ANTI-MULTIPACTOR DEVICE

Abstract

The invention relates to anti-multipactor coating deposited onto a substrate that can be exposed to the air and its procedure of obtainment by simple chemical methods. Furthermore, the present invention relates to its use for the fabrication of high power devices working at high frequencies.

Claims

1. Anti-multipactor coating deposited onto a substrate characterized in that it comprises at least two contacting high conductive metal layers with an electrical conductivity greater than 4×10.sup.7 S.Math.m.sup.−1, it has a secondary electron emission yield below 1 in air, between 0.4 and 0.9 for a incident electron energy range between 0 and 5000 eV, it has a final surface roughness with a grooves aspect ratio greater than 4, with a surface grooves density greater than 70%, and it has a insertion loss of between 0.1 and 0.14 dB, wherein the substrate consists of a metal or a mixture of metals.

2. Anti-multipactor coating according to claim 1, wherein the substrate consists of a metal or a mixture of metals selected from Ni doped with P, Al, Cu and Ag.

3. Anti-multipactor coating according to any of claim 1 or 2, wherein the high conductive metal of each layer is selected independently from Ag and Cu.

4. A process of obtainment of the anti-multipactor coating deposited onto a substrate according to any of claims 1 to 3, wherein the process comprises at least the following steps: a) deposition of a high conductive metal layer, with an electrical conductivity greater than 4×10.sup.7 S.Math.m.sup.−1, onto a substrate, b) etching of the deposited high conductive metal layer of step a) by an acid dissolution, c) activating of the etched layer obtained in step b), and d) electroless plating of a high conductive metal, of an electrical conductivity greater than 4×10.sup.7 S.Math.m.sup.−1, onto the activated etched layer obtained in step c) using a solution of high conductive metal ions and a reducing agent.

5. The process of obtainment, according to the previous claim, wherein the high conductive metal layer of step a) is made of Ag or Cu.

6. The process of obtainment according to any of claim 4 or 5, wherein the deposition of step a) is performed by conventional chemical deposition techniques such as plating, chemical solution deposition, spin coating, chemical vapor deposition and atom layer deposition, and/or physical deposition techniques such as electron beam evaporator, molecular beam epitaxy, pulsed laser deposition, sputtering, cathodic arc deposition and electrospray deposition.

7. The process of obtainment, according to any of claims 4 to 6, wherein the acid dissolution of step b) comprises hydrofluoric acid, nitric acid, acetic acid, deionized water or a mixture thereof.

8. The process of obtainment, according to any of claims 4 to 7, wherein step c) is performed by adding an aqueous solution of SnCl.sub.2 or PdCl.sub.2.

9. The process of obtainment, according to any of claims 4 to 8, wherein step c) is performed by adding an aqueous solution of SnCl.sub.2 in a concentration range between 0.05-1.2% in weight to the etched layer obtained in step b).

10. The process of obtainment, according to any of claims 4 to 9, wherein the high conductive metal used during step d) of electroless plating is selected from Ag or Cu.

11. The process of obtainment, according to any of claims 4 to 10, wherein step d) of electroless plating is performed under continuous agitation and using a bath temperature between 30 and 80° C.

12. The process of obtainment, according to any of claims 4 to 11, wherein the solution of high conductive metal ions of step d) is an aqueous solution of AgNO.sub.3.

13. The process of obtainment, according to any of claims 4 to 12, wherein the reducing agent of step d) is selected from triethanolamine, diethanolamine or monoethanolamine.

14. Use of the anti-multipactor coating deposited onto a substrate according to any of claims 1 to 3 for the fabrication of high power devices, operating at powers higher than 0.1 kW, working at high frequencies, from MHz range up to tens of GHz.

15. Use according to the previous claim, wherein the device is a microwave, a radio frequency device for space, thermonuclear or large accelerator instrumentation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0058] FIG. 1 a) photo of a Ku band filter and b) photo of a Ku band filter.

[0059] FIG. 2. Scanning electron microscopy (SEM) image of the transversal section of the silver flat coating deposited on Ni(P)/Al substrate.

[0060] FIG. 3 SEM images of the silver coating and a scheme of the monolayer silver structure deposited on Ni(P)/Al substrate.

[0061] FIG. 4 SEY curves of the filter sample with the optimum roughness as measured in the corrugated part of the filter before and after anti-multipactor treatment.

[0062] FIG. 5 Primary energy and angular dependences of the SE yield of electrons colliding with filters surface with primary energies of E=0-1000 eV, at incoming angles in interval −40°≦θ≦40°, before and after anti-multipactor treatment.

EXAMPLE

Preparation of Waffle-Iron Type Filter Samples and its Characterization

[0063] A chemical deposition treatment was developed for creating an appropriate submicron surface roughness on a Ag plating of the waffle-iron type filters.

[0064] FIG. 1a shows a photo of a Ku band filter, FIG. 1b shows a photo of a Ku band filter, 1 indicates the inner part.

[0065] A silver coated aluminum sample of 2 cm.sup.2 was etched in a Teflon baker of 50 ml with dissolution of HNO.sub.3, HF and deionized water 1:1:1 during 10 s. The sample was cleaned in water and treated in a dissolution of SnCl.sub.2 (0.03 g) and deionized water (50 ml) during 1 h.

[0066] An electroless plating process was required for the preparation of the top microstructured silver coating of the filters. The procedure was performed in a round glassware or baker of 50 ml containing AgNO.sub.3 (0.25 g) and deionized water (5 ml) of 16.8 Mohms.Math.cm; drops of triethanolamine were subsequently added and the solution take on light brown in color and subject to energetic agitation until to achieve a transparent dissolution, then more deionized water is added up to obtain 40 ml. at 40° C. The pretreated samples (prismatic shape or plates of 20×20×2 mm) were placed in the center of the baker with its small side parallel to the base of the baker during 30 min.

[0067] FIG. 2 shows a scanning electron microscopy (SEM) image of the transversal section of the silver flat coating deposited on Ni/Al substrate.

[0068] A homogeneous silver thickness is observed along the sample surface. It is remarkable the good interlayer adhesion.

[0069] FIG. 3 a) and b) show SEM images of the silver coating and c) shows a scheme of the monolayer silver structure deposited on Ni(P)/Al substrate.

[0070] The surface roughness of high aspect ratio is produced by the continuous silver growing on the previously etched surface of the standard silver plating of the aluminum alloy device. The dark black regions represent a sinkhole area of ˜51%. The 3D surface shown in this figure is a realistic simulation obtained by the AFM software. In the inset of the upper right is remarked the monolayer structure of this antimultipactor coating.

[0071] SEY tests were performed in an ultra-high vacuum chamber (<10.sup.−9 hPa) equipped with two Kimball Physics electron guns in the range 0-5000 eV, ion-gun, a concentric hemispherical analyzer. The energy of the electrons leaving the sample are determined using this analyzer and the excitation sources energetic electrons or x-ray, MgKα radiation (hvν=1253.6 eV). The sample can be rotated in front of the electron spectrometer for the surface composition or cleanliness examination, and in front of the programmable electron guns for the SEY measurements by using two micrometric XYZθ manipulators, and liquid helium cryostat for sample cooling, and also can be heated (<1200 K).

[0072] The SEY measurements were made via computer-controlled data acquisition; the sample is connected to a precision electrometer (conductive samples). The electron beam is pulsed by counter-bias of the wehnelt. The primary beam current can be measure by a Faraday cup attached to the system.

The yield of SEY (σ) is defined as a σ=(I.sub.0−I.sub.s)I.sub.0.

[0073] The current I.sub.0 is always negative, while I.sub.s can be positive or negative depending on the primary energy and SEY values of the sample. Low primary electron current (I.sub.0 <5 nA) was used to avoid surface contamination or modification.

[0074] No witness samples were required because filters can be directly measured in this SEY set-up.

[0075] FIG. 4 shows SEY curves of the filter sample with the optimum roughness as measured in the corrugated part of the filter before and after anti-multipactor treatment.

[0076] It is remarkable SEY of the coated filter is lower than 1 in all primary energy range SEY of pillars.

[0077] FIG. 5 discloses the primary energy and angular dependences of the SE yield of electrons colliding with filters surface with primary energies of E=0-1000 eV, at incoming angles in interval −40°≦θ≦40°, before and after anti-multipactor treatment.

[0078] A relevant decrease of the SEY after anti-multipactor treatment compared with as-received filter is obtained. SEY rises as the incidence angle of primary electrons is increased. The variation is lower for the anti-multipactor coating and higher for the silver flat reference sample. It is remarkable that microstructured coating (coated filter) achieves a constant SEY as a function of the incident angle, and SEY<1 in all primary energy range.

[0079] The incident-angle dependence of the total SEY data is well fitted by Furman and Pivi equation

SEY(θ)=1+α(1−cos.sup.β θ)

[0080] A good fit of SEY (θ) (secondary and backscattered electrons) is achieved with a constant value of α=9626.4 and β ranges from 2.82.Math.10.sup.−5 to 4.75.Math.10.sup.−5 for the primary energy range 200-900 eV.

[0081] The return loss of these coated Ku band samples, as well as the insertion loss, was measured at Tesat Spacecom by using a network analyzer equipment. S-parameter measurements were performed on each DUT (Device under test) before and after treatment.

[0082] A low value of insertion loss was measured, 0.14 dB.

[0083] Multipactor test were performed at the European High Power Laboratory in Valencia (Spain). Reference document: ECSS Space Engineering—T\TuHipact.ioll design and t.est RCSS-E-20-01A.

[0084] The filter sample was installed inside a vacuum chamber and one .sup.90Sr radioactive β-source and one UV lamp were employed simultaneously during the tests. A total of two electron probes were used during the test. It is worth mentioning that the detection systems as well as the radioactive source and the optical fiber (UV light) were positioned nearby the critical area of the filter sample.

[0085] The filter sample was kept under vacuum for around 60 h before starting the test. No discharges were observed up to at least 15000 W. Once the profile was completed, the RF power was increased progressively up to 15000 W. No discharge was observed. The maximum power attainable in this test-bed is 15000 W. The Multipactor test indicated that not discharge was produced, even at the maximum attainable power of the test bed (15 kW).