Post on 11-Jan-2016
Silicon pad detectors for LCCAL: characterisation and first results
Antonio BulgheroniUniversity of Milan – Italy
on behalf of
LCCAL: Official INFN R&D project, official DESY R&D project PRC R&D 00/02Contributors (Como, LNF, Padova, Trieste): M. Alemi, M.Bettini, S. Bertolucci, E. Borsato, M. Caccia, P.Checchia, C. Fanin, G. Fedel, J. Marczewski, S. Miscetti , M. Nicoletto, M. Prest, R. Peghin, L. Ramina, E. Vallazza.
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Calorimeter Layout
Absorber
Scintillator Silicon pad detectors
25 x 25 x 0.3 cm3
25 Cells 5 x 5 cm2
3 layers725 Pads ~ 1 x 1 cm2
2, 6 and 12 X0
Total of 50 layers27 X0
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Sensor details
Main characteristics:– Sensor thickness: 300m– Resistivity: 4-6k– AC coupling
• Silicon dioxide thickness: 265 nm
– Bias grid and guard ring
• 3M bias resistors• Symmetric
structureGuard ring pad
Bias pad
7 cm
6 cm
~0.9
cm
~0.9 cm
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Hybridisation details Hybridisation through
conductive glue Analogue Readout Chip:
VA-HDR9c (IdeAs)– VA Viking family
– HDR High dynamic range
– 9c Four selectable gains
Gain*
[mv/fC]
Dynamic Range [mip]
3.3 ± 100
2.5 ± 140
1.7 ± 200
1.2 ± 300 *Measured value
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Motherboard design 6 sensors per motherboard with serial readout. Status of production:
– 16 sensors available– 2 motherboards fully and 1 partially equipped
Signal routing through Erni connectors
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Test beam: preliminary results*Two electrons with energy 750 MeV
X silicon chambers
Y silicon chambers
First layer
Second layer
Third layer
Cluster recognition
*Plots filled only with pads with SNR>10
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How we get there: details of the sensor characterisation
2 technological runs
First batch of 11 sensors
(spring ’02)
Second batch of 9 sensors
(summer ’02)
Next batch available in summer ‘03
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Measurement setup
KI 590 & 595HF & QS CV meters
SCS 4200With 2 SMU
Manual
prober
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I – V Measurement: the method
Total and bias current measured directly by an SMU Guard ring current calculated from the others two
A
ASMU2
SMU1
Total
Bias
Guard ring
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I – V measurements: the results
High guard-ring current (> 50A)
Dicing edge too close to the guard ring structure, but it works and the sensor
performances are NOT spoiled!
n
n+
Depletion region
metal
p+
Cutting edgeGuard ring
Solution: keep the cutting edge far away from the guard ring!
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Soft breakdown Bias current reasonable
(few A) Strange shape with a
“soft” breakdown n+ or metal shallow
impurities on the backplane
Metal
n
n+
Impurities
Depletion region
Solution: replace the implanted backside contact with a diffused one, but …
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I – V Characteristics
BATCH 12Total wafers produced 11
Rejected wafers 1
Mean depl. voltage 32.5 V
Mean bias current @ depl. 2.1 A
BATCH 13Total wafers produced 9
Rejected wafers 2
Mean depl. voltage 26.6 V
Mean bias current @ depl. 0.8 A
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C – V measurements
Useful technique to calculate the depletion voltage
Quite uniform behaviour of the depletion voltage
YIELD Batch 12 Batch 13
Not depleted
pads0/420 8/294
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“Leaky” pads: the discovery
In batch 12: the great part (90%) of the pads seems to be DC coupled
In batch 13: only few percents
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“Leaky” pads: the explanation
No pin holes in SiO2
Surface leakage residua of polysilicon after the etching of the polysilicon layer
Equivalent circuit with two opposite diodes.
Polysilicon residua
Readout metal
Al bridge
Resistor
Bias grid
R
C
D
D1
D2
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“Leaky” pads: the solution
External AC coupling SMD capacitors on the PCB
Next batch will be DC coupled with external capacitors
It will improve also the quality of the p-n junction reducing the thermal budget SMD capacitor
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Summary
Three motherboards equipped with 16 sensors
First test beam on going Yield satisfactory New batch with simpler technology has
been started yet promising a better yield