Elastic wave device, high-frequency front-end circuit, and communication apparatus

An elastic wave device comprising:

• a piezoelectric substrate;
• and
• an interdigital transducer electrode on the piezoelectric substrate;
• wherein
• the piezoelectric substrate includes:
• a piezoelectric layer;
• and
• a high-acoustic-velocity member layer in which an acoustic velocity of a bulk wave that propagates through the high-acoustic-velocity member layer is higher than an acoustic velocity of an elastic wave that propagates through the piezoelectric layer, the piezoelectric layer being stacked directly or indirectly on the high-acoustic-velocity member layer;
• the piezoelectric layer includes lithium tantalate;
• the interdigital transducer electrode includes:
• a first busbar;
• a second busbar facing the first busbar;
• first electrode fingers each including an end portion connected to the first busbar;
• and
• second electrode fingers each including an end portion connected to the second busbar, the first electrode fingers being interdigitated with the second electrode fingers;
• wherein
• denoting an elastic wave propagation direction as a first direction, and denoting a direction perpendicular or substantially perpendicular to the first direction as a second direction, a portion in which the first electrode fingers overlap the second electrode fingers in the first direction is defined as an intersecting region;
• the intersecting region includes:
• a central region located in a middle of the intersecting region in the second direction;
• a first low-acoustic-velocity region located on a side of the central region adjacent to the first busbar, an acoustic velocity in the first low-acoustic-velocity region being lower than an acoustic velocity in the central region;
• and
• a second low-acoustic-velocity region located on a side of the central region adjacent to the second busbar, an acoustic velocity in the second low-acoustic-velocity region being lower than an acoustic velocity in the central region;
• the first low-acoustic-velocity region and the second low-acoustic-velocity region include mass-adding films disposed on the first electrode fingers and the second electrode fingers;
• the interdigital transducer electrode includes:
• a first high-acoustic-velocity region;
• and
• a second high-acoustic-velocity region, an acoustic velocity in the first high-acoustic-velocity region and the second high-acoustic-velocity region being higher than an acoustic velocity in the central region;
• the first low-acoustic-velocity region is located between the central region and the first high-acoustic-velocity region;
• the second low-acoustic-velocity region is located between the central region and the second high-acoustic-velocity region;
• and
• denoting a film thickness normalized to a wavelength determined by an electrode finger pitch of the interdigital transducer electrode as a wavelength-normalized film thickness (%), a product of the wavelength-normalized film thickness of the mass-adding films and a density (g/cm3) of the mass-adding films is about 13.4631 (% ·g/cm3) or less.