Cavity-less film bulk acoustic resonator (FBAR) devices

• US 7,332,985 B2
• Filed: 10/19/2004
• Issued: 02/19/2008
• 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: Oshmyansky, Yury, Bradley, Paul A., Larson, John D III, Ellis, Stephen
• Primary Examiner(s): Summons; Barbara
• Application Number:
  US10/969,744
• Publication Number:
  US 20050104690A1
• Time in Patent Office: 1,218 Days
• Field of Search: 333187-189, 333/133
• US Class Current: 333/187
• CPC Class Codes: H03H 9/02102 of temperature influence cutting angles H03H9/02015
• CPC Class Codes: H03H 9/132 characterized by a particular shape
• CPC Class Codes: H03H 9/175 Acoustic mirrors
• CPC Class Codes: H03H 9/584 Coupled Resonator Filters [CFR]
• CPC Class Codes: H03H 9/587 Air-gaps
• CPC Class Codes: H03H 9/589 Acoustic mirrors
• CPC Class Codes: H03H 9/605 consisting of a ladder configuration

Abstract

The film bulk acoustic resonator (FBAR) device comprises a substrate, an acoustic Bragg reflector over the substrate, a piezoelectric element over the acoustic Bragg reflector, and a remote-side electrode over the piezoelectric element. The acoustic Bragg reflector comprises a metal Bragg layer juxtaposed with a plastic Bragg layer. The large ratio between the acoustic impedances of the plastic material of the plastic Bragg layer and the metal of the metal Bragg layer provides sufficient acoustic isolation between the FBAR and the substrate for the frequency response of the FBAR device to exhibit minor, if any, spurious artifacts arising from undesirable acoustic coupling between the FBAR and the substrate.

Claims

1. A film bulk acoustic resonator (FBAR) device, comprising:

a substrate;

an acoustic Bragg reflector over the substrate, the acoustic Bragg reflector comprising a metal Bragg layer and a plastic Bragg layer juxtaposed with the metal Bragg layer;

a piezoelectric element over the acoustic Bragg reflector; and

a remote-side electrode over the piezoelectric element wherein;

the FBAR device has a band-pass characteristic having a center frequency;

at least one of the Bragg layers has a nominal thickness equal to one quarter of the wavelength in the material of the respective Bragg layer of an acoustic signal equal in frequency to the center frequency; and

the metal Bragg layer is thinner than the nominal thickness.

2. The FBAR device of claim 1, in which the metal Bragg layer is patterned to define a substrate-side electrode.

3. The FBAR device of claim 2, in which:

the substrate-side electrode, the piezoelectric element and the remote-side electrode collectively comprise a lower FBAR; and

the FBAR device additionally comprises;

an upper FBAR stacked on the lower FBAR, the upper FBAR comprising opposed planar electrodes and a piezoelectric element between the electrodes, and an acoustic decoupler between the FBARs.

4. The FBAR device of claim 3, in which:

the lower FBAR, the upper FBAR and the acoustic decoupler comprise a first decoupled stacked bulk acoustic resonator (DSBAR); and

the FBAR device additionally comprises;

a second DSBAR over the plastic Bragg layer, the second DSBAR comprising a lower FBAR, an upper FBAR and an acoustic decoupler between the FBARs, and a first electrical circuit interconnecting the lower FBARs, and a second electrical circuit interconnecting the upper FBARs.

5. The FBAR device of claim 1, in which the plastic Bragg layer comprises polyimide.

6. The FBAR device of claim 1, in which the plastic Bragg layer comprises parylene.

7. The FBAR device of claim 1, in which the plastic Bragg layer comprises a crosslinked polyphenylene polymer.

8. The FBAR device of claim 7, in which the crosslinked polyphenylene polymer is formed from a precursor solution.

9. The FBAR device of claim 1, in which the metal Bragg layer comprises a refractory metal.

10. The FBAR device of claim 1, in which the acoustic Bragg reflector has sides inset from the sides of the substrate.

11. The FBAR device of claim 1, additionally comprising a substrate-side electrode between the acoustic Bragg reflector and the piezoelectric element.

12. The FBAR device of claim 11, in which:

the substrate-side electrode, the piezoelectric element and the remote-side electrode collectively comprise a lower FBAR; and

the FBAR device additionally comprises;

an upper FBAR stacked on the lower FBAR, the upper FBAR comprising opposed planar electrodes and a piezoelectric element between the electrodes, and an acoustic decoupler between the FBARs.

13. The FBAR device of claim 12, in which:

the lower FBAR, the upper FBAR and the acoustic decoupler constitute a first decoupled stacked bulk acoustic resonator (DSBAR); and

the FBAR device additionally comprises;

a second DSBAR over the acoustic Bragg reflector, the second DSBAR comprising a lower FBAR, an upper FBAR and an acoustic decoupler between the FBARs, and a first electrical circuit interconnecting the lower FBARs, and a second electrical circuit interconnecting the upper FBARs.

14. The FBAR device of claim 11 in which at least one of the plastic Bragg layers comprises polyimide.

15. The FBAR device of claim 11, in which at least one of the plastic Bragg layers comprises parylene.

16. The FBAR device of claim 11, in which at least one of the plastic Bragg layer comprises a crosslinked polyphenylene polymer.

17. The FBAR device of claim 16, in which the crosslinked polyphenylene polymer is formed from a precursor solution.

18. The FBAR device of claim 11, in which the metal Bragg layer comprises a refractory metal.

19. The FBAR device of claim 11, in which:

the metal Bragg layer is a first metal Bragg layer;

the acoustic Bragg reflector additionally comprises a second metal Bragg layer juxtaposed with the plastic Bragg layer.

20. The FBAR device of claim 19, in which:

the plastic Bragg layer is a first plastic Bragg layer; and

the acoustic Bragg reflector additionally comprises a second plastic Bragg layer juxtaposed with the first metal Bragg layer.

21. The FBAR device of claim 11, in which:

the plastic Bragg layer is a first plastic Bragg layer;

the acoustic Bragg reflector additionally comprises a second plastic Bragg layer juxtaposed with the metal Bragg layer.

22. A film bulk acoustic resonator (FBAR) device, comprising:

a substrate;

an acoustic Bragg reflector over the substrate, the acoustic Bragg reflector comprising a first Bragg layer and a second Bragg layer juxtaposed with the first Bragg layer, the first Bragg layer comprising a first material having an acoustic impedance less than five Mrayl, the second Bragg layer comprising a second material having an acoustic impedance greater than 50 Mrayl;

a piezoelectric element over the acoustic Bragg reflector; and

a remote-side electrode over the piezoelectric element, wherein;

the FBAR device has a band-pass characteristic having a center frequency;

at least one of the Bragg layers has a nominal thickness equal to one quarter of the wavelength in the material of the respective Bragg layer of an acoustic signal equal in frequency to the center frequency; and

the metal Bragg layer is thinner than the nominal thickness.

23. The FBAR device of claim 22, in which the one of the Bragg layers is patterned to define a substrate-side electrode.

24. The FBAR device of claim 22, additionally comprising a substrate-side electrode between the acoustic Bragg reflector and the piezoelectric element.

25. The FBAR device of claim 22, in which:

the first material has an acoustic impedance less than three; and

the second material has an acoustic impedance greater than 60 Mrayl.

26. A film bulk acoustic resonator (FBAR) device, comprising:

a substrate;

an acoustic Bragg reflector over the substrate, the acoustic Bragg reflector comprising a first Bragg layer and a second Bragg layer juxtaposed with the first Bragg layer, the first Bragg layer comprising a first material having a first acoustic impedance, the second Bragg layer comprising a second material having a second acoustic impedance, the second acoustic impedance and the first acoustic impedance having a ratio greater than ten;

a piezoelectric element over the second Bragg layer; and

a remote-side electrode over the piezoelectric element, wherein;

the FBAR device has a band-pass characteristic having a center frequency;

at least one of the Bragg layers has a nominal thickness equal to one quarter of the wavelength in the material of the respective Bragg layer of an acoustic signal equal in frequency to the center frequency; and

the metal Bragg layer is thinner than the nominal thickness.

27. The FBAR device of claim 26, in which one of the Bragg layers is patterned to define a substrate-side electrode.

28. The FBAR device of claim 26, additionally comprising a substrate-side electrode between the third Bragg layer and the piezoelectric element.

29. The FBAR device of claim 26, in which the second acoustic impedance and the first acoustic impedance have a ratio greater than 16.