ptp and the inter-strip capacitance and resistance for irradiated atlas07 mini-sensors
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PTP and the inter-strip capacitance and resistance for irradiated ATLAS07 mini-sensors. Jan Bohm , Institute of Physics ASCR, Prague Peter Kodys , Zdenek Dolezal , Jan Scheirich , Charles University in Prague - PowerPoint PPT PresentationTRANSCRIPT
J.Bohm, 8th Trento Workshop, Trento, Italy 1
PTP and the inter-strip capacitance and resistance for irradiated ATLAS07 mini-sensors.
Jan Bohm, Institute of Physics ASCR, Prague
Peter Kodys, Zdenek Dolezal, Jan Scheirich, Charles University in Prague
Petr Masek, Michael Solar, Institute of Experimental and Applied Physics of Czech Technical University in Prague
18/02/2013
J.Bohm, 8th Trento Workshop, Trento, Italy 218/02/2013
1. Introduction2. IV characteristics of heavily irradiated sensors3. Interstrip capacitance and bias dependence4. Time evolution of interstrip and bulk capacitances5. Interstrip resistance6. Characteristics of punch through structures7. Summary and conclusions
The performance of the sample of 75 n-in-p ATLAS07 HPK miniature 1cm*1cm sensors developed by ATLAS Collaboration for LHC upgrade [Y. Unno, et.al., Nucl. Inst. Meth. A636 (2011) S24-30] with different punch through structures, BZ4A-D, and with three different ion concentrations of 2E12, 4E12 and 1E13 ion/cm^2 of the P-stop and P-stop + P-spray separation is studied before and after irradiation with the aim to select the P-stop ion concentration and punch through structure as the most effective protection against beam splashes
J.Bohm, 8th Trento Workshop, Trento, Italy 3
Sample of HPK miniature sensors
18/02/2013
From Hamburg we received next 12 sensors BZ4A-D of Series 3 (wafers 264,278 and 281) with P-stop ion concentration 4E12 ion/cm^2. Many thanks to colleagues from DESY.
Wafer Isolation Ion/cm^2 Fluency neq/cm^2 Particles Where AnnealingW06 Pspr+Pstp 2E+12 4E+14 neutrons Ljubljana 80min/60degCW10 Pspr+Pstp 2E+12 2E+15 neutrons Ljubljana 80minn/60degCW17 Pstop 2E+12 4E+14 neutrons Ljubljana 80min/60degCW19 Pstop 2E+12 2E+15 neutrons Ljubljana 80min/60degC
W278 Pstop 4E+12 4E+14 neutrons Ljubljana 80min/60degCW281 Pstop 4E+12 2E+15 neutrons Ljubljana 80min/60degCW31 Pstop 2E+12 4E+14 p 23GeV/c CERN 80min/60degCW91 Pstop 1E+13 4E+14 neutrons Rez Prague 80min/60degCW93 Pstop 1E+13 2E+15 neutrons Rez Prague 80min/60degCW97 Pstop 1E+13 1E+16 neutrons Rez Prague 80min/60degC
Irradiation of sensors BZ4A, B, C and D for each wafer
Many thanks to Vlado Cindro , Morris Glaser and Jan Kucera for irradiation
J.Bohm, 8th Trento Workshop, Trento, Italy 4
Punch Through Protection Structures for ATLAS07
18/02/2013
A protection of AC coupling capacitors against the beam splashes should ensure special structures, BZ4A,B,C on the HPK ATLAS07 mini-sensors.A beam splash generates a spike of voltage across the AC coupling insulator.When the distance between the bias rail and the n-strip implants is appropriate,this voltage between the bias rail and the n-strip implant ends can be limited. This distance is 20 µ and is used in all special structures BZ4A,B,C and sensor BZ4D
Sensor BZ4D has no special structure and it is used for comparison with structures BZ4A, B and C.
BZ4A BZ4B
BZ4C BZ4D
J.Bohm, 8th Trento Workshop, Trento, Italy 5
IV characteristics of non-irradiated ATLAS07 sensors
-4
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0
ATLAS07 pre-series3 P-stop 2E12 BZ4A-D
W14 A W14 B W14 C W14 D W17 A W17 B W17 C W17 D W19 A W19 B W19 C W19 D W31 A W31 B W31 C W31 D
Bias [V]
Curr
ent [
nA]
-1000-800-600-400-2000
-4
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0
ATLAS07 Series3 P-stop 4E12BZ4A-D
W264 AW264 BW264 CW264 DW278 AW278 BW278 CW278 DW281 A W281 BW281 CW281 D
Bias [V]
Curr
ent [
nA]
-4
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0
ATLAS07 series 2nd STD P-stop 1E13 BZ4A-D
W75 A W75 B W75 C W75 D W78 A W78 B W78 C W78 DW80 A W80 B W80 C W80 D W81 A W81 B W81 C W81 D
Bias [V]
Curr
ent [
nA]
0 -60-120
-180-240
-300-360
-420-480
-540-600
-660-720
-780-840
-900-960
-4
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0
ATLAS07 series 2nd HPK P-stop 1E13 BZ4A-D
W89 A W89 B W89 C W89 D W91 A W91 B W91 C W91 D W93 A W93 B W93 C W93 D W97 A W97 B W97 C W97 DBias [V]
Curr
ent [
nA]
Measured sensors were placed on the table without vacuum chuck jig to avoid possible strong stresses which could cause breakdowns.
18/02/2013
J.Bohm, 8th Trento Workshop, Trento, Italy 6
-1000-800-600-400-20001
10
100
1000 W91 A 4E14W91 B 4E14W91 C 4E14W91 D 4E14W93 A 2E15 W93 B 2E15 W93 C 2E15 W93 D 2E15W278A 4E14W278B 4E14W278C 4E14W278D 4E14W281A 2E15W281B 2E15W281C 2E15W281D 2E15W19A 2E15W19B 2E15W19D 2E15W17B 4E14W97 A 1E16W97 B 1E16W97 C 1E16W97 D 1E16W31 A p 4E14W31 B p 4E14W31 C p 4E14W31 D p 4E14
Bias [V]
Leak
age
Curr
ent
[µΩ
]
2E15n/cm2
Proton irradiation at CERN
18/02/2013
IV Characteristics of irradiated ATLAS07 sensors
The heavily irradiated sensors (≥ 2E15n/cm2) with p-stop isolation of different ion concentrations were successfully operating up to 1000V with the exception of fluency4E14n/cm2 where an onset of micro-discharges was observed above ~700V
1E16n/cm2
4E14n/cm2
J.Bohm, 8th Trento Workshop, Trento, Italy 7
Interstrip Capacitance - Method of measurement
18/02/2013
0 100 200 300 400 500 6000.600000000000001
0.800000000000001
1
1.2
1.4
1.6
1.8
2
2.2
Cinter CpRp 100kHz Sensor W37
Vbias [-V]
Cin
t [p
F]
2 probes
5 probes GND
3 probes
5probes –outer strips to LCR Low 2-probes
3-probes
5-probes
LCR High
DC pad
LCR Low
Outer strips to GND
Cint(5-pr)/Cint(3-pr)=0.939 and 0.913 for 100kHz and 1MHz, respect.Cint(2-pr)/Cint(5-pr)=0.57
AC pad
J.Bohm, M.Mikestikova et.al, NIM A636 (2011)S104-S110
J.Bohm, 8th Trento Workshop, Trento, Italy 8
Interstrip Capacitance – non-irradiated
18/02/2013
0.1 1 10 100 10000
0.2
0.4
0.6
0.8Cinterstrip vs Frequency
W78-STD Pstop 1E13; W89-HPK Pstop 1E13;
W14-Pstop 2E12; W04-PstopSpray 2E12
W264-Pstop 4E12 W78 B
W89 B
W14 B
W04 B
W264 B
Frequency [kHz]
Cint
er [p
F]
-600-400-20000.5
0.6
0.7
0.8Interstrip Capacitance
p-stop 1E13 ion/cm^2, Series 2 STD & HPK
W78 A
W78 B
W78 C
W78 D
W89 A
W89 B
W89 C
W89 D
Bias [V]
Cint
erst
rip
[pF]
Vfd
-600-400-20000.2
0.4
0.6
0.8
1
1.2 Interstrip CapacitanceATLAS07 pre-Series3 p-stop&spray
2E12ion/cm^2W14 A
W14 B
W14 C
W14 D
W04 A
W04 B
W04 C
W04 D
Bias [V]
Cint
er [p
F]
Vfd
Interstrip capacitance is measured by 3 probesat 1 MHz and CpRpC interstrip for frequency above 100kHz is slowly increasing up to 1MHz.For Vbias<Vfd the values of C interstrip depend on the P-stop & P-spray ion concentration but above Vfd the Cinter is constant and the same for all p-stop doses.
There is narrow deep minimum of Cint at Vbias =-4V for P-stop+P-spray isolation.
J.Bohm, 8th Trento Workshop, Trento, Italy 9
0.1 1 10 100 10000
0.2
0.4
0.6
0.8
Irradiated ATLAS07 sensors
1.E+13 W97 D 1E161.E+13 W97 A 1E164.E+12 W281A 2E154.E+12 W281B 2E152.E+12 W19 A 2E152.E+12 W10 A 2E15 PstSpr2.E+12 W10 B 2E15 PstSpr2.E+12 W19 B 2E151.E+13 W91 A 4E141.E+13 W91 C 4E14
Frequency [kHz]
Cint
er [p
F]
0.1 1 10 100 10000
0.2
0.4
0.6
0.8 Non-irradiated ATLAS07 sensorsW78-STD Pstop 1E13; W89-HPK Pstop 1E13;
W14-Pstop 2E12; W04-PstopSpray 2E12
W78 B
W89 B
W14 B
W04 B
W264 B
Frequency [kHz]
Cint
er [p
F]
18/02/2013
Interstrip Capacitance Dependence on Frequency
J.Bohm, 8th Trento Workshop, Trento, Italy 1018/02/2013
-600-400-20000.2
0.4
0.6
0.8
1
1.2Inter-strip Capacitance
ATLAS07 Series2, pre-Series3 & Series3W89 AW89 BW89 CW89 DW14 AW14 BW14 CW14 DW04 AW04 BW04 CW04 DW264 AW264 BW264 CW264 DW78 AW78 BW78 CW78 DReverse Bias [V]
Cint
er [p
F]
The inter-strip capacitance, Cint, is constant for bias voltages higher than respective full depletion voltages and Cint does not depend in this region on an ion concentration andthe punch through protection structures within measuring error of ±0.02pF.
Interstrip Capacitance – non-irradiated
J.Bohm, 8th Trento Workshop, Trento, Italy 11
-500-450-400-350-300-250-200-150-100-5000.58
0.62
0.66
0.7
0.74ATLAS07 Pstop 1E13 ion/cm2 W91 A 4E14
W91 B 4E14
W91 C 4E14
W91D 4E14
W93 A 2E15
W93 B 2E15
W93 C 2E15
W93 D 2E15
W97 A 1E16
W97 B 1E16
W97C 1E16
W97 D 1E16
W89 A nonirrad
W89 B nonirrad
W89 C nonirrad
W89 D nonirrad
Bias [V]
Cint
er [p
F] 0.04pF
18/02/2013
Interstrip Capacitance of Heavily Irradiated Sensors
Cinter before irradiation for p-stop dose 1E13ion/cm2 is also shown. Cinter is not changed by irradiation up to 1E16n/cm2.A slow decrease is observed with growing bias voltage which is more pronouncedfor fluency 4E14n/cm2 than for higher doses.
J.Bohm, 8th Trento Workshop, Trento, Italy 12
-500-400-300-200-10000.6
0.640000000000001
0.680000000000001
0.720000000000001
0.760000000000001
2.E+12 W10 A 2E15 PstSpr
2.E+12 W10 B 2E15 PstSpr
2.E+12 W10 C 2E15 PstSpr
2.E+12 W19A 2E15
2.E+12 W19 B 2E15
2.E+12 W19 C 2E15
4.E+12 W281A 2E15
4.E+12 W281B 2E15
4.E+12 W281C 2E15
1.E+13 W93 A 2E15
1.E+13 W93 B 2E15
1.E+13 W93 C 2E15
Bias [V]
Cint
er [p
F]
18/02/2013
Interstrip Capacity and p-stop ion concentration
Interstrip capacitance does not depend on ion concentration ofp-stop implant within measuring error of ~0.02pF.A decrease of Cinter with bias voltage is the same for all p-stopand p-stop+p-spray implant doses. It is supposed that this decrease of Cinteris due to small contribution of Cg, capacitance between strip and the backplane.Cg is decreasing function of bias voltage.
Fluency 2E15n/cm2
J.Bohm, 8th Trento Workshop, Trento, Italy 1318/02/2013
0 10 20 30 40 50 60 70 800.640000000000001
0.680000000000001
0.720000000000001
0.760000000000001
0.800000000000001Time Evolution of Interstrip Capacity
W91 A 4E14 Vb-300V
W97 A 1E16 Vb-300V
Time [min]
Cint
er [p
F]
Time Evolution of Interstrip and Bulk Capacitances
-400-20000
40
80
120
160C-V Characteristics
p-stop 1E13ion/cm2 T=-32CW91 D 4E14
W93 D 2E15
W97 B 1E16
Revers Bias [V]
Bulk
Cap
acita
nce
[pF]
0 20 40 60 80 100 120 140 160 18040
45
50
55 Evolution of Bulk Capacitance
W97 C 1E16 Vb-300V
Time [min]
Cbul
k [p
F]
Total strip capacitanceCint=Cg + 2Cs in the first approximation.Here Cs is capacitance between 2 stripsand Cg between the strip and backplane,Cs>>Cg.Cg one can estimate as Cbulk/n strips.
Ruther long time is needed to rearrangecharge carriers in the un-depleted regionso as to bring the electric field back to zero.
Vb -300V
A decrease of Cinter with time at constant biasvoltage could be due to decrease of Cbulk with time.
J.Bohm, 8th Trento Workshop, Trento, Italy 1418/02/2013
-400-20000.56
0.6
0.64
0.68
0.72
0.760000000000001
0.8
0.84
Comparison of two Cinter measurements
W91 A
W91 A stable
Bias [V]
Cint
erst
rip [p
F]
0 200 4000.660000000000002
0.680000000000002
0.700000000000002
0.720000000000002Interstrip Capacitance after Stabiliza-
tion
W91 A 4E14
W97 A 1E16
W93 A 2E15
Bias [V]Ci
nter
strip
[pF]
0 10 20 30 40 50 600.600000000000001
0.640000000000002
0.680000000000002
0.720000000000002
0.760000000000002
ATLAS07 fluency 4E14neq/cm2
W91 A Vb-5VW91 A Vb-10VW91 A Vb-40VW91 A Vb-100VW91 A Vb-300VW91 A Vb-500V
Time [min]
Cint
erstr
ip [p
F]Time evolution at constant Vbias
Time Evolution of Interstrip Capacitance
Measurement of Cinter must be donewith appropriate time delay betweenconsecutive steps.
Cinter data taken after stabilization period agree well with Cinter results measured by the program
J.Bohm, 8th Trento Workshop, Trento, Italy 15
Interstrip Resistance - non-irradiated
18/02/2013
0E+00 2E+12 4E+12 6E+12 8E+12 1E+130
200
400
600
800BZ4A 300V
BZ4B 300V
BZ4C 300V
BZ4D 300V
BZ4A 100V
BZ4B 100V
BZ4C 100V
BZ4D 100V
BZ4A 50V
BZ4B 50V
BZ4C 50V
BZ4D 50V
P-stop ion concentration/cm^2
Resi
stan
ce [G
Ω]
Rbias
Bias ring
AC pad
DC pad
VV
I
Rint = 2*dV/dI measured at Vbias=-50V, -100V and -300V
Interstrip resistance increases with P-stop ion concentration from 4E12ion/cm^2 up to 1E13 ion/cm^2
PT structures
J.Bohm, 8th Trento Workshop, Trento, Italy 16
1E+10 1E+12 1E+14 1E+160
50
100
150
200
ATLAS07 Pstop 1E13ion/cm2
Fluency [neq/cm2]
Rint
[GΩ
]
18/02/2013
Interstrip resistance is decreasing with increasing fluency
K.Hara et al: Nucl.Instrum.Meth. A636 (2011) S83-S89
Interstrip Resistance – heavily irradiated
Resistance before irradiation Rint=587 GΩ
Resistance for fluency 1E16n/cm2is about 0.7 GΩ which is many times higher than bias resistor ~1.5MΩ.
J.Bohm, 8th Trento Workshop, Trento, Italy 1718/02/2013
Punch Through Protection Structures for ATLAS07
The punch-through (PT) develops via 20µm gap between the strip implant edge and the bias rail . The gap is the same for all three structures and also for case of no structure.Characteristics of punch through structures are studied by DC method:Negative Vtest is an applied voltage to DC pad and Itest is current between DC pad and the bias ring.The effective resistance Reff=dVtest/dItest which is constant and equal to bias resistor Rbias for low values of Vtest and is rapidly decreasing when PT is developed.
Then Rpt is supposed to be parallel to Rbias: 1/Reff=1/Rbias+1/Rpt.
DC method S.Lindgren et.al NIM A636(2011)S111-S11&
Punch-Through Voltage is the Test Voltage for Rbias=Rpt, i.e. for Reff=Rbias/2.PT voltage is evaluated at bias voltages -100, -300, -500, -700 and -900V .
-50 -30 -10 100
0.4
0.8
1.2
ATLAS07 Series 3 P-stop 4E12 ion/cm^2
W264 BZ4B P10
Vb -100VVb -300VVb -500VVb -700VVb -900V
Vtest [V]
Reff
[MΩ
]
PT voltage
-800000 -600000 -400000 -200000 00.01
0.1
1
10 Rpt vs ItestW89 Series 2 P-stop 1E13
ion/cm^2Vbias=-300V
BZ4DBZ4CBZ4BBZ4A
Itest [nA]
Rpt [
MΩ
]Rbias/2
Laser method: C.Betancourt at al. IEEE Vol. 59, No3, June 2012
J.Bohm, 8th Trento Workshop, Trento, Italy 18
Punch Through Voltagenon-irradiated
18/02/2013
-900-700-500-300-100
-40
-20
0
W89 C
W89 A
W89 B
W89 D
W14 A
W14 B
W14 C
W14 D
W281 A
W264 B
W264 C
W281 D
Bias [V]
PT V
olta
ge [V
]
1e13 ion/cm^2
4E12 ion/cm^2
2E12 ion/cm^2
-Punch through voltage dominantly depends on P-stop ion concentration for all punch through structures.-Differences among PT voltages for structures BZ4A-D are small for all concentrations, several volts only-PT voltage increases with applied bias, for concentration 1E13 ion/cm^2 is observed nearly saturation for Vb>500V.-PT voltages are smaller than 50V, i.e. they are significantly below the hold-off voltages of the coupling capacitor which are typically tested to 100V.
-70 -50 -30 -10 100
0.4
0.8
1.2
1.6
ATLAS07 Series 2HPK P-stop 1E13 ion/cm^2W89 BZ4A P04
Vb -100V
Vb -300V
Vb -500V
Vb -700V
Vb -900V
Vtest [V]
Reff
[MΩ
]
J.Bohm, 8th Trento Workshop, Trento, Italy 1918/02/2013
-1000-800-600-400-2000
-60
-40
-20
0
Punch-Through VoltageATLAS07 Pstop 4E12 ion/cm^2 W281 A 2E15
W281 B 2E15W281 C 2E15W281 D 2E15W278 A 4E14W278 B 4E14W278 C 4E14W278 D 4E14W281A nonirrW264B nonirrW264C nonirrW281D nonirr
Bias [V]
PT V
olta
ge [V
]
-1000-800-600-400-2000
-60
-40
-20
0
Punch-Through VoltageATLAS07 Pstop 2E12 ion/cm^2 W19A 2E15
W19B 2E15
W19C 2E15
W19D 2E15
W17A 4E14
W17B 4E14
W17C 4E14
W17D 4E14
W14A nonirr
W14B nonirr
W14C nonirr
W14D nonirr
Bias [V]
PT V
olta
ge [V
]
-PT voltage increases predominantly with fluency and very slowly with ion concentration-At fluency 2E15 n/cm^2 and for all tested ion concentrations the PT voltage for structure BZ4A reaches minimum value and BZ4D without any special structure –the maximum.The same behaviour of structure BZ4A is observed also for p-stop doses 4E12 and 2E12 ion/cm2.
Punch Through Voltage irradiated
-1000-800-600-400-2000
-70
-60
-50
-40
-30
-20
Fluency 2E15n/cm2
W93 A Pst 1E13
W93 D Pst 1E13
W281A Pst 4E12
W281D Pst 4E12
W19 A Pst 2E12
W19 D Pst 2E12
Reverse Bias [V]
PT V
olta
ge [V
]
J.Bohm, 8th Trento Workshop, Trento, Italy 20
-1000-800-600-400-2000
-60
-40
-20
Punch-Through VoltageATLAS07 Pstop 1E13 ion/cm^2
W93 A 2E15
W93 B 2E15
W93 C 2E15
W93 D 2E15
W91 A 4E14
W91 B 4E14
W91 C 4E14
W91 D 4E14
W89 A nonirr
W89 B nonirr
W89 C nonirr
W89 D nonirr
W97 A 1E16
W97 B 1E16
W97 C 1E16
W97 D 1E16Bias [V]
PT V
olta
ge [V
]
18/02/2013
Punch Through Protection Structures for ATLAS07
1E+12 1E+14 1E+16
-80
-60
-40
-20
PT VoltageATLAS07 Pstop 1e13ion/cm2W89, W91, W93 and W97 A 300V
B300V
C 300V
D 300V
A 700V
B 700V
C 700V
D 700V
Fluence [neq/cm2]PT
Vol
tage
[V]
-PT voltages for P-stop ion concentration 1E13 ion/cm^2 and fluency 1E16n/cm2 are surprisingly below the PTV for lower fluency and even smaller than safety level of 50V and do not depend on the bias voltage (saturation)
J.Bohm, 8th Trento Workshop, Trento, Italy 2118/02/2013
-80 -60 -40 -20 00
1
2
W97 BZ4A P-stop 1E13ion/cm2 Fluency 1E16n/cm2 T-32C
W97 A 100VW97 A 300VW97 A 500VW97 A 700V
Vtest [V]
Reff
[MΩ
]Punch Through Voltage
irradiated
Saturation
J.Bohm, 8th Trento Workshop, Trento, Italy 2218/02/20130 20 40 60 80 100
0
100000
200000
PT structure BZ4A
W91 A 4E14
W93 A 2E15
W97 A 1E16
W89 A nonirrad
Test voltage [-V]
Stri
p Cu
rren
t [-n
A]
Punch-Through Current for ATLAS07
0 20 40 60 80 1000
100000
200000No structure BZ4D W91 D 4E14
W93 D 2E15
W97 D 1E16
W89 D nonirrad
Test Voltage [-V]
Stri
p Cu
rren
t [-n
A]
PT current
At low volts the current flows to BR only through the bias resistor and grows linearly with voltage. At higher volts the PT current appears as a component additional to the linear rise.
Typically the PT current grows very steeply with voltage above the onset value thus preventingthe sensor.
A.Chilingarov: Report on 21st RD50 Workshop, 15.11.2012, CERN
100µA
J.Bohm, 8th Trento Workshop, Trento, Italy 2318/02/2013
0 10 20 30 40 50 60 70 800
100000
200000 P-stop 1E13ion/cm2 Fluency 1E16n/cm2
W97 A 1E16
W97 B 1E16
W97 C 1E16
W97 D 1E16
-Vtest [V]
-Ites
t [nA
]
0 10 20 30 40 50 60 70 800
100000
200000 P-stop 4E12ion/cm2 Fluency 2E15n/cm2
W281 A 2E15
W281 B 2E15
W281 C 2E15
W281 D 2E15
-Vtest [V]
-Ites
t [nA
]Comparison of PT structures
Punch-through current grows rapidlyfor structure BZ4A only .
A difference among structures BZ4B, BZ4C and no-structure BZ4D is negligible.
The better performance of zone BZ4Awould be due to the gate effect sincelarger portion of the channel length iscovered by the bias resistor (conformation of previous results).
Radiation damage reduces theeffectiveness of PTP structures. It is thequestion to what extent the effectivenessdepends on p-stop implant dose. It will be tested with new irradiated In Ljubljana sensors up to 1E16n/cm2 and with several p-implant doses.
J.Bohm, 8th Trento Workshop, Trento, Italy 2418/02/2013
Summary and Conclusions
1 The heavily irradiated sensors (≥ 2E15n/cm2) with p-stop isolation of different ion concentrations were successfully operating up to 1000V but not for fluency 4E14n/cm2 where an onset of micro-discharges was observed above 700V. 2 Interstrip capacitance is the same within measuring error of ~0.02pF for irradiated (4E14, 2E15 and 1E16n/cm2) and non-irradiated sensors as well as for all tested p-stop ion concentrations (2E12, 4E12 and 1E13ion/cm2). 3 An observed decrease of interstrip capacitance after irradiation with growing bias voltage could be qualitatively explained by the contribution of the bulk capacitance.4 Time evolution measurement has shown a slow decrease of the bulk and interstrip capacitances of irradiated sensors before the plateau is reached. 5 Interstrip resistance is decreasing with increasing fluency ; Resistance for fluency of 1E16n/cm2 is still ~0.7 GΩ which is significantly higher than Rbias ~ 1.5MΩ.6 Punch-through protection was characterized by parameters of DC method: Effective resistance, PT voltage and PT resistance as a function of bias voltage.7 An investigation of punch-through current allowed to estimate PT structure BZ4A as the most effective protection against beam splashes8 Next 16 sensors were already irradiated in Ljubljana as the last step of investigation.
J.Bohm, 8th Trento Workshop, Trento, Italy 2518/02/2013
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