Acoustic wave device with reduced higher order transverse modes

An acoustic wave device comprising:

• a piezoelectric substrate;
• a pair of IDT electrodes formed on the piezoelectric substrate, a first IDT electrode of the pair of IDT electrodes including a first bus bar and a first plurality of electrode fingers extending from the first bus bar, a second IDT electrode of the pair of IDT electrodes including a second bus bar and a second plurality of electrode fingers extending from the second bus bar, the first plurality of electrode fingers interleaved with the second plurality of electrode fingers;
• and
• a first dielectric film covering at least a part of the piezoelectric substrate and the pair of IDT electrodes, the first dielectric film covering an intersection area in which the first plurality and second plurality of electrode fingers are arranged interleaved with each other and edge areas adjacent to the intersection area, an acoustic velocity of an acoustic wave in the intersection area being greater than the acoustic velocity of the acoustic wave in the edge areas, the first dielectric film including a first area covering the intersection area and/or one of the edge areas and having a first thickness, a second area adjacent the intersection area and/or the one of the edge areas and having a second thickness, and a tapered area formed at an intersection of the first area and the second area, a thickness of the first dielectric film continuously changing in the tapered area.