Surface acoustic wave (SAW) device with one or more intermediate layers for self-heating improvement
Certain aspects of the present disclosure provide a surface acoustic wave (SAW) device with one or more intermediate layers for reduced self-heating and methods for fabricating such a SAW device. One example SAW device generally includes a piezoelectric layer and an interdigital transducer (IDT) disposed above the piezoelectric layer. The IDT generally includes a first electrode having a first busbar and a first plurality of fingers. The first electrode generally includes a first copper layer disposed above the piezoelectric layer, a first intermediate layer disposed above the first copper layer, the first intermediate layer comprising a different material than the first copper layer, and a second copper layer disposed above the first intermediate layer.
1. A surface acoustic wave (SAW) device comprising:
a piezoelectric layer; and
an interdigital transducer (IDT) disposed above the piezoelectric layer and comprising a first electrode having a first busbar and a first plurality of fingers extending from the first busbar, wherein the first electrode comprises:
a first copper layer disposed above the piezoelectric layer;
a first intermediate layer disposed above the first copper layer, the first intermediate layer comprising a different material than the first copper layer;
a second copper layer disposed above the first intermediate layer;
a second intermediate layer disposed above the second copper layer, the second intermediate layer comprising a different material than the second copper layer; and
a third copper layer disposed above the second intermediate layer.
2. The SAW device of claim 1 , wherein the first intermediate layer is insoluble to copper.
3. The SAW device of claim 1 , wherein the first intermediate layer comprises chromium or chromium silver.
4. The SAW device of claim 1 , wherein the first intermediate layer comprises tantalum, nickel, tungsten, a nitride, or a carbide.
5. The SAW device of claim 1 , wherein a grain size of the first copper layer is at most 120 nm.
6. The SAW device of claim 1 , wherein the first intermediate layer has a thickness of less than 50 nm.
7. The SAW device of claim 1 , wherein the first intermediate layer has a thickness in a range of 0.1 to 5.0 nm.
8. The SAW device of claim 1 , wherein the first intermediate layer is located in a lower portion of the first electrode.
9. A plurality of resonators forming a filter circuit, wherein the SAW device of claim 1 is a resonator in the plurality of resonators.
10. The SAW device of claim 1 , wherein the second intermediate layer comprises a different material than the first intermediate layer.
11. The SAW device of claim 1 , wherein at least one of the first intermediate layer or the second intermediate layer has a thickness of less than 50 nm.
12. The SAW device of claim 1 , wherein the second intermediate layer has a thickness in a range of 0.1 to 5.0 nm.
13. The SAW device of claim 1 , wherein a thickness of the third copper layer is greater than a thickness of the first copper layer and a thickness of the second copper layer.
14. The SAW device of claim 1 , wherein the SAW device is a temperature-compensated SAW device.
15. The SAW device of claim 1 , wherein the first electrode further comprises:
a silver layer disposed beneath the first copper layer; and
an adhesion layer disposed beneath the silver layer.
16. A wireless device comprising:
a radio frequency (RF) circuit; and
a surface acoustic wave (SAW) filter coupled to the RF circuit, the SAW filter comprising:
a piezoelectric layer; and
an interdigital transducer (IDT) disposed above the piezoelectric layer and comprising a first electrode having a first busbar and a first plurality of fingers extending from the first busbar, wherein the first electrode comprises:
a first copper layer disposed above the piezoelectric layer, wherein a grain size of the first copper layer is at most 120 nm;
a first intermediate layer disposed above the first copper layer, the first intermediate layer comprising a different material than the first copper layer; and
a second copper layer disposed above the first intermediate layer.
17. The wireless device of claim 16 , wherein the RF circuit comprises a low-noise amplifier (LNA) and wherein the SAW filter is coupled to an output of the LNA.
18. The wireless device of claim 16 , wherein the RF circuit comprises a transmit path and a receive path and wherein the SAW filter forms a portion of a duplexer coupled to an output of the transmit path and to an input of the receive path.
19. A method of fabricating a surface acoustic wave (SAW) device, the method comprising:
forming an interdigital transducer (IDT) above a piezoelectric layer, wherein forming the IDT comprises forming a first electrode of the IDT, the first electrode having a first busbar and a first plurality of fingers extending from the first busbar, and wherein forming the first electrode comprises:
forming a first copper layer above the piezoelectric layer;
forming a first intermediate layer above the first copper layer, the first intermediate layer comprising a different material than the first copper layer, wherein the first intermediate layer has a thickness in a range of 0.1 to 5.0 nm; and
forming a second copper layer above the first intermediate layer.
20. The method of claim 19 , wherein forming the first electrode further comprises:
forming an adhesion layer above the piezoelectric layer; and
forming a silver layer disposed above the adhesion layer, wherein the first copper layer is formed above the silver layer.
21. The method of claim 19 , wherein the first intermediate layer is insoluble to copper.
22. The method of claim 19 , wherein the first intermediate layer comprises chromium or chromium silver.
23. The method of claim 19 , wherein the first intermediate layer comprises tantalum, nickel, tungsten, a nitride, or a carbide.
24. The method of claim 19 , wherein a grain size of the first copper layer is at most 120 nm.
25. The method of claim 19 , wherein forming the first electrode further comprises:
forming a second intermediate layer above the second copper layer, the second intermediate layer comprising a different material than the second copper layer; and
forming a third copper layer above the second intermediate layer.
26. The method of claim 25 , wherein the second intermediate layer comprises a different material than the first intermediate layer and has a thickness in a range of 0.1 to 5.0 nm.
27. The method of claim 25 , wherein a thickness of the third copper layer is greater than a thickness of the first copper layer and a thickness of the second copper layer.
28. A surface acoustic wave (SAW) device comprising:
a piezoelectric layer; and
an interdigital transducer (IDT) disposed above the piezoelectric layer and comprising a first electrode having a first busbar and a first plurality of fingers extending from the first busbar, wherein the first electrode comprises:
a first copper layer disposed above the piezoelectric layer;
means for interrupting grain growth in the first copper layer, disposed above the first copper layer;
a second copper layer disposed above the means for interrupting grain growth in the first copper layer;
a silver layer disposed beneath the first copper layer; and
an adhesion layer disposed beneath the silver layer.
29. The SAW device of claim 28 , further comprising:
means for interrupting grain growth in the second copper layer, disposed above the second copper layer; and
a third copper layer disposed above the means for interrupting grain growth in the second copper layer.