Boundary acoustic wave device and communication equipment

A filter comprising a double-mode resonator,

• the double-mode resonator comprising:
• a piezoelectric substrate having piezoelectricity;
• an interdigitated electrode formed on the piezoelectric substrate;
• a first medium formed on the piezoelectric substrate so as to cover the interdigitated electrode;
• a second medium formed on the first medium;
• and
• a third medium formed on the first medium,
• wherein the interdigitated electrode has a plurality of electrode fingers and a bus bar that connects ends of the plurality of electrode fingers,
• the second medium and the third medium are in contact with the first medium,
• the first medium, the second medium, and the third medium respectively are formed of different materials, and
• a ratio in length of a part with the third medium formed with respect to a length of a propagation path of boundary acoustic waves in a cross-section perpendicular to a longitudinal direction of the electrode fingers varies in the longitudinal direction of the electrode fingers, and
• wherein the first medium is divided into halves in a direction perpendicular to the longitudinal direction of the electrode fingers, as a region on which the third medium is formed and a region on which the third medium is not formed.

A boundary acoustic waves device, comprising:

• a piezoelectric substrate having piezoelectricity;
• an interdigitated electrode formed on the piezoelectric substrate;
• a first medium formed on the piezoelectric substrate so as to cover the interdigitated electrode;
• and
• a second medium formed on the first medium, the interdigitated electrode having a plurality of electrode fingers and a bus bar that connects ends of the plurality of electrode fingers,
• wherein the boundary acoustic waves device includes a third medium formed on the first medium,
• the second medium and the third medium are in contact with the first medium,
• the first medium, the second medium, and the third medium respectively are formed of different materials, and
• a ratio in length of a part with the third medium formed with respect to a length of a propagation path of boundary acoustic waves in a cross-section perpendicular to a longitudinal direction of the electrode fingers varies in the longitudinal direction of the electrode fingers, and
• wherein the first medium is divided into halves in a direction perpendicular to the longitudinal direction of the electrode fingers, as a region on which the third medium is formed and a region on which the third medium is not formed.

A filter comprising a one-port resonator,

• the one-port resonator comprising:
• a piezoelectric substrate having piezoelectricity;
• an interdigitated electrode formed on the piezoelectric substrate;
• a first medium formed on the piezoelectric substrate so as to cover the interdigitated electrode;
• a second medium formed on the first medium;
• and
• a third medium formed on the first medium,
• wherein the interdigitated electrode has a plurality of electrode fingers and a bus bar that connects ends of the plurality of electrode fingers,
• the second medium and the third medium are in contact with the first medium,
• the first medium, the second medium, and the third medium respectively are formed of different materials, and
• a ratio in length of a part with the third medium formed with respect to a length of a propagation path of boundary acoustic waves in a cross-section perpendicular to a longitudinal direction of the electrode fingers varies in the longitudinal direction of the electrode fingers, and
• wherein the first medium is divided into halves in a direction perpendicular to the longitudinal direction of the electrode fingers, as a region on which the third medium is formed and a region on which the third medium is not formed.