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

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En

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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

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silicon sensors

pitc

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2 A

SIC

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rap

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flex c

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cooling points

Nois

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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