GOSSIP : Gas On Slimmed SIlicon Pixels NIKHEFAuke-Pieter Colijn Alessandro Fornaini Harry van der Graaf Peter Kluit Jan Timmermans Jan Visschers Saclay CEA DAPNIAMaximilien Chefdeville Paul Colas Yannis Giomataris Arnaud Giganon Univ. Twente/Mesa+Jurriaan Schmitz CERN/Medipix ConstmEric Heijne Xavie Llopart Michael Campbell Thanks to: Wim Gotink Joop Rovenkamp

Cathode foil Gem foils Support plate Medipix 2 Drift Space The MediPix2 pixel CMOS chip We apply the ‘naked’ MediPix2 chip without X-ray convertor!

MediPix2 pixel sensor Brass spacer block Printed circuit board Aluminum base plate Micromegas Cathode (drift) plane 55 Fe Baseplate Drift space: 15 mm Very strong E-field above (CMOS) MediPix!

We always knew, but never saw: the conversion of 55 Fe quanta in Ar gas No source, 1s 55 Fe, 1s 55 Fe, 10s Friday 13 (!) Feb 2004: signals from a 55 Fe source (220 e- per photon); 300  m x 500  m clouds as expected 14 mm The Medipix CMOS chip faces an electric field of 350 V/50 μm = 7 kV/mm !!

Eff = e -Thr/G Thr: threshold setting (#e-) G: Gas amplification Prob(n) = 1/G. e -n/G 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

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 – New Medipix New Micromegas Gas: He/Isobutane 80/20 !Gain up to 30 k! He/CF4 80/20 …… It Works!

He/Isobutane 80/20 Modified MediPix Sensitive area: 14 x 14 x 15 mm 3 Drift direction: Vertical max = 15 mm

He/Isobutane 80/20 Modified MediPix

He/Isobutane 80/20 Modified MediPix

He/Isobutane 80/20 Non Modified MediPix Americium Source

He/Isobutane 80/20 Modified MediPix

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

MediPix modified by MESA+, Univ. of Twente, The Netherlands Pixel Pitch: 55 x 55 μm 2 Bump Bond pad: 25 μm octagonal 75 % surface: pacivation SiN New Pixel Pad: 45 x 45 μm 2 Insulating surface was 75 % Reduced to 20 % Non ModifiedModified

Non Modified Modified 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!

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

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

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

1.WSLC-Paris 2004: LC ready in 2015…, not known where….. 2.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

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

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

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

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 3 rd 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

Position resolution Transversal coordinates limited by: pixel dimensions: 20 x 20 – 50 x 50 μm 2 Note: we MUST have pixels: no strips (pad capacity/noise) Good resolution in non-bending plane! Pixel number has NO cost consequence (m 2 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 0Q0Q 20 – 50 ns

Rate effects time 0Q0Q 20 – 50 ns 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: max 2 cm from beam pipe: 10 tracks cm ns MHz cm -2 ! 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?

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)

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

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

Power dissipation MediPix2: 1 W/cm 2 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!

Material budget ‘Slimmed’ Si CMOS chip: 30 μm Si Pixel resistive layer5 μm SiN 2 Anode pads5 μm Al Grid1 μm Al Grid resistive layer5 μm SiN2 Cathode1 μm Al CF string support, gas tubing, power

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.