Micropattern on CMOS pixels

NIKHEF Maximilien ChefdevilleAuke-Pieter ColijnAlessandro FornainiHarry van der GraafPeter KluitJan TimmermansJan Visschers

Saclay CEA-DAPNIA Paul ColasYannis GiomatarisArnaud Giganon

Univ. Twente/Mesa+ Jurriaan Schmitz

CERN/Medipix Constm Erik HeijneXavie LlopartMichael Campbell

Thanks to:Wim GotinkJoop RovenkampArnaud Giganon

Harry van der Graaf

NIKHEF

SECOND WORKSHOP ON LARGE TPCFORLOW ENERGY RARE EVENT DETECTION

LPNHE - Paris VI and VII Universities  PARIS, France 20 December 2004

Time Projection Chamber (TPC): 2D/3D Drift ChamberThe Ultimate Wire (drift) Chamber

E-field(and B-field)

Wire Plane+Readout Pads

track ofchargedparticle

Wire plane

Pad plane

Giomataris & Charpak1995: Micromegas

Ideally: a preamp/shaper/discriminator channel below each hole….

Let us eliminate wires:• wireless wire chambers• better granularity

1996: F. Sauli: Gas Electron Multiplier (GEM)

The MediPix2 pixel CMOS chip

256 x 256 pixelspixel: 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 chipwithout X-ray convertor!

Problem

With wires: measure charge distribution over cathode pads:c.o.g. is a good measure for track position;With GEMs or Micromegas: narrow charge distribution(only electron movement)

wireavalanche

Cathode pads

GEMMicromegas

Solutions: - cover pads with resistive layer- ‘Chevron’ pads- many small pads: pixels

DriftSpace

GEM foils

MediPix CMOS pixel sensorBrass spacer blockPrinted circuit boardAluminium base plate

Our GEM-equipped TPCWe have constructed a small test TPC equipped with three GEM foils whichcan be read out by means of the MEDIPIX2 CMOS pixel sensor.The GEM foils were obtained from the CERN/Sauli/GEM group;hole-to-hole distance (hexagonal geometry): 140 µm, hole diameter 85 µm,fiducial surface 100 mm x 100 mm, thickness 50 µm.The drift volume (vol. 100x100x100 mm3) is surrounded by square wire loops,spaced 6.3 mm, put at decreasing potential. Three GEM foils are placed 7.4 mmbehind the plane of the bottom wire loop; the distance between GEM foils is 1.6 mm.The anode plane, at ground potential, is 6.6 mm below the third GEM foil.

A new readout for the TESLA TPC:Each GEM hole gets its own preamp/shaper/discriminator:

Cathode foil

Gem foils

Support plate

Medipix 2

Drift Space

The MediPix2 pixel CMOS chip

We apply the ‘naked’ MediPix2 chipwithout X-ray convertor!

First events, recorded on March 29, 2003.Drift space irradiated with 55Fe quantaGas: Ar/Methane 90/10

No source; exposed 0.01 s No source; exposed 2 s No source; exposed 2 s

No source; exposed 0.1 s 90Sr source; exposed 0.01 s

Fiducial field:14 x 14 mm2

Collected ionisationin 14 x 14 x 100 mm3

during exposure timeGas: Ar/Isobutane 90/10

Feb 9, 2004

MediPix2 pixel sensorBrass spacer blockPrinted circuit boardAluminum base plate

Micromegas

Cathode (drift) plane

55Fe

Baseplate

Drift space: 15 mm

With Paul Colas & Yannes Giomataris:MediPix2 & Micromegas

Very strong E-field above (CMOS) MediPix!

MediPix modified by MESA+, Univ. of Twente, The Netherlands

Pixel Pitch: 55 x 55 μm2

Bump Bond pad: 25 μm octagonal75 % surface: pacivation SiNNew Pixel Pad: 45 x 45 μm2

Insulating surface was 75 %Reduced to 20 %

We always knew, but never saw: the conversion of 55Fe quanta in Ar gas

No source, 1sNo source, 1s5555Fe, 1sFe, 1s

5555Fe, 10sFe, 10s

Friday 13 (!) Feb 2004: signals from a 55Fe source (220 e- per photon); 300 m x 500 m clouds as expected

14 mm

The Medipix CMOS chip facesan electric field of 350 V/50 μm

= 7 kV/mm !!

Eff = e-Thr/G

Thr: threshold setting (#e-)G: Gas amplification

Single electron efficiency

0.00

0.20

0.40

0.60

0.80

1.00

0 1000 2000 3000 4000

Threshold setting (number of electrons)

Eff

icie

ncy

(-)

G=500

G=1000

g=2000

g=4000

g=8000

Expon. (G=500)

Expon. (G=1000)

Expon. (g=2000)

Expon. (g=4000)

Expon. (g=8000)

single-electron avalanche distribution

0

0.0005

0.001

0.0015

0.002

0 1000 2000 3000 4000

electrons in avalanche

Pro

b(n

)

G=500

G=1000

G=2000

G=4000

G=8000

Expon. (G=500)

Expon. (G=1000)

Expon. (G=2000)

Expon. (G=4000)

Expon. (G=8000)Prob(n) = 1/G . e-n/G

• no attachment• homogeneous field in avalanche gap• low gas gain

No Curran or Polyadistributions but simply:

Single electron efficiency

New trial: NIKHEF, March 30 – April 2, 2004Essential: try to see single electrons from cosmic muons (MIPs)

Pixel preamp threshold: 3000 e-Required gain: 5000 – 10.000

New MedipixNew Micromegas

Gas: He/Isobutane 80/20Ar/Isobutane 80/20He/CF4 80/20

…… It Works!

He/Isobutane80/20Modified MediPix

Sensitive area:14 x 14 x 15 mm3

Drift direction:Verticalmax = 15 mm

He/Isobutane80/20Modified MediPix

He/Isobutane80/20Modified MediPix

He/Isobutane80/20Non ModifiedMediPix

Amaricium Source

He/Isobutane80/20Modified MediPix

He/Isobutane80/20Modified MediPix

δ-ray!

For TPCs: all primary electron info is used, onlydiffused by diffusion!

• Simulations: TPC performance in view of single electron detection:

• spatial resolution (= momentum resolution)• precision dE/dX by cluster counting (M. Hauschild)• multi track separation• corrections for scattering• δ-ray suppression

Low diffusionlow number of clusters?

• Form collaboration to develop TimePix CMOS pixel chip:

• based on MediPix: change pixel counters into TDCs• require full scale! Submit costs 150 kE for 6 wafers…• MediPix Consortium (CERN based) likes to design TimePix1

INtegrate (Micromegas) GRID and pixel sensor

‘Micromegas’

By ‘wafer post processing’at MESA+, Univ. of Twente

InGrid

InGrid + Pixel chip=

GridPix

Integrate GEM/Micromegas and pixel sensor: InGrid

‘GEM’ ‘Micromegas’

By ‘wafer post processing’

First InGrid has been delivered

Wafer dia.: 100 mm30 fields with a variety of pillar (spacer) geometry

HV breakdowns: issue for InGrid 2

4) Protection Network

1) High-resistive layer

2) High-resistive layer

3) ‘massive’ pads

Vernier, Moire, Nonius effect

Pitch MediPix: 55 μmPitch Micromegas: 60 μm

Periodic variation in gain per 12 pixels

Focussing on (small) anode padContinues anode plane is NOT requiredReduction of source capacity!

Non-modified MediPixModified MediPix has much less Moire effect

No charge spread over2 or 4 pixels

Modified

Non Modified

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

focusing De-focussingLow E-fieldLow gas gain

GridPix could become a general way toreadout gaseous chambers

Other applications of GridPix:

- μ-TPC- Transition Radiation Detectors- GOSSIP: vertex detector for intense radiation environment

CMOS pixel array

MIP

Micromegas (InGrid)

GOSSIP: Gas On Slimmed SIlicon Pixels

Drift gap: 1 mmMax drift time: 15 ns

MIP

CMOS chip

Cathode foil

GOSSIP?

AgeingEfficiencyPosition resolutionRate effectsRadiation hardnessHV breakdownsPower dissipationMaterial budget

AgeingRemember 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!Now being set-up with X-ray generator (Panalytical/Philips)

Spatial resolution: pixels down to 20x 20 μm2 may be useful

After all: TPC! 3D track info

Counting rate in Super LHC (no Si Vertex compatitor) :10 tracks/ (cm2 25 ns): ions reach grid within 10 – 30 ns

Radiation hardness:- Replace electron-hole pair generation in Si by gas + gas amplification- Sufficient signal charge to eliminate low-noise amplifiers in pixels- CMOS readout circuit: only digital gates (130 nm technology)

Material budget: only slimmed Si (40 μm), 1 mm gas

Cooling: CMOS chip power < 0.1 W/cm2: use gas flow as cooling…..

If it works: interesting for ATLAS, CMS, LHCb, ALICE, D0 etc

How to proceed?

- InGrid 1 available for tests:- 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)

- TimePix: convincing 5 institutes to participate (we have 3 already!)

- GOSSIPO: CMOS chip for Multi Project Wafer test chip in 130 nm tech.

- Apply InGrid 2 on ATLAS FE Pixel chip: GOSSIP proof-of-principle

Dummy wafer

Micropattern on CMOS pixels

NIKHEF Maximilien ChefdevilleAuke-Pieter ColijnAlessandro FornainiHarry van der GraafPeter KluitJan TimmermansJan Visschers

Saclay CEA DAPNIA Paul ColasYannis GiomatarisArnaud Giganon

Univ. Twente/Mesa+ Jurriaan Schmitz

CERN/Medipix Constm Eric HeijneXavie LlopartMichael Campbell

Thanks to:Wim GotinkJoop RovenkampArnaud Giganon

Harry van der Graaf

NIKHEF

SECOND WORKSHOP ON LARGE TPCFORLOW ENERGY RARE EVENT DETECTION

LPNHE - Paris VI and VII Universities  PARIS, France 20 December 2004