METHOD OF MANUFACTURING THIN-FILM DIELECTRICS AND CAPACITORS ON METAL FOILS
Disclosed is a method of making a thin-film dielectric, comprising providing a base metal foil, forming a barium titanate-based dielectric precursor layer over a base metal foil, pre-annealing the dielectric precursor layer and base metal foil, rapidly heating the pre-annealed dielectric precursor layer from a temperature of less than 530° C. to an annealing temperature of more than 800° C. in less than 15 seconds; and annealing the dielectric to form a crystalline barium titanate-based dielectric on the base metal foil, wherein the crystalline barium titanate-based dielectric has grains with an average grain size that is greater or equal to 50 nanometers. Also disclosed is a method of making a capacitor comprised of the thin-film dielectric formed on a base metal foil according to the method described above with a second conductive layer formed over the dielectric.
1 . A method of making a thin-film dielectric, comprising:
providing a base metal foil;
forming a barium titanate-based dielectric precursor layer over a base metal foil;
pre-annealing the dielectric precursor layer and base metal foil at a temperature in the range of 300° C. to 530° C.; and
rapidly heating the pre-annealed dielectric precursor layer from a temperature of less than 530° C. to an annealing temperature of more than 800° C. in less than 15 seconds; and
annealing the dielectric at the annealing temperature of more than 800° C. to form a crystalline barium titanate-based dielectric on the base metal foil, wherein the annealed crystalline barium titanate-based dielectric has grains with an average grain size that is equal to or greater than 50 nanometers.
2 . The method of claim 1 wherein step of rapidly heating the pre-annealed dielectric occurs at a heating rate in the range of 100° C. per second to 200° C. per second.
3 . The method of claim 1 wherein the pre-annealed dielectric precursor layer is rapidly heated from a temperature of less than 530° C. to an annealing temperature of more than 800° C. in less than 5 seconds.
4 . The method of claim 1 wherein the pre-annealed dielectric precursor layer is rapidly heated from a temperature of less than 530° C. to an annealing temperature of more than 800° C. in a period in the range of from 1 to 3 seconds.
5 . The method of making a dielectric of claim 1 , wherein the annealing is conducted in a vacuum atmosphere having an oxygen partial pressure of less than about 10 −6 atmospheres.
6 . The method of making a dielectric of claim 1 wherein the annealing temperature is in the range of 800° C. to 1200° C., and the annealing period is in the range of 10 to 30 minutes.
7 . The method of making a dielectric of claim 1 wherein the base metal foil comprises a metal foil having a nickel surface.
8 . The method of making a dielectric of claim 1 wherein forming the dielectric precursor layer comprises coating a surface of the base metal foil with a dielectric precursor solution comprising a first component selected from barium isopropoxide, barium acetate, barium propionate, or mixtures thereof and a second component selected from titanium isopropoxide, titanium butoxide, acetylacetone stabilized titanium butoxide, or mixtures thereof.
9 . The method of making a dielectric of claim 1 , wherein after pre-annealing of the dielectric precursor layer, an additional dielectric precursor layer is formed over the pre-annealed dielectric precursor layer, and wherein said additional dielectric precursor layer is pre-annealed at a temperature in the range of 300° to 530° C.
10 . The method of making a dielectric of claim 1 , wherein the annealing results in a thin-film dielectric with a thickness of less than 2 microns and comprising crystalline barium titanate or crystalline barium strontium titanate.
11 . The method of claim 1 wherein the annealed dielectric has an average grain size that with an range defined by and including any two of the following sizes: 50 nanometers; 100 nanometers; 200 nanometers and 400 nanometers.
12 . The method of making a dielectric of claim 1 , wherein the dielectric has an area of greater than 4 cm 2 .
13 . A method of making a capacitor, comprising:
providing a base metal foil;
forming a barium titanate-based dielectric precursor layer over a base metal foil;
pre-annealing the dielectric precursor layer and base metal foil at a temperature in the range of 300° C. to 530° C.; and
rapidly heating the pre-annealed dielectric precursor layer from a temperature of less than 530° C. to an annealing temperature of more than 800° C. in less than 10 seconds;
annealing the dielectric at the annealing temperature of more than 800° C. to form a crystalline barium titanate dielectric on the base metal foil, wherein the crystalline barium titanate dielectric has an average grain size that greater or equal to 50 nanometers; and
forming a second conductive layer over the dielectric, wherein the metal foil, the dielectric, and the second conductive layer to form the capacitor.
14 . The method of claim 13 , wherein the second conductive layer is deposited by sputtering.
15 . The method of claim 13 wherein the pre-annealed dielectric precursor layer is rapidly heated from a temperature of less than 530° C. to an annealing temperature of more than 800° C. in less than 5 seconds.
16 . The method of claim 13 wherein the pre-annealed dielectric precursor layer is rapidly heated from a temperature of less than 530° C. to an annealing temperature of more than 800° C. in a period in the range of from 1 to 3 seconds.
17 . The method of claim 13 wherein the annealing is conducted in a vacuum atmosphere having an oxygen partial pressure of less than about 10 −6 atmospheres.
18 . The method of making a dielectric of claim 13 wherein the annealing temperature is in the range of 800° C. to 1200° C.
19 . The method of making a dielectric of claim 13 wherein the base metal foil comprises a metal foil having a nickel surface.
20 . The method of claim 13 wherein forming the dielectric precursor layer comprises coating a surface of the base metal foil with a dielectric precursor solution comprising a first component selected from barium isopropoxide, barium acetate, barium propionate, or mixtures thereof and a second component selected from titanium isopropoxide, titanium butoxide, acetylacetone stabilized titanium butoxide, or mixtures thereof.
21 . The method of claim 13 wherein the annealing results in a thin-film dielectric with a thickness of less than 2 microns and comprising crystalline barium titanate or crystalline barium strontium titanate.
22 . The method of claim 13 wherein the capacitor has an average capacitance density of about 2.0 μF/cm 2 .