Filter using lithium niobate and lithium tantalate transversely-excited film bulk acoustic resonators
Acoustic filters are disclosed. A bandpass filter has a passband between a lower band edge and an upper band edge. The bandpass filter includes a plurality of transversely-excited film bulk acoustic resonators (XBARs) connected in a ladder filter circuit. The plurality of XBARs includes at least one lithium tantalate XBAR and at least one lithium niobate XBAR.
1. A filter having a passband between a lower band edge and an upper band edge, the filter comprising:
a plurality of transversely-excited film bulk acoustic resonators (XBARs) connected in a ladder filter circuit, wherein:
the plurality of XBARs includes at least one lithium tantalate (LT) XBAR and at least one lithium niobate (LN) XBAR,
the plurality of XBARs each include a piezoelectric layer and an interdigital transducer (IDT) on only one surface of the piezoelectric layer,
the lower band edge is defined by one or more LN XBARs from the plurality of XBARs, the piezoelectric layer of the one or more LN XBARs consisting of LN, and
the upper band edge is defined by one or more LT XBARs from the plurality of XBARs the piezoelectric layer of the one or more LT XBARs consisting of LT.
2. The filter of claim 1 , wherein the one or more LT XBARS are shunt resonators in the ladder filter circuit.
3. The filter of claim 1 , wherein the one or more LT XBARS are series resonators in the ladder filter circuit.
4. The filter of claim 1 , wherein the lower band edge is defined by a first LT XBAR from the plurality of XBARs and the upper band edge is defined by a second LT XBAR from the plurality of XBARs.
5. The filter of claim 4 , wherein the first LT XBAR is a shunt resonator in the ladder filter circuit and the second LT XBAR is a series resonator in the ladder filter circuit.
6. A filter having a passband between a lower band edge and an upper band edge, comprising:
a first chip comprising one or more lithium tantalate (LT) transversely-excited film bulk acoustic resonators (XBARs); and
a second chip comprising one or more lithium niobate (LN) XBARs, wherein
the one or more LT XBARs and the one or more LN XBARs are connected to form a ladder filter circuit.
7. The filter of claim 6 , wherein the first chip comprises:
a first substrate having a surface;
an LT plate-attached to the surface of the first substrate, portions of the LT plate forming one or more LT diaphragms spanning cavities in the first substrate; and
a first conductor pattern on the LT plate, the first conductor pattern including a respective interdigital transducer (IDT) of each of the one or more LT XBARS, interleaved fingers of each IDT disposed on a respective one of the one or more LT diaphragms.
8. The filter of claim 6 , wherein the second chip comprises:
a second substrate having a surface;
an LN plate-attached to the surface of the second substrate, portions of the LN plate forming one or more LN diaphragms spanning cavities in the second substrate; and
a second conductor pattern on the LN plate, the second conductor pattern including a respective interdigital transducer (IDT) of each of the one or more LN XBARs, interleaved fingers of each IDT disposed on a respective one of the one of more LN diaphragms.
9. The filter of claim 6 , wherein the lower band edge is defined by a first LT XBAR of the one or more LT XBARs.
10. The filter of claim 9 , wherein the first LT XBAR is a shunt resonator in the ladder filter circuit.
11. The filter of claim 6 , wherein the upper band edge is defined by a first LT XBAR of the one or more LT XBARs.
12. The filter of claim 11 , wherein first LT XBAR is a series resonator in the ladder filter circuit.
13. The filter of claim 6 , wherein
the one or more LT XBARs is at least two LT XBARS,
the lower band edge is defined by a first LT XBAR of the at least two LT XBARs, and
the upper band edge is defined by a second LT XBAR of the at least two LT XBARs.
14. The filter of claim 13 , wherein the first LT XBAR is a shunt resonator in the ladder filter circuit and the second LT XBAR is a series resonator in the ladder filter circuit.
15. The filter of claim 6 , further comprising:
at least one conductor that connects an LT XBAR of the first chip to an LN XBAR of the second chip.
16. A method for fabricating a filter, comprising:
fabricating a first chip containing one or more lithium tantalate (LT) transversely-excited film bulk acoustic resonators (XBARs);
fabricating a second chip containing one or more lithium niobate (LN) XBARs; and
connecting the first chip to the second chip,
wherein the connecting comprises connecting an LT XBAR of the first chip to an LN XBAR of the second chip by at least one conductor.
17. The method of claim 16 , wherein the first chip comprises:
a first substrate having a surface;
an LT plate attached to the surface of the first substrate, portions of the LT plate forming one or more LT diaphragms spanning cavities in the first substrate; and
a first conductor pattern on the LT plate, the first conductor pattern including a respective interdigital transducer (IDT) of each of the one or more LT XBARS, interleaved fingers of each IDT disposed on a respective one of the one or more LT diaphragms.
18. The method of claim 16 , wherein the second chip comprises:
a second substrate having a surface;
an LN plate-attached to the surface of the second substrate, portions of the LN plate forming one or more LN diaphragms spanning cavities in the second substrate; and
a second conductor pattern on the LN plate, the second conductor pattern including a respective interdigital transducer (IDT) of each of the one or more LN XBARs, interleaved fingers of each IDT disposed on a respective one of the one of more LN diaphragms.
19. The method of claim 16 , further comprising defining a lower band edge of the filter by a first LT XBAR of the one or more LT XBARs.
20. The method of claim 19 , wherein the first LT XBAR is a shunt resonator in the filter, which comprises a ladder filter circuit.
21. The method of claim 16 , further comprising defining an upper band edge of the filter by a first LT XBAR of the one or more LT XBARs.
22. The method of claim 21 , wherein the first LT XBAR is a series resonator in the filter, which comprises a ladder filter circuit.
23. The method of claim 16 , wherein;
the one or more LT XBARs is at least two LT XBARS,
a lower band edge of the filter is defined by a first LT XBAR of the at least two LT XBARs, and
upper band edge of the filter is defined by a second LT XBAR of the at least two LT XBARs.
24. The method of claim 23 , wherein the first LT XBAR is a shunt resonator in the filter and the second LT XBAR is a series resonator in the filter.