Bulk acoustic wave devices with tuned acoustic impedance
Aspects of this disclosure relate to bulk acoustic wave devices that have a raised frame structure. The raised frame structure can include a first raised frame layer that has a relatively low acoustic impedance. The raised frame structure can include a second raised frame layer that has a relatively high acoustic impedance. The first raised frame layer can have a thickness that is between about 0.02 and about 0.4 times the combined thickness H of the bulk acoustic wave device. The first raised frame layer can have a thickness that is between about 0.01 and about 0.2 times the resonant wavelength λ of the bulk acoustic wave device.
1 . A bulk acoustic wave device comprising:
a first electrode;
a second electrode;
a piezoelectric layer between the first electrode and the second electrode, the bulk acoustic wave device configured to have a main resonant frequency for an acoustic wave having a resonant wavelength λ; and
a raised frame structure including a first raised frame layer below a second raised frame layer that extend into an active region of the piezoelectric layer, the first raised frame layer having a first non-gradient region and a first gradient region, the second raised frame layer having a higher acoustic impedance than the first raised frame layer, and the first non-gradient region of the first raised frame layer having a thickness between about 0.01 to about 0.2 times the resonant wavelength λ, and the first gradient region of the first raised frame layer extends into the active region to a lesser extent than the second raised frame layer extends into the active region.
2 . The bulk acoustic wave device of claim 1 , wherein the thickness of the first raised frame layer is between about 0.02 to about 0.1 times the resonant wavelength λ.
3 . The bulk acoustic wave device of claim 1 , wherein the thickness of the first raised frame layer is between about 0.04 to about 0.05 times the resonant wavelength λ.
4 . The bulk acoustic wave device of claim 1 , wherein the first electrode, the second electrode, and the piezoelectric layer have a combined thickness H, and the resonant wavelength λ is about 2 times the combined thickness H.
5 . The bulk acoustic wave device of claim 4 , wherein the combined thickness H is at a main acoustically active region of the bulk acoustic device.
6 . The bulk acoustic wave device of claim 1 , wherein the second raised frame layer at least partially overlaps the first raised frame layer.
7 . The bulk acoustic wave device of claim 1 , wherein the first raised frame layer is between the first electrode and the second electrode.
8 . The bulk acoustic wave device of claim 7 , wherein the piezoelectric layer is over the first electrode, the second electrode over the piezoelectric layer, and the first raised frame layer between the second electrode and the piezoelectric layer.
9 . The bulk acoustic wave device of claim 8 , wherein the second raised frame layer is over the second electrode.
10 . The bulk acoustic wave device of claim 7 , wherein the piezoelectric layer is over the first electrode, the second electrode is over the piezoelectric layer, and the first raised frame layer is between the first electrode and the piezoelectric layer.
11 . The bulk acoustic wave device of claim 10 , wherein the second raised frame layer is over the second electrode.
12 . The bulk acoustic wave device of claim 1 wherein the first raised frame layer includes silicon dioxide.
13 . The bulk acoustic wave device of claim 1 wherein the second raised frame layer includes the same material as the second electrode.
14 . The bulk acoustic wave device of claim 1 wherein the second raised frame layer includes at least one of molybdenum, tungsten, ruthenium, platinum, or iridium.
15 . A bulk acoustic wave device comprising:
a first electrode;
a second electrode;
a piezoelectric layer between the first electrode and the second electrode, the bulk acoustic wave device configured to have a main resonant frequency for an acoustic wave having a resonant wavelength λ; and
a raised frame structure including a first raised frame layer below a second raised frame layer that extend into an active region of the piezoelectric layer, the first raised frame layer having a first non-gradient region and a first gradient region, the second raised frame layer having a second non-gradient region and a second gradient region, the first raised frame layer having a lower acoustic impedance than at least one of the first electrode, the second electrode, and the piezoelectric layer, and the first raised frame layer having a thickness between about 0.01 to about 0.2 times the resonant wavelength λ, and the first gradient region of the first raised frame layer extends into the active region to a lesser extent than the second gradient region of the second raised frame layer extends into the active region.
16 . The bulk acoustic wave device of claim 15 , wherein the thickness of the first raised frame layer is between about 0.02 to about 0.1 times the resonant wavelength λ.
17 . The bulk acoustic wave device of claim 15 , wherein the thickness of the first raised frame layer is between about 0.04 to about 0.05 times the resonant wavelength λ.
18 . The bulk acoustic wave device of claim 15 , wherein the first electrode, the second electrode, and the piezoelectric layer have a combined thickness H, and the resonant wavelength λ is about 2 times the combined thickness H.
19 . The bulk acoustic wave device of claim 15 , wherein the first raised frame layer is between the first electrode and the second electrode, the piezoelectric layer is over the first electrode, the second electrode is over the piezoelectric layer, and the first raised frame layer is between the second electrode and the piezoelectric layer.
20 . The bulk acoustic wave device of claim 15 , wherein the first raised frame layer is between the first electrode and the second electrode, the piezoelectric layer is over the first electrode, the second electrode is over the piezoelectric layer, and the first raised frame layer is between the first electrode and the piezoelectric layer.
21 . The bulk acoustic wave device of claim 15 , wherein the first raised frame layer has a lower acoustic impedance than the first electrode.
22 . The bulk acoustic wave device of claim 15 , wherein the first raised frame layer has a lower acoustic impedance than the second electrode.
23 . The bulk acoustic wave device of claim 15 , wherein the first raised frame layer has a lower acoustic impedance than the piezoelectric layer.
24 . The bulk acoustic wave device of claim 15 , wherein the second raised frame layer has a higher acoustic impedance than the first raised frame layer.