Metal-piezoelectric-metal capacitor
An acoustic resonator is provided that includes a substrate; a piezoelectric layer coupled to the substrate by one or more dielectric layers and having first and second surfaces that oppose each other; an interdigital transducer on at least one of the first and second surfaces of the piezoelectric layer and including interleaved fingers; and a capacitor electrically coupled in parallel to the interdigital transducer and including at least one first electrode on the first surface of the piezoelectric layer and a metal layer on the second surface of the piezoelectric layer, such that the piezoelectric layer is sandwiched between the at least one first electrode and the metal layer.
1 . An acoustic resonator comprising:
a substrate;
a piezoelectric layer coupled to the substrate by one or more dielectric layers and having first and second surfaces that oppose each other;
an interdigital transducer (IDT) on at least one of the first and second surfaces of the piezoelectric layer and including interleaved fingers that extend from opposing busbars including a first busbar and a second busbar; and
a capacitor electrically coupled in parallel to the IDT and including: (i) at least one first electrode that comprises an anode connected to the first busbar, and (ii) at least one second electrode connected to the second busbar, the at least one first electrode and the at least one second electrode disposed on the first surface of the piezoelectric layer and a metal layer directly disposed on the second surface of the piezoelectric layer, such that the piezoelectric layer is sandwiched between the at least one first electrode and the metal layer,
wherein the metal layer is a floating metal that at least partially overlaps both the anode and a cathode disposed on the first surface of the piezoelectric layer.
2 . The acoustic resonator according to claim 1 , wherein a portion of the piezoelectric layer forms a diaphragm that is over a cavity that extends at least partially in the one or more dielectric layers.
3 . The acoustic resonator according to claim 2 , wherein the IDT is disposed on the second surface of the piezoelectric layer that faces the cavity.
4 . The acoustic resonator according to claim 2 , wherein the IDT is configured such that a radio frequency signal applied to the IDT excites a bulk shear acoustic wave in the diaphragm where acoustic energy propagates along a direction substantially orthogonal to first surface of the piezoelectric layer, which is transverse to a direction of an electric field created by the interleaved fingers of the IDT.
5 . The acoustic resonator according to claim 1 , wherein the at least one first electrode comprises a pair of electrodes including the anode and the cathode of the capacitor.
6 . The acoustic resonator according to claim 5 , wherein the anode and the cathode are each elongated and extend in parallel with a plurality of the interleaved fingers of the IDT.
7 . The acoustic resonator according to claim 1 , wherein:
the first busbar and the second busbar each extend in a first direction from a first end to a second end thereof,
the IDT comprises a first plurality of electrode fingers extending from the first busbar in a second direction towards the second busbar, with the second direction intersecting the first direction, and
the IDT further comprises a second plurality of electrode fingers extending from the second busbar in the second direction towards to the first busbar, such that the first and second plurality of electrode fingers form the interleaved fingers of the IDT.
8 . The acoustic resonator according to claim 7 , wherein:
the anode of the capacitor extends in parallel to the first plurality of electrode fingers; and
the at least one first electrode includes the cathode of the capacitor that is coupled to the second busbar and extends in parallel to the second plurality of electrode fingers.
9 . The acoustic resonator according to claim 1 , further comprising a Bragg mirror disposed between the piezoelectric layer and the substrate.
10 . The acoustic resonator according to claim 1 , wherein the piezoelectric layer comprises a pair of through holes that extend along sides of the at least one first electrode of the capacitor in a thickness direction of the piezoelectric layer.
11 . The acoustic resonator according to claim 1 , wherein the piezoelectric layer comprises:
a first piezoelectric layer comprising a material with a first cut having a first crystallographic orientation; and
a second piezoelectric layer attached to the first piezoelectric layer and comprising a material with a second cut having a second crystallographic orientation, such that a piezoelectric tensor of the second piezoelectric layer is an opposite polarity to a piezoelectric tensor of the first piezoelectric layer.
12 . A filter device comprising:
a plurality of bulk acoustic wave resonators, wherein at least one of the plurality of bulk acoustic wave resonators comprises:
a substrate;
a piezoelectric layer coupled to the substrate by one or more dielectric layers and having first and second surfaces that oppose each other;
an interdigital transducer (IDT) on at least one of the first and second surfaces of the piezoelectric layer and including interleaved fingers that extend from opposing busbars including a first busbar and a second busbar; and
a capacitor electrically coupled in parallel to the IDT and including: (i) at least one first electrode that comprises an anode connected to the first busbar, and (ii) at least one second electrode connected to the second busbar, the at least one first electrode and the at least one second electrode disposed on the first surface of the piezoelectric layer and a metal layer directly disposed on the second surface of the piezoelectric layer, such that the piezoelectric layer is sandwiched between the at least one first electrode and the metal layer,
wherein the metal layer is a floating metal that at least partially overlaps both the anode and a cathode disposed on the first surface of the piezoelectric layer.
13 . The filter device according to claim 12 , wherein the at least one first electrode comprises a pair of electrodes including the anode and the cathode of the capacitor.
14 . The filter device according to claim 13 , wherein the anode and the cathode are each elongated and extend in parallel with a plurality of the interleaved fingers of the IDT.
15 . The filter device according to claim 12 , wherein a portion of the piezoelectric layer forms a diaphragm that is over a cavity that extends at least partially in the one or more dielectric layers, and the IDT is disposed on the second surface of the piezoelectric layer that faces the cavity.
16 . The filter device according to claim 15 , wherein the IDT of the at least one bulk acoustic wave resonator is configured such that a radio frequency signal applied to the IDT excites a bulk shear acoustic wave in the diaphragm where acoustic energy propagates along a direction substantially orthogonal to the first and second surfaces of the piezoelectric layer, which is transverse to a direction of an electric field created by the interleaved fingers of the IDT.
17 . The filter device according to claim 12 , wherein for at least one bulk acoustic wave resonator:
the first busbar and the second busbar each extend in a first direction from a first end to a second end thereof,
the IDT comprises a first plurality of electrode fingers extending from the first busbar in a second direction towards the second busbar, with the second direction intersecting the first direction, and
the IDT further comprises a second plurality of electrode fingers extending from the second busbar in the second direction towards to the first busbar, such that the first and second plurality of electrode fingers form the interleaved fingers of the IDT.
18 . The filter device according to claim 17 , wherein:
the anode of the capacitor extends in parallel to the first plurality of electrode fingers; and
the at least one first electrode includes the cathode of the capacitor that is coupled to the second busbar and extends in parallel to the second plurality of electrode fingers.
19 . A radio frequency module comprising:
a filter device including a plurality bulk acoustic wave resonators connected in parallel; and
a radio frequency circuit coupled to the filter device, the filter device and the radio frequency circuit being enclosed within a common package, wherein at least one of the plurality of bulk acoustic wave resonators of the filter device includes:
a substrate;
a piezoelectric layer coupled to the substrate by one or more dielectric layers and having first and second surfaces that oppose each other;
an interdigital transducer (IDT) on at least one of the first and second surfaces of the piezoelectric layer and including interleaved fingers that extend from opposing busbars including a first busbar and a second busbar; and
a capacitor electrically coupled in parallel to the IDT and including: (i) at least one first electrode that comprises an anode connected to the first busbar, and (ii) at least one second electrode connected to the second busbar, the at least one first electrode and the at least one second electrode disposed on the first surface of the piezoelectric layer and a metal layer directly disposed on the second surface of the piezoelectric layer, such that the piezoelectric layer is sandwiched between the at least one first electrode and the metal layer,
wherein the metal layer is a floating metal that at least partially overlaps both the anode and a cathode disposed on the first surface of the piezoelectric layer.