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Analysis of Edge and Surface TCTs for Irradiated 3D Silicon Strip Detectors

Analysis of Edge and Surface TCTs for Irradiated 3D Silicon Strip Detectors. Graeme Stewart a , R. Bates a , C. Corral b , M. Fantoba b , G. Kramberger c , G. Pellegrini b , M. Milovanovic b a: SUPA, School of Physics and Astronomy, University of Glasgow, Glasgow, UK

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Analysis of Edge and Surface TCTs for Irradiated 3D Silicon Strip Detectors

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  1. Analysis of Edge and Surface TCTs for Irradiated 3D Silicon Strip Detectors Graeme Stewarta,R.Batesa, C. Corralb, M. Fantobab, G. Krambergerc, G. Pellegrinib, M. Milovanovicb a: SUPA, School of Physics and Astronomy, University of Glasgow, Glasgow, UK b: Centro Nacional de Microelectrónica, Campus Universidad Autónoma de Barcelona, Spain c: J. Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia

  2. Contents • Introduction • TCT Measurements • 3D Detectors • TCT Results • Non-Irradiated Top and Edge TCTs • Irradiated Top TCTs • Annealing Effects • Conclusions

  3. Introduction • Transient Current Techniques (TCTs) provide a method for investigating electric fields in silicon detectors. • In a TCT measurement, a short, IR laser pulse is incident on a particular line through the detector. • Current data is collected giving information on the charge and velocity of carriers in 3D devices. • This can be repeated at many points across a detector’s surface to map the electric field.

  4. Columns etched from opposite sides of substrate and don't pass through full thickness All fabrication done at CNM Distance between columns is 80 μm, with a 25 μm wide Aluminium strip connecting n-type columns. Substrate is 245 μm thick. 11 strips were bonded up but with readout only from the central strip. 3D Detector Design IR Photon Full, under-column depletion at 40V Inter-column depletion at ~2V

  5. Peltier controller The system is set in dry air atmosphere Cooling to -20oC y table TCT setup Cooled support Cu block Detector The whole system is completely computer controlled 100 ps pulse 200 Hz repetition l=1064 nm cooling pipes x table z table 1 GHz oscilloscope detector HV Bias T Laser 2 fast current amplifiers (2.5 GHz) Laser driver trigger line

  6. Top and Edge TCTs Top TCT λ = 1064 nm Advantages of TCTs: • Position of e-h generation can be controlled by moving tables • The amount of injected e-h pairs can be controlled by tuning the laser power • Not charge but induced current is measured – a lot more information is obtained FWHM ~8 μm Edge TCT λ = 1064 nm

  7. Top and Edge TCTs Top TCT λ = 1064 nm Drawbacks of TCTs Edge TCT: • Applicable only for strip/pixel detectors if 1064 nm laser is used (light must penetrate guard ring region) • Only the position perpendicular to strips can be used due to widening of the beam! Beam is “tuned” for a particular strip • Light injection side has to be polished to have a good focus – depth resolution • It is not possible to study charge sharing due to illumination of all strips Top TCT: • Cannot illuminate under Al strips. FWHM ~8 μm Edge TCT λ = 1064 nm

  8. P-type column Rise time of first peak gives velocity profile N-type column Charge Deposition First Rise: Electrons Move towards Collection Column Integration of peaks gives charge collected Third Rise: Holes Approach Column First Fall: Holes Move into Region of Lower Space Charge Second Rise: Electrons Move to Very High Space Charge Region Second Fall: Electrons Collected at Column Example Waveform (Top Illumination)

  9. Non-readout n-type Electrodes p-type Electrodes Laser scans across surface Unit Cell Readout n-type Electrodes Non-Irradiated Top TCT Charge Collected [Arb. Units] Map is charge collected in 20 ns after laser pulse.

  10. 62 V Non-Irradiated Top TCT Charge Collected [Arb. Units]

  11. Non-Irradiated Top TCT – Charge Collection

  12. Non-Irradiated Top TCT – Velocity Maps

  13. Velocity [Arb. Units] Non-Irradiated Top TCT – Velocity Maps (80 V)

  14. P-type Electrodes Laser scans across edge N-type Electrodes Non-Irradiated Edge TCT Charge Collected [Arb. Units]

  15. Non-Irradiated Edge TCT - Charge Collection Charge Collected [Arb. Units] • Full depletion of inter-column region by 4 V • Depletion of the region beneath the electron collecting n-type columns beginning by 4 V • Column ends not fully depleted by 20 V 4 V 0 V 2 V 10 V 6 V 8 V 20 V

  16. Non-Irradiated Edge TCT - Velocity Profiles Velocity [Arb. Units] • Non-uniform velocity profile across the device • Velocity increases past lateral depletion voltage of 4 V • Edges of detector show low velocities, even at 20 V 4 V 0 V 2 V 10 V 6 V 8 V 20 V

  17. Irradiation and Annealing • Sample irradiated in Ljubljana facilities. • Irradiation fluence was 5x1015 1 MeV nequ cm-2. • Sample always annealed in the setup with the Peltier element • constant sample temperature: -20 oC • stable position/laser • sample temperature stabilized to less than 1°C • Annealing at 60°C for a cumulative time of 600 minutes. • After each annealing step, voltage scans from 0V up to 400V were performed

  18. Irradiated Top TCT Charge Collected [Arb. Units] 100 V 400 V

  19. Charge Collected [Arb. Units] 60 V 40 V 20 V 80 V 120 V 160 V 400 V 300 V 200 V Irradiated Top TCT - Charge Collection

  20. Velocity [Arb. Units] 60 V 40 V 20 V 80 V 120 V 160 V 400 V 300 V 200 V Irradiated Top TCT - Velocity Profile

  21. Resistance vs Annealing time, shown by C. Fleta at 15 RD50, June 2010. • Significant annealing beyond beneficial annealing leads to a decrease in the interstrip resistance. • Eventually, the strips short together. Annealing Effects • End of beneficial annealing at around 80 mins. • After 100 minutes, we have a longer term reverse annealing [M. Moll, PhD thesis 1999, Uni. Hamburg]

  22. Charge Collected [Arb. Units] 20 minutes 40 minutes 300 minutes 100 minutes Post-Annealed Irradiated Top TCT - Charge Collected 400V bias

  23. Velocity [Arb. Units] 20 minutes 40 minutes 300 minutes 100 minutes Post-Annealed Irradiated Top TCT - Velocity Profiles

  24. Conclusions • Edge and top TCTs provide a new method to probe 3D devices. • Velocity information can be collected. • In a non-irradiated device, the velocity continues increasing after full charge collection is achieved. • Velocity and charge collection is greater below n-type columns than p-type columns at same bias voltage. • Irradiation and subsequent annealing alters the collection of electrons and holes. • Charge Trapping suppresses hole signal • After annealing, charge multiplication effects at 400 V

  25. Future Work • Edge TCT scan of non-irradiated device up to saturated velocity (80 V) • Edge TCT of irradiated device

  26. Backup Slides

  27. Leakage Current

  28. 50V 100V 0V 150V 200V 250V 300V 350V 400V 0V - 400V in steps of 50V Annealing Effects – 20 mins

  29. 50V 100V 0V 150V 200V 250V 300V 350V 400V 0V - 400V in steps of 50V Annealing Effects – 40 mins

  30. 50V 100V 0V 150V 200V 250V 300V 350V 400V 0V - 400V in steps of 50V Annealing Effects – 100 mins

  31. 50V 100V 0V 150V 200V 250V 300V 350V 400V 0V - 400V in steps of 50V Annealing Effects – 300 mins

  32. 100V - 300V in steps of 100V Annealing Effects – 600 mins 100V 200V 300V

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