Noise suppression method for wave filter

• US 7,057,476 B2
• Filed: 05/25/2004
• Issued: 06/06/2006
• Est. Priority Date: 12/30/2003
• Status: Active Grant

• Current Assignee: Industrial Technology Research Institute
• Original Assignee: Industrial Technology Research Institute
• Inventors: Hwu, Keh-Long
• Primary Examiner(s): Summons, Barbara
• Application Number:
  US10/853,873
• Publication Number:
  US 20050140465A1
• Time in Patent Office: 742 Days
• Field of Search: 333187-189, 310/312, 310/320
• US Class Current: 333/187
• CPC Class Codes: H03H 9/0211 of reflections
• CPC Class Codes: H03H 9/02118 of lateral leakage between adjacent resonators

Abstract

A noise suppression method of a wave filter used to eliminate standing wave signal interferences in the acoustic wave filter consisted by a plurality of film bulk acoustic resonators (FBARs). The method is to provide a plurality of scatterers in the structured consisted by the FBARs, thereby creating an band-gap structure due to the material characteristics difference, which consequently generates a destructive interfering effect to the transverse higher harmonics vibration within a specific operating frequency range, and ultimately decreases or even eliminates any parasitic effects. Therefore, within the operation frequency range of this band-gap structure, abnormal signals created by any transverse wave modes cannot exist. In addition, an acoustic shield can be provided by phononic crystal structures between different FBARs, thus acoustic shielding any mutual interference within the operation frequency range.

Claims

1. A noise suppression method for a wave filter, the wave filter being provided with at least one film bulk acoustic resonator (FBAR), a piezoelectric film being located at the center of the FBAR, the piezoelectric film having an upper surface and a lower surface, said upper and lower surfaces being plated with conductive material to be used as an upper working electrode and a lower working electrode, respectively, wherein a region overlapping the piezoelectric film and the upper and lower working electrodes forms an acoustic resonant cavity, the noise suppression method comprising at least the following steps of:

selecting the region overlapping the piezoelectric film and the upper and lower working electrodes in the structure of the FBAR; and

providing a plurality of noise scatterers in the structure embodied by the region, wherein said noise scatterers are filled with material that increases a material characteristic difference and a cross section of the scatters is of a random geometrical shape.

2. The method as claimed in claim 1, wherein the noise scatterers are hollow cylindrical structures penetrating the piezoelectric film to connect together the upper and lower working electrodes.

3. The method as claimed in claim 1, wherein the noise scatterers are void structures located on the surfaces of the upper and lower working electrodes.

4. The method as claimed in claim 1, wherein the conductive material with which said upper and lower surfaces are plated is a metal film material.

5. The method as claimed in claim 4, wherein the metal film material is one of Aluminum (Al), Gold (Au), and Molybdenum (Mo).

6. The method as recited in claim 1, wherein the piezoelectric film is a mechanical-electrical convertible film material.

7. The method as claimed in claim 6, wherein the mechanical-electrical convertible film material consists of one of Aluminum Nitride (AlN), lead zirconate titanate (PZT), lead lanthanum zirconium titanate (PLZT), Cadmium Sulphide (CdS), Gallium Arsenide (GaAs), and Zinc Oxide (ZnO).

8. The method as claimed in claim 1, wherein the noise to be suppressed comprises transverse waves produced by transverse strain vibration of the acoustic resonant cavity.

9. The method as claimed in claim 1, wherein the noise scatterers are arranged into a periodic array or are randomly arranged.

10. The method as claimed in claim 1, wherein the FBAR is constructed as an air bridge on a substrate, on a frontside or backside etched cavity or a Bragg acoustic reflector.

11. A noise suppression method for a wave filter, the wave filter being provided with at least one film bulk acoustic resonator (FBAR), a piezoelectric film being located at the center of the FBAR, the piezoelectric film having an upper surface and a lower surface, said upper and lower surfaces being plated with conductive material to be used as upper working electrode and a lower working electrode, respectively, wherein a region overlapping the piezoelectric film and the upper and lower working electrodes forms an acoustic resonant cavity, the noise suppression method comprising at least the following steps of:

selecting a the region not overlapping the piezoelectric film and the upper and lower working electrodes in the structure of the FBAR; and

providing a plurality of noise scatterers in the structure embodied by said region, wherein said noise scatterers are filled with material that increases a material characteristic difference and a cross section of the scatterers is of a random geometrical shape.

12. The method as claimed in claim 11, wherein the noise scatterers are arranged into a periodic array or are randomly arranged.

13. The method as claimed in claim 11, wherein the FBAR is constructed as an air-bridge on the a substrate, or in a front-side and backside etched cavity or a Bragg acoustic reflector.

14. The method as claimed in claim 11, wherein the noise to be suppressed comprises transverse waves produced by transverse strain vibration of the acoustic resonant cavity.

15. The method as claimed in claim 11, wherein the conductive material with which said upper and lower surfaces are plated is a metal film material.

16. The method as claimed in claim 15, wherein the metal film material is one of Aluminum (Al), Gold (Au), and Molybdenum (Mo).

17. The method as claimed in claim 11, wherein the piezoelectric film is a mechanical-electrical convertible film material.

18. The method as claimed in claim 17, wherein the mechanical-electrical convertible film material consists of one of Aluminum Nitride (AlN), lead zirconate titanate (PZT), lead lanthanum zirconium titanate (PLZT), Cadmium Sulphide (CdS), Gallium Arsenide (GaAs), and Zinc Oxide (ZnO).

19. A noise suppression method of for a wave filter, the wave filter being provided with at least one film bulk acoustic resonator (FBAR), a piezoelectric film being located at the center of the FBAR, the piezoelectric film having an upper surface and a lower surface, said upper and lower surfaces being plated with conductive material to be used as an upper working electrode and a lower working electrode, respectively, wherein a region overlapping the piezoelectric film and the upper and lower working electrodes forms an acoustic resonant cavity, the noise suppression method comprising at least the following step of:

providing a plurality of noise scatterers over the entire piezoelectric film.

20. The method as claimed in claim 19, wherein the noise scatterers are filled with material that increases a material characteristic difference and a cross section of the scatterers is of a random geometrical shape.

21. The method as claimed in claim 19, wherein the noise scatterers are arranged into a periodic array or are randomly arranged.

22. The method as claimed in claim 19, wherein the FBAR is constructed as an air-bridge on a substrate, or in a front-side and backside etched cavity or a Bragg acoustic reflector.

23. The method as claimed in claim 19, wherein the noise to be suppressed comprises transverse waves produced by transverse strain vibration of the acoustic resonant cavity.

24. The method as claimed in claim 19, wherein the noise scatterers are hollow cylindrical structures penetrating the piezoelectric film to connect together the upper and lower working electrodes.

25. The method as claimed in claim 19, wherein the noise scatterers are void structures located on the upper and lower working electrodes.

26. The method as claimed in claim 19, wherein the conductive material is a metal film material.

27. The method as claimed in claim 26, wherein the metal film material is one of Aluminum (al), Gold (Au), and Molybdenum (Mo).

28. The method as claimed in claim 19, wherein the piezoelectric film is a mechanical-electrical convertible film material.

29. The method as claimed in claim 28, wherein the mechanical-electrical convertible film material consists of one of Aluminum Nitride (AlN), lead zirconate titanate (PZT), lead lanthanum zirconium titanate (PLZT), Cadmium Sulphide (CdS), Gallium Arsenide (GaAs), and Zinc Oxide (ZnO).