Tunable Q resonator
View Patent ↗A tunable Q resonator using a capacitive-piezoelectric transducer provides a flexible top electrode above an AlN resonator. The top electrode can be pulled electrostatically towards the resonator and substrate, forming a frictional contact with either the resonator or the combined resonator-electrode structure to the substrate, allowing for electrical tuning the Q of the resonator. With a sufficient electrostatic bias voltage V b , the resonator may be completely turned OFF, allowing for an integrated switchable AlN resonator. Such switchable resonator may be integrated into a radio frequency (RF) front end as a digitally selectable band pass filter element, obviating the need for ancillary micromechanical switches in the signal path. The device has been demonstrated with a Q approaching 9,000, together with ON/OFF switchability and electromechanical coupling up to 0.63%. Flexible positioning of the top electrode allows for actively controlling the series resonant frequency of the resonator through changes in capacitive coupling.
1. A resonator, comprising:
a substrate comprising a bottom electrode;
a radial contour mode resonator disposed above the substrate; and
a top electrode disposed above the resonator;
a bias voltage V b source electrically connected between the top electrode and the bottom electrode;
wherein the top electrode is attached in part to the substrate.
2. The resonator of claim 1 , wherein the resonator is suspended over the substrate by a central stem.
3. The resonator of claim 1 , wherein the resonator is an aluminum nitride (AlN) resonator.
4. The resonator of claim 3 , wherein the resonator is a disk.
5. The resonator of claim 1 , wherein a Q of the resonator is selected from a group of Q's consisting of: Q≥1000, Q≥2000, Q≥6000, Q≥8000, and Q≥8800.
6. The resonator of claim 1 , wherein the top electrode is flexed into at least partial mechanical contact with the resonator upon application of a sufficient bias voltage V b between the top electrode and the bottom electrode.
7. The resonator of claim 6 , wherein the flexure of the top electrode is due to electrostatic forces generated through the application of the sufficient bias voltage V b from the bias voltage source between the top electrode and the bottom electrode.
8. The resonator of claim 7 , wherein the flexure of the top electrode reduces the Q of the resonator through frictional losses.
9. The resonator of claim 8 , wherein the resonator is a variable Q resonator.
10. The resonator of claim 8 , wherein the resonator is a switched resonator.
11. The resonator of claim 10 , wherein one or more of the switched resonators are present within a radio frequency (RF) front end.
12. The resonator of claim 1 , wherein the resonator is flexed into at least partial mechanical contact with the substrate upon application of a sufficient bias voltage V b from the bias voltage source.
13. The resonator of claim 1 , wherein the resonator is flexed into at least partial mechanical contact with the substrate and the top electrode upon application of a sufficient bias voltage V b from the bias voltage source between the top electrode and the bottom electrode.
14. The resonator of claim 1 , wherein a sufficient bias voltage V b between the top electrode and the bottom electrode causes a mechanical contact between the resonator and the top and bottom electrodes.
15. A method of signal switching, comprising:
(a) providing a switching resonator, comprising:
a substrate comprising a bottom electrode;
a radial contour mode resonator disposed above the substrate; and
a top electrode disposed above the resonator;
wherein the top electrode is attached in part to the substrate; and
(b) applying a bias voltage V b between the bottom electrode and the top electrode.
16. The method of signal switching of claim 15 , further comprising:
applying the bias voltage V b sufficient to dampen resonator oscillation through energy loss mechanisms of the resonator with other components of the switching resonator;
wherein an input signal applied to the resonator is not output, resulting in an OFF state for the switching resonator.
17. The method of signal switching of claim 15 , further comprising:
applying the bias voltage V b where the resonator oscillation experiences no frictional contact with other components of the switching resonator;
wherein an input signal applied to the resonator is output, resulting in an ON state for the switching resonator.
18. The method of signal switching of claim 15 , further comprising:
applying the bias voltage V b where the resonator oscillation experiences no frictional contact with other components of the switching resonator;
wherein a series resonant frequency of the resonator is changed.
19. A capacitive-piezoelectric disk resonator having a construct comprising:
a silicon substrate;
an SiO 2 layer disposed on the silicon substrate;
a silicon nitride layer disposed on the SiO 2 layer;
an AlN layer disposed on the silicon nitride layer;
a polysilicon central stem disposed on the AlN layer;
an AlN disk resonator supported by the central stem;
a molybdenum bottom electrode disposed on the AlN layer; and
a polysilicon deformable top electrode attached in part to the AlN layer;
wherein the top electrode is disposed in part above the AlN disk resonator;
wherein the bottom electrode is disposed in part below the AlN disk resonator; and
wherein absent an electrical potential between the top and bottom electrodes, the AlN disk resonator does not contact either electrode.
20. A tunable resonator, comprising:
a substrate comprising a bottom electrode;
a resonator disposed above the substrate; and
a top electrode disposed above the resonator;
wherein the top electrode is attached in part to the substrate through a compliant structure;
wherein when a bias voltage, V b , is applied between the bottom electrode and the top electrode, the top electrode is displaced by the bias voltage, V b , through movement of the top electrode through movement of the compliant structure;
a top gap, g t , disposed between the resonator and one of the electrodes;
wherein a series resonant frequency f s of the resonator is changed through alteration of the top gap, g t ;
a feedback control system that controls the bias voltage, V b ;
wherein the series resonant frequency fs of the resonator is controlled within a design range.
21. A filter, comprising:
(a) a tunable resonator, comprising:
a substrate comprising a bottom electrode;
a tunable resonator disposed above the bottom electrode;
a top electrode disposed above the tunable resonator;
wherein the top electrode is attached in part to the substrate; and
a bias voltage V b source electrically connected between the top electrode and the bottom electrode;
(b) an input resonator, comprising:
an input substrate, comprising an input bottom electrode;
an input resonator disposed above the input substrate; and
an input top electrode disposed above the input substrate;
wherein an input capacitance at the input resonator has a value of C i ;
(c) an output resonator, comprising:
an output substrate, comprising an output bottom electrode;
an output resonator disposed above the output substrate; and
an output top electrode disposed above the output substrate;
wherein an output capacitance at the output resonator has a value of C o ;
(d) an input coupler, wherein vibration from the input resonator is mechanically coupled to the tunable resonator; and
(e) an output coupler, wherein vibration from the tunable resonator is mechanically coupled to the output resonator.
22. The filter of claim 21 , wherein the input capacitance C i and the output capacitance C o remain unchanged regardless of the applied bias voltage V b .
23. The filter of claim 21 , wherein the application of the bias voltage V b. effects a change in a resonant frequency of the tunable resonator.
24. The filter of claim 21 , wherein the application of a sufficient bias voltage V b. effectively switches the filter ON or OFF.
25. The filter of claim 21 , wherein the tunable oscillator substrate, the input substrate, and the output substrate are disposed on a wafer.