Monolithic thin-film piezoelectric filters

• US 20080079515A1
• Filed: 07/25/2007
• Published: 04/03/2008
• Est. Priority Date: 07/27/2006
• Status: Active Grant

• Current Assignee: Georgia Tech Research Corporation (University System of Georgia)
• Original Assignee: Georgia Tech Research Corporation (University System of Georgia)
• Inventors: Abdolvand, Reza, Ayazi, Farrokh
• Granted Patent: US 7,847,656 B2
• Time in Patent Office: Days
• US Class Current: 333/187
• CPC Class Codes: H03H 2009/241 Bulk-mode MEMS resonators
• CPC Class Codes: H03H 9/02228 Guided bulk acoustic wave devices or Lamb wave devices having interdigital transducers situated in parallel planes on either side of a piezoelectric layer
• CPC Class Codes: H03H 9/132 characterized by a particular shape
• CPC Class Codes: H03H 9/564 implemented with thin-film techniques

Abstract

Disclosed are exemplary monolithic acoustically coupled thin film piezoelectric-on-substrate filters that operate in a wide frequency range. The monolithic thin-film-piezoelectric acoustic filters includes a resonant structure that is released from and supported by a substrate that comprises a thin-film piezoelectric layer disposed between a lower electrode and a plurality of electrically isolated upper electrodes. Second order narrowband filters are realized by utilizing coupled resonance modes of a single microstructure. Narrow-bandwidth filters are disclosed that are suitable for channel-select applications in IF and RF bands. Filter Q values of 800 at 250 MHz, 470 at 360 MHz, and 400 at 3.5 GHz for small footprint second-order filters are disclosed. The measured power handling of these devices is high due to the use of high energy density structural material, showing a 0.2 dB compression point of >15 dBm at 360 MHz.

Claims

1. Microelectromechanical acoustic filter apparatus comprising:

a substrate; and

a resonant structure released from and supported by the substrate that comprises;

a thin-film piezoelectric layer disposed between a lower electrode and a plurality of electrically isolated upper electrodes patterned to excite coupled resonance mode shapes of the resonant structure.

2. The apparatus recited in claim 1 wherein the piezoelectric material is selected from a group including zinc oxide (ZnO), aluminum nitride (AlN), and lead zirconate titanate (PZT).

3. The apparatus recited in claim 1 wherein the upper and lower electrodes excite fundamental or high-order width- or length-extensional, resonance modes of the structure.

4. The apparatus recited in claim 1 wherein the upper and lower electrodes excite fundamental or high-order thickness-extensional resonance modes of the structure.

5. The apparatus recited in claim 1 wherein the upper and lower electrodes excite a shear resonance modes of the structure.

6. The apparatus recited in claim 1 wherein the resonant structure further comprises a portion of the substrate.

7. The apparatus recited in claim 1 wherein the substrate comprises an insulating layer disposed on a lower support substrate and wherein the resonant structure further comprises a portion of the insulating layer.

8. The apparatus recited in claim 1 wherein a cavity if formed beneath the resonant structure to release it from the substrate.

9. The apparatus recited in claim 1 wherein the resonant structure is connected by way of support beams to the substrate.

10. The apparatus recited in claim 1 wherein the substrate comprises a silicon-on-insulator substrate.

11. Microelectromechanical acoustic filter apparatus comprising:

a substrate; and

a resonant structure released from and supported by the substrate that comprises;

a thin-film piezoelectric layer disposed between a lower electrode and a plurality of electrically isolated upper electrodes that comprise interdigitated fingers to provide a second order filter that operates in fundamental or high-order thickness-extensional mode.

12. The method recited in claim 11 wherein the pattern and/or the dimensions of electrically isolated interdigitated fingers are altered to design for the filter bandwidth.

13. The apparatus recited in claim 11 wherein a cavity if formed beneath the resonant structure to release it from the substrate.

14. The apparatus recited in claim 11 wherein the substrate comprises a silicon-on-insulator substrate and the resonant structure further comprises a portion of the silicon device layer.

15. The apparatus recited in claim 11 wherein the substrate comprises an insulator disposed on a silicon substrate and the resonant structure further comprises a portion of the insulating layer.

16. Microelectromechanical acoustic filter apparatus comprising:

a substrate; and

a resonant structure released from and supported by the substrate that comprises;

a thin-film piezoelectric layer disposed between a lower electrode and a plurality of electrically isolated upper electrodes that comprise two sets of spaced apart opposed electrically connected fingers to provide a second order filter that operates in lateral, fundamental or high-order width- or length-extensional, resonance mode.

17. The method recited in claim 16 wherein the pattern and/or the dimensions of the spaced apart sets of connected fingers are altered to design for the filter bandwidth.

18. The method recited in claim 16 wherein a cavity is formed beneath the resonant structure to release it from the substrate.

19. The apparatus recited in claim 16 wherein the substrate comprises a silicon-on-insulator substrate and wherein the resonant structure further comprises a portion of the silicon device layer.

20. The apparatus recited in claim 16 wherein the substrate comprises an insulator disposed on a silicon substrate and the resonant structure further comprises a portion of the insulating layer.