To be ready for the challenging conditions of the High Luminosity phase of the LHC accelerator at CERN, the ATLAS Inner Detector will be completely replaced with a new all-silicon Inner Tracker, the ITk. Sensors in the innermost layer will be exposed to a fluence up to 1.9⋅10¹⁶~nₑq/cm² (considering a safety factor of 1.5) at the half of the HL-LHC program, after which it is scheduled to be replaced together will the full innermost system. Pixel sensors with 3D technology have been chosen to instrument it due to their radiation hardness. Sensors with 25x100~μm² pixel pitch will be used in the central region of the innermost layer (barrel) while sensors with a pitch of 50x50~μm² will instrument its two side regions (end-caps). The Fondazione Bruno Kessler (FBK) has been chosen as one of the two vendors for the production of these sensors. This paper will present the performance of 3D pre-production sensors with both pixel pitches produced by FBK measured in test beams with devices irradiated up to and beyond the sensor end-of-life fluence

Calderini, Giovanni

Carcone, Thibuad Idriss

Carlotto, Juan Ignacio

Chabrillat, Paul

Dalla Betta, Gian Franco

Gemme, Claudia

Grigorev, Alexey

Heim, Timon

Meng, Lingxin

Mironova, Maria

Ravera, Simone

Ressegotti, Martina

Rummler, Andre

Samy, M. Abdulla

Skaf, Ali

Sorenson, Joseph Daniel

Sultan, D.M.

Zanzottera, Riccardo

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PoS(VERTEX2023)072Qualification of irradiated 3D pixel sensors produced byFBK for the pre-production of the ATLAS ITk detectorM.A. Abdulla Samy,a,b G. Calderini,c T. I. Carcone,c J. I. Carlotto,d P. Chabrillat,cG.-F. Dalla Betta,a,b C. Gemme,e A. Grigorev,f T. Heim,g L. Meng,h M. Mironova,gS. Ravera,e,i M. Ressegotti,e A. Rummler,j A. Skaf,k J. D. Sorenson,l D M SSultana and R. Zanzotteram,naTIFPA INFN, Via Sommarive 14, 38123 Trento, ItalybDepartment of Industrial Engineering, University of Trento, Via Sommarive 9, 38123 Trento, ItalycLPNHE, Sorbonne Université, Université Paris Cité, CNRS/IN2P3, Paris; FrancedInstitut de Física d’Altes Energies (IFAE), Barcelona Institute of Science and Technology, Barcelona;SpaineINFN Sezione di Genova; ItalyfDepartment of Physics, University of Oslo, Oslo; NorwaygPhysics Division, Lawrence Berkeley National Laboratory, Berkeley CA; United States of AmericahPhysics Department, Lancaster University, Lancaster; United KingdomiDipartimento di Fisica, Università di Genova, Genova; ItalyjCERN, Geneva; SwitzerlandkII. Physikalisches Institut, Georg-August-Universität Göttingen, Göttingen; GermanylDepartment of Physics and Astronomy, University of New Mexico, Albuquerque, NM, United StatesmINFN Sezione di Milano; ItalynDipartimento di Fisica, Università Statale di Milano, Milano; ItalyE-mail: simone.ravera@cern.chTo be ready for the challenging conditions of the High Luminosity phase of the LHC acceleratorat CERN, the ATLAS Inner Detector will be completely replaced with a new all-silicon InnerTracker, the ITk. Sensors in the innermost layer will be exposed to a fluence up to 1.9·1016 neq/cm2(considering a safety factor of 1.5) at the half of the HL-LHC program, after which it is scheduledto be replaced together will the full innermost system. Pixel sensors with 3D technology havebeen chosen to instrument it due to their radiation hardness. Sensors with 25x100 µm2 pixel pitchwill be used in the central region of the innermost layer (barrel) while sensors with a pitch of50x50 µm2 will instrument its two side regions (end-caps). The Fondazione Bruno Kessler (FBK)has been chosen as one of the two vendors for the production of these sensors. This paper willpresent the performance of 3D pre-production sensors with both pixel pitches produced by FBKmeasured in test beams with devices irradiated up to and beyond the sensors end-of-life fluence.The 32nd International Workshop on Vertex Detectors (VERTEX2023)16-20 October 2023Sestri Levante, Genova, Italy© Copyright owned by the author(s) under the terms of the Creative CommonsAttribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). https://pos.sissa.it/PoS(VERTEX2023)072ATLAS ITk irradiated 3D pixel sensors qualification1. IntroductionThe Large Hadron Collider (LHC) [1] High Luminosity (HL) program is going to start in2029 bringing the instantaneous luminosity of the machine up to the nominal (ultimate) value of5 · 1034 cm−2 s−1 (7.5 · 1034 cm−2 s−1) and the average number of inelastic proton-proton collisionsper bunch-crossing close to 140 (200) [2]. The HL scenario will push the ATLAS detector [3] tooperate in an extremely challenging environment, well beyond the one for which it was designed.The ATLAS detector has been upgraded in stages to be ready for the HL phase: calorimeters, muonsspectrometer and the trigger and DAQ system have been improved during the Phase-I upgrades,while the ATLAS Inner Detector (ID) is going to be completely replaced with a new all-silicon InnerTracker (ITk) [4, 5] during the LS3 of the LHC in the context of the Phase-II upgrades. Phase-IIupgrades will also include improvements in the ATLAS hardware trigger increasing the total triggeraccept rate from 100k to 1MHz and minimising the latency time. The new technologies involvedwill allow the ITk to survive an unprecedented level of radiation and guarantee performance closeto the current ID with extended coverage.In section 2 the ITk detector is briefly present, section 3 describes the novel 3D technology of theITk innermost layer pixel sensors, while sections 4 and 5 are devoted to the irradiation results andbeam tests performance of pre-production 3D pixel sensors.2. ATLAS ITk overviewThe current ATLAS ID, consisting of silicon pixel and strip detectors and a transition radiationtracker, is going to be replaced with the ITk. The ITk will consist of 13 m2 of pixel detectors with5 billion read-out channels and 160 m2 of strip detectors with 50 million read-out channels. Withrespect to the current ID, the two sub-detectors have three times and seven times larger surfaces forStrip and Pixel, respectively. The 5-layer layout of the pixel detector provides extended coverageup to |𝜂 | <4. It minimizes multiple scattering effects by reducing the material budget compared tothe current ID. This is achieved primarily by using DC-DC powering and data transmission withoptical links and lpGBT in Strip; thinner modules serial powering and inclined sections in Pixel[6]. The pixel detector is organised into three mechanically independent sub-systems. The InnerSystem (IS) includes the first two innermost pixel layers (Layer 0, 1), the Outer Barrel (OB) andthe Outer Endcap (EC) (Layer 2, 3, 4) with the three outermost pixel layers of flat staves, inclinedsections, and rings [7]. Currently, no pixel technology can sustain efficient operation for the entireduration of the high luminosity program due to the high radiation damage. However, pixel sensorsdeveloped using 3D technology have been identified as good candidates for the L0 since they cansustain a fluence up to 1.9·1016 neq/cm2 and Total Ionising Dose (TID) of 1 GRad which is closeto the fluence received by the L0 after 2000 fb−1, when the IS is foreseen to be replaced. Almost900 pixel 3D sensor tiles will be hybridized each with the ITkPix readout chip [8], implementedin 65 nm technology. Three single bare modules will be placed on a common flexible PCB forpowering and readout, forming a triplet module. Sensors with a single charge collection electrodein the centre of the pixel cell will instrument the ITk L0: a pixel cell of 25x100 µm2 is used for thebarrel and a 50x50 µm2 layout in the end-caps. The choice of the two pitches is mainly driven bythe tracking performance to improve the performance of the high-level objects, such as b-tagging2PoS(VERTEX2023)072ATLAS ITk irradiated 3D pixel sensors qualificationand pile-up jet rejection. For example, with a 25x100 µm2 pixel pitch barrel, the light-jets rejectionimproves of 10-20% with respect to an all-50x50 µm2 scenario. Two vendors will deliver the entireproduction of the ITk 3D pixel sensors: Sintef (Stiftelsen for industriell og teknisk forskning) andFBK (Fondazione Bruno Kesseler). The production of the 50x50 µm2 layout is split between thetwo vendors while FBK will take care of the complete 25x100 µm2 layout production.3. Pixel sensors 3D-technologyThe increased pileup of the HL-LHC will require a small granular pixel design, with smallinter-electrode distances in the order of 50 µm or less. These values can be reached with the 3Dtechnology, consisting of direct drilling of the electrodes in the silicon substrate, which allows thesensor thickness to be decoupled from the inter-electrode distance and makes it possible to realizeextremely radiation-hard pixel detectors. With such a small pitch design, the dead area due to the3D electrodes is potentially a concern for the detector efficiency. Several processing technologieshave been explored for FBK 3D Si sensors [9]. A small electrode diameter of about 5 µm hasbeen implemented at FBK using a state-of-the-art Deep Reactive Ion-Etching (DRIE) process toaddress this issue, reducing the input capacitance of the ReadOut Chip (ROC). Sensors are realizedat FBK in 6-inches wafers using a single-side approach. This simplified production process assuresmechanical integrity, a lower risk of high wafer bow, and bump-bonding complexity [10]. Thecharge collection electrode is drilled in the 150 µm thickness active material up to a safety distanceof about 35 µm from the handle wafer (100 µm thickness) to avoid early breakdown.4. IrradiationsDuring 2022 and 2023 several pre-production single sensor tiles delivered by FBK havebeen hybridised by IZM (The Fraunhofer Institute for Reliability and Microintegration) and LND(Leonardo SpA) with pre-production ITkPix v1.1 front-end chips. In total 16 modules including thetwo different sensors layout 50x50 µm2 (8) and 25x100 µm2 (8) were mounted on Single Chip Card(SCC) to validate the pre-production. All the modules have been tested in the Genova laboratoryfollowing a standard quality control (QC) procedure including Front-End (FE) tuning and X-rayscans for the bump-bonding validation. It has been decided to irradiate 8 sensors, 4 per sensorlayout, at different irradiation facilities. Half of the modules have been irradiated in Bonn and KIT(Karlsruhe Institute of Technology) with low energy protons beam (13-23 MeV) up to a uniformfluence of 1·1016 neq/cm2, and half at the CERN IRRAD facility up to higher fluence close to2.4·1016 neq/cm2. The IRRAD facility, contrary to the first two, can not deliver uniform irradiationover the entire sensor surface given the beam size of 1 cm2, despite a scan on the horizontal axes.The local fluence received by the sensor is reconstructed starting from an Aluminum foil placedon the back of the sensor during the whole irradiation. The reconstruction is then refined by theinformation on the noise and efficiency of the device that respectively grows and decreases as afunction of the fluence received. An example of a reconstructed fluence map is shown in figure 1.3PoS(VERTEX2023)072ATLAS ITk irradiated 3D pixel sensors qualificationFigure 1: Reconstructed irradiation profile of FBK 25x100 µm2 pixel pitch irradiated at CERN IRRADfacility. The coloured area is the fluence profile, while the white halo is the area where test-beam performancewas evaluated [13].5. Beam test performanceIrradiated modules have been tested on the H6A SPS 120 GeV pion beam line during 2022-2023in several test beam campaigns. The same setup was used for all test beam campaigns mentionedin this report [11]. It includes an ACONITE telescope with six MIMOSA26 planes and an FE-I4single chip module as a timing reference plane, two scintillators at the two ends of the setup whosecoincidence triggers the signal readout via a Trigger Logic Unit (TLU) and a data acquisition systembased on YARR and EUDAQ. The resulting position resolution delivered by the beam telescopeon the surface of the Devices Under Test (DUTs) is ∼2µm. Test beam data were analysed with theC++ based framework Corryvreckan. In particular, reconstructed particle tracks passing throughdisabled or masked pixels on DUTs or through neighbouring pixels are not used in the efficiencycalculation. Hence the resulting efficiency applies to pixels not masked or disabled [12]. Particularattention was paid to the study of the efficiency of sensors and the number of pixels disabled. TheITk requirements for excellent particle tracking ask for modules with the 96% (97%) efficiency atnormal (inclined) incidence reached with at most the 3% of masked pixels, even after irradiation.Modules including both pixel pitches, have been irradiated close to 1·1016 neq/cm2 showing similarperformance. The efficiency is close to 97% at 40 V (60 V) for the 50x50 µm2 (25x100 µm2) innormal incidence conditions and it reaches 99% when modules are inclined with an angle of 15◦ tothe beam, as shown in figure 2 (left). In both cases, the number of noisy pixels is lower than the 0.1%.Modules with the 50x50 µm2 layout, irradiated up to the IS end-of-life fluence (1.9·1016 neq/cm2),showed excellent performance with the 96% efficiency (normal incidence) reached at 100 V biaswith the 3% of masked pixels. Due to the not uniform irradiation in IRRAD, 25x100 µm2 moduleshave been irradiated with a peak fluence far behind the sensor end-of-life fluence, reaching a peakfluence close to 2.4·1016 neq/cm2, as described in section 3. Test beam performance has beenevaluated in two fiducial areas on the modules, that received a different mean fluence. In thefirst area, the mean fluence is close to 2.3·1016 neq/cm2: efficiency reaches 96% (97%) at normal(inclined) incidence with a bias of 160 V (150 V) although 5% of the pixels are disabled; while4PoS(VERTEX2023)072ATLAS ITk irradiated 3D pixel sensors qualificationFigure 2: Left: Test beam performance of FBK 50x50 µm2 and 25x100 µm2 irradiated at a fluence close to1·1016 neq/cm2. Right: Test beam performance of FBK 25x100 µm2 irradiated beyond the sensors end-of-lifefluence, the number of noisy pixels per each bias is reported in the histogram [13].in the second area, the mean fluence is about 1.9·1016 neq/cm2 and the efficiency is close to 97%(inclined incidence) with 3% of disabled pixels thus fulfilling the requirements. The number isunder control up to a bias of 120 V where it stays below 3% and grows up to 35% at 170 V bias.Results are shown in figure 2 (right).6. ConclusionsFBK has delivered the pre-production of the 3D pixel sensors during 2022-2023, includingboth sensor layouts: 50x50 µm2 and 25x100 µm2. Sensors, hybridised with ITkPix v1.1 pre-production FEs, have been irradiated at different fluence in several facilities. Modules meet theITk requirements in terms of efficiency and disabled pixels even after irradiation up to the sensor’send-of-life fluence. Pixel sensors with 3D technology could be confirmed as the viable choice forthe ITk L0. These results contributed to the positive outcome of the review and allowed to launchof the full production of the FBK 3D sensors for ITk.7. AcknowledgementsThis project has received funding from the European Union’s Horizon Europe Research andInnovation program under the Grant Agreement No 101057511.References[1] L. Evans and P. Bryant (editors), LHC Machine,2008 JINST 3 S08001.[2] Apollinari G., Béjar Alonso I., Brüning O., Fessia P., Lamont M., Rossi L., and TavianL., High-Luminosity Large Hadron Collider (HL-LHC): Technical Design Report, CERN,Geneva, 2020. https://cds.cern.ch/record/2749422/files/127-117-PB.pdf[3] ATLAS Collaboration,2008 JINST 3 S08003, 10.1088/1748-0221/3/08/S08003.5PoS(VERTEX2023)072ATLAS ITk irradiated 3D pixel sensors qualification[4] ATLAS Collaboration,Technical Design Report for the ATLAS Inner Tracker Pixel Detector,Technical report, CERN, Geneva, Sept 2017. https://cds.cern.ch/record/2285585?ln=it[5] ATLAS Collaboration,Technical Design Report for the ATLAS Inner Tracker Strip Detector,Technical report, CERN, Geneva, Apr 2017. https://cds.cern.ch/record/2257755?ln=it[6] C. Gemme, The ATLAS Tracker Detector for HL-LHC, Proceedings of the 29th InternationalWorkshop on Vertex Detectors (VERTEX2020), 10.7566/JPSCP.34.010007[7] J. Francisca et al 2022 J. Phys.: Conf. Ser. 2374 012061[8] RD53 Collaboration, RD53B Design Requirements, CERN-RD53-PUB-19-001 (2019).[9] C. Da Via, G.-F. Dalla Betta and S.I. Parker, Radiation Sensors with 3D Electrodes, ch 4, CRCPress, Boca Raton, FL (2019).[10] D M S Sultan et al, Quality Control (QC) of FBK preproduction 3D Si sensors for ATLASHL-LHC Upgrades, 2022 JINST 17 C12016.[11] H. Jansen, S. Spannagel, J. Behr et al., Performance of the EUDET-type beam telescopes.EPJTechn Instrum3, 7 (2016).[12] Giovanni Calderini et al. Qualification of the first pre-production 3D FBK sensors withITkPixV1 readout chip. In: PoS Pixel2022 (2023), p. 025. doi: 10.22323/1.420.0025.[13] ATLAS Collaboration, ATLAS ITk detector public plots 2023 ITK-2023-004, https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PLOTS/ITK-2023-0036

Qualification of irradiated 3D pixel sensors produced by FBK for the pre-production of the ATLAS ITk detector

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Qualification of irradiated 3D pixel sensors produced by FBK for the pre-production of the ATLAS ITk detector

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