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Meeting on Investigations into the effect
of beam splash on SCT Modules
CERN, 3.08.09
Punch-through protection in ATLAS SCT sensors
A.Chilingarov,
Lancaster University, UK
Outline
1. Measurement method
2. Main results reported in 2007
3. Some recent results
A.Chilingarov, Punch-through
protection in ATLAS SCT sensors
2
1. Punch-through (PT) resistance measurement method
A
Rb
Rstr
e
Rdyn
Positive DC potential, Ustrip, varying
from 0.5 to 50 V is applied to the strip
implant and the resulting current, Istrip, is
measured. The slope dUs/dIs gives an
effective dynamic resistance, Reff,
between the strip and the bias rail. Note
that the PT behaviour is not necessarily
polarity independent.
Reff consists of the bias resistor, Rb, with
Rdyn + Rstr in parallel. Rdyn is the
dynamic resistance of the 8 mm punchthrough gap. Above the PT onset
voltage Rdyn decreases quickly with
Ustrip. The Rstr is the strip implant
resistance between the punch-through
gap and the contact point.
A.Chilingarov, Punch-through
protection in ATLAS SCT sensors
3
2. Main results reported in 2007
Meeting on Silicon Strip Sensors
for ATLAS Upgrade
CERN, 2.07.07
Measurement of the punch-through protection
voltage for ATLAS SCT sensors
A.Chilingarov,
Lancaster University, UK
(extracts)
Strip IV for 7 Endcap detectors under 100 V bias
1000
100
Istrip (mA)
The punch-through
protection voltage Upth
was measured with the
detectors biased by 100 V,
which is above Ud for all
detectors.
w12-406
w21-9
w22-18
w31-225
w31-405
w31-1277
w32-560
10
1
0.8 1
2
4
6
8
10
20
40
The positive bias from a
separate source-meter
was applied to the strip
implant and the resulting
current was measured as
a function of bias. At low
volts the slope of the IV
curve reflects the value of
the polysilicon bias
resistor. The punchthrough appears as a soft
breakdown in the IV.
Ustrip (V)
A.Chilingarov, Punch-through
protection in ATLAS SCT sensors
5
Lancaster 9-14.05.07: strips with highest Up-through in 7 SCT sensors
1800
w12-406
w21-9
w22-18
w31-225
w31-405
w31-1277
w32-560
1600
1400
dU/dI (k)
1200
Differential resistance
dU/dI was calculated from
the measured IV curves. It
has a similar shape for all
7 detectors
A non-smooth behaviour
of some characteristics is
an artefact related to an
insufficient precision of the
voltage settings in earlier
measurements. This was
fixed later (e.g. for the
measurements with w12406 and w31-225).
1000
800
600
400
200
0
0
2
4
6
8
10
12
14
16
18
20
22
24
26
Ubias (V)
A.Chilingarov, Punch-through
protection in ATLAS SCT sensors
28
PT onset voltage lies
between 8 and 14 V.
6
3. Some recent results
PT operation was tested up to ~1 mA strip current with the sensor
w31-2055 under 150 V bias at room temperature and ~50% RH.
The measurements were performed with four different strips.
w31-2055 at 150V, 23.7.09: total strip current vs potential
1200
1000
Current, m A
800
600
400
strip 388
strip 446
200
strip 360
strip 416
0
0
5
10
15
20
25
30
35
40
45
Ustrip, V
A.Chilingarov, Punch-through
protection in ATLAS SCT sensors
7
w31-2055: dynamic resistance vs strip potential
10
1
dU/dI, M
strip 388
strip 446
strip 360
strip 416
0.1
0.01
0
4
8
12
16
20
24
28
32
36
40
44
Ustrip , V
For all strips the PT onset voltage is ~8.5 V and the minimum
dynamic resistance is slightly above 10 k.
A.Chilingarov, Punch-through
protection in ATLAS SCT sensors
8
Concluding remarks
1.
The punch-through protection in the SCT sensors seems
to work as expected.
2.
The PT onset voltage lies between 8 and 14 V.
3.
All reported measurements were made at about +21oC
temperature and 30-50% relative humidity.
A.Chilingarov, Punch-through
protection in ATLAS SCT sensors
9