Measurement of coating resistivity on Mo coated samples with H011 cavity

N.Biancacci, F.Caspers, A.Kurtulus

C.Accettura, S.Antipov, G.Arduini, E.Berthome, H.Bursali, S.Calatroni, N. Catalan Lasheras,F.Carra, F.Di Lorenzo, K.Fellag, A.Gilardi, A.Grudiev, J.Guardia Valenzuela, I.Llamas Garcia,B. Louis Schafer, E.Métral, S.Redaelli, B.Salvant, M.Taborelli, W.Vollenberg, C.Vollinger,M.Volpi, C.Zannini and the mechanic lab bat.152 (D.Gacon, R.Martinez).

Introduction

• Accurate measurement of coating surface resistance is needed to characterize the production process of HL-LHC baseline collimators jaws made of 5um Mo coated MoGr.

• Extensive characterization studies done in the past by means of eddy current coils at low frequency (10kHz – 2MHz).

• 2 companies called for large production (DTI, Politeknik) and compared to CERNproduction.

• Measurements of resistivity was done on small blocks based on eddy current testing (see https://indico.cern.ch/event/773228/contributions/3219381/attachments/1754354/2843771/Outcome_of_recent_Mo_coating_resistivity_measurements.pdf ) with good outcome for DTI.

• Attempted measurement also on real (thicker and larger) blocks: more sensitivity to bulk not homogeneity affected the results and triggered the study of an alternative method (161th HSC meeting https://indico.cern.ch/event/775773/ )

• Alternative approach quickly developed and based on the application of a pillbox cavity optimized for H011 mode operation -> huge transversal team work!

H011 cavity

Measurement setup:• Copper cavity with open cap• DUT placed as end cap: wall resistivity change -> Q change

Cavity w/o end cap Cavity w/ end cap Cavity w/ DUT end cap

Many thanks Denis Gacon and Ruan Martinez for the manufacturing (in only ½ day!).

H field of H011 mode

vacuum

Cu mitered partDUT

H011 cavity

[1] Microwave Electronics: Measurement and Materials Characterization, Di L. F. Chen et al. pp. 100-101[2] Microwave paint thickness sensor, US patent #7898265 B2 https://patentimages.storage.googleapis.com/f1/e8/42/09ab717ddc8033/US7898265.pdf[3] M. Ye, L. Wang, Y. He and M. Daneshmand, "In SituTest of Thickness and Sheet Resistance of Conductive Nanomaterial Using Microwave Cavity," in IEEE Microwave and Wireless Components Letters, vol. 27, no. 10, pp. 942-944, Oct. 2017.

Measurement setup:• Copper cavity with open cap• DUT placed as end cap: wall resistivity change -> Q change• Frequency of operation: mode H011 (most insensitive to cap contacts)• Mitered internal part to separate adjacent E modes.• Known methodology to make frequency meters (e.g. [1,2,3])

Measurement of resonant modes

Excellent agreement of measurements w.r.t. simulations.

A.Kurtulus

Simulated Q change vs end cap resistivity

Change in Q vs change in resistivity simulated in CST and reproduced by curve𝑄𝑚

𝑄𝑟𝑒𝑓=

𝑎 + 𝑏

𝑎 𝑥 + 𝑏

with 𝑥 = 𝜌𝑚/𝜌𝑟𝑒𝑓, 𝑎 and 𝑏 resp. power dissipated in the end cap and rest of the cavity.

Example: Ref = Cu,𝑓𝐻011~16.8GHz

• We are changing only part of the cavity -> the gain is less than √𝑥! -> cavity shape optimized for the bestaspect ratio to improve Q change sensitivity.

• High frequency of operation (16.8 GHz) above Impedance Lab VNA (max 4.5 GHz). Many thanks to Nuria,Alexej, Matteo and Hikmet for the support with the 50 GHz VNA!

Data acquisition

• Probes cross-talk gives “typical” notch pattern after the H011 resonance at 16.5 GHz.• Relative Q factor measurement still possible but minimum Q attainable limited.• Design refinement can avoid this effect.

Mo on DTI Mo on CFC

• Transmission Q-factor for all acquired samples:

Good Q measurement Q measurement at the limit

Measured Q change vs end cap resistivity

• Measured relative Q change for thick metals (e.g. Cu, Al, In, Ta, Mo, SS, …) borrowedfrom TE-VSC-SCC (many thanks!).

• Resistivity was accurately measured with the Sigmameter (at 900kHz, many thanksCarlotta, Fede and Jorge for the support!)

• Curve in excellent agreement with measured data!

Measured Q change vs end cap resistivity

• Measured Q change for Mo coated (6-7um) real blocks allows to deduce the unknown coating resistivity:

(*) DTI block thermal treated at 400 ºC.(**) CERN and Politeknik coated blocks had long manipulation history which helped our understanding but probably degraded the surface quality.

DTI

Politeknik

CERN

Mo on Gr

Mo (DTI*) Mo (CERN**) Mo (Politeknik**) Mo on Graphite

~54 nOhm.m ~523 nOhm.m ~418 nOhm.m ~192 nOhm.m

Requirements for HL-LHC

All details in https://edms.cern.ch/document/2016583/1

Quality control during price enquiry foresees:1. 𝜌 < 250 𝑛Ω𝑚 at DC (4-points, 4-wires on glass) 2. 𝜌 < 100 𝑛Ω𝑚 at RF (eddy current)

(1.) implies (2.) based on empirical observations (e.g. J.Guardia Valenzuela in https://indico.cern.ch/event/751839/contributions/3113528/attachments/1704247/2746297/SEM_Mo_coat_comparison_substrates_aug18.pdf)

Requirements for HL-LHC

RF DC

Measured Mo (DTI) ~54 nOhm.m [1] 100 nOhm.m [2]

Measured Mo (CERN) ~523 nOhm.m [1] 210 +/- 20 nOhm*m [3]

Measured Mo (Politeknik) ~418 nOhm.m [1] Not done by the company

Requirements ~<100nOhm.m ~<250nOhm.m

[1] Measured with H011 cavity at 16.5 GHz[2] Measured with 4-points on glass by DTI company.[3] Measured by Wil with 4-points method on 6 µm Mo coated on glass: comparable to 250nOhm.m in 4-wires method and ~200 nOhm.m measured by eddy current (e.g. J.Guardia Valenzuela in https://indico.cern.ch/event/751839/contributions/3113528/attachments/1704247/2746297/SEM_Mo_coat_comparison_substrates_aug18.pdf)

Summary of measurements done and requirements: DTI compliant with specs.

Requirements for HL-LHC

RF DC

Measured Mo (DTI) ~54 nOhm.m [1] 100 nOhm.m [2]

Measured Mo (CERN) ~523 nOhm.m [1] 210 +/- 20 nOhm*m [3]

Measured Mo (Politeknik) ~418 nOhm.m [1] Not done by the company

Requirements ~<100nOhm.m ~<250nOhm.m

[1] Measured with H011 cavity at 16.5 GHz[2] Measured with 4-points on glass by DTI company.[3] Measured by Wil with 4-points method on 6 µm Mo coated on glass: comparable to 250nOhm.m in 4-wires method and ~200 nOhm.m measured by eddy current (e.g. J.Guardia Valenzuela in https://indico.cern.ch/event/751839/contributions/3113528/attachments/1704247/2746297/SEM_Mo_coat_comparison_substrates_aug18.pdf)

Summary of measurements done and requirements: DTI compliant with specs.

DTI compliant with requirements.

Summary and outlook

• Huge team work effort: many thanks to all people involved, particularly Fritz for the constantfollow-up of the measurement developments (we also developed an resonant eddy currentmeter at ~4GHz which could be useful for quick bulk characterizations).

• Thin Mo coating resistivity measured designing and building a H011 cavity:

– High reproducibility (low contact loss)

– High sensitivity (high Q factor and optimized aspect ratio)

– Fast measurement: could allow quick and clean measurement of all the incoming blocks!

• Simulations and measurements in good agreement with expectation for operational mode.

• Known metals used for cross-calibration between instruments (Sigmameter to H011 cavity)

• Mo coating shows best resistivity on DTI sample (very close to bulk value).

• High resistivity on CERN and Politeknick blocks probably due to several manipulations of theblocks.

• Mo on Graphite in the order of 200nOhm.m (eddy current showed 350nOhm.m)

• Mo on CFC induces strong damping -> high resistivity, at the limit of measurability for presentsetup.

Summary and outlook

• Improve the cavity design to minimize the probe crosstalk.

• Produce a second cavity for measuring smaller samples (20x20x15).

• Investigate measurements in second H mode insensitive to contacts at ~20GHz.

• Detailed comparison with eddy current testing on known samples.

• SEM on DTI sample: probing the coating structure to understand the good electricalconductivity.

• …

… and produce a nice document to summarize all the work done!

BACKUP

Skin depth

Small blocks: magnetic field mostly outside bulk material.Large blocks: magnetic field always inside bulk material -> more sensitive to non homogeneity.

Eddy current testing applied to small blocks

• Bulk resistivity obtained by changing lift-off to match measured curve.• Coating resistivity obtained by scaling to the peak of simulated/measured data

(accounts for lift-off/bulk resistivity error)

Eddy current testing applied to small blocks

Measurements of Mo on MoGrSame procedure applied but large impact on bulk non homogeneity affecting the measurement.

Mo on Graphite Mo on MoGr

• Graphite ~10 times larger resistivity than MoGr: less sensitive to non homogeneity.• So far only 5 measurements done on random position on the sample.

N.Biancacci et al., 161th HSC meeting https://indico.cern.ch/event/775773/

Introduction

• Three producers contacted for Mo on MoGr collimator blocksforeseen for collimators’ HL-LHC upgrade: CERN, DTI,Politeknik.

• Resistivity of coating characterized by eddy current testing inimpedance lab.

• Measured small samples (20x20x1.5)mm and collimator-likeblocks .

Mo on Graphite

Mo on MoGr (small)

Mo on MoGr (large)

Effect of coil lift-off

• Coil lift-off position influences magnitude:• Coil close to surface -> low impedance difference• Coil far from surface -> high impedance difference

• Known parameter (within 30% for small distances).

Effect of bulk resistivity

• Similar to lift-off effect:• The more the resistivity difference w.r.t. bulk, the higher the signal

• MoGr/CFC usually between 1uΩm and 5-7uΩm resistivity

Eddy current testing

http://zfp.cbm.bgu.tum.de/mediawiki/index.php/Datei:ECT_tactile_probe.png