Digitally Programmable RF Mems Filters with Mechanically Coupled Resonators

• US 20100171570A1
• Filed: 10/29/2009
• Published: 07/08/2010
• Est. Priority Date: 10/29/2008
• Status: Active Grant

• Current Assignee: Cornell University
• Original Assignee: Cornell University
• Inventors: BHAVE, Sunil Ashok, CHANDRAHALIM, Hengky
• Granted Patent: US 8,390,398 B2
• Time in Patent Office: Days
• US Class Current: 333/186
• CPC Class Codes: H03H 2009/2442 Square resonators
• CPC Class Codes: H03H 9/2436 Disk resonators
• CPC Class Codes: H03H 9/462 Microelectro-mechanical filters
• CPC Class Codes: H03H 9/505 for microelectro-mechanical filters

Abstract

A digitally-tunable RF MEMS filter includes a substrate and a plurality of mechanically coupled resonators, wherein a first and a last resonator of the plurality of mechanically coupled resonators are configured to be electrostatically transduced. One or more of the plurality of mechanically coupled resonators are configured to be biased relative to the substrate such that the one or more biased resonators may be brought substantially in contact with the substrate. In a method of digitally tuning an RF MEMS filter having a mechanically coupled resonator array, a DC bias voltage is applied to at least a first resonator and a last resonator of the mechanically coupled resonator array such that motional boundary conditions for the at least first resonator and last resonator are selectable in proportion to the DC bias voltage.

Claims

1. A digitally-tunable RF MEMS filter comprising:

a substrate; and

a plurality of mechanically coupled resonators wherein;

at least a first and a last resonator of the plurality of mechanically coupled resonators are configured to be electrostatically transduced; and

one or more of the plurality of mechanically coupled resonators are configured to be biased relative to the substrate such that the one or more biased resonators may be brought substantially in contact with the substrate.

2. The RF MEMS filter of claim 1, wherein substantially zero-displacement boundary conditions are imposed on the one or more resonators that are substantially brought into contact with the substrate.

3. The RF MEMS filter of claim 1, wherein each of the one or more of the plurality of mechanically coupled resonators configured to be biased relative to the substrate comprises one or more electrodes configured to receive a DC bias voltage relative to the substrate.

4. The RF MEMS filter of claim 1, further comprising one or more bias regions coupled to the substrate, and wherein each of the one or more bias regions are configured to receive a DC bias voltage relative to the one or more of the plurality of mechanically coupled resonators configured to be biased relative to the substrate.

5. The RF MEMS filter of claim 4, wherein the one or more bias regions are located between the substrate and the plurality of mechanically coupled resonators.

6. The RF MEMS filter of claim 4, wherein the substrate is located between the one or more bias regions and the plurality of mechanically coupled resonators.

7. The RF MEMS filter of claim 4, wherein the substrate comprises the one or more bias regions.

8. The RF MEMS filter of claim 1, further comprising:

first and second RF input ports coupled to the first resonator; and

first and second RF output ports coupled to the last resonator.

9. The RF MEMS filter of claim 1, further comprising:

a first RF input port coupled to the first resonator;

a second RF input port coupled to a second resonator of the plurality of mechanically coupled resonators;

a first RF output port coupled to a third resonator of the plurality of mechanically coupled resonators; and

a second RF output port coupled to the last resonator.

10. The RF MEMS filter of claim 1, further comprising a non-conducting layer between the substrate and the plurality of mechanically coupled resonators.

11. The RF MEMS filter of claim 1, wherein at least one of the plurality of mechanically coupled resonators comprises a 2D square extensional mode resonator.

12. The RF MEMS filter of claim 11, wherein the 2D square extensional mode resonator further comprises checkered electrodes for transduction.

13. The RF MEMS filter of claim 1, wherein each of the plurality of mechanically coupled resonators comprises:

one or more conducting top electrodes;

a compressible film layer; and

a device layer.

14. The RF MEMS filter of claim 13, wherein the one or more conducting top electrodes for each of the plurality of mechanically coupled resonators are configured to be coupled to an independent DC bias superimposed with either an RF input or an RF output.

15. The RF MEMS filter of claim 1, further comprising at least one intermediate resonator of the plurality of mechanically coupled resonators that is coupled between the first and last resonator, and wherein the at least one intermediate resonator is not configured to receive a DC bias.

16. The RF MEMS filter of claim 1, wherein the plurality of mechanically coupled resonators are coupled by quarter wavelength suspensions at low velocity nodes.

17. A method of digitally tuning an RF MEMS filter having a mechanically coupled resonator array, the method comprising:

applying a DC bias voltage to at least a first resonator and a last resonator of the mechanically coupled resonator array such that motional boundary conditions for the at least first resonator and last resonator are selectable in proportion to the DC bias voltage.

18. The method of claim 17, wherein:

the mechanically coupled resonator array comprises the first resonator, a second resonator, a third resonator, and the last resonator; and

applying the DC bias voltage comprises applying one of three states in a tri-state voltage control to each of the resonators in the resonator array.

19. The method of claim 18, wherein the three states of the tri-state voltage control comprise:

a positive bias voltage;

an off bias voltage; and

a negative bias voltage.

20. The method of claim 19, wherein a four-pole filter response is enabled by:

applying the positive bias voltage to the first resonator;

applying the off bias voltage to the second resonator;

applying the off bias voltage to the third resonator; and

applying the positive bias voltage to the last resonator.

21. The method of claim 19, wherein a two-pole lower sub-band filter is enabled by:

applying the positive bias voltage to the first resonator;

applying the negative bias voltage to the second resonator;

applying the positive bias voltage to the third resonator; and

applying the negative bias voltage to the last resonator.

22. The method of claim 19, wherein a two-pole higher sub-band filter is enabled by:

applying the positive bias voltage to the first resonator;

applying the positive bias voltage to the second resonator;

applying the positive bias voltage to the third resonator; and

applying the positive bias voltage to the last resonator.

23. A digitally-tunable RF MEMS filter comprising:

a) a substrate; and

b) a plurality of mechanically coupled 2D square extensional mode resonators having checkered electrodes for transduction comprising;

1) a first resonator;

2) a second resonator;

3) a third resonator; and

4) a last resonator; and

c) wherein;

1) at least the first and the last resonator of the plurality of mechanically coupled resonators are configured to be electrostatically transduced;

2) the plurality of mechanically coupled resonators are coupled by quarter wavelength suspensions at low velocity nodes; and

3) one or more of the plurality of mechanically coupled resonators are configured to be biased relative to the substrate such that the one or more biased resonators may be brought substantially in contact with the substrate.