Piston mode acoustic wave device and method providing a high coupling factor

An surface acoustic wave device comprising:

• a piezoelectric substrate having a surface for propagating acoustic waves;
• a first elongate busbar and an opposing second elongate busbar extending generally along a longitudinal path of the acoustic waves;
• a plurality of first electrodes electrically connected to and extending from the first busbar;
• a plurality of second electrodes electrically connected to and extending from the second busbar, wherein the opposing busbars and the plurality of electrodes form an interdigital transducer carried on the piezoelectric substrate for the propagating acoustic waves, wherein each of the plurality of the electrodes has a first end electrically connected to one of the first and second busbars and an opposing second end having an edge spaced from the opposing busbar so as to form a gap between the edge of each electrode and the opposing busbar, the gaps proximate the opposing busbars forming a gap region extending longitudinally along the transducer, and wherein a length dimension of the gap is at least a wavelength of the propagating acoustic waves;
• and
• a first layer covering the transducer, a second layer extending longitudinally along the transducer, the second layer covering the electrode portions within the edge regions, wherein a velocity of the acoustic waves within opposing gap regions is greater than a velocity in a transducer center region between the gap regions, and wherein the wave velocity of the edge region is less than the wave velocity of the center region, the layers formed from at least one of a dielectric material and a metal material.

An surface acoustic wave device comprising:

• a piezoelectric substrate having a surface for propagating acoustic waves;
• a first elongate busbar and an opposing second elongate busbar extending generally along a path of the acoustic waves;
• a plurality of first electrodes electrically connected to and extending from the first busbar;
• a plurality of second electrodes electrically connected to and extending from the second busbar, wherein the opposing busbars and the plurality of electrodes form an interdigital transducer carried on the piezoelectric substrate for the propagating acoustic waves, and wherein each of the plurality of the electrodes has a first end electrically connected to one of the first and second busbars and an opposing second end having an edge spaced from the opposing busbar so as to form a gap between the edge of each electrode and the opposing busbar, the gaps proximate the opposing busbars forming opposing gap regions extending longitudinally along the transducer, and wherein a length dimension of the gap within each of the opposing gap regions is at least a wavelength for the propagating acoustic waves;
• each electrode within the plurality of electrodes is further defined by a first transversely extending portion proximate the electronically connected busbar and generally contained within the gap regions, a second transversely extending portion proximate the edge and defining the edge regions extending longitudinally along the transducer, and a third transversely extending portion of the electrode therebetween, the third transversely extending portion defined within a transducer center region;
• a first layer covering the transducer;
• and
• a second layer extending longitudinally along the transducer, the second layer covering only electrode portions within a transducer center regions,
• wherein a velocity of the acoustic waves within opposing gap regions is greater than a velocity in a transducer center region between the gap regions, and wherein the wave velocity of the edge region is less than the wave velocity of the center region, the layers formed from at least one of a dielectric material and a metal material.