Reaction on the review document Gossip_091215x dd 11-1-2010 of the Gossip R&D proposal

Fred Hartjes 1

Review of the Gossip R&D proposal for ATLAS at the sLHC

CERN, February 8, 2010

Reaction on the review document Gossip_091215.pptx dd 11-1-2010 of the Gossip R&D proposal

Discussion on the review of the Gossip R&D proposalCERN, February 8, 2010

Reviewers Tatsuo Kawamoto Werner Riegler Mike Tyndal Norbert Wermes

Reaction by Harry van der Graaf Fred Hartjes Nigel Hessey

Reviewed by Atlas Upgrade Steering Group

Fred Hartjes 2



Points of discussion distilled from the review document Gossip_091215.pptx

The committee would like to have more details about advantages and disadvantages of Gossip

Replacing Si with gas does not substantially reduce the material budget

What’s the point with dE/dx? How does it work?

Do we want TR, how would it be achieved?

What’s the advantage of getting rid of delta rays?

Gaseous detector is not better with neutrons

Why is the power less, there is more digital power?

Power reduction only applies to analogue part (<50%)

Is InGrid technology cheaper than bump bonding?

We will not address these points as such, but in the framework of the answers to the other points of discussion the committee brought forward

Fred Hartjes 3



Scope of this presentation

Focussing on subjects specific for Gossip technology

Ignoring generic subjects like Optical links (Iflink) Powering (optical) Cooling technology (CO2) Mechanical support

Questions classified in general subjects

Fred Hartjes 4



Questions/ comments by the committee

Fred Hartjes 5



Classes of questions

1. Working point2. Target regions3. Performance

ageing, rate tolerance, efficiency, delta rays, track segment info, field distortions, X/X0

4. Sparking5. Frontend electronics

Noise level, threshold, power consumption, readout

6. Photolithography Production of Ingrid

7. Miscellaneous Grid capacity, cooling

8. Organization of the Gossip R&D Collaboration, milestones

Fred Hartjes 6



1. Working point

2. Target regions1. Working point

Grid voltage gap width cell size gas mixture shaping time ionization

2. What are the target regions for putting the Gossip technology? => formulate essential goals to be met for Gossip working in these regions Outer GridPix detector with 50% of silicon material?

Fred Hartjes 7



3. Performance Ageing

Expectations How to study?

Rate performance Field distortion by ions Rate limit How to study?

Efficiency Delta rays

Why is it good to get rid of them? Compared to silicon

How to deal with track segment info? Implementing L1 trigger? Implications on RO rate?

Cooling Required capacity compared to silicon? Why dependence on operation temperature?

X/X0 In reality 1.5 – 2% What’s the difference with silicon and where does it come from?

Fred Hartjes 8



4. Sparking

Protection layer What materials are considered? Are there pinholes, can they cause damage, how likely? Temperature sensitivity? Pulse height dependence on layer thickness and resistivity? Effect on rate? Omitting Si3N4 layer in case of layer on InGrid or when using TwinGrid?

=> all these questions to be answered at session 6. (photolithography)

Demonstration for large system

Sparking rate?

How long insensitive and across which surface?

Demonstrate proper operation in harsh environment (fwd region of present LHC)

Fred Hartjes 9



5. Frontend electronics

Threshold should be increased because of threshold dispersion

Operating at threshold of 350 e- (= 5 x 70 e-) is not realistic => need ≥ 5 times higher threshold

Why less power consumption?

Readout How to handle the 3 – 10x larger data volume

Fred Hartjes 10



6. Photolithography

InGrid technology Processing temperature? Which companies are able to produce it? On wafer scale? Testing? Yield? Imperfections? How far advanced? Processing a 50 µm thick wafer? Maximum thickness? Any stresses?

TwinGrid Is gain of TwinGrid the multiplication of the gains of each of the grids? TwinGrid yield?

Fred Hartjes 11



7. Miscellaneous

Grid capacity of 100 nF? Typo => InGrid of 15 x 15 mm2 has ~40 pF capacity

Thinning How to do thinning in practise? (I think: thin chips with handle on CMOS side, put handle on back-side, make InGrid,

add gasCap, release handle?)

Fred Hartjes 12



8. Organization of the Gossip R&D

Collaboration Present sharing of workload and costs? Resources to prototype full wafers?

Define path cq milestones (with dates) leading to the production of a few demonstrators To become a serious option for an application in ATLAS at the sLHC

Fred Hartjes 13



Answers to the questions

Fred Hartjes 14



1. Working point Grid voltage

Depends on the gas mixture - 400 – 450 V for mixtures with a large content of

inert gases (He/iC4H10 80/20, Ar/CH2 90/10, ....) - 550 - 600 V for a very slow gas like DME/CO2

50/50 (present favourite)

Width drift gap 1.0 – 1.2 mm, depending on the ionization of the

applied gas mixture and the required efficiency Example: DME/CO2 50/50 Efficiency on any ionization from a MIP for a

drift gap of 1.0 mm => 98.9%

Cell size Simulations have shown that a smaller cell sizes

gives better resolution 60 x 60 µm possible for 130 nm technology

Estimate for Gossipo-4 chip

Fig. . The spatial resolution X – X0 vs agle of incidence φ for different (square) pixel pitches, assuming a perfect time measurement.

InGrid -550V

Pixel chip

Amplification gap

10 kV/mm

100 - 700 V/mm

50 µ

m

0V

Fred Hartjes 15



1. Working point (cntd)gas mixture

Our favourite is presently DME/CO2 50/50 Low diffusion (70 – 100 µm/√cm) Low Lorentz angle (9º @ 2T) Good cluster density (45 cl/cm)

125 electrons/cm

80 pixels (4.4 mm) 80 pixels (4.4 mm)

Ar/iC4H10 80/20(June 2009 testbeam)

CO2/DME 50/50

Testbeam Septem

ber 2009

Limited (38%) si

ngle e- ef

f.

Fred Hartjes 16



1. Working point (cntd)gas mixture

Gossip working point

DME/CO2 is a very “viscous” gas for electrons Vd ≈ 50 µm/ns @ E = 6 kV/cm

Fred Hartjes 17



1. Working point (cntd)Shaping time

Aim making peaking time half the ionic drift

time Gossipo-2: peaking time 30 ns Gossipo-3: will be reduced to 25 ns

Shaping time ~ 30 ns for delta pulse ~ 70 ns for detector signal

More details in the ASIC session

7500 e-deltapulse

Gossippulse

Simulation Gossipo-2

Fred Hartjes 18



2. Possible target regions for Gossip and GridPixsLHC fluences

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2. Possible target regions for Gossip and GridPixHigh rate pixel layers at the sLHC (R = 37 mm, b-layer)

Motivation Outlook for constant charge signal over the full lifetime at the sLHC

Without retuning grid voltage Less material for the full structure including services and support than for most

other technologies [ref. slide 37] Hard to quantify at this stage of development, but substantial reduction of X/X0 expected Absence of detection material (only gas) No bump bonds Relaxed cooling requirements

Requirements Radiative dose: until 2*1016 neq/cm2 => 3.4*1016 hadrons/cm2 (mostly pions) Rate up to 900 MHz/cm2 charged particles Background of

~ 200 MHz/cm2 neutrons Gammas, alfas, slow electrons .....

Fred Hartjes 20



2. Possible target regions for Gossip and GridPixintermediate region (R ≈ 400 - 600 mm)

“Outer GridPix detector with 50% of silicon material?”

Motivation Rather cheap coverage with high granularity layer Mass expected to be lower than using siliconBut less advantage than in the hot parts of Atlas Silicon has here less dense RO less generated heat less dense services

Requirements Radiative dose: ~1014 hadrons/cm2 (mostly pions) Rate up to ~3 MHz/cm2 charged particles Background of ~10 MHz/cm2 neutrons Gammas, alfas, slow electrons .....

Fred Hartjes 21



2. Possible target regions for Gossip and GridPixGridPix as a L1 trigger

R = 850 -1150 mm Drift gap ~ 16 mm Using “regular” gas mixture for drift chambers (not DME/CO2)

Motivation Using ID tracker info for sharper L1 trigger

Requirements Radiative dose: ~ 3*1013 hadrons/cm2 mostly pions Rate ~ 1 MHz/cm2 charged particles Background of ~7 MHz/cm2 neutrons Gammas, alfas, slow electrons .....

Fred Hartjes 22



2. Possible target regions for Gossip and GridPixGridPix as TRT Like L1 trigger layers

R = 850 -1150 mm Drift gap ~ 16 mm

Using Xe based mixture

Motivation e/ separation

Investigated in 2008 test beam 90% electron efficiency with 2% false pions achievable using two

layers

Requirements Radiative dose: ~ 3*1013 hadrons/cm2

mostly pions Rate ~ 1 MHz/cm2 charged particles Background of

~7 MHz/cm2 neutrons Gammas, alfas, slow electrons .....

Fig. . Measured pion rejection power for two detector layers using the cluster counting method.

1 layer

2 layers

0.001

0.01

0.1

1

0.6 0.7 0.8 0.9 1Electron efficiency

Pio

n ef

ficie

ncy

Cluster counting

Pion registration efficiency as a function of electron efficiency for 1 and 2 layers of the

detector. Cluster counting method.TRD with two detector layers (total thickness ~ 40 cm) allows to

achieve rejection factor of ~ 50 for 90% electron efficiency.

1 layer

2 layers

0.001

0.01

0.1

1


Pio

n ef

ficie

ncy

Cluster counting1 layer

2 layers

0.001

0.01

0.1

1


Pio

n ef

ficie

ncy

Cluster counting

Pion registration efficiency as a function of electron efficiency for 1 and 2 layers of the

detector. Cluster counting method.TRD with two detector layers (total thickness ~ 40 cm) allows to

achieve rejection factor of ~ 50 for 90% electron efficiency.

Fred Hartjes 23



3. Performanceageing

No ageing of the detection medium (chamber gas) Ageing of the construction materials

Not incorporated in Gossip research (not Gossip specific) Metals, ceramics, glass can (reasonably) sustain 2*1016 neq/cm2 (950 Mrad) Also some plastics (PEEK) are OK

For Gossip R&D we presently focus on ageing by gas avalanche => figure of merit is collected charge, NOT accumulated dose Ageing in the form of a continuous or grainy deposit, disturbing the avalanche field

=> smaller charge signals, broader signal distribution Accelerated ageing (3 – 4 orders of magnitude possible) may be induced by minor

concentrations (ppM – ppB level) of certain (organic) pollutants Can be avoided by careful gas handling

Avoiding suspicious (most) plastics Constructing detectors from safe materials Not using glues (Araldite) but metals, ceramics, glass Using appropriate filters (molecular sieves)

Note: Ageing by gas avalanche only proceeds under grid voltage => no ageing during beam fill, tuning, machine development

A. Romaniuk et al, A. Romaniuk et al, Nucl. Instr. and Meth. A515(2003)166Nucl. Instr. and Meth. A515(2003)166

Fred Hartjes 24



3. Performanceageing (cntd)

Fluence on the b-layer at sLHC in phase II Dose@R = 37 mm

At b-layer radiative dose is dominated by direct tracks Assume 3000 fb-1 data * safety factor 2 * 79 mb pp Xsec * 6.3 tracks/ /interaction 3*1017 tracks/ (mostly pions) At R = 37 mm, 1 cm is 0.269 units of and 0.268 units of out of 2

at R = 37 mm we get 3.4*1016 charged particles/cm2

(Damage factor ~0.6 for pions 2.0*1016 neq/cm2 relevant for Si)

Rate 0.9 GHz/cm2 for 25ns sLHC Corres

ponds to 9.5 * 106 Gy (950 Mrad

)

Data from Atlas experts (Craig Buttar, Ian Dawson and Nigel Hessey)

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3. Performanceageing (cntd)

Target dose values for Gossip radiation tolerance

Expressing dose as charge per cm2 (rather than neq/cm2) Assume

Gas gain = 5000 12.6 e- average ionization across 1.0 mm (DME/CO2 50/50)

1 MIP => 10 fC

sLHC BL dose of 3.4*1016 MIPs/cm2 translates into 342 C/cm2

Comparison to numbers for wire chambers Assume sense wire Ø 20 µm

342 C/cm2 ↔ 2.1 C/cm

Fair number for wire chambers

Well possible if outgassing elements are avoided

Fred Hartjes 26



Performanceageing (cntd)

Example: wire chamber ageing

Obtaining 2.1 C/cm well possible

R. Openshaw et al, Tests of wire chamber ageing with CF4/isobutane (80:20), argon/ethane (50:50) and argon/ethane/CF4 (48:48:4), IEEE Transactions on Nuclear Science, Vol. 36, No. 1, February 1989

Fred Hartjes 27



3. Performanceageing (how to study)

Target for b-layer at sLHC 2*1016 neq/cm2 => 3.4*1016 cm-2 charged hadrons (mostly pions)

Ageing studies harder than for solid state detectors because of the rate limitations of the avalanche process Gossip will not operate at 100 – 1000 x increased sLHC rate X-rays (like from GIF++) cannot be used

Other ionization profile (large clusters instead of short MIP tracks) Upgraded PS beam too intense Present PS beam might be just OK, but we cannot claim continuously it for many months

Solution: dedicated MIP source (up to ~ 1.8 GHz/cm2) at Nikhef

In addition ageing tests at other particle sources (neutrons) have to be done as well

Fred Hartjes 28



Calculated particle rate as a function of the distance d to a 90Sr sourceCorrected for ionization measurement on 9-4-08 and for 2.5% covered pixels

d(mm)

5 10 15 20 25 30

rate

(GH

z/cm

2 )

0.03

0.04

0.05

0.06

0.07

0.080.09

0.2

0.3

0.4

0.5

0.6

0.7

0.80.9

2

3

0.1

1

Correction factor 0.860

source activity 5 GBqsource diameter 5 mm13-5-2008

3. Performanceageing (Nikhef facility)

Nikhef setup using powerful 90Sr source (5 GBq)

Tiny irradiated surface (< 1 cm2)

Emitting ~ 2 MeV s (~MIPs) MIP rate up to 1.8 GHz/cm2

Tests time consuming Up to 4.8 x 1015/month ~ some 7 months for full b-

layer lifetime

Fred Hartjes 29



Gossip 23Nov 28Ar/iC4H10 70/30Particle flux: 1.6 GHz

Gossip ageing using mips from 90Sr source

Time (days)0 5 10 15 20 25

I cent

re (n

A)

0

50

100

150

200

G = 1000 G = 1000

Fluence (mips/cm2)0 1e+15 2e+15 3e+15

C/cm20 2 4 6 8 10 12

switch fromVgrid = -635 to -640 V

3. Performanceageing (experimental results)

16.1 C/cm2 obtained so far Ar/iC4H10 70/30 Non-clean gas system Epoxies used (Araldite) measurement terminated because of sparking

Tests with other mixtures showed rapid ageing

Goal: 342 C/cm2

Using dummy Gossip (glass substrate with pixel pattern)

Fred Hartjes 30



3. Performancerate behaviour limits Target

Atlas b-layer at sLHC: 0.9 GHz/cm2

Occupancy Dead time ~ 50 ns (ionic drift) => occupancy limit (50%) at 20 MHz/pixel Assume

55 x 55 µm2 pixels 12.5 hits per track (only for high angle of incidence)

=> rate limit reached at 53 GHz/cm2

Ionic drift Avalanche gap (nearly all ions collected by the grid)

Average current density 9 µA/cm2

Assume 50 ns stay in the gap => space charge of 0.45 pC/cm2

=> Induced counter field ~ 2.5 V/cm Ref: amplification field ~ 100 kV/cm

=> rate effect from ionic drift in avalanche gap may be neglected

Fred Hartjes 31



3. Performancerate behaviour limits (cntd)

Ionic drift (cntd) Limit by ions in the drift gap that are NOT collected by the InGrid

Assume drift field 2 kV/cm Ion mobility ~ 3 x 10-4 m2/V.s => ions stay in 1 mm gap for ~ 16 µs Assume G = 5000 and 12.5 primary e-/MIP => 0.01 pC/MIP or 14.4 nC/cm2 for the full b-layer rate and if all ions would pass the drift

volume Only ~ 2% of the ions is passing the InGrid¥ => 288 pC/cm2 counter charge

=> counter field due to ionic charge 32 V/cm => < 2% of field

Limitations by protective layer Permit voltage drop of 10V across protective layer => bulk resistivity should be 1.6 x 109 Ω.cm For Si3N4 to be tuned by silicon dope

¥ M. Chefdeville, Charge transparancies and amplification properties of Integrated Micromegas detectors, 2nd RD51 Workshop, Nikhef, April 17, 2008

Fred Hartjes 32



3. Performancerate dependence (experimental result)

Measurement of induced DC current Using Gossip with dummy ROC (aluminium

pixel pattern on glass) No InGrid but glued Micromegas

=> gap > 50 µm No protection layer yet Done after some loss of gain due to rapid ageing

(non-clean gas system) MIP rate 1.6 GHz/cm2

No sign of loss of gain until G = 900 Sparking starting at G = 1000 Protection layer probably would have extended

the sparking limit

=> reliable operation of Gossip at b-layer environment (G = 5000) not yet fully proven

Gas gain of Gossip 23

Vgrid (-V)

500 520 540 560 580 600 620 640

I anod

e (n

A)

20

30

40

50

60

708090

200

10

100

G = 1000

Fit: y = 0.0047e0.0161

Ar/iC4H10 30/70mip rate 1.6 GHz/cm2

27-11-07

Fred Hartjes 33



3. Performanceefficiency depends on

Gas gain distribution for single electrons

Normalized gain

0 1 2 3 4 5

P

0.0

0.2

0.4

0.6

0.8

1.0

pdf = 1pdf = 2pdf = 3

1. Primary ionization (cluster density) Assume gas gap of 1 mm From Poisson statistics = 1 – e-cl,

where cl is the average number of clusters in the drift gap

For DME/CO2 => 98.9% (4.5 clusters on average)

2. Charge signal distribution for single electron starts at zero Never 100% single electron

efficiency Pólya distribution factor pdf >1 makes

distribution narrower

3. Discriminator threshold and required overdrive Accepted drift time error

(k = pdf – 1)

Fred Hartjes 34



3. Performancedelta rays

Typical artefact of gaseous detectors Do not exist in solid state detectors because of their short range

Affecting ~ 1 - 2% of the events Deteriorate resolution for most gaseous detectors since they are averaged with the rest of the track In Gossip most of them can be rejected in the track fitting using its high granularity

Using track info from other detectors

Examples of data rays in test beam data of run Sept 2009 using DME/CO2 50/50. Gossip gas gap 1.5 mm

4 mm

2.8 mm

Fred Hartjes 35



Fig. . Coordinate system and nomenclature of track parameters. The X-Y coordinate (X0, Y0) is given by the crossing point of the fitted track with the reference plane.

3. Performancehow to handle track segments

1. Track is fitted in the frontend electronics through reconstructed 3D hit points

2. Crossing point between the fitted track and the reference plane is determined

3. Output has format of crossing point in X-Y (fixed Z) + angles φ and θ 4 parameters

Fred Hartjes 36



3. Performancecooling

“Required capacity compared to silicon?” Exact number not to be given at present, but expected to be

substantially lower, especially for the b-layer Reasons

Less emitted frontend power including digital part (50% of silicon frontend??)

Negligible environmental heat load at room temperature Sensor bias current (may be 1W/cm2 for silicon, zero for Gossip) No risk on thermal runaway Bigger temperature gradient across heat spreader permitted (running at

+ 20º C instead of -20º C) No problem with CTE mismatch when running at room temperature

“Why dependence on operation temperature?” Better heat transfer at higher cooling pipe temperature => thinner cooling pipe

Fred Hartjes 37



3. Performancematerial budget (X/X0)

Double layer to provide 100% coverage Dominated by services and support (78%) ~50% of that of silicon (2.5 – 3%) because of

Much less cooling material Massless detecting medium Less material in LV cables

Radiation length (X/X0)

Thinned (50 m) pixel chips 2 x 0.053%

Cathode frame 2 x 0.083%

TPG layer 100 m 2 x 0.048%

PG body 20 mm2 1 x 0.5%

Cooling tube (glass) 1 x 0.083%

Carbon fibre composite 3 x 0.1%

Total for stave 1.25%

Fred Hartjes 38



3. PerformanceExperimental results from testbeam September 2009

Using T10 at PS 6 GeV pions, low duty cycle Detectors built using TimePix chip

55 x 55 µm2 cell size; TDC running at 80 MHz

Using DME/CO2 for the first time, not tested beforehand Beam entering under ~ 12º

Gossip 1 => excellent SE efficiency (close to 100%) Gossip 2 => not working Gossip 3 => very poor SE efficiency (~16%) GridPix (DICE) => poor SE efficiency (~ 38%)

Fred Hartjes 39



3. Performancedata analysis testbeam September 2009

Noisy events rejected (discharges)

Noisy pixels masked (1 – 2%, mostly at

the edges)

DICE (GridPix detector) used as

reference

Tracks found in DICE were traced

backwards in Gossip 3 and Gossip 1

Edge zones rejected

Field lines bend because of bad field

shaping

4 mm

2.8 mm

DICE

Fred Hartjes 40



3. Performanceangular resolution

Detector Gossip 1 1.5 mm drift gap Single hit events excluded

X – Z plane slope 4.1 mrad (0.23⁰) Resolution 15 mrad (0.9⁰) in X Good for 1.5 mm of gas

Y – Z plane Y – Z plane: slope 220 mrad (12.6⁰) Resolution 70 mrad (4 ) in Y⁰ Deteriorated by discriminator delay

Note the asymmetric distribution => long erroneous drift time make angle smaller

Fred Hartjes 41



Draw straight line between master points in Gossip 1 and DICE

1. Calculate the master point in Gossip 3 as the simple average of all the pixel hits in X, Y and Z

2. Calculate the distance between the straight line and the Gossip 3 master point

3. PerformanceMeasuring position resolution

Gossip 3

Fred Hartjes 42



3. Performanceposition resolution

Limited statistcs: 75 events 40% track efficiency in Gossip 3

Residuals in X: σ = 30 - 35 µm This number includes

Accuracy of the fitted track (10 µm?) Multiple scattering in 6 GeV beam (10 – 30 µm) Poor hit statistics

average 1.5 hit pixels instead of 4.5 expected => σ ≈ 15 µm expected for well operating Gossip

Residuals in Y: σ = 70 - 80 µm => same correction: σ ≈ 45 µm expected for well operating Gossip

Time info used for all three detectors Worse result if you don’t use it

Fred Hartjes 43



3. PerformanceTrack efficiency

Method tracing tracks in Gossip1 that were found in DICE

(GridPix reference detector) At least one hit in Gossip 1 required

Good track efficiency of Gossip 1 (1.5 mm gap) 99.5%

But in hit spectrum 1 single-hit event and 5 two-hit events

=> if we would use a 1 mm drift gap instead, we would miss on the average: 1/3 event from 1 event with one hit 5/9 event from 5 events with two hits

=> based on this measurement expected efficiency for 1 mm gap: ~99.1% But beware of limited statistics (197 events)

Expected from known cluster density for 1 mm gap 98.9%

Fred Hartjes 44



3. Performancenumber of hits per track

Method tracing tracks in Gossip1 that were found in DICE

(GridPix reference detector Tracks entering under 12º

Measurement MIP through DME/CO2 gives on average 18.8

electrons per track => naively expected 18.8 hits/track (one hit per

electron) Measured 6.7 hits/track Caused by pile up

1 pixel is hit by several electrons

Projection length surface: 0.21 mm => less than 4 pixel cells

Gossip 1

Fred Hartjes 45



4. Sparkingorigin

Occasional sparking is normal for each gaseous detector (exceeding Raether limit) At the Landau tail Alfas Ions; converting neutrons; gammas

Most probable Gossip charge signal at working point: 62 ke-

Sparking limit for G=5000: 300 ke-

~ 5 x most probable charge signal

There are indications that a protection layer extends this limit

Still to be investigated using high rate MIP source at Nikhef

Gossip

wor

king p

oint

(b-lay

er)

MIP response for SiProt2Fitted with RD42 Landau expression

charge signal (ke-)

0 50 100 150 200

# of

eve

nts

0

100

200

300

400

Measured histogramFitted primary Landau Assumed pedestal peak

Preliminary resultVmesh = - 600 VVcath = -800 VDrift gap 1.2 mm=> Edrift = 1.67 kV/cmSiProt waferBrass Micromegasgas: CO2/DME about 50/50Exitation by mips from 90Sr source5.1% pedestal events25-8-06

Overflow events

Fred Hartjes 46



Functioning protection layer1.Surface part near discharge is charged up2.Discharge cannot sustain itself and jumps to neighbouring cell3.Discharge process continues until grid potential is sufficiently small

4. Sparkinghow to survive sparks

1. Limit the energy of the spark Reducing the capacity of InGrid

High supply resistorand Small or no decoupling capacitor

InGrid capacity 40 pF for 15 x 15 mm

Adding protection layer => acts as small coupling

capacitance in the input circuit => Spark energy is distributed

across multitude of pixels

2. Limit the peak current in case of a discharge

Adding resistivity in the discharge circuit (resistive InGrid)

3. Incorporate input protection (diodes) in the frontend ASIC

Pixel chip

Si3N4

InGrid

Fred Hartjes 47



4. SparkingHV connections

Spark protection by external HV circuitry

Vcath

Vgrid

GND

100 M 100 M

10 M 10 M

10 n 10 n0-100 p

0-30 p

Gossip/GridPix

Pixel chip

Filtering HVLimiting

discharge current

Cathode

InGrid

Component values only indicative

Fred Hartjes 48



Pixelman software: IEAP, Prague

Limiting the discharge current. Reduce amount of charge. Spread the charge.

4. Sparkingtesting using alfas

α tracks having high primary ionisation exceeding Raether limit of 108 e- in the avalanche

Fred Hartjes 49



4. Sparkingvarious questions

“Demonstration for large system” Should be done

“Sparking rate?” Particle rate dependent, to be investigated

“How long insensitive and across which surface?” Also to be investigated Wild guess:

Small discharges: insensitive during few µs and across ~ 1 mm Large discharges: insensitive during ~ 1 ms and across full InGrid

“Demonstrate proper operation in harsh environment (fwd region of present LHC)” Test like this is crucial after successful tests at the Nikhef facility

Fred Hartjes 50



5. Frontend electronics “Threshold should be increased because of threshold dispersion” Present Gossipo chips have a threshold trim DAC for

each channel

“Operating threshold of 350 e- is not realistic, need 5x higher threshold” Gossipo-2 (pixel chip with 16 x 16 matrix) operates

on 350 e- ASIC designers estimate a threshold of 500 e- a

workable value for a big system Still to be tried out

note very low detector capacity

“Why less power consumption?” Absence of bias current and negligible input capacity

enable a low current in the input stage Preamp Gossipo-2 => 2 µW

Ref.: FE-I4: 10 µW Limited contribution of digital electronics (0.4 µW) Note: local track fitting processor not yet

implemented

Gossipo-2 chip

Fred Hartjes 51



5. Frontend electronicsshaping time

Aim of ASIC designers making shaping time 2 x shorter than total ionic drift time

Shaping time presently 30 ns Gossipo-3 => 25 ns

0 20 40 60 80 100 120 140

0 20 Time, ns40 60 80

Threshold =350 e-

time jitter / internal delay ≈ 8 ns

time jitter / internal delay ≈ 3 ns

Fred Hartjes 52



5. Frontend electronics (cntd)additional drift time delay

Comparator causes additional drift time delay and jitter for small charge signals

Simulations for Gossipo-2 at 350 e- threshold

Rejecting small pulses helps at the cost of a strongly reduced efficiency

0 5 10 15 20 25 30 35 400

1000

2000

3000

4000

5000

time, ns

Entries

Gas Gain =8000Inefficiency = 0.4%

Gas Gain =4000Inefficiency = 1.3%

Gas Gain =2000Inefficiency = 5%

0 5 10 15 20 25 30 35 400

1000

2000

3000

4000

5000

time, ns

Entries




Signal cut is made on the basis of ToT information:

Only signals with ToT values larger than 100ns (2000e) are taken into account. No signal cut

Fred Hartjes 53




In TimePix, delay may be over 100 ns for small pulses

1000

Thre

shol

d =3

50 e

-

Signal size, electrons

Delay on the comparator

2000 3000 4000

∆tmin

Gossip 1Gossip 3

Good SE eff.

Poor (16%) SE eff.

Testbeam

examples

Fred Hartjes 54




Behaviour for Gossipo preamp is expected to be better than with TimePix Depending on Itail setting

Further improvement possible by Using amplitude info from Time Over

Threshold (TOT) Constant fraction discriminator

Vthr

OutputInput

Itail

Vdd=1.2 V

Fred Hartjes 55



6. PhotolithographyInGrid

Presently consisting of aluminium mesh supported by pillars of SU8 (photoresist)

Poor attachment of aluminium Not suited for wire bonding => not production ready

Encouraging tests with SiO2 as a mesh support

Value InGrid thickness being debated Presently 50 µm May become 30 µm

Fred Hartjes 56



6. PhotolithographyInGrid (cntd)

InGrid technology “Processing temperature?”

Comparatively low < 200 ºC (Si3N4)

“Which companies are able to produce it?” University of Twenthe (MESA+) (R&D scale) SMC (Edinburgh) started with it IZM Berlin might do it

“On wafer scale?” Not yet, problem is dicing afterwards Using laser dicing?

“Testing?” We have not worked this out yet

“Yield?” No mass production yet

“Imperfections?” Not known at this stage

Fred Hartjes 57



6. PhotolithographyInGrid(cntd)

InGrid technology (cntd) “How far advanced?”

Prototype production on lab scale “Processing a 50 µm thick wafer?”

Not yet worked out “Maximum thickness?”

We use presently 50 µm amplification gap, no plans to go bigger, we may go to 30 µm

“Any stresses?” Not known, surface limited to ~ 20 x 20 mm2

TwinGrid “Is gain of TwinGrid the multiplication of

the gains of each of the grids?” Probably yes, we might use TwinGrid to get

rid of the avalanche close to the pixel chip (ageing, ion drift)

In this case there will be hardly any gas gain at the second stage

“TwinGrid yield?” Hardly any lab experience, so no info yet

Fred Hartjes 58



6. PhotolithographyInGrid (production)

“Production costs compared to silicon?” No production ready process has been developed => hard to give solid statement

SU-8 process 4 step process Two masks involved

Alternative SiO2 process in development Growing 30 – 50 µm thick SiO2 layer => might involve long processing time

Fred Hartjes 59



6. Photolithographyprotection layer

Good results with Si3N4, but still under development Initially aSi used (20 µm) Finding best thickness: 7 µm?, << pixel pitch Tuning best resistivity for a given particle rate by

modifying Si dope 1.6 x 109 Ω.cm needed for sLHC b-layer

Performs mostly well But still occasional chip damage

Pinholes? => many years of slow progress ahead Should be always there, also when using resistive

InGrid Production

Expected to be cheap Easy technology, can be done at many places Single step, no mask needed

5 layers of 1.4 µm Si3N4

Fred Hartjes 60



7. Miscellaneousthinning

“It would be good to explain conceptually how we thin chips (I think: thin chips with handle on CMOS side, put handle on back-side, make InGrid, add gasCap, release handle?)”

We have not worked this out Thinning is not a specific subject for Gossip

Fred Hartjes 61



8. Organisation of the R&DNikhef physicists involved

# of persons Position Available (%)2 Senior with permanent contract 90; 104 Temporary contract (postdoc, 65+) 90; 90; 20; 703 PHD student 90; 90; 80?2 Graduate student 80; 805 Engineer (mechanical or electronic) 10; 10; 10; 60; 50

Total: 16 ~ 60% on average

R&D subjects on GridPix/Gossip Gossip in ATLAS GridPix for TPC in ILC (Eudet) XENON

GridPix as a single electron detector in bi-phase Xenon filled WIMP search experiments PolaPix

GridPix as a detector for the measurement of the polarization of X-rays from space

Present staff at Nikhef Amsterdam and Nijmegen

Fred Hartjes 62



8. Organisation of the R&D collaboration on GridPix/Gossip development

“Present sharing of workload and costs”

Institute # staff Time fraction (%)

Subjects

Nikhef-Amsterdam and Nijmegen

16 60 All GridPix Gossip R&D

Univ. of Bonn (Claus Desch) 4 30 ASIC design (RO architecture)

Techn. Univ. Twenthe (MESA+)

1 30 Photolithography (prototype scale) using Nikhef staff

IRFU-CEA/Saclay (Paul Colas) 4 30 Development of large TPC for ILC (Eudet)

Moscow Physics and Engineering Institute (MEPHI) (Anatoli Romaniouk)

3 50 GridPix as a L1 trigger and TRT

Fred Hartjes 63



8. Organisation of the R&Dcollaboration with industry

New photolithography just started at SMC Edinburgh Commercial company closely linked to University of Edinburgh Mask making started Positive approach on collaboration

Nikhef staff at Edinburgh

“Resources to prototype full wafers” At Nikhef there are two wafer probers and various instrumentation for prototyping and

small scale production Automatic wirebonders Pick and place machine Lapper Plasma cleaner

Fred Hartjes 64



Milestones of Gossip development

Completion (%)

0 20 40 60 80 100

Mass production

Production ready prototype

Robust prototype

Proof of principle

Concept

8. Organisation of the R&Dmilestones

“Define path cq milestones (with dates) leading to the production of a few demonstrators” “To become a serious option for an application in ATLAS at the sLHC”

Crude estimate

Fred Hartjes 65



Concluding Gossip R&D addresses fundamentally different subjects compared to the

semiconductor technologies => Vast amount of R&D needed

Advantages Lower mass (<50% for the hottest regions) Outlook for unrivaled radiation tolerance No bias current Relaxed cooling operation

Drawbacks New technology, not established Complication by more services Bit less good position resolution More critical operation because of avalanche process

Fred Hartjes 66



SPARE

Fred Hartjes 67



Variation of the gas gain Dominated by Poisson statistics Basically exponential distribution for single electron But in practice a bit less variation

Curve can be described by the (empirical) Pólya function pdf = 1 pure statistical avalanche growth

pdf = 2 avalanche growth depending on its size

Experimental results: pdf 1.0 – 2.5Distribution function for three electrons after gas avalanche

Charge (arb. units)

0 2 4 6 8

P

0.0

0.1

0.2

0.3

0.4

pdf = 1

pdf = 2

Distribution function for one electron after gas avalanche

Charge (arb. units)

0.0 0.5 1.0 1.5 2.0 2.5 3.0

P

0.0

0.2

0.4

0.6

0.8

1.0

pdf = 1

pdf = 2

x

N

e eNxNnxP

!1

,1

xN

N

e exN

NnxP 2122

!122,

Fred Hartjes 68



Testbeam setup in T10 (East hall) 3 Gossips and one GridPix ~ 10 cm apart

Fred Hartjes 69



Example of events in Gossip 1 and DICE Pixel chip on X-Y plane

DICE19.3 mm gap

Gossip 11.5 mm gap

173.txt

Fred Hartjes 70



Spoiling Z resolution by time slewing

Simulation for Gossipo preamp State of the art frontend

130 nm technology 2 µW power

Without any compensation, time slewing destroys Z resolution 15 – 50 ns delay, exceeding range of drift

time measurement (25 ns) => Z errors ~300 µm rms => compensation really required

Possible compensation by Time-over-threshold (TOT) measurement => use this value to correct the measured

arrival time

Constant fraction discriminator

TOT

7500 e-deltapulse

Gossippulse

Time to threshold

Fred Hartjes 71



Cuts to the recorded events DICE (19.3 mm drift gap) used as a reference

detector

1. Noisy events removed (microdischarges) > 400 kb instead of few kb

2. Noisy pixels masked (> 2% occurrence)3. Empty events in DICE removed (< 3 hit pixels)4. Tracks fitted in DICE with high slope residuals

Limit: > 0.1 rad From double tracks, slow tracks, large deltas ........

5. Tracks having extreme slopes (> 10 mm/mm)6. Tracks outside fiducial volume in X (3.6 – 9.1

mm) Tracks at edge deformed by bad field shaping

Main run: => 197 out of 778 events seen in DICE accepted

DICE

Fred Hartjes 72



# of hit pixels vs grid voltage

Gossip 1 (1.5 mm drift gap) well single electron

efficient (plateau)

Gossip 3 (1.0 mm drift gap) No plateau Poor single electron

efficiency

Much higher number of hits at 12º incidence Avoiding pile-up effect

Angle of incidence 12º

Gossip 3

Gossip 1

Perpendicular incidence

Fred Hartjes 73



Drift time spectrum DICE: cut at 2.2 µs by common stop

About at end of drift region Deviation from ideal shape (block) due to poor

S.E. efficiency Gossip 1 (1.5 mm): basically ideal block shape

Deformed by convolution with slewing effect Gossip 3 (1.0 mm): broad distribution because of

time slewing

DICE

Gossip 1Gossip 3

Fred Hartjes 74



Measured track angle in DICE Angles measured in projection of the track on X-Z plane and

Y-Z plane respectively rather than in φ and θ

More practical for this analysis

X – Z plane

Slope: -4.16 mrad (-0.24⁰)

Resolution 2.35 mrad (0.13⁰) in X

To be corrected for beam divergence (1 – 2 mrad)

“not bad for 2 cm of gas”

Y – Z plane Slope: - 270 mrad (-15,5⁰)

Correcting for 10% lower drift field => -14⁰

Resolution 12.6 mrad (0.7⁰) in Y

Worse because of slewing

Fred Hartjes 75



Hits per track Gossip 1: 6.7 hits/track across 1.5 mm

Single electron efficiency close to 100% expected # of hits less than # of electrons (~19) (pile up)

DICE: ~ 33 hits/track across 19.3 mm => 38% single electron efficiency

Gossip 3 (1.0 mm gap): 0.73 hits/track 16% single electron efficiency Poor track efficiency (48%)

Gossip 1

DICEGossip 3

Fred Hartjes 76



Measured X-Y residuals Residues clustered in sub mm area

Deviating points from noisy pixels in Gossip 3

Fred Hartjes 77



Gaussian fits through distributions 75 events

40% track efficiency in Gossip 3

Residuals in X: σ = 30 - 35 µm This number includes

Accuracy of the fitted track (10 µm?) Multiple scattering in 6 GeV beam (10 – 30 µm) Poor hit statistics

average 1.5 hit pixels instead of 4.5 in Gossip 3 => σ ≈ 15 µm expected for well operating Gossip

Residuals in Y: σ = 70 - 80 µm => same correction: σ ≈ 45 µm expected for well operating Gossip

Z info used for all three detectors Worse result if you don’t use it

Fred Hartjes 78



Track efficiency

Good track efficiency of Gossip 1 (1.5 mm gap)

One missing track for 197 good tracks in DICE

But 1 event with 1 hit and 5 events with 2 hits

If we would use a 1 mm drift gap instead, we would miss on

the average:

1/3 event from 1 event with one hit

5/9 event from 5 events with two hits

=> expected efficiency for 1 mm gap: ~99.1%

But beware of limited statistics (197 events)

Expected from known cluster density: 98.9%

Documents

Reaction on the review document Gossip_091215x dd 11-1-2010 of the Gossip R&D proposal