Latest IV and CV tests on microstrip silicon sensors …...Latest IV and CV tests on microstrip...

Latest IV and CVtests on

microstrip siliconsensors for theCMS Tracker

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Elena Graverini

Latest IV and CV tests on microstrip siliconsensors for the CMS Tracker Upgrade

Elena Graverini

August 30, 2012



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Elena Graverini

The test MSSDs

Region 1 2 3 4 5 6 7 8 9 10 11 12Strip width (µm) 16 34 10 8.5 28 58 18 15.5 40 82 26 22.5Strip pitch (µm) 120 240 80 70 120 240 80 70 120 240 80 70

Al (µm) 29 47 23 21.5 41 71 31 28.5 53 95 39 35.5Al/W 1.81 1.38 2.30 2.53 1.46 1.22 1.72 1.84 1.33 1.16 1.50 1.56W/P 0.13 0.14 0.13 0.12 0.23 0.24 0.23 0.22 0.33 0.34 0.33 0.32



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Elena Graverini

Tested MSSDs

Not irradiatedSensor IV CV Cint

FZ200P 02 MSSD 1 August 20 August 13FZ200Y 04 MSSD 1 August 20 August 10FZ200N 10 MSSD 2 August 17 August 13FZ320N 05 MSSD 2 August 21 August 22 August 15FZ320N 07 MSSD 2 August 21 August 14FZ320P 03 MSSD 2 August 20 August 21 August 14

IrradiatedSensor Irradiation IV CV

M200N 04 MSSD 1 8.2 1014 p; 5 1014 n August 27 August 27FZ200N 04 MSSD 2 1.0 1015 p; 5 1014 n August 28 August 28FZ320N 05 MSSD 1 8.6 1014 p; 5 1014 n August 29 August 29FZ320Y 05 MSSD 1 9.5 1014 p; 5 1014 n August 30 August 30

All tests performed at -20◦CDatabase CV data from 2011 for FZ200P 02 MSSD 1,FZ200Y 04 MSSD 1, FZ200N 10 MSSD 2 and FZ320N 07 MSSD 2FZ320P 02 MSSD 2 (irradiated) was broken during shipment from CERN



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Elena Graverini

Leakage current

If the bias voltage is raised over VFD , thermally generated pairsbegin to be pulled out of the depleted region, giving a reversecurrent Ileak proportionalto the dopant concentration (' chargecarriers concentration) ni .The charge carriers densities at the termalequilibrium are given by:

n ∝ e− EC −E fkT (electrons)

p ∝ e− Ef −E VkT (holes)

where EC is the energy of the condution band, EV that of the valence bandand Ef is the Fermienergy.Mass Action Law

n · p ≡ n2i ∝ e− ∆EkT with ∆E ≡ EC − EV =⇒ n i ∝ e− ∆E

2kT

A decrease of 7◦C in temperature results approximately in a factor12 of

leakage current reduction.



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Elena Graverini

IV measurements at -20◦C

IV measurements at -20◦C and comparison with database data(+20◦C)Ileak should fallby a factor 25 to 26

Observed factor:I+20◦I−20◦

' 30Preliminary! Background/pedestalcurrent is not constant andhas not been subtracted from the data samples.



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Elena Graverini

Light insulation

Added light insulation to theautomatic probe station.



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Elena Graverini

CV measurements at -20◦C

As a check, a CV measurement was performed twice, at -20◦C and+20◦C:



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Elena Graverini

Irradiated sensors

M200N 04 MSSD 1Irradiation:8.2 1014p/cm2 plus 5 1014n/cm2

It was stored at -20◦C =⇒ need to warm it up in a dry box beforetransporting it to the probe station, to avoid moisture biassing themeasurementsAfter irradiation the leakage current is much greater than before.Fixed two missing ground connections in the test circuit



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Elena Graverini

Irradiated sensors

FZ200N 04 MSSD 2 (IV)Irradiation:1015p/cm2 plus 5 1014n/cm2

It seems that there was a problem with the IV test performed in July 2012at CERN: all the regions show the same current, very lowIt also seems that the sensor was irradiated before the measurementsperformed at CERN in April 2012 (flat lines:September 2011, same regions)



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Elena Graverini

Irradiated sensors

FZ200N 04 MSSD 2 (CV)It looks like something bad happened with the CV test performed in July 2012 atCERN: there’s no agreement between that data set and any other, while ourlatest tests are similar to those of April2012



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Elena Graverini

Irradiated sensors

FZ320N 05 MSSD 1 (IV)Irradiation:8.6 1014p/cm2 plus 5 1014n/cm2

Probably irradiated before April2012What happened between 2012 and 2011?



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Elena Graverini

Irradiated sensors

FZ320N 05 MSSD 1 (CV)After irradiation the Vfd goes from ∼250V to ∼650V

Latest IV and CV tests on microstrip silicon sensors …...Latest IV and CV tests on microstrip...

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