Transcript Slide 1

The ATLAS SemiConductor Tracker
Marko Mikuž, University of Ljubljana & Jožef Stefan Institute, Ljubljana, Slovenia
on behalf of the ATLAS SCT Collaboration
Abstract
The ATLAS SemiConductor Tracker (SCT) is presented. About 16000 silicon micro-strip sensors with a total active surface of over 60 m2 and with 6.3 million read-out channels are built into 4088 modules arranged into
four barrel layers and nine disks covering each of the forward regions up to pseudo-rapidity of 2.5. Challenges are imposed by the hostile radiation environment with particle fluences up to 2x1014 cm-2 1 MeV neutron
NIEL equivalent and 100 kGy TID, the 25 ns LHC bunch crossing time and the need for a hermetic lightweight tracker. The solution adopted is carefully designed strip detectors operated at -7oC, biased up to 500 V and
read out by binary rad-hard fast BiCMOS electronics. A zero-CTE carbon fibre structure provides mechanical support. 30 kW of power are supplied on aluminium/Kapton tapes and cooled by C3F8 evaporative cooling.
Data and commands are transferred by optical links.
Prototypes of detector modules have been built, irradiated to the maximum expected fluence and successfully tested. The detector is in full production now. This will be followed by integration starting in 2004 and
installation in 2006 to match the LHC start-up in 2007.
Modules
Requirements
 building blocks
 2 pairs of daisy-chained sensors glued to high thermal
conductivity TPG substrate
 flexible circuit Cu/Kapton hybrid with 6 ASIC’s per side laminated
on carbon-carbon substrate
o barrel: wrap around over detector surface
o end-cap: at detector edge, flex wrapped & laminated on
substrate, see N44-4 by C. Ketterer
 glass pitch adapters for bonding from ASIC to detector
 provide precision space-points for robust particle tracking at
intermediate inner detector radii
 back to back 40 mrad stereo angle 80 µm pitch strip sensors
provide 16 µm x 500 µm resolution
 4 barrel layers & 9 disks per end-cap hermetically cover solid
angle up to η < 2.5
 > 99 % single-plane efficiency for MIP’s detection
 stiff zero-CTE lightweight carbon fibre structure provides
precision support for detector modules
 tight module building tolerances down to 5 µm
 frequency scanning interferometry on-line alignment system
 survive 10 years in LHC environment with up to 2x1014 cm-2 NIEL and
100 kGy ionizing dose
 operation at -7ºC limits reverse bias current and suppresses
reverse annealing
 detector reverse bias up to 500 V ensures full depletion and
efficient charge collection
 detector and module irradiation to full dose as part of standard
quality control
Barrel module
hybrid: 12 ASIC’s on
wrapped flex circuit
around CC substrate
Exploded end-cap
module view
silicon sensors
cooling points
End-cap module
 barrel module assembly
 four production clusters: Japan, UK, US, Scandinavia, with
400-800 modules to produce per site
 ~ 750 modules produced up to date out of 2112 needed
 extensive mechanical & electrical QA
 very good quality: on average < 1 dead channel out of 1512
 end-cap module assembly
 seven production clusters with distributed assembly / QA
 several clusters qualified for production
 problems with start-up due to delays in component delivery
Performance
 binary – single bit digital – R/O electronics
 in experiment provides hit/no-hit information only
 figure of merit: MIP’s efficiency & noise occupancy vs. threshold
 specification: > 99 % efficiency & < 5 x10-4 noise occupancy (NO)
 diagnostics: threshold scan and calibration charge injection:
cumulative distributions – S-curves
Layout
32
384
2
40
480
3
48
576
4
56
672
Total
SCT system-test:
barrel (↑) & end-cap (↓)
1.04 m
1
S-curve: 50 % point
gives the gain, width
the noise, both are
extracted from erfc fit
5.6 m
2112 modules
1.53 m
Barrel
9 wheels
End-cap
9 wheels
End-cap
 bench & system-test performance figures
see N28-6 by R. Bates
 non-irradiated modules
o gain ~ 55 mV/fC
o noise ~ 1500 e ENC
o noise occupancy @ 1 fC: ~ 10-5
 irradiated to 3 x 1014 p/cm2 > full dose in 10 years
o gain ~ 30 mV/fC
o noise ~ 1900-2100 e
o operational threshold for 5 x 10-4 NO: 1.0 – 1.2 fC
 test beam performance
 end-cap: three rings (inner, middle, outer) per fully populated disk,
strips in r-direction, two sensors/side on outer & middle, one on inner
Disk
1
2
3
4
5
6
7
8
9
Rings
# modules
Total
M,O
92
I,M,O I,M,O I,M,O I,M,O I,M,O
132
132
132
132
M,O
M,O
O
92
92
52
132
2 x 988 = 1976 modules
Detectors
 single-sided AC-coupled p+-n detectors with 768 strips processed
on 285 µm thick high-resistivity 4” wafers
 > 99 % good strips spec, tested at manufacturer
 leakage current specs before and after full dose irradiations
 6 detector types: 1 square – barrel, 5 wedge – end-cap
 ~ 20000 detectors procured from Hamamatsu (~ 85 %) and CiS (~ 15
%), all detectors in hand
 detector QA on
 every detector: visual inspection, I-V
 sample: C-V, full strip test, I stability
 excellent detector quality: 99.9 % good strips
 samples per batch irradiated to full dose
 I-V on all detectors
 S/N-V with β-source on sample
Log scale !
Schematic of SCT set-up in SPS H8 test beam
QA: Detector current @ 350 V
& number of strip defects
SCT set-up in SPS H8 test
beam in May 2003
operational
range
operational
range
Test beam efficiency & noise occupancy for
non-irradiated (←) and irradiated (→) module
ASIC’s
S/N-V after irradiation to 3x1014 p/cm2
I-V @ -18ºC after irradiation
 ABCD – 128 R/O channels, bi-polar front-end & CMOS back-end, produced in
biCMOS rad-hard DMILL process at ATMEL
 front-end with ~ 20 ns shaping, 50 ns double-pulse resolution, ~ 50
mV/fC gain
 discriminator with 8-bit programmable threshold and 4-bit per-channel
adjustment in 4 selectable ranges
 132 cell deep binary 40 MHz pipeline for L1 trigger latency, 24 cell
derandomizing buffer storing 8 events
 R/O of compressed binary data via 40 MHz optical link
 radiation hardness
 tested with X-rays, protons, pions and neutrons
 meets specifications after full dose
 anomalous gain degradation observed with thermal neutrons – see N20-4
by I.Mandić
 procurement
 order placed under CERN-ATMEL frame contract with 26 % guaranteed
yield
 acceptance testing at wafer level performed at CERN, UCSC and RAL
 yield problems in recent ATMEL runs
 ~ 85 % perfect chips in hand, CERN negotiating with ATMEL
Services & structures
Two SCT barrels with
module mounting parts (↑),
end-cap cylinder with one
out of nine disks(↓)
 R/O, control and power
 2 R/O & 1 clock/command fibre per module
 1 power supply channel with cable/tape (17 leads) per module
 cooling
 ~ 30 kW of power, C3F8 evaporative cooling @ ~ -20ºC
 active, thermally neutral thermal enclosure
 support structures
 carbon fibre barrels & cylinders with disks
 lots of small parts: inserts, brackets… (~40000 for barrel only)
Integration & schedule
 modules mounted on barrels @ Oxford & KEK
 barrels integrated & commissioned @ CERN
 modules mounted on disks and assembled into
cylinders @ Liverpool & NIKHEF
 final end-cap commissioning @ CERN
 ATLAS integration schedule calls for
 SCT barrel available in December 2004
 SCT end-caps available in March & May 2005
 very tight schedule to meet !
Noise occupancy
 barrel: two daisy chained silicon sensors per module side with strips ~
in z-direction, tilted by 11º to the barrel, arranged by 12 on staves
along z
Barrel
# staves
# modules