Radiation hardness of CMOS detector prototypes for ATLAS Phase II ITk upgrade

Hiti, Bojan (author), Mandić, Igor (mentor)

This thesis presents a study of charge collection properties and its dependence on displacement damage caused by irradiation in CMOS detector prototypes developed for the phase-II upgrade of the Inner Tracker (ITk) in ATLAS experiment. Investigated samples were developed in four separate development lines and manufactured in different industrial processes. The main design parameters studied in this work are initial resistivity and the size of collection electrode. Samples were irradiated with reactor neutrons to fluences between $\rm 10^{13}~n_{eq}/cm^2$ and $\rm 10^{16}~n_{eq}/cm^2$ and with protons to fluences between $\rm 10^{14}~n_{eq}/cm^2$ and $\rm 3.6~\dot~10^{15}~n_{eq}/cm^2$. Charge collection in the samples was characterised with Edge-TCT, radioactive $\rm ^{90}Sr$ beta source and in a highly energetic pion test beam. Measurements of effective space charge concentration with Edge-TCT show significant radiation dependence influenced by initial acceptor removal. Acceptor removal is slower at lower initial substrate resistivity and is typically finished at a fluence of $\rm \sim 10^{13}~n_{eq}/cm^2$ in highly resistive $\rm 2~k\Omega cm$ material and $\rm \sim 10^{15}~n_{eq}/cm^2$ in material with initial resistivity of $\rm 20~\Omega cm$. Acceptor removal may cause the increase of the depth of depletion zone in certain range of fluences which was observed by both Edge-TCT and $\rm ^{90}Sr$. Measurements of in-pixel hit detection efficiency with test beam revealed significant efficiency gaps on pixel edges in samples with a small collection electrode after irradiation. These results prompted modifications of pixel design in form of additional implanted structures which are expected to significantly improve detector performance.

• Language: English
• Keywords: ATLAS ITk, CERN, HL-LHC, Silicon detectors, Radiation damage, Charge transport, Acceptor removal, Radiation hard detectors, DMAPS, HV-CMOS, HR-CMOS
• Work type: Doctoral dissertation
• Typology: 2.08 - Doctoral Dissertation
• Organization: FMF - Faculty of Mathematics and Physics
• Year: 2020
• PID: 20.500.12556/RUL-115344
• COBISS.SI-ID: 3418724
• Publication date in RUL: 23.04.2020

HITI, Bojan, 2020, Radiation hardness of CMOS detector prototypes for ATLAS Phase II ITk upgrade [online]. Doctoral dissertation. [Accessed 6 April 2025]. Retrieved from: https://repozitorij.uni-lj.si/IzpisGradiva.php?lang=eng&id=115344

Secondary language

• Language: Slovenian
• Title: Sevalna odpornost detektorjev CMOS za nadgradnjo notranjega sledilnika ATLAS

Abstract

V doktorskem delu je predstavljena študija zbiranja naboja v odvisnosti od sevalnih poškodb v detektorjih CMOS zasnovanih za nadgradnjo (Phase-II) Notranjega sledilnika ATLAS ITk. Preučevani vzorci so bili razviti v štirih vzporednih razvojnih smereh in izdelani v različnih industrijskih procesih. Glavna dejavnika preučevana v tem delu sta začetna upornost senzorja in velikost zbiralne elektrode. Vzorci so bili obsevani z reaktorskimi nevtroni v območju fluenc $\rm 10^{13}~n_{eq}/cm^2 - 10^{16}~n_{eq}/cm^2$ in s protoni od $\rm 10^{14}~n_{eq}/cm^2 - 3.6~\dot~10^{15}~n_{eq}/cm^2$. Zbiranje naboja v vzorcih je bilo opredeljeno z meritvami z metodo e-TCT, radioaktivnim virom $\beta~\rm ^{90}Sr$ in v visokoenergijskem testnem žarku pionov. Meritve efektivne koncentracije prostorskega naboja z metodo e-TCT kažejo na veliko odvisnost od obsevanja, na katero vpliva tudi efektivna odstranitev začetnih akceptorjev. Ta poteka počasneje v materialih z nižjo začetno upornostjo in se tipično konča okoli fluence $\rm 10^{13}~n_{eq}/cm^2$ v materialu z visoko začetno upornostjo $\rm 2~k\Omega cm$ ter okoli fluence $\rm 10^{15}~n_{eq}/cm^2$ v materialu z nizko začetno upornostjo $\rm 20~\Omega cm$. Odstranitev akceptorjev lahko povzroči povečanje osiromašenega področja v senzorju v določenem območju fluenc, kar je bilo opaženo v meritvah z metodo e-TCT in z radioaktivnim virom $\rm ^{90}Sr$. Meritve v detektorju z majhno zbiralno elektrodo s testnim žarkom so razkrile območja z nizko učinkovitostjo znotraj blazinice po obsevanju. Na podlagi teh rezultatov so bile uvedene spremembe zasnove blazinic, ki bodo po pričakovanjih izboljšale zbiranje naboja v tem detektorju.

• Keywords: ATLAS ITk, CERN, HL-LHC, Silicijevi detektorji, Detektorji odporni na sevanje, Sevalne poškodbe, Transport nosilcev naboja, Odstranitev akceptorjev, DMAPS, HV-CMOS, HR-CMOS