Thin-film acoustically-coupled transformer
View Patent ↗The acoustically-coupled transformer includes first and second stacked bulk acoustic resonators (SBARs), each having a stacked pair of film bulk acoustic resonators (FBARs) with an acoustic decoupler between them. In one embodiment, the acoustic decoupler comprises a layer of decoupling material has having a nominal thickness equal to an odd integral multiple of one quarter of the wavelength of an acoustic wave having a frequency equal to the transformer's center frequency. In another embodiment, the acoustic decoupler comprises a Bragg stack. Each FBAR has opposed planar electrodes with piezoelectric material between them. The transformer additionally has first terminals, second terminals, a first electrical circuit connecting one FBARs of the first SBAR to one FBAR of the second SBAR and the first terminals, and a second electrical circuit connecting the other FBAR of the first SBAR to the other FBAR of the second SBAR and the second terminals.
1. An acoustically-coupled transformer having a pass band characterized by a center frequency the transformer comprising:
a first stacked bulk acoustic resonator (SBAR) and a second SBAR, each SBAR comprising:
a stacked pair of film bulk acoustic resonators (FBARs), each of the FBARs comprising opposed planar electrodes and a layer of piezoelectric material between the electrodes, and
an acoustic decoupler between the FBARs, the acoustic decoupler comprising a layer of acoustic decoupling material having nominal thickness equal to an odd integral multiple of one quarter of the wavelength in the acoustic decoupling material of an acoustic wave having a frequency equal to the center frequency;
first terminals;
second terminals;
a first electrical circuit connecting one of the FBARs of the first SBAR to one of the FBARs of the second SBAR and to the first terminals, and
a second electrical circuit connecting the other of the FBARs of the first SBAR to the other of the FBARs of the second SBAR and to the second terminals.
2. The transformer of claim 1 , in which the first terminals constitute primary terminals and the second terminals constitute secondary terminals.
3. The transformer of claim 1 , in which:
the piezoelectric material has an acoustic impedance; and
the acoustic decoupling material has an acoustic impedance less than the acoustic impedance of the piezoelectric material.
4. The transformer of claim 3 , in which the acoustic decoupling material has an acoustic impedance intermediate between the acoustic impedance of the piezoelectric material and the acoustic impedance of air.
5. The transformer of claim 1 , in which the acoustic decoupling material has an acoustic impedance in the range from about 2 Mrayl to about 16 Mrayl.
6. The transformer of claim 1 , in which the acoustic decoupling material comprises plastic.
7. The transformer of claim 1 , in which the acoustic decoupling material comprises polymide.
8. The transformer of claim 1 , in which the acoustic decoupling material comprises poly(para-xylylene).
9. The transformer of claim 1 , in which:
the first electrical circuit connects the one of the FBARs of the first SBAR in one of (a) parallel and (b) anti-series with the one of the FBARs of the second SBAR; and
the second electrical circuit connects the other of the FBARs of the first SBAR in one of (c) parallel and (d) anti-series with the other of the FBARs of the second SBAR.
10. The transformer of claim 9 , in which the first terminals constitute primary terminals and the second terminals constitute secondary terminals.
11. The transformer of claim 9 , in which:
the piezoelectric material has an acoustic impedance; and
the acoustic decoupling material has an acoustic impedance less than the acoustic impedance of the piezoelectric material.
12. The transformer of claim 9 , in which the acoustic decoupling material has an acoustic impedance in the range from about 2 Mrayl to about 16 Mrayl.
13. The transformer of claim 9 , in which the acoustic decoupling material comprises plastic.
14. The transformer of claim 1 , in which:
the first electrical circuit connects the one of the FBARs of the first SBAR in one of (a) series and (b) anti-parallel with the one of the FBARs of the second SBAR; and
the second electrical circuit connects the other of the FBARs of the first SBAR in one of (c) series and (d) anti-parallel with the other of the FBARs of the second SBAR.
15. The transformer of claim 14 , in which:
the piezoelectric material of each of the SBARs has an acoustic impedance; and
the acoustic decoupling material has an acoustic impedance less than the acoustic impedance of the piezoelectric material.
16. The transformer of claim 14 , in which the acoustic decoupling material has an acoustic impedance in the range from about 2 Mrayl to about 16 Mrayl.
17. The transformer of claim 14 , in which:
the transformer additionally comprises a substrate arranged support the SBARs;
in the one of the FBARs of each the SBARs, one of the electrodes thereof is a first electrode, the other of the electrodes thereof is a second electrode, and the first electrode is closer to the substrate than the second electrode; and
the first electrical circuit comprises:
an electrical connection between the first electrode of the first SBAR and the second electrode of the second SBAR, and
an electrical connection between the second electrode of the first SBAR and the first electrode of the second SBAR.
18. The transformer of claim 1 , in which the first terminal constitute primary terminals and the second terminals constitute secondary terminals.
19. The transformer of claim 1 , in which:
the transformer additionally comprises a substrate arranged support the SBARs;
in the one of the FBARs of each the SBARs, one of the electrodes thereof is a first electrode, the other of the electrodes thereof is a second electrode, and the first electrode is closer to the substrate than the second electrode; and
the first electrical circuit comprises:
an electrical connection between the first electrode of the first SBAR and the second electrode of the second SBAR, and
an electrical connection between the second electrode of the first SBAR and the first electrode of the second SBAR.
20. An acoustically-coupled transformer, comprising:
a first stacked bulk acoustic resonator (SBAR) and a second SBAR, each SBAR comprising:
a stacked pair of film bulk acoustic resonator (FBARs), each of the FBARs comprising opposed planar electrodes and a layer of piezoelectric material between the electrodes, and
an acoustic decoupler between the FBARs, the acoustic decoupler comprising a Bragg stack:
first terminal;
second terminals;
a first electrical circuit connecting one of the FBARs of the first SBAR to one of the FBARs of the second SBAR and to the first terminals, and
a second electrical circuit connecting the other of the FBARs of the first SBAR to the other of the FBARs of the second SBAR and to the second terminals.
21. The transformer of claim 20 , in which the Bragg structure comprises one or more low acoustic impedance Bragg elements interleaved with high acoustic impedance Bragg elements.
22. The transformer of claim 21 , in which two of the high acoustic impedance Bragg elements additionally serve as one of the electrodes of each of the FBARs.
23. The transformer of claim 20 , in which:
the first electrical circuit connects the one of the FBARs of the first SBAR in one of (a) series and (b) anti-parallel with the one of the FBARs of the second SBAR; and
the second electrical circuit connects the other of the FBARs of the first SBAR in one of (c) series and (d) anti-parallel with the other of the FBARs of the second SBAR.
24. The transformer of claim 23 , in which:
the transformer additionally comprises a substrate arranged support the SBARs;
in the one of the FBARs of each the SBARs, one of the electrodes thereof is a first electrode, the other of the electrodes thereof is a second electrode, and the first electrode is closer to the substrate than the second electrode; and
the first electrical circuit comprises:
an electrical connection between the first electrode of the first SBAR and the second electrode of the second SBAR, and
an electrical connection between the second electrode of the first SBAR and the first electrode of the second SBAR.
25. The transformer of claim 23 , in which the Bragg structure comprises one or more low acoustic impedance Bragg elements interleaved with high acoustic impedance Bragg elements.
26. The transformer of claim 25 , in which two of the high acoustic impedance Bragg elements additionally serve as one of the electrodes of each of the FBARs.
27. The transformer of claim 20 , in which:
the first electrical circuit connects the one of the FBARs of the first SBAR in one of (a) parallel and (b) anti-series with the one of the FBARs of the second SBAR; and
the second electrical circuit connects the other of the FBARs of the first SBAR in one of (c) parallel and (d) anti-series with the other of the FBARs of the second SBAR.
28. The transformer of claim 27 , in which the Bragg structure comprises one or more low acoustic impedance Bragg elements interleaved with high acoustic impedance Bragg elements.
29. The transformer of claim 28 , in which two of the high acoustic impedance Bragg elements additionally serve as one of the electrodes of each of the FBARs.
30. The transformer of claim 20 , in which:
the transformer additionally comprises a substrate arranged support the SBARs;
in the one of the FBARs of each the SBARs, one of the electrodes thereof is a first electrode, the other of the electrodes thereof is a second electrode, and the first electrode is closer to the substrate than the second electrode; and
the first electrical circuit comprises:
an electrical connection between the first electrode of the first SBAR and the second electrode of the second SBAR, and
an electrical connection between the second electrode of the first SBAR and the first electrode of the second SBAR.
31. The transformer of claim 30 , in which the Bragg structure comprises one or more low acoustic impedance Bragg elements interleaved with high acoustic impedance Bragg elements.
32. The transformer of claim 31 , in which two of the high acoustic impedance Bragg elements additionally serve as one of the electrodes of each of the FBARs.