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Reviewers Tatsuo Kawamoto Werner Riegler Mike Tyndal Norbert Wermes. Reaction on the review document Gossip_091215.pptx dd 11-1-2010 of the Gossip R&D proposal. Reviewed by Atlas Upgrade Steering Group. Reaction by Harry van der Graaf Fred Hartjes Nigel Hessey. - PowerPoint PPT Presentation
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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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
Questions/ comments by the committee
Fred Hartjes 5
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
Answers to the questions
Fred Hartjes 14
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
2. Possible target regions for Gossip and GridPixsLHC fluences
Fred Hartjes 19
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
0.6 0.7 0.8 0.9 1Electron efficiency
Pio
n ef
ficie
ncy
Cluster counting1 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.
Fred Hartjes 23
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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)
Fred Hartjes 25
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
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Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
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Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
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Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
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Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
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Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Gas Gain =8000Inefficiency = 10%
Gas Gain =4000Inefficiency = 27%
Gas Gain =2000Inefficiency = 60%
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
5. Frontend electronics (cntd)additional drift time delay
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
5. Frontend electronics (cntd)additional drift time delay
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
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Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
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Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
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Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
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Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
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Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
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Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
SPARE
Fred Hartjes 67
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
Testbeam setup in T10 (East hall) 3 Gossips and one GridPix ~ 10 cm apart
Fred Hartjes 69
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
# 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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
Measured X-Y residuals Residues clustered in sub mm area
Deviating points from noisy pixels in Gossip 3
Fred Hartjes 77
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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
Review of the Gossip R&D proposal for ATLAS at the sLHC
CERN, February 8, 2010
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%