The ATLAS The ATLAS SSemiemiCConductoronductor TTrackerracker
The ATLAS The ATLAS SSemiemiCConductoronductor TTrackerracker
AbstractThe 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.
Marko Mikuž, University of Ljubljana & Jožef Stefan Institute, Ljubljana, Sloveniaon behalf of the ATLAS SCT Collaboration
Requirements 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
Layout 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
end-cap: three rings (inner, middle, outer) per fully populated disk, strips in r-direction, two sensors/side on outer & middle, one on inner
Barrel # staves#
modules
1 32 384
2 40 480
3 48 576
4 56 672
Total 2112 modules
Disk 1 2 3 4 5 6 7 8 9
Rings M,OI,M,O
I,M,O
I,M,O
I,M,O
I,M,O
M,O M,O O
# modules
92 132 132 132 132 132 92 92 52
Total 2 x 988 = 1976 modulesDetectors
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
QA: Detector current @ 350 V & number of strip defects
I-V @ -18ºC after irradiationS/N-V after irradiation to 3x1014 p/cm2
ASIC’s 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
Log scale !
9 wheels
9 wheels
5.6 m
1.04
m
1.53 m9 wheels
9 wheels
5.6 m
1.04
m
1.53 m
Barrel End-capEnd-cap
Modules 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 substrateo barrel: wrap around over detector surfaceo 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
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
Barr
el m
od
ule
En
d-c
ap
mod
ule
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
bench & system-test performance figures see N28-6 by R. Bates
non-irradiated moduleso gain ~ 55 mV/fCo noise ~ 1500 e ENCo noise occupancy @ 1 fC: ~ 10-5
irradiated to 3 x 1014 p/cm2 > full dose in 10 yearso gain ~ 30 mV/fCo noise ~ 1900-2100 e o operational threshold for 5 x 10-4 NO: 1.0 – 1.2 fC
test beam performance
S-curve: 50 % pointgives the gain, widththe noise, both are extracted from erfc fit
strip direction
strip direction
Exp
lod
ed
en
d-c
ap
m
od
ule
vie
wTPG spine
silicon sensors
pitc
h ad
apte
r
hyb
rid: 1
2 A
SIC
’s o
nw
rap
ped
flex c
ircu
it aro
un
d C
C s
ub
stra
te
cooling points
Nois
e o
ccu
pan
cy
SCT system-test:barrel (↑) & end-cap (↓)
Schematic of SCT set-up in SPS H8 test beam
Test beam efficiency & noise occupancy for non-irradiated (←) and irradiated (→)
module
operationalrange
operationalrange
Services & structures 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)
Two SCT barrels with module mounting parts (↑), end-cap cylinder with one out of nine disks(↓)
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 !
SCT set-up in SPS H8 test beam in May 2003
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