Method of making an acoustic wave resonator with mass loading strip for suppression of hyperbolic mode
Aspects of this disclosure relate to a method for making an acoustic wave resonator with hyperbolic mode suppression. The acoustic wave resonator can include a piezoelectric layer, an interdigital transducer electrode, a temperature compensation layer, and a mass loading strip. The mass loading strip can be a conductive strip. The mass loading strip can overlap edge portions of fingers of the interdigital transducer electrode. A layer of the mass loading strip can have a density that is at least as high as a density of a material of the interdigital transducer electrode. The material of the interdigital transducer can impact acoustic properties of the acoustic wave resonator.
1. A method of manufacturing a surface acoustic wave resonator, the method comprising:
forming or providing a surface acoustic wave resonator structure with a temperature compensation layer over an interdigital transducer electrode, the interdigital transducer electrode positioned on a piezoelectric layer and extending along a first length, the interdigital transducer electrode including one or more fingers extending from a bus bar to an edge portion; and
forming a mass loading strip that overlaps with the edge portion of the one or more fingers, the mass loading strip including a layer having a density that is at least as high as a density of a material of the interdigital transducer electrode that is in contact with the piezoelectric layer, the mass loading strip extending from a proximal end to a distal end along a second length shorter than the first length to thereby suppress a hyperbolic mode of the interdigital transducer electrode.
2. The method of claim 1 wherein forming the mass loading strip includes forming a conductive strip.
3. The method of claim 1 wherein the layer includes tungsten.
4. The method of claim 1 wherein at least a portion of the temperature compensation layer is disposed over the layer of the mass loading strip.
5. The method of claim 1 wherein the temperature compensation layer is a silicon dioxide layer.
6. The method of claim 1 wherein the second length is shorter than the first length by at least 1% of the first length.
7. The method of claim 6 wherein the second length is shorter than the first length by between 1% and 20% of the first length.
8. The method of claim 7 wherein the second length is shorter than the first length by 4% of the first length.
9. The method of claim 7 wherein the second length is shorter than the first length by 10% of the first length.
10. A method of filtering a radio frequency signal, the method comprising:
receiving the radio frequency signal at an input port of an acoustic wave filter that includes a surface acoustic wave resonator; the surface acoustic wave resonator including an interdigital transducer electrode extending along a first length and including a bus bar and one or more fingers extending from the bus bar to an edge portion, and a mass loading strip overlapping the edge portion of the one or more fingers, the mass loading strip extending from a proximal end to a distal end along a second length shorter than the first length; and
filtering the radio frequency signal with the acoustic wave filter, the filtering including suppressing a hyperbolic mode using the mass loading strip of the surface acoustic wave resonator.
11. The method of claim 10 wherein the mass loading strip is a conductive strip.
12. The method of claim 10 wherein the interdigital transducer electrode is disposed on a piezoelectric layer, a temperature compensation layer is disposed over the interdigital transducer electrode, and the mass loading strip is embedded in the temperature compensation layer, the mass loading strip overlapping the edge portions of the one or more fingers of the interdigital transducer electrode.
13. The method of claim 12 wherein the interdigital transducer electrode includes tungsten.
14. The method of claim 12 wherein the mass loading strip includes tungsten.
15. The method of claim 12 wherein at least a portion of the temperature compensation layer is disposed over the mass loading strip.
16. The method of claim 12 wherein the temperature compensation layer is a silicon dioxide layer.
17. The method of claim 10 wherein the second length is shorter than the first length by at least 1% of the first length.
18. The method of claim 17 wherein the second length is shorter than the first length by between 1% and 20% of the first length.
19. The method of claim 18 wherein the second length is shorter than the first length by 4% of the first length.
20. The method of claim 18 wherein the second length is shorter than the first length by 10% of the first length.