Charge Collection in irradiated Si Sensors

June ‘09 RD50 Meeting Freiburg Hartmut Sadrozinski, SCIPP, UC Santa Cruz1

SCIPPSCIPP

Charge Collection in irradiated Si Sensors

C. Betancourt, B. Colby, N. Dawson, V. Fadeyev M. Gerling, F. Hurley, S. Lindgren, P. Maddock, H. F.-W. Sadrozinski, S. Sattari, J. v. Wilpert, J. Wright

SCIPP, UC Santa Cruz

• Monitoring the health of the Charge Collection System• New Parameter: Efficiency Voltage• Correlation between efficiency and cluster size


SCIPPSCIPP

Charge Collection and C-V Measurementsin irradiated Si Sensors

C. Betancourt, B. Colby, N. Dawson, V. Fadeyev M. Gerling, F. Hurley, S. Lindgren, P. Maddock, H. F.-W. Sadrozinski, S. Sattari, J. v. Wilpert, J. Wright

SCIPP, UC Santa Cruz

• Monitoring the health of the Charge Collection System• New Parameter: Efficiency Voltage• Correlation between efficiency and cluster size• Admittance Measurement


SCIPPSCIPPFluence in the sATLAS Tracker “du jour”

ATLAS Radiation Taskforce http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/RADIATION/RadiationTF_document.html

5 - 10 x LHC Fluence

Mix of n, p, depending on radius R

sATLAS Fluences for 3000fb-1

1.E+12

1.E+13

1.E+14

1.E+15

1.E+16

1.E+17

0 20 40 60 80 100 120

Radius R [cm]

Flu

en

ce

ne

q/c

m2

All: RTF Formulan (5cm poly)pionproton

Pixels

Radial Distributionof Sensors determined by Occupancy < 2%, still emerging

ShortStrips

LongStrips

Design fluences for sensors (includes 2x safety factor) :B layer (r=3.7 cm) 2.5*1016 neq/cm2 1140 MRad Innermost Pixel Layer (r=5cm): 1.4*1016 neq/cm2 712 MRad 2nd Pixel Layer (r=7cm): 7.8*1015 neq/cm2 420 MRad Outer Pixel Layers (r=11cm): 3.6*1015 neq/cm2 207 MRad Short strips (r=38cm): 6.8*1014 neq/cm2 30 MRad Long strips (r=85cm): 3.2*1014 neq/cm2 8.4 MRad

Strips damage largely due to neutrons

Pixels Damage due to neutrons+pions


SCIPPSCIPP

<100><100><100><100>Orientation

3.3 kcm13 kcm1.4 kcm1.9 kcmResitivity

V(FD) [V] 9575220520

Fz (n-n), (p-n)Fz (n-p)MCz(n-n), (p-n)MCz (n-p)

<100><100><100><100>Orientation

3.3 kcm13 kcm1.4 kcm1.9 kcmResitivity

V(FD) [V] 9575220520

Fz (n-n), (p-n)Fz (n-p)MCz(n-n), (p-n)MCz (n-p)

4” : IRST(SMART)

Towards Commercialization of P-type

6” : Micron (RD50) HPK: (ATLAS07)

n-on-n, p-on-n, n-on-pFZ and Mcz

Testing: UC Santa Cruz, Liverpool U. , Ljubljana

n-on-p, FZn-on-n, p-on-n, n-on-pFZ and Mcz


SCIPPSCIPP

5

Charge Collection System

CCE System is beta source (90Sr) with trigger from single thick scintillation counter. Measurements carried out in freezer at low temperature (-30 oC)

Accelerated Annealing at elevated temperature (60oC): about 440 times faster than at RT: 1000 min @ 60oC = 305 days at RTActivation energy E = 1.28 eV (Ziock et al. 1994)Annealing important for thermal management.

Binary readout with 100 ns shaping timePositive and negative charge readout

Measurement of collected charge with min. ion. particles (MIPs) combines all effects of radiation damage: depletion voltage increase, inversion, trapping…


SCIPPSCIPP

6

Collected Charge: CCE

2. event-by-event: analogTime-over-Threshold ToT -> peak of distribution -> ToT Q

Good agreement between MedQ and ToTAccuracy: ~10% sample-to-samplefew % within one sample during anneal.

N.B. Complicated bias dependence!!

Charge Collection Efficiency vs Threshold (600V Bias )

0

0.5

1

0 50 100 150 200 250 300 350 400

Threshold [mV]

Eff

icie

ncy

2552-6-11-2 n-on-p MCz proton 1.3e1580min anneal ntcorr bias=600V

2552-6-11-2 n-on-p MCz proton 1.3e15 1000min anneal ntcorr bias=600V

W27-BZ3-P3 Proton-KEK proton 1.3e1580min anneal bias=600V

W27-BZ3-P3 Proton-KEK proton 1.3e151000min anneal bias=600V

Determination of collected charge

1. statistical: binaryThreshold curves -> Efficiency

-> Median Q (50% efficiency point)

0

0.5

1

1.5

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3.5

4

0 200 400 600 800 1000 1200Bias (V)

Med

ian

Q (

e-)

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7

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9

10

To

T [

sec

]

Med Q 2535-9-3-3 p-on-n FZMed Q n-on-p MCz 2552-6-3-1TOT 2535-9-3-3 p-on-n FZTOT 2552-6-3-1 n-on-p MCz

Comparison after 6.1e14 pion: Medium Q / Time over Threshold ToT


SCIPPSCIPPCollected Charge and Single Rate

Sensor single rate is crucial for health of apparatus.Single rate can foretell problems in charge collection measurement, which can’t be detected

efficiency or collected charge orleakage current

0

1

2

3

4

5

0 200 400 600 800 1000Bias (V)

Med

ium

Q [

fC]

0.000

0.005

0.010

0.015

Rat

e [a

.u.]

Med Q

Single Rate

P-on-N FZ 3e14 neq PROTON2535-8 3-1


SCIPPSCIPPCollected Charge, Single Rates and Efficiency

Collected Charge, Single Rate and Efficiency

0

5000

10000

15000

20000

25000

0 200 400 600 800 1000 1200Bias [V]

Cou

nt R

ate

(kH

z)

0

0.5

1

1.5

2

2.5

Eff

icie

ncy

@ 1

fC T

hres

hold

Med Q [e-]

Single rate @ 1fC

Efficiency @ 1fC Threshold

HPK ATLAS07W27-BZ3-P3 1.3e15 neq/cm2 Proton

Sensor single rate at 1 fC threshold is tracking the median collected charge well.Efficiency at 1fC threshold saturates at much lower voltage and reaches 100% if

signal/threshold S / T > 2,2 Signal/Noise > 9 in the experiment

Determine the required voltage for 98.5% efficiency: “Efficiency Voltage” (e.g. 1 fC threshold)

Depletion VoltageEfficiency Voltage


SCIPPSCIPPCollected Charge and Efficiency

Complete universal correlation between collected charge and efficiency

Eff. Voltage vs. Med QAll Sensors, Fluences, Anneal Times

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0 5000 10000 15000 20000 25000

Med Q (e-)

Eff

icie

ncy

Micron 2552-6-11-2 n-on-p Proton MCz 1.3e15 neqMicron 2535-8-3-1 P-on-N FZ 3e14 neq ProtonMicron 2552-6-9-1 N-on-P MCz 1.3e14 protonHPK-ATLAS07 W27-BZ3-P3 n-on-p FZ no spray 1.3e15 protons2535-9 3-3 p-on-n FZ 6.1e14 pion 2552-6 3-1 n-on-p MCz 6.1e14 pion Micron 2552-7-11 n-on-p MCz 1e15 neutronMicron 2552-7-9 N-on-P MCz 5e14 neutronMicron 2553-11-11 n-on-n MCz 1e15 neutronMicron 2552-6-11-2 n-on-p Proton MCz 1.3e15 neqMicron 2535-8-3-1 P-on-N FZ 3e14 neq ProtonMicron 2552-6-9-1 N-on-P MCz 1.3e14 protonHPK-ATLAS07 W27-BZ3-P3 n-on-p FZ no spray 1.3e15 protons2552-6 3-1 n-on-p MCz 6.1e14 pion Micron 2552-7-11 n-on-p MCz 1e15 neutronMicron 2552-7-9 N-on-P MCz 5e14 neutronMicron 2553-11-11 n-on-n MCz 1e15 neutronMicron 2552-6-11-2 n-on-p Proton MCz 1.3e15 neqMicron 2535-8-3-1 P-on-N FZ 3e14 neq ProtonMicron 2552-6-9-1 N-on-P MCz 1.3e14 protonHPK-ATLAS07 W27-BZ3-P3 n-on-p FZ no spray 1.3e15 protons2535-9 3-3 p-on-n FZ 6.1e14 pion 2552-6 3-1 n-on-p MCz 6.1e14 pion Micron 2552-7-9 N-on-P MCz 5e14 neutronMicron 2553-11-11 n-on-n MCz 1e15 neutronMicron 2552-6-11-2 n-on-p Proton MCz 1.3e15 neqMicron 2535-8-3-1 P-on-N FZ 3e14 neq ProtonMicron 2552-6-9-1 N-on-P MCz 1.3e14 protonHPK-ATLAS07 W27-BZ3-P3 n-on-p FZ no spray 1.3e15 protons2552-6 3-1 n-on-p MCz 6.1e14 pion Micron 2552-7-11 n-on-p MCz 1e15 neutronMicron 2552-7-9 N-on-P MCz 5e14 neutronMicron 2553-11-11 n-on-n MCz 1e15 neutronMicron 2552-6-11-2 n-on-p Proton MCz 1.3e15 neqMicron 2535-8-3-1 P-on-N FZ 3e14 neq ProtonMicron 2552-6-9-1 N-on-P MCz 1.3e14 protonHPK-ATLAS07 W27-BZ3-P3 n-on-p FZ no spray 1.3e15 protons2535-9 3-3 p-on-n FZ 6.1e14 pion 2552-6 3-1 n-on-p MCz 6.1e14 pion Micron 2552-7-11 n-on-p MCz 1e15 neutronMicron 2552-7-9 N-on-P MCz 5e14 neutronMicron 2553-11-11 n-on-n MCz 1e15 neutron


SCIPPSCIPPEfficiency Voltage (Threshold Dependence)

Efficiency Voltage is threshold dependent.

Threshold 1 fC -> 0.7 fC:

gives reduction of Efficiency Voltage of 100-200 V.

For stable operation:Breakdown Voltage >> Efficiency Voltage

Efficiency Voltage vs Anneal Time

0

200

400

600

800

1000

1 10 100 1000Anneal Time (min@60C)

Eff

icie

ncy

Vo

ltag

e [V

] HPK-ATLAS07 W27-BZ3-P3 n-on-p FZ no spray 1.3e15 protons

Saturation Voltage at70mV Threshold

Saturation Voltage at97mV Threshold

Breakdown Voltage vs Anneal Time

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400

600

800

1000

1200

1400

1 10 100 1000Anneal Time (min@60C)

Bre

ak

do

wn

Vo

lta

ge

[V

]

HPK-ATLAS07 W27-BZ3-P3 n-on-p FZ no spray 1.3e15 protons

Breakdown Voltage at70mV ThresholdBreakdown Voltage at97mV Threshold


SCIPPSCIPPAnnealing of Efficiency Voltage (@ 1fC)

Annealing benign for all but p-on-n FZ

0

500

1000

1500

2000

1 10 100 1000 10000Anneal Time @ 60° C (min)

Eff

icie

ncy

Vo

ltag

e (V

)

n-on-p MCz p+ 1.3e15 neq

p-on-n FZ p+ 3e14 neq


n-on-p FZ p+ 1.3e15 neq

p-on-n FZ pi 6.1e14 neq

n-on-p MCz pi 3.8e14 neq

n-on-p MCz n 5e14

n-on-n MCz n 1e15


SCIPPSCIPPAnnealing of Efficiency Voltage (@ 1fC)

No big difference between proton/pion and neutron irradiationN-on-n MCz shows “typical n-type” annealing, but on a small scale.

0

500

1000

1 10 100 1000 10000

Anneal Time @ 60° C (min)

Eff

icie

ncy

Vo

ltag

e (V

)n-on-p MCz p+ 1.3e15 neq


n-on-p FZ p+ 1.3e15 neq

n-on-p MCz pi 3.8e14 neq

n-on-p MCz n 5e14

n-on-n MCz n 1e15


SCIPPSCIPP

If one adjust the Efficiency voltage with difference in fluence, the Eff Voltage vs. Anneal curve will be above the Vfd curve, indicating that n-on-p MCz inverts with pion (also proton) irradiation. This is also seen in the Vfd as a function of fluence curve.

n-onp MCz Pions: Eff Voltage & Vfd vs Anneal time

0

200

400

600

800

1 10 100 1000 10000 100000

Anneal time @ 60° C (min)

Vo

ltag

e (V

)

Eff Voltage n-on-p MCz pi 3.8e14

2552-6-1-2 n-on-p MCz pi 5.6e14

Vfd vs Fluence (pions)

0

100

200

300

400

500

600

0 2E+14 4E+14 6E+14 8E+14 1E+15

Fluence (neq)

Vfd

(vo

lts) n-on-p FZ

n-on-p MCz

Comparison Efficiency Voltage - Vfd


SCIPPSCIPP

Once the Efficiency voltage is scaled with the fluence, it would clearly be much larger than the Vfd for either Vfd fluence, indicating strong inversion of p-on-n FZ after proton irradiation

For n-on-p FZ, it can be seen that at a given fluence, the efficiency voltage will be lower than Vfd, indicating no inversion after prtoton irradiation. This is consistent with the p-on-n FZ being inverted (bulk becomes more p-type)

n-on-p FZ p+

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Anneal time @ 60deg C (min)

Vo

ltag

e (V

)

n-on-p FZ Eff Voltage 1.3e15 neq UCSC

n-on-p FZ Vfd 1.1e15 neq UNM

n-on-p FZ Vfd 1.5e14 neq UNM

p-on-n FZ p+

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1 10 100 1000 10000

Anneal time @ 60deg C (min)

Vo

ltag

e (V

)

p-on-n FZ Eff Voltage 3e14 neq UCSC

p-on-n FZ Vfd 1.5e14 neq UNM

p-on-n FZ Vfd 1.1e15 neq UNM

Comparison Efficiency Voltage - Vfd


SCIPPSCIPPWhat to do with C-V Measurements?

“C-V” means here “ learn something about the depletion of the sensor, to be used to predict CCE or learn something about the state of the sensor when compared to CCE”

At least 4 diferent approaches:

1. Measure C-V at 10 kHz and low temperature: wrong2. Measure C-V at R.T and 10 kHzless less wrong, good convention

(Gregor showed is ~ ok for diodes: Vdep(CEE) =Vdep(CV) within 200V)

3. Measure C-V at lower temperature, adjust frequency C-V(f,T) better4. Measure Admittance, extract the width of the space charge region best ?


SCIPPSCIPPC-V(f,T)

3. Measure C-V at lower temperature, adjust frequency

Measure C-V at lower temperature, adjust frequency to match according to the emission coefficicnt C-V(f,T). (usual current temperature dependence)

M.K. Petterson, et al., RRESMDD06, Nucl. Inst. Meth. A 583, 189(2007)


SCIPPSCIPPAdmittance

4. Measure Admittance, extract the width of the space charge region

Introduce Debye length to characterize non-abrupt junction(s)Since trapping and de-trapping is important, measure both Capacitance C and Conductance G as a function of temperature T and frequency

Frequency dependence of conductance reveals dynamics of trapping C, Betancourt , et al.,

RRESMDD08, IEEE 2009, Senior Thesis

Measured and simulated C and G/ω as a function of frequency for a pion irradiated n-type FZ detector taken at 100V and 22 degrees C


SCIPPSCIPPResults of Admittance Measurement

Extracted depth of the space charge region from CCE andAdmittance

p-on-n FZ pion irradiated sensor and diode

n-on-p MCz neutron irradiated Sensor and diode


SCIPPSCIPPResults of Admittance Measurement

Depleted depth of the space chare region for various pion detectors Extracted from Admittance measurements


SCIPPSCIPPClustersize and Efficiency

Cluster size is given by the “Cluster Ratio” = # of clusters with multiple strips / # of clusters with one strips

Good Correlation, p-on-n FZ inverted.

Efficiency vs Cluster Ratio (1000min-Anneal)

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Cluster Ratio

Eff

icie

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Micron 2552-6-11-2 n-on-p MCz1.3e15 neq Proton

Micron 2535-8-3-1 p-on-n FZ 3e14 neqProton

Micron 2552-6-9-1 n-on-p MCz 1.3e14Proton

ATLAS07 W27-BZ3-P3 n-on-p FZ nospray 1.3e15 neq Proton

2535-9 3-3 p-on-n FZ 6.1e14 Pion

2552-6 3-1 n-on-p MCz 6.1e14 Pion

Micron 2552-7-11 n-on-p MCz 1e15Neutron

Micron 2552-7-9 n-on-p MCz 5e14Neutron

Micron 2553-11-11 n-on-n MCz 1e15Neutron



Cluster size changes during annealing for n-type FZ

Efficiency vs Cluster RatioMicron 2535-8-3-1 p-on-n FZ 3e14 neq Proton

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Cluster Ratio

Eff

icie

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Pre-Anneal 10min

80min 1000min

10000min

Efficiency vs Cluster Ratio2535-9 3-3 p-on-n FZ 6.1e14 Pion

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Cluster Ratio

Eff

icie

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Pre-Anneal 10min

1000min



All p-type ~ same ?

Efficiency vs Cluster RatioMicron 2552-6-9-1 n-on-p MCz 1.3e14 Proton

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Cluster Ratio

Eff

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Pre-Anneal 10min

80min 1000min

10000min

Efficiency vs Cluster Ratio2552-6 3-1 n-on-p MCz 6.1e14 Pion

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Cluster Ratio

Eff

icie

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Pre-Anneal 10min

80min 1360min

10000min

Efficiency vs Cluster RatioMicron 2552-6-11-2 n-on-p MCz 1.3e15 neq Proton

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Cluster Ratio

Eff

icie

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Pre-Anneal 10min

80min 1000min

10000min

Efficiency vs Cluster RatioATLAS07 W27-BZ3-P3 n-on-p FZ no spray 1.3e15 neq Proton

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Cluster Ratio

Eff

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Pre-Anneal 10min

80min 1000min

10000min


SCIPPSCIPP

For charge collection studies, the health of the system can be determined by monitoring the singles rate. It signals breakdown and thus unphysical behavior even before the leakage current or the collected charge do it.

In order to quantify the performance, we introduce the “efficiency voltage” as the bias voltage at which the efficiency reaches 100%. Very little annealing is observed, with the exception in p-on-n FZ.

The efficiency voltage for p-type material is about the same for FZ and MCz in this fluence range.

Comparison between efficiency voltage for SSD and full depletion voltage Vfd of diodes permits insight into the fact of “inversion”.

The correlation of the efficiency with the clustersize is uniform across many different sensor types, particle species during irradiation, and anneal steps (with the exception of the p-on-n FZ sensors,)

Admittance allows extraction the depth of the depleted region of irradiated sensors

Conclusions


SCIPPSCIPP

Thanks to

the foundries and institutes who supplied sensors in a collaborative manner

staff in Ljubljana, Louvain, CERN, Karlsruhe, PSI, BNL, LANL, UCSC for carrying out the irradiations.

RD50 and ATLAS07 collaborators and the many students who spend their evenings and nights taking and analyzing the data.

Acknowledgments

Documents

Charge Collection in irradiated Si Sensors