GOSSIP: a vertex detector combining a

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GOSSIP a vertex detector combining a thin gas
layer as signal generator with a CMOS readout
pixel array
GOSSIP
Gas On Slimmed SIlicon Pixels
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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
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Let us eliminate wires wireless wire
chambers 1996 F. Sauli Gas Electron Multiplier
(GEM)
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1995 Giomataris Charpak MicroMegas
Ideally a preamp/shaper/discriminator channel
below each hole.
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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!
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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 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!
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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
Sensitive area 14 x 14 x 15 mm3
Drift direction Vertical max 15 mm
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He/Isobutane 80/20 Modified MediPix
d-ray?
Sensitive area 14 x 14 x 15 mm3
Drift direction Vertical max 15 mm
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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 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
capacity!
No charge spread over 2 or 4 pixels
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De-focussing
Modified
focusing
De-focussing
Non Modified
focusing
InGrid perfect alignment of pixels and grid
holes! Small pad small capacitance!
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INtegrate Micromegas GRID and pixel sensor
InGrid
By wafer post processing at MESA, Univ. of
Twente
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Integrate GEM/Micromegas and pixel sensor InGrid
GEM
Micromegas
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
  tomorrow.
• - The protection issue is essential in all
  Micromegas applications.

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

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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 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

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Position resolution

• Transversal coordinates limited by
• Diffusion single electron diffusion 0 40/70
  µm
• 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
  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
• 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

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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

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

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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!
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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!

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

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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
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• 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

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• 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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• 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!

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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

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• 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

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• 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

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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
(Row/Column/Pixel)
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• Gossipo
• MultiProjectWafer submit in 130 nm CMOS
  technology
• Test of essential GOSSIP ingredients
• Low power, low input capacity preamp/shaper/discr
  iminator
• 1.5 ns TDC (per discriminator output)
• Data transfer
• Maybe not all of this in a first submit
• Maybe with less ambitious specifications

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• 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
  clock?
• 640 MHz clock distribution (per pixel?!)
• DLL?

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• (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?