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Gas-On-Slimmed-Silicon Pixels (GOSSIP): A Vertex Detector Combining a Thin Gas Layer as Signal Generator with a CMOS Rea

This paper discusses the development of the Gas-On-Slimmed-Silicon Pixels (GOSSIP) vertex detector, which combines a thin gas layer as a signal generator with a CMOS readout pixel array. The detector achieves high efficiency and resolution, with low radiation damage and power dissipation.

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Gas-On-Slimmed-Silicon Pixels (GOSSIP): A Vertex Detector Combining a Thin Gas Layer as Signal Generator with a CMOS Rea

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  1. GOSSIP: a vertex detector combining a thin gas layer as signal generator with a CMOS readout pixel array Harry van der Graaf, NIKHEF Vertex 2004, Menaggio, 17 sept Gas On SlimmedSIlicon Pixels NIKHEF Auke-Pieter Colijn Alessandro Fornaini Harry van der Graaf Peter Kluit Jan Timmermans Jan Visschers Maximilien Chefdeville Saclay CEA DAPNIA Paul Colas Yannis Giomataris Arnaud Giganon Univ. Twente/Mesa+ Jurriaan Schmitz CERN/Medipix Constm Eric Heijne Xavie Llopart Michael Campbell GOSSIP

  2. Original motivation: Si pixel readout for the Time Projection Chamber (TPC) at TESLA (now ILC)

  3. Time Projection Chamber (TPC): 2D/3D Drift Chamber The Ultimate Wire (drift) Chamber track of charged particle E-field (and B-field) Wire plane Wire Plane + Readout Pads Pad plane

  4. Let us eliminate wires: wireless wire chambers 1996: F. Sauli: Gas Electron Multiplier (GEM)

  5. 1995 Giomataris & Charpak: MicroMegas Ideally: a preamp/shaper/discriminator channel below each hole….

  6. The MediPix2 pixel CMOS chip 256 x 256 pixels pixel: 55 x 55 μm2 per pixel: - preamp - shaper - 2 discr. - Thresh. DAQ - 14 bit counter - enable counting - stop counting - readout image frame - reset We apply the ‘naked’ MediPix2 chip without X-ray convertor!

  7. Cubic drift volume: 14 x 14 x 14 mm3 Cathode (drift) plane: - 700 V Drift space: 15 mm (gas filled) Micromegas: - 350 V Baseplate MediPix2 pixel sensor Brass spacer block Printed circuit board Aluminum base plate cosmic muon Very strong E-field above (CMOS) MediPix!

  8. 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

  9. 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

  10. 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 analog-digital 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!

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

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

  13. He/Isobutane 80/20 Modified MediPix δ-ray? Sensitive area: 14 x 14 x 15 mm3 Drift direction: Vertical max = 15 mm

  14. 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: passivation Si3N4 New Pixel Pad: 45 x 45 μm2 Insulating surface was 75 % Reduced to 20 %

  15. ‘Micromegas’ INtegrate Micromegas GRID and pixel sensor InGrid By ‘wafer post processing’ at MESA+, Univ. of Twente

  16. ! With 1 mm layer of (Ar/Isobutane) gas we have a fast TPC! • thick enough for 99 % MIP detection efficiency • thin enough for max. drift time < 25 ns (LHC bunchX) • Replace {Si sensor + amplifier} by gas layer: •  tracker for intense radiation environment After all: until 1990 most vertex detectors were gas detectors! Si solved granularity problems associated with wires.

  17. GOSSIP: Gas On Slimmed SIlicon Pixels MIP MIP Micromegas (InGrid) Cathode foil CMOS pixel array CMOS pixel chip Drift gap: 1 mm Max drift time: 16 ns

  18. 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 preamps • No detector bias current • 1 mm gas layer + 20 μm gain gap + CMOS (almost digital!) chip • After all: it is a TPC with 1 mm drift length (parallax error!) Max. drift length: 1 mm Max. drift time: 16 ns Resolution: 0.1 mm  1.6 ns

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

  20. Ageing Remember the MSGCs…… • Little ageing: • the ratio (anode surface)/(gas volume) is very high w.r.t. wire chambers • little gas gain: 5 k for GOSSIP, 20 – 200 k for wire chambers • 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) • But: critical issue: ageing studies can not be much accelerated!

  21. Efficiency • Determined by gas layer thickness and gas mixture: • Number of clusters per mm: 3 (Ar) – 10 (Isobutane) • Number of electrons per cluster: 3 (Ar) - 15 (Isobutane) • Probability to have min. 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 16 ns; σ = 0.1 mm; σ = 1.6 ns: feasible! • Lorentz angle • We want fast drifting ions (rate effect) • little UV photon induced avalanches: good quenching gas

  22. Position resolution 0 Q 20 ns • Transversal coordinates limited by: • Diffusion: single electron diffusion 0 – 40/70 µm • weighed fit: ava 20/30 µm • 10 e- per track: σ = 8/10 µm • pixel dimensions: 20 x 20 – 50 x 50 μm2 • Note: we MUST have sq. 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 • δ-rays: can be recognised & eliminated • 3rd (drift) coordinate • limited by: • Pulse height fluctuation • gas gain (5 k), pad capacity, # e- per cluster • With Time Over Threshold: σ = 1 ns ~~ 0.1 mm

  23. Rate effects 0 Q 20 ns SLHC @ 2 cm from beam pipe: 10 tracks cm-2 25 ns-1 400 MHz cm-2! • ~10 e- per track (average) • gas gain 5 k • most ions are discharged at grid • after traveling time of 20 ns • a few percent enter the drift space: time • Some ions crossing drift space: takes 20 – 200 μs! • 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: change in lorentz angle ~0.1 rad • B-field should help

  24. Data rate Hit Pixel (single electron) data: 8 bit column ID 8 bit row ID 4 bit timing leading edge 4 bit timing trailing edge total 24 bits/hit pixel 100 e-/ 25 ns cm2 380 Gb/s per chip (2 x 2 cm2) Cluster finding: reduction factor 10: 40 Gb/s Horisberger: Data rate, DAQ, data transmission is a limiting factor for SLHC Required: rad hard optical links with 1 mm3 light emittors per chip!

  25. Radiation hardness • Gas is refreshed: no damage • CMOS 130 nm technology: ? TID • ? NIEL • ? SEU: design/test • need only modest pixel input stage • How is 40 Gb/s hit pixel data transferred? • need rad hard optical link per chip!

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

  27. Power dissipation • For GOSSIP CMOS Pixel chip: • Per pixel: • - input stage (1.8 μA/pixel) • monostable disc/gate • Futher: data transfer logic • guess: 0.1 W/cm2 •  Gas Cooling feasible!

  28. Detector Material budget ‘Slimmed’ Si CMOS chip: 20 μm Si Pixel resistive layer 1 μm SU8 eq. Anode pads 1 μm Al Grid 1 μm Al Grid resistive layer 5 μm SU8 eq. Cathode 1 μm Al

  29. Gas instead of Si • Pro: • no radiation damage in sensor • modest pixel input circuitry • no bias current, no dark current (in absence of HV breakdowns..!) • requires (almost) only digital CMOS readout chip • low detector material budget • Typical: Si foil. New mechanical concepts: • self-supporting pressurised co-centric balloons • low power dissipation • (12”) CMOS wafer  Wafer Post Processing  dicing 12” pcs • no bump bonding • ‘simple’ assembly • operates at room temperature • less sensitive for X-ray background • 3D track info per layer • Con: • Gas chamber ageing: not known at this stage • Needs gas flow (but can be used for cooling….)

  30. How to proceed? • InGrid 1 available for tests in October: • rate effects (all except change in drift direction) • ageing (start of test) •  Proof-of-principle of signal generator: Xmas 2004! • InGrid 2: HV breakdowns, beamtests with MediPix (TimePix1 in 2005) • TimePix2: CMOS chip for Multi Project Wafer test chip • GOSSIPO ! Dummy wafer

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