Filter using lithium niobate and rotated 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 (LT) XBAR and at least one lithium niobate XBAR. Each of the at least one LT XBAR includes an LT piezoelectric plate with Euler angles (0°, β, 0°), where β is greater than zero and less than or equal to 40 degrees.
1. A bandpass filter having a passband between a lower band edge and an upper band edge, 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, and
each of the at least one LT XBAR comprises an LT piezoelectric layer with Euler angles (0°, β, 0°), where β is greater than zero and less than or equal to 40 degrees.
2. The bandpass filter of claim 1 , wherein the lower band edge is defined by one or more LT XBARs from the plurality of XBARs.
3. The bandpass filter of claim 2 , wherein the one or more LT XBARS are shunt resonators in the ladder filter circuit.
4. The filter of claim 1 , wherein the upper band edge is defined by one or more LT XBARs from the plurality of XBARs.
5. The bandpass filter of claim 4 , wherein the one or more LT XBARS are series resonators in the ladder filter circuit.
6. The bandpass 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.
7. The bandpass filter of claim 6 , 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.
8. The bandpass filter of claim 1 , wherein β is selected to minimize a temperature coefficient of frequency of at least one of the upper band edge and the lower band edge.
9. A bandpass filter having a passband between a lower band edge and an upper band edge, comprising:
a circuit card;
a first chip mounted on and connected to the circuit card, the first chip comprising one or more lithium tantalate (LT) transversely-excited film bulk acoustic resonators (XBARs), each of the one or more LT XBARs comprising an LT layer with Euler angles (0°, β, 0°), where β is greater than zero and less than or equal to 40 degrees; and
a second chip mounted on and connected to the circuit card, the 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.
10. The bandpass filter of claim 9 , wherein the first chip comprises:
a first substrate having a surface;
the LT layer, a back surface of the LT layer attached to the surface of the first substrate, portions of the LT layer forming one or more LT diaphragms over cavities in the first substrate; and
a first conductor pattern at a surface of the LT layer, 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.
11. The bandpass filter of claim 9 , wherein the second chip comprises:
a second substrate having a surface;
an LN layer, a back surface of the LN layer attached to the surface of the second substrate, portions of the LN layer forming one or more LN diaphragms over cavities in the second substrate; and
a second conductor pattern at a surface of the LN layer, 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.
12. The bandpass filter of claim 9 , wherein the lower band edge is defined by a first LT XBAR of the one or more LT XBARs.
13. The bandpass filter of claim 12 , wherein the first LT XBAR is a shunt resonator in the ladder filter circuit.
14. The bandpass filter of claim 9 , wherein the upper band edge is defined by a first LT XBAR of the one or more LT XBARs.
15. The bandpass filter of claim 14 , wherein the first LT XBAR is a series resonator in the ladder filter circuit.
16. The bandpass filter circuit of claim 9 , 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.
17. The bandpass filter of claim 16 , 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.
18. The bandpass filter of claim 9 , the circuit card comprising:
at least one conductor connecting an LT XBAR of the one or more LT XBARs of the first chip to an LN XBAR of the one or more LN XBARs of the second chip.
19. The bandpass filter of claim 9 , wherein β is selected to minimize a temperature coefficient of frequency of at least one of the upper band edge and the slower band edge.
20. 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), each of the one or more LT XBARs comprising an LT piezoelectric layer with Euler angles (0°, β, 0°), where β is greater than zero and less than or equal to 40 degrees;
fabricating a second chip containing one or more lithium niobate (LN) XBARs; and
connecting the first chip and the second chip to a circuit card,
wherein the circuit card comprises at least one conductor for connecting an LT XBAR of the one or more LT XBARs of the first chip to an LN XBAR of the one or more LN XBARs of the second chip.