Temperature compensated surface acoustic wave device and methods of manufacturing the same
Embodiments described herein may provide a surface acoustic wave (SAW) device, methods of fabricating the SAW device, and a system incorporating the SAW device. The SAW device may include a piezoelectric substrate and individual resonators may be formed by a plurality of electrodes on the surface of the piezoelectric substrate. A dielectric layer having a positive thermal coefficient of frequency (TCF) may be formed on each of the plurality of electrodes. In various embodiments, temperature compensation may be achieved by providing more or less of the dielectric layer on at least one resonator than on the other resonators based on a configuration of the resonators. In various embodiments, temperature compensation may be achieved by providing at least one resonator with a different duty factor than the other resonators based on a configuration of the resonators.
1. A surface acoustic wave (SAW) device comprising:
a piezoelectric substrate having a surface to support an acoustic wave;
a plurality of resonators including at least a first resonator and a second resonator, wherein individual resonators of the plurality of resonators are formed by a plurality of electrodes on the surface of the piezoelectric substrate 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 individual electrodes of the plurality of electrodes forming the second resonator is such that a duty factor of a plurality of series resonators is at least 10% greater than a duty factor of a plurality of shunt resonators and the plurality of resonators includes the plurality of series resonators and the 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 temperature coefficient of frequency (TCF) and formed on each of the plurality of electrodes, wherein a first amount of the dielectric layer formed on the first resonator is different than a second amount of the dielectric layer formed on the second resonator such that the first resonator or the second resonator is to obtain a TCF between +/−10 ppm/deg. C.
2. The SAW device of claim 1 , wherein the dielectric layer is formed of a silicon oxide material, the plurality of electrodes are formed of a material having a density that is greater than a density of aluminum (Al), and the piezoelectric substrate is formed of lithium niobate (LiNbO3) having a cut angle between Y+120 degrees and Y+140 degrees.
3. The SAW device of claim 1 , wherein individual series resonators of the plurality of series resonators are covered by the first amount of the dielectric layer and individual shunt resonators of the plurality of shunt resonators are covered by the second amount of the dielectric layer.
4. The SAW device of claim 1 , wherein only a series resonator of the plurality of series resonators having a lower resonance frequency than other ones of the plurality of series resonators is covered by the first amount of the dielectric layer.
5. The SAW device of claim 1 , wherein the second resonator is a coupled resonator filter and the first resonator is coupled in series with the coupled resonator filter, wherein the second amount of the dielectric layer covers an entirety of the coupled resonator filter, and wherein the second amount is substantially greater than the first amount.
6. The SAW device of claim 1 , wherein a thickness of the first amount above the plurality of electrodes forming the first resonator or the second amount above the plurality of electrodes forming the second resonator is between about 0.65 and about 0.85 times an electrode period of the plurality of electrodes forming the first resonator or the second resonator, wherein the electrode period of the first resonator is based on a physical distance between each of the plurality of electrodes forming the first resonator, and the electrode period of the second resonator is based on a physical distance between each of the plurality of electrodes forming the second resonator.
7. The SAW device of claim 1 , wherein a thickness of the first amount is about 5% less than a thickness of the second amount and the first resonator is a series resonator.
8. The SAW device of claim 1 , wherein the first amount of the dielectric layer formed on the first resonator is greater than the second amount of the dielectric layer formed on the second resonator.
9. The SAW device of claim 8 , wherein the first amount is at least 30% greater than the second amount.
10. The SAW device of claim 1 , wherein the plurality of electrodes are formed of a material comprising copper (Cu) or an alloy including Cu, and the plurality of electrodes have a thickness that is between 5% and 15% of a first electrode period and a second electrode period.
11. The SAW device of claim 1 , wherein an electrode period of the second resonator is set such that a duty factor of the second resonator is between 35% and 45%, and an electrode period of the first resonator is set such that a duty factor of the first resonator is greater than 50% and the first resonator is a series resonator.
12. A surface acoustic wave (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 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.
13. The SAW device of claim 12 , wherein the plurality of resonators includes the plurality of series resonators including the first resonator and the plurality of shunt resonators including the second resonator, and the second duty factor is smaller than a duty factor of other ones of the plurality of shunt resonators.
14. The SAW device of claim 12 , wherein each of the plurality of series resonators have the first duty factor and each of the plurality of shunt resonators have the second duty factor.
15. The SAW filter of claim 12 , wherein the second resonator is a coupled resonator filter, and the first resonator is coupled in series with the coupled resonator filter, wherein the coupled resonator filter is formed to have the second duty factor.
16. The SAW filter of claim 12 , wherein the piezoelectric substrate is lithium niobate (LiNbO3) with an orientation between Y+120 degrees and Y+140 degrees, a thickness of the dielectric layer above the plurality of electrodes is between 65% and 85% of an electrode period.
17. A wireless communication device comprising:
a 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, coupled with the power amplifier module, comprising:
a piezoelectric substrate having a surface to support an acoustic wave;
a plurality of resonators including at least a first resonator having a plurality of electrodes on the surface of the piezoelectric substrate, and a second resonator having a plurality of electrodes on the surface of the piezoelectric substrate 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 and the plurality of resonators includes a plurality of series resonators, 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 are such that a duty factor of the plurality of series resonators is at least 10% greater than a duty factor of a plurality of shunt resonators and the plurality of shunt resonators is 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 formed on each of the plurality of electrodes, wherein an amount of the dielectric layer formed on the first resonator is different than an amount of the dielectric layer formed on the second resonator such that the first resonator or the second resonator is to obtain a TCF between +/−10 ppm/deg. C.; and
a transceiver, coupled with the RFFE circuitry, to receive an incoming RF signal through the RFFE circuitry and provide the outgoing RF signal to the RFFE for transmission.
18. The wireless communication device of claim 17 , wherein the first resonator and the second resonator are formed such that the first resonator has a different duty factor than the second resonator.