Method for fabrication of ceramic dielectric films on copper foils
The present invention provides a method for fabricating a ceramic film on a copper foil. The method comprises applying a layer of a sol-gel composition onto a copper foil. The sol-gel composition comprises a precursor of a ceramic material suspended in 2-methoxyethanol. The layer of sol-gel is then dried at a temperature up to about 250° C. The dried layer is then pyrolyzed at a temperature in the range of about 300 to about 450° C. to form a ceramic film from the ceramic precursor. The ceramic film is then crystallized at a temperature in the range of about 600 to about 750° C. The drying, pyrolyzing and crystallizing are performed under a flowing stream of an inert gas. In some embodiments an additional layer of the sol-gel composition is applied onto the ceramic film and the drying, pyrolyzing and crystallizing steps are repeated for the additional layer to build up a thicker ceramic layer on the copper foil. The process can be repeated one or more times if desired.
1. A method for fabricating a ceramic film on a copper substrate, the method comprising the steps of:
(a) applying onto a copper substrate a layer of a sol-gel composition comprising a precursor of a ceramic material in 2-methoxyethanol;
(b) drying the layer of step (a) at a temperature up to about 250° C. in air;
(c) pyrolyzing the dried layer from step (b) at a temperature in the range of about 300 to about 450° C. under a flowing stream of an inert gas to form a ceramic film from the ceramic precursor;
(d) optionally applying one or two additional layers of the sol-gel composition onto the ceramic film from step (c) and repeating steps (b), and (c) for each additional layer, to build up a thicker ceramic film on the copper substrate;
(e) crystallizing the ceramic film at a temperature in the range of about 600 to about 750° C. under a flowing stream of an inert gas; and
(f) optionally applying one or more additional layers of the sol-gel composition onto the crystallized ceramic film from step (e), and repeating (b), (c), (d), and (e) for each additional layer;
wherein the flowing stream of inert gas in step (e) maintains a partial pressure of oxygen (pO 2 ) of about 10 −6 atm to 10 −8 atm; and wherein the ceramic material is a lead-lanthanum-zirconium-titanium oxide material and the ceramic precursor comprises a lead compound, a lanthanum compound, a zirconium compound and a titanium compound.
2. The method of claim 1 wherein the applying a layer of a sol-gel composition comprises spin coating the sol-gel composition onto the copper substrate.
3. The method of claim 1 wherein the ceramic precursor comprises a lead salt, a titanium alkoxide, a zirconium alkoxide, and a lanthanum salt.
4. The method of claim 3 wherein the lead salt comprises lead acetate.
5. The method of claim 3 wherein the titanium alkoxide comprises titanium isopropoxide.
6. The method of claim 3 wherein the zirconium alkoxide comprises zirconium propoxide.
7. The method of claim 3 wherein the lanthanum salt comprises lanthanum nitrate.
8. The method of claim 1 wherein the copper substrate comprises a copper foil having a thickness in the range of about 0.01 mm to about 1 mm.
9. The method of claim 8 wherein the copper foil has a thickness in the range of about 0.2 to about 0.5 mm.
10. The method of claim 1 wherein the copper substrate has a polished surface with a RMS surface roughness of not more than about 10 nm.
11. The method of claim 1 wherein the drying is performed at about 250° C.
12. The method of claim 1 wherein the pyrolyzing is performed at a temperature of about 450° C.
13. The method of claim 1 wherein the crystallizing is performed at a temperature of about 650 to about 700° C.
14. The method of claim 1 wherein the inert gas comprises nitrogen.
15. The method of claim 1 comprising applying one or two additional layers of the sol-gel composition onto the ceramic film from step (c) and repeating steps (b), and (c) for each additional layer, to build up a thicker ceramic film on the copper substrate, prior to crystallizing the ceramic film.
16. The method of claim 15 comprising applying one or more additional layers of the sol-gel composition onto the crystallized ceramic film from step (e), and repeating (b), (c), (d), and (e) for each additional layer.
17. A method for fabricating a lead-lanthanum-zirconium-titanium (PLZT) ceramic film on a copper substrate, the method comprising the steps of:
(a) applying onto the copper substrate a layer of a sol-gel composition containing a ceramic precursor comprising a lead compound, a lanthanum compound, a zirconium compound, and a titanium compound in 2-methoxyethanol;
(b) drying the layer of step (a) at a temperature up to about 250° C.;
(c) pyrolyzing the dried layer from step (b) at a temperature in the range of about 300 to about 450° C. under a flowing stream of an inert gas to form a PLZT ceramic film from the ceramic precursor;
(d) applying one or two additional layers of the sol-gel composition onto the ceramic film from step (c) and repeating steps (b), and (c) for each additional layer, to build up a thicker ceramic film on the copper substrate;
(e) crystallizing the ceramic film from step (c) at a temperature in the range of about 600 to about 750° C. under a flowing stream of an inert gas; and
(f) applying one or more additional layers of the sol-gel composition onto the crystallized ceramic film from step (e), and repeating (b), (c), (d), and (e) for each additional layer;
wherein the flowing stream of inert gas in step (e) maintains a partial pressure of oxygen (pO 2 ) of about 10 −6 atm to 10 −8 atm.
18. The method of claim 17 wherein the pyrolyzing is performed at a temperature of about 450° C.
19. The method of claim 17 wherein the crystallizing is performed at a temperature of about 650 to about 700° C.