m. aleppo - a measurement of lorentz angle of rad-hard pixel sensors - pixel 2000 genova 1 a...

M. Aleppo - A measurement of Lorentz angle of rad-hard pixel sensors - Pixel 2000 Genova 1

A measurement of Lorentz angle of rad-hard pixel sensors

Dipartimento di Fisica dell’Università di Milano

for the ATLAS Pixel Collaboration

Mario Aleppo

International Workshop on Semiconductor Pixels Detectors for Particles and X-rays

Pixel2000


Partecipating Institutes• Canada Canada

– University of Toronto• Czech Republic Czech Republic

– Academy of Sciences - Institue of Physics of Prague, Charles University of Prague, Czech Technical University of Prague

• France France – CPPM, Marseille

• Germany Germany – Bonn University, Dortmund University, Siegen University, Bergische University -

Wuppertal, MPI Munich (R&D only) • ItalyItaly

– INFN and University of Genova, INFN and University of Milano, INFN and University of Udine

• Netherlands Netherlands – NIKHEF - Amsterdam

• USAUSA– University of New York - Albany, LBL and University of California - Berkeley,

University of New Mexico - Albuquerque, University of Oklahoma-Norman, University of California - Santa Cruz, University of Wisconsin - Madison, Ohio State University-Columbus


Test sensors are irradiated at a fluence of 51014neq/cm2 and 11015 neq/cm2.

Every chip is a matrix of 18 columns and 160 rows

Pixel size is 50 400

Thickness 280

+++

E


Test beam setup


The importance of the Lorentz angle measurement

Modules are tilted to take into account the effect of Lorentz angle on the charge drift.

Charge sharing depends upon the Lorentz angle.

Charge drifts with an angle L respect to the direction of the Electric field in presence of a Magnetic field

B

This affects detector performances: space resolution, efficiencyand occupancy.

Measurement of the mean cluster size as a function of the angle


L=5.90

L=2.60

L=9.00

L=3.10


Lorentz angle model

/1

c

csd

22

dL

E/E1

/Ev/

Br)tg(

r

1-66.02

1-55.1

-187.09

scmT1057.2

VcmT01.1E

scmT1053.1v

c

s

NI FIHI150V HI600V


The Electric field is not constant,due to the spatial charge.

The charge distributionis assumed to be uniform.

EE

y

2 V/d

(V + Vd )/d

(V Vd )/d

n type

p type

n+ n+n+n+

n+n+n+n+

y


An effective Lorentz angle has been defined as the angle corresponding to the minimum cluster size.

TyEBrydy

dxd ),()()tg( L

y y

xx


Lorentz angle measurement• Measured mean cluster size for different angleswith Bon (1.4 Tesla) and Boff

• Data with Boff are used to check systematic effects

• Fits with a parabola

• Comparison with results obtained with the model:

– Depletion taken from data– Threshold fitted from data taken with Boff


Depletion depth measurement• Performed rotating the sensor around the pixel axis parallel to the long size of pixels.

• Strategy based on the determination of the entrance and exit points of tracks

• Charge segment depthplots


Depletion depth results


Lorentz angle fits

Predicted value L=8.60 0.40

Measured value L=3.10 0.40 0.60


Measured value L=9.00 0.400.50


Lorentz angle fits

Measured value L=2.60 0.200.30


Measured value L=5.90 1.00 0.30



Lorentz angle results


Conclusions• Lorentz angle of ATLAS Pixel rad-hard sensors has been measured.

• The observed behavior is well explained by a model based on charge drift in silicon.

• The Lorentz angle ( through the mobility ) depends upon the Electric field inside sensors.

• At the operating conditions for ATLAS pixel sensor we expect a Lorentz angle of 130 at the beginning of data taking. After 10 years we expected a Lorentz angle of 40.

• Depletion depth of sensors irradiated at two different fluences has been measured and characterized as a function of the operation voltage.

m. aleppo - a measurement of lorentz angle of rad-hard pixel sensors - pixel 2000 genova 1 a...

Documents

hard pixel sensors pixel

angle slide

university of genova

effect of lorentz angle

effective lorentz angle

university of milano

university of california

rows pixel size