Design and Construction of Pixel Detectors
for the ATLAS ITk at HL-LHCKoji Nakamura (KEK) on behalf of ATLAS group

26 November 2021

TCHoU meeting1

High Luminosity LHC (HL-LHC)

Now• High Luminosity LHC (HL-LHC) start in 2027 to take 10 times
higher integrated luminosity (3000-4000fb-1) in 10 years.
– Center of Mass Energy will be 14TeV– Instantaneous luminosity after leveling is ~5x1034cm-2s-1• Requirement : No major degradation of performance upto 7.5x1034cm-2s-1
instantaneous luminosity with 200 multiple interaction per bunch crossing.

26 November 2021

TCHoU meeting2

Physics motivation• Why we need 300→3000fb-1 ?
– New Physics+400GeV• Especially for the BSM by Weak interaction• Mass degenerated DM candidate (Long Lived)
ex. Δm=160MeV Pure Wino
95% C.L. lower limit 400GeV→ 800GeV# of expected signal @ 800GeV : 11.9event– Higgs measurement• Precise measurement of Higgs couplings• Observation of rare decay (H→µµ)• Higgs tri-linear coupling (self-coupling)
Observe Higgs pair production :HH→bbγγ

Signal : 9.5 event
Background: 90.5 event
interference

HL-LHC is the only experiment we see these physics in next 15 years
26 November 2021

TCHoU meeting3

ATLAS inner tracker(ITK) project for HL-LHCCurrent ATLAS Detector

ITK upgrade detector

StripPixel
η=4.0• Larger coverage area–– Strip : current 34m2 ➔upgrade 165m2

Pixel : current 2.7m2 ➔upgrade 8.2m2

Inclined part
Flat part• Higher Forward coverage– Current η<2.5 ➔ upgrade η<4.0– Better Pileup removal & background rejection• Mechanics : inclined– Reduce material– Higher tracking resolution.
26 November 2021

TCHoU meeting4Inner Tracker (ITk) Layout
Strip Detector
Pixel Detector

η=2.4
Current coverage

26 November 2021

TCHoU meeting5Inner Tracker (ITk) Layout
strip

Pixel
Inner 2 layers can be replaced.

26 November 2021

TCHoU meeting6Inner Tracker (ITk) Layout
Type of sensors
Layer 0

3D type

Strip Detector

Layer 1Thin planar(100um)

Pixel Detector

Layer 2-4

Thick planar(150um)

Flat

26 November 2021

Inclined

TCHoU meeting

Endcap7

Inner Tracker (ITk) Layout
3D : Triplet structured by single modules

Planar : Quad module (single sensor)

Readout ASIC
20mm20mm

26 November 2021

TCHoU meeting8Requirement : Pixel Detector• Pixel size

IBL type– 1/5 (Z axis) of current pixel (IBL)– 50umx50um (25umx100um inner most layer)– Limitation by readout electronics• Sensor Thickness

ITK typeφ– Thinner : Material budget + lower occupancy– Layer 0,1 : 100um Layer 2,3,4 : 150um– Limitation by charge production (7ke by 100um)b-tag

Z
Z axis pitchthickness
thickness

Z axis pitchthicknessthickness

26 November 2021

TCHoU meeting9Requirement : Radiation tolerance• Expected radiation level @ 4000fb-1– Non Ionizing Energy Loss :• L2 2.8x1015 neq /cm2 L0 2.6x1016neq/cm2– Total Ionizing Dose :• L2 1.6MGy L0 19.8MGy

26 November 2021

TCHoU meeting

L0, 1 can be replaced@ 2000fb-1

10

Requirement : Front-End ASIC
ASIC size : 20mmx20mm → limited by ASIC fabrication process (Yield)
Pixel size : 50umx50um → limited by the size of threshold DAC (5bit).
TSMC 65nm fabrication process.
Data rate / 20mmx20mm (400x384px)––––Pixel region
1px4px4 bit Time-over-Threshold (ToT) based ADC.
Equivalent Noise Count(ENC) ~50e, minimum in-time threshold 600.
Define Pixel region with 1x4 pixel and readout together.
Readout 32bit / region•

16 bit (7bit+9bit) address + 4 x 4 bit ToT (Less data >1.6hit/region.)– Data Rate = reg-hit/chip * Nbit * ftrig * Nchip• Layer0 : 100 * 32bit * 1MHz ~ 3.2Gbps• Layer3 : 5 * 32bit * 1MHz * 4(quad) ~ 0.6Gbps→ 1.28Gbps x 4 lane readout (4 lane for L0 but less lane for outer)

384px (phi)••••400px (eta) : 100reg

Ttbar (@ PU=200)

Pitch : z-axis
thickthick

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TCHoU meeting11

Power dissipation / consumption• Power dissipation– Sensor power : < 50mW/cm2•

Before irradiation
2 measured
2oTotalleakage
≤
0.75
µA/cm
Total
leakage
After radiation damage : 45uA/cm @600V@-25
Cocurrent
at 20 Ccurrent
and Vdepl +50 V
2Depletion voltage Vdepl < Depletion
100 V (Lot-1)
voltageVdepl < 60 V (Lot-2)
Requirement from coolingpower
Current stability Max. deviation
Current withinstability
Beforein time25%
over2irradiation
days ofin timemeasurement
Total
leakage ≤0.75 µA/cm
measured
Total 2measured
leakagecurrent
at 20 o Ccurrent
and Vdepl +50 V
Depletion
voltage Vdepl < Depletion
100 V (Lot-1)
voltage
Breakdown
Breakdown> Vdepl + 70V
Requirement from PowersupplyvoltageVdepl < voltage
60 V (Lot-2)
2stability
Hit efficiency
at
Hit efficiency
atCurrent
Max. deviation
withinCurrent
stability
1.8V 1.5A /4cm2 =0.67W/cm> 98.5% at Vdepll +50 V
orthogonal
orthogonal
intime25% over2 days ofintime
measurement
measuredincidenceincidenceat 20 o C and Vdepl +50 V
Breakdown
Breakdown> Vdepl + 70V
voltagevoltage
Hit efficiency at
Hit efficiency at> 98.5% at Vdepll +50 V
orthogonal
orthogonal
incidenceincidence– FE ASIC < 0.7W/cm (12W / 4chip module)•

Leakage current after radiation damage• Current consumption– Quad chip module : <6A →1.5A/chip••

15 n /cm2
15 n 2 /cm2
15 n /cmΦ =2x10Φ =5x10
Beforeirradiation
Φ =2x10eqeqeq
2222< 0.7525 µA/cm
400V (Lot-1)< 45 µA/cm@ 600V(Lot-1)≤µA/cm@measured< 25 µA/cm@ 400V(Lot-1)< 452 @ 300V
2 @ 400V
2 @ 300V< 20< 35 µA/cm(Lot-2)at20 oµA/cm
C and V< 20 µA/cm(Lot-2)< 35depl +50 V(Lot-2)
Vdepl < 100 V (Lot-1)
Vdepl < 60 V (Lot-2)
Max. deviation within
15 n /cm2
15 n2 /cm215 n /cm
Φ =2x10
Φ =5x10BeforeΦ =2x1025%over2irradiation
days
ofeq
eqeq
2@
2 @ 600V
2measured
2 @ 400V
measurement<25 µA/cm
400V (Lot-1)< 45 µA/cm(Lot-1)≤0.75µA/cm
measured< 25 µA/cm(Lot-1)< 45
2 @ 300V
2 @ 400V
2 @ 300V< 20(Lot-2)<35µA/cm(Lot-2)at
20 oµA/cm
C and V+50
V
<20µA/cm(Lot-2)< 35
depl
VV (Lot-1)>400(Lot-1)
V (Lot-1)>400 >600
V (Lot-1)>600
depl <V100> Vdepl + 70V>300(Lot-2)
V (Lot-2)>300 >400
V (Lot-2)>400VV (Lot-2)
depl <V60
Max. deviation within
97.0% at
V +50(Lot-1)>97.0%at V
600
V (Lot-1) >97.0> 98.5%at400
Vdepll
V> 97.0%
at 400(Lot-1)
25% over 2 daysof> 97.0% at 300 V (Lot-2) > 97.0%>97.0%
atV
400
V (Lot-2) >97.0
at 300(Lot-2)
measurement measured
at 20 o C and Vdepl +50 V>400 V (Lot-1)
V (Lot-1)>400 >600
V (Lot-1)>600> Vdepl + 70V>300 V (Lot-2)
V (Lot-2)>300 >400V (Lot-2)>400• Powering scheme:

HV : parallel*Lot1 150um Lot2 100um

97.0% at
V +50(Lot-1)> 98.5%at400
Vdepll
V> 97.0% at 300 V (Lot-2)>97.0%
atV600V (Lot-1)> 97.0%at 400(Lot-1)>97.0%
atV
400
V (Lot-2)> 97.0%at 300(Lot-2)

LV Serial Powering

26 November 2021

TCHoU meeting

12>97.0>97.0Semiconductor tracking detector• Basic principle :– Backside is negative bias and n+ isground.
– Detect electron-hole pairs created byionizing energy loss from MIP particle.

• Strip detector– n+ can easily ground at the end ofstrip.
– Readout usually via “wire bonding”
strips to the readout ASIC.

AlSiO2e- hee- hhn+P-stop

p Bulk-V• Pixel detector (new technology)– Electrode placed two dimensionally.
– To ground all pixels, high resistivity
biasing grid is necessary.
– Readout ASIC is connected by “bumpbonding”.
26 November 2021

TCHoU meeting13

Semiconductor tracking detector• Basic principle :– Backside is negative bias and n+ isground.
– Detect electron-hole pairs created byionizing energy loss from MIP particle.

• Strip detector– n+ can easily ground at the end ofstrip.
– Readout usually via “wire bonding”
strips to the readout ASIC.

AlSiO2e- hee- hh• Pixel detector (new technology)n+P-stop

p Bulk-V
4 chip module– Electrode placed two dimensionally.
– To ground all pixels, high resistivity
biasing grid is necessary.
– Readout ASIC is connected by “bumpbonding”.

Our development is together with Hamamatsu Photonics K.K (HPK)26 November 2021

TCHoU meeting14

Final Sensor design• Basic Sensor structure has been developed during R&D• Final pitch (50umx50um) pixel size and full size
(40mmx40mm) sensors are produced.
• Full size sensor and ASIC are produced in 2019.
– Now sensor pre-production is ongoing with final design.
• Quality control and Quality Assurance are prepared.

40mm x 40mm full size prototype sensors

40mm x 40mm production modules(20mm x 20mm ASIC size)
HPK Pre-production mask
40mm

40mm
20mmp+n+ p+ 20mm
P-bulk

26 November 2021

TCHoU meeting

ITKpix-v115

Irradiation and Testbeam• CYRIC@Tohoku Univ.

– An irradiation facility with 70MeV proton beam(~1μA beam current).

• 3-5 hours for 3x1015neq/cm2 irradiation with (600nA beam)– This allows 2-3 pixel modules with Al plate at thesame time(3% E loss/module).
– Operated at -15oC temprature with dry N2 gas.
– Scanning over full pixel surface at irradiation.

• Testbeam– Extremely important to test device performance– Efficiency/Noise monitoring during production– Testbeam facility

EUDET telescopes• CERN SPS : 120GeV π+ beam
• DESY : 4-5GeV e+ beam
• FNAL : 120GeV proton beam

– Telescope planes (Track pointing to device)• EUDET based on MIMOSA26 monolithic CMOS detector placedin beamline at CERN/DESY/SLAC (~3um pointing resolution).
• Huge experience of the testbeam operation as having
testbeam 3-4 times a year

26 November 2021

TCHoU meeting

16Efficiency result (irrad 3x1015neq/cm2)• Efficiencies of HV scan 200-800V have been evaluated.

– Analyzed both 1500e and 2400e threshold data for different types.
– All types have over 98% efficiency at 600V.
• 1500e threshold results have over 99% efficiency.
• Small n+ w/ BR have low efficiency at 200V

K. Nakamura Pixel 2018th2400th1500w/o BR
Large n+ w/ BR
Small n+ w/ BR
p+n+p+ p+P-bulk
26 November 2021

TCHoU meetingn+p+P-bulk17

Sensor – AISC attachment at HPK
ASIC• To readout signals from 2
Bias-rail
dimensionally placed electrodes(pixels), readout ASIC needed to be
SiOconnected.
BAln+n+e-2– the signal from each channel is readout through a solder bump
– Bump bonding :BumpPoly-Siee-hP-stophhP-bulk-V

Bump bonding• Solder bump deposition to the ASIC side
• Under bump metallization to Sensor side
• Flip-chipping : 4 chips to one sensor.
ITKpix ASIC

Quad sensor

Solder bump
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Sensor – AISC attachment at HPK• Development of Lead-free(SnAg)
Bumpbonding (Since 2012)
1.
2.
3.
4.

No Flux used (to avoid corrosion)• confirmed flux improve connection, though

No backside compensation• Improvement of Vacuum chuck jig to hold andflatten the ASIC/Sensor…(jig size ~ FE-I4 area)

Special UBM (key element: confidential…)• Simple Ni/Au UBM do not reach 100% yield …

Hydrogen plasma reflow to remove surfaceoxide• Thin sensor/Thin ASIC : 150um/150um– Established Bumpbonding method in thebeginning of 2016.
– Quite stable quality for both single and four
ASICs. 100% yield for last one year (>100chips are bumpbonded.)
26 November 2021

TCHoU meeting

19End of life and HV spark protection• In principle, it’s break down voltage.

– HPK sensors are very good quality (Vbd>1000V)– Other vendor : Vbd ~ Full Depletion(Vfd)+70V.
• Vfd voltage go up by radiation damage• End-of-life when Vbd<Vfd• HV spark protection(Dicing and backside process)
HPK sensor (before radiation)– Large potential difference btw ASIC-Sensor.
Spark happened ~400V.
– HV protection is necessary.
• Parylene coating : survive upto 1000V

P+Sensor
ASIC
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TCHoU meeting20

Flex assembly and CTE mismatch• To read signal from ASIC, Flex Printed
Circuit (FPC) is glued to the module byAraldite 2011.
• Cooling TPG/CFRP will attach to thebackside of ASIC.
• Then wire bond ASIC pad to FPC.
• Coefficient of Thermal Expansion (CTE) isdifferent for silicon/copper/Carbon.
– E.g. Silicon 2.6ppm/oC Copper 16.7ppm/oC• Huge bump stress during thermal cycling.

Assembly tool

– During 10 years operation, expected 400
times TC from -45oC to 40oC
– Qualification : 100 cycle with -55oC to 60oC
Temp range

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Flex assembly and CTE mismatch• The close-to-final condition of modules– No bump delamination increased during thermal cycle.
90Sr β ray souce results

Temperature cycle in climate chamber

Total 400x384 pixels (1.5e5)

26 November 2021

TCHoU meeting22Support & services
Prototype ring tape• Prototyping
Outer Barrel
Prototype of inclined ring
Layer 1 Type-0 ring flex

26 November 2021

TCHoU meeting

23

PDR : Preliminary Design Review
FDR : Final Design Review
PRR : Production Readiness Review

Schedule
2020
Q
1

Q
2

Q
32021
Q
4

Q
1

Q
2

Q
32022
Q
4

Q
1

Q
22023

Q
3

Q
4Sensor FDRSensor

Q
1

Q2Q
32024
Q
4Q
1Q
2Q
32025
Q
4Q
1Q
2Q
32026
Q
4Q
1Q
2Q
3Q
4Sensor PRR
Sensor ProductionSensor
Pre-ProdHybridization PRR

Hybridization FDR
HybridPre-Prod

Module FDR

Front End ASIC
ITKpix-v1 :pre-production
Full size chip
ITKpix-v2 :ITKpix-v1
production
26 November 2021

Hybrid Production

Module PRR
Module Ass. Module Assembly
Pre-Prod

Installation to Support
ITKpix-v2
TCHoU meeting

24

ITk Need-by-date

Flip-chip &Module build

Conclusion
Long R&D phase finishedStarting Construction phase:
Pixel sensor pre-production started

Will obtain discovery machine in 2027!
Defined Final Design now

26 November 2021

TCHoU meeting25

backup

26 November 2021

TCHoU meeting

26

ATLAS Detector Upgrade
Inner Tracking Detectors
Straw Tube gas chamber (TRT)
Silicon Strip Detector (SCT)
Pixe Detector (Pixel)

Muon Detectors
Trigger chamber (TGC,RPC)
Drift Tube chamber (MDT)[Toroid Magnet]

26 November 2021

Calorimeter
LAr EM calorimeter
Hadron calorimeter
Forward calorimeter[Solenoid Magnet]
TCHoU meeting27

ATLAS Detector Upgrade
Inner Tracking Detectors
Straw Tube gas chamber (TRT)
Silicon Strip Detector (SCT)
Pixe Detector (Pixel)
Replace All tracking
To all silicon detectors

Muon Detectors
Trigger chamber (TGC,RPC)
Drift Tube chamber (MDT)[Toroid Magnet]
More flexible trigger system
26 November 2021

No detector replacement
TCHoU meeting

Calorimeter
LAr EM calorimeter
Hadron calorimeter
Forward calorimeter[Solenoid Magnet]
28

ATLAS Pixel Detector Upgrade• Japan group : Pixel Detector development
Target : 3rd – 5th layers– High Efficiency Sensor design– Readout ASIC and DAQ development– Sensor – ASIC attachment– Flex PCB design and assembly– Module loading to the support

StripPixel

Contributing to all steps
Build detector in Japan
Layer 2 + Layer 3 Demonstrator

1.6m
26 November 2021

TCHoU meeting29