Thin film bulk acoustic resonator with a mass loaded perimeter
View Patent ↗A resonator structure (FBAR) made of electrodes sandwich a piezoelectric material. The intersection of the two conducting electrodes defines the active area of the acoustic resonator. The active area is divided into two concentric areas; a perimeter or frame, and a central region. An annulus is added to one of the two conducting electrodes to improve the electrical performance (in terms of Q).
1. A device for trapping mechanical energy comprising:
a first electrode;
a second electrode positioned proximate and above the first electrode; the overlap of the first and the second electrodes defining an active area;
a dielectric sheet of a type II piezoelectric material interposing the first and the second electrodes;
a raised annulus positioned on a surface of one of the first and second electrodes;
wherein the area within the raised annulus has a first acoustic impedance, the raised annulus has a second acoustic impedance, and the region external to the raised annulus has a third acoustic impedance; and
the second acoustic impedance being greater than the first and the third acoustic impedances to improve the Q factor of the device near a parallel resonant frequency (f p ) of the device.
2. A device, as defined in claim 1 , wherein the annulus is positioned along the periphery of the second electrode.
3. A device, as defined in claim 1 , wherein the annulus is positioned within the first electrode and directly opposes the periphery of the second electrode.
4. A device, as defined in claim 1 , wherein the annulus is integrated into the one of the first and the second electrode.
5. A device, as defined in claim 1 , wherein:
the one of the first and second electrode has a first specific gravity; and
the annulus has a second specific gravity that is greater than the first specific gravity.
6. A device, as defined in claim 1 , wherein:
the one of the first and second electrode has a first specific gravity; and
the annulus has a second specific gravity that is less than the first specific gravity.
7. A device, as defined in claim 6 , the annulus comprising a dielectric material.
8. A device, as defined in claim 6 , the annulus comprising a metallic material.
9. A device, as defined in claim 1 , further comprising a substrate having a cavity in a surface, the first electrode bridging the cavity.
10. A device, as defined in claim 9 , wherein the annulus is positioned along the periphery of the second electrode.
11. A device, as defined in claim 9 , wherein the annulus is positioned within the first electrode and directly opposes the periphery of the second electrode.
12. A device, as defined in claim 9 , wherein the annulus is integrated into the one of the first and the second electrode.
13. A device, as defined in claim 9 , wherein:
the one of the first and second electrode has a first specific gravity; and
the annulus has a second specific gravity that is greater than the first specific gravity.
14. A device, as defined in claim 9 , wherein:
the one of the first and second electrode has a first specific gravity; and
the annulus has a second specific gravity that is less than the first specific gravity.
15. A device, as defined in claim 14 , the annulus comprising a dielectric material.
16. A device, as defined in claim 14 , the annulus comprising a metallic material.
17. A method for trapping mechanical energy, comprising:
providing a first electrode;
providing a second electrode positioned proximate and above the first electrode; the overlap of the first and the second electrodes defining an active area;
providing a dielectric sheet of a type II piezoelectric material interposing the first and the second electrodes;
providing a raised annulus positioned on a surface of one of the first and second electrodes; wherein the area within the raised annulus has a first acoustic impedance, the raised annulus has a second acoustic impedance, and the region external to the raised annulus has a third acoustic impedance; and
the second acoustic impedance being greater than the first and the third acoustic impedances to improve a Q factor near a parallel resonant frequency (f p ).
18. A device, as defined in claim 1 , where the type II piezoelectric material is AlN.
19. A device, as defined in claim 1 , where the dielectric sheet is part of a free standing membrane.