1. Annealing effects in irradiated HPK strip detectors measured with SCT128 chip Igor Mandić 1, Vladimir Cindro 1, Gregor Kramberger 1, Marko Zavrtanik 1, Marko Milovanović 1 and Marko Mikuž 1,2 1 Jožef Stefan Institute, Ljubljana, Slovenia 2 Faculty of Mathematics and Physics, University of Ljubljana, Slovenia 1 I. Mandić, 16th RD50 Workshop, Barcelona, Spain, 31 May-2 June 2010

2. miniature microsctrip Hamamatsu detectors from ATLAS strip upgrade project p-type, FZ, 320 µm thick, 75 µm pitch, 1x1 cm2 (ATLAS07A, Z3, W44) detectors irradiated with neutrons in Ljubljana reactor signals from 90 Sr electrons measured with SCT128 chip 2 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 irradiated to 5∙10 15 n/cm 2 Φ = 5·10 15 n/cm 2  repeat this measurement with new detector and new SCT128 chip Plot showed at the last RD50 workshop at CERN: 3 I. Mandić, 16th RD50 Workshop, Barcelona, Spain, 31 May-2 June 2010

4. 44 because of problems with test board, anneaing measurements made only up to Bias = 1000 V.  Rise of MPV with annealing time confirmed

5. 55 I. Mandić, 16th RD50 Workshop, Barcelona, Spain, 31 May-2 June 2010 black: new blue: old  Good agreement with first measuremnt

6. 66 I. Mandić, 16th RD50 Workshop, Barcelona, Spain, 31 May-2 June 2010 black: new blue: old black: new blue: old Noise: Signal/Noise

7. 77 I. Mandić, 16th RD50 Workshop, Barcelona, Spain, 31 May-2 June 2010 Current: rise of leakage current with annealing time agreement with previous measurmenet found

8. 888 I. Mandić, 16th RD50 Workshop, Barcelona, Spain, 31 May-2 June 2010 problem on test board was fixed, measurements up to 1400 V good agreement with old data at high voltages spectra not Landau, fit doesn’t make much shape

9. 999 I. Mandić, 16th RD50 Workshop, Barcelona, Spain, 31 May-2 June 2010 Measurements with detector irradiated to Φ eq =1∙10 15 n/cm 2  Sharp rise of MPV with annealing time at high voltage: multiplication effects  the highest voltage at which measurements can be taken falls with annealing time: multiplication effects

10. 10 I. Mandić, 16th RD50 Workshop, Barcelona, Spain, 31 May-2 June 2010 shown by G. Casse at Trento 2010 workshop  agreement with Liverpool measurements if annealing acceleration factor t 60 /t 20 ~ 500 Φ eq =1∙10 15 n/cm 2, Most Probable Signal:

11. 11 I. Mandić, 16th RD50 Workshop, Barcelona, Spain, 31 May-2 June 2010 Φ eq =1∙10 15 n/cm 2, Current: G. Casse, Trento 2010:  increase of current with annealing at high voltages  multiplication  at lower voltages agreement with Liverpool results

12. 12 Φ eq =1∙10 15 n/cm 2, Noise: 12 I. Mandić, 16th RD50 Workshop, Barcelona, Spain, 31 May-2 June 2010  after certain annealing time sharp increase of noise, s  signal becomes very unstable, measurements not possible at this or higher voltages any more

13. 13 I. Mandić, 16th RD50 Workshop, Barcelona, Spain, 31 May-2 June 2010 Normal event: Φ eq =1∙10 15 n/cm 2 Bias = 800 V:Bias = 1400 V: Typical event at t = 2480 min:

14. 14 I. Mandić, 16th RD50 Workshop, Barcelona, Spain, 31 May-2 June 2010  at same current higher noise measured in more annealed detector  before multiplication large noise scales with current  in more annealed detector: more multiplication noise vs. current, measured at different annealing times Voltages:600,800,1000 1200,1400 Φ eq =5∙10 15 n/cm 2

15. 15 I. Mandić, 16th RD50 Workshop, Barcelona, Spain, 31 May-2 June 2010 Φ eq =5∙10 15 n/cm 2 Noise distribution measured in dedicated run (no signals):  Pedestals and common mode subtracted cumulative distribution of noise  measure of noise occupancy cumulative distribution of “signal” from fit of Landau + Gaus  estimate of efficiency 22 mV = 1 fC Log scale Lin scale

16. 16 I. Mandić, 16th RD50 Workshop, Barcelona, Spain, 31 May-2 June 2010 Φ eq =1∙10 15 n/cm 2

17. 17 I. Mandić, 16th RD50 Workshop, Barcelona, Spain, 31 May-2 June 2010 Conclusions at high fluences and high bias voltages multiplication effects influence annealing behavior: - multiplication effects increase with annealing time  increase of space charge concentration  higher electric fields  more multiplication with detector irradiated to 5∙10 15 n/cm 2 measurements could be done up to Bias = 1400 V at all annealing times with detector irradiated to 1∙10 15 n/cm 2 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 possible noise increases because of multiplication above the expected from shot noise  but noise distribution remains gaussian signal distribution changes but Signal/Noise (or effciency vs noise occupancy) increases with multiplication  sufficient cooling needed, because detector current increases