US-12627278-B2 - Surface acoustic wave device comprising multi-layer interdigital transducer electrode

Abstract

A surface acoustic wave device includes a piezoelectric substrate and a multi-layer interdigital transducer electrode disposed on the piezoelectric substrate. The multi-layer interdigital transducer electrode includes a first electrode layer and a second electrode layer. The second electrode layer is disposed between the piezoelectric substrate and the first electrode layer. The first electrode layer has a higher density than a density of the second electrode layer. The second electrode layer has a higher conductivity than a conductivity of the first electrode layer. Related radio frequency modules and wireless communication devices are also provided.

Inventors

• Kezia Cheng
• Alan Sangone Chen
• Benjamin Paul Abbott
• Rei GOTO
• Yosuke Hamaoka
• Michael David Hill

Assignees

• SKYWORKS SOLUTIONS, INC.

Dates

Publication Date

20260512

Application Date

20220810

Claims (20)

1. 1 . A surface acoustic wave device comprising: a piezoelectric substrate; and a multi-layer interdigital transducer electrode disposed on the piezoelectric substrate, the multi-layer interdigital transducer electrode including a first electrode layer and a second electrode layer, the second electrode layer being disposed between the piezoelectric substrate and the first electrode layer, the first electrode layer having a higher density than a density of the second electrode layer, the second electrode layer having a higher conductivity than a conductivity of the first electrode layer, the first electrode layer having a greater thickness than a thickness of the second electrode layer.
2. 2 . The surface acoustic wave device of claim 1 wherein the first electrode layer is made mainly of tungsten.
3. 3 . The surface acoustic wave device of claim 1 wherein the first electrode layer has a thickness of between 100 nanometers and 500 nanometers.
4. 4 . The surface acoustic wave device of claim 1 wherein the first electrode layer has a density of at least 10 grams per cubic centimeter.
5. 5 . The surface acoustic wave device of claim 1 wherein the first electrode layer is the uppermost layer of the multi-layer interdigital transducer electrode.
6. 6 . The surface acoustic wave device of claim 1 wherein the second electrode layer is made mainly of copper.
7. 7 . The surface acoustic wave device of claim 1 wherein the second electrode layer has a conductivity of at least 5×10 7 Siemens per meter.
8. 8 . The surface acoustic wave device of claim 1 wherein the second electrode layer has a thickness of between 100 nanometers and 500 nanometers.
9. 9 . The surface acoustic wave device of claim 1 wherein the second electrode layer has an upper surface in contact with a lower surface of the first electrode layer.
10. 10 . The surface acoustic wave device of claim 1 wherein the second electrode layer has a lower surface in contact with an upper surface of piezoelectric substrate.
11. 11 . The surface acoustic wave device of claim 1 wherein a difference between a coefficient of thermal expansion of the second electrode layer and a coefficient of thermal expansion of the first electrode layer is no more than 18 ppm/degree K.
12. 12 . The surface acoustic wave device of claim 1 wherein the multi-layer interdigital transducer electrode further includes a third electrode layer disposed between the piezoelectric substrate and the second electrode layer.
13. 13 . The surface acoustic wave device of claim 12 wherein the third electrode layer is made mainly of tungsten.
14. 14 . The surface acoustic wave device of claim 12 wherein the third electrode layer has an upper surface in contact with a lower surface of the second electrode layer.
15. 15 . The surface acoustic wave device of claim 12 wherein the third electrode layer has a lower surface in contact with an upper surface of piezoelectric substrate.
16. 16 . The surface acoustic wave device of claim 12 wherein the third electrode layer has a density of at least 10 grams per cubic centimeter.
17. 17 . The surface acoustic wave device of claim 12 wherein the third electrode layer has a higher density than the density of the second electrode layer.
18. 18 . The surface acoustic wave device of claim 12 wherein the third electrode layer has a lower conductivity than the conductivity of the second electrode layer.
19. 19 . The surface acoustic wave device of claim 12 wherein the third electrode layer is made mainly of a same material as a material forming first electrode layer.
20. 20 . The surface acoustic wave device of claim 12 wherein the multi-layer interdigital transducer electrode further includes a fourth electrode layer disposed between the piezoelectric substrate and the third electrode layer.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application Ser. No. 63/231,818, titled “SURFACE ACOUSTIC WAVE DEVICE COMPRISING MULTI-LAYER INTERDIGITAL TRANSDUCER ELECTRODE,” filed Aug. 11, 2021, the entire contents of which is incorporated herein by reference for all purposes. BACKGROUND Field Aspects and embodiments disclosed herein relate to surface acoustic wave devices. More particularly, at least some embodiments are directed to radio frequency modules and wireless communication devices having surface acoustic wave devices. Description of the Related Technology A surface acoustic wave filter can include a plurality of resonators arranged to filter a radio frequency signal. Each resonator can include a surface acoustic wave (SAW) device. The SAW device comprises a plurality of electrodes arranged as interleaved fingers on top of a piezoelectric substrate and attached to one or more busbars linking a subset of the electrodes together. The SAW device generates acoustic waves which propagate across the piezoelectric substrate between the electrodes. Surface acoustic wave filters can be implemented in radio frequency electronic systems. For instance, filters in a radio frequency front end of a mobile phone can include surface acoustic wave filters. SUMMARY According to one embodiment, there is provided a surface acoustic wave device including a piezoelectric substrate and a multi-layer interdigital transducer electrode disposed on the piezoelectric substrate. The multi-layer interdigital transducer electrode includes a first electrode layer and a second electrode layer. The second electrode layer is disposed between the piezoelectric substrate and the first electrode layer. The first electrode layer has a higher density than a density of the second electrode layer. The second electrode layer has a higher conductivity than a conductivity of the first electrode layer. In one example the first electrode layer is made mainly of tungsten. In one example the first electrode layer has a thickness of between 100 nanometers and 500 nanometers. The first electrode layer may have a thickness of between 300 nanometers and 500 nanometers. The first electrode layer may have a thickness of 400 nanometers. In one example the first electrode layer has a density of at least 10 grams per cubic centimeter. In one example the first electrode layer has a density of at least 19 grams per cubic centimeter. In one example the first electrode layer is the uppermost layer of the multi-layer interdigital transducer electrode. In one example the second electrode layer is made mainly of copper. In one example the second electrode layer has a conductivity of at least 4×107 Siemens per meter. In one example the second electrode layer has a conductivity of at least 5×107 Siemens per meter. In one example the second electrode layer has a conductivity of at least 5.9×107 Siemens per meter. In one example the second electrode layer has a thickness of between 100 nanometers and 500 nanometers. The second electrode layer may have a thickness of between 100 nanometers and 300 nanometers. The second electrode layer may have a thickness of 200 nanometers. In one example the first electrode layer has a greater thickness than a thickness of the second electrode layer. The thickness of the first electrode layer may be at least two times higher than the thickness of the second electrode layer. In one example the first electrode layer has a thickness that is substantially the same as a thickness of the second electrode layer. In one example the second electrode layer has an upper surface in contact with a lower surface of the first electrode layer. In one example the second electrode layer has a lower surface in contact with an upper surface of the piezoelectric substrate. In one example the difference between a coefficient of thermal expansion of the second electrode layer and a coefficient of thermal expansion of the first electrode layer is no more than 18 ppm/degree K. The difference between a coefficient of thermal expansion of the second electrode layer and a coefficient of thermal expansion of the first electrode layer may be no more than 15 ppm/degree K. The difference between a coefficient of thermal expansion of the second electrode layer and a coefficient of thermal expansion of the first electrode layer may be no more than 13 ppm/degree K. In one example the multi-layer interdigital transducer electrode further includes a third electrode layer disposed between the piezoelectric substrate and the second electrode layer. In one example the third electrode layer is made mainly of tungsten. In one example the third electrode layer is made mainly of titanium. In one example the third electrode layer has an upper surface in contact with a lower surface of the second electrode layer. In one example the third electrode layer has a lower surface in contact with an upper