Production Accompanying Testing of the ATLAS Pixel Module

Production accompanying testing of the ATLAS Pixel module Daniel Adam Dobos CERN-THESIS-2007-016 31/06/2004 Lehrstuhl für Experimentelle Physik IV Universität Dortmund Dortmund, June 2004 Production accompanying testing of the ATLAS Pixel module Daniel Adam Dobos Diploma thesis Lehrstuhl für Experimentelle Physik IV Fachbereich Physik Universität Dortmund Otto-Hahn-Str. 4 D-44221 Dortmund Dortmund, June 2004 Abstract: The ATLAS Pixel detector, innermost sub-detector of the ATLAS experiment at LHC, CERN, can be sensibly tested in its entirety the first time after its installation in 2006. Because of the poor accessibility (probably once per year) of the Pixel detector and tight scheduling the replacement of damaged modules after integration as well as during operation will become a highly exposed business. Therefore and to ensure that no affected parts will be used in following production steps, it is necessary that each production step is accompanied by testing the components before assembly and make sure the operativeness afterwards. Probably 300 of about total 2000 semiconductor hybrid pixel detector modules will be build at the Universität Dortmund. Thus a production test setup has been build up and examined before starting serial production. These tests contain the characterization and inspection of the module components and the module itself under different envi- ronmental conditions and diverse operating parameters. Once a module is assembled the operativeness is tested with a radioactive source and the long-time stability is as- sured by a burn-in. A fully electrical characterization is the basis for module selection and sorting for the ATLAS Pixel detector. Additionally the charge collection behavior of irradiated and non irradiated modules has been investigated in the H8 beamline with 180 GeV pions. he Titan Atlas, son of the Titan Iapetus and the Oceanid Clymene, nephew of Zeus and king of the legendary Atlantis T(country of Atlas) tried to attack the Olympus during the insurrection of the Titans against gods. Zeus punished him with the task to carry the Earth on his shoulders for all times. After two generations Hercules asked Atlas to help him to fulfill the eleventh of his twelve labors, purging the sin of murdering his family. Atlas, be all set to do everything not to carry the globe anymore, agreed and stole the three golden apples, a wedding gift from Hera to Zeus, from the Garden of Hesperides. Hercules knew that only Atlas was able to approach the fierce dragon Ladon, guarding the apples carefully, because Atlas owned the garden. Ladon was napping when he heard the footsteps of Atlas. He glanced at his master and went back to sleep. After Atlas realized he no longer had to carry the Earth on his shoulders he told Hercules he would deliver the apples himself. Hercules told him he did not mind carrying the Earth, but first he would need to get a shoulder pad to rest it on. Atlas took back the globe and Hercules ... Table of contents 1 Introduction 1 1.1 LHC at CERN 3 1.2 In search of the Higgs 5 2 ATLAS and its subdetectors 7 2.1 Concept and magnet system 7 2.2 Muon spectrometer 9 2.3 Calorimeters 10 2.4 Inner detector 13 2.5 Trigger and data-acquisition system 15 3 Semiconductor detectors 19 3.1 Basic semiconductor properties 19 3.2 Photon energy loss in matter 19 3.3 Charged particle energy loss in matter 21 3.4 Charge carrier pairs production 23 3.5 Functionality of semiconductor detectors 23 3.6 Radiation damages 27 3.7 Strips and pixels 29 3.8 Induced current and charge on segmented detectors 30 4 The ATLAS Pixel detector 31 4.1 Barrel, disks and staves 31 4.2 Module layout 33 II Table of contents 4.3 Bare module 35 4.4 The sensor 37 4.5 Front-end electronics 42 4.6 MCC 49 4.7 Readout chain 51 5 Module Assembly and testing 55 5.1 Module assembly and testing setup 55 5.2 Bare module probing 61 5.3 Module testing, tuning and calibration 67 5.4 TurboDAQ and TurboDUCK 72 6 Testbeam setup and processing of runs 79 6.1 Testbeam setup 79 6.2 h8-run script package 85 7 Results and analysis 91 7.1 Module cooling 91 7.2 Bare module probing & flex-MCC tests 95 7.3 Initial electrical tests 98 7.4 Burn-in and post burn-in tests 114 7.5 Final electrical characterization 117 7.6 Space resolved charge collection 128 8 Summary and Outlook 133 Appendix A – Module testing checklists Appendix B – Abbreviations Appendix C – References Acknowledgments Chapter 1 Introduction Physics searches for general laws of nature and tries to quantify the nature by explain- ing new phenomena and furthermore by finding fundamental relations between measured values in experiments. The basic aim of modern particle physics is to investigate and characterize elementary particles, the components of matter, and the fundamental forces between them. The particle physics wants to know how and why the elementary particles have mass, if and how the known four elementary forces can be combined to a single primal force, if until today not observed elementary particles do exist and if the four known dimen- sions are enough to describe our universe or we do have to search for hidden ones. One of the applied measurement methods to answer these questions uses collisions of high energy particles, generating a multiplicity of new, most of them very short living, particles. By measuring the impact parameters of all involved particles the collision can be reconstructed and conclusions to the properties of particles and their interactions are possible. The standard model combines the today's knowledge of the known elementary particles and their fundamental interactions. Hints exist, that the standard model is not able to describe all observed phenomena so the verification of the today's standard model or ways to expand it has to be an aim of the particle physics, too. In order to extract new conclusions from this method a particle accelerator is needed, which is able to accelerate the primary colliding particles by electromagnetic fields to the requested energy. In addition a detector system with the possibility to measure tracks of new generated particles in a magnetic field by a tracking system and the energy deposition of these particles in a calorimeter system is necessary. This allows to identify, calculate the mass, momentum and energy of involved particles and to con- clude by which interactions they have been generated. Furthermore the detector trigger has to filter the rare interesting events out of the background of well known ones. The LHC1 accelerator is currently built at CERN2 and will provide collisions of pro- tons with an energy of 7 TeV each with 40 MHz bunch crossing rate. It will make en- ergies and event rates of artificially accelerated particles accessible to physics, which 1 Large Hadron Collider 2 Conseil Européen pour la Recherche Nucléaire – since the laboratory has reoriented its research more to particle physics, only 'CERN' is the common name 2 Chapter 1 - Introduction are not possible today. One of the multi-purpose detectors that will analyze the LHC reactions is the currently built ATLAS3 detector, which is one of today's most ambi- tious particle detectors. The ATLAS Pixel detector, used for the innermost tracking, will consist of 1744 modules with about 47000 pixels each. Some of the basic require- ments are the extremely high radiation-tolerance of the Pixel detector system up to 50 Mrad and a track resolution of about 12 µm. About 300 modules will be assembled at the Universität Dortmund. Only the proper testing of all incoming components and production accompanying testing of all modules guarantee the needed production rate and yield. Infant mortality has to be detect- ed by long-time stability tests with thermo cycling, since the modules are hardly accessible inside ATLAS and can be only replaced by a complicate, time consuming and dangerous procedure. The modules have to be fully characterized at operating conditions for selection and sorting, due to maximization of the Pixel detector physical performance. The module testing and characterization is very time consuming, therefore automation with as less operator intervention as possible has to be realized. Besides this the physical performance of the modules, like the space resolved charge collection of pixels, has to be measured with real high energy particles, in order to op- timize the tracking accuracy for charged particle trajectories. Subjects of this diploma thesis are the testing and quality assurance of ATLAS Pixel modules in consideration of production accompanying testing steps performed for each module and the analysis of measurements with a 180 GeV pion beam for a small subset of modules in consideration of space resolved charge collection. The primary aims are the adaptation and enhancement of already existing module testing hardware and software, the development of new ones, the development and automation of measurement procedures to cope with the module production rate and the measurement and comparison of the space resolved charge collection between unirradiated and near to end-of-lifetime-dose irradiated modules and between two different sensor vendors. In chapter 1 a short overview of the LHC and the basic motivation of ATLAS, namely the search of the higgs boson are presented. In order to understand the global concept of the ATLAS detector and the task of the ATLAS Pixel detector in this experiment, the different ATLAS subsystems and their aims are described in chapter 2. The fundamental physical concept, functionality and properties of semiconductor particle detectors are presented in chapter 3.

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