1. Performance and operation of the ATLAS Semi Conductor Tracker (SCT) Paul Dervan The University of Liverpool, UK on behalf of the ATLAS SCT Collaboration RD13 Florence, July 20131

2. Outline ATLAS and the SCT Silicon and modules Operation Radiation Damage RD13 Florence, July 20132

3. ATLAS RD13 Florence, July 20133 Size:25m × 44m Weight: 7000 Tons Sub detectors: Tracking Calorimeters Muon

4. The Semi Conductor Tracker (SCT) RD13 Florence, July 20134 61 m 2 of silicon with 6.3 million readout channels 4088 silicon modules in 4 Barrels and 18 EC disks C 3 F 8 Cooling (-7°C to +6°C silicon) 5.6m 1.4m

5. SCT module layout RD13 Florence, July 20135 outer middle inner B6 B5 B4 B3 IP Barrel Endcap side-A middle short modules with Hamamatsu sensors modules with CiS sensors side-C

6. SCT Sensors RD13 Florence, July 20136 Single sided p-in-n 285μm thick 768+2 AC-coupled strips Barrel: 8448 barrel sensors 8081 sensors with 367 sensors with 64.0 × 63.6 mm 2 80 μm strip pitch 100% Hamamatsu Endcap: 6944 wedge sensors 56.9-90.4μm strip pitch 4 different shapes 74.9% Hamamatsu 17.1% CIS 8.0% CIS oxygen-enriched Barrel sensors (Hamamatsu) Endcap sensors (CiS)

7. SCT Modules 2 sensors connected by wire bonding to form 12cm long strips 4 sensors/module Glued back to back with < 8μm accuracy between two planes Stereo angle 40 mrad Thermal pyrolitic graphite (TPG) heat spreaders for good thermal conduction and mechanical strength Cu-Polyimide flexible circuits 12 bi-CMOS binary readout chips (128ch) with 1fC threshold Power: 6W (chips) and 2W (sensors) Radiation length 1.17%X 0 (barrel) RD13 Florence, July 20137 Thermistors for temperature meas.

8. SCT operation and performance RD13 Florence, July 20138 Keeping a low percentage of defect chips/modules (as of Feb 2013) componentsTotal defect components BarrelEndcapSCTFraction(%) modules40881119*300.73 % chips490563811490.10 % strips627916841118020121310.21 % * Due to one cooling loop failure Mainly thanks to built-in redundancy.

9. Track Efficiency RD13 Florence, July 20139 High efficiency for charge particles > 99.5% at 8GeV Stop-less recovery of the ROD busy case Periodical auto-configuration of modules

10. SCT Cooling RD13 Florence, July 201310 C 3 F 8 evaporative system Very stable operation To be replace by thermo-siphon system during LS1 Cooling pipes Number of active cooling loops

11. Hybrid Temperature RD13 Florence, July 201311 Very uniform in ϕ and z direction Bumps in B3 is due to one cooling loop set to a higher value Sensor temperature = hybrid temp – 3.7°C (FEA results) Barrel Red: link 0 (outer face) Blue: link 1 (inner face)

12. Noise (response curve) RD13 Florence, July 201312 Noise (response curve) is deduced from the width of threshold curves at 2fC charge injection in the gain calibration runs. Middle CiS modules show ~10% increase from 2010 to 2012 Oct. 2010 Dec. 2012

13. Noise of each module (EC) RD13 Florence, July 201313 Middle CiS module (green, pink) show excess noise Inner CiS modules (O2 enriched) stay comparable with others Hamamatsu: red: C-side blue: A-side CiS: green: C-side pink: A-side

14. Stability of Noise and Gain RD13 Florence, July 201314 ENC of modules decreased in 2010 with chip # dependency Middle CiS modules show increase of 10% in ENC in 2012 All chip gain decreased in mid 20122 Luminosity middle (CiS)<100> inner (HMT/CiS) short middle (CiS)

15. HV Current (Barrel Dec 2012) RD13 Florence, July 201315 Raw HV current observed. Temperature corrected current at 0 o C, assuming all are due to the bulk leakage current. Scaling formula of bulk leakage current:

16. Evolution of Leakage Current and model Prediction RD13 Florence, July 201316 The data are the average current at 0°C from module with HV > 140V The lines are prediction by Hamburg/Dortmund module using temperature sensor data Results from FLUKA simulations are used to convert the delivered Lumi into 1MeV neutron-equivalent fluence at corresponding barrel layers SCT Barrel

17. Estimated radiation level by the end of 2012 RD13 Florence, July 201317 1 MeV n-eq fluence received Integrated luminosity delivered = 5.8 (7 TeV) + 23.8 (8 TeV) fb -1 + using the Fluka simulation 10 15 cm -2  n-eq [cm -2 ] 10 12 10 13 10 14 10 15 10 16 SCT Pixel

18. Raw HV (EC) RD13 Florence, July 201318 Modules of side-A systematically show higher current by ~20% (due to N 2 temperature) Disks 8 and 9 show higher current (expected from FLUKS simulations) Difficult to normalize to 0°C due to large uncertainty in sensors temperature (work in progress) Hamamatsu: red: C-side blue: A-side CiS: green: C-side pink: A-side

19. Anomalous CiS Currents RD13 Florence, July 201319 In May 2012 we started getting unrecoverable ROD busy after a few hours of stable beam (high luminosity) 19 Online display Example of HV current deterioration red : Bias Voltage, blue : HV Current It was due to high current of EC middle CiS modules The HV current varies during the beam time Tentative solution: standy-by voltage kept at 5V (normal 50V) Some sensors now operate at lower bias voltages, but this only marginally affecting efficiency

20. RD13 Florence, July 201320 HV/Current profiles in early Nov 2012 with long stable beam runs Typical 3 modules with HPK (left) and CiS (right) sensors The last run is a day-long calibration run (no beam) All Hamamatsu modules show stable current with/without beam CiS modules simultaneously (but with different amount) exhibit similar current shapes only during beam time, in both sides A and C. However, the current shape differs run by run. Excess current disappears by turning HV down to 5V during stand-by. Anomalous CiS Currents…

21. RD13 Florence, July 2013 21 Sensor Differences Points of differences ManufacturersHamamatsuCiS Bias resistors (1.25MW)polysiliconimplant meander Al strip/implant widths22/16 mm16/20 mm Guard ringsingle ring, floating 11+5 p + rings, potential by punch-through current Front surface passivationSiO 2 SiO 2 and Si 3 N 4 Rear metal HV contactunpolishedpolished Bulk materialstandard standard (middle) oxygen-enriched (inner) Micro-dischargenoa problem at low(<30%) RH

22. RD13 Florence, July 2013 22 The Barrel layer B3 received 5x10 12 1 MeV n eq cm -2 fluence by the end of 2012. The cooling system has been working very well sustaining the uniform and stable temperatures for all modules. The noise (ENC) and gain have been rather stable except for noise of the middle modules with CiS sensors. The HV current at 150V steadily increased. Barrel layers show very flat distribution. The model predictions including annealing effects reproduce the leakage current within 1σ (~20%) with no parameter re-adjustments. All modules with CiS sensors are showing simultaneously anomalous current. No such anomalies are seen in any of modules with Hamamatsu sensors. Summary

23. RD13 Florence, July 2013 23 Backup

24. RD13 Florence, July 2013 24 Hamburg/Dortmund Model Based on Moll’s thesis [1], the leakage current coefficient a is given by Krasel [2] is: Note : last two equations in [2] are corrected here. [1] M. Moll, DESY-THESIS-1999-040 (Dec 1999) [2] Oraf Krasel, Dortmund Dissertation, July 2004