Academic literature on the topic 'Silicon pixel detectors'

The inner tracking detectors at the LHC operate in a region of unprecedented particle rates. Thousands of hits must be detected, time-stamped and stored in every 25 ns bunch crossing interval. The silicon pixel detector for the CMS experiment has been designed to meet the requirements of position resolution, rate capability and radiation tolerance with a minimal amount of material. Its unique ability to provide three-dimensional high precision space points plays an important role in the tracking system of the CMS detector.

Abstract I present the design of two vertex detector systems for proton particle trajectory tracking based on multiple layers of single photon counting hybrid pixel area detectors. The detector used in both systems is UFXC, which is a matrix of 128 × 256 pixels with silicon sensor. The first system enables proton transition registration with the speed of up to 50 kfps. The second system is a portable device with large detection area.

Abstract Speed, dynamic range, and radiation hardness make hybrid pixel detectors suitable image detectors for diffraction experiments. At synchrotrons and X-ray free electron lasers they are ubiquitous. However, for electron microscopy their spatial resolution is limited by multiple scattering in the sensor layer. In this paper we examine the use of two high Z sensor materials: CdTe and GaAs, as a way to mitigate this problem. The sensors were bonded to a JUNGFRAU readout chip which is a charge integrating hybrid pixel detector developed for use at X-ray free electron lasers. Using in-pixel gain switching, it can detect single particles down to 2 keV while maintaining a dynamic range of 120 MeV/pixel/frame. The characteristics of JUNGFRAU, besides being a capable detector, make it a good tool for sensor characterization since we can measure dark current and energy deposition per pixel. The high Z material shows better spatial resolution than silicon at 200 and 300 keV, however, their practical use with integrating detectors is still limited by material defects.

The innermost layer of the Belle silicon vertex detector operates 1.5 cm away from the collision point of the highest luminosity collider in the world. Occupancy in this innermost layer is already 10% and expected to continue increasing with the planned significant luminosity increases. A pair of prototype detectors has been developed to address this problem, based upon the same CMOS camera technology now widely deployed in low-cost consumer devices such as cellular telephones. Problems unique to operating in a high luminosity B-factory environment are discussed. Results from a number of tests are presented, demonstrating the viability of this detector technology.

In our previous work on ultra-fast silicon detectors, extremely small carrier drift times of 50–100 picoseconds were predicted for electrode spacing of 5–10 μm. Expanding on these previous works, we systematically study the electrical characteristics of the ultra-fast, 3D-trench electrode silicon detector cell with p-type bulk silicon, such as electric potential distribution, electric field distribution, hole concentration distribution, and leakage current to analyze the full detector depletion voltage and other detector properties. To verify the prediction of ultra-fast response times, we simulate the instant induced current curves before and after irradiation with different minimum ionizing particle (MIP) hitting positions. High position resolution pixel detectors can be fabricated by constructing an array of these extremely small detector cells.

Recent advances in particle accelerators have increased the demands being placed on detectors. Novel detector designs are being implemented in many different areas including, for example, high luminosity experiments at the LHC or at next generation synchrotrons. The purpose of this thesis was to characterise some of these novel detectors. The first of the new detector types is called a 3D detector. This design was first proposed by Parker, Kenney and Segal (1997). In this design, doped electrodes are created that extend through the silicon substrate. When compared to a traditional photodiode with electrodes on the opposing surfaces, the 3D design can combine a reasonable detector thickness with a small electrode spacing resulting in fast charge collection and limited charge sharing. The small electrode spacing leads to the detectors having lower depletion voltages. This, combined with the fast collection time, makes 3D detectors a candidate for radiation hard applications. These applications include the upgrades to the Large Hadron Collider (LHC) leading to the High Luminosity Large Hadron Collider (HL-LHC). The limited charge sharing of the devices can also improve their performance when being employed as imaging sensors. This will provide benefits in X-ray diffraction experiments. The first experiment to evaluate the 3D detector design analysed for this thesis involved utilising a telescope consisting of 6 calibrated detector planes and a beam of pions from the Super Proton Synchrotron (SPS) at CERN. Once the tracks through the telescope were reconstructed, these gave predicted hits on the 3D detector that could be compared to the recorded energy depositions. By making this comparison, a measure of the detector’s efficiency in various regions of the pixels was made. The overall efficieny of the pixel was measured at 93.0±0.5%. The detector was also rotated with respect to the incident beam, increasing the efficiency to 99.8±0.5% for an angle of 10◦, and the detector bias was altered to measure the effect of over-depletion. Measurements of the charge sharing and resolution properties of the device were also reported. Another detector design that was investigated was a slim edge detector. Instead of the typical guard ring structures that a normal device would employ, this detector reduced the size of these structures to enable easier tiling of the detectors. This was done by scanning the reduced edge and the standard edge of the detector with an X-ray beam with a width FWHM of 7 μm and 15 keV. The noise level of the strip closest to the cleaved edge was twice as large as that of the adjacent strip with no degradation of the charge collection capacity. The next experiment to evaluate a short, double sided 3D strip detector was a Transient Current Technique (TCT) experiment. The TCT technique allows the electric field in the 3D devices to be probed in a way not possible before. The TCT technique uses the current waveform produced by the detector in response to a near delta function point laser pulse (illumination). The waveforms are recorded as a function of illumination position over the surface of the device under test as a function of detector bias. This data gives information on the portion of the induced signal from electron or hole motion. From the rise times of the signals the velocity profile of the carriers in the devices and therefore electric fields can be determined. The collected charge was calculated from the integral of the waveforms. The detectors were tested prior to irradiation, after irradiating to a dose of 5 x 10^15 1MeV equivalent neutrons/cm^2, and after periods of annealing at elevated temperatures. Annealing was achieved in situ by warming to 60 ◦C for 20 to 600 minutes corresponding to room temperature annealing of between 8 and 200 days. Before irradiation, full lateral depletion between the columns occurs at low bias voltages, at approximately 3 V. A uniform carrier velocity between the columns is not achieved until the bias is equal to 40 V. Both the drift of electrons and holes provide equal contributions to the measured signals. After irradiation there is clear charge multiplication enhancement along the line between columns with a very non-uniform velocity profile in the unit cell of the device. In addition, charge trapping greatly suppresses the contribution of the holes on the signal produced. The final novel detector type was an Active Pixel Sensor (APS). Recent developments in CMOS fabrication processes have allowed new sensors to be developed and tailor-made for specific applications. These challenge traditional Charge Coupled Devices (CCD) in some areas. The characterisation of the APS device took place in an X-ray diffraction experiment at the Diamond Light Source where it was evaluated alongside a CCD. The camera gain and stability had been determined prior to the experiment taking place. During the experiment, the dark current, noise, signal to noise and image lag performance was evaluated and compared between the APS and the CCD. The signal to noise of the APS and the CCD was comparable (150 and 200 respectively) when the same integration time was used.

After ten years of massive success, the Large Hadron Collider (LHC) at CERN is going for an upgrade to the next phase, The High Luminosity Large Hadron Collider (HL-LHC) which is planned to start its operation in 2029. This is expected to have a fine boost to its performance, with an instantaneous luminosity of 5.0×1034 cm-2s -1 (ultimate value 7.5×1034 cm-2s -1 ) with 200 average interactions per bunch crossing which will increase the fluences up to more than 1016 neq/ cm2 , resulting in high radiation damage in ATLAS detector. To withstand this situation, it was proposed to make the innermost layer with 3D silicon sensors, which will have radiation tolerance up to 2×1016 neq/cm2 with a Total Ionization Dose of 9.9 MGy. Two-pixel geometries have been selected for 3D sensors, 50 × 50 µm2 for Endcap (ring), which will be produced by FBK (Italy) and SINTEF (Norway), and 25 × 100 µm2 for Barrel (stave), will be produced by CNM (Spain). A discussion is made in this thesis about the production of FBK on both geometries, as they have made a breakthrough with their Stepper lithography process. The yield improved, specifically for the geometry 25 × 100 µm2 with two electrode readouts, which was problematic in the mask aligner approach. Their sensors were characterized electrically at waferlevel as well as after integration with RD53a readout chip (RoC) on single-chip cards (SCC) and were verified against Innermost Tracker criteria. The SCCs were sent for irradiation up to 1×1016 neq/cm2 and were tested under electron test beam, and a hit efficiency of 97% was presented. Some more SCCs have been sent to Los Alamos for irradiating them up to 1.5×1016 neq/cm2 fluence. As the 3D sensors will be mounted as Triplets, a discussion is also made on their assembly and QA/QC process. A reception testing and electrical testing setup both at room temperature and the cold temperature was made and discussed, with results from some early RD53a RoC-based triplets. The pre-production sensors are already evaluated, and soon they will be available bump-bonded with ITkPixV1 RoC for further testing.

Aquesta tesi tracta el desenvolupament de detectors de silici de tecnologia avançada per experiments de Física d'Altes Energies (HEP en anglès). La mida dels detectors de silici per determinar traces en experiments de HEP ha de disminuïr per millorar la resolució espacial en les mesures i millorar l'ocupancia en l'electrònica. Els experiments al CERN hauran de funcionar amb fluencies de fins a 2·10 16 n eq 1cm2 , i els detectors de silici més petits tindran menys atrapament de les parelles electró-forat generats al volum, que porta a un millor comportament sota un medi amb alts nivells de radiació. Aquesta tesi estudia detectors de silici fabricats al CNM-Barcelona per aplicacions de HEP amb dos tipus d'arquitectura nou: 3D i detectors d'allau amb guany moderat (LGAD en anglès). Els detectors 3D afavoreixen la reducció de la mida de la regió buidada dins del detector i permet treballar a voltatges més baixos, mentres que els detectors LGAD tenen guany intern que incrementa la senyal col·leccionada amb un mecanisme de multiplicació. El capítol 1 introdueix els detectors de silici aplicats a HEP. Els capítols 2 i 3 exploren els dissenys de detectors 3D de silici fabricats al CNM-Barcelona. Els detectors 3D de silici van ser introduïts per primera vegada a un experiment de HEP durant el 2013 per una nova capa del experiment ATLAS, la Insertable B-Layer (IBL), i alguns d'aquests detectors han sigut caracteritzats durant aquest treball. Actualment, detectors 3D de silici amb dimensions de píxel més petites seran operatius per noves posades a punt de l'ATLAS, i aquests detectors s'han simulat en aquest treball. El capítol 4 està dedicat a detectors LGAD segmentats i fabricats en oblies epitaxials amb la intenció de disminuïr el gruix dels detectors i augmentar la càrrega col·leccionada amb el mecanisme de multiplicació. Aquesta tesi mostra simulacions tecnològiques, el procés de fabricació, simulació elèctrica i caracterització elèctrica i de càrrega d'aquests detectors.
This thesis presents the development of advanced silicon technology detectors fabricated at CNM-Barcelona for High Energy Physics (HEP) experiments. The pixel size of the tracking silicon detectors for the upgrade of the HL-LHC will have to decrease in size in order to enhance the resolution in position for the measurements and they need to have better occupancy for the electronics. The future experiments at CERN will cope with fluences up to 2·10 16 n eq 1cm2 , and the smaller 3D silicon detectors will have less trapping of the electron-holes generated in the bulk leading to a better performance under high radiation environment. This thesis studies silicon detectors fabricated at CNM-Barcelona applied to HEP experiments with two different kinds of novel projects: 3D and Low Gain Avalanche Detectors (LGAD). The 3D detectors make it possible to reduce the size of the depleted region inside the detector and to work at lower voltages, whereas the LGAD detectors have an intrinsic gain which increase the collected signal with a multiplication mechanism. Chapter 1 introduces the silicon detectors applied to HEP experiments. Chapters 2 and 3 explore the new designs for 3D silicon detectors fabricated at CNM-Barcelona. 3D silicon detectors were first introduced in a HEP experiment in 2013 for a new ATLAS layer, the Insertable B layer (IBL), and some of them are characterized in this work. Now, it is expected that 3D silicon detectors with smaller pixel size will be operative for the next ATLAS upgrade, and they are also simulated in this thesis. Chapter 4 is devoted to segmented LGAD detectors fabricated on epitaxial wafer with the intention to decrease the thickness of the detector and increase the charge collected with the multiplication mechanism. This thesis shows technological simulations, fabrication process, electrical simulations and electrical and charge characterization of those devices.

ALICE (A Large Ion Collider Experiment) is a general-purpose, heavy-ion detector at the CERN LHC designed to study the physics of strongly interacting matter, and in particular the properties of the Quark-Gluon Plasma (QGP), using Pb-Pb collisions at unprecedented energy densities. During the first three years of operation, it has demonstrated very good capabilities for measurements at high energy Pb-Pb collisions. But there are certain measurements like high precision measurements of rare probes over a wide range of momenta, which would require high statistics and are not satisfactory or even possible with the current experimental setup. These measurements would help to achieve the long term physics goals of ALICE and would go a long way forward in understanding and characterizing the Quark Gluon Plasma (QGP). To enhance its physics capabilities, ALICE has formulated an upgrade of its detectors, motivated by an upgrade of the LHC during the LHC Long Shutdown 2 (2018-2020). The LHC upgrade features which primarily motivated the ALICE upgrade programme are, in particular, Pb-Pb collisions with a high interaction rate of up to 50 kHz corresponding to an instantaneous luminosity, L = 6 × 1027cm−2s−1 and, the installation of a narrower beam pipe. Accordingly, ALICE would require detector upgrades to cope with the upgrade scenario. These upgrades should help to improve tracking and vertexing capabilities, radiation hardness and allow readout of all interactions to accumulate enough statistics for the upgrade physics programme. The objective is to accumulate 10 nb−1 of Pb–Pb collisions, recording about 1011 interactions. Within this upgrade strategy, the Inner Tracking System (ITS) upgrade forms an important cornerstone, providing improved vertexing and readout capabilities. The new ITS will have a barrel geometry consisting of seven layers of Monolithic Active Pixel Sensors (MAPS) with high granularity which would cater to the material budget, readout and radiation hardness requirements for the upgrade. The geometry is optimized for high efficiency, both in standalone tracking and ITS-TPC combined tracking. TowerJazz 0.18 μm technology is selected for designing the pixels for ITS upgrade. This technology provides attractive features like the option to implement a deep pwell allowing the implementation of a full CMOS process in the pixel. The ongoing research and development on these pixels investigates different design strategies and would converge towards the final design of the detector by the end of 2014. Several prototypes have been designed to investigate and validate the different design strategies and the different components of the pixel detector using this technology. The work presented in this thesis can be categorized in two parts. The first part concerns the results of characterization of some of the pixel prototype circuits developed for the ITS upgrade, in particular MIMOSA32, MIMOSA32Ter and Explorer-1. The second part discusses the detector performance studies of the upgraded ITS. MIMOSA32 and MIMOSA32Ter were one of the first prototypes designed with the TowerJazz technology in the upgrade programme. The motivation was to validate the technology. This thesis includes the results of tests and characterization of pixel structures of these prototypes and qualifies the technology in terms of charge collection and radiation tolerance and the usage of the deep p-well structure. This provides a starting point for future prototypes where the deep p-well could be implemented in a full CMOS process, thus allowing in-pixel sophisticated signal processing circuits. The Explorer prototypes are developed at CERN with the main motivation towards developing a detector with low power density, lower than the maximum permissible limits for the upgrade programme. This would provide a margin to reduce the material budget of the detection layers, improving the detector performance. The Explorer prototypes are designed to study the ratio of the collected charge to the input capacitance (Q/C), in particular, its dependence on the size of the collection diode and its distance to the adjacent p-well of the input transistors. The Explorer prototypes allows the application of a back-bias voltage which has an effect on the signal collection properties. In a pixel detector, improvement of the Q/C ratio enhances the signal amplitude at the collection node of the pixel circuit which is connected to the analog frontend. This would help in optimizing the analog frontend to improve the signal to noise ratio of the detector, which has a direct consequence in minimizing the power consumption of the detector. This thesis includes the test and characterization of Explorer-1 prototype circuits with different starting materials. The results show that Q/C improves with higher back bias voltage and increased spacing between the collection electrode and the adjacent p-well. With these results, the future prototypes of Explorer could concentrate on Optimizing the size of the input transistors to study its effects on the Random Telegraph Signal noise. In parallel, optimization of the signal processing circuits would also be carried out in other prototypes. The second part of the thesis studies the performance of a baseline configuration of the upgraded detector in terms of impact parameter resolution, momentum resolution and tracking efficiency both in standalone tracking mode and ITS-TPC combined tracking. The performance is compared with the current ITS to study the improvements in the upgraded ITS. The performance is affected by the radial position and material budget of the layers and the detector intrinsic resolution. The detector specifications in this regard are still evolving specially for the Outer Barrel (the outermost four layers). The studies show the effects of variation of the specifications in terms of material budget and intrinsic resolution on the detector performance. This would help to finalize the detector specifications for an optimized detector performance. The thesis also concludes that a reduction in the beam pipe radius (lower than the baseline upgrade scenario) would not affect detector performance but may facilitate the installation of the Inner Barrel. Redundancy studies show that the presence of a dead layer can degrade the detector performance significantly. This defines a key requirement of easy and rapid accessibility to the detector in the design of the upgraded ITS. The ITS upgrade timeline foresees the finalization of the final pixel architecture in late 2014. Mass production of the final circuit is planned for 2015. The construction of the detector modules, tests, assembling and pre-commissioning will be carried out throughout 2016-2017 followed by the installation of the detector in the ALICE cavern in 2018.

Tracking particle in space is a crucial instance on a large number of space experiments. Measurements of charged cosmic rays based on spectrometers, observation of γ-rays, study of space weather and many other applications require systems equipped with tracking detectors. The sensitive area of detectors required for tracking spans from cm2 to m2. Silicon microstrip detectors have been the elective technology for tracking particles in space for several decades. Their stability, reliability and low power consumption are supported by years of expertise and provided a vast number of significant results on fundamental physics, reached with different experiments. An example of magnetic spectrometers is AMS-02, operated on International Space Station, and the satellite-borne PAMELA, that measure the charged component of cosmic rays and use tracking planes immersed in a magnetic field produced by permanent magnets to discriminate matter from antimatter. AMS-02 mounts several squared meters of microstrip tracker. The strip technology also has some limits. The spatial resolution depends on the pitch of the strips implanted on silicon buffer, that depends on the capabilities of the facility in charge of device construction. The fabrication sites have to use dedicated infrastructures, making costs relatively higher than in the past. Moreover, it is difficult to reduce the detector thickness below about 150 μm. This thickness impacts on measurements because of multiple scattering and reduces the lower threshold of low energy nuclear experiments. Another problem arises when the detector operates in radiation-dense environment. When the same frame shows multiple hits, the correct reconstruction of each interaction point is subject to degeneracy, due to the ambiguity in associating x− and y−hits in the microstrip sensor. The problem worsens if we consider that microstrips show equivalent charge noise generally up to hundreds of electrons if we take into account all the contributions from readout electronics. The resulting signal-to-noise ratio is generally good, but rarely exceeding 10 for Minimum Ionising Particles (MIP). The migration towards a new technology based on pixel devices is interesting because it solves some of these limitations. In particular, the hit position is uniquely defined by the position of the pixels involved in the event and pixel detectors can be thinned down to about 50 μm, with a potential gain in resolution. This thesis focuses on Monolithic Active Pixel Sensors (MAPS). They have the advantage, with respect to both the microstrip detectors and the other pixel families, of having the first stages of readout (front-end amplification, discrimination, digitisation and zero suppression) included on the sensor substrate. The detectors are realised with standard CMOS technology, the same used by foundries for most of commercial applications. Once the design is defined, the mass production of the devices is possible, and it reduces the cost of the single detector. Other pixel detectors do not provide this advantage since the design of sensors is based on different custom technologies, and after the production, the detector must be bump bonded to a readout chip, an expensive and low-yield technique. MAPS also have some limits. The most critical for the use in space is power consumption. A second relevant problem to face is that most of the devices realised with this technique have a digital readout, that does not allow measurement of dE/dx, important for particle identification. The requirement of space experiments to cover large surfaces with a tracking detector implies that using pixels the number of channels to handle increases. MAPS approach solves this issue by including on the detector a smart readout that passes to the DAQ system only data from pixels interested by the event. The MAPS detectors have been proposed for the first time at the end of the nineties. The technology reached maturity in the last years. The ALICE experiment, first of the four main LHC experiments, have installed MAPS detectors for its Inner Tracker Upgrade. For the upgrade the collaboration designed a new MAPS detector, ALPIDE. It is realised by TowerJazz foundry in 180 nm technology. The pixel pitch is 28 μm. The matrix is composed of 512×1024 pixels, for a total surface of 1.5×3 cm2. Although smaller if compared to microstrip ladders, that can reach several tenths of squared cm, the ALPIDE is one of the largest detector realised with this technology. Among the properties of ALPIDE, one particularly interesting for the space application is low power consumption. In ALICE, the low power consumption is required because of the difficulties of power distribution and cooling of the Inner Tracker. The power density is still one order of magnitude higher than for microstrip, but it starts to be interesting for space applications. In this thesis, we explore the possibility to use ALPIDE to realise the tracker for the second High Energy Particle Detector (HEPD-02), a payload of the second China Seismo-Electromagnetic Satellite (CSES-02). The CSES constellation is devoted to the observation of Earth from space and in particular to the study of ionosphere perturbation that might be related to seismic activity on Earth. We organised the study into two parts. The first is dedicated to the optimisation of the detector for space, dealing with the power consumption reduction, thermal control and space compliance tests, another section is devoted to the study of the ALPIDE response to low energy nuclei. The section devoted to space compliance starts with a description of the strategies for power consumption reduction. Some strategies are applied to the detector (use of low-speed lines, smart clock distribution) and require an optimised design of the full tracker and trigger. The design of the different sub-detectors allows distribution of the clock only to a limited section that has a higher probability of being involved in the event. With this approach, we can keep the power consumption of the full tracker below 10 W, as required by the design limits. High power consumption has a large impact on the temperature control of the device. The ALPIDE has an ideal operative temperature of about 30◦, which must be kept constant on the whole detector. ALICE cools down the detector with a water-based system, a solution not applicable in space, where convection is discouraged. A carbon fibre cold plate, designed to optimise the thermal conduction, is applied to control the temperature. The carbon fibre placement is studied to minimise the thickness of the plate and the impact of inert material on tracking performance. The thesis reports the results of various tests of space compliance made on a modified ALICE tracker module, an engineering model of the HEPD-02 module. It was made of 14 ALPIDE detectors disposed into two columns and glued and wire bonded to a Flexible Printed Circuit (FPC). On the other side, the detectors are glued to a carbon fibre plate. The device has been tested according to the requirements of the Chinese Space Agency for vibrations and in thermal-vacuum. A study of the response of the detector to low energy nuclei has been also carried out. The HEPD-02 detector is devoted to the detection of electrons between 3 and 150 MeV and protons between 30 and 300 MeV. We base the study on measurements, taken with protons and low energy nuclei at different test facilities in Italy, as well as simulations. Measurements have been analysed with different tools and used to build a model of the detector response. The only observable of the detector is the cluster, and in particular on the cluster size, i.e. the number of pixels over the set threshold for each interaction. The analysis characterises the dependence of the cluster dimension on the energy deposited in silicon by the particle. The energy release inside ALPIDE has been evaluated using GEANT4 simulations of the beam tests. The values obtained have been used as an input for the analysis and to initialise the charge diffusion process in the device in a second simulation tool, Synopsis TCAD. The TCAD simulation includes the electrical properties of silicon and reproduces the detector structure and the electrical property of the materials. The simulation results have been used to verify our knowledge of the detector details, evaluated as the capability of the simulation to reproduce the experimental data. The simulation is the base of a tool that I developed to predict the cluster size as a function of a given number of parameters. This tool works after the GEANT4 simulation and provides essential information for the event reconstruction software of the experiment. In conclusion, this work reports on space compliance tests performed on the ALPIDE sensor, demonstrating technology readiness level 7 on the scale of space agencies. The dependence of the observed cluster size on the energy deposit has been fully characterised for highly ionising particles. This parametrisation will be a crucial element of the event reconstruction and particle identification algorithms of the HEPD-02 experiment. Given the energy of the nuclei under consideration, this study contains information useful for applications in proton and hadrotherapy.

Tracking particle in space is a crucial instance on a large number of space experiments. Measurements of charged cosmic rays based on spectrometers, observation of γ-rays, study of space weather and many other applications require systems equipped with tracking detectors. The sensitive area of detectors required for tracking spans from cm2 to m2. Silicon microstrip detectors have been the elective technology for tracking particles in space for several decades. Their stability, reliability and low power consumption are supported by years of expertise and provided a vast number of significant results on fundamental physics, reached with different experiments. An example of magnetic spectrometers is AMS-02, operated on International Space Station, and the satellite-borne PAMELA, that measure the charged component of cosmic rays and use tracking planes immersed in a magnetic field produced by permanent magnets to discriminate matter from antimatter. AMS-02 mounts several squared meters of microstrip tracker. The strip technology also has some limits. The spatial resolution depends on the pitch of the strips implanted on silicon buffer, that depends on the capabilities of the facility in charge of device construction. The fabrication sites have to use dedicated infrastructures, making costs relatively higher than in the past. Moreover, it is difficult to reduce the detector thickness below about 150 μm. This thickness impacts on measurements because of multiple scattering and reduces the lower threshold of low energy nuclear experiments. Another problem arises when the detector operates in radiation-dense environment. When the same frame shows multiple hits, the correct reconstruction of each interaction point is subject to degeneracy, due to the ambiguity in associating x− and y−hits in the microstrip sensor. The problem worsens if we consider that microstrips show equivalent charge noise generally up to hundreds of electrons if we take into account all the contributions from readout electronics. The resulting signal-to-noise ratio is generally good, but rarely exceeding 10 for Minimum Ionising Particles (MIP). The migration towards a new technology based on pixel devices is interesting because it solves some of these limitations. In particular, the hit position is uniquely defined by the position of the pixels involved in the event and pixel detectors can be thinned down to about 50 μm, with a potential gain in resolution. This thesis focuses on Monolithic Active Pixel Sensors (MAPS). They have the advantage, with respect to both the microstrip detectors and the other pixel families, of having the first stages of readout (front-end amplification, discrimination, digitisation and zero suppression) included on the sensor substrate. The detectors are realised with standard CMOS technology, the same used by foundries for most of commercial applications. Once the design is defined, the mass production of the devices is possible, and it reduces the cost of the single detector. Other pixel detectors do not provide this advantage since the design of sensors is based on different custom technologies, and after the production, the detector must be bump bonded to a readout chip, an expensive and low-yield technique. MAPS also have some limits. The most critical for the use in space is power consumption. A second relevant problem to face is that most of the devices realised with this technique have a digital readout, that does not allow measurement of dE/dx, important for particle identification. The requirement of space experiments to cover large surfaces with a tracking detector implies that using pixels the number of channels to handle increases. MAPS approach solves this issue by including on the detector a smart readout that passes to the DAQ system only data from pixels interested by the event. The MAPS detectors have been proposed for the first time at the end of the nineties. The technology reached maturity in the last years. The ALICE experiment, first of the four main LHC experiments, have installed MAPS detectors for its Inner Tracker Upgrade. For the upgrade the collaboration designed a new MAPS detector, ALPIDE. It is realised by TowerJazz foundry in 180 nm technology. The pixel pitch is 28 μm. The matrix is composed of 512×1024 pixels, for a total surface of 1.5×3 cm2. Although smaller if compared to microstrip ladders, that can reach several tenths of squared cm, the ALPIDE is one of the largest detector realised with this technology. Among the properties of ALPIDE, one particularly interesting for the space application is low power consumption. In ALICE, the low power consumption is required because of the difficulties of power distribution and cooling of the Inner Tracker. The power density is still one order of magnitude higher than for microstrip, but it starts to be interesting for space applications. In this thesis, we explore the possibility to use ALPIDE to realise the tracker for the second High Energy Particle Detector (HEPD-02), a payload of the second China Seismo-Electromagnetic Satellite (CSES-02). The CSES constellation is devoted to the observation of Earth from space and in particular to the study of ionosphere perturbation that might be related to seismic activity on Earth. We organised the study into two parts. The first is dedicated to the optimisation of the detector for space, dealing with the power consumption reduction, thermal control and space compliance tests, another section is devoted to the study of the ALPIDE response to low energy nuclei. The section devoted to space compliance starts with a description of the strategies for power consumption reduction. Some strategies are applied to the detector (use of low-speed lines, smart clock distribution) and require an optimised design of the full tracker and trigger. The design of the different sub-detectors allows distribution of the clock only to a limited section that has a higher probability of being involved in the event. With this approach, we can keep the power consumption of the full tracker below 10 W, as required by the design limits. High power consumption has a large impact on the temperature control of the device. The ALPIDE has an ideal operative temperature of about 30◦, which must be kept constant on the whole detector. ALICE cools down the detector with a water-based system, a solution not applicable in space, where convection is discouraged. A carbon fibre cold plate, designed to optimise the thermal conduction, is applied to control the temperature. The carbon fibre placement is studied to minimise the thickness of the plate and the impact of inert material on tracking performance. The thesis reports the results of various tests of space compliance made on a modified ALICE tracker module, an engineering model of the HEPD-02 module. It was made of 14 ALPIDE detectors disposed into two columns and glued and wire bonded to a Flexible Printed Circuit (FPC). On the other side, the detectors are glued to a carbon fibre plate. The device has been tested according to the requirements of the Chinese Space Agency for vibrations and in thermal-vacuum. A study of the response of the detector to low energy nuclei has been also carried out. The HEPD-02 detector is devoted to the detection of electrons between 3 and 150 MeV and protons between 30 and 300 MeV. We base the study on measurements, taken with protons and low energy nuclei at different test facilities in Italy, as well as simulations. Measurements have been analysed with different tools and used to build a model of the detector response. The only observable of the detector is the cluster, and in particular on the cluster size, i.e. the number of pixels over the set threshold for each interaction. The analysis characterises the dependence of the cluster dimension on the energy deposited in silicon by the particle. The energy release inside ALPIDE has been evaluated using GEANT4 simulations of the beam tests. The values obtained have been used as an input for the analysis and to initialise the charge diffusion process in the device in a second simulation tool, Synopsis TCAD. The TCAD simulation includes the electrical properties of silicon and reproduces the detector structure and the electrical property of the materials. The simulation results have been used to verify our knowledge of the detector details, evaluated as the capability of the simulation to reproduce the experimental data. The simulation is the base of a tool that I developed to predict the cluster size as a function of a given number of parameters. This tool works after the GEANT4 simulation and provides essential information for the event reconstruction software of the experiment. In conclusion, this work reports on space compliance tests performed on the ALPIDE sensor, demonstrating technology readiness level 7 on the scale of space agencies. The dependence of the observed cluster size on the energy deposit has been fully characterised for highly ionising particles. This parametrisation will be a crucial element of the event reconstruction and particle identification algorithms of the HEPD-02 experiment. Given the energy of the nuclei under consideration, this study contains information useful for applications in proton and hadrotherapy.

Already since the early 1960s semiconductor detectors have been employed in nuclear physics, in particular for gamma ray energy measurement. This chapter concentrates on position sensitive semiconductor detectors which have been developed in particle physics since the 1980s and which feature position resolutions in the range of 50–100 μ‎m by structuring the electrodes, thus reaching the best position resolutions of electronic detectors. For the first time this made the electronic measurement of secondary vertices and therewith the lifetime of heavy fermions possible. The chapter first conveys the basics of semiconductor physics, of semiconductor and metal-semiconductor junctions used in electronics and detector applications as well as particle detection with semiconductor detectors. It follows the description of different detector types, like strip and pixel detectors, silicon drift chambers and charged-coupled devices. New developments are addressed in the sections on ‘Monolithic pixel detectors’ and on ‘Precision timing with silicon detectors’. In the last sections detector deterioration by radiation damage is described and an overview of other semiconductor detector materials but silicon is given.