A wireless communication device comprising:
- radio frequency front end (RFFE) circuitry comprising:
- a power amplifier module including one or more power amplifiers to amplify an outgoing radio frequency (RF) signal;
- and
- a surface acoustic-wave (SAW) device that is coupled with the power amplifier module and that defines a passband having a lower side and an upper side, the SAW device comprising:
- a piezoelectric substrate having a surface to support an acoustic wave;
- a plurality of resonators on the surface of the piezoelectric substrate, the plurality of resonators including at least a first resonator and a second resonator, wherein the plurality of resonators are formed by a plurality of electrodes, the first resonator has a first duty factor, the second resonator has a second duty factor, the first duty factor is larger than the second duty factor, and the first resonator is a series resonator where a width of individual electrodes of the plurality of electrodes forming the first resonator is larger than a width of individual electrodes of the plurality of electrodes forming the second resonator, wherein the width of the individual electrodes of the plurality of electrodes forming the first resonator and the width of the individual electrodes of the plurality of electrodes forming the second resonator is such that the first duty factor is at least 10% greater than the second duty factor and the plurality of resonators includes a plurality of series resonators and a plurality of shunt resonators arranged in a ladder filter configuration, and the first resonator is one of the plurality of series resonators and the second resonator is one of the plurality of shunt resonators;
- and
- a dielectric layer having a positive thermal coefficient of frequency (TCF) and covering the plurality of resonators, wherein:
- the dielectric layer has a first thickness that covers the plurality of electrodes forming the first resonator and the dielectric layer has a second thickness that covers the plurality of electrodes forming the second resonator;
- a first electrode period is a first physical distance between each of the plurality of electrodes forming the first resonator and a second electrode period is a second physical distance between each of the plurality of electrodes forming the second resonator;
- the first thickness is a first ratio times the first electrode period;
- the second thickness is a second ratio times the second electrode period;
- the first ratio is between 0.65 to 0.85 when the upper side has a steeper transition than the lower side and is less than or equal to 0.5 when the lower side has the steeper transition than the upper side;
- and
- the second ratio is less than or equal to 0.50 when the upper side has the steeper transition than the lower side and is between 0.65 to 0.85 when the lower side has the steeper transition than the upper side;
- wherein one of the upper side and the lower side has a steeper transition than the other of the upper side and the lower side.