SWITCHABLE TUNABLE ACOUSTIC RESONATOR USING BST MATERIAL

Abstract

An acoustic resonator includes a first electrode, a second electrode, and a barium strontium titanate (BST) dielectric layer disposed between the first electrode and the second electrode, where the acoustic resonator is switched on as a resonator with a resonant frequency if a DC (direct current) bias voltage is applied across the BST dielectric layer. The acoustic resonator is also switched off in no DC bias voltage is applied across the BST dielectric layer. Furthermore, the resonant frequency of the acoustic resonator can be tuned based on a level of the DC bias voltage, with the resonant frequency increasing as the level of the DC bias voltage applied to the BST acoustic resonator increases.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The teachings of the embodiments of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings.

FIG. 1 is a block diagram illustrating a typical metal-insulator-metal (MIM) parallel plate configuration of a thin film BST capacitor according to one embodiment of the present invention.

FIG. 2 is a graph illustrating RF transmission measurements of the BST capacitor of FIG. 1 as a function of the frequency of the RF signal.

FIG. 3 is a graph illustrating RF transmission measurements of the BST capacitor of FIG. 1 as a function of the frequency of the RF signal under different DC bias voltages.

FIG. 4 is a diagram of an equivalent circuit modeling a piezo-electric transducer.

FIG. 5 illustrates the structure and use of the BST-based FBAR (Film Bulk Acoustic Resonator) according to one embodiment of the present invention.

FIG. 6 illustrates the structure of the BST-based FBAR, according to one embodiment of the present invention.

FIG. 7A illustrates the structure of the BST-based FBAR, according to another embodiment of the present invention.

FIG. 7B illustrates the various structures of the acoustic reflector that can be used with the BST-based FBAR of FIG. 7A.

FIG. 8 illustrates the structure of the BST-based FBAR device, according to still another embodiment of the present invention.

FIG. 9 illustrates the simulated behavior of a single BST-based FBAR device in series and shunt configurations.

FIG. 10A illustrates a band pass filter circuit implemented using the BST-based FBAR devices according to one embodiment of the present invention.

FIG. 10B is a graph illustrating RF transmission measurements, as a function of the frequency of the RF signal, of the band pass filter circuit of FIG. 10A implemented using the BST-based FBAR devices according to one embodiment of the present invention.

FIG. 10C is a graph illustrating how the RF transmission measurements of the band pass filter circuit of FIG. 10A implemented using the BST-based FBAR devices change depending upon different DC bias voltages.

FIG. 11 illustrates a duplexer implemented using the BST-based FBAR devices according to one embodiment of the present invention.

FIG. 12A illustrates a conventional switched filter bank.

FIG. 12B illustrates a switched filter bank implemented using the BST-based FBAR devices according to one embodiment of the present invention.

Claims

1. An acoustic resonator comprising: a first electrode;a second electrode;a barium strontium titanate (BST) dielectric layer disposed between the first electrode and the second electrode, the acoustic resonator being switched on with a resonant frequency if a DC (direct current) bias voltage is applied across the BST dielectric layer.

2. The acoustic resonator of claim 1, wherein the acoustic resonator is switched off if no DC bias voltage is applied across the BST dielectric layer.

3. The acoustic resonator of claim 1, wherein the resonant frequency is tuned based on a level of the DC bias voltage.

4. The acoustic resonator of claim 3, wherein the resonant frequency increases as the level of the DC bias voltage increases.

5. The acoustic resonator of claim 1, wherein the acoustic resonator is formed on a sapphire substrate.

6. The acoustic resonator of claim 1, wherein the acoustic resonator is formed over an air gap disposed between the second electrode and a substrate supporting the acoustic resonator.

7. The acoustic resonator of claim 1, wherein the acoustic resonator is formed over an acoustic reflector disposed between the second electrode and a substrate supporting the acoustic resonator, the acoustic reflector reducing damping of resonance of the acoustic resonator caused by the substrate.

8. The acoustic resonator of claim 7, wherein the acoustic reflector comprises a Platinum (Pt) layer.

9. The acoustic resonator of claim 7, wherein the acoustic reflector comprises a plurality of alternating layers of Platinum (Pt) and Silicon Dioxide (SiO2).

10. The acoustic resonator of claim 1, wherein the acoustic resonator includes a first part formed over a substrate and a second part formed over an air gap.

11. The acoustic resonator of claim 1, wherein the acoustic resonator is used as part of a switchable filter.

12. The acoustic resonator of claim 1, wherein the acoustic resonator is used as part of a duplexer for transmitting and receiving a radio frequency signal over an antenna.

13. A filter for filtering a frequency range of a signal, the filter comprising: at least a capacitor; andat least an acoustic resonator coupled to the capacitor, the acoustic resonator including: a first electrode;a second electrode;a barium strontium titanate (BST) dielectric layer disposed between the first electrode and the second electrode, the acoustic resonator being switched on with a resonant frequency if a DC (direct current) bias voltage is applied across the BST dielectric layer.

14. The filter of claim 13, wherein the acoustic resonator is switched off if no DC bias voltage is applied across the BST dielectric layer.

15. The filter of claim 13, wherein the resonant frequency is tuned based on a level of the DC bias voltage.

16. The filter of claim 15, wherein the resonant frequency increases as the level of the DC bias voltage increases.

17. The filter of claim 13, wherein the acoustic resonator is formed over an air gap disposed between the second electrode and a substrate supporting the acoustic resonator.

18. The filter of claim 13, wherein the acoustic resonator is formed over an acoustic reflector disposed between the second electrode and a substrate supporting the acoustic resonator, the acoustic reflector reducing damping of resonance of the acoustic resonator caused by the substrate.

19. The filter of claim 13, wherein the acoustic reflector comprises a plurality of alternating layers of Platinum (Pt) and Silicon Dioxide (SiO2).

20. The filter of claim 13, wherein the acoustic resonator includes a first part formed over a substrate and a second part formed over an air gap.