Robust optical filter utilizing pairs of dielectric and metallic layers
View Patent ↗“Corrosion” performance of an optical filter is enhanced when a relatively thick zinc-based film functions as a seed layer for a subsequently formed silver-based film. At least two pairs of dielectric and metallic layers are included within the optical filter, where the zinc-based film is a second film of the dielectric layer and where the silver-based film is the metallic layer. The zinc-based film has a zinc content of at least 80 percent and has a thickness of at least 15 nm. In order to further improve the corrosion performance, gold may be incorporated into the silver-based film.
1. A method of providing an optical filter comprising:
forming a layer stack on a substrate to include pairs of dielectric and metallic layers, including defining each said pair by:
forming an indium-based transparent dielectric film as a first film of said dielectric layer, said transparent dielectric film having a refractive index of at least 1.1;
forming a zinc-based film as a second film of said dielectric layer, said zinc-based film having a zinc content of at least 80 percent and having a thickness of at least 15 nm, said zinc-based film being in contact with the indium-based transparent dielectric film; and
forming a silver-based film as said metallic layer, said silver-based film being in contact with said zinc-based film.
2. The method of claim 1 wherein forming said layer stack to include said pairs include forming said zinc-based film of the pair adjacent to said substrate to be thinner than said zinc-based film of each said pair further from said substrate.
3. The method of claim 1 wherein forming said silver-based film includes depositing an alloy of silver and gold in which said gold is included to control corrosion of said layer stack.
4. The method of claim 1 further comprising selecting said thickness of said zinc-based film and selecting the percentage of said zinc content on a basis of promoting formation of said silver-based film.
5. The method of claim 1 wherein forming said indium-based transparent dielectric films of said pairs of dielectric and metallic layers includes using sputtering techniques to deposit the indium-based transparent dielectric films.
6. The method of claim 1 wherein forming said zinc-based provides a film thickness in the range of 15 nm to 40 nm.
7. The method of claim 1 further comprising attaching said layer stack to a window.
8. A method of providing an optical filter comprising:
forming a layer stack on a substrate to include pairs of dielectric and metallic layers, including defining each said pair by:
forming a transparent dielectric film as a first film of said dielectric layer, said transparent dielectric film having a refractive index of at least 1.1;
forming a zinc-based film as a second film of said dielectric layer, said zinc-based film having a zinc content of at least 80 percent and having a thickness of at least 15 nm; and
forming a silver-based film as said metallic layer, said silver-based film being in contact with said zinc-based film;
wherein forming said silver-based film includes depositing an alloy of silver and gold in which said gold is included to control corrosion of said layer stack;
wherein depositing said alloy includes intentionally incorporating different percentages of gold among said silver-based films on a basis of distance from said substrate.
9. The method of claim 8 wherein said silver-based film furthest from said substrate is formed to have a higher percentage of gold than said silver-based film nearest to said substrate.
10. A filtering arrangement comprising:
a transparent substrate; and
a layer stack on said substrate, said layer stack including pairs of dielectric and metallic layers, each said pair being defined by:
an indium-based transparent dielectric film as a first film of said dielectric layer, said transparent dielectric layer having a refractive index of at least 1.1;
a zinc-based film as a second film of said dielectric layer, said zinc-based film having a zinc content of at least 80 percent and having a thickness in the range of 15 nm to 40 nm, said zinc-based film being in contact with said indium-based transparent dielectric film; and
a silver gold film as said metallic layer, said silver gold film being in contact with said zinc-based film.
11. The filtering arrangement of claim 10 wherein said zinc-based film in the pair of dielectric and metallic layers adjacent to said substrate is thinner than said zinc-based film of each of the other said pairs.
12. The filtering arrangement of claim 11 wherein each said zinc-based film is zinc tin or zinc aluminum and said zinc content is approximately 90 percent.
13. The filtering arrangement of claim 10 wherein each said indium-based transparent dielectric layer is indium oxide.
14. The filtering arrangement of claim 10 wherein said substrate is attached to a window.
15. The filtering arrangement of claim 10 including three said pairs of dielectric and metallic layers.
16. The filtering arrangement of claim 10 wherein each said transparent dielectric film is In 2 O 3 .
17. A filtering arrangement comprising:
a transparent substrate; and
a layer stack on said substrate, said layer stack including pairs of dielectric and metallic layers, each said pair being defined by:
a transparent dielectric film as a first film of said dielectric layer, said transparent dielectric layer having a refractive index of at least 1.1;
a zinc-based film as a second film of said dielectric layer, said zinc-based film having a zinc content of at least 80 percent and having a thickness in the range of 15 nm to 40 nm; and
a silver gold film as said metallic layer, said silver gold film being in contact with said zinc-based film;
wherein said silver gold film in said pair of dielectric and metallic layers that is furthest from said substrate has a higher gold content than said silver gold film of each of the other said pairs.