Bulk acoustic wave resonator and circuit comprising same

• US 20060164183A1
• Filed: 09/18/2003
• Published: 07/27/2006
• Est. Priority Date: 10/08/2002
• Status: Active Grant

• Current Assignee: Snaptrack Incorporated (Qualcomm, Inc.)
• Original Assignee: Epcos AG (TDK Corporation)
• Inventors: Unterberger, Michael, Tikka, Pasi, Schmidhammer, Edgar, Stommer, Ralph
• Granted Patent: US 7,616,079 B2
• Time in Patent Office: Days
• US Class Current: 333/133
• CPC Class Codes: H03H 9/583 comprising a plurality of piezoelectric layers acoustically coupled

Abstract

The invention relates to a resonator operating with bulk acoustic waves (BAW resonator, BAW=Bulk Acoustic Wave) and band-pass filters constructed of such resonators. To increase the edge steepness of the transmission band of a BAW band-pass filter, the invention proposes reducing the effective coupling of a BAW resonator by using the connection in parallel of a BAW resonator and a capacitor instead of only one resonator. In addition, to increase the edge steepness of the transmission band, the use of a connection of coupled BAW resonators in the serial branch of a filter circuit with another resonator or resonator stack in the parallel branch of the filter circuit is proposed, the additional resonator or resonator stack being connected to the center electrode of the resonator stack specified initially.

Claims

1. An apparatus comprising:

a resonator for use with bulk acoustic waves, the resonator comprising;

a lower layer region comprising a first electrode;

an upper layer region comprising a second electrode; and

a piezoelectric layer between the first electrode and the second electrode; and

a capacitor in parallel with the resonator or in series with the resonator.

2. The apparatus of claim 1, further comprising a carrier substrate, the resonator and the capacitor being on the carrier substrate.

3. The apparatus of claim 1, wherein each of the upper layer region and the lower layer region comprises a plurality of layers.

4. The apparatus of claim 3, wherein a plurality of layers in the upper layer region comprises layers that include different materials, and a plurality of layers in the lower layer region comprises layers that include different materials.

5. The apparatus of claim 1, wherein at least one of the upper layer region and the lower layer region comprises an acoustic mirror, the acoustic mirror comprising at least two alternating layers having different acoustic impedances.

6. The apparatus of claim 5, wherein at least one layer of the acoustic mirror comprises an electrode layer.

7. The apparatus of claim 2, wherein the carrier substrate includes an air gap;

and

wherein the resonator is over the air gap.

8. A filter comprising resonators for use with bulk acoustic waves,

each of the resonators comprising:

a lower layer region comprising a first electrode;

an upper layer region comprising a second electrode; and

a piezoelectric layer between the first electrode and the second electrode;

wherein the resonators are in at least one of a ladder-type arrangement, a lattice-type arrangement, and a stacked crystal filter arrangement; and

a capacitor in parallel with at least one or the resonators or in series with at least one of the resonators.

9. The filter of claim 8, wherein the capacitor is connected to only one of the resonators, the capacitor being connected in a circuit path that is in series with, or in parallel with, the one of the resonators.

10. A duplexer comprising a filter according to claim 8.

16. The filter of claim 8, further comprising a carrier substrate, at least one of the resonators and the capacitor being on the carrier substrate.

17. The filter of claim 8, wherein, for each of the resonators, an upper layer region and a lower layer region comprises a plurality of layers.

18. The filter of claim 17, wherein a plurality of layers in each upper layer region comprises layers that include different materials, and a plurality of layers in each lower layer region comprises layers that include different materials.

19. The filter of claim 8, wherein each upper layer region and each lower layer region comprises an acoustic mirror, each acoustic mirror comprising at least two alternating layers having different acoustic impedances.

20. The filter of claim 19, wherein at least one layer of each acoustic mirror comprises an electrode layer.

21. The filter of claim 16, wherein the carrier substrate includes an air gap;

and

wherein at least one or the resonators is over the air gap.

22. A duplexer comprising a filter according to claim 9.

11. An electrical circuit comprising:

a stack of resonators comprising;

first resonators that operate with bulk acoustic waves, the first resonators comprising an upper resonator and a lower resonator, each of the upper resonator and the lower resonator comprising upper and lower electrodes; and

a second resonator the operates with bulk acoustic waves, the second resonator comprising electrodes;

wherein the first resonators and the second resonator each comprise;

a lower electrode, an upper electrode, and a piezoelectric layer arranged between the upper and lower electrodes; and

wherein an upper electrode of the lower resonator and a lower electrode of the upper resonator are electrically connected to an electrode of the second resonator.

12. The electrical circuit of claim 11, wherein an electrode of the second resonator is connected to ground.

13. The electrical circuit of claim 11, wherein the stack of resonators further comprises:

a coupling layer between the upper electrode of the lower resonator and the lower electrode of the upper resonator.

14. The electrical circuit of claim 11, wherein the second resonator comprises an LC resonator.

15. The electrical circuit of claim 11, further comprising a second stack of resonators, the second stack of resonators containing the second resonator.