Electrode geometry to minimize stress in transversely-excited film bulk acoustic resonators
An acoustic resonator device includes a piezoelectric plate attached to a substrate. A portion of the piezoelectric plate forms a diaphragm suspended over a cavity in the substrate. A first conductor level includes first and second interdigital transducer (IDT) first-level busbars disposed along opposing sides of the diaphragm, and first and second sets of IDT fingers extending from the first and second busbars, respectively, wherein the first and second sets of IDT fingers are interleaved and disposed on the diaphragm. A second conductor level includes first and second second-level busbars that overlap at least a portion of the first and second busbars, respectively.
1 . An acoustic resonator device comprising:
a substrate;
a piezoelectric plate disposed on the substrate and that includes a diaphragm that extends across a cavity over the substrate;
a first conductor level disposed on a surface of the piezoelectric plate and including:
first and second interdigital transducer (IDT) first-level busbars extending along opposing sides of the diaphragm, and
first and second sets of IDT fingers extending from the first and second first-level busbars, respectively, with the first and second sets of IDT fingers being interleaved and disposed on the diaphragm; and
a second conductor level that extends at least partially over the first conductor level and that includes first and second second-level busbars that overlap at least portions of the first and second first-level busbars, respectively, in a thickness direction of the acoustic resonator device,
wherein a portion of at least one of the first and second second-level busbars has a rounded corner disposed above the diaphragm in the thickness direction of the acoustic resonator device.
2 . The device of claim 1 , wherein the piezoelectric plate and the first conductor level are configured such that a radio frequency signal applied between the interleaved IDT fingers excites a shear primary acoustic mode in the diaphragm.
3 . The device of claim 1 , wherein the piezoelectric plate is one of lithium niobate and lithium tantalate.
4 . The device of claim 3 , wherein the piezoelectric plate is one of Z-cut, rotated Z-cut, and rotated YX-cut.
5 . The device of claim 1 , further comprising a dielectric layer disposed on the surface of the piezoelectric plate between the interleaved IDT fingers.
6 . The device of claim 1 , wherein respective rounded corners of the first-level busbars and second-level busbars are concentric.
7 . The device of claim 1 , wherein:
portions of the first and second second-level busbars that are not on the diaphragm have a first thickness tm 2 ,
portions of the first and second second-level busbars that extend onto the diaphragm have a second thickness tm 2 r , and
tm 2 r≤tm 2.
8 . The device of claim 7 , wherein:
tm 2 r≤ 0.5( tm 2).
9 . The device of claim 1 , wherein the cavity extends beyond both ends of the first-level busbars, and the first conductor level includes structures that overlap at least portions of the cavity extending beyond the first-level busbars.
10 . The device of claim 1 , further comprising a dielectric layer disposed on the cavity and that defines the cavity over which the diaphragm extends.
11 . An acoustic resonator device comprising:
a substrate;
a piezoelectric plate disposed on the substrate and that includes a diaphragm;
a first conductor disposed on a surface of the piezoelectric plate and including:
a first pair of interdigital transducer (IDT) busbars that extend along opposing sides of the diaphragm, and
first and second sets of IDT fingers that extend from the first pair of IDT busbars, respectively, with the first and second sets of IDT fingers being interleaved and disposed on the diaphragm; and
a second conductor that extends at least partially over the first conductor and that includes a second pair of busbars disposed on the first pair of IDT busbars, respectively,
wherein each of the first pair of IDT busbars and the second pair of busbars at least partially overlap the diaphragm in a thickness direction of the acoustic resonator device, and
wherein a portion of the first pair of IDT busbars of the first conductor has a rounded corner that is disposed above the diaphragm in the thickness direction of the acoustic resonator device.
12 . The device of claim 11 , wherein the diaphragm of the piezoelectric plate extends across a cavity over the substrate.
13 . The device of claim 12 , further comprising a dielectric layer disposed on the cavity and that defines the cavity over which the diaphragm extends.
14 . The device of claim 12 , wherein the cavity extends beyond both ends of the first pair of IDT busbars, and the first conductor includes structures that overlap at least portions of the cavity extending beyond the first pair of IDT busbars.
15 . The device of claim 11 , wherein the piezoelectric plate and the first and second conductors are configured such that a radio frequency signal applied between the interleaved IDT fingers excites a shear primary acoustic mode in the diaphragm.
16 . The device of claim 11 , further comprising a dielectric layer disposed on the surface of the piezoelectric plate between the interleaved IDT fingers.
17 . The device of claim 11 , wherein the rounded corners of the first pair of IDT busbars of the first conductor are concentric with rounded corners of the second pair of busbars of the second conductor.
18 . The device of claim 11 , wherein:
portions of the first pair of IDT busbars and the second pair of busbars that are not on the diaphragm have a first thickness tm 2 ,
portions of the first pair of IDT busbars and the second pair of busbars that extend onto the diaphragm have a second thickness tm 2 r , and
tm 2 r≤tm 2.
19 . The device of claim 18 , wherein:
tm 2 r≤ 0.5( tm 2).