RF resonator membranes and methods of construction
View Patent ↗A single crystal membrane of Ba x Sr (1-x) TiO 3 (BST) has been fabricated for the first time using molecular beam epitaxy. The membrane typically has a thickness of 200 nm to 500 nm and the thickness may be controlled to within 1%. It may be fabricated on a sapphire wafer carrier from which it may subsequently be detached. The smoothness of the membrane has an RMS of less than 1 nm. This membrane is very promising for the next generation of RF filters.
1. A single crystal film comprising Ba x Sr (1-x) TiO 3 having an <111> orientation coupled to a c-axis <0001> sapphire membrane by a <0001> GaN release layer and further comprising a <100> rutile TiO 2 and/or a <111> Sr (1-x) TiO 3 buffer layer between the GaN and the Ba x Sr (1-x) TiO 3 .
2. The single crystal film of claim 1 wherein x is 0.5 to a tolerance of ±1%.
3. The single crystal film of claim 1 wherein x is 0.35 to a tolerance of ±1%.
4. The single crystal film of claim 1 wherein x is 0.2 to a tolerance of ±1%.
5. The single crystal film of claim 1 wherein the <0001> GaN release layer has a thickness in the range of 1 to 10 nm.
6. The single crystal film of claim 1 wherein the <0001> GaN release layer has a thickness in the range of 3 to 5 nm.
7. The single crystal film of claim 1 wherein the <0001> GaN release layer has a thickness of 4 nm.
8. The single crystal film of claim 1 wherein the buffer layer has a thickness in the range of 4 to 5 nm.
9. The single crystal film of claim 1 wherein the buffer layer is 4.4 nm thick.
10. A method to fabricate the single crystal film of claim 1 , comprising co-depositing barium, strontium and titanium oxides on a substrate by molecular beam epitaxy.
11. The method of claim 10 , wherein a heat dissipation layer is deposited onto a back side of the sapphire crystal.
12. The method of claim 11 , wherein the heat dissipation layer comprises titanium.