1. Status report of the ATLAS SCT optical links
John Matheson (RAL)
for the ATLAS opto-links team
links architecture
total dose radiation hardness
investigation of SEU
cooling issues
mechanical issues
system tests
pre-production harness
conclusions 1

2. silicon microstrip detector readout chips
silicon barrel module
silicon microstrip detector
readout chips
need timing, trigger, control in
need data out
optical links for low mass, crosstalk 2

3. 40 MHz clock and control on single fibre by biphase mark encoding
links architecture
40 MHz clock and control on single fibre
by biphase mark encoding
2 data fibres/module, 40 MHz NRZ
radiation hardness (10yr):
10 Mrad, 2 MeV neutrons cm-2 3

4. power budget 4

5. DORIC and VDC barrel harness opto package (2 VCSELs, 1 p-i-n)
power tapes, redundancy system
furcation tube (now black !)
each harness serves 6 modules 5

6. 20 VCSELs irradiated at INER, Taiwan 30 MeV protons, 21014 cm-2
VCSEL irradiation 1
20 VCSELs irradiated at INER, Taiwan
30 MeV protons, 21014 cm-2
168 hr at 10 mA, 168 hr at 20 mA 6

7. VCSELs degrade i.t.o. threshold, efficiency
VCSEL irradiation 2
VCSELs degrade i.t.o. threshold, efficiency
injection annealing foreseen in ATLAS
60 Mrad gamma - little change 7

8. VCSEL ageing 20 VCSELs aged at 100°C for 2534 hr no failures
R = (1/Nt) ln(1/(1-C))
AF = (I2/I1)2 exp[EA/KB (1/T1 - 1/T2)]
duty cycle during data transfer 50%
fraction of time sending data 50%
fraction of time LHC operates 33% 8

9. Irradiation of other components
VDC/DORIC 50 Mrad, 2.5×1014cm-2 n
1 week at 100°C no failures  0.3% max chip failure in SCT (redundancy makes OK)
wafers being qualified for production
p-i-n diode 1×1015cm-2 n, 0.5 0.35 A/W
aged 60°C   5 failures in SCT
passives 3×1014cm-2 24 GeV p, no change
opto-flex assembly 3×1014cm-2 24 GeV p, behaviour as expected from component-level irradiations 9

10. energy deposition in p-i-n diode may cause SEU
single event upset
energy deposition in p-i-n diode may cause SEU
window A => command bit error
window B => BC clock error
clock arrives up to 6.25ns early
ABCD may lose synchronisation 10

11. single event upset in command signals
Links measured in loop-back mode
measure errors in command bits
loop-back link
DORIC
VDC
SEU irradiations at PSI
pions, protons MeV/c
vary light power
DORIC threshold varies 11 11 11 11

12. single event upset in bunch crossing clock
BC clock SEU measured in 24 GeV PS beam
forward module in beam - optical link
barrel module in counting room - Cu link
L1 trigger
beam spill
L1 triggers
BC counter of ABCD is read out after each L1 trigger
difference between the modules => SEU
SEU  error rate (s-1) / flux 12

13. single event upset summary
minimum Ip-i-n = 75A
max SCT flux 2106cm-2s-1
fraction of module data lost:
9  10-4 command bit (worst case)
7.8  10-5 BC clock error 13

14. defines T at opto-package component lifetime is T dependent
cooling measurement 1
heat load from chips 0.4W
defines T at opto-package
component lifetime is T dependent
need to get the heat to the cooling block 14

15. Lower face dT1 through flex cooling measurement 2 (Cooling block) dT3
T drop = dT1 + dT2 +dT3
minimise dT1 using vias below chips
AlN backing, BN-loaded epoxy 15

16. total dT ~ 18°C at -7°C ambient
cooling measurement 3
total dT ~ 18°C at -7°C ambient
expect opto-package T ~ 0°C
up to 10°C tolerable for lifetime
FEA predicts total dT ~ 25°C with no heat transfer to environment, shows importance of vias 16

17. mechanical issues: design clearance
clearance between top of opto-package/chip cover and lower side of module is most critical point
compliance of flex must compensate variations in:
barrel eccentricity
tape stack height 17

18. mechanical issues: clearance measurement
clearance measured using jig (Geneva) and envelope module
worst case uses max. barrel eccentricity, 6 tapes to push opto-package upwards
1.4mm clearance measured using slip gauges in agreement with the design value 18

19. send 2 closely spaced L1 triggers
CERN system test: a surprise
send 2 closely spaced L1 triggers
module being read out when second trigger arrives
excess noise correlated with position 19

20. excess noise is due to light leaking from optical fibres
CERN system test - light leaks
excess noise is due to light leaking from optical fibres
different colour furcation tubes measured at RAL - black is opaque 20

21. first pre-production harness
harnesses to be made by Radiantech Inc, Taiwan
before full-scale production, 8 pre-series harnesses will be made
pre-series harnesses to be used in system test at RAL with at least 6 modules at low T on B3 sector
first harness received August 02
some minor issues to be resolved
optical links are fully functional 21

22. pre-production harness: optical measurements22
pre-production harness: optical measurements
p-i-n diode responsivity
mean 0.44 A/W
VCSEL LI curves (50% duty cycle)

23. pre-production harness: bit error rate measurements
ttc link operating point
data link operating point
both links have been operated for 12 hr with no errors 23

24. pre-production harness: towards a system test at RAL
barrel module on pre-series harness
fully functional, 1600 e- noise
pre-series tests completion will define start of production in industry 24

25. industrial production of scheduled to begin late 2002
conclusions
SCT harnesses must be rad-hard to 10Mrad, 11014 n/cm2
fibre, ASICs, VCSELs, p-i-n diodes, optical interconnects qualified
harnesses are not immune to SEU but the level is tolerable
mechanical tolerances must be respected to preserve clearances
cooling must be adequate to preserve device longevity
on-sector tests at RAL will be completed before production begins
industrial production of
352 barrel harnesses
scheduled to begin late 2002 25