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Radiation-Hard Optical Link for the ATLAS Pixel Detector

Development and testing of radiation-hard optical links for the ATLAS Pixel Detector at Ohio State University, with detailed specifications and performance measurements. The project involves the production of Opto-boards, VCSEL driver circuits, digital optical receivers, and more to meet the detector's requirements.

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Radiation-Hard Optical Link for the ATLAS Pixel Detector

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  1. Radiation-Hard Optical Link for the ATLAS Pixel Detector Richard Kass The Ohio State University W. Fernando, K.K. Gan, P. D. Jackson, M. Johnson, H. Kagan, R. Kass, A. Rahimi, C. Rush, S. Smith, R. Ter-Antonian The Ohio State University P. Buchholz, M. Holder, A. Roggenbuck, P. Schade, M. Ziolkowski Universitaet Siegen, Germany OUTLINE Introduction Proton irradiation results Opto-board production Summary IEEE05/Puerto Rico

  2. The ATLAS Pixel Detector • Inner most charged particle tracking • Pixel size 50mm by 400 mm • ~100 million pixels • Barrel layers at r = 5.1 - 12.3 cm • Disks at z = 50 - 65 cm • Dosage after 10 years: • optical link 17 Mrad or 3.7 x 1014 1-MeV neq/cm2 ~380mm ~1850mm disks barrel layers IEEE05/Puerto Rico

  3. ATLAS Pixel Opto-link VCSEL:Vertical Cavity Surface Emitting Laser diode VDC:VCSEL Driver Circuit PIN:PiNdiode DORIC:Digital Optical Receiver Integrated Circuit Opto-board:Holds VDCs, DORICs, PINs, VCSELs Uses BeO as substrate IEEE05/Puerto Rico

  4. VCSELDriverCircuitSpecs • Convert LVDS input signal into single-ended signal appropriate to drive the VCSEL diode • Output (bright) current: 0 to 20 mA, controlled by externally controllable current (Iset) • Standing (dim) current: ~ 1 mA for fast off-to-on switching of VCSEL • Rise & fall times: 1 ns nominal (40 MHz signals) • Duty cycle: (50 ± 4)% • “On” voltage of VCSEL: up to 2.3 V at 20 mA for 2.5 V supply • Constant current consumption balanced between ON and OFF state • Use IBM 0.25 mm CMOS for radiation hardness • Use TRUELIGHT “high power oxide” common cathode VCSEL arrays IEEE05/Puerto Rico

  5. 40MHz clock Command BPM Digital OpticalReceiverICSpecs • lDecode Bi-Phase Mark encoded (BPM) clock and command • signals from PIN diode • lInput signal size: • 40 mA - 1000 mA • lExtract 40 MHz clock • lDuty cycle: (50± 4)% • lTotal timing error: <1ns • lBit Error Rate (BER): • < 10-11 at end of life • Use Truelight common cathode PIN array • lUse IBM 0.25 CMOS for • radiation hardness IEEE05/Puerto Rico

  6. The Opto-board Optical signal electrical signal conversion occurs here Contains 7 optical links, each link serving one Pixel module Fabricated in 2 flavors • Layer B: for inner barrel, two data link per module for high occupancy • Layer D: for outer barrel and disks Fabricated with BeO for heat management • initial prototypes with FR4 for fast turn around and cost saving Need: 44 B boards 226 D boards Housing 2cm Opto-pack VCSEL array Pin array VDC DORIC IEEE05/Puerto Rico

  7. Opto-board Performance & Status Detailed measurements are done on all critical electrical and optical parameters to check performance/quality • LVDS rise/fall times, jitter…, • Optical power, optical rise/fall times, duty cycle… • The opto-boards meet or exceed all the pixel detector requirements Optical power @ 10 mA significantly > 500mW spec Minimum PIN current for No BIT Errors Optical power spec. spec. Minimum PIN current for no BIT errors significantly < 40mA spec IEEE05/Puerto Rico

  8. Radiation Hardness Measurements • Important to measure/certify radiation hardness of ASICs and opto-board and its components: • VCSEL and PIN arrays • VDC and DORIC chips • Encapsulant, fibers, glues, etc. • Use CERN’s T7 beam (24 GeV Proton) for radiation hardness studies • “Cold box” setup: electrical testing of DORIC and VDC • Exposed up to 62 Mrad • Shuttle setup: testing of optical links on opto-boards using DORIC and VDC • Can be moved in and out of beam remotely for VCSEL annealing • Exposed up to 32 Mrad IEEE05/Puerto Rico

  9. Opto-board clock PIN DORIC data VDC VCSEL VCSEL VDC Real Time Monitoring in Beam Test 25 meter optical fiber cable Real time testing of opto-board system using loop-back setup Signal routed back to opto-baord via test board attached to 80-pin connector bi-phase marked optical signal decoded data decoded clock Bit error test board In control room In beam lCompare transmitted and decoded data measure minimum PIN current for no bit errors lMeasure optical power IEEE05/Puerto Rico

  10. PIN Current Threshold vs Dosage 24 GeV protons @ CERN spec PIN current thresholds for no bit errors remain constant IEEE05/Puerto Rico

  11. Optical Power vs. Dosage • Irradiate ~5 Mrad/day (10 hours) with annealing rest of the day • Optical power decreases with dosage as expected due to VCSELs • Limited annealing recovers some lost power • Still acceptable power after 30 Mrad Spec IEEE05/Puerto Rico

  12. Opto-board Production Challenges lRigorous QA procedure: u72 hours of burn-in at 50oC u18 hours of 10 thermal cycles between -25oC and 50oC u8 hours of optical and electrical measurements lUse 2 ovens and 2 environmental chambers lImplemented an “early shift” to extend the work day But no shifts on weekends. lAggressive goals: uproduce 10 boards/week acomplete production in early October 2005 IEEE05/Puerto Rico

  13. Initial Production Problem lInitial plan was not to test chips before mounting on opto-board due to high yield during pre-production lA bunch of produced boards drew excessive current uthermal imaging showed power to ground shorts atest all chips before mounting on opto-boards Chip yield turned out to be ~98% VDC DORIC IEEE05/Puerto Rico

  14. Opto-board Production Status Recovered 18 opto-boards by stacking new chips on top of bad chips These re-worked boards passed the standard rigorous QA procedure Will use these boards as spares. 160 MHz opto-boards 80 MHz opto-boards lRelatively smooth production lOpto-board yield ~ 93% Production finished at OSU IEEE05/Puerto Rico

  15. Summary JOpto-boards of ATLAS pixel detector satisfy design spec. and radiation hardness requirement: low PIN current thresholds for no bit errors excellent optical power radiation hard up to ~ 30 Mrad JSimple & modular design allows smooth production opto-board production completed in seven months! For More Details see: ATLAS PIXEL OPTO-ELECTRONICS, K. E. Arms et al., Apr 2005. Submitted to NIM, e-Print Archive: physics/0504142 IEEE05/Puerto Rico

  16. Backup Slides IEEE05/Puerto Rico

  17. Setup for Irradiation in Shuttle at CERN OSU Shuttle test electronics prior to shipping to CERN 25 meter optical fiber Rad hard optical fibers Opto-boards CERN T7 Remotely moves in/out of beam CERN T7

  18. Proton Induced Bit Errors in PIN Convert observed bit errors into bit error rate at opto-link location: sSEU nBit error rate decreases with PIN current as expected bit error rate ~ 3 x 10-10 at 100 mA (1.4 errors/minute) FDORIC spec: 10-11 IEEE05/Puerto Rico

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