Development of ATLAS Pixel Detector for the HL-LHC
University of Tsukuba
Junki Suzuki
2018/3/27
TCHOU SYMPOSIUM

Overview Introduction
 High luminosity LHC
 Radiation damage in silicon detectors

 New Pixel detector for HL-LHC Detectors for HL-LHC Planner pixel sensor
 Biasing structure Summary

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Introduction
 High Luminosity LHC (2026)
 Instantaneous luminosity : 7.5×1034 cm-2s-1
 Integrated luminosity : 3000 fb-1
 Radiation damage : 1×1016 1MeV neqcm-2
 Number of interaction : ~200 per crossing

Increase Radiation damage and Pile-up How can we maintain physics performances?
 Radiation Tolerance
New Silicon Tracker
 Fine Pixel(ITkPixelandITkStrip)
 High speed readout Trigger logic upgrade
are needed.
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Radiation damage in Si detectors
 Bulk damage
 Main effect for Si sensors
 Collision with particles make defects→ Many exogenous level will be created Defect’s effect Increase p-type impurity→ Higher depletion voltage
 Recombination center→ Noise, leakage current
 Trapping center→ Charge Collection Efficiency

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Detectors for HL-LHC Inner Detector (current)
 Detector is composed of PixelSilicon
 SCTGas
 TRT
 Silicon area : ~65m2
 Channel : ~100M

TRT
1m

SCTPixel3m

 Inner Tracker (upgrade) Detector is composed of ITk Pixel
All Silicon ITk Strip Silicon area : ~200m2
 Channel : ~5G
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ITk Strip
1m
ITk Pixel

Cost is very important point

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Planner Pixel Sensor
 n+-in-p pixel sensor
 Implanting n+ into p-type Si Lower costs
 Radiation tolerance up to~3×1015 1MeV neqcm-2
 No type inversion
 Bond to ASIC with metal bump Device structure Pixel Size
→ 50×50 or 25×100 μm2→ One of the most smallest
planner hybrid sensor
 Biasing Structure
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Biasing structures IV-testing before bump-bonding Cost of bump-bonding is quite high (accounted for ~50%)
 IV-testing before bump-bonding is important for good yield→ Need to set all pixel GND for biasing

 How can we do? - two choices Temporary metal : Metal structure (will be etching), high costs
 Bias rail : High resistivity Poly-Si rail, radiation damage issue

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Bias rail structure Efficiency drop after irradiation
 Typical efficiency drop observed at under biasing structure→ Changing concentrations of impurity and charge collection field→ Some carrier induced on biasing structure (not electrode)
Type2Type5
Type1
 Succeed to reduce efficiency
drop by “Offset structure”
Type1 (no offset, 1000V)
Long pixel

50x50

50x50

Long pixel

Type2 (offset, 1000V)

89.3%
Type5 (no structure, 1000V)

Long pixelLong pixel

93.8%
Long pixelLong pixel

97.1%
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Efficiency value is improved by 4% !!

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8Summary Development of ATLAS pixel detector
 ATLAS Inner detectors will be replaced with new silicondetectors for higher luminosity experiment.
Need to maintain physics performance in high luminosity
environment.
 We are developing finer pixel, with lower cost and higher
radiation tolerance detector.
 Low cost can be materialized by IV-testing before bumpbonding.
 Biasing structures are needed. Efficiency drop of
3%(no-bias), 4%(with bias structure) is observed afterirradiation.

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