The present application is related to x-ray windows.
X-ray windows are designed to transmit a high percent of x-rays, including low energy x-rays. X-ray windows are used in expensive systems requiring high reliability. High system requirements result in demanding characteristics of the x-ray window.
(Drawings Might not be Drawn to Scale)
The following definitions, including plurals of the same, apply throughout this patent application.
As used herein, the terms “on”, “located on”, “located at”, and “located over” mean located directly on or located over with some other solid material between. The terms “located directly on”, “adjoin”, “adjoins”, and “adjoining” mean direct and immediate contact.
As used herein, the term “nm” means nanometer(s) and the term “μm” means micrometer(s).
Useful characteristics of x-ray windows include low gas permeability, low outgassing, high strength, low visible and infrared light transmission, high x-ray flux, low atomic number materials, corrosion resistance, high reliability, and low-cost, Each x-ray window design is a balance between these characteristics.
An x-ray window can combine with a housing to enclose an internal vacuum. The internal vacuum can aid device performance. For example, an internal vacuum for an x-ray detector (a) minimizes gas attenuation of incoming x-rays and (b) allows easier cooling of the x-ray detector.
Permeation of a gas through the x-ray window can degrade the internal vacuum. Thus, low gas permeability is a desirable x-ray window characteristic.
Outgassing from x-ray window materials can degrade the internal vacuum of the device. Thus, selection of materials with low outgassing is useful.
The x-ray window can face vacuum on one side and atmospheric pressure on an opposite side. Therefore, the x-ray window may need strength to withstand this differential pressure.
Visible and infrared light can cause undesirable noise in the x-ray detector. The ability to block transmission of visible and infrared light is another useful characteristic of x-ray windows.
High x-ray flux through the x-ray window allows (a) rapid functioning of the x-ray detector and (b) increased x-ray flux out of an x-ray tube. Therefore, high x-ray transmissivity through the x-ray window is useful.
Detection and analysis of low-energy x-rays is needed in some applications. High transmission of low-energy x-rays is thus another useful characteristic of x-ray windows.
X-rays can be used to analyze a sample. X-ray noise from surrounding devices, including from the x-ray window, can interfere with a signal from the sample. X-ray noise from high atomic number materials are more problematic. It is helpful, therefore, for the x-ray window to be made of low atomic number materials.
X-ray windows are used in corrosive environments, and may be exposed to corrosive chemicals during manufacturing. Thus, corrosion resistance is another useful characteristic of an x-ray window.
X-ray window failure is intolerable in many applications. For example, x-ray windows are used in analysis equipment on Mars. High reliability is a useful x-ray window characteristic.
X-ray window customers demand low-cost x-ray windows with the above characteristics. Reducing x-ray window cost is another consideration.
The x-ray windows 10 described herein, and x-ray windows manufactured by the methods described herein, can have these useful characteristics (low gas permeability, low outgassing, high strength, low visible and infrared light transmission, high x-ray flux, low atomic number materials, corrosion resistance, high reliability, and low-cost). Each example may satisfy one, some, or all of these useful characteristics.
As illustrated in
The film 11 can have ≥70, ≥80, ≥85, ≥90, ≥95, ≥99 mass percent carbon. The film 11 can have ≤99, ≤99.5, or ≤99.9 mass percent carbon. The mass percent carbon value ranges of this paragraph can be such value ranges across the entire film 11 or across an aperture 32 or 42 of a frame 31 or housing 41 (see
The film 11 can be thin to improve x-ray transmission. For example, the film 11 can have a maximum thickness T11 that is in one of the following ranges: T11≤15 μm, T11≤25 μm, T11≤50 μm, T11≤100 μm, or T11≤400 μm.
The film 11 can be thick to provide sufficient strength to span an aperture 32 or 42 (see
The maximum thickness T11 value ranges of the prior two paragraphs can be such value ranges across the entire film 11 or just across a portion spanning an aperture 32 (see
As illustrated in
The graphite layer 21 can include ≥80, ≥85, ≥90, ≥95, ≥99, or ≥99.9 mass percent carbon. The polymer layer 22 can include polyimide.
The polymer layer 22 can be thinner than the graphite layer 21. For example, T21/T22>1, T21/T22≥10, T21/T22≥50, or T21/T22≥75, where T21 is a thickness of the graphite layer 21 and T22 is a thickness of the polymer layer 22. As another example, T21/T22≤150, T21/T22≤200, T21/T22≤500, or T21/T22≤1000. Example thicknesses of the graphite layer 21 include 1 μm≤T21, 2 μm≤T21, 5μ≤T21, or 10 μm≤T21; and T21≤14 μm, T21≤20 μm, T21≤40 μm, T21≤60 μm, or T21≤100 μm, Example thicknesses of the polymer layer 22 include 10 nm≤T22, 20 nm≤T22, 50 nm≤T22, or 80 nm≤T22; and T22≤120 nm, T22≤250 nm, T22≤500 nm, or T22≤2 μm.
Combining a thick graphite layer 21 with a very thin polymer layer 22 is preferred for achieving the characteristics desirable described above. These characteristics are preferably achieved by a film 11 that consists essentially of the graphite layer 21 and the polymer layer 22. These characteristics are preferably achieved through the method described below.
As illustrated in
As illustrated in
An interior 44 of the housing 41 can be a vacuum. An exterior 43 of the housing 41 can be ambient pressure. The film 11 can include a polymer layer 22 facing the vacuum at the interior 44, and a graphite layer 21 facing the ambient pressure at the exterior 43. This arrangement is preferred for reducing outgassing of material of the x-ray window 10 into the vacuum of the interior 44 of the housing 41.
Following are example characteristics of the film 11: T21/T22=120, T21=12 μm, T22=100 nm, T11=12.1 μm. The film 11 can have about 99.7% mass percent carbon. The polymer layer 22 can be polyimide. The film 11 can consist essentially of the graphite layer 21 and the polymer layer 22 across the aperture 42.
Method
A Method of Making an x-Ray Window can Include Some or all of the Following Steps:
Step 50 (
Step 60 (
The polymer precursor 63 can include an imide dissolved in N-methyl-2-pyrrolidone. The imide can be biphenyldianhydride/1,4 phenylenediamine. A volume of the N-methyl pyrrolidone divided by a volume of the imide can be ≥1.5 and ≤6. Baking step 70 can form the imide into a polyimide in the polymer layer 22.
Step 70 (
The polymer precursor 63 is shown in
Steps 80-90 (
Step 100 (
The steps of the method can be performed in the above order, or other order if so specified in the claims. Some of the steps can be performed simultaneously unless explicitly noted otherwise in the claims. Components of the x-ray window, made by this method, can have properties as described above the method description.
Here are steps of one example method: DSN5012 is used for the graphite layer 21 and the flexible substrate 51. The flexible substrate Si is a 75 μm thick layer of polyethylene terephthalate. The graphite layer 21 is 12 μm thick. The polymer precursor 63 is biphenyldianhydride/1,4 phenylenediamine dissolved in N-methyl-2-pyrrolidone, in a 1:3 ratio. A spin coat tool 61 with a silicon wafer is used, with the flexible substrate 51 adjoining the silicon wafer. The film 11 is baked on a hot plate about 80° C. for 10 minutes, then left to cure for 24 hours at room temperature. The film 11 is then laser cut by an Nd:YAG laser. Tweezers are then used to peel the flexible substrate 51 off of the graphite layer 21.
This application claims priority to U.S. Provisional Patent Application No. 63/243,846, filed on Sep. 14, 2021, which is incorporated herein by reference.
Number | Name | Date | Kind |
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20130051535 | Davis | Feb 2013 | A1 |
20130094629 | Liddiard | Apr 2013 | A1 |
Number | Date | Country | |
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20230082103 A1 | Mar 2023 | US |
Number | Date | Country | |
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63243846 | Sep 2021 | US |