Increased bandwidth thin film resonator having a columnar structure

• US 6,486,751 B1
• Filed: 09/26/2000
• Issued: 11/26/2002
• Est. Priority Date: 09/26/2000
• Status: Expired due to Term

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Agere Systems Incorporated (Broadcom, Inc.)
• Inventors: Barber, Bradley Paul, Chan, Edward, Graebner, John Edwin
• Primary Examiner(s): Pascal, Robert J.
• Assistant Examiner(s): Summons, Barbara
• Application Number:
  US09/669,944
• Time in Patent Office: 791 Days
• Field of Search: 333/186-192, 310/321, 310/322, 310/324, 310/335, 29/253.5
• US Class Current: 333/187
• CPC Class Codes: H03H 3/02 for the manufacture of piezoelectric or electrostrictive resonators or networks H03H3/08 takes precedence
• CPC Class Codes: H03H 9/172 Means for mounting on a substrate, i.e. means constituting the material interface confining the waves to a volume
• CPC Class Codes: H03H 9/173 Air-gaps
• CPC Class Codes: H03H 9/175 Acoustic mirrors
• CPC Class Codes: Y10T 29/42 Piezoelectric device making

Abstract

Improved bandwidths and oscillation uniformity is obtained through a rod type BAW TFR structure formed over a semiconductor support. The resonator includes a first and a second electrode and a plurality of distinct elemental piezoelectric structures between the electrodes. Each of the piezoelectric structures has a length, a width and a height, the height being the distance between the electrodes. The height of the piezoelectric structures is at least equal to or more than one of the length or the width, or both. Such resonator is made by forming on a common bottom a plurality of distinct piezoelectric structures each having a length, a width and a height, wherein the height is formed at least equal to the width or the length of the piezoelectric structure, and forming a common top electrode thereover.

Claims

1. A thin film resonator comprising a plurality of distinct elemental resonators separated by spaces and connected in parallel, each of said resonators having a length, a width and a height, wherein said height is at least equal to one of said width and said length, wherein said spaces separating said elemental resonators are filled with a low dielectric constant filler material and electrical connection means for connecting said parallel connected elemental resonators to other circuitry.

2. The thin film resonator according to claim 1, wherein said plurality of distinct elemental resonators share at least one common electrode.

3. The thin film resonator according to claim 1 wherein said height is at least equal to both said length and said width.

4. The thin film resonator according to claim 1 wherein said low constant dielectric filler material has a dielectric constant <

5 and exhibits acoustic impedance lower than the acoustic impedance exhibited by the piezoelectric material.

5. The thin film resonator according to claim 1 further comprising an acoustic mirror.

6. The thin film acoustic resonator according to claim 5 wherein said acoustic mirror is located only under said plurality of distinct elemental resonators.

7. The thin film resonator according to claim 1 wherein said elemental resonators each comprise a piezoelectric material over a first supporting membrane extending over a cavity, said cavity located under the plurality of distinct elemental resonators.

8. The thin film resonator according to claim 1 wherein said elemental resonators are each self supporting and bridge over a cavity located under the plurality of distinct elemental resonators.

9. The thin film acoustic resonator according to claim 8 wherein under each of said elemental resonators and in contact therewith is a first conductive thin film.

10. The thin film acoustic resonator according to claim 9 further comprising a second conductive film opposite said first conductive film, said second conductive film being over said elemental resonators and in contact therewith.

11. A thin film acoustic resonator comprising a support, a first electrode over said support, a piezoelectric layer on said first electrode and a second electrode on said piezoelectric layer wherein said piezoelectric layer comprises a plurality of substantially identical distinct piezoelectric structures adjacent and separated from each other by spaces, said spaces filled with a low dielectric constant filler material, each of said structures having a length, a width and a height, said height being at least equal to one of said width and said length, said electrodes electrically connecting said piezoelectric structures in parallel, a first electrical connection means for connecting to said first electrode and a second electrical connection means for connecting to said second electrode.

12. The thin film acoustic resonator according to claim 11 wherein said piezoelectric structures are elongated piezoelectric structures having a length and at least one of said first and second electrode extends over and along said length of said elongated piezoelectric structures in contact therewith and does not extend substantially over the spaces.

13. The thin film resonator according to claim 12 wherein said at least one of said second and first electrode is the second electrode and wherein the first electrode comprises a plurality of conductive strips extending in a direction crossing the length of said plurality of elongated piezoelectric structures.

14. The thin film resonator according to claim 13 wherein said direction is substantially perpendicular to said length of said structures.

15. The thin film bulk acoustic resonator according to claim 11 further comprising at least one conductive bus along a side of at least one of said second and first electrode said conductive bus having lower resistance than said second and first electrodes.

16. The thin film resonator according to claim 11 wherein said support comprises a stack of acoustically reflecting layers under said thin film resonator.

17. The thin film resonator according to claim 11 wherein said support comprises a membrane extending over a cavity in said support, and wherein said resonator is over said membrane and said cavity.

18. The thin film resonator according to claim 11 wherein said piezoelectric material comprises an element selected from the group consisting of AlN, CdS, ZnO and combinations thereof.

19. The thin film resonator according to claim 18 wherein the electrodes comprise Al, Mo, Ti, Cr, Ag, Pt, Cu, Au and combinations thereof.

20. An electronic circuit on a semiconductor substrate comprising at least one thin film acoustic resonator comprising a plurality of distinct elemental resonators separated by spaces and connected in parallel wherein said spaces separating said elemental resonators are filled with a low dielectric constant filler material, each of said elemental resonators having a length, a width and a height, wherein said height is at least equal to one of said width and said length.

21. The electronic circuit according to claim 20 wherein said circuit is an acoustic resonator filter.

22. A method of manufacturing a thin film resonator comprising:

forming a first electrode on a support;

forming a piezoelectric layer on said first electrode, said layer having a thickness;

etching said piezoelectric layer to form a pattern of a plurality of distinct piezoelectric structures on said first electrode, each of said structures having a length, a width and a height, the height being substantially the same as the piezoelectric layer thickness, wherein one of said length and said width is equal to or less than the structure height;

filling said spaces with a low dielectric constant dielectric filler material that has a dielectric constant >

5 and exhibits acoustic impedance lower than the acoustic impedance exhibited by the piezoelectric material; and

forming a second electrode on said etched and filled piezoelectric layer, said second electrode spaced from said first electrode.

23. The method according to claim 22 wherein said dielectric material is a low temperature oxide (LTO).

24. The method according to claim 22 wherein said dielectric material is porous SiO₂.

25. The method according to claim 22 wherein said dielectric material is a polymer.

26. The method according to claim 22 wherein said dielectric material is a polyimide.

27. The method according to claim 22 further comprising forming said first electrode over an acoustic mirror formed in said supporting structure.

28. The method according to claim 22 further comprising forming said first electrode as a self supporting membrane over a cavity on a supporting structure.

29. A thin film acoustic resonator comprising a support, a first electrode over said support, a piezoelectric layer on said first electrode and a second electrode on said piezoelectric layer wherein said first electrode comprises a plurality of elongated strips extending along a first direction substantially parallel to said support, said second electrode also comprises a plurality of strips extending along a second direction also parallel to said support, said second direction crossing said first direction forming a plurality of crossover areas, and wherein said piezoelectric layer comprises a plurality of substantially identical distinct piezoelectric structures adjacent and separated from each other by spaces, each of said structures having a length, a width and a height, said height being at least equal to one of said width and said length, said piezoelectric structures located substantially between said first and said second electrodes in said crossover area.