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GOSSIP : G as O n S limmed SI licon P ixels

GOSSIP : G as O n S limmed SI licon P ixels. 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

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GOSSIP : G as O n S limmed SI licon P ixels

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  1. GOSSIP: Gas On SlimmedSIlicon Pixels NIKHEF Auke-Pieter Colijn Alessandro Fornaini Harry van der Graaf Peter Kluit Jan Timmermans Jan Visschers Saclay CEA DAPNIA Maximilien ChefdevillePaul 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

  2. 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!

  3. 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!

  4. 55Fe, 1s No source, 1s 55Fe, 10s 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

  5. Single electron efficiency • no attachment • homogeneous field in • avalanche gap • low gas gain • simple exponential grown • of avalanche •  • No Curran or Polya • distributions but simply: Prob(n) = 1/G . e-n/G Eff = e-Thr/G Thr: threshold setting (#e-) G: Gas amplification

  6. 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!

  7. He/Isobutane 80/20 Modified MediPix Sensitive area: 14 x 14 x 15 mm3 Drift direction: Vertical max = 15 mm

  8. He/Isobutane 80/20 Modified MediPix

  9. He/Isobutane 80/20 Modified MediPix

  10. He/Isobutane 80/20 Non Modified MediPix Americium Source

  11. He/Isobutane 80/20 Modified MediPix

  12. He/Isobutane 80/20 Modified MediPix δ-ray?

  13. 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 %

  14. Peter Kluit: cluster & electron density versus MC of MIP cosmic rays: single electron efficiency > 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

  15. Modified Non Modified InGrid: perfect alignment of pixels and grid holes! Small pad: small capacitance!

  16. InGrid Integrate GEM/Micromegas and pixel sensor ‘GEM’ ‘Micromegas’ By ‘wafer post processing’

  17. First InGrid expected in July Wafer dia.: 100 mm 30 fields with variety of pillar geometry

  18. 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

  19. MIP Micromegas CMOS pixel array GOSSIP: Gas On Slimmed SIlicon Pixels MIP Cathode foil CMOS pixel chip Drift gap: 1 mm Max drift time: 10 ns

  20. 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

  21. Efficiency Position resolution Rate effects Ageing Radiation hardness HV breakdowns Power dissipation Material budget

  22. Efficiency • Single electron efficiency: > 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 / σ = 0.1 mm / σ = 1 ns (not easy….) • Lorentz angle • We want light ions (rate effect), and little UV photon induced avalanches

  23. Position resolution 0 Q 20 – 50 ns • 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 (?) • δ-rays • Drift coordinate • limited by: • Pulse height fluctuation • gas gain (3 k), pad capacity, # e- per cluster

  24. Rate effects 0 Q 20 – 50 ns LHC @ max lumi: @ 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?

  25. 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)

  26. Radiation hardness • CMOS 130 nm technology: OK up to ? rad • need only modest input FETs

  27. HV breakdowns 1 High-resistive layer 3 ‘massive’ pads 2 High-resistive layer 4 Protection Network

  28. 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!

  29. 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

  30. 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.

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