Film acoustically-coupled transformer with increased common mode rejection

• US 20050093659A1
• Filed: 10/13/2004
• Published: 05/05/2005
• Est. Priority Date: 10/30/2003
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Avago Technologies Wireless IP Singapore Pte Limited (Broadcom, Inc.)
• Inventors: Larson, John D. III, Ellis, Stephen L., Sarkeshik, Naghmeh
• Granted Patent: US 7,388,455 B2
• Time in Patent Office: Days
• US Class Current: 333/191
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/49175 Parallel arrangements
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H03H 9/132 characterized by a particular shape
• CPC Class Codes: H03H 9/584 Coupled Resonator Filters [CFR]
• CPC Class Codes: H03H 9/587 Air-gaps
• CPC Class Codes: H03H 9/605 consisting of a ladder configuration
• CPC Class Codes: Y10T 29/42 Piezoelectric device making

Abstract

The film acoustically-coupled transformer (FACT) has a first and second decoupled stacked bulk acoustic resonators (DSBARs). Each DSBAR has a lower film bulk acoustic resonator (FBAR), an upper FBAR atop the lower FBAR, and an acoustic decoupler between them FBARs. Each FBAR has opposed planar electrodes and a piezoelectric element between the electrodes. A first electrical circuit interconnects the lowers FBAR of the first DSBAR and the second DSBAR. A second electrical circuit interconnects the upper FBARs of the first DSBAR and the second DSBAR. In at least one of the DSBARs, the acoustic decoupler and one electrode of the each of the lower FBAR and the upper FBAR adjacent the acoustic decoupler constitute a parasitic capacitor. The FACT additionally has an inductor electrically connected in parallel with the parasitic capacitor. The inductor increases the common-mode rejection ratio of the FACT.

Claims

1. A film acoustically-coupled transformer (FACT), comprising:

a first decoupled stacked bulk acoustic resonator (DSBAR) and a second DSBAR, each DSBAR comprising;

a lower film bulk acoustic resonator (FBAR) and an upper FBAR, the upper FBAR stacked atop the lower FBAR, each FBAR comprising opposed planar electrodes and a piezoelectric element between the electrodes, and

an acoustic decoupler between the FBARs;

a first electrical circuit interconnecting the lower FBARs; and

a second electrical circuit interconnecting the upper FBARs;

in which;

in at least one of the DSBARs, the acoustic decoupler, one of the electrodes of the lower FBAR adjacent the acoustic decoupler and one of the electrodes of the upper FBAR adjacent the acoustic decoupler constitute a parasitic capacitor; and

the FACT additionally comprises an inductor electrically connected in parallel with the parasitic capacitor.

2. The FACT of claim 1, in which:

the FACT has a pass band; and

the inductor and the parasitic capacitor constitute part of a parallel resonant circuit having a resonant frequency in the pass band.

3. The FACT of claim 1, in which:

the FACT additionally comprises a substrate arranged to support the DSBARs, the substrate having a major surface; and

the inductor is located over the substrate.

4. The FACT of claim 3, in which:

the substrate comprises a cavity extending into the substrate from the major surface thereof; and

the inductor is suspended over the cavity.

5. The FACT of claim 3, in which the inductor comprises:

a layer of insulating material; and

an inductive element over the layer of insulating material.

6. The FACT of claim 5, in which at least part of the layer of insulating material and the piezoelectric element of one of the FBARs are portions of a common layer.

7. The FACT of claim 5, in which at least part of the layer of insulating material and the acoustic decoupler are portions of a common layer.

8. The FACT of claim 5, in which the layer of insulating material is located on the major surface of the substrate.

9. The FACT of claim 5, in which at least part of the inductive element and one of the electrodes of one of the FBARs of each of the DSBARs are portions of a common layer.

10. The FACT of claim 1, in which:

the FACT additionally comprises;

a substrate supporting the DSBARs, and

a daughter board comprising electrically-conducting traces; and

the substrate and the inductor are mounted on the daughter board electrically interconnected by the conductive traces.

11. The FACT of claim 1, in which:

the FACT additionally comprises a package housing the DSBARs, the package comprising;

a first substrate supporting the DSBARs,

a second substrate disposed parallel to the first substrate, and

a gasket extending between the first substrate and the second substrate; and

the inductor is mounted on the second substrate facing the first substrate.

12. The FACT of claim 11, in which the substrates and the gasket collectively define an hermetic chamber in which the DSBARs and the inductor are located.

13. The FACT of claim 11, in which:

the package additionally comprises an interconnection post extending between the first substrate and the second substrate; and

the inductor is electrically connected to one of the electrodes constituting the parasitic capacitor via the interconnection post.

14. The FACT of claim 1, in which:

the FACT additionally comprises a package, comprising;

a first substrate supporting the DSBARs,

a second substrate disposed parallel to the first substrate, and

a gasket extending between the first substrate and the second substrate; and

the inductor is defined in a metal layer located on a surface of the second substrate.

15. The FACT of claim 14, in which:

the package additionally comprises an interconnection post extending between the first substrate and the second substrate; and

the inductor is electrically connected to one of the electrodes of the parasitic capacitor via the interconnection post.

16. The FACT of claim 1, additionally comprising an isolating capacitor electrically connected in series with the inductor.

17. The FACT of claim 16, in which:

the inductor is part of a parallel resonant circuit having a resonant frequency; and

the inductor and the isolating capacitor have a series resonance at a frequency differing from the resonant frequency by more than one octave.

18. The FACT of claim 17, in which:

the isolating capacitor comprises a pair of parallel plates and a dielectric between the parallel plates;

one of the parallel plates and one of the electrodes of the parasitic capacitor are parts of a first conductive common layer;

the other of the parallel plates and the other of the electrodes of the parasitic capacitor are parts of a second common conductive layer; and

the dielectric of the isolating capacitor and the acoustic coupler are parts of a third common layer.

19. The FACT of claim 1, in which:

the FACT has a pass band having a center frequency; and

each of the acoustic decouplers comprises a layer of acoustic decoupling material having a thickness nominally equal to one quarter of the wavelength in the acoustic decoupling material of an acoustic signal equal in frequency to the center frequency.

20. The FACT of claim 1, in which the acoustic decoupling material comprises one of polyimide, paralene and crosslinked polyphenylene polymer.

21. A film acoustically-coupled transformer (FACT) having a pass band, the FACT comprising:

a first decoupled stacked bulk acoustic resonator (DSBAR) and a second DSBAR, each DSBAR comprising;

a lower film bulk acoustic resonator (FBAR) and an upper FBAR, the upper FBAR stacked atop the lower FBAR, each FBAR comprising opposed planar electrodes and a piezoelectric element between the electrodes, and

an acoustic decoupler between the FBARs,

a first electrical circuit interconnecting the lower FBARs; and

a second electrical circuit interconnecting the upper FBARs;

in which;

in at least one of the DSBARs, the acoustic decoupler, one of the electrodes of the lower FBAR adjacent the acoustic decoupler and one of the electrodes of the upper FBAR adjacent the acoustic decoupler constitute a parasitic capacitor; and

the FACT additionally comprises means for forming with the parasitic capacitor a parallel resonant circuit having a resonant frequency in the pass band.

22. The FACT of claim 21, in which the means for forming comprises an inductor and an electrical circuit electrically connecting the parasitic capacitor to the inductor.

23. A DSBAR device having a band-pass characteristic characterized by a center frequency, the DSBAR device comprising:

a lower film bulk acoustic resonator (FBAR) and an upper FBAR stacked on the lower FBAR, each FBAR comprising opposed planar electrodes and a piezoelectric element between the electrodes; and

an acoustic decoupler between the FBARs, the acoustic decoupler structured to impose a phase change nominally equal to π

/2 on an acoustic signal equal in frequency to the center frequency.

24. The DSBAR device of claim 23, in which:

the acoustic decoupler comprises no more than one acoustic decoupling layer of acoustic decoupling material; and

the acoustic decoupling layer has a thickness nominally equal to one quarter of the wavelength of the acoustic signal in the acoustic decoupling material.

25. The DSBAR device of claim 23, in which the acoustic decoupler comprises acoustic decoupling layers of acoustic decoupling materials having different acoustic impedances.

26. The DSBAR device of claim 23, in which:

the acoustic decoupler and adjacent ones of the electrodes of the lower FBAR and the electrodes of the upper FBAR constitute a parasitic capacitor; and

the DSBAR device additionally comprises an inductor electrically connected in parallel with the parasitic capacitor.