Acoustic wave guide device and method for minimizing trimming effects and piston mode instabilities

An acoustic wave device comprising:

• a piezoelectric substrate;
• a plurality of electrodes forming an interdigital transducer on a surface of the piezoelectric substrate, wherein each of the plurality of electrodes includes a transversely extending center region and transversely opposing edge regions for guiding an acoustic wave longitudinally through the transducer;
• a first dielectric layer covering the interdigital transducer;
• a second dielectric layer covering the first dielectric layer at least within the center and edge regions of the electrodes, the second dielectric layer sufficient for providing a frequency modification to the acoustic wave within the center region;
• and
• a metal layer extending only within each of the opposing edge regions, the metal layer sufficient for reducing a velocity of the acoustic wave within the edge regions, wherein the velocity in the edge regions is less than the wave velocity within the transducer center region.

A method of manufacturing a surface acoustic wave device for operating as a piston mode wave guide, the method comprising:

• forming a plurality of electrodes into an interdigital transducer on a surface of a piezoelectric substrate, wherein each of the plurality of electrodes includes a transversely extending center region and transversely opposing edge regions for guiding an acoustic wave longitudinally through the interdigital transducer;
• covering the interdigital transducer with a first dielectric layer to form an overcoat;
• positioning a third layer within only each of the opposing edge regions, the third layer sufficient for reducing a velocity of the acoustic wave within the edge regions, wherein the velocity in the edge regions is less than the wave velocity within the transducer center region;
• and
• covering the first dielectric layer with a second dielectric layer at least over the center and edge regions of the electrodes, the second dielectric layer sufficient for providing a frequency modification to the acoustic wave within the center region.