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WG1 Satellite session on practical use of resistive coatings

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  1. WG1 Satellite session on practical use of resistivecoatings P. Colas • Use of resistivecoatings for: • Spreading the charge to improveresolutionwhilelimiting the number of electronicreadoutchannels • StabilizingRPCs • Stabilizing Micromegas detectors (spark suppression) • Protectingintegrated circuits • Numerous techniques triedsince a decade or more : • Characterization of coverlays : measurement of surface resistivity, bulkresistivity and thru-resistivity

  2. Terminilogy -A Resistor is define by: -Value Ohms -Precision % -TCR ppm/Deg C -max power W or W/m2 -breakdown voltage V -Resistivity in Ohm*m -Sheet resistance or surface resistivity in Ohm/sqr -TCR: Temperature coefficient of the resistor -Cermet: is a composite material composed of ceramic (cer) and metallic (met) materials. Rui De Oliveira

  3. Rs: Sheet resistance Ω/sq Rui De Oliveira

  4. Polymer resistive pastes 1 Mohms/Sqr seems to be the limit for these polymers Rui De Oliveira

  5. Polymer Resistive foils Rui De Oliveira

  6. Jose Repond: RPC for DHCAL calorimeter Spraying glass Constraints on resistive paint Surface resistivity in the range of 1 – 5 MΩ/□ Easily applicable Resistivity not dependent on humidity (very important!!!) Paint Used commercial spray (LICRON) in the past, but new product not useful Identified some 2-component ‘artist paint’ → satisfies constraints Paint needs to be mixed appropriately and sprayed (with spraying gun) Spraying booth Built large booth to exhaust (non-toxic) fumes Movement of spraying gun controlled with step motors (~ 2minutes/plate) Spraying procedure Significant preparation needed: cleaning of glass, masking off rims, mixing paint, cleaning tools 1-botton operation Could spray up to 8 plates in one day Jose Repond - Spraying of glass plates

  7. Results Uniformity obtained by adjusting - Speeds - Distance to glass plate - Order of spraying - Air flow in booth MΩ/□ Jose Repond - Spraying of glass plates

  8. I. Laktineh / N. Lumb – DHCAL with glass RPCs Experience with resistive coatings

  9. Experience with resistive coatings

  10. ILC-TPC : charge spreading Resistivebulk Micromegas Continuous RC circuit spreads the charge -> resolutionimprovement 60 µ resolutionat 0 drift with 3 mm pads ! Experience with resistive coatings

  11. Also the resistive foil stabilizes Micromegas: no more breakdown, stable current Argon/Isobutane 90/10 Cr (SiO2)ncermet P.C., M. Dixit, I. Giomataris 2005 LC workshop, Stanford Experience with resistive coatings

  12. Standard Micromegas Resistive Micromegas MAMMA beam test, 15 kHz hadron beam, October 2009 Experience with resistive coatings

  13. ResistivedepositsalsoprotectTimePix Chips fromsparks (10 microns of aSi:H, 4-7 microns of SixNy (H. VdGraaf, N. Wyrsch) Experience with resistive coatings

  14. Deposition of thinlayers (10 µ thick) of a-SiH (1013W.cm) Neuchatel, N. Wyrsch Possibility to add a doped layer on top Experience with resistive coatings

  15. Weusedseveral techniques to measureresistivities. • May depend on voltage, pressure of the contact,… • Oftenseediscrepancies, inhomogeneities, unstabilities • Thru-resistivitysometimesinconsistentwith surface resistivity 4-point probe (Neuchatel) Circular probe Conducting tape, insulatingsubstrate lxLresistivesample = L/l ’squares’ Measureresistance, divide by number of squares Experience with resistive coatings

  16. Diagnostic tools : thermal image of the prototype with a high-resistivity layer and a lower-resistivity layer on top (N. Wyrsch, EPFL, Neuchatel) Hot spots due to leakagecurrent Experience with resistive coatings

  17. Experience with resistive coatings