11th RD50 Workshop, CERN 12-14 Nov. 20071

Results with thin and standard p-type detectors

after heavy neutron irradiation

G. Casse

11th RD50 Workshop, CERN 12-14 Nov. 20072

OUTLINE:

• Introduction

• Motivations for using p-type substrates in high radiation environments

• Motivations for investigating thin (140µm) vs standard (300µm) detectors

• Charge Collection Efficiency results up to 1x1016 n cm-2

• Summary and future work

11th RD50 Workshop, CERN 12-14 Nov. 20073

N-side read-out for tracking in high radiation environments?

Schematic changes of Electric field after irradiation

Effect of trapping on the Charge Collection

Efficiency (CCE)

Collecting electrons provide a sensitive advantage with respect to holes due to a much shorter tc. P-type detectors are the most natural solution for e collection on the segmented side.

Qtc Q0exp(-tc/tr), 1/tr = .

N-side read out to keep lower tc

11th RD50 Workshop, CERN 12-14 Nov. 20074

Effect of trapping on the Charge Collection

Distance

Qtc Q0exp(-tc/tr), 1/tr = .

After heavy irradiation thin detectors should have a similar CCE as thicker ones.

vsat,e x tr = av

av (=1e14) 2400µm

av (=1e16) 24µm

From G. Kramberger et al., NIMA 476(2002), 645-651.

e = cm-2/ns

h = cm-2/ns

11th RD50 Workshop, CERN 12-14 Nov. 20075

Silicon miniature microstrip detectors and irradiation

Mini microstrip, ~1x1 cm2, 128 strips, 80 µm pitch, designed by Liverpool and produced by Micron on 300µm and 140µm thick wafers.

RD50 mask (see: http://rd50.web.cern.ch/rd50/)

Irradiation and dosimetry:TRIGA Mark II research reactor Reactor Centre of the Jozef Stefan Institute, Ljubljana, Slovenia

11th RD50 Workshop, CERN 12-14 Nov. 20076

Method: measure the charge collection of the segmented devices using an analogue electronics chip (SCT128) clocked at LHC speed (40MHz clk, 25ns shaping time). The system is calibrated to the most probable value of the m.i.p. energy loss in a non-irradiated 300µm thick detector (~23000 e-).

Fast electron source: 90Sr, triggered with scintillators in coincidence.

11th RD50 Workshop, CERN 12-14 Nov. 20077

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After 3 10 1̂5 n/cm 2̂

After 1.6 10 1̂5 n/cm 2̂

After 1 10 1̂6 n/cm 2̂

After 0.5 10 1̂5 n/cm 2̂

Now µ-strip detector CCE measurements up to 1x1016 n cm-2!!

Results with neutron irradiated Micron detectors

11th RD50 Workshop, CERN 12-14 Nov. 20078

A correction of the result at 5x1014 n cm-2

Comparison of the measurements on 30k Micron detectors irradiated to the nominal of 5x1014 cm-2 in March 2006 and October 2007

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11th RD50 Workshop, CERN 12-14 Nov. 20079

Now µ-strip detector CCE measurements up to 1x1016 n cm-2!!

Results with neutron irradiated Micron detectors

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11th RD50 Workshop, CERN 12-14 Nov. 200710

Charge collection efficiency vs fluence for micro-strip detectors

irradiated with n and p read-out at LHC speed (40MHz, SCT128 chip).

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Proton irradiation 800V

11th RD50 Workshop, CERN 12-14 Nov. 200711

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Comparison of CCE with 140µm and 300µm thick detectors from Micron

irradiated to various n fluences, up to 1x1016 cm-2!

11th RD50 Workshop, CERN 12-14 Nov. 200712

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Comparison of CCE with 140µm and 300µm thick detectors from Micron

irradiated to various n fluences, up to 1x1016 cm-2!

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300 micron (new irr)

11th RD50 Workshop, CERN 12-14 Nov. 200713

Ratio of the charge collected by thick to thin detectors as a function of fluence

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3x10^15 cm -̂2 2nd meas.

11th RD50 Workshop, CERN 12-14 Nov. 200714

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Annealing of irradiated dettectors after 1x1016 n cm-2

11th RD50 Workshop, CERN 12-14 Nov. 200715

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Ratio of the charge collected by thick to thin detectors as a function of the annealing

time for detectors irradiated to 1x1016 n cm-2

11th RD50 Workshop, CERN 12-14 Nov. 200716

CONCLUSIONS:P-type detectors tested up to 1x1016 n cm-2 show a extremely good signal and adequate radiation tolerance for the LHC upgrade to 10 times higher luminosity.

These measurements are the first reference measurements for highly segmented silicon detector made in planar technology (microstrip and pixel detectors) at these doses!

After heavy irradiations the CCE of thin and thick detectors becomes similar. The choice of optimal thickness can be dictated by the need of reducing the detector mass rather than increase of the signal after irradiation (at least up the remarkable dose of 1x1016 n cm-2!!).