein a length of at least one of said first and second resonant layers is different from lengths of at least one of said first, second, third and fourth electrodes.

9. A coupled Lamb wave resonator filter according to claim 1, wherein at least a portion of said periodic lattice comprises a resonant material.

10. A coupled Lamb wave resonator filter according to claim 9, wherein said resonant material has a length equal to about

$\frac{(2}{}$

m + 1 ) ⁢

λ

c 4 ,

where

$f_c=\frac{c}{{\mathrm{\lambda <br><br>}}_c}$

is a central frequency of an output spectrum from the coupled Lamb wave resonator filter, c is an acoustic propagation speed of Lamb waves, λ

_c is a wavelength corresponding to a required central frequency at the filter output, where m is a natural non-zero integer number;

said resonant material being arranged between m pairs of metal areas with a length of about

$\frac{{\mathrm{\lambda <br><br>}}_c}{4},$

and metal areas of each of said m pairs being aligned one above the other, and all of the metal areas of said m pairs located on the same side of said resonant material are separated from each other and from said first, second, third or fourth electrodes of said first and second Lamb wave resonators by a distance equal to about

$\frac{{\mathrm{\lambda <br><br>}}_c}{4}.$

11. A coupled Lamb wave resonator filter according to claim 9, wherein said resonant material is arranged between metal areas, and wherein all of said first, second, third, and fourth electrodes, and all of said metal areas that are located on one side of said resonant material are all electrically connected together.

12. A coupled Lamb wave resonator filter according to claim 1, further comprising:

a third Lamb wave resonator comprising at least a third resonant layer, and at least fifth and sixth electrodes on opposite sides of said third resonant layer; and

an acoustic coupler for acoustically coupling at least one of said first and second Lamb wave resonators to said third Lamb wave resonator.

13. A coupled Lamb wave resonator filter according to claim 12, wherein said acoustic coupler comprises a second periodic lattice, and at least a portion of said second periodic lattice comprising a resonant material.

14. A coupled Lamb wave resonator filter according to claim 12, wherein said first, second and third resonant layers form a contiguous single layer.

15. A coupled Lamb wave resonator filter according to claim 1, further comprising at least one Bragg mirror acoustically coupled to one of said first and second Lamb wave resonators, and one of said first and second Lamb wave resonators being arranged between said at least one Bragg mirror and the other one of said first and second Lamb wave resonators.

16. A coupled Lamb wave resonator filter according to claim 15, wherein said at least one Bragg mirror comprises at least one layer of resonant material with a length equal to about

$\frac{n}{}$

⁢

λ

c 4 ,

where

$f_c=\frac{c}{{\mathrm{\lambda <br><br>}}_c}$

is a central frequency of an output spectrum from the coupled Lamb wave resonator filter, c is an acoustic propagation speed of Lamb waves, λ

_c is a wavelength corresponding to a required central frequency at the filter output, where n is a natural non-zero integer number;

said at least one layer of resonant material being arranged between n pairs of metal areas with a length of about

$\frac{{\mathrm{\lambda <br><br>}}_c}{4},$

the two metal areas of each of said n pairs being aligned one above the other, and all of the metal areas of said n pairs located on the same face of said at least one layer of resonant material are separated from each other and from said first, second, third or fourth electrodes of said first and second Lamb wave resonators by a distance equal to about

$\frac{{\mathrm{\lambda <br><br>}}_c}{4}.$

17. A coupled Lamb wave resonator filter according to claim 1, further comprising at least one Bragg mirror comprising a first resonant material, and said periodic lattice comprising a second resonant material, and portions of said first and second resonant material having alternating impedances.

18. A coupled Lamb wave resonator filter comprising:

at least one first Lamb wave resonator comprising a first resonant layer, and first and second electrodes on opposite sides of said first resonant layer;

at least one second Lamb wave resonator comprising a second resonant layer, and third and fourth electrodes on opposite sides of said second resonant layer;

at least one of the sides of said first resonant layer belonging to a plane parallel to a plane corresponding to one of the sides of said second resonant layer, with both planes passing between said third and fourth electrodes of said second Lamb wave resonator; and

an acoustic coupler between said first and second resonant layers, and comprising a resonant material arranged between m pairs of metal areas, with metal areas of each of said m airs being aligned one above the other, where m is a natural non-zero integer number.

19. A coupled Lamb wave resonator filter according to claim 18, wherein at least one of said first and second resonant layers comprises one of a piezoelectric material and an electrostrictive material.

20. A coupled Lamb wave resonator filter according to claim 18, wherein said first and second electrodes of said first Lamb wave resonator are separated, and are not electrically connected to said third and fourth electrodes of said second Lamb wave resonator.

21. A coupled Lamb wave resonator filter according to claim 18, wherein one of said first and second electrodes of said first Lamb wave resonator is electrically connected to one of said third and fourth electrodes of said second Lamb wave resonator.

22. A coupled Lamb wave resonator filter according to claim 18, wherein a length of at least one of said first and second resonant layers is different from lengths of at least one of said first, second, third and fourth electrodes.

23. A coupled Lamb wave resonator filter according to claim 18, wherein the metal areas located on the same side of said resonant material are electrically connected together.

24. A coupled Lamb wave resonator filter according to claim 18, further comprising:

at least one Bragg mirror acoustically coupled to one of said first and second Lamb wave resonators, and one of said first and second Lamb wave resonators being arranged between said at least one Bragg mirror and the other one of said first and second Lamb wave resonators; and

said at least one Bragg mirror comprising at least one layer of resonant material arranged between n pairs of metal areas, the two metal areas of each of said n pairs being aligned one above the other; and

all of the metal areas of said m pairs located on the same side of said resonant material of said acoustic coupler being electrically connected together, where n is a natural non-zero integer number.

25. A coupled Lamb wave resonator filter according to claim 24, wherein said first resonant layer, said second resonant layer, and said resonant material of said acoustic coupler form a contiguous single layer.

26. A method for making a coupled Lamb wave resonator filter comprising:

providing at least one first Lamb wave resonator comprising a first resonant layer, and first and second electrodes on opposite sides of the first resonant layer;

providing at least one second Lamb wave resonator comprising a second resonant layer, and third and fourth electrodes on opposite sides of the second resonant layer;

at least one of the sides of the first Lamb wave resonant layer belonging to a plane parallel to a plane corresponding to one of the sides of the second Lamb wave resonant layer, with both planes passing through the third and fourth electrodes of the second Lamb wave resonator; and

providing a periodic lattice for acoustically coupling the first and second Lamb wave resonant layers.

27. A method according to claim 26, wherein at least one of the first and second resonant layers comprises one of a piezoelectric material and an electrostrictive material.

28. A method according to claim 26, wherein the first and second electrodes of the first Lamb wave resonator are separated, and are not electrically connected to the third and fourth electrodes of the second Lamb wave resonator.

29. A method according to claim 26, wherein one of the first and second electrodes of the first Lamb wave resonator is electrically connected to one of the third and fourth electrodes of the second Lamb wave resonator.

30. A method according to claim 26, wherein a length of at least one of the first and second resonant layers is different from lengths of at least one of the first, second, third and fourth electrodes.

31. A method according to claim 26, wherein at least a portion of the periodic lattice comprises a resonant material.

32. A method according to claim 31, wherein the resonant material is arranged between m pairs of metal areas, and metal areas of each of the m pairs being aligned one above the other, and all of the metal area of said m pairs located on the same side of the resonant material being electrically connected together, where m is a natural non-zero integer number.

33. A method according to claim 26, further comprising providing at least one Bragg mirror that is acoustically coupled to one of the first and second Lamb wave resonators, and one of the first and second Lamb wave resonators being arranged between the at least one Bragg mirror and the other one of the first and second Lamb wave resonators.