WG1 Satellite session on practical use of resistive coatings
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Transcript of WG1 Satellite session on practical use of resistive coatings
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WG1 Satellite session on practical use of resistive coatings
Use of resistive coatings for:-Spreading the charge to improve resolution while limiting the number of electronic readout channels-Stabilizing RPCs-Stabilizing Micromegas detectors (spark suppression)-Protecting integrated circuits
Numerous techniques tried since a decade or more :
Characterization of coverlays : measurement of surface resistivity, bulk resistivity and thru-resistivity
P. Colas
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Rui De Oliveira 2
Terminilogy
13/04/2011
-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.
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Rui De Oliveira 3
Rs: Sheet resistance Ω/sq
13/04/2011
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Rui De Oliveira 4
Polymer resistive pastes
13/04/2011
1 Mohms/Sqr seems to be the limit for these polymers
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Rui De Oliveira 5
Polymer Resistive foils
13/04/2011
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Jose Repond - Spraying of glass plates 6
Spraying glassConstraints 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: RPC for DHCAL calorimeter
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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/□
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Experience with resistive coatings 813/04/2011, RD51 CERN
I. Laktineh / N. Lumb – DHCAL with glass RPCs
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Experience with resistive coatings 913/04/2011, RD51 CERN
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Experience with resistive coatings 10
ILC-TPC : charge spreading
13/04/2011, RD51 CERN
Resistive bulk Micromegas
Continuous RC circuit spreads the charge -> resolution improvement
60 µ resolution at 0 drift with 3 mm pads !
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Experience with resistive coatings 11
Argon/Isobutane 90/10 Cr (SiO2)n cermet
P.C., M. Dixit, I. Giomataris2005 LC workshop, Stanford
13/04/2011, RD51 CERN
Also the resistive foil stabilizes Micromegas: no more breakdown, stable current
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Experience with resistive coatings 1213/04/2011, RD51 CERN
Standard Micromegas Resistive Micromegas
MAMMA beam test, 15 kHz hadron beam, October 2009
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Experience with resistive coatings 1313/04/2011, RD51 CERN
Resistive deposits also protect TimePix Chips from sparks(10 microns of aSi:H, 4-7 microns of SixNy (H. VdGraaf, N. Wyrsch)
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Experience with resistive coatings 14
Deposition of thin layers (10 µ thick) of a-SiH (1013 W.cm)Neuchatel, N. Wyrsch
Possibility to add a doped layer on top
13/04/2011, RD51 CERN
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Experience with resistive coatings 15
lxL resistive sample = L/l ’squares’
Conducting tape, insulating substrate
Measure resistance, divide by number of squares
4-point probe (Neuchatel)
Circular probe
We used several techniques to measure resistivities. -May depend on voltage, pressure of the contact,…-Often see discrepancies, inhomogeneities, unstabilities-Thru-resistivity sometimes inconsistent with surface resistivity
13/04/2011, RD51 CERN
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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 leakage current
13/04/2011, RD51 CERN
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Experience with resistive coatings 17
Type of coating PROs CONs
Cermet (Sheldal; M. Dixit et al.)
Tunable resistivity, homogeneousStable once laminated
Fragile / scratchable
Carbon-Loaded polyimide (Dupont; M. Dixit et al.)
Accurate thickness (25 µ)Large surfaces easy
Thin layer deposition(H. VdGraaf, N. Wyrsch, EPFL)
Limited to few micron thickness
Limited to small surfaces (10x10cm2). Very clean substrate needed.
Sprays(G. Mikenberg, Tel Aviv, J. Répond, I.Laktineh)
Large surfaces. Needs tuning 10-20% homogeneity
paints Can be patterned. Large surfaces.
inhomogeneous
13/04/2011, RD51 CERN