Methods to fabricate and improve stand-alone and integrated filters
Embodiments of the invention provide for fabricating a filter, for electromagnetic radiation, in at least three ways, including (1) fabricating integrated thin film filters directly on a detector; (2) fabricating a free standing thin film filter that may be used with a detector; and (3) treating an existing filter to improve the filter's properties.
1. A method of fabricating a filter for electromagnetic radiation, comprising:
growing a filter as a film comprising one or more materials and under growth conditions, on or above a surface of a substrate comprising a detector, wherein:
the film has a thickness with a thickness uniformity and thickness accuracy of 5% or less,
a transparency of the film is 10% or greater at one or more frequencies in a pass band of the filter, and
the detector is for receiving and detecting the electromagnetic radiation transmitted through the filter (“transmitted radiation”).
2. The method of claim 1 , wherein the growing comprises controlling the thickness of the filter with atomic layer precision.
3. The method of claim 2 , wherein the growing comprises:
depositing one or more atomic monolayers of an insulating layer or a barrier layer on the surface; and
depositing the filter on the insulating layer or barrier layer.
4. The method of claim 3 wherein the insulating layer or barrier layer is aluminum oxide and the detector is a silicon imager.
5. The method of claim 2 , wherein the filter comprises aluminum and magnesium fluoride multilayers.
6. The method of claim 1 , wherein the thickness and one or more material qualities of the filter are such that the filter reduces a flux of the electromagnetic radiation at Lyman-alpha frequencies by a factor of at least while at least 10 −4 , while at least 10% of the electromagnetic radiation having a wavelength between 900 Angstroms and 1100 Angstroms is transmitted through the filter.
7. The method of claim 1 , wherein the growing comprises depositing the filter by Atomic Layer Deposition (ALD) on or above the surface.
8. The method of claim 1 , further comprising:
treating the filter with a plasma to remove undesired contaminants from the filter that reduce transmission at one or more frequencies of the transmitted radiation.
9. A method of fabricating a filter for electromagnetic radiation, comprising:
depositing a stop layer on a sacrificial substrate, wherein a transparency of the stop layer is 10% or greater at one or more frequencies in a pass band of the filter;
depositing filter material on or above the stop layer; and
at least partially removing the sacrificial substrate up to the stop layer to form the filter, so that one or more thicknesses of one or more regions of the filter are sufficient to support the filter.
10. The method of claim 9 , wherein the sacrificial substrate is formed into a mesh or perimeter supporting the filter in the free-standing form.
11. The method of claim 9 , wherein the stop layer is deposited by Atomic Layer Deposition (ALD).
12. The method of claim 1 , further comprising treating the fabricated filter with one or more plasmas to improve one or more of the fabricated filter's properties.
13. The method of claim 12 wherein the treating increases transmission at one or more frequencies of the electromagnetic radiation transmitted through the filter.
14. The method of claim 1 , wherein the growing is by molecular beam epitaxy.
15. The method of claim 1 , wherein the growing is by thermal evaporation.
16. The method of claim 1 , wherein the conditions are such that a surface of the film is conformal to the surface of the detector over an entire sensing area of the detector.
17. The method of claim 1 , wherein the thickness uniformity, the thickness accuracy, and density variations of the filter, are <2%.
18. The method of claim 1 , wherein the thickness uniformity, thickness accuracy, and the density variations are over an entire sensing area of the detector.
19. The method of claim 1 , wherein the thickness uniformity and thickness accuracy are over an entire sensing area of the detector.
20. The method of claim 1 , further comprising controlling one or more of a density, impurity concentration, phase, stochiometry, index of refraction, and composition of the filter, to obtain the transparency.
21. The method of claim 1 , wherein the conditions do not deteriorate or destroy the detector.
22. The method of claim 1 , wherein the growth conditions include growing the filter at a temperature below a maximum temperature that depends on the detector.
23. The method of claim 1 , wherein the filter comprises one or more indium layers.
24. The method of claim 1 , wherein the filter comprises one or more magnesium layers.