1. Preliminary Analysis of Edge and Top TCTs for Irradiated 3D Silicon Strip Detectors
Graeme Stewarta, R. Batesa, G. Pellegrinib, G. Krambergerc, M. Milovanovicc
a: University of Glasgow, School of Physics and Astronomy, Kelvin Building, University Avenue, Glasgow, G12 8QQ
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 Results Conclusions 3D Detectors
TCT Measurements
TCT Results
Non-Irradiated Top and Edge TCTs
Irradiated Top TCTs
Annealing Effects
Conclusions

3. Introduction
Radiation hard 3D detectors are a candidate for LHC upgrades.
Transient Current Techniques (TCTs) provide a method for investigating electric fields in silicon detectors.
In a TCT measurement, a short laser pulse is shone in a particular line through the detector.
Charge and current data is collected giving new information on the operation of 3D devices.
This can be repeated at many points across a detector’s surface to map the electric field.

4. 3D Detector Design
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 285 μm thick.
11 strips were bonded up but with readout only from the central strip.
IR Photon 4 4

5. TCT setup The system is set in dry air atmosphere! Cooling to ~-20oC
Peltier controller
The system is set in dry air atmosphere!
Cooling to ~-20oC
y table
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
G. Kramberger – 15th RD50 Meeting, 2009

6. Top and Edge TCTs Advantages of TCTs:
FWHM ~8 μm
Top TCT
λ = 1064nm
Edge TCT
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
Easier mounting and handling
Not only charge but also induced current is measured – a lot more information is obtained

7. Top and Edge TCTs Drawbacks of TCTs:
FWHM ~8 μm
Top TCT
λ = 1064nm
Edge TCT
Drawbacks of TCTs:
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

8. Example Waveform Rise time of fastest peak can give velocity profile
Reflection
Integration of peaks gives charge collected
Faster electron peak
Slower hole peak

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

10. Non-Irradiated Top TCT
20V
Add columns and less waveforms
20V

11. Non-Irradiated Top TCT0V 3V 6V 9V
12V
15V
Inter-column depletion at ~2V
Full, under-column
depletion at 40V

12. Non-Irradiated Edge TCT
Laser scans across edge
N-type Electrodes
Waveforms collected at 20V
P-type Electrodes

13. Non-Irradiated Edge TCT0V 1V 2V 3V 4V 5V
Full depletion of inter-column region by 3V
Depletion of the region beneath the electron collecting n-type columns beginning by 4V
P-type columns not fully depleted by 6V 6V
20V

14. Irradiation and Annealing
Sample irradiated in Ljubljana facilities.
Irradiation fluence was 5x1015 1MeV Nequ cm-2.
Sample always annealed in the setup with the Peltier element
constant laboratory temperature: 21 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

15. Irradiated Top TCT 400V 60V 200V 200V
Add in columns
Waveforms from the region between n-type columns show a double peak for electron and hole collection and a postive electron signal past 40 μm
Waveforms from the region across the p-type column show the same peaks without the bipolar signal

16. Annealing Effects End of beneficial annealing at around 80 mins.
After type inversion 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 2010.

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

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

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

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

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

22. Conclusions Future Analysis:
Edge and top TCTs provide a new method to probe 3D devices.
Substantial depletion occurs at very low voltages.
Irradiation and subsequent annealing alters the collection of electrons and holes.
Future Analysis:
Compare the velocity profiles of non-irradiated and irradiated detectors.
From the velocity profiles, electric field can be derived.
Edge TCTs of an irradiated sample, before and after annealing.