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Annealing effects in irradiated HPK strip detectors measured with SCT128 chip

Annealing effects in irradiated HPK strip detectors measured with SCT128 chip Igor Mandić 1 , Vladimir Cindro 1 , Andrej Gorišek 1 , Gregor Kramberger 1 , Marko Milovanović 1 , Marko Mikuž 1,2 , Marko Zavrtanik 1 1 Jožef Stefan Institute, Ljubljana, Slovenia

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Annealing effects in irradiated HPK strip detectors measured with SCT128 chip

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  1. Annealing effects in irradiated HPK strip detectors measured with SCT128 chip Igor Mandić1, Vladimir Cindro1, Andrej Gorišek1,GregorKramberger1, Marko Milovanović1,Marko Mikuž1,2, Marko Zavrtanik1 1Jožef Stefan Institute, Ljubljana, Slovenia 2 Faculty of Mathematics and Physics,University of Ljubljana, Slovenia I. Mandić, 16th RD50 Workshop, Barcelona, Spain, 31 May - 2 June 2010

  2. Setup: • SCTA128VG chip • VME module SEQSI (for clock, commands...) • Tektronix digital scope for data acquisition • 90Sr source, photomultiplier, scintillator, • power supplies, coincidence circuit ...... • Most probablevalue (MPV) fromfitofLandau + Gaus to • distributionofmeasured signal clusterheights •  scale defined with signals from non-irradiated detector • Detectors: • p-type, FZ, 320 µm thick, 75 µm strip pitch, 1x1 cm2, producedbyHamamatsu • 1) ATLAS07-PSSSSD_Series I, W16, BZ3-P21: Φ = 5∙1015 n/cm2 • 2) ATLAS07-PSSSSD_Series I, W22, BZ3-P3: Φ = 1∙1015 n/cm2 • detectors irradiated with neutrons in reactor in Ljubljana I. Mandić, 16th RD50 Workshop, Barcelona, Spain, 31 May - 2 June 2010

  3. Motivation • large rise of collected charge with annealing time at high bias voltage • measured with detector (ATLAS07A, Z3, W44) irradiated to 5∙1015 n/cm2 Plot showed at the last RD50 workshop at CERN: Φ = 5·1015 n/cm2  repeat this measurement with new detector and new SCT128 chip I. Mandić, 16th RD50 Workshop, Barcelona, Spain, 31 May - 2 June 2010

  4. Φ =5∙1015 n/cm2, MPV vs time, newmeasurement • because of problems with test board, annealing measurements made • only up to 1000 V. rise of MPV with annealing time confirmed 4 I. Mandić, 16th RD50 Workshop, Barcelona, Spain, 31 May - 2 June 2010

  5. Φ =5∙1015 n/cm2, comparison with old measurement black: new blue: old  Good agreement with first measuremnt 5 I. Mandić, 16th RD50 Workshop, Barcelona, Spain, 31 May - 2 June 2010

  6. Φ =5∙1015 n/cm2, comparison with old measurement black: new blue: old Noise: black: new blue: old Signal/Noise: 6 I. Mandić, 16th RD50 Workshop, Barcelona, Spain, 31 May-2 June 2010

  7. Φ =5∙1015 n/cm2, current: New measurement:  rise of leakage current with annealing time black: new blue: old • Good agreement with previous • measuremenet 7 I. Mandić, 16th RD50 Workshop, Barcelona, Spain, 31 May - 2 June 2010

  8. Φ =5∙1015 n/cm2: • problem on test board was fixed, • measurements up to 1400 V • good agreement with old data also • at high voltage • at high voltages spectra not Landau • multiplication Bias = 900 V Bias = 1400 V 8 8 I. Mandić, 16th RD50 Workshop, Barcelona, Spain, 31 May - 2 June2010

  9. Measurements with detector irradiated to Φeq =1∙1015 n/cm2 Space charge anneals, electric field drops: high voltage: less multiplication  less charge lower voltages: larger depleted region, less trapping  more charge • rise of MPV at long annealing times at high voltage: • space charge concentration rises => higher electric field => more multiplication • the highest voltage at which measurements can be taken falls with increasing • annealing time: too much multiplication 9 9 I. Mandić, 16th RD50 Workshop, Barcelona, Spain, 31 May-2 June 2010

  10. Φ =1∙1015n/cm2 • agreement with Liverpool measurements if annealing acceleration factor t60/t20 ~ 500 •  1000 days at 20 C ~ 3000 minutes at 60C Plotsshowed by G. Casse at Trento 2010 workshop: 10 10 10 I. Mandić, 16th RD50 Workshop, Barcelona, Spain, 31 May-2 June 2010

  11. Φeq =1∙1015 n/cm2, Current: • increase of current with annealing at high voltages • agreement with Liverpool measurements G. Casse, Trento 2010: 11 11 11 11 I. Mandić, 16th RD50 Workshop, Barcelona, Spain, 31 May-2 June 2010

  12. Φeq =1∙1015 n/cm2, Noise: • after certain annealing time sharp increase of noise at bias above 800 V • signal becomes very unstable, measurements not possible at this or • higher voltage any more 12 12 12 12 12 I. Mandić, 16th RD50 Workshop, Barcelona, Spain, 31 May-2 June 2010

  13. Φeq =1∙1015 n/cm2 Bias = 800 V: Bias = 1400 V: Not used Typical event at t = 2480 min: Normal event: 13 13 13 13 I. Mandić, 16th RD50 Workshop, Barcelona, Spain, 31 May-2 June 2010

  14. Φeq =5∙1015n/cm2 • noise vs. current, measured at different annealing times • at same current higher noise measured in more annealed detector •  after annealing: more multiplication, larger noise at same current •  if multiplication not large noise scales with current as expected 14 14 14 14 14 I. Mandić, 16th RD50 Workshop, Barcelona, Spain, 31 May-2 June 2010

  15. Φeq =5∙1015n/cm2, annealdfor 5040 min. • distribution of hits measured in dedicated • noise run (no 90Sr source): •  pedestals and common mode subtracted • cumulative distribution of noise  measures • probability to find a noise hit above given voltage •  no significant change of shape with bias • calculated from fit of Landau + Gauss •  estimate of signal efficiency Log scale 22 mV = 1 fC Lin scale 15 15 15 15 15 I. Mandić, 16th RD50 Workshop, Barcelona, Spain, 31 May-2 June 2010

  16. Φeq =1∙1015n/cm2, annealedfor 5040 min. • no lagre multiplication at these voltages • (no increase of leakage current, no increase • of MPV) • if noise distribution Gaussian (no significant • tails), good signal efficiency achieved at low • noise occupancy already at modest bias voltages • in real application many noise sources •  good to have large signals 20 mV = 1 fC Log scale Lin scale 16 16 16 16 16 I. Mandić, 16th RD50 Workshop, Barcelona, Spain, 31 May-2 June 2010

  17. Conclusions • at high fluences and high bias voltages multiplication effects influenceannealing • behavior: • multiplication effects increase withannealing time larger than • ~ 500 minutes @ 60°C (~170 days @ 20°C) • increase of space charge concentration  higher electric fields  more multiplication • with detector irradiated to 5∙1015 n/cm2 measurements could be done up to Bias = 1400 V • at all annealing times • with detector irradiated to 1∙1015 n/cm2 bias voltage at which output gets unstable • lowers with increasing annealing time •  at lower fluences operation in high multiplication regime not stable • higher collected charge can be measured with more irradiated detectors after annealing • because running in high multiplication mode possible • noise increases because of multiplication •  shape of noise distribution does not change significantly 17 17 17 17 17 17 I. Mandić, 16th RD50 Workshop, Barcelona, Spain, 31 May-2 June 2010

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