Acoustic wave device

An acoustic wave device comprising:

• a support substrate including first and second surfaces that oppose each other;
• a piezoelectric layer on the first surface of the support substrate and including first and surfaces that oppose each other;
• and
• first and second resonators that each include first and second electrodes on the first surface of the piezoelectric layer,
• wherein, in each of the first and second resonators, a bulk wave in a first thickness-shear mode is enclosed in the piezoelectric layer by one of:
• a space defining a cavity in the support substrate or an air gap between the support substrate and the piezoelectric layer;
• or
• an acoustic reflection layer that includes one or more low acoustic impedance layers and one or more high acoustic impedance layers between the support substrate and the piezoelectric layer, and
• wherein the second surface of the support substrate has a first roughness that is greater than a second roughness of the first surface of the piezoelectric layer.

An acoustic wave device comprising:

• a support substrate;
• a piezoelectric layer on the support substrate and extending in a first direction of the support substrate;
• an acoustic reflection layer that is between the support substrate and the piezoelectric layer and that includes one or more low acoustic impedance layers and one or more high acoustic impedance layers;
• and
• a first electrode and a second electrode on the piezoelectric layer that oppose each other and that extend in a direction that intersects with the first direction,
• wherein at least a portion of each of the first and the second electrodes overlaps the acoustic reflection layer in a plan view of the piezoelectric layer, and
• wherein a major surface of the support substrate that is opposite the piezoelectric layer has a first roughness that is greater than a second roughness of a major surface of the piezoelectric layer on which the first and second electrodes are disposed.