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Preliminary Analysis of Edge and Top TCTs for Irradiated 3D Silicon Strip Detectors. Graeme Stewart a , R. Bates a , G. Pellegrini b , G. Kramberger c , M. Milovanovic c a: University of Glasgow, School of Physics and Astronomy, Kelvin Building, University Avenue, Glasgow, G12 8QQ - PowerPoint PPT Presentation
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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 8QQb: Centro Nacional de Microelectrónica, Campus Universidad Autónoma de Barcelona, Spain
c: J. Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia
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Contents
• Introduction– 3D Detectors– TCT Measurements
• TCT Results– Non-Irradiated Top and Edge TCTs– Irradiated Top TCTs– Annealing Effects
• Conclusions
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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.
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• 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.
3D Detector Design
IR Photon
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Detector
Co
ole
d s
up
po
rt
y table
Laser
Laser driver
detector HV
Peltier controller
The whole system is completely computer controlled!
z tablex 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 ~-20oC
Bias T
100 ps pulse200 Hz repetition=1064 nm
G. Kramberger – 15th RD50 Meeting, 2009
TCT setup
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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• Easier mounting and handling• Not only charge but also induced current is measured – a lot more
information is obtained
FWHM ~8 μm
Top TCTλ = 1064nm
Edge TCTλ = 1064nm
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Top and Edge TCTs
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
FWHM ~8 μm
Top TCTλ = 1064nm
Edge TCTλ = 1064nm
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Example Waveform
Faster electron peak
Slower hole peak
Reflection
Rise time of fastest peak can give velocity profile
Integration of peaks gives charge collected
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Non-Irradiated Top TCT
Map is charge collected in 20 ns after laser pulse.
Readout n-type Electrodes
Non-readout n-type Electrodes p-type Electrodes
Laser scans across surface
Unit Cell
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Non-Irradiated Top TCT
20V
20V
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Non-Irradiated Top TCT
0V 3V 6V
9V 12V 15VInter-column depletion at ~2V
Full, under-columndepletion at 40V
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Non-Irradiated Edge TCT
N-type Electrodes
P-type Electrodes
Waveforms collected at 20V
Laser scans across edge
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Non-Irradiated Edge TCT
0V 1V 2V
3V 4V 5V
6V
• 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
20V
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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
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• 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
60V
Irradiated Top TCT
200V
200V400V
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Annealing Effects
• End of beneficial annealing at around 80 mins.
• After type inversion we have a longer term reverse annealing
NC
NC0
gC eq
NYNA
1 10 100 1000 10000annealing time at 60oC [min]
0
2
4
6
8
10
N
eff [
1011
cm-3
]
[M.Moll, PhD thesis 1999, Uni Hamburg]
• 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.
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Annealing Effects – 20 mins
0V - 400V in steps of 50V
0V 50V 100V
150V 200V 250V
300V 350V 400V
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Annealing Effects – 40 mins
0V - 400V in steps of 50V
0V 50V 100V
150V 200V 250V
300V 350V 400V
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Annealing Effects – 100 mins
0V - 400V in steps of 50V
0V 50V 100V
150V 200V 250V
300V 350V 400V
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Annealing Effects – 300 mins
0V - 400V in steps of 50V
0V 50V 100V
150V 200V 250V
300V 350V 400V
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Annealing Effects – 600 mins
100V - 300V in steps of 100V
100V
200V
300V
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Conclusions
• 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.
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