Filter device

A filter device comprising:

• a plurality of acoustic wave resonators including first and second acoustic wave resonators each including:
• at least one first acoustic wave resonator including a piezoelectric substrate and first and second IDT electrodes, the piezoelectric substrate including a piezoelectric layer with first and second main surfaces facing each other, the first IDT electrode being located on the first main surface, the second IDT electrode being located on the second main surface and facing the first IDT electrode;
• and
• at least one second acoustic wave resonator including a piezoelectric substrate and a third IDT electrode, the piezoelectric substrate of the at least one second acoustic wave resonator including a piezoelectric layer with third and fourth main surfaces facing each other, the third IDT electrode being located on one of the third and fourth main surfaces;
• wherein
• when it is assumed that λ is a wavelength determined by an electrode finger pitch of an IDT electrode, a thickness of the piezoelectric layer is about 1λ or smaller, regardless of whether the electrode finger pitch of the first IDT electrode, the second IDT electrode, or the third IDT electrode is used to determine the wavelength.

A filter device comprising:

• a plurality of acoustic wave resonators including first and second acoustic wave resonators each including:
• at least one first acoustic wave resonator including a piezoelectric substrate and first and second IDT electrodes, the piezoelectric substrate including a piezoelectric layer with first and second main surfaces facing each other, the first IDT electrode being located on the first main surface, the second IDT electrode being located on the second main surface and facing the first IDT electrode;
• and
• at least one second acoustic wave resonator including a piezoelectric substrate and a third IDT electrode, the piezoelectric substrate of the at least one second acoustic wave resonator including a piezoelectric layer with third and fourth main surfaces facing each other, the third IDT electrode being located on one of the third and fourth main surfaces;
• wherein
• each of the first, second, and third IDT electrodes includes at least one pair of electrode fingers that are interdigitated with each other, and an interdigital width of the third IDT electrode is wider than an interdigital width of each of the first and second IDT electrodes.