Filter using transversely-excited film bulk acoustic resonators
A 6 GHz Wi-Fi bandpass filter includes a ladder filter circuit with two or more shunt transversely-excited film bulk acoustic resonators (XBARs) and two or more series XBARs. Each of the two or more shunt XBARS includes a diaphragm having an LN-equivalent thickness greater than or equal to 310 nm, and each of the two or more series XBARS includes a diaphragm having an LN-equivalent thickness less than or equal to 305 nm.
1. A bandpass filter comprising:
a ladder filter circuit comprising a series transversely-excited film bulk acoustic resonator (XBAR) and a shunt XBAR,
wherein the series XBAR comprises:
a lithium niobate (LN) piezoelectric layer;
a front-side dielectric layer of silicon oxide between interleaved fingers of an interdigital transducer disposed on the LN piezoelectric layer of the series XBAR,
wherein the series XBAR has an LN-equivalent thickness teqa less than or equal to 305 nanometers, and the LN-equivalent thickness tega of the series XBAR is given by the formula tp+ka*(tfsd), where tp is a thickness of the LN piezoelectric layer of the series XBAR, ka is a constant for the series XBAR and ka=0.45, and tfsd is a thickness of the front side dielectric layer of the series XBAR,
wherein the shunt XBAR comprises:
a LN piezoelectric layer;
a front-side dielectric layer of silicon oxide between interleaved fingers of an interdigital transducer disposed on the LN piezoelectric layer of the shunt XBAR, and
wherein the shunt XBAR has an LN-equivalent thickness teqr greater than or equal to 310 nanometers and the LN piezoelectric layer has a thickness that is less than 1500 nanometers, and the LN-equivalent thickness teqr of the shunt XBAR is given by the formula tp+kr*(tfsd), where tp is a thickness of the LN piezoelectric layer of the shunt XBAR, and kr is a constant for the shunt XBAR and kr=0.57, and tfsd is a thickness of the front-side dielectric layer of the shunt XBAR.
2. The bandpass filter of claim 1 , wherein the LN piezoelectric layer of the series XBAR has a thickness less than or equal to the thickness of the LN piezoelectric layer of the shunt XBAR.
3. The bandpass filter of claim 1 , wherein the series XBAR is disposed on a first chip and the shunt XBAR is disposed on a second chip.
4. The bandpass filter of claim 1 , wherein one or more of the series XBAR and the shunt XBAR are composed of multiple sub-resonators.
5. The bandpass filter of claim 4 , wherein the multiple sub-resonators have a same length and a same aperture as each other.
6. The bandpass filter of claim 1 , wherein the LN piezoelectric layer of the shunt XBAR has an LN-equivalent thickness greater than or equal to 320 nm.
7. The bandpass filter of claim 1 , wherein the LN piezoelectric layer of the series XBAR has an LN-equivalent thickness of less than 295 nanometers.
8. The bandpass filter of claim 1 , wherein the series XBAR is one of a plurality of series XBARs that each have an LN-equivalent thickness that is less than 295 nanometers.
9. The bandpass filter of claim 1 , wherein the LN piezoelectric layer of the series XBAR has a thickness less than or equal to a thickness of the LN piezoelectric layer of the shunt XBAR.
10. The bandpass filter of claim 1 , wherein the LN piezoelectric layer of the series XBAR has Euler angles [0°, β, 0°], where 30°≤β≤38°, and wherein the LN piezoelectric layer of the shunt XBAR has Euler angles [0°, β, 0°], where 30°≤β≤38°.
11. A ladder filter circuit comprising:
a series bulk acoustic resonator and a shunt bulk acoustic resonator,
wherein the series bulk acoustic resonator comprises:
a lithium niobate (LN) piezoelectric layer;
a dielectric layer of silicon oxide between interleaved fingers of an interdigital transducer disposed on the LN piezoelectric layer of the series bulk acoustic resonator,
wherein the series bulk acoustic resonator has an LN-equivalent thickness tega that is less than or equal to 305 nanometers, and the LN-equivalent thickness tega of the series bulk acoustic resonator is given by the formula tp+ka*(tfsd), where tp is a thickness of LN piezoelectric layer of the series bulk acoustic resonator, ka is a constant for the dielectric layer of silicon oxide of the series bulk acoustic resonator and ka=0.45, and tfsd is a thickness of the dielectric layer of the series bulk acoustic resonator,
wherein the shunt bulk acoustic resonator comprises:
a LN piezoelectric layer;
a dielectric layer of silicon oxide between interleaved fingers of an interdigital transducer disposed on the LN piezoelectric layer of the shunt bulk acoustic resonator, and
wherein the shunt bulk acoustic resonator has an LN-equivalent thickness teqr greater than or equal to 310 nanometers and a thickness of the LN piezoelectric layer is less than 1500 nanometers, and the LN-equivalent thickness teqr of the shunt bulk acoustic resonator is given by the formula tp+kr*(tfsd), where tp is a thickness of the LN piezoelectric layer of the shunt bulk acoustic resonator, and kr is a constant for the dielectric layer of silicon oxide for the shunt bulk acoustic resonator and kr=0.57, and tfsd is a thickness of the dielectric layer of the shunt bulk acoustic resonator.
12. The ladder filter circuit of claim 11 , wherein the LN piezoelectric layer of the series bulk acoustic resonator has a thickness less than or equal to the thickness of the LN piezoelectric plate of the shunt bulk acoustic resonator.
13. The ladder filter circuit of claim 11 , wherein the series bulk acoustic resonator is disposed on a first chip and the shunt bulk acoustic resonator is disposed on a second chip.
14. The ladder filter circuit of claim 11 , wherein one or more of the series bulk acoustic resonator and the shunt bulk acoustic resonator are composed of multiple sub-resonators.
15. The ladder filter circuit of claim 14 , wherein the multiple sub-resonators have a same length and a same aperture as each other.
16. The ladder filter circuit of claim 11 , wherein the LN piezoelectric layer of the shunt bulk acoustic resonator has an LN-equivalent thickness that is greater than or equal to 320 nm.
17. The ladder filter circuit of claim 11 , wherein the LN piezoelectric layer of the series bulk acoustic resonator has an LN-equivalent thickness that is less than 295 nanometers.
18. The ladder filter circuit of claim 11 , wherein the series bulk acoustic resonator is one of a plurality of series bulk acoustic resonators that each have an LN-equivalent thickness that is less than 295 nanometers.
19. The ladder filter circuit of claim 11 , wherein the LN piezoelectric layer of the series bulk acoustic resonator has a thickness less than or equal to a thickness of the LN piezoelectric layer of the shunt bulk acoustic resonator.
20. The ladder filter circuit of claim 11 , wherein the LN piezoelectric layer of the series bulk acoustic resonator has Euler angles [0°, β, 0°], where 30°≤β≤38°, and wherein the LN piezoelectric layer of the shunt bulk acoustic resonator has Euler angles [0°, β, 0°], where 30°≤β≤38°.