Bulk acoustic wave resonator having doped piezoelectric layer

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

a first electrode having a first electrode thickness;

a second electrode having a second electrode thickness; and

a piezoelectric layer having a piezoelectric layer thickness and being disposed between the first and second electrodes, the piezoelectric layer comprising a piezoelectric material doped with at least one rare earth element, wherein for a particular acoustic coupling coefficient (kt 2 ) value and series resonance frequency (F s ) of the BAW resonator, the first electrode thickness and the second electrode thickness are respectively greater than a thickness of a first electrode and a thickness of a second electrode of a comparable BAW resonator comprising identical layers and materials except for comprising an undoped piezoelectric layer of the same piezoelectric material.

2. A BAW resonator as claimed in claim 1 , wherein, for the particular F s and kt 2 value, the piezoelectric layer comprising the piezoelectric material doped with at least one rare earth element is thinner than a thickness of the undoped piezoelectric layer of the comparable BAW resonator.

3. A BAW resonator as claimed in claim 2 , wherein, for the particular F s and kt 2 value, the first electrode thickness and the second electrode thickness are respectively approximately twice the first electrode thickness and the second electrode thickness of the comparable BAW resonator comprising the undoped piezoelectric layer.

4. A BAW resonator as claimed in claim 2 , wherein, for the particular F s and kt 2 value, the thickness of the piezoelectric layer comprising the piezoelectric material doped with at least one rare earth element is approximately one-half the thickness of the undoped piezoelectric layer of the comparable BAW resonator.

5. A BAW resonator as claimed in claim 1 , wherein, for the particular F s and kt 2 value, the first electrode thickness and the second electrode thickness are respectively approximately twice the first electrode thickness and the second electrode thickness of the comparable BAW resonator comprising the undoped piezoelectric layer.

6. A BAW resonator as claimed in claim 1 , wherein the kt 2 is approximately 7.0%.

7. A BAW resonator as claimed in claim 6 , wherein the piezoelectric layer comprising the piezoelectric material doped with at least one rare earth element has a thickness of approximately 5800 Å.

8. A BAW resonator as claimed in claim 6 , wherein the first electrode has a thickness of approximately 4100 Å.

9. A BAW resonator as claimed in claim 6 , wherein the second electrode has a thickness of approximately 3000 Å.

10. A BAW resonator as claimed in claim 1 , wherein the kt 2 is in the range of approximately 6.5% to approximately 9.0%.

11. A BAW resonator as claimed in claim 10 , wherein the piezoelectric layer comprising the piezoelectric material doped with at least one rare earth element has a thickness in the range of approximately 4600 Å to approximately 12000 Å.

12. A BAW resonator as claimed in claim 10 , wherein the second electrode has a thickness in the range of approximately 3300 Å to approximately 2000 Å.

13. A BAW resonator as claimed in claim 10 , wherein the first electrode of has a thickness in the range of approximately 4500 Å to approximately 2500 Å.

14. A BAW resonator as claimed in claim 1 , further comprising an acoustic reflector disposed beneath the first electrode, the second electrode and the piezoelectric layer, wherein an overlap of the acoustic reflector, the first electrode, the second electrode and the piezoelectric layer defines an active area of the acoustic resonator.

15. A BAW resonator as claimed in claim 14 , wherein the acoustic reflector comprises a cavity disposed in a substrate over which the first electrode, the second electrode and the piezoelectric layer are disposed.

16. A BAW resonator as claimed in claim 14 , wherein the acoustic reflector comprises a plurality of layers having alternating high acoustic impedance and low acoustic impedance.

17. A BAW resonator as claimed in claim 1 , wherein the piezoelectric material comprises aluminum nitride (AlN).

18. A BAW resonator as claimed in claim 17 , wherein the at least one rare earth element is incorporated into a crystal lattice of the AlN piezoelectric material.

19. A BAW resonator as claimed in claim 17 , wherein the at least one rare earth element comprises scandium (Sc).

20. A BAW resonator as claimed in claim 19 , wherein an atomic percentage of the Sc in the AlN piezoelectric material is approximately 0.5% to less than approximately 10.0%.

21. A BAW resonator as claimed in claim 19 , wherein an atomic percentage of the Sc in the AlN piezoelectric material is approximately 0.5% to approximately 44%.

22. A BAW resonator as claimed in claim 19 , wherein an atomic percentage of the Sc in the AlN piezoelectric material is approximately 2.5% to less than approximately 5.0%.

23. A BAW resonator as claimed in claim 17 , wherein the at least one rare earth element comprises two or more rare earth elements incorporated into a crystal lattice of the AlN piezoelectric material.

24. A BAW resonator as claimed in claim 23 , wherein the two or more rare earth elements comprise scandium (Sc) and erbium (Er).

25. An BAW resonator as claimed in claim 24 , wherein the two or more rare earth elements further comprise yttrium (Y).