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GOSSIP: a vertex detector combining a


Title: Slide 1 Author: Harry van der Graaf Last modified by: Harry van der Graaf Created Date: 4/5/2004 1:18:21 PM Document presentation format: On-screen Show – PowerPoint PPT presentation

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Title: GOSSIP: a vertex detector combining a

GOSSIP a vertex detector combining a thin gas
layer as signal generator with a CMOS readout
pixel array
Gas On Slimmed SIlicon Pixels
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
Let us eliminate wires wireless wire
chambers 1996 F. Sauli Gas Electron Multiplier
1995 Giomataris Charpak MicroMegas
Ideally a preamp/shaper/discriminator channel
below each hole.
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
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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
  • 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
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!
He/Isobutane 80/20 Modified MediPix
Sensitive area 14 x 14 x 15 mm3
Drift direction Vertical max 15 mm
He/Isobutane 80/20 Modified MediPix
Sensitive area 14 x 14 x 15 mm3
Drift direction Vertical max 15 mm
He/Isobutane 80/20 Modified MediPix
Sensitive area 14 x 14 x 15 mm3
Drift direction Vertical max 15 mm
MediPix modified by MESA, Univ. of Twente, The
Non 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
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Vernier, Moire, Nonius effect
Pitch MediPix 55 µm Pitch Micromegas 60
µm Periodic variation in gain per 12 pixels
Non-modified MediPix Modified MediPix has much
less Moire effect
Focussing on (small) anode pad Continues anode
plane is NOT required Reduction of source
No charge spread over 2 or 4 pixels
Non Modified
InGrid perfect alignment of pixels and grid
holes! Small pad small capacitance!
INtegrate Micromegas GRID and pixel sensor
By wafer post processing at MESA, Univ. of
Integrate GEM/Micromegas and pixel sensor InGrid
By wafer post processing
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  • For KABES II, there are two options.
  • The TPC with transverse drift option would need
    strips rather than pixels.
  • But it could be interesting to have an
    InGrid-like integrated mesh.
  • The thin Si or CMOSgas option would need a very
    high rate capability.
  • CAST (CERN Axion Solar Telescope) seems to be a
    more straightforward application.
  • It simply requires a possibility of triggering a
    common stop.
  • This is why Esther Ferrer-Ribas, from CAST, will
    join us.
  • - The polarimetry application (challenging
    Belazzini) is very interesting
  • for people from the Astrophysics division. The
    requirement is very similar to CAST's.
  • - The MicroTPC might have applications in
    nuclear physics or in Babar, for instance.
  • - There are other applications (X-ray beam
    monitor for SOLEIL) which I can talk about
  • - The protection issue is essential in all
    Micromegas applications.

  • ! 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 lt 25 ns (LHC
  • Replace Si sensor amplifier by gas
  • ? tracker for intense radiation environment

After all until 1990 most vertex detectors were
gas detectors! Si solved granularity problems
associated with wires.
GOSSIP Gas On Slimmed SIlicon Pixels
Micromegas (InGrid)
Cathode foil
CMOS pixel array
CMOS pixel chip
Drift gap 1 mm Max drift time 16 ns
  • 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, required for Si
    charge signals
  • 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
Ageing Efficiency Position resolution Rate
effects Radiation hardness HV breakdowns Power
dissipation Material budget
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!

  • Determined by gas layer thickness and gas
  • Number of clusters per mm 3 (Ar) 10
  • Number of electrons per cluster 3 (Ar) - 15
  • Probability to have min. 1 cluster in 1 mm Ar
  • 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 s 0.1 mm s 1.6
    ns feasible!
  • Lorentz angle
  • We want fast drifting ions (rate effect)
  • little UV photon induced avalanches good
    quenching gas

Position resolution
  • Transversal coordinates limited by
  • Diffusion single electron diffusion 0 40/70
  • weighed fit ava 20/30 µm
  • 10 e- per track s 8/10 µm
  • pixel dimensions 20 x 20 50 x 50 µm2
  • Note we MUST have sq. pixels no strips (pad
  • Good resolution in non-bending plane!
  • Pixel number has NO cost consequence (m2 Si
  • Pixel number has some effect on CMOS power
  • d-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 s 1 ns 0.1 mm

Rate effects
SLHC _at_ 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

  • Some ions crossing drift space takes 20 200
  • 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

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!
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!

HV breakdowns InGrid issue
1) High-resistive layer
3) massive pads
2) High-resistive layer
4) Protection Network
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!

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
  • 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

  • How to proceed?
  • InGrid 1 available for tests in October
  • rate effects (all except change in drift
  • 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

Dummy wafer
  • Essential Ingredients of GOSSIP CMOS chip
  • RATE
  • Assume application in Super LHC
  • Bunch crossing 25 ns
  • 10 tracks per (25 ns cm2)
  • 10 e- per track (average Landau fluct.)
  • So 4 MHz/mm2 tracks!, 40 MHz/mm2
    single electrons!

Charge signal on pixel input pad
  • Signal shape is well defined and uniform
  • No bias current, no dark current
  • Signal is subject to exponential distribution
  • may be large, but limited by
  • chamber ageing
  • space charge (rate) effects

  • Input Pad capacity
  • preamp stage, noise, power
  • Input pads may be small focusing
  • Too small pads chamber ageing
  • capacity to neighbors metal layers
  • capacity due to gas gain grid
  • Pixel size 50 x 50 - 20 x 20 µm2
  • 4 fF seems feasible

  • Time resolution
  • preamp-disc speed, noise, power
  • Measurement 3rd coordinate sdrift time 25/16
    1.5 ns
  • Time over threshold slewing correction
  • drift time related to BX
  • Record leading edge - BX
  • trailing edge - BX
  • BX ID

Data Readout ALL data 80 MB s-1 mm-2 ( 15 GB/s
per chip) Maybe possible in 10 years from
now - optical fibre per chip - Vertex can
be used as trigger For SLHC Use BX ID info
(typical Vertex policy) - tell BX ID to all
(Rows/Columns/Pixels) - get data from
  • Gossipo
  • MultiProjectWafer submit in 130 nm CMOS
  • Test of essential GOSSIP ingredients
  • Low power, low input capacity preamp/shaper/discr
  • 1.5 ns TDC (per discriminator output)
  • Data transfer
  • Maybe not all of this in a first submit
  • Maybe with less ambitious specifications

  • Amplifier-shaper-discriminator
  • How to apply a test pulse?
  • using gas gain grid (all channels fire)
  • capacitive coupling test pulse strip
  • reality with a gas gain grid(!)
  • What to do with the output?
  • (bonded) contact digital feedback?!
  • TDC DAQ?
  • TDC
  • - 1.5 ns clock derived on-board from 40 MHz BX
  • 640 MHz clock distribution (per pixel?!)
  • DLL?

  • (My) goal of this meeting
  • Are there any showstoppers in this stage?
  • can we define a Gossipo concept (block diagram)?
  • Can we estimate the amount of work?
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