US-20260128728-A1 - ACOUSTIC WAVE DEVICE

Abstract

An acoustic wave device includes a resonator including a piezoelectric layer including first and second principal surfaces opposed to each other, an upper electrode on the first principal surface of the piezoelectric layer, and a lower electrode on the second principal surface of the piezoelectric layer, and a capacitive element on one of the first and second principal surfaces of the piezoelectric layer and electrically connected to the resonator. The capacitive element includes an interdigital transducer (IDT) electrode including electrode fingers arranged in a predetermined direction.

Inventors

• Kazumasa Haruta
• Hirotsugu Mori

Assignees

• MURATA MANUFACTURING CO., LTD.

Dates

Publication Date

20260507

Application Date

20260106

Priority Date

20230814

Claims (17)

1. 1 . An acoustic wave device comprising: a resonator including a piezoelectric layer including a first principal surface and a second principal surface opposite to the first principal surface, an upper electrode on the first principal surface of the piezoelectric layer, and a lower electrode on the second principal surface of the piezoelectric layer; and a capacitive element on the first principal surface or the second principal surface of the piezoelectric layer and electrically connected to the resonator; wherein the capacitive element includes an interdigital transducer (IDT) electrode including a plurality of electrode fingers arranged in a predetermined direction.
2. 2 . The acoustic wave device according to claim 1 , wherein the resonator includes a series-arm resonator and the capacitive element includes a parallel-arm capacitive element; the series-arm resonator is connected in series between an input terminal and an output terminal; and one terminal of the parallel-arm capacitive element is connected to a signal path between the input terminal and the output terminal and another terminal of the parallel-arm capacitive element is connected to a reference potential.
3. 3 . The acoustic wave device according to claim 2 , wherein a resonant frequency of the IDT electrode of the parallel-arm capacitive element is equal or substantially equal to a resonant frequency of the series-arm resonator.
4. 4 . The acoustic wave device according to claim 2 , wherein the series-arm resonator and the parallel-arm capacitive element include a common node.
5. 5 . The acoustic wave device according to claim 4 , wherein one of the upper electrode and the lower electrode included in the series-arm resonator is connected to the common node; and the parallel-arm capacitive element is located on a same layer of the one of the upper electrode and the lower electrode connected to the common node.
6. 6 . The acoustic wave device according to claim 2 , wherein the series-arm resonator and the parallel-arm capacitive element are connected via another element.
7. 7 . The acoustic wave device according to claim 1 , wherein the resonator includes a parallel-arm resonator and the capacitive element includes a series-arm capacitive element; the series-arm capacitive element is connected in series between an input terminal and an output terminal; and one terminal of the parallel-arm resonator is connected to a signal path between the input terminal and the output terminal and another terminal of the parallel-arm resonator is connected to a reference potential.
8. 8 . The acoustic wave device according to claim 7 , wherein a resonant frequency of the IDT electrode of the series-arm capacitive element is equal or substantially equal to a resonant frequency of the parallel-arm resonator.
9. 9 . The acoustic wave device according to claim 7 , wherein the parallel-arm resonator and the series-arm capacitive element include a common node.
10. 10 . The acoustic wave device according to claim 9 , wherein one of the upper electrode and the lower electrode included in the parallel-arm resonator is connected to the common node; and the series-arm capacitive element is located on a same layer of the one of the upper electrode and the lower electrode connected to the common node.
11. 11 . The acoustic wave device according to claim 7 , wherein the parallel-arm resonator and the series-arm capacitive element are connected via another element.
12. 12 . The acoustic wave device according to claim 1 , further comprising: a plurality of the resonators and a plurality of the capacitive elements; wherein the plurality of the resonators include a series-arm resonator and a parallel-arm resonator; the plurality of the capacitive elements include a series-arm capacitive element and a parallel-arm capacitive element; the series-arm resonator is connected in series between an input terminal and an output terminal; the series-arm capacitive element is connected in series between the input terminal and the output terminal and is connected in parallel to the series-arm resonator; the parallel-arm resonator is connected in parallel between a signal path between the input terminal and the output terminal and a reference potential; and the parallel-arm capacitive element is connected in parallel between the signal path between the input terminal and the output terminal and the reference potential and is connected in parallel to the parallel-arm resonator.
13. 13 . The acoustic wave device according to claim 12 , wherein a resonant frequency of the IDT electrode of the parallel-arm capacitive element is equal or substantially equal to a resonant frequency of the series-arm resonator; and a resonant frequency of the IDT electrode of the series-arm capacitive element is equal or substantially equal to a resonant frequency of the parallel-arm resonator.
14. 14 . The acoustic wave device according to claim 12 , wherein the series-arm resonator, the parallel-arm resonator, the series-arm capacitive element, and the parallel-arm capacitive element include a common node.
15. 15 . The acoustic wave device according to claim 1 , wherein the electrode fingers included in the capacitive element extend in a parallel or substantially parallel direction; and at least one of the plurality of electrode fingers extends in a direction tilted with respect to an extending direction of the upper electrode and the lower electrode included in the resonator.
16. 16 . The acoustic wave device according to claim 1 , further comprising: a plurality of the capacitive elements; wherein each of the plurality of the capacitive elements includes a series-arm capacitive element; and a plurality of the series-arm capacitive elements are connected in series between an input terminal and an output terminal; the resonator includes a parallel-arm resonator; and one terminal of the parallel-arm resonator is connected to a signal path between the plurality of the series-arm capacitive elements and another terminal of the parallel-arm resonator is connected to a reference potential.
17. 17 . The acoustic wave device according to claim 1 , wherein the piezoelectric layer includes monocrystalline lithium niobate or lithium tantalate.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority to Japanese Patent Application No. 2023-132070 filed on Aug. 14, 2023 and is a Continuation Application of PCT Application No. PCT/JP2024/019502 filed on May 28, 2024. The entire contents of each application are hereby incorporated herein by reference. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to acoustic wave devices. 2. Description of the Related Art In U.S. Pat. No. 9,602,076, an acoustic wave device is described in which a flat-shaped upper electrode and a flat-shaped lower electrode are provided on both surfaces of a piezoelectric layer. In the acoustic wave device as described above, it is demanded to suppress an unwanted wave occurring from a resonator. In the acoustic wave device described in U.S. Pat. No. 9,602,076, a capacitive electrode is provided on a dielectric layer supporting the piezoelectric layer, and there is a possibility that it is difficult to adjust a capacitive value generated by the capacitive electrode and so forth. As a result, in the acoustic wave device described in U.S. Pat. No. 9,602,076, there is a possibility that it is difficult to suppress an unwanted wave occurring from the resonator. SUMMARY OF THE INVENTION Example embodiments of the present invention provide acoustic wave devices each able to reduce or prevent an unwanted wave occurring from a resonator. An acoustic wave device according to an example embodiment of the present invention includes a resonator including a piezoelectric layer including a first principal surface and a second principal surface opposite to the first principal surface, an upper electrode on the first principal surface of the piezoelectric layer, and a lower electrode on the second principal surface of the piezoelectric layer, and a capacitive element on the first principal surface or the second principal surface of the piezoelectric layer and electrically connected to the resonator. The capacitive element includes an interdigital transducer (IDT) electrode including a plurality of electrode fingers arranged in a predetermined direction. Acoustic wave devices according to example embodiments of the present invention are each able to reduce or prevent an unwanted wave occurring from a resonator. The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the example embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing an acoustic wave device according to a first example embodiment of the present invention. FIG. 2 is a plan view showing the acoustic wave device according to the first example embodiment of the present invention. FIG. 3 is a III-III′ sectional view of FIG. 2. FIG. 4 is a IV-IV′ sectional view of FIG. 2. FIG. 5 is a graph schematically showing bandpass characteristics of an acoustic wave device according to a comparative example. FIG. 6 is a graph schematically showing bandpass characteristics of an acoustic wave device according to an example of an example embodiment of the present invention. FIG. 7 is a descriptive drawing for describing a relationship between resonant frequency of unwanted wave indicated by a dotted line F1 of FIG. 5 and resonant frequency of a parallel-arm capacitive element and a series-arm capacitive element. FIG. 8 is a plan view of an IDT electrode schematically enlarged. FIG. 9 is a circuit diagram showing an acoustic wave device according to a second example embodiment of the present invention. FIG. 10 is a plan view showing the acoustic wave device according to the second example embodiment of the present invention. FIG. 11 is a circuit diagram showing an acoustic wave device according to a modification of an example embodiment of the present invention. FIG. 12 is a plan view showing an acoustic wave device according to a modification of an example embodiment of the present invention. FIG. 13 is a circuit diagram showing an acoustic wave device according to a third example embodiment of the present invention. FIG. 14 is a plan view showing the acoustic wave device according to the third example embodiment of the present invention. FIG. 15 is a circuit diagram showing an acoustic wave device according to a fourth example embodiment of the present invention. FIG. 16 is a plan view showing the acoustic wave device according to the fourth example embodiment of the present invention. FIG. 17 is a plan view showing an acoustic wave device according to a fifth example embodiment of the present invention. FIG. 18 is a circuit diagram showing an acoustic wave device according to a sixth example embodiment of the present invention. DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS In the following, example embodiments of the present disclosure are described in detail with reference to the drawings. The present