Filters

• US 20040061416A1
• Filed: 03/20/2003
• Published: 04/01/2004
• Est. Priority Date: 11/29/2000
• Status: Active Grant

• Current Assignee: Snaptrack Incorporated (Qualcomm, Inc.)
• Original Assignee: TDK Corporation
• Inventors: Whatmore, Roger W, Kirby, Paul B, Imura, Masaaki, Su, Qingxin, Komuro, Eiju
• Granted Patent: US 7,187,254 B2
• Time in Patent Office: Days
• US Class Current: 310/312
• CPC Class Codes: H03H 3/04 for obtaining desired frequency or temperature coefficient
• CPC Class Codes: H03H 9/174 Membranes
• CPC Class Codes: H03H 9/568 consisting of a ladder configuration

Abstract

Multiple thin film bulk acoustic resonators (10, 11) configured in series (10) and parallel (11) within a coplanar waveguide line structure provides a compact ladder filter. The resonators (10, 11) are formed over an opening (28) in a substrate (20) and connected to associated circuitry by one or more transmission lines formed on the substrate (20). The arrangement of the resonators (10, 11) between the ground and signal lines of a coplanar line structure provides a means of minimising the area of the filter. Embedding a ladder filter within the coplanar transmission line structure eliminates the need for wire bonds, thus simplifying fabrication. Embodiments for 2×2, and hither order filters are described.

Claims

1. An electric filter comprising a plurality of FBARs (A,B;

10,11) consisting of a thin layer of piezoelectric material (23) sandwiched between two metal layers (24,25), the FBARs (A,B;

10,11) being linked in a series (A;

10) and parallel (B;

11) connection arrangement such that the series FBARs electrodes (24) form part of the signal line of a coplanar waveguide transmission line, while the parallel FBAR electrodes (27) are linked to one side or both sides of the ground coplanar transmission line.

2. An electric filter according to claim 1, wherein the FBARs (A,B;

10,11) are positioned in an ABBA configuration.

3. An electric filter according to claim 1, wherein the FBARs (A,B;

10,11) are positioned in an ABAB configuration.

4. An electric filter according to any preceding claim, wherein the FBARs (A,B;

10,11) are positioned without air-bridges or metal tracks formed over the edge of the piezoelectric layer.

5. An electric filter according to any preceding claim, wherein the piezoelectric material (23) is zinc oxide.

6. An electric filter according to any one of claims 1 to 4, wherein the piezoelectric material (23) is aluminium nitride.

7. An electric filter according to any one of claims 1 to 4, wherein the piezoelectric material (23) is lead titanate zirconate.

8. An electric filter according to any one of claims 1 to 4, wherein the piezoelectric material (23) is lead scandium tantalum oxide.

9. An electric filter according to any one of claims 1 to 4, wherein the piezoelectric material (23) is bismuth sodium titanium oxide.

10. An electric filter according to claim 1, wherein access (26) is provided to electrodes for poling ferroelectric FBAR filters.

13. A filter according to any one of the preceding claims wherein the FBARs (A,B;

10,11) have a common bottom electrode (25).

11. A ladder filter comprising series and parallel FBARs (A,B;

10,11) arranged within a coplanar waveguide structure such that a top electrode (24) of each series FBAR (A;

10) forms part of a signal line of the coplanar waveguide structure and a top electrode (27) of each parallel FBAR (B;

11) forms part of a ground line of the coplanar waveguide structure.

12. A ladder filter according to claim 11, wherein the signal line is positioned between two ground lines.

14. A ladder filter comprising a plurality of FBARs (A,B;

10,11) in series (A;

10) and parallel (B;

11) configuration within a coplanar waveguide structure wherein the FBARs (A,B;

10,11) have electrodes (24,27) formed as part of transmission lines of the coplanar waveguide structure.

15. A ladder filter comprising a plurality of FBARs (A,B;

10,11) in series (A;

10) and parallel (B;

11) configuration within a coplanar waveguide structure wherein the FBARs (A,B;

10,11) formed on a substrate (20) are connected to associated circuitry by one or more transmission lines formed on the substrate (20).

16. A ladder filter comprising a plurality of FBARs (A,B;

10,11) in series (A;

10) and parallel (B;

11) configuration included within a transmission line structure of a coplanar waveguide.