Acoustic wave device, high frequency front end circuit, and communication apparatus

An acoustic wave device comprising:

• a piezoelectric substrate made of LiNbO3 (lithium niobate);
• a plurality of interdigital transducer (IDT) electrodes provided on the piezoelectric substrate and including a first IDT electrode and a second IDT electrode;
• and
• a dielectric film provided on the piezoelectric substrate to cover the plurality of IDT electrodes;
• wherein
• the first IDT electrode and the second IDT electrode include main electrode layers;
• when a wave length determined by an electrode finger pitch of the first IDT electrode is denoted as λ1, a wave length determined by an electrode finger pitch of the second IDT electrode is denoted as λ2, an average value λ0 of the wave length λ1 and the wave length λ2 is defined by an equation of λ0=(λ1+λ2)/2, λ1/λ0=1+X, and λ2/λ0=1−X;
• among the plurality of IDT electrodes, the wave length λ1 of the first IDT electrode is larger than the wave length λ2 of the second IDT electrode;
• when a thickness obtained by normalizing, with the average value λ0, at least one of film thicknesses of the main electrode layer of the first IDT electrode and the main electrode layer of the second IDT electrode is denoted as T, and a density ratio of a material of the main electrode layer to Pt is denoted as r, in Euler angles (φ, θ, ψ) of the piezoelectric substrate, φ is 0°±5°, ψ is 0°±10°, and θ satisfies Expression 1 below:
• −A1/(T×r−B1)+C1≤θ≤−A2/(T×r−B2)+C2 Expression 1
• and
• A1, B1, C1, A2, B2, and C2 in the Expression 1 are represented by Expression 2 through Expression 8 below using X:
• A1=0.056×10−4.93×x+0.0016 Expression 2
• B1=−0.088×X2+0.066×X+0.0386(0.05≤X≤0.375) Expression 3
• B1=0.051(0.375≤X≤0.65) Expression 4,
• C1=0.714×10−5.26×x+28.37 Expression 5 ,
• A2=0.0987×X2−0.0918×X+0.0644 Expression 6,
• B2=−0.0651×X2+0.1114×X+0.0351 Expression 7,
• and
• C2=0.7830×X2−1.7424×X+32.70 Expression 8.