tct measurements with irradiated strip detectors
DESCRIPTION
TCT measurements with irradiated strip detectors Igor Mandić 1 , Vladimir Cindro 1 , Andrej Gorišek 1 , Gregor Kramberger 1 , Marko Milovanović 1 , Marko Mikuž 1,2 , Marko Zavrtanik 1 1 Jožef Stefan Institute, Ljubljana, Slovenia - PowerPoint PPT PresentationTRANSCRIPT
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TCT measurements with irradiated strip
detectors
Igor Mandić1, Vladimir Cindro1, Andrej Gorišek1, Gregor Kramberger1, Marko Milovanović1, Marko Mikuž1,2, Marko Zavrtanik1
1Jožef Stefan Institute, Ljubljana, Slovenia2 Faculty of Mathematics and Physics, University of Ljubljana, Slovenia
Most measurements made by diploma student Mitja Krnel
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• TCT with focused IR laser light • light beam directed on the surface of strip detector: Top-TCT
• “Spaghetti” detectors produced by Micron: - p-type, FZ, 300 µm thick, 4x4 mm2 - strip pitch: 80 µm - implant width: 20 µm, DC coupled
Spaghetti: all strips connected on one side only one wire bond faster work… E field as in strip detector, weighting field as in pad detector Spaghetti Type 1 500 µm of implant not covered by metal
• detectors irradiated to 1∙1015 , 2∙1015 and 5∙1015 n/cm2
• measurements after several annealing steps at 60°C up to total annealing of 5120 minutes at 60°C
Motivation: check the uniformity of response with Spaghetti T1 laser measurement possible also under implants
Introduction:
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Setup
Detector box
Cooled support
y table
Laser
Laser driver
detector HV
Peltier controller
z table x table
1GHz oscilloscope
cooling pipes
fast current amplifier
trigger line
optical fiber & focusing system
width of light pulses ~ 100 ps , repetition rate 200 Hz
beam diameter in the silicon FWHM~7 mm
Bias-T
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All strips connected togetherE field as in strip detector weighting field as pad detector signal is a sum of currents induced on all strips
Last 500 µm of implants not covered with metal
Detector
4 m
m
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Signals
Before irradiation
Bias = 100 V
scan laser spot across the surface
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Signals inducedby laser beamat different locations:
No metal
metal
Guard ring• before irradiation• bias = 100 V (depleted)
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Before irradiation: scan over detector surface (step x: 2.5 µm, y: 50 µm)Bias = 100 V (depleted)
Metal
End of implants
Guard ring
Charge = integral of current pulse (offline)
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Some signal also when beam on metal tails of light spot
guard ring
met
alno
met
al
Reflection from metal
Before irradiation
Bias = 100 V
No significant difference between metal and no-metal!
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Irradiated detector
Φeq = 5·1015 n/cm2
Bias = 1000 VAnnealed 5120 minutes at 60°C
multiplication expected
End of implants
Large signals close to guard ring
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Irradiated detector
Φeq = 5·1015 n/cm2; Bias = 1000 V; Annealed 5120 minutes at 60 C
high signals also near the guard-ring parallel to the strip
strips Guard ring
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Δt = 0.2 ns
Δt = 0.6 ns
Δt = 0.7 ns
Step: 50 µm(dot colors correspond to line colors)
Irradiated detector
Φeq = 5·1015 n/cm2
Bias = 1000 VAnnealed 5120 minutes at 60°C
guard ring
met
alno
met
al
The second peak from high field at the end of implant.
v = 107 cm/sΔt ~ 0.5 ns v·Δt ~ 50 µm
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guard ring
met
alno
met
al
Scan over “no metal”
Pulses from scan over“no metal” part
Pulses from scan over “metal”
Scan over “metal”
Irradiated detector Φeq = 5·1015 n/cm2 ,Bias = 1000 V, annealed 5120 minutes at 60°C
Complicated behavior near guard rings!
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Signals on edges increase with long term annealing multiplication effects
Irradiated detector Φeq = 5·1015 n/cm2 , Bias = 1000 V
80 min at 60°C 320 min at 60°C
1280 min at 60°C 5120 min at 60°C
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Irradiated detector: effect of annealing
Φeq = 5·1015 n/cm2;Bias = 1000 V;
Scan over metalized strips ~ 1 mm from guard ring
Scan over non metalized implants (~ 0.5 mm from guard ring)
impl
ant
more non-uniform with annealing multiplication at the edge of implants• effect increases closer to guard-ring
1000 V
1000 V
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• Annealing of CCE depends on location
Increase of charge with long term annealing near implant edge
Annealing Φeq = 5·1015 n/cm2
Bias = 1000 V
impl
ant
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Bias = 600 V;Φeq = 5·1015 n/cm2;
smaller changes of charge variations with annealing charge drops with reverse annealing no (or less) multiplication
Irradiated detector: annealing at lower bias voltage
600 V
Scan over metalized strips ~ 1 mm from guard ring
Scan over non metalized implants ~ 0.5 mm from guard ring im
plan
t
600 V
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2e15, annealed 5120 min 5e15, annealed 5120 minVoltage scan
Charge variations increase with bias voltage!
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Spaghetti detectors:
all strips connected sum of signals from all strips measured opposite polarity contributions from neighbor strips added variations of CCE dumped in spaghetti detectors!
Hamamatsu detector irradiated to 1015 , ~5000 min at 60C, only one strip connected to amplifier: (see talk from Bari: https://indico.cern.ch/materialDisplay.py?contribId=5&sessionId=5&materialId=slides&confId=175330)
Red: measured
Blue: sum of signals fromall strips at equivalentlocation:
k Pitchkii xsxs )()(
to amplifier
metalized strips
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Summary
• Top – TCT measurements with spaghetti detectors
• large signals (multiplication) close to guard ring care should be taken to get realistic CCE (e.g. in test beam ….)
• largest charge measured at edges of implants signs of charge multiplication (annealing behavior, bias dependence … ) largest at the edge of implant
• variations of collected charge across detector increase with multiplication
variations are dumped in spaghetti diodes because of negative contributions from neighbor strips
test beam experiment can tell how problematic are these variations, if there are dead regions where CCE falls below threshold …. ( in HEP experiments most tracks are crossing the detector at an angle)
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Annealing Φeq = 2·1015 n/cm2
Bias = 1000 V
• larger non-uniformity after long annealing
• annealing of CCE depends on location
• increase of charge with long annealing larger closer to implant edge
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Annealing Φeq = 2·1015 n/cm2
Bias = 1000 V
• slightly different behavior at larger distance from guard-ring
metal