Acoustic wave device

An acoustic wave device comprising:

• a piezoelectric layer made of one of lithium niobate or lithium tantalate and including first and second main surfaces;
• first and second electrodes on the first main surface of the piezoelectric layer;
• and
• a dielectric film in a region of the first main surface of the piezoelectric layer in which no first or second electrode is provided, the dielectric film extending in a lengthwise direction of the first and second electrodes;
• wherein
• the first electrode and the second electrode are adjacent electrodes;
• when a center thickness of the piezoelectric layer in a region between the first electrode and the second electrode is denoted by tp1, and a center-to-center distance between the first electrode and the second electrode is denoted by p, tp1/p is about 0.5 or less;
• when a thickness of the piezoelectric layer in a region where at least one of the first electrode and the dielectric film is located is denoted by tp3, tp1>tp3;
• and
• when a density of the piezoelectric layer is denoted by ρp, a density of the first electrode is denoted by ρm, a thickness of the first electrode is denoted by tm, an acoustic velocity of a transversal bulk wave propagating in the piezoelectric layer is denoted by vps, and an acoustic velocity of a transversal bulk wave propagating in the first electrode is denoted by vms, Formula (1) below is satisfied:
• t
• p
• ⁢
• 2
• t
• p
• ⁢
• 1
• ≥
• arctan
• ⁡
• (
• -
• ρ
• p
• ⁢
• v
• ps
• ρ
• m
• ⁢
• v
• ms
• ⁢
• tan
• ⁡
• (
• t
• m
• ⁢
• v
• ps
• t
• p
• ⁢
• 1
• ⁢
• v
• ms
• ⁢
• π
• )
• )
• π
• .
• Formula
• ⁢
• (
• 1
• )

An acoustic wave device comprising:

• a piezoelectric layer made of one of lithium niobate or lithium tantalate and including first and second main surfaces;
• first and second electrodes on the first main surface of the piezoelectric layer;
• and
• a dielectric film in a region of the first main surface of the piezoelectric layer in which no first or second electrode is provided, the dielectric film extending in a lengthwise direction of the first and second electrodes;
• wherein
• the first electrode and the second electrode are adjacent electrodes;
• when a center thickness of the piezoelectric layer in a region between the first electrode and the second electrode is denoted by tp1, and a center-to-center distance between the first electrode and the second electrode is denoted by p, tp1/p is about 0.5 or less;
• when a thickness of the piezoelectric layer in a region where at least one of the first electrode and the dielectric film is located is denoted by tp3, tp1>tp3;
• the first main surface of the piezoelectric layer includes at least one recess;
• the first electrode is in any one of the at least one recess;
• and
• a width of the first electrode is less than a width of the at least one recess such that a portion of a side wall of the at least one recess is spaced apart from the first electrode.