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A TITANIUM NITRIDE COATING TESTED IN PASSIVE INTERMODULATION

A TITANIUM NITRIDE COATING TESTED IN PASSIVE INTERMODULATION. F. Suárez (1), C. Palacios (2), C. Montesano (3) and F. Rueda (1) (1) Universidad Autónoma de Madrid (2) Distcom Antenas, S.L. (3) Construcciones Aeronáuticas S.A. (CASA)-División Espacio. INTRODUCTION.

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A TITANIUM NITRIDE COATING TESTED IN PASSIVE INTERMODULATION

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  1. A TITANIUM NITRIDE COATING • TESTED IN PASSIVE INTERMODULATION • F. Suárez (1), C. Palacios (2), C. Montesano (3) • and F. Rueda (1) • (1) Universidad Autónoma de Madrid • (2) Distcom Antenas, S.L. • (3) Construcciones Aeronáuticas S.A. (CASA)-División Espacio

  2. INTRODUCTION Titanium Nitride (TiN) is the most used coatingto prevent Multipactor (MP) due to its stability in RF field: they have solved the MP problems of high RF power (MegaWatt) in particle accelerators (Los Alamos, Fermilab, DESY…), at wave guides and wave guide windows, with metallic and ceramic surfaces (W.D.Cornelius and R.J. Grieggs; J. Lorkiewickz et al.).

  3. TiN has metallic conduction, due to one electron per Ti atom not entering the covalent bond. A thin layer of TiN (>40nm) is enough to reduce the SEE coefficient. The sublimation of Ti by heating a simple filament inside the RF element in N2 or NH3 atmosphere is used as anti-multipactor remedy.

  4. Metallic electrical conductivity ( max. for x=1). • Thermalmand chemical stability. • NaCl Crystal structure (0.6< x < 1.2). • Lattice Parameter 4.22 - 4.25 A (0.6 < x < 1.2). • Absorción in visible and near IR. • Híbryd bond of N and Ti. • Color of broze. • Hardness similar to diamond. PROPERTIES OF THE TINX COMPOUNDS

  5. In previous work in our laboratory and in ESTEC several coatings were tested for multipactor threshold power. when deposited with ion assistance TiN has shown the best results. • “Alodine” has also shown a considerable threshold power, as shows the next transparecy.

  6. TiN ion assissted coating presents 2 times the “Alodine” threshold power (Final Report ESTEC Contract No. P.O. 162594 /1996).

  7. For satellite applications a coating such as TiN has to fulfill a complementary requirement not applicable in particle accelerators: to be PIM compatible. • “The present work had as objective to test two types of TiN coatings for PIM.

  8. The difficulty in obtaining a coating to prevent MP lies both in compositional reproducibility and stability of the SEE coefficient after long exposures to air and contamination at the vacuum chamber during subsystem or satellite qualification tests.The approach of this work has been: 1) To obtain a relatively thick coating of TiN so that its crystal structure and bulk composition can be measured. 2) To test this coating for PIM.

  9. Among the proposed PIM generating processes, leading to non linear interaction function between field and induced current, the tunnel effect at localized electrical contacts in flanges or connectors has been the most studied.

  10. The absence of surface oxides does not seem to be sufficient to guarantee a PIM free circuit, as saturated non ohmic contacts can develop even in gold coated connectors (Weibel and Hügel).

  11. PIM level as a function of the applied voltage to a piezoelectric crystal by Weibel and Hügel. (1998). Voltaje

  12. The TiN coatings were deposited by evaporation of Titanium with a “Varian e-gun” in a N2 atmosphere of 10-4 torr at a bakeable metal bell jar pumped by 500l/s turbo molecular and ionic pumps, reaching after baking at 250ºC for 12h a base vacuum of 2x10-8 torr. This deposition was preceded by 500eV Ar ion cleaning of the substrate and subsequently by an Ion Beam Assisted Deposition ( IBAD) of Ti. This was done either by Ar ions ions resulting from feeding a “Commonwealth Scientific Co ” Kaufman 3 cm diameter ion gun either with Ar or with an Ar + N2 mixture at a current of 15mA and 200-300 eV. COATING DEPOSITION - 1

  13. COATING DEPOSITION - 2 • The Indium of 99.999% purity (Fa. Haart & Co) was evaporated at 1 10-7 torr up to about 1 micrometer thickness. • The Ti and In sources were near the normal of the substrate at about 20 cm distance and a shutter collected the first fractions. The ion beam angle with the sample normal was about 45º for TiN deposition.

  14. COATING DEPOSITION - 3 • AA 2017 Al alloy gaskets with different surface finish, glass microscope slides and graphite were used as substrates During the evaporation the substrates attain about 50oC (thermocouple on substrate). The film thickness, in the range of 0.12-1.0m, was monitored with a quartz crystal oscillator (APT) and verified with a stylus type apparatus (Talystep, Taylor  Hobson, U. K.). The titanium based coating deposition rate was between 25 and 35Å/min.

  15. COATING DEPOSITION - 4 • The surface morphology and EDAX bulk composition measurements were performed in a Philips XL 30 scanning electron microscope in “as-grown” films on graphite substrate.

  16. PIM TEST DESCRIPTION - 1 • The purpose of subjecting the different coated gaskets to the PIM test is to check the behaviour of these coatings in terms of PIM-free generation and confirm that this type of coating is valid to be used in space antenna elements (horns, orthomode-transducers, polarisers…) with restrictive specification both for multipaction and PIM. • Hence, it seemed interesting to perform the test according to the most restrictive requirements requested for a real component designed and manufactured by EADS Casa Espacio.

  17. PIM TEST DESCRIPTION - 2 • The test consisted in applying two carriers of 84 W (49.24 dBm) each at Ku band. The selected TX frequency band was 11.5GHz to 12.3 GHz. The combination of this carriers produced a 5th order PIM falling into the RX frequency, ranging from 13.5 GHz to 14.0 GHz.  • To guarantee the proper reception of the PIM level, the receiving system must present a good noise floor, providing during the test performance a SNR of 10 dBm.  • Table 1 summarises the main parameters which define the PIM test performed on the gaskets under study. 

  18. PARAMETER VALUE UNITS TX carrier nr. 1 12.202 GHz TX carrier nr. 2 11.500 GHz RX PIM frequency (5th order) 13.606 GHz Power per carrier 84 Watts Resolution Band Width (Spectrum Analyser) 10 Hz Noise floor level (Spectrum Analyser) <-150 dBm SNR 10 dB

  19. Figure 1. Type 1 gasket layout Figure 2. Type 2 gasket layout

  20. COATING TYPE TEST Nr. GASKET REFERENCE Alodine 1200 2 1 PIM-L0-01 2 3 PIM-L0-02 2 5 PIM-L0-03 1 2 PIM-L0-01R 1 4 PIM-L0-02R 1 6 PIM-L0-03R TiN 2 7 PIM-L1-01 2 9 PIM-L1-05 1 8 PIM-L1-01R 1 10 PIM-L1-05R In 2 11 PIM-L2-02 • SAMPLES DEFINITION Two types of geometry gaskets have been designed based on WR75. Type 1 corresponds to a piece of wave-guide of 4mm-length with a PIM-free flange design which presents lips, hatched in black colour, at both sides. Type 2 corresponds to a similar piece but without PIM-free flange. The purpose of this Type 2 is to see if a proper coating can or cannot replace a PIM-free flange mechanisation.

  21. Conventional ALODINE coating on AA1200

  22. Gasket surface prior to treatment .

  23. Gasket after Alodine treatment .

  24. Gasket surface after Alodine treatment .

  25. Gasket after TiN ion assisted deposition

  26. a TiN-4/Al (111)Al (200)Al (111)TiN (200)TiN (311)Al (220)TiN (220)Al INTENSITY (a. u) b TiN 5 Ar+ass./Al (111)Al (200)Al (220)Al (140)TiO (102)TiO (311)Al (111)TiN (220)TiN (200)TiN 40 50 60 70 80 2q º

  27. SAMPLE COATING E1 (eV) TiN_1 TiN 1 99 TiN_5 TiN 1 74 TiN_6 TiN 1 116 TiN_8 TiN 2 64 PIM – L0 – 01 ALODINE 98 PIM – L0 – 01R ALODINE 144 • SEE film properties

  28. Crystalline TiN phase with high nitrogen content is reproduced in ion assisted depositions. The TiN coated flanges showed similar PIM levels to those of Alodine 1200. This indicates that ion beam assisted TiN coatings may also be accepted as PIM compatible for mechanical contacts in RF wave-guides. • CONCLUSIONS

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