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 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 Inter-column depletion at ~2V Full, under-column depletion at 40V

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

6 Top and Edge TCTs 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 Top TCT λ = 1064 nm Edge TCT λ = 1064 nm

7 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 Top TCT λ = 1064 nm Edge TCT λ = 1064 nm Top and Edge TCTs

8 Example Waveform (Top Illumination) Rise time of first peak gives velocity profile Integration of peaks gives charge collected N-type column P-type column Charge Deposition First Rise: Electrons Move towards Collection 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 Third Rise: Holes Approach Column

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

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

11 Non-Irradiated Top TCT – Charge Collection

12 Non-Irradiated Top TCT – Velocity Maps

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

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

15 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 Non-Irradiated Edge TCT - Charge Collection 0 V2 V 4 V 6 V8 V 10 V 20 V Charge Collected [Arb. Units]

16 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 0 V2 V 4 V 6 V8 V 10 V Non-Irradiated Edge TCT - Velocity Profiles 20 V Velocity [Arb. Units]

17 Irradiation and Annealing Sample irradiated in Ljubljana facilities. Irradiation fluence was 5x MeV n equ cm -2. Sample always annealed in the setup with the Peltier element constant sample temperature: -20 o C 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 100 V 400 V Charge Collected [Arb. Units]

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

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

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

22 400V bias Charge Collected [Arb. Units] 20 minutes40 minutes 100 minutes 300 minutes Post-Annealed Irradiated Top TCT - Charge Collected

23 Post-Annealed Irradiated Top TCT - Velocity Profiles Velocity [Arb. Units] 20 minutes40 minutes 100 minutes 300 minutes

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

27 Backup Slides

28 Leakage Current

29 Annealing Effects – 20 mins 0V - 400V in steps of 50V 0V 50V100V 150V200V250V 300V350V400V

30 Annealing Effects – 40 mins 0V - 400V in steps of 50V 0V 50V100V 150V200V250V 300V350V400V

31 Annealing Effects – 100 mins 0V - 400V in steps of 50V 0V 50V100V 150V200V250V 300V350V400V

32 Annealing Effects – 300 mins 0V - 400V in steps of 50V 0V 50V100V 150V200V250V 300V350V400V

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