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GOSSIP : a vertex detector combining a thin gas layer as signal generator with a CMOS readout pixel array. GOSSIP. G as O n S limmed SI licon P ixels. Time Projection Chamber (TPC): 2D/3D Drift Chamber The Ultimate Wire (drift) Chamber. track of charged particle. E-field

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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 SlimmedSIlicon 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 (GEM)


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 convertor!


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!


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


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


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

δ-ray?

Sensitive area:

14 x 14 x 15 mm3

Drift direction:

Vertical

max = 15 mm


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 %


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


De-focussing

Modified

focusing

De-focussing

focusing

Non Modified

InGrid: perfect alignment of pixels and grid holes!

Small pad: small capacitance!


‘Micromegas’

INtegrate Micromegas GRID and pixel sensor

InGrid

By ‘wafer post processing’

at MESA+, Univ. of Twente


Integrate GEM/Micromegas and pixel sensor: InGrid

‘GEM’

‘Micromegas’

By ‘wafer post processing’


  • 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 CMOS+gas 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.


After all: until 1990 most vertex detectors were gas detectors!

Si solved granularity problems associated with wires.


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


  • 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


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!


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


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


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


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

  • Needs gas flow (but can be used for cooling….)


  • 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


  • 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!


Q

10 - 20 ns

Chargesignal 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: σdrift 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 (Row/Column/Pixel)


  • Gossipo

  • MultiProjectWafer submit in 130 nm CMOS technology

  • Test of essential GOSSIP ingredients:

  • Low power, low input capacity preamp/shaper/discriminator

  • 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 clock?

  • 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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