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Development of fast and radiation hard Monolithic Active Pixel Sensors MAPS

De
233 pages
Niveau: Supérieur
Development of fast and radiation hard Monolithic Active Pixel Sensors (MAPS) optimized for open charm meson detection with the CBM - vertex detector Dissertation zur Erlangung des Doktorgrades der Naturwissenschaften vorgelegt beim Fachbereich Physik der Johann Wolfgang Goethe - Universitat in Frankfurt am Main These presentee pour obtenir le grade de Docteur de l'Universite Louis Pasteur Strasbourg 1 Discipline: Physique Michael Deveaux aus/ne a Idar-Oberstein Frankfurt/Strasbourg (2007) (D30) Revision: 1.04

  • maps against ionizing

  • cbm

  • charge collection efficiency

  • collection efficiency

  • pixel sensors

  • ionizing radiation

  • der johann

  • maps


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Development of fast and radiation hard
Monolithic Active Pixel Sensors (MAPS)
optimized for open charm meson detection
with the CBM - vertex detector
Dissertation zur Erlangung des Doktorgrades
der Naturwissenschaften
vorgelegt beim Fachbereich Physik
der Johann Wolfgang Goethe - Universit at
in Frankfurt am Main
These presentee pour obtenir le grade de Docteur
de l’Universite Louis Pasteur Strasbourg 1
Discipline: Physique
Michael Deveaux
aus/ne a Idar-Oberstein
Frankfurt/Strasbourg (2007)
(D30)
Revision: 1.04Vom Fachbereicht Physik der
Johann Wolfgang Goethe - Universit at als Dissertation angenommen.
Dekan: Prof. D.-H. Rischke
Gutachter:
Prof. Dr. J. Stroth, Goethe Universit at, Frankfurt am Main
Dr. habil. M. Winter, Institut Pluridisciplinaire Hubert Curien, Strasbourg
Datum der Disputation: 20.03.2008
2Contents
Sommaire fran cais 11
Deutsche Zusammenfassung 17
Introduction 21
1. The CBM experiment: Physics motivations and detector concept 25
1.1. The physics of the CBM experiment . . . . . . . . . . . . . . . . . . . . . . . . . . 25
1.1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
1.1.2. The phase diagram of hadronic matter . . . . . . . . . . . . . . . . . . . . . 27
1.1.3. Experimental access to the phase diagram . . . . . . . . . . . . . . . . . . . 27
1.2. CBM, an experiment to explore the nuclear phase diagram . . . . . . . . . . . . . 30
1.3. The Silicon Tracking System (STS) of CBM . . . . . . . . . . . . . . . . . . . . . . 32
1.3.1. Requirements and running conditions . . . . . . . . . . . . . . . . . . . . . 32
1.3.2. The initial design proposal for the CBM silicon tracking system . . . . . . . 35
1.4. Questions on the pixel detector technology of the STS and the task of this work . . 36
1.5. Summary of this chapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
2. Monolithic Active Pixel Sensors 41
2.1. The detection principle of silicon detectors . . . . . . . . . . . . . . . . . . . . . . . 42
2.1.1. A short introduction into semiconductors . . . . . . . . . . . . . . . . . . . 42
2.1.1.1. The band model . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
2.1.1.2. Direct and indirect . . . . . . . . . . . . . . . . . . 43
2.1.1.3. Doping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
2.1.2. Particle detection with a silicon detector . . . . . . . . . . . . . . . . . . . . 44
2.1.3. The PN-Junction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
2.1.4. The PN-junction as detector for minimum ionizing particles . . . . . . . . . 47
2.1.5. The strategy of di erent pixel detectors . . . . . . . . . . . . . . . . . . . . 48
2.2. Building a Sensor in a CMOS process . . . . . . . . . . . . . . . . . . . . . . . . . 50
2.2.1. Why CMOS pixels? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
2.2.2. Structures in a typical CMOS process . . . . . . . . . . . . . . . . . . . . . 50
2.2.3. The sensor of a MAPS-detector . . . . . . . . . . . . . . . . . . . . . . . . . 52
2.2.3.1. Basic design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
2.2.3.2. Integration of the sensor into a CMOS process . . . . . . . . . . . 54
2.2.3.3. Thickness of the sensitive volume . . . . . . . . . . . . . . . . . . 54
2.2.4. The on-pixel preampli ers: Properties and signal encoding . . . . . . . . . 54
2.2.4.1. The charge-to-voltage conversion . . . . . . . . . . . . . . . . . . . 55
2.2.4.2. Deriving the collected charge from measurements: The correlated
double sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
2.2.4.3. Currents in a MAPS pixel . . . . . . . . . . . . . . . . . . . . . . 56
2.2.4.4. The need for leakage current compensation . . . . . . . . . . . . . 57
2.2.4.5. Leakage current compensation in the 3T-pixel . . . . . . . . . . . 57
3Contents
2.2.4.6. Leakage current compensation in the SB-pixel . . . . . . . . . . . 58
2.2.4.7. Signal encoding . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
2.2.5. Readout of the pixel arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
2.3. Established performances of MAPS . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
2.4. CBM requirements versus MAPS abilities . . . . . . . . . . . . . . . . . . . . . . . 66
3. Conceptiunal considerations for a vertex detector based on MAPS 69
3.1. A concept for fast MAPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
3.1.1. Fundamental considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
3.1.2. On-pixel functionalities required . . . . . . . . . . . . . . . . . . . . . . . . 71
3.1.3. Status of the R&D on readout speed . . . . . . . . . . . . . . . . . . . . . . 71
3.1.4. Outlook: On-chip ADCs and data sparsi cation . . . . . . . . . . . . . . . 72
3.1.5. Expected performance and geometrical layout . . . . . . . . . . . . . . . . . 73
3.2. Material budget . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
3.2.1. Minimum thickness of the detector chips . . . . . . . . . . . . . . . . . . . . 74
3.2.2. Material budget of the support structures . . . . . . . . . . . . . . . . . . . 74
3.2.2.1. Requirements on the support structures . . . . . . . . . . . . . . . 75
3.2.2.2. Design guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
3.2.2.3. Mechanics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
3.2.2.4. Heat evacuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
3.2.2.5. Vibrations and deformation . . . . . . . . . . . . . . . . . . . . . . 80
3.2.2.6. Vacuum aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
3.2.2.7. Cables and connectors . . . . . . . . . . . . . . . . . . . . . . . . . 81
3.2.3. Material budget of the full detector stations . . . . . . . . . . . . . . . . . . 81
3.3. Summary and conclusion on readout speed and material budget . . . . . . . . . . . 82
4. Assessment of the radiation tolerance of MAPS 85
4.1. Radiation damage in silicon detectors . . . . . . . . . . . . . . . . . . . . . . . . . 85
4.1.1. Fundamental radiation e ects . . . . . . . . . . . . . . . . . . . . . . . . . . 85
4.1.2. E ects of ionizing radiation doses on CMOS-devices . . . . . . . . . . . . . 86
4.1.3. E ects of non-ionizing radiation and the NIEL-model . . . . . . . . . . . . 88
4.2. Observables and precision goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
4.2.1. Observables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
4.2.2. Precision goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
4.3. The hardware setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
4.3.1. The external readout electronics . . . . . . . . . . . . . . . . . . . . . . . . 92
554.3.2. The dark chamber and Fe-source . . . . . . . . . . . . . . . . . . . . . . . 93
4.4. Algorithms for interpreting the output signal of 3T-Pixel and the SB-pixel. . . . . 94
4.4.1. De nitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
4.4.2. The noise of MAPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
4.4.2.1. Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
4.4.2.2. Sources of noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
4.4.3. Categories distinguished by the analysis software . . . . . . . . . . . . . . . 95
4.4.4. Algorithms used for assessing the 3T-pixel . . . . . . . . . . . . . . . . . . . 96
4.4.4.1. Insulating the leakage current in the absence of a hit . . . . . . . 97
4.4.4.2. the common mode in the of a hit . . . . . . . . 98
4.4.4.3. Estimating the noise in the absence of a hit . . . . . . . . . . . . . 98
4.4.4.4. the signal charge and hit detection . . . . . . . . . . . 99
4.4.4.5. Clusterisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
4Contents
4.4.4.6. Estimating leakage current, noise and common mode in the pres-
ence of hits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
4.4.4.7. Update of leakage current and noise estimate . . . . . . . . . . . . 100
4.4.5. Limits of the algorithm when being applied to data from SB-pixels . . . . . 102
4.5. Procedures for measuring the electronic properties of MAPS . . . . . . . . . . . . . 103
4.5.1. Gain and charge collection e ciency . . . . . . . . . . . . . . . . . . . . . . 103
4.5.1.1. The charge collection distribution . . . . . . . . . . . . . . . . . . 103
4.5.1.2. Impact of the charge collection process on the distribution for X-rays104
4.5.1.3. Classes of interactions between X-rays and the detector . . . . . . 104
4.5.1.4. Charge collection distributions for groups of pixels . . . . . . . . . 104
4.5.1.5. Peaks in the charge collection distribution . . . . . . . . . . . . . . 106
4.5.1.6. The calibration peak in single and multi pixel distribution: A side
remark. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
4.5.1.7. Estimating gain and charge collection e ciency . . . . . . . . . . 108
4.5.2. Leakage currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
4.5.3. Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
4.5.4. The time constant of the recharge current () . . . . . . . . . . . . . . . . . 110
5. Ionizing radiation tolerance of MAPS 113
5.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
5.2. Native radiation tolerance of MAPS against ionizing radiation damage . . . . . . . 114
5.2.1. Early studies on the 3T-pixel . . . . . . . . . . . . . . . . . . . . . . . . . . 114
5.2.1.1. MIMOSA-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
5.2.1.2. MIMOSA-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
5.2.2. First studies on the SB-Pixel (MIMOSA-4) . . . . . . . . . . . . . . . . . . 118
5.2.3. Discussion of the results for native detectors . . . . . . . . . . . . . . . . . . 126
5.3. Design improvements for enhanced ionizing radiation tolerance . . . . . . . . . . . 128
5.3.1. Strategies to identify the weak points of the early pixel designs . . . . . . . 128
5.3.2. Identi cation of the weak point of the 3T-pixels of MIMOSA-4 . . . . . . . 129
5.3.3. Iden of the weak point of the 3T-pixel of MIMOSA-2 . . . . . . . . 131
5.3.4. Design improvements to reduce the leakage current . . . . . . . . . . . . . . 137
5.3.4.1. MIMOSA-9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
5.3.4.2. MIMOSA-11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
5.3.4.3. MIMOSA-15 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
5.4. Summary and conclusion on the ionizing radiation tolerance of MAPS . . . . . . . 149
5.4.1. Radiation damage e ects observed . . . . . . . . . . . . . . . . . . . . . . . 149
6. Non-ionizing radiation tolerance of MAPS 151
6.1. In uence of the epitaxial layer thickness and number of diodes per pixel . . . . . . 151
6.1.1. Motivation of the measurements . . . . . . . . . . . . . . . . . . . . . . . . 151
6.1.2. Irradiation procedure and measurements . . . . . . . . . . . . . . . . . . . . 152
6.1.3. Results for gain, leakage current and noise . . . . . . . . . . . . . . . . . . . 152
6.1.4. for the charge collection e ciency and signal over noise . . . . . . . 154
6.1.4.1. The charge e ciency of irradiated MAPS . . . . . . . . 155
6.1.4.2. The expected signal of minimum ionizing particles (MIP) in irra-
diated MAPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156
6.1.4.3. The expected signal over noise ratio for MIPs in irradiated MAPS: 157
6.1.5. Summary and Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
6.2. Radiation tolerance of MAPS collecting from the substrate (MIMOSA-4) . . . . . 160
5Contents
6.3. Dependence on the pixel size (MIMOSA-9) . . . . . . . . . . . . . . . . . . . . . . 161
6.4. The state of the art (MIMOSA-15) . . . . . . . . . . . . . . . . . . . . . . . . . . . 164
6.5. Random Telegraph Signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
6.5.1. Random Telegraph Signal in MAPS . . . . . . . . . . . . . . . . . . . . . . 166
6.5.2. Potential sources of RTS in . . . . . . . . . . . . . . . . . . . . . . . 167
6.5.3. Consequences for the detector operation . . . . . . . . . . . . . . . . . . . . 169
6.5.4. Methods to overcome problems induced by RTS: Temperature dependence . 169
6.5.5. Summary and conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
6.6. Summary and conclusion on non-ionizing radiation tolerance . . . . . . . . . . . . 172
7. Detection of open charm with a MAPS based vertex detector: A simulation study 175
7.1. Introduction: The simulation strategy . . . . . . . . . . . . . . . . . . . . . . . . . 175
7.1.1. The proposed running scenario . . . . . . . . . . . . . . . . . . . . . . . . . 175
7.1.2. Questions addressed by the detector simulations . . . . . . . . . . . . . . . 177
7.1.3. The approach of the simulations. . . . . . . . . . . . . . . . . . . . . . . . . 177
7.2. The simulation procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178
7.2.1. The simulation software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178
7.2.2. The sim model of the STS . . . . . . . . . . . . . . . . . . . . . . . . 181
7.2.3. Representation of the global CBM experiment in the simulation . . . . . . . 181
7.3. The simulation of the expected radiation doses in the CBM MVD . . . . . . . . . . 183
7.3.1. Radiation sources and their simulation model . . . . . . . . . . . . . . . . . 183
7.3.2. Particle generation for the radiation dose simulations . . . . . . . . . . . . . 184
7.3.3. Event and particle generators . . . . . . . . . . . . . . . . . . . . . . . . . . 184
7.3.3.1. Simulating non-ionizing radiation doses . . . . . . . . . . . . . . . 185
7.3.3.2. Sim ionizing radiation doses . . . . . . . . . . . . . . . . . . 186
7.3.3.3. The - electron absorber . . . . . . . . . . . . . . . . . . . . . . . 186
7.3.4. Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
7.3.4.1. Radiation dose simulations for the standard MVD geometry . . . 186
7.3.4.2. doses as a function of the vertex detector . . 191
7.3.5. Summary and conclusion on the radiation dose simulations . . . . . . . . . 193
7.4. Choice of the detector geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
7.4.1. The approach used for reconstructing open charm . . . . . . . . . . . . . . 195
7.4.2. The simulation of the secondary vertex and the invariant mass resolution of
di erent MVD geometries . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196
7.4.3. Benchmarking di erent detector geometries . . . . . . . . . . . . . . . . . . 199
7.4.4. Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203
7.5. A preliminary simulation of the physics performances of CBM . . . . . . . . . . . . 203
7.5.1. Generating very high background statistics: The super-event approach . . . 204
7.5.2. Selection Cuts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205
7.5.2.1. Cuts on the single tracks . . . . . . . . . . . . . . . . . . . . . . . 205
7.5.2.2. Cuts on track pairs . . . . . . . . . . . . . . . . . . . . . . . . . . 206
7.5.2.3. Finding the appropriate cut values: De nition of the problem and
standard method . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206
7.5.2.4. An algorithm for multidimensional cut optimization . . . . . . . . 209
7.5.3. Statistics and setup of the simulation . . . . . . . . . . . . . . . . . . . . . 210
7.5.4. Normalization and S/B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
7.5.5. Signi cance of the signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
07.5.6. Acceptance of the CBM experiment for D -mesons . . . . . . . . . . . . . . 213
7.5.7. Robustness of the results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
6Contents
7.6. Summary and Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
8. Summary and conclusion 219
A. Appendix 223
A.1. Preliminary requirements on spatial resolution and material budget of the vertex
detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223
7Contents
8Acknowledgments
I would like to express my gratitude to all those, who supported me in completing this thesis,
in particular to my Ph.D. advisors, Prof. Marc Winter, Prof. Joachim Stroth and Prof. Herbert
Str obele for their continuous personal and scienti c support.
The research presented was embedded into the activities of research teams of IPHC, GSI and
nally the Johann-Wolfgang-Goethe University Frankfurt. Among the people who contributed to
the results shown are:
Dr. Fouad Rami, who invested all his patience into advising me in detector simulation,
Christina Dritsa, who saved the simulation chapter by accumulating within her master thesis the
statistics required for signi cant results,
Dr. Mohammad Al-Turany and Dr. Dennis Bertini, who introduced me into FAIRRoot,
Dr. Y. Vassiliev, who provided me his simulation code as a starting point for my work.
The radiation hardness studies presented would not have been possible without the dedication
of Samir Amar, August Besson, Johannes Bol, Gilles Claus, Arnaud Gay, G otz Gaycken, Mathieu
Go e, Y. Gornushkin, Damien Grandjean, Kimmo Jaaskelainen, Levin Jungermann, Alexandre
Shabetai and Michal Szelezniak, who helped me in preparing and performing the extensive tests
of irradiated detectors and allowed me presenting our results.
C. Colledani, G. Deptuch, W. Dulinski, A. Himmi, C. Hu, I. Valin together with the MIMOSA
design team supported me with many discussions, teaching me the basics of chip design, and
realizing the chips and radiation hard structures discussed in this work.
My brother Thomas Deveaux, student of architecture, helped me performing the structural cal-
culations used for estimating the material budget of the MAPS stations.
Unforgotten is the support, which I received from outside the scienti c community. Whenever
needed, I could count on my family. Special thanks are to my aunt and my uncle Christa and
Pierre Christoph, who accommodated me in their home in Berstett when my plans to move to
Frankfurt were delayed by some months. And to my little nephews Janis and Elija for their smile
and for reintroducing me into playing with toy cars.
I would also like to thank my friends from the Flugsportverein Kirn, for reconnecting me with the
\real world" and giving me the power to continue my studies. And last but not least Wolfram
Stiller for his friendship and a helpful bet.
9Contents
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