GOSSIP: Gas On Slimmed SIlicon Pixels

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GOSSIP Gas On Slimmed SIlicon Pixels
NIKHEF Auke-Pieter Colijn Alessandro
Fornaini Harry van der Graaf Peter
Kluit Jan Timmermans Jan Visschers Saclay
CEA DAPNIA Maximilien Chefdeville Paul
Colas Yannis Giomataris Arnaud
Giganon Univ. Twente/Mesa Jurriaan
Schmitz CERN/Medipix Constm Eric Heijne Xavie
Llopart Michael Campbell
Thanks to Wim Gotink Joop Rovenkamp
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The MediPix2 pixel CMOS chip
Cathode foil
Drift Space
Gem foils
Support plate
Medipix 2
We apply the naked MediPix2 chip without X-ray
convertor!
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55Fe
Cathode (drift) plane
Drift space 15 mm
Micromegas
Baseplate
MediPix2 pixel sensor Brass spacer block Printed
circuit board Aluminum base plate
Very strong E-field above (CMOS) MediPix!
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14 mm
Friday 13 (!) Feb 2004 signals from a 55Fe
source (220 e- per photon) 300 ?m x 500 ?m
clouds as expected
The Medipix CMOS chip faces an electric field of
350 V/50 µm 7 kV/mm !!
We always knew, but never saw the conversion of
55Fe quanta in Ar gas
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• no attachment
• homogeneous field in
• avalanche gap
• low gas gain
• simple exponential grown
• of avalanche
• ?
• No Curran or Polya
• distributions but simply

Single electron efficiency
Prob(n) 1/G . e-n/G
Eff e-Thr/G
Thr threshold setting (e-) G Gas amplification
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New trial NIKHEF, March 30 April 2,
2004 Essential try to see single electrons from
cosmic muons (MIPs) Pixel preamp threshold 3000
e- (due to X-talk) Required gain 5000
10.000 New Medipix New Micromegas Gas
He/Isobutane 80/20 !Gain up to 30
k! He/CF4 80/20 It Works!
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He/Isobutane 80/20 Modified MediPix
Sensitive area 14 x 14 x 15 mm3
Drift direction Vertical max 15 mm
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He/Isobutane 80/20 Modified MediPix
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He/Isobutane 80/20 Modified MediPix
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He/Isobutane 80/20 Non Modified MediPix Americi
um Source
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He/Isobutane 80/20 Modified MediPix
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He/Isobutane 80/20 Modified MediPix
d-ray?
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MediPix modified by MESA, Univ. of Twente, The
Netherlands
Non Modified
Modified
Pixel Pitch 55 x 55 µm2 Bump Bond pad 25 µm
octagonal 75 surface pacivation SiN New Pixel
Pad 45 x 45 µm2
Insulating surface was 75 Reduced to 20
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Peter Kluit cluster electron density versus MC
of MIP cosmic rays single electron efficiency gt
0.95 AND Good explanation for Moire
effect pitch Micromegas holes 60 µm pitch
MediPix pixels 55 µm Periodic position of hole
w.r.t. pixel repeats after 12 pixels!
Non Modified
Modified
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Modified
Non Modified
InGrid perfect alignment of pixels and grid
holes! Small pad small capacitance!
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InGrid
Integrate GEM/Micromegas and pixel sensor
GEM
Micromegas
By wafer post processing
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First InGrid expected in July Wafer dia. 100
mm 30 fields with variety of pillar geometry
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• WSLC-Paris 2004 LC ready in 2015, not known
  where..
• People with power and what is the relevance
  for LHC?!
• So
• Other applications of TimePixGrid
• µ-TPC
• upgrades of TPCs STAR, ALICE
• Transition Radiation Detectors
• GOSSIP tracker for intense radiation environment

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GOSSIP Gas On Slimmed SIlicon Pixels
MIP
Cathode foil
CMOS pixel chip
Drift gap 1 mm Max drift time 10 ns
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• Essentials of GOSSIP
• Generate charge signal in gas instead of Si
  (e-/ions versus e-/holes)
• Amplify electrons in gas (electron avalanche
  versus FET preamps)
• Then
• No radiation damage in depletion layer or pixel
  preamp FETs
• No power dissipation of preamp FETs
• GOSSIP 1 mm gas layer 20 µm gain gap CMOS
  (digital!) chip
• After all it is a TPC with 1 mm drift length
  (parallax!)

Max. drift length 1 mm Max. drift time 10
ns Resolution 0.1 mm ? 1 ns
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Efficiency Position resolution Rate
effects Ageing Radiation hardness HV
breakdowns Power dissipation Material budget
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Efficiency

• Single electron efficiency gt 0.95
• Number of clusters per mm 3 (Ar) 10
  (Isobutane)
• Number of electrons per cluster 3 (Ar) - ?
  (Isobutane)
• Probability to have 1 cluster in 1 mm Ar 0.95
• With nice gas eff 0.99 in 1 mm thick layer
  should be possible
• But.
• Parallax error due to 1 mm thick layer, with 3rd
  coordinate 0.1 mm
• TPC/ max drift time 10 ns / s 0.1 mm / s 1
  ns (not easy.)
• Lorentz angle
• We want light ions (rate effect), and little UV
  photon induced avalanches

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Position resolution

• Transversal coordinates
• limited by
• pixel dimensions 20 x 20 50 x 50 µm2
• Note we MUST have pixels no strips (pad
  capacity/noise)
• Good resolution in non-bending plane!
• Pixel number has NO cost consequence (m2 Si
  counts)
• Pixel number has some effect on CMOS power
  dissipation
• Diffusion max. drift length 1 mm little effect
  (?)
• d-rays
• Drift coordinate
• limited by
• Pulse height fluctuation
• gas gain (3 k), pad capacity, e- per cluster

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Rate effects
LHC _at_ max lumi _at_ 2 cm from beam pipe 10
tracks cm-2 25 ns-1 400 MHz cm-2!

• only (average) 10 e- per track
• gas gain only 3 k
• most ions are discharged at grid
• after traveling time of 20 50 ns
• a few percent enter the drift space

time

• Some ions crossing drift space takes 20 200
  µs!
• B-field should help
• ion space charge has NO effect on gas gain
• ion charge may influence drift field, but this
  does little harm
• ion charge may influence drift direction (?)
• Recombination?

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Ageing
Remember the MSGCs

• Little ageing
• the ratio (anode surface)/(gas volume) is very
  high w.r.t. i.e. MDTs
• little gas gain (3k)
• homogeneous drift field homogeneous
  multiplication field
• versus 1/R field of wire. Absence of high
  E-field close to a wire
• no high electron energy little production of
  chemical radicals
• Confirmed by measurements (Alfonsi, Colas)

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Radiation hardness

• CMOS 130 nm technology OK up to ? rad
• need only modest input FETs

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HV breakdowns
1 High-resistive layer
3 massive pads
2 High-resistive layer
4 Protection Network
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Power dissipation

• MediPix2 1 W/cm2 preamp power
• Large part in preamps 2 discr per pixel
• For GOSSIP CMOS Pixel chip
• Array of 512 x 512 monostable gates
• Row OR, Column OR, decoders, TimeStamp,
• shift registers
• 10 M transistors, most in rest
• ? Gas Cooling feasible!

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Material budget
Slimmed Si CMOS chip 30 µm Si Pixel resistive
layer 5 µm SiN2 Anode pads 5 µm Al Grid 1
µm Al Grid resistive layer 5 µm
SiN2 Cathode 1 µm Al CF string support, gas
tubing, power
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• How to proceed?
• InGrid 1 available for tests in July
• rate effects (all except change in drift
  direction)
• ageing
• ? Proof-of-principle of signal
  generator Xmas 2004!
• InGrid 2 HV breakdowns, beamtests with MediPix
  (TimePix1 in 2005)
• TimePix2 CMOS chip for GOSSIP CERN
  MediPix/ATLAS Pixel
• Needed calculations/simulations
• PhD student
• students
• (NIKHEF) vertex experts i.e. Henk T, Els K,
  Nigel H, Jos S, Marcel D.