Nuclear Inst. and Methods in Physics Research, A 924 (2019) 108–111

Contents lists available at ScienceDirect

Nuclear Inst. and Methods in Physics Research, A
journal homepage: www.elsevier.com/locate/nima

Test beam evaluation of silicon strip modules for ATLAS phase-II strip
tracker upgrade
A.J. Blue 1 ,∗, A.A. Affolder 22 , X. Ai 13,25 , P.P. Allport 3 , J.-H. Arling 9 , R.J. Atkin 5 , L.S. Bruni 2 ,I. Carli 18 , G. Casse 16 , L. Chen 13,25,29 , A. Chisholm 7 , K. Cormier 26 , W. Cunningham 1 ,P. Dervan 16 , S. Diez 9 , Z. Dolezal 18 , J. Dopke 21 , E. Dreyer 24 , J. Dreyling-Eschweiler 9 ,C. Escobar 12 , V. Fabiani 17 , V. Fadeyev 22 , J. Fernandez-Tejero 8 , C. Fleta 8 , A. Gabrielli 15 ,B. Gallop 21 , C. García Argos 10 , A. Greenall 16 , I.M. Gregor 9 , G. Greig 24 , F. Guescini 27 ,K. Hara 28 , M. Hauser 10 , Y. Huang 13,25 , R.F.H. Hunter 6 , J.S. Keller 6 , C.T. Klein 4 , P. Kodys 18 ,U. Koetz 9 , T. Koffas 6 , Z. Kotek 19 , J. Kroll 19 , S. Kühn 7,10 , S.J. Lee 6 , Y. Liu 13,25 , K. Lohwasser 23 ,L. Mészárosová 18 , M. Mikestikova 19 , M. Miñano Moya 12 , R. Mori 10 , B. Moser 10 ,K. Nikolopoulos 3 , R. Peschke 9 , G. Pezzullo 7 , P.W. Phillips 21 , L. Poley 9 , M. Queitsch-Maitland 9 ,F. Ravotti 7 , D. Rodriguez 12 , E. Rossi 9 , A. Rummler 7 , C. Sawyer 21 , D. Sperlich 11 , S. Sullivan 21 ,J. Suzuki 28 , M. Sykora 18 , E. Tahirovic 20 , O. Theiner 18 , J. Thomas 3 , Y. Unno 14 , S. Wada 28 ,M. Warren 30 , M. Wiehe 10 , S. Wonsak 16 , M. Wormald 16 , K. Wraight 1 , N. Zakharchuk 9 ,H. Zhu 13,25
1

SUPA School of Physics and Astronomy, University of Glasgow , Kelvin Building, University Avenue, Glasgow G12 8QQ, Scotland, United Kingdom

2 University of Amsterdam/NIKHEF, Amsterdam, Netherlands
3 Particle Physics Group, School of Physics and Astronomy, University of Birmingham, Birmingham

B15 2TT, United Kingdom
CB3 0HE, United KingdomDepartment of Physics, University of Cape Town, University Avenue, Rondebosch, Cape Town 7700, South Africa
6Physics Department, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario, K1S 5B6, Canada
7
CERN, Geneva, Switzerland
8Centro Nacional de Microelectronica (IMB-CNM, CSIC), Campus UAB-Bellaterra, 08193 Barcelona, Spain
9
Deutsches Elektronen-Synchrotron, Notkestraße 85, 22607 Hamburg, Germany
10 Physikalisches Institut, Albert-Ludwigs-Universität Freiburg, Hermann-Herder-Str. 3, 79104 Freiburg-im-Breisgau, Germany
11 Institut für Physik, Humboldt-Universität zu Berlin, Newtonstraße, Berlin, Germany
12 Instituto de Física Corpuscular (IFIC) - CSIC-University of Valencia, Parque Científico, C/Catedrático José Beltrán 2, E-46980 Paterna, Spain
13
Institute of High Energy Physics, Chinese Academy of Science, Beijing, China
14
IPNS, KEK, 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan
15
Physics Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
16
Particle Physics, University of Liverpool, Oliver Lodge Building, Department of Physics, Oxford Street, Liverpool, L69 7ZE, United Kingdom
17
Institute for Mathematics, Astrophysics, and Particle Physics, Radboud University Nijmegen/NIKHEF, Nijmegen, Netherlands
18 Faculty of Mathematics and Physics, Charles University, V Holesovickach 2, Prague, CZ18000, Czech Republic
19 Academy of Sciences of the Czech Republic, Institute of Physics, Na Slovance 2, 18221 Prague 8, Czech Republic
20 School of Physics and Astronomy, Queen Mary University of London, London, United Kingdom
21
Particle Physics Department, STFC Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX, United Kingdom
22
Santa Cruz Institute for Particle Physics (SCIPP), University of California, Santa Cruz, CA 95064, USA23
Department of Physics and Astronomy, University of Sheffield, Hicks Bldg, Sheffield S3 7R, United Kingdom
24
Department of Physics, Simon Fraser University, Burnaby, British Columbia, Canada
25
State Key Laboratory of Particle Detection and Electronics, Beijing, China
26 Department of Physics, University of Toronto, 60 Saint George St., Toronto M5S 1A7, Ontario, Canada
27 Physical Sciences Division, TRIUMF, 4004 Wesbrook Mall, Vancouver, BC, Canada V6T 2A3
28 Institute of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8571, Japan
29
University of Chinese Academy of Sciences, Beijing, China
30
Department of Physics and Astronomy, University College London, London, United Kingdom
4 Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge
5∗ Corresponding author.
E-mail address: andrew.blue@glasgow.ac.uk (A.J. Blue).

https://doi.org/10.1016/j.nima.2018.09.041
Received 4 February 2018; Received in revised form 6 September 2018; Accepted 12 September 2018
Available online 22 September 20180168-9002/© 2018 Published by Elsevier B.V.

A.J. Blue, A.A. Affolder, X. Ai et al.

ARTICLEINFO

Keywords:
Semiconductor
Silicon
Detector

Nuclear Inst. and Methods in Physics Research, A 924 (2019) 108–111

ABSTRACTThe planned High Luminosity Large Hadron Collider is being designed to maximise the physics potentialof the LHC with 10 years of operation at instantaneous luminosities of 7.5 × 1034 cm−2 s−1 . A consequence of
this increased luminosity is the expected radiation damage requiring the tracking detectors to withstand hadron
fluence to over 1 × 1015 1 MeV neutron equivalent per cm2 in the ATLAS Strips system. Fast readout electronics,
deploying 130 nm CMOS front-end electronics are glued on top of a silicon sensor to make a module. Theradiation hard n-in-p micro-strip sensors used have been developed by the ATLAS ITk Strip Sensor collaborationand produced by Hamamatsu Photonics. A series of tests were performed at the DESY-II test beam facility toinvestigate the detailed performance of a strip module with both 2.5 cm and 5 cm length strips before irradiation.
The DURANTA telescope was used to obtain a pointing resolution of 2 μm, with an additional pixel layer installed
to improve timing resolution to ∼25 ns. Results show that prior to irradiation a wide range of thresholds (0.5–2.0fC) meet the requirements of a noise occupancy less than 1 × 10−3 and a hit efficiency greater than 99%.

first device (LS4) was a barrel short strip sensor connected to a barrel
hybrid populated with 10 ABC130 (130 nm prototype) chips [4]. Thesensor used was an ATLAS012 300 μm thick n-in-p micro-strip sensor
developed by the ATLAS ITk Strip Sensor collaboration and produced
by Hamamatsu Photonics [5]. In order to compare results for longand short strips under the same conditions, a long-strip module wasapproximated by connecting adjacent short-strip columns with wirebonds to form long (4.8 cm) strips. However, sections of the module
were connected to only one column to allow direct comparisons between
the two lengths on the same sensor connected to the same front-end
ASIC (Fig. 1). In addition, a second device (DAQload10) consisting of apartially populated hybrid with three ABC130s and one ATLAS12 minisensor was assembled. This assembly allowed for rapid testing without
using large number of ABC130s or full size sensors (Fig. 1).

1. Introduction
1.1. ATLAS upgrade for HL-LHC
The High Luminosity Large Hadron Collider (HL-LHC) will operate at
an ultimate peak instantaneous luminosity of 7.5 × 1034 cm−2 s−1 whichcorresponds to approximately 200 inelastic proton–proton collisions per
beam crossing (pile-up) [1]. It will be operational for more than 10 years
and in that time ATLAS aims for a total data set of 4000 fb−1 . To operate
at the higher data rates, withstand the radiation levels, and maintain low
occupancy in the high pile-up environment, the current ATLAS InnerDetector (ID) [2] will be replaced by a new Inner Tracker (ITk). TheITk will be an all-silicon tracking system that consists of a pixel detector
at small radius close to the beam line and a large area strip tracker
surrounding it.

2.2. Test beam setup

1.2. ITK strips system

For the DESY test beams an electron beam energy of 4.4 GeV wasused, with tracking performed using the EUDET-style telescopes, which
consist of six MIMOSA26 pixel sensors with a pitch of 18.4 μm [6]. Anadditional pixel layer with an FEi4 [7] read-out was used to improve
the timing of the telescope, allowing individual tracks to be matched tohits on the strip module under test. Tracks were reconstructed using theGeneral Broken Lines algorithm [8], resulting in a pointing resolutionof 2 μm [6]. The strip modules were mounted between the third andfourth telescope planes. All devices were read out using the current test
hardware (ATLYS FPGA development board) and software (ITSDAQ),
integrated with the telescope data acquisition software (EUDAQ) [9].
The beam was incident on the surface of the device, with the size of thebeam spot chosen to be ∼1 cm2 , allowing for hits on strips wire-bonded
to an individual ABC130 at a time. For each strip device, thresholdscans were performed with a minimum of 200,000 events taken for eachthreshold setting (∼2k events/strip). The scans were repeated for eachsensor bias voltage being studied, and then for the different positions onthe sensors.

The ITk strips system is composed of modules [3]. The strip modules
are single-sided with the hybrid circuits carrying the front-end microelectronic ASICs glued to the sensor surface. Modules are sandwiched on
both sides of low mass carbon-fibre support structures with embedded
bi-phase CO2 cooling. Each module consists of multiple rows of strips
with a pitch of 74.5 μm in the central (barrel) region, and ranging from69 μm to 85 μm in the forward (end-cap) regions. The local support
structures for the barrels are staves with 14 modules on each side while
the end-cap discs are built from petals with 9 modules of different types
per side. For the central barrel region of the strips system, the strips on
the inner two cylinders are 24.1 mm long (short-strips) and those on
the outer two cylinders are 48.2 mm long (long-strips). The short-strip
barrel modules contain two hybrids, each with ten ABC read-out ASICs,
whereas the long-strip modules contain one hybrid with ten ABC ASICs.
1.3. Motivation for testing
It is important to understand the performance of the strip modules
before irradiation, with the most critical parameters being the Equivalent Noise Charge (ENC) in electrons, the gain, the collected charge,
the hit efficiency, and the noise occupancy. In addition to standard labtests, the characterisation of a module operated at a particle test beamis then a vital tool for the evaluation of the module and its associatedcomponents.

3. Results
3.1. Lab results
The module LS4 was fully characterised in the lab for noise and gain
by injecting a known amount of charge in the chip and performing athreshold scan. Shown in Fig. 2 are the data for both long and short strips
whilst operated at 400 V, where 𝑉𝐷𝐸𝑃 = 370 V. The increase in noise
between long and short strips due to the difference in strip capacitanceis in agreement with predictions from the ASIC design simulations [1].

2. Setup
2.1. Devices under test
To improve the understanding of modules operating under a seriesof different conditions, 2 devices were examined at test beam. The109

A.J. Blue, A.A. Affolder, X. Ai et al.

Nuclear Inst. and Methods in Physics Research, A 924 (2019) 108–111

Fig. 1. Left: a fully assembled ABC130 Long-Strip Barrel Module (LS4); Right: a DAQload (DAQload10).

Fig. 2. Left: Gain averaged per ABC130 read-out chip for the long and short strips in module LS4 operated at 400 V. Right: Input nose in e− ENC and averaged per read-out chip forlong-strip module utilising ABC130 chips, where the long strips are read out in Stream 1 and short strips in Stream 0.

the effect of charge sharing between strips. Charge sharing can also beseen by looking at the average cluster size at relatively low thresholds(necessary for binary read-out systems), shown in Fig. 4. The likelihoodof two-strip clusters increases for electrons passing in between twostrips, where charge sharing is the highest.

3.2. Module test beam results
In all test beam measurements, threshold scans were performed andthe tracks reconstructed with telescope data were used to determine theefficiency at each threshold. The efficiency is defined as the fraction of
events in which a cluster is recorded whose centre is within 200 μm
from the track position as it passes the device under test. The thresholdscans can be used to infer the distribution of the collected charge,
as the difference between two points corresponds to the fraction ofelectrons producing a signal between those two threshold values. Thethreshold scans are then fit to a skewed error function, allowing fora determination of the most probable value (MPV) for the collectedcharge. The efficiency curves were evaluated at the DESY test beam forthe long-strip and short-strip regions of the LS4 module at two different
bias voltages, shown in Fig. 3. The differences in the curves arise fromthe module being operated in undepleted and over-depleted modes,
where 𝑉𝐷𝐸𝑃 = 370 V. The noise occupancy as a function of the thresholdis fit with an error function; the shape describes the distribution wellwith a minimal non-Gaussian tail in the noise spectrum [3]. The signalto-noise ratio yields values of 30 to 35 for a sensor bias voltage of
400 V [1].
The excellent pointing resolution from the telescope allows forinvestigation of the behaviour within and between the strips. Fig. 4
shows the hit occupancy as a function of the distance a track passes
from the centre of a strip for a wide range of thresholds for DAQload10.
The curves show a flat efficiency in the central region of the strips,with a drop in the efficiency near the strip edges which is attributable to4. Conclusions
An ATLAS ITk Strip barrel module was fully evaluated at a test beamfor electrical performance. The efficiency is greater than the ATLAS
specification of 99% for thresholds of up to 2.5 fC at a bias voltage of400 V. The signal-to-noise ratio yields values of 30 to 35. In addition, aflat efficiency in the central region of the strips with a width consistent
with the strip pitch is measured. The results are as expected for a nonirradiated module and are well in agreement with the requirements
for the ITk. Further test beams with irradiated parts are necessary tovalidate the modules and their components for end of life performanceat the HL-LHC.
Acknowledgements
The research was supported and financed in part by Canada Foundation for Innovation, Canada, the National Science and Engineering Research Council (NSERC) of Canada under the Research and Technology
Instrumentation (RTI) grant SAPEQ-2016-00015; the National Key Program for S&T Research and Development (Grant No. 2016YFA0400101)
of China and CAS-Helmholtz Joint Research Group, China; the Ministry110

A.J. Blue, A.A. Affolder, X. Ai et al.

Nuclear Inst. and Methods in Physics Research, A 924 (2019) 108–111

Fig. 3. Left: The efficiency versus the threshold for two bias voltages and two positions on the module LS4. Right: Fit of the noise occupancy vs. threshold distributions with an error
function (ERFC).

Fig. 4. Left: Hit occupancy, defined as the probability that a hit will be recorded in a given strip, given the distance of a track from the centre of such strip. The strip width (74.5 μm)
is indicated with dashed lines. Right: Cluster size versus in-strip position. Average cluster size versus hit position, along three strips. The integer position values correspond to the centreof the strips.

of Education, Youth and Sports of the Czech Republic coming from theproject LM2015058-Research infrastructure for experiments at CERN;
the DST/NRF in South Africa; the Spanish Ministry of Economy andCompetitiveness through the Particle Physics National Program, Spain,ref. FPA2015-65652-C4-4-R (MINECO/FEDER, UE), and co-financedwith FEDER funds, Spain; the UK’s Science and Technology Facilities
Council, UK; USA Department of Energy, USA, Grant DE-SC0010107;
and the European Union’s Horizon 2020 Research and Innovation programme, Spain, under Grant Agreement no. 654168. The measurements
leading to these results have been performed at the Test Beam Facility
at DESY Hamburg (Germany), a member of the Helmholtz Association(HGF).

[2] The ATLAS Collaboration, The ATLAS experiment at the CERN large hadron collider,
JINST 3 (2008) S08003.
[3] S. Diez, et al., A double-sided, shield-less stave prototype for the ATLAS Upgrade
strip tracker for the High Luminosity LHC, J. Inst. 9 (2014).
[4] C. Argos, et al., The ATLAS ITk strip detector. Status of R&D, Nucl. Instrum. Methods
Phys. Res. A845 (2017).
[5] B. Hommels, et al., Detailed studies of full-size ATLAS12 sensors, Nucl. Instrum.
Methods Phys. Res. A831 (2016).
[6] H. Jansen, et al., Performance of the EUDET-type beam telescopes, EPJ Technol.
Instrum. (2016).
[7] M. Garcia-Sciveres, et al., The FE-I4 pixel readout integrated circuit, Nucl. Instrum.
Methods A636 (2011).
[8] C. Kleinwort, et al., General Broken Lines as advanced track fitting method, Nucl.
Instrum. Methods Phys. Res. A673 (2012).
[9] H. Perrey, et al., EUDAQ and EUTelescope software frameworks for test beam dataacquisition and analysis, PoS 353 (2014).

References[1] The ATLAS Collaboration, Technical Design Report for the ATLAS Inner Tracker Strip
Detector, Technical Report CERN-LHCC-2017-005. ATLAS-TDR-025, CERN, Geneva,
04, 2017.

111