Acoustic wave device

An acoustic wave device defining a filter device with a pass band, the acoustic wave device comprising:

• a laminated substrate including a first layer and a second layer, the first layer laminated on the second layer;
• a piezoelectric layer laminated on the first layer of the laminated substrate;
• and
• an excitation electrode on the piezoelectric layer;
• wherein
• the laminated substrate includes a support substrate;
• the first layer is a dielectric layer and is included in an intermediate layer laminated on the piezoelectric layer;
• the intermediate layer is a laminated body including the first layer and the second layer;
• when a center frequency in the pass band of the filter device is defined as fc, an acoustic velocity of a transversal wave propagating in at least one layer included in the intermediate layer is defined as vi, a thickness of the at least one layer is defined as ti, and any one of natural numbers is denoted by m, the thickness ti is within a range of (vi/fc)×(½)×(m±0.3);
• and
• when an acoustic velocity of a transversal wave propagating through the first layer is defined as v, a frequency included in the pass band of the filter device is defined as f, a wavelength derived from v/f is defined as λ, an acoustic impedance of the piezoelectric layer is defined as Zp, an acoustic impedance of the first layer is defined as Zd, an acoustic impedance of the second layer is defined as Zs, a thickness of the first layer is defined as td, and any one of natural numbers is denoted by n, combinations of a magnitude relationship of acoustic impedances of the piezoelectric layer, the first layer, and the second layer, and the thickness td are as shown in Table 1:
• TABLE 1
• Magnitude
• Relationship of
• Acoustic Impedance
• Zp > Zd
• Zp < Zd
• Zs > Zd
• td = n (½) λ
• td = (2n − 1) (14) λ
• Zs < Zd
• td = (2n − 1) (¼) λ
• td = n (½) λ.