Transversely-excited film bulk acoustic resonator with interdigital transducer with varied mark and pitch

1. An acoustic resonator device comprising:

a piezoelectric plate having a front surface and a back surface; and

an interdigital transducer (IDT) on the piezoelectric plate, the IDT comprising:

a first pitch/mark zone comprising interleaved fingers having a pitch equal to a first pitch value P 1 and a mark equal to a first mark value M 1 , and

a second pitch/mark zone comprising interleaved fingers having a pitch equal to a second pitch value P 2 not equal to P 1 and a mark equal to a second mark value M 2 not equal to M 1 ,

wherein a radio frequency signal applied to the IDT causes excitation of a same shear primary acoustic mode by both the first pitch/mark zone and the second pitch/mark zone, and wherein P1, M1, P2, and M2 are selected such that an amplitude of spurious modes is reduced as compared to a device having a same primary acoustic mode and a single pitch/mark zone.

2. The acoustic resonator device of claim 1 , further comprising:

three or more pitch/mark zones including the first pitch/mark zone and the second pitch/mark zone, each of the three or more pitch/mark zones having a pitch between adjacent interleaved fingers equal to a respective unique pitch value and a mark of the interleaved fingers equal to a respective unique mark value,

wherein a radio frequency signal applied to the IDT causes excitation of the same shear primary acoustic mode by all of the three or more pitch/mark zones.

3. The acoustic resonator device of claim 2 , wherein the IDT cycles between the three or more pitch/mark zones along a length of the IDT.

4. The acoustic resonator device of claim 2 , wherein every pitch/mark zone comprises two or more pairs of interleaved fingers.

5. The acoustic resonator device of claim 2 , wherein the IDT comprises two or more unit cells juxtaposed along a length of the IDT, each unit cell comprising all of the three or more pitch/mark zones.

6. The acoustic resonator device of claim 1 , wherein the IDT comprises multiple first pitch/mark zones and multiple second pitch/marks zones, the first and second pitch/mark zones alternating along a length of the IDT.

7. The acoustic resonator device of claim 6 , wherein each first pitch/mark zone and each second pitch/mark zone comprises two or more pairs of interleaved fingers.

8. The acoustic resonator device of claim 6 , wherein the IDT comprises two or more unit cells juxtaposed along the length of the IDT, each unit cell comprising at least one first pitch/mark zone and at least one second pitch/mark zone.

9. The acoustic resonator device of claim 1 , wherein the IDT changes between the first pitch/mark zone and the second pitch/mark zone across an aperture of the IDT.

10. The acoustic resonator device of claim 9 , wherein the IDT changes between the first pitch/mark zone and the second pitch/mark zone in one or more steps.

11. The acoustic resonator device of claim 9 , wherein the IDT pitch and mark change continuously across the aperture of the IDT.

12. The acoustic resonator device of claim 1 , wherein

the IDT comprises a first set of first fingers extending from a first busbar interleaved with a second set of fingers extending from a second busbar,

a mark of each first finger tapers between M 1 and M 2 across an aperture of the IDT,

a mark of each second finger is (M 1 +M 2 )/2, and

a portion of each second finger within the aperture is not perpendicular to the second busbar.

13. The acoustic resonator device of claim 12 , wherein an angle between the portion of each second finger within the aperture and the second busbar is 90°±arctangent((P 2 -P 1 )/AP), where AP is a distance across the aperture of the IDT.

14. The acoustic resonator device of claim 1 , wherein a portion of the piezoelectric plate forms a diaphragm spanning a cavity in a substrate, and the interleaved fingers of the IDT are on the diaphragm.

15. The acoustic resonator device of claim 1 , further comprising:

an acoustic Bragg reflector between a surface of a substrate and the back surface of the piezoelectric plate.

16. The acoustic resonator device of claim 1 , wherein the radio frequency signal applied to the IDT causes excitation of different spurious acoustic modes by the first pitch/mark zone and the second pitch/mark zone.

17. The acoustic resonator device of claim 1 , wherein the IDT comprises two or more unit cells juxtaposed along a length of the IDT, each unit cell including at least one step between the first pitch/mark zone and the second pitch/mark zone across an aperture of the IDT.

18. An acoustic resonator device comprising:

a piezoelectric plate; and

an interdigital transducer (IDT) comprising interleaved fingers on the piezoelectric plate,

wherein the IDT transitions between a first pitch/mark combination and a second pitch/mark combination different from the first pitch/mark combination along a length of the IDT, and

wherein a radio frequency signal applied to the IDT causes excitation of a same shear primary acoustic mode by both the first pitch/mark combination and the second pitch/mark combination, and wherein P1, M1, P2, and M2 are selected such that an amplitude of spurious modes is reduced as compared to a device having a same primary acoustic mode and a single pitch/mark combination.

19. An acoustic resonator device comprising:

a piezoelectric plate; and

an interdigital transducer (IDT) comprising interleaved fingers on the piezoelectric plate,

wherein the IDT transitions between a first pitch/mark combination and a second pitch/mark different from the first pitch/mark combination across an aperture of the IDT, and

wherein a radio frequency signal applied to the IDT causes excitation of a same shear primary acoustic mode by both the first pitch/mark combination and the second pitch/mark combination, and wherein P1, M1, P2, and M2 are selected such that an amplitude of spurious modes is reduced as compared to a device having a same primary acoustic mode and a single pitch/mark combination.