Boundary acoustic wave device

A boundary acoustic wave device comprising:

• a piezoelectric substrate made of LiTaO3 and including a groove in an upper surface thereof;
• an IDT electrode arranged such that at least a portion of the IDT electrode is buried in the groove of the piezoelectric substrate;
• a silicon oxide layer stacked on the piezoelectric substrate;
• and
• a dielectric layer made of a dielectric exhibiting a higher acoustic velocity than the silicon oxide layer;
• wherein
• the IDT electrode includes a main electrode layer made of a metal having a density of about 16 g/cm3 or higher, and an auxiliary electrode layer made of a metal having a density of about 4 g/cm3 or higher, but lower than 16 g/cm3;
• and
• where a wavelength of a boundary acoustic wave excited by the IDT electrode is λ, a depth A of the groove corresponding to a partial length of the IDT electrode buried in the groove is within a range of about 0.1% to about 10% of λ, a film thickness B of the silicon oxide layer is within a range of about 20% to about 140% of λ, the density of the main electrode is denoted by C (g/cm3), a thickness D of the main electrode layer is within a range of about 1% to about 10% of λ, the density of the auxiliary electrode is denoted by E (g/cm3), a thickness F of the auxiliary electrode positioned above the main electrode layer is within a range of about 0% to about 10% of λ, and a duty ratio G of the IDT electrode is within a range of about 0.4 to about 0.7, θ of Euler angles (0°, θ, 0°) of the piezoelectric substrate made of LiTaO3 is within a range of about (θ0−20°) or more to about (θ0+20°) or less with respect to θ0 expressed by:
• θ0=65.53G+0.7568F+0.8454E+7.091D+1.609C−0.03789B−3.535A+60.85.