Annealing study of a highly irradiated FZ CMS mini sensor with the ALiBaVa setup at KIT

KIT – University of the State of Baden-Wuerttemberg and National Research Center of the Helmholtz Association

Institut für Experimentelle Kernphysik

www.kit.edu

Annealing study of a highly irradiated FZ CMS mini sensor with the ALiBaVa setup at KIT

Robert Eber, Tanja PfisterA. Nürnberg, T. Barvich, W. de Boer, A. Dierlamm, M. Frey, Th. Müller, P. Steck, A. Kornmayer

17th RD50 Workshop218.11.2010

Robert EberInstitut für Experimentelle Kernphysik, KIT

Overview

Alibava setup at Karlsruhe

Annealing study of a FZ CMS mini sensorReverse bias

Forward bias

Leakage current

Signal to noise ratio

Comparison of operating modes

Conclusion



ALiBaVa Station at Karlsruhe

Setup shielded inside a metal box

Daughterboard thermally isolated from sensor

Temperature rangeCooling to -30°C

Heating to +80°C for annealing studies inside the setup

Signal generation byLaser 1060nm90Sr beta source

XYZ-stage for position dependent studies

Fully automated software and temperature control for complete annealing study



ALiBaVa Station at Karlsruhe

XYZ stage

Collimator for source

IR laser mount

Sensor

Daughterboard

Peltier cooling

Primary cooling

Scintillator

Isolation and shielding



Sensors above expected LHC fluenceSensor

CMS mini: FZ p-in-n sensor, 295µm active thickness, 192 strips

Irradiation: 7.5E14 Neq/cm2, 25MeV protons (@KA)

Fluence is equivalent to around 10 years of LHC operation at radius 4 – 5cm (pixel region), 300fb-1

Outer barrel SLHC strip region

Annealing study

Signal and signal to noise ratio

Current

Reverse bias

Forward bias, CID

Time [h] 0.5 0.5 0.5 0.5 0.84 1.33

Temperature 60 60 60 70 70 70

Approx. time at RT [h] 130 130 130 400 700 1400

Sum approx time[h] 130 260 390 800 1500 2900



Reverse bias operation

Higher collected chargeHigher voltage

Lower temperature

As expected

Sensor at 500V is not fully depletedSignal and S/N drops with longer annealing times

1 ADC ~ 80e-

500V-30°C

No annealing



CID MeasurementsForward bias

Generation of electric field throughout whole sensor volume

Entire sensor depth is sensitive

Current fills trap levels permanently

Lower bias voltage necessary to collect charges

Landau-Gauss fits well

Signal

Signal to noise ratio

Fluence 7.5e14 Neq/cm2 and T= -30°C not optimal for CID mode

Investigate operability

-150V-30°C

No annealing

[5]

𝐸 (𝑥 )=32𝑉𝑑 √ 𝑥𝑑[4]



CID Measurements

Signal increases with voltage

S/N shows maximum at certain bias voltage:

Noise increase

Related to current

Overall annealing behaviour:

Slight drop in S/N with annealing



Current annealing

Leakage current shows known annealing behaviour with reverse bias applied

LC decreases

More impact at higher temperatures

Under forward bias condition, current increases drastically with annealing

Noise rises due to current

Operation at lower temperatures necessary to reduce current level

Powerful cooling required

Current annealing at first step only

Reverse bias Forward bias



Comparison: CID – reverse bias (Signal)

Reverse bias

Signal level increases at lower voltages after short annealing

Signal decreases with longer annealing

Forward bias

Annealing has almost no influence on signal height

10d RT annealing

100d RT annealing

No annealing



Comparison: CID – reverse bias (S/N)

Reverse biasSignal to Noise ratio improved due to beneficial annealing

Forward biasSlight decrease in S/N due to current increase

No beneficial annealing observed

No annealing 10d RT annealing

100d RT annealing



Summary

Sensor in CID mode outperforms the sensor with reverse bias with no annealing at only -150V

It almost reaches the reverse bias 10d at RT annealing level

500V, no annealing, fits well into known data

500V, 10d annealing almost doubles the collected charge

1000V, 10d annealing even performs like the n-in-n pixels at 600V

No improvement during annealing in CID mode

References:[1] p/n-FZ, 300µm (-30°C,25ns), strip [Casse 2008][2] n/n-FZ, 285µm (-10°C,40ns), pixel [Rohe et al. 2005][3] p/n-FZ, 295µm (-30°C,25ns), strip [Pfister 2010]



Conclusion

Sensor could be operated in CID mode with fluence of „only“ 7.5e14 Neq/cm2 and temperature -30°C

CID is possible readout mode…

Feasible S/N can be achieved at much lower voltages compared to reverse bias

But..

Applicable in detectors only when not annealed

Operation at low temperature and high forward current requires very powerful cooling

Lack of beneficial annealing rules out advantages of forward bias

With appropriate annealing the sensor can resist fluences above the expected ones at LHC (300fb-1)

Known FZ p-in-n material could be chosen for outer barrel strip regions at SLHC



Thank you for your attention!

Diploma Thesis, Tanja Pfister, KIT 2010: IEKP-KA/2010-20



References

[4] Beatti, L.J., et al. Forward-bias operating of Si detectors: a way to work in high-radiation environment. Nuclear Instruments and Methods in Physics Research, 439:293, 2000.

[5] Zheng, L. et col. Cryogenic Si detectors for ultra radiation hardness in SLHC environment. Nuclear Instruments and Methods in Physics Research, 579(A):775-781, 2007.

Prof. Max Mustermann - Title



Landau-Gauss fits at 600V, -10°CSignal: No Annealing 10d Annealing at RT

S2N: No Annealing 10d Annealing at RT



Landau-Gauss fits at -150V, -30°CSignal: No Annealing 10d Annealing at RT

S2N: No Annealing 10d Annealing at RT



Current – Voltage at different T



Current – Voltage at different annealing



Clustersignal – Time Plots

Reverse Bias

Forward Bias

Annealing study of a highly irradiated FZ CMS mini sensor with the ALiBaVa setup at KIT

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