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ATLAS Tracker Upgrade
UK Workshop
Coseners House, 8.07.08
Electrical characteristics of un-irradiated
ATLAS07 mini strip sensors
A.Chilingarov,
Lancaster University
Outline
1. Sensors
2. C-V, I-V measurements
3. Punch-through voltages
4. Interstrip resistance
5. Interstrip capacitance
6. Summary
7. Conclusions
2
A.Chilingarov, ATLAS07 mini sensors
Available versions (“Zones”) of the ATLAS07 mini-SSDs. Here we report the
results for zone 1 (no isolation structure) and for zone 3 (baseline option)
sensors. Each zone may additionally have a thin lightly p-doped layer on the
surface (“p-spray”). PTP means Punch-Through Protection structure.
3
A.Chilingarov, ATLAS07 mini sensors
CV – IV measurements
e
to LCR meter
Backplane
Cs
. . . . .
Rs
Rb
Bias rail
A
Both C-V and I-V
measurements are made
simultaneously. The
impedance is measured
between the backplane and
the bias rail by the LCR
meter in Cs-Rs mode
(standard frequency is
10kHz).
The Cs represents the total
capacitance between the
strips and the backplane,
while the Rs is the average
bias resistor divided by the
number of strips.
4
A.Chilingarov, ATLAS07 mini sensors
IV for ATLAS07 minis at Lancaster
Rs-V for ATLAS07 minis at Lancaster
0.04
35
w02-BZ1-P19
w04-BZ1-P7
w27-BZ1-P7
w28-BZ1-P19
w23-BZ3-P21
w04-BZ3-P3
w07-BZ3-P3
25
Rs, kOhm
Current, mA
0.03
30
0.02
20
15
w02-BZ1-P19
w04-BZ1-P7
w27-BZ1-P7
w28-BZ1-P19
w23-BZ3-P21
w04-BZ3-P3
w07-BZ3-P3
10
0.01
5
0.00
0
100
200
300
400
500
600
700
800
900
1000
Bias, V
0
0
100
200
300
400
500
600
700
800
Bias, V
CV for ATLAS07 minis at Lancaster
1600
Five out of 7 sensors can withstand
1000V bias, two develop a breakdown
above 800V. Typical current is below
10 nA (for ~1cm2 area). Depletion
voltage values lie between 150 and
180V. Resistance agrees with
expectation within a factor of ~1.5
2
1/C , nF
-2
1200
800
w02-BZ1-P19
w04-BZ1-P7
w27-BZ1-P7
w28-BZ1-P19
w23-BZ3-P21
w04-BZ3-P3
w07-BZ3-P3
400
0
0
100
200
300
400
500
600
700
800
Bias, V
5
A.Chilingarov, ATLAS07 mini sensors
Punch-through resistance measurements
A
Rb
Rstr
e
Rdyn
Negative DC potential, U, varying
from 0.5 to 50 V is applied to a
strip implant and the resulting
current, I, is measured. The slope
dU/dI gives the value of effective
resistance, Reff, between the strip
and the bias rail.
Reff represents the bias resistor,
Rb, with Rdyn + Rstr in parallel. Here
Rdyn is the dynamic resistance of
the punch-through gap quickly
decreasing with U above the
break-through voltage and the Rstr
is the strip implant resistance (if
the punch-through gap is at the
strip end opposite to the contact
point).
6
A.Chilingarov, ATLAS07 mini sensors
Dynamic resitance for fresh Zone 1 sensors (no p-stops)
10
10
Dynamic resistance for Zone 3 sensors with p-spray: fresh and after 3h at 220V bias
w27-bz1-p7
w28-bz1-p19
w02-bz1-p19
w04-bz1-p7
dU/dI, MOhm
dU/dI, Mohm
1
with p-spray
1
fresh
0.1
biased for 3h
no p-spray
w07-bz3-p3
w04-bz3-p3
w07-bz3-p3
w04-bz3-p3
0.01
0
5
10
15
20
25
30
-Ustrip, V
0.1
24
28
32
36
40
44
48
52
-Ustrip, V
Dynamic resitance for Zone 3 sensor w23-bz3-p21 (no p-spray) for different time @ 220V bias
10
As expected, zone 1 sensors have a
relatively low break-through voltage of ~5
or ~15V. For zone 3 sensors the breakthrough is also observed above 45 V. For
all sensors this voltage decreases with
time under bias.
1
dU/dI, Mohm
fresh
biased for 3h
0.1
fresh
1h bias
2h bias
3h bias
0.01
24
28
32
36
-Ustrip, V
40
44
48
52
Note that the strip bias resistors can
tolerate up to ~50V voltage drop across
them without being burnt.
7
A.Chilingarov, ATLAS07 mini sensors
Interstrip resistance measurements
A “master” DC potential U0 is
applied to a strip implant and the
“slave” potential U1 induced at the
neighbouring strip implant is
measured by a high impedance
voltmeter.
U1
Io
Uo
A
e
Ris
V
Rb
Bias rail
The U0 is varied by a few volts
around zero and the resulting
current I0 is measured. The slope
dU0/dI0 gives the value of effective
resistance between the strip and
the bias rail, R0. The slope dU1/dU0
allows calculation of the effective
interstrip resistance, Ris, using an
assumption of bias resistor, Rb,
being the same at both strips.
8
A.Chilingarov, ATLAS07 mini sensors
Fresh w07-bz3-p3, 13.5.08: Uslave vs. Umaster for different Ubias
328
326
324
322
320
Uslave, mV
318
316
314
312
310
308
Ub=10V
306
Ub=20V
304
-4
-2
0
2
4
Umaster, V
Typical dependence of the induced voltage (Uslave) vs. the voltage applied to
the neighbouring strip (Umaster). Normally the slope dU1/dU0 is ~1mV/V which
means Ris ~ 106 Rbias i.e. ~1000 GOhm. The spread of the points around the
linear fit determines the Ris error.
9
A.Chilingarov, ATLAS07 mini sensors
Interstrip R for Zone 3 sensor w23-bz3-p21 (no p-spray): bias ramps up
and down after 3 hours at 200 V
1600
1400
Ris, GOhm
1200
1000
800
600
400
200
fresh
3h bias
0
1
10
Ubia s , V
100
1000
Interstrip R for Zone 3 sensors w ith p-spray: bias ram ps up
and dow n after a tim e @ 200 V
2000
1800
For zone 3 sensors the interstrip
resistance Ris does not depend on
bias in the range 10-200V and
doesn’t change after sensor
remaining at 200V bias during 3
hours.
1600
Ris, GOhm
1400
Typical Ris value is ~1000 GOhm.
1200
1000
800
600
400
w07-bz3-p3 fresh
w07-bz3-p3 3h bias
200
w04-bz3-p3 fresh
w04-bz3-p3 10' bias
0
1
10
Ubia s , V
100
10
1000
A.Chilingarov, ATLAS07 mini sensors
Interstrip R for Zone 1 sensors w ith p-spray: bias ram ps up
and dow n after 3 hours at 200 V
1400
1200
Ris, GOhm
1000
800
600
400
w02-bz1-p19 fresh
200
w02-bz1-p19 3h bias
w04-bz1-p7 fresh
w04-bz1-p7 3h bias
0
1
10
100
Ubia s , V
1000
For zone 1 sensors without pspray the Ris behaviour is more
complicated. Nevertheless above
100V bias the Ris remains above
100 GOhm even after 3 hours at
200V bias.
Interstrip R for Zone 1 sensors w ithout p-spray: bias ram ps up
and dow n after ~3 hours at 200 V
1.E+03
1.E+02
fresh senso rs,
ramp up
1.E+01
after 3h bias,
ramp do wn
Ris, GOhm
1.E+00
For fresh zone 1 sensors with pspray the Ris also doesn’t depend
on bias in the range 10-200V but
after 3 hour biasing by 200V it
decreases and becomes slightly
bias dependent with Ris value of
~500 GOhm above 100V bias.
1.E-01
1.E-02
1.E-03
w28-bz1-p19 fresh
w28-bz1-p19 3h bias
1.E-04
w27-bz1-p7 fresh
w27-bz1-p7 3.5h bias
11
1.E-05
1
10
Ubia s , V
100
1000
A.Chilingarov, ATLAS07 mini sensors
Interstrip capacitance measurements
The capacitance is measured
between an aluminium outer strip
and two its nearest neighbours
connected together. The LCR
meter operates in Cp-D mode.
Standard measurement frequency
is 100 kHz.
to LCR meter
The strips are grounded through
~1 MW resistors to keep their DC
potential fixed.
12
A.Chilingarov, ATLAS07 mini sensors
Interstrip capacitance Cis vs. Ubias
Interstrip capacitance versus bias (sensors w01-17 have p-spray)
0.8
Zone 1(no p-stop)
0.7
Below 300V the Cis has a
complicated behaviour
with bias but above 300V
it almost flattens and
gradually converges to a
value of ~0.6 pF for all
sensor types.
p-spray
0.6
no spray
Cis, pF
0.5
Zone 3 (with p-stop)
0.4
0.3
w28-bz1-p19
w27-bz1-p7
w02-bz1-p19
w04-bz1-p7
w23-bz3-p21
w04-bz3-p3
w07-bz3-p3
KEK data
0.2
0.1
Our results are in a
reasonable agreement
with KEK measurements.
0
0
100
200
300
Ubias, V
400
500
600
13
A.Chilingarov, ATLAS07 mini sensors
Interstrip capacitance Cis vs. time at Ubias = 600V
Interstrip C vs. time at 600V (sensors w01-17 have p-spray)
0.64
0.63
Zone 1 (no p-stop)
At 600V bias the Cis
further converges with
time to a common value
of ~0.61 pF for all
sensor types.
0.62
Cis, pF
0.61
0.6
0.59
Zone 3 (with p-stop)
0.58
w28-bz1-p19
w27-bz1-p7
w02-bz1-p19
w04-bz1-p7
w23-bz3-p21
w04-bz3-p3
w07-bz3-p3
0.57
0.56
The measurements
were made at ~22oC
temperature and 3545% relative humidity.
0.55
0
40
80
Time, min
120
160
200
14
A.Chilingarov, ATLAS07 mini sensors
Interstrip C for different sensors
0.615
0.614
0.613
The strip length, L, is 8000 mm for
zone 3 sensors and 8060 mm for
zone 1 sensors. Assuming the
whole measured capacitance
being scalable with L the
capacitance per unit length was
calculated.
0.612
Cis, pF
0.611
L=8060 mm
0.61
L=8000 mm
0.609
0.608
0.607
0.606
0.605
0
0.5
1
1.5
2
2.5
3
3.5
4
Zone+0.5*(p-spray)
No systematic difference due to
the sensor type or the p-spray
presence was observed. The
average Cis value is 0.758+-.003
pF/cm where the error is the points
r.m.s. spread.
Interstrip C per unit length for different sensors
0.762
0.761
0.760
Cis/L, pF/cm
0.759
0.758
<C> = 0.758 +- .003 pF/cm
0.757
0.756
0.755
0.754
0.753
0
0.5
1
1.5
2
2.5
3
3.5
4
15
Zone+0.5*(p-spray)
A.Chilingarov, ATLAS07 mini sensors
Comparison with the SCT sensors
Interstrip capacitance per unit length versus pitch
0.85
SCT wedges/Lancs
Atlas07 minis
SCT MPI/NIKHEF
0.01 pF abs.uncertainty
Linear (SCT wedges/Lancs)
0.80
NIKHEF
Cis, pF/cm
0.75
0.70
y = -0.007x + 1.2664
2
R = 0.996
0.65
w12
w32
w31 w21
w22
0.60
60
65
70
75
80
85
90
Average pitch, um
The observed Cis/L agrees well with the data measured for the SCT sensors.
An absolute LCR meter uncertainty of 0.01 pF is also shown in the error.
Thus the Cis in ATLAS07 minis can be regarded as simply geometrical one.
16
A.Chilingarov, ATLAS07 mini sensors
Frequency dependence of the Cis
Normalised Cis vs frequency for two measurements with w32-312
Frequency dependence of the interstrip capacitance
1.02
0.85
w23-bz3-p21/400V
w23-bz3-p21/600V
w07-bz3-p3/600V
w04-bz3-p3/600V
w02-bz1-p19/600V
w04-bz1-p7/600V
w28-bz1-p19/600V
w27-bz1-p7/600V
0.80
0.98
0.96
Cis/Cis(100kHz)
Cis, pF
0.75
1.00
0.70
0.65
0.94
0.92
0.90
0.88
0.60
19.06.08
25.06.08
0.86
0.84
0.55
0
100
200
300
400
500
600
Frequency, kHz
700
800
900
1000
10
100
1000
Frequency, kHz
For the frequencies above 100kHz the Cis for the mini SSDs is by ~10% higher.
However for the SCT sensors there is <1% difference between the Cis values in the
range from 100kHz to 1MHz. Measurements with longer strips are necessary to
distinguish between the changes with frequency due to the whole strip (scalable
with L) and to the strip edges (independent of L).
17
A.Chilingarov, ATLAS07 mini sensors
Summary of the results presented in this talk
Sensor name
p-spray
Breakdown
onset, V
I, mA
at 1000V
I, mA at
brkd.onset
Vdep,V
Rbias,
MOhm
Interstrip
R, GOhm
Zone 1 - PTP*, no p-stops
p-through
onset, V
Interstrip
C, pF
(in fresh sensors)
w02-BZ1-P19
Yes
>1000
0.0084
174
1.22
442
15
0.608
w04-BZ1-P7
Yes
>1000
0.0317
174
1.32
535
15
0.613
w27-BZ1-P7
No
>1000
0.0068
153
1.30
604
5.5
0.614
w28-BZ1-P19
No
>1000
0.0061
159
1.25
280
4.5
0.610
>1000
0.0071
167
1.21
890
47.5
0.607
Zone 3 - no PTP, p-stops
w23-BZ3-P21
No
w04-BZ3-P3
Yes
810
20.1
0.0078
183
1.23
853
48.5
0.606
w07-BZ3-P3
Yes
830
18.4
0.0078
182
1.19
1008
48.5
0.608
* PTP – Punch-Through Protection structure
Note: the interstrip resistance values are given at 200V bias and after 3 hours where appropriate.
18
A.Chilingarov, ATLAS07 mini sensors
Conclusions
1.
2.
3.
4.
5.
Typically ATLAS mini SSDs show a stable behaviour up to at least
800 V. More than a half of them can be operated up to 1000V bias.
The depletion voltage values are below 200V.
The punch-through protection structure implemented in zone 1
sensors operates according to expectations with a break-through
voltage below 15 V.
For all sensor types the interstrip resistance exceeds 100 GOhm for
bias voltage above 100V.
The interstrip capacitance values for all sensor types are very
similar and agree with those for ATLAS SCT sensors scaled by the
length.
The bias resistors have the value in the range 1.2 - 1.3 MOhm. They
are able to withstand up to ~50V voltage drop across them without
thermal destruction.
19
A.Chilingarov, ATLAS07 mini sensors