Transcript Silicon pad detectors for LCCAL: characterisation and first results Antonio Bulgheroni University of Milan – Italy on behalf of LCCAL: Official INFN R&D project, official.

Silicon pad detectors for LCCAL:
characterisation and first results
Antonio Bulgheroni
University of Milan – Italy
on behalf of
LCCAL: Official INFN R&D project, official DESY R&D project PRC R&D 00/02
Contributors (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.
ECFA – DESY Amsterdam, 1st – 4th April ‘03
Calorimeter Layout
Total of 50 layers
27 X0
Absorber
25 x 25 x 0.3 cm3
Scintillator
25 Cells 5 x 5 cm2
Silicon pad
detectors
3 layers
725 Pads ~ 1 x 1 cm2
2, 6 and 12 X0
Main characteristics:
– Sensor thickness: 300mm
– Resistivity: 4-6k
– AC coupling
~0.9 cm

6 cm
7 cm
ECFA – DESY Amsterdam, 1st – 4th April ‘03
Sensor details
~0.9 cm
• Silicon dioxide thickness:
265 nm
– Bias grid and
guard ring
• 3M bias resistors
• Symmetric
structure
Bias pad
Guard
ring pad
ECFA – DESY Amsterdam, 1st – 4th April ‘03
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
2.5
1.7
1.2
± 100
± 140
± 200
± 300
*Measured value
ECFA – DESY Amsterdam, 1st – 4th April ‘03
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
ECFA – DESY Amsterdam, 1st – 4th April ‘03
Test beam: preliminary results*
Two electrons with energy 750 MeV
X silicon
chambers
Y silicon
chambers
Cluster
recognition
First layer
Second layer
Third layer
*Plots filled
only with pads
with SNR>10s
ECFA – DESY Amsterdam, 1st – 4th April ‘03
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
ECFA – DESY Amsterdam, 1st – 4th April ‘03
Measurement setup
KI 590 & 595
HF & QS CV meters
SCS 4200
With 2 SMU
ECFA – DESY Amsterdam, 1st – 4th April ‘03
I – V Measurement: the method
Guard ring
A
SMU2
SMU1
Total


A
Total and bias current measured directly by an SMU
Guard ring current calculated from the others two
ECFA – DESY Amsterdam, 1st – 4th April ‘03
I – V measurements: the results
High guard-ring current (> 50mA)
Dicing edge too close to the guard
ring structure, but it works and the
sensor performances are NOT
spoiled!
Cutting edge
Guard ring
p+
Depletion region
n
n+
metal
Solution: keep the cutting edge far
away from the guard ring!
ECFA – DESY Amsterdam, 1st – 4th April ‘03
Soft breakdown
Bias current reasonable
(few mA)
Strange shape with a
“soft” breakdown
n+ or metal shallow
impurities on the
backplane



Depletion region
n
n+
Metal
Impurities
Solution: replace the implanted backside contact with a
diffused one, but …
ECFA – DESY Amsterdam, 1st – 4th April ‘03
I – V Characteristics
BATCH 12
Total wafers produced
11
Rejected wafers
1
Mean depl. voltage
32.5 V
Mean bias current @ depl.
2.1 mA
BATCH 13
Total wafers produced
9
Rejected wafers
2
Mean depl. voltage
26.6 V
Mean bias current @ depl.
0.8 mA
ECFA – DESY Amsterdam, 1st – 4th April ‘03
C – V measurements


Useful technique to
calculate the depletion
voltage
Quite uniform behaviour
of the depletion voltage
YIELD
Batch 12
Batch 13
Not
depleted
pads
0/420
8/294
ECFA – DESY Amsterdam, 1st – 4th April ‘03
“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

Readout metal
Resistor
Al bridge
Polysilicon residua
Bias grid
C
R
D
No pin holes in
SiO2
 Surface leakage 
residua of
polysilicon after the
etching of the
polysilicon layer
 Equivalent circuit
with two opposite
diodes.
D1

D2
ECFA – DESY Amsterdam, 1st – 4th April ‘03
“Leaky” pads: the explanation
ECFA – DESY Amsterdam, 1st – 4th April ‘03
“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
ECFA – DESY Amsterdam, 1st – 4th April ‘03
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
