Layer structures for RF filters fabricated using rare earth oxides and epitaxial aluminum nitride
Layer structures for RF filters can be fabricated using rare earth oxides and epitaxial aluminum nitride, and methods for growing the layer structures. A layer structure can include an epitaxial crystalline rare earth oxide (REO) layer over a substrate, a first epitaxial electrode layer over the crystalline REO layer, and an epitaxial piezoelectric layer over the first epitaxial electrode layer. The layer structure can further include a second electrode layer over the epitaxial piezoelectric layer. The first electrode layer can include an epitaxial metal. The epitaxial metal can be single-crystal. The first electrode layer can include one or more of a rare earth pnictide, and a rare earth silicide (RESi).
1. A layer structure, comprising:
an epitaxial crystalline rare earth oxide (REO) layer over a substrate;
a first epitaxial electrode layer directly over the crystalline REO layer;
an epitaxial piezoelectric layer over the first epitaxial electrode layer;
a second epitaxial crystalline rare earth (RE)-containing layer over the epitaxial piezoelectric layer; and
one or more device layers over the second epitaxial crystalline RE-containing layer.
2. The layer structure of claim 1 , further comprising a second electrode layer over the epitaxial piezoelectric layer.
3. The layer structure of claim 1 , wherein the first electrode layer comprises epitaxial metal.
4. The layer structure of claim 3 , wherein the epitaxial metal is single-crystal.
5. The layer structure of claim 1 , wherein the first electrode layer comprises a rare earth pnictide.
6. The layer structure of claim 1 , wherein the first electrode layer comprises a rare earth silicide (RESi).
7. The layer structure of claim 1 , further comprising an amorphous oxide layer between the epitaxial crystalline rare earth oxide layer and the substrate.
8. The layer structure of claim 1 , further comprising an acoustic mirror structure between the epitaxial crystalline REO layer and the substrate, wherein the acoustic mirror structure comprises alternating crystalline REO and mirror material layers.
9. The layer structure of claim 1 , wherein the epitaxial piezoelectric layer comprises at least one of aluminum nitride and aluminum scandium nitride.
10. The layer structure of claim 1 , wherein the second epitaxial crystalline RE-containing layer comprises a REO.
11. The layer structure of claim 1 , wherein the second epitaxial crystalline RE-containing layer comprises a rare earth pnictide.
12. The layer structure of claim 1 , wherein the second epitaxial crystalline RE-containing layer comprises a RESi.
13. The layer structure of claim 1 , wherein a density of the crystalline REO layer is between approximately 5×10 3 kg/m 3 and approximately 15×10 3 kg/m 3 .
14. The layer structure of claim 1 , wherein a density of the crystalline REO layer is between approximately 7×10 3 kg/m 3 and approximately 10×10 3 kg/m 3 .
15. The layer structure of claim 1 , wherein the one or more device layers comprise one or more high electron mobility transistor (HEMT) layers.
16. The layer structure of claim 1 , wherein the one or more device layers comprise one or more heterojunction bipolar transistor (HBT) layers.
17. The layer structure of claim 1 , wherein the one or more device layers comprise one or more pseudomorphic HEMT (pHEMT) layers.
18. The layer structure of claim 1 , wherein the first electrode layer comprises a compositionally graded layer.
19. The layer structure of claim 1 , wherein the first electrode layer comprises a multi-layer structure.
20. The layer structure of claim 1 , further comprising at least one of a rare earth pnictide layer and a RESi layer adjacent to the first electrode layer.
21. The layer structure of claim 1 , wherein the substrate comprises a silicon substrate.
22. The layer structure of claim 1 , wherein the substrate comprises a silicon carbide substrate.
23. The layer structure of claim 1 , wherein the substrate comprises a sapphire substrate.
24. A method of fabricating a layer structure, comprising:
depositing an epitaxial crystalline rare earth oxide (REO) layer over a substrate;
depositing a first epitaxial electrode layer directly over the crystalline REO layer;
depositing an epitaxial piezoelectric layer over the first epitaxial electrode layer;
depositing a second epitaxial crystalline rare earth (RE)-containing layer over the epitaxial piezoelectric layer; and
depositing one or more device layers over the second epitaxial crystalline RE-containing layer.
25. The method of claim 24 , further comprising depositing a second electrode layer over the epitaxial piezoelectric layer.
26. The method of claim 24 , wherein the first electrode layer comprises epitaxial metal.
27. The method of claim 26 , wherein the epitaxial metal is single-crystal.
28. The method of claim 24 , wherein the first electrode layer comprises a rare earth pnictide.
29. The method of claim 24 , wherein the first electrode layer comprises a rare earth silicide (RESi).
30. The method of claim 24 , further comprising depositing an amorphous oxide layer between the epitaxial crystalline rare earth oxide layer and the substrate.
31. The method of claim 24 , further comprising depositing an acoustic mirror structure between the epitaxial crystalline REO layer and the substrate, wherein the acoustic mirror structure comprises alternating crystalline REO and mirror material layers.
32. The method of claim 24 , wherein the epitaxial piezoelectric layer comprises at least one of aluminum nitride and aluminum scandium nitride.
33. The method of claim 24 , wherein the second epitaxial crystalline RE-containing layer comprises a REO.
34. The method of claim 24 , wherein the second epitaxial crystalline RE-containing layer comprises a rare earth pnictide.
35. The method of claim 24 , wherein the second epitaxial crystalline RE-containing layer comprises a RESi.
36. The method of claim 24 , wherein a density of the crystalline REO layer is between approximately 5×10 3 kg/m 3 and approximately 15×10 3 kg/m 3 .
37. The method of claim 24 , wherein a density of the crystalline REO layer is between approximately 7×10 3 kg/m 3 and approximately 10×10 3 kg/m 3 .
38. The method of claim 24 , wherein the one or more device layers comprise one or more high electron mobility transistor (HEMT) layers.
39. The method of claim 24 , wherein the one or more device layers comprise one or more heterojunction bipolar transistor (HBT) layers.
40. The method of claim 24 , wherein the one or more device layers comprise one or more pseudomorphic HEMT (pHEMT) layers.
41. The method of claim 24 , wherein the first electrode layer comprises a compositionally graded layer.
42. The method of claim 24 , wherein the first electrode layer comprises a multi-layer structure.
43. The method of claim 24 , further comprising depositing at least one of a rare earth pnictide layer and a RESi layer adjacent to the first electrode layer.
44. The method of claim 24 , wherein the substrate comprises a silicon substrate.
45. The method of claim 24 , wherein the substrate comprises a silicon carbide substrate.
46. The method of claim 24 , wherein the substrate comprises a sapphire substrate.
47. A layer structure, comprising:
an epitaxial crystalline rare earth oxide (REO) layer over a substrate;
a first epitaxial electrode layer directly over the crystalline REO layer;
an epitaxial piezoelectric layer over the first epitaxial electrode layer; and
an acoustic mirror structure between the epitaxial crystalline REO layer and the substrate, wherein the acoustic mirror structure comprises alternating crystalline REO and mirror material layers.