Dissertations / Theses on the topic 'Silicon pixel detectors'

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.

El Gran Colisionador de Hadrones (LHC) tiene previsto aumentar su luminosidad hasta siete veces su valor actual con el objetivo de ampliar su actual programa de física. Esta mejora se conoce con el nombre de High Luminosity LHC (HL-LHC) y está prevista para el año 2024-2026. El actual Inner Detector (ID) del detector de ALTAS será completamente reemplazado por uno nuevo para ajustarse a los rigurosos requisitos que impone el HL-LHC. Nuevos detectores de píxeles están siendo investigados para su utilización en todo el ID cuando el HL-LHC entre en operación. La utilización de sensores de píxeles tipo monolítico dentro del ID de ATLAS supondría una nueva era para los detectores de píxeles en física de altas energías debido a sus muchas ventajas con respecto a las tecnologías que se usan actualmente. Las principales ventajas son: mejor resolución espacial, menor densidad, mayor rendimiento, y menor coste. En este contexto, un nuevo tipo de sensor monolítico conocido como Depleted Monolithic Active Pixel Sensor on silicon-on-insulator ha sido investigado en esta tesis. El capítulo 1 describe el LHC, el experimento ATLAS, y las mejoras previstas para el HL-LHC. Este capítulo también describe los requerimientos y desafíos del futuro Inner Detector, al ser el subdetector más cercano al punto de interacción. El capítulo 2 describe la base de los detectores de partículas en física de altas energías. Este capítulo abarca la interacción de partículas con la materia, los conceptos básicos para la construcción de un detector de píxeles, y la resolución de momento transverso, vértice, y parámetro de impacto de un detector. El capítulo 3 describe los daños que la radiación produce en detectores de silicio, tanto en la electrónica como en el sensor, cuyo impacto es crucial en el rendimiento de los detectores especialmente para experimentos en el HL-LHC. El capítulo 4 revisa la evolución y tendencias en detectores de pixeles, abarcando desde los ya bien establecidos pixel híbridos, hasta los CMOS píxeles. La sección dedicada a los CMOS píxeles describe los diferentes tipos que se están considerando en ATLAS: High resistivity CMOS, high voltage CMOS, y monolíticos CMOS-on-SOI. Este ultimo compone el núcleo de estudio de esta tesis y es descrito en detalle. Los siguientes capítulos detallan el programa de caracterización y medidas realizado en el contexto de esta tesis. El capitulo 5 se centra en la caracterización del daño creado por la radiación en la electrónica hasta las dosis esperadas en el ID de ATLAS durante su operación en el HL-LHC. Las propiedades del detector, como son las corrientes de fuga, el cociente entre señal y ruido, la colección de carga y la profundidad de depleción, son descritas en el capitulo 6. El Capítulo 7 describe la caracterización de sensores monolíticos CMOS-on-SOI en un haz de piones, donde la colección de carga, el reparto de carga entre píxeles, la resolución espacial, y la eficiencia son discutidas. Este trabajo concluye con un resumen, con vistas al futuro de las tecnologías monolíticas CMOS-on-SOI en la física de altas energías.
A major upgrade of the Large Hadron Collider (LHC) called High Luminosity LHC (HL-LHC) is scheduled for 2024-2026. This will lead to an increase of the luminosity by seven times the current value and to the extension of the currently ongoing physics programme. A completely new Inner Detector for the ATLAS experiment needs to be developed to withstand the extremely harsh environment at the HL-LHC. New pixel detector concepts are being investigated as a possible candidate to the inner and outer layers of the HL-LHC ATLAS Inner Detector. The use of monolithic pixel sensors in the ATLAS Inner Tracker would lead to a new era of pixel detectors as a consequence of its many advantages with respect to the current technologies. The achievement of smaller spatial resolution, lower density, bigger production yield and throughput, and smaller budget cost are the main arguments to pursue this technology. In this context, a novel Depleted Monolithic Pixel Active Detector built on a thick film Silicon-On-Insulator has been fully investigated in this thesis. Chapter 1 introduces LHC and the ATLAS experiment as well as their foreseen scenarios at the HL-LHC upgrade. This naturally motivates the stringent requirements and challenges of the closest sub-detector to the interaction point, the Inner Detector. Chapter 2 describes the basis of a tracking detector for high energy physics applications, detailing the interactions of particles with matter to the formation of a pixel detector from a semiconductor material. Then the momentum, vertex, and impact parameter resolution of a tracking detector are calculated leading to a set of requirements for the detector design. Chapter 3 describes the radiation damage in silicon detectors whose impact to the detector performance is crucial specially for HL-LHC experiments. The radiation damage in the electronics and in the silicon bulk is treated. Chapter 4 revises the current developments and trends on pixel detectors from the well established hybrid pixel technologies to the commercial CMOS pixels. The commercial CMOS pixels section describes the current technologies being considered at ATLAS: high resistivity, high voltage CMOS (currently built as hybrid and as monolithic), and monolithic CMOS-on-SOI. The latter one composes the core of study of this thesis and is described in great detail. The final chapters are dedicated to the description of the validation programme performed to the CMOS-on-SOI technology, together with characterization methods used, measurements performed, and results analysis description. Chapter 5 focuses on the measurements performed to characterize the radiation hardness of the technology against the ionizing radiation expected in the HL-LHC ATLAS detector. The crucial charge collection properties to fulfil the ATLAS detector requirements were measured and are described in Chapter 6. These measurements include leakage current, signal-to-noise ratio, collected charge, and depletion depth on unirradiated and irradiated samples. Additionally, different techniques as radioactive sources, pion beams, and laser beams were used in order to calculate the depletion depth. Chapter 7 describes the characterization of the monolithic CMOS-on-SOI in a pion beam test. The measured charge collection, charge sharing, spatial resolution, and tracking efficiency are discussed. Within the summary, an outlook towards the future of depleted monolithic active pixel sensors on silicon-on-insulator technology for high energy physics is presented.

3D silicon pixel detectors are a novel technology where the electrodes penetrate the sili- con bulk perpendicularly to the wafer surface. As a consequence the collection distance is decoupled from the wafer thickness resulting in a radiation hard pixel detector by design. Between 2010 and 2012, 3D silicon pixel detectors have undergone an intensive programme of beam test experiments. As a result, 3D silicon has successfully qualified for the ATLAS upgrade project, the Insertable B-Layer (IBL), which will be installed in the long-shutdown in 2013-14. This thesis presents selected results from these beam test studies with 3D sensors bonded to both current ATLAS readout cards (FE-I3) and newly developed readout cards for the IBL (FE-I4). 3D devices were studied using 4 GeV positrons at DESY and 120 GeV pions at the SPS at CERN. Measurements presented include tracking efficiency (of the whole sensor, the pixel and the area around the electrodes), studies of the active edge pixels of SINTEF devices and cluster size distributions as a function of incident angle for IBL 3D design sensors. A simulation of 3D silicon sensors in an antiproton beam test for the AEgIS experiment, with comparison to experimental results and a previous simulation, are also presented.

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2003.
Includes bibliographical references (leaves 67-69). Also available in electronic version. Access restricted to campus users.

The ALICE experiment at CERN has planned an upgrade of the Inner Tracking System (ITS), named ITS3, for the LHC Long Shutdown 3, in 2025. The cornerstone of the upgrade is a new CMOS pixel sensor built in 65 nm technology and in bent-cylindrical configuration, replacing the inner layers of the existing detector, the ITS2. The ITS3 will reach much better tracking and vertexing performance, thanks to the improved spatial resolution and the much reduced material budget with respect to the previous Inner Tracking System. The aim of this thesis is to report on the analysis of the data collected at beam tests on new ALPIDE chips (used for ITS2, based on Monolithic Active Pixel Sensor, MAPS) which have been bent in a cylindrical configuration as foreseen for the ITS3. This is the first bending proof of concept for a silicon detector. In particular, data from beam test taken in 2020 have been studied through a data analysis framework that I have personally written to accomplish this task; the complexity of the data analysis is driven by the fact that each ALPIDE chip has a total of 1024x512 pixel MAPS and by the bent geometry of the sensor. In this thesis, the promising performances obtained by studying the sensor total efficiency and spatial resolution in different experimental configurations will be presented and discussed.

Le trajectographe interne (ITk) de l'expérience ATLAS sera amélioré pour la nouvelle phase de prise de données du grand collisionneur de hadrons du CERN à haute luminosité (HL-LHC) en 2026. Le HL-LHC fonctionnera avec l’énergie nominale de collision est de 14 TeV et la luminosité instantanée maximale de 7,5 x (10)34 cm(−2) s(−1), cinq fois plus élevée qu’à présent. La luminosité accrue se traduira par des niveaux de rayonnement et des débits de données environ dix fois plus élevés. Afin de faire face aux exigences d’ATLAS en termes d’intensite du rayonnement, de vitesse de lecture et de granularité au HL-LHC, le remplacement de l’actuel ATLAS Inner Tracker (ITk) est nécessaire. Deux capteurs CMOS épuisés à grande échelle dans la technologie LF de 150 nm, appelés LF-CPIX et LF-MONOPIX, ont été développés dans le cadre de la mise à niveau ATLAS Inner Tracker (ITK) pour le LHC à haute luminosité. Le travail présenté ici montre la caractérisation de ces trois prototypes, avec des contributions concernant le développement de la configuration, le calibrage source 55 Fe et 90 Sr, les modifications du microprogramme FPGA et le développement de programmes de test. L’enquête sur la dureté du rayonnement pour l’électronique et les composants du capteur a été une préoccupation majeure. Nous montrerons les résultats concernant les caractérisations de ces prototypes dans les performances de laboratoire du CPPM, ainsi que les résultats de multiples campagnes de rayonnement conduites à l’installation de protons IRRAD de 24 GeV du CERN, afin d’étudier les effets de la perte d’énergie non ionisante (NIEL) et du Dose ionisante (TID) sur les prototypes
The Inner Tracker (ITk) system of the ATLAS experiment will be upgraded for the 2026 High Luminosity Large Hadron Collider (HL-LHC) run. The HL-LHC will operate with a center of mass energy of 14 TeV and a peak instantaneous luminosity five times higher than at present. The increased luminosity will result in roughly ten times higher radiation levels and data rates. To cope with the ATLAS requirements in terms of radiation hardness, readout speed and granularity at the HL-LHC, the replacement of the present ATLAS Inner Tracker (ITk) is needed. Two large-scale depleted CMOS sensors in the 150 nm LF-technology called LF-CPIX and LF-MONOPIX, developed in the framework of the ATLAS Inner Tracker (ITK) upgrade for High Luminosity LHC. The work presented here shows the characterization for these three prototypes, with contributions concerning the setup development, 55Fe and 90Sr source calibration, modifications of the FPGA firmware and development of test programs. A main concern was the investigation on the radiation hardness for both the electronics and the sensor parts. We will show results concerning characterizations for these prototypes in the laboratory performance at CPPM, as well as results in multiple radiation campaigns performed at the 24 GeV IRRAD proton facility at CERN, to study the effects of Non-Ionizing Energy Loss (NIEL) and Total Ionizing Dose (TID) on the prototypes

For the X-ray astronomy project Advanced Telescope for High ENergy Astrophysics (Athena) wafer-scale DEpleted P-channel Field Effect Transistor (DEPFET) detectors are proposed as Focal Plane Array (FPA) for the Wide Field Imager (WFI). Prototype structures with different pixel layouts, each consisting of 64 x 64 pixels, were fabricated to study four different DEPFET designs. This thesis reports on the results of the electrical and spectroscopic characterization of the different DEPFET designs. With the electrical qualification measurements the transistor properties of the DEPFET structures are investigated in order to determine whether the design intentions are reflected in the transistor characteristics. In addition, yield and homogeneity of the prototypes can be studied on die, wafer and batch level for further improvement of the production technology with regard to wafer-scale devices. These electrical characterization measurements prove to be a reliable tool to preselect the best detector dies for further integration into full detector systems. The spectroscopic measurements test the dynamic behavior of the designs as well as their spectroscopic performance. In addition, it is revealed how the transistor behavior translates into the detector performance. This thesis, as the first systematic study of different DEPFET designs on die and detector level, shows the limitations of the current DEPFET assessment methods. Thus, it suggests a new concise characterization procedure for DEPFET detectors as well as guidelines for expanded testing in order to increase the general knowledge of the DEPFET. With this study of four different DEPFET variants not only designs suitable for Athena mission have been found but also improvement impulses for the starting wafer-scale device production are provided.

The second decade of Large Hadron Collider operations, from about 2020 onwards, envisages a remarkable increase in collider instantaneous luminosity, one order of magnitude above the project one. This luminosity increase presents several challenges to the LHC experiments. The present Tracker of the Compact Muon Solenoid experiment must be replaced with a system providing excellent tracking quality at higher luminosities, as well as Tracking Trigger inputs to the existing "Level 0" CMS Trigger system at the full 40 MHz bunch-crossing rate. The minimal requirements for a Tracking Trigger would be the capability to confirm the presence of high-pT tracks associated with Calorimeter and/or Muon Level 0 Triggers. The ability to provide effective isolation criteria may also be required, and would in any case substantially improve the Trigger performance. Maintaining the data rates generated by Tracking Trigger inputs within a manageable bandwidth requires sensor modules able to locally sparsify the data. Measuring at detector module level the track direction in the transverse plane, and hence deriving its transverse momentum, is the most promising solution to provide such a detector-embedded data reduction feature. These so-called "pT-modules"' would only transmit to the Level 1 Trigger "stubs", pairs of correlated hits in two closely separated sensors, derived by tracks with pT above a given threshold. To exemplify, a 2 GeV/c threshold would cut data rate of more than a factor 10, hence providing a data rate well within the capabilities of present data links. The pT-modules design discussed in this work consists of two, closely spaced segmented silicon sensors, featuring both pattern hit correlation across the module and a single hit position resolution high enough to compute stubs with the required accuracy to resolve track directions despite a lever arm of about only 1 mm. A concept Tracker layout, the so-called "Long Barrel", consisting in an Outer Tracker completely built out of pT-modules, has been proposed. The Long Barrel Tracker is particularly flexible in simulation studies of Tracking Trigger as it allows for information from several layers of the Tracker to be combined in a projective geometry. For this reason, it is meant as a testing ground to compare the performance of different designs and configurations. The Long Barrel layout also allows the generation of even more structured Trigger Objects such as "tracklets", consisting of pairs of stubs in opportunely paired layers, which can in turn be used as seeds to generate "Level 1 tracks", including even more stubs. The choice of stacked sensors for pT-modules has been recently strengthened by test beam results obtained with novel prototypes of Monolithic Active Pixel Sensors and reported in this thesis. The developement of Tracking Trigger simulations is also presented as a major step towards the design of a realistic Trigger capable Tracker upgrade. A particular challenge for the Trigger system is given by tau leptons produced in many rare processes searched at the LHC. The performance of a Tracking Trigger on final states with tau leptons will be crucial at very high luminosities and is presented at the and of this document as the natural step forward in the work on the subject.
Durante il secondo decennio di operazioni al Large Hadron Collider, a partire dall'anno 2020, è previsto un notevole aumento della luminosità istantanea del collisionatore, di un ordine di grandezza superiore rispetto a quella di progetto. Questa luminosità presenta numeose sfide per gli esperimenti a LHC. Il Tracciatore attualmente impiegato nell'esperimento Compact Muon Solenoid dovrà essere rimpiazzato con un sistema in grado di garantire una tracciatura di qualità eccellente ad alte luminosità e, allo stesso tempo, fornire informazioni utili per l'attuale "Livello 0" del sistema di Trigger a CMS, alla frequenza di collisioni di 40 MHz. Le richieste minime per un Trigger basato sul Tracciatore sono la capacità di confermare la presenza di tracce ad alto pT associate a Trigger di Livello 0 ottenuti con i Calorimetri o i rivelatori di muoni. La capacità di fornire criteri efficaci di isolazione può essere ulteriormente richiesa e in ogni caso migliorerebbe significativamente le prestazioni del Trigger. Il rateo dei dati associati con la generazione nel Tracciatore di informazione di Trigger può essere mantenuto in una larghezza di banda sufficientemente maneggevole richiedendo che i moduli sensitivi siano in grado di ridurre localmente i dati. I principali candidati per una simile riduzione locale del rateo i dati sono caratterizzati dalla capacità di fornire la direzione della traccia nel piano trasverso, oltre alla sua posizione, da cui poter dedurre la quantità di moto della traccia stessa. Questi "pT-modules" trasmetterebbero di conseguenza al Trigger di primo livello degli abbozzi di traccia ("stub") generati da particelle con pT al di sopra di 2 GeV/c. La scelta di una simile soglia permetterebbe la riduzione dei dati di un fattore superiore a 10, consentendo quindi un rateo facilmente tollerabile. I moduli di Trigger possono essere realizzati con due sensori di silicio paralleli leggermente separati, caratterizzati da una risoluzione sulla misura del singolo punto d'impatto tale che gli stub, ottenuti tramite correlazione tra i punti misurati nel modulo, possano fornire un'adeguata misura della direzione della traccia, nonostante il braccio di leva sia dell'ordine del millimetro. Un'ipotetica configurazione per il Tracciatore, composto da "lunghi barili", che prevede un Tracciatore esterno realizzato totalmente con moduli di Trigger, è stata proposta. Essa è particolarmente flessibile negli studi di simulazione per il Trigger realizzato con il Tracciatore giacché consente di combinare tra loro, tramite proiezioni geometriche, le informazioni provenienti da diversi strati del Tracciatore. Pertanto è un campo di prova per confrontare le prestazioni di diverse concezioni e diverse configurazioni. Il Tracciatore proposto permette anche la generazione di oggetti più articolati degli stub per il Trigger, come ad esempio le "tracklet", che consistono in coppie di stub opportunamente associate tra loro, le quali possono a loro volta essere usate come punto di partenza per la costruzione di Tracce di Primo Livello. La scelta di moduli di Trigger realizzati con sensori accoppiati è rafforzata da risultati recenti ottenuti con dei prototipi innovativi di rivelatori a Pixel Monolitici durante dei test sotto fascio riportati in questa tesi. Lo sviluppo di simulazioni per un Trigger con il Tracciatore è anch'esso presentato come un significativo progresso verso la progettazione di un nuovo Tracciatore realistico e capace di fornire informazioni utili per il Trigger. Particolarmente impegnativo è lo sforzo per un Trigger che selezioni i leptoni tau prodotti in numerosi processi rari di interesse per gli esperimenti a LHC. Le prestazioni di un Trigger con il Tracciatore su stati finali contenenti leptoni tau saranno fondamentali a luminosità molto elevate e sono illustrate alla fine di questo documento, come naturale prosecuzione del lavoro descritto.

Abstract Research on X-ray imaging sensors and systems have been carried out for several decades. To make these X-ray scanners smaller with better performance and higher operating speed is an important subject for scientific research and industrial applications. This thesis covers a whole X-ray line-scan camera system. Special attention is given to the smart sensor micromodule design and processing technology. The smart sensor micromodule is an integrated sensor card that includes both silicon X-ray sensor array and signal-processing integrated circuits, which can perform the functions of both an optical sensor and an analog signal processor. Digital signal processing (DSP) made by application specific integrated circuits (ASICs) is also covered in this thesis. Processing technology of the photodiode array, design of the integrated circuit, design and packaging of the micromodules are presented in this thesis. The mechanism of photodiode leakage current is studied in detail. Measured results show that the leakage current level of the photodiode array achieves 80 pA/cm2 under zero bias condition, which outperforms the best photodiode reported so far. The algorithm of the digital signal processing is also studied. The X-ray scanning system can achieve 2 m/s scanning speed with a spatial resolution of 400 mm.

Computed tomography (CT) is a widely used medical imaging modality. By rotating an x-ray tube and an x-ray detector around the patient, a CT scanner is able to measure the x-ray transmission from all directions and form an image of the patient’s interior. CT scanners in clinical use today all use energy-integrating detectors, which measure the total incident energy for each measurement interval. A photon-counting detector, on the other hand, counts the number of incoming photons and can in addition measure the energy of each photon by comparing it to a number of energy thresholds. Using photon- counting detectors in computed tomography could lead to improved signal-to-noise ratio, higher spatial resolution and improved spectral imaging which allows better visualization of contrast agents and more reliable quantitative measurements. In this Thesis, the feasibility of using a photon-counting silicon-strip detector for CT is investigated. In the first part of the Thesis, the necessary performance requirements on such a detector is investigated in two different areas: the detector element homogeneity and the capability of handling high photon fluence rates. A metric of inhomogeneity is proposed and used in a simulation study to evaluate different inhomogeneity compensation methods. Also, the photon fluence rate incident on the detector in a scanner in clinical use today is investigated for different patient sizes through dose rate measurements together with simulations of transmission through patient im- ages. In the second part, a prototype detector module is used to demonstrate new applications enabled by the energy resolution of the detector. The ability to generate material-specific images of contrast agents with iodine and gadolinium is demonstrated. Furthermore, it is shown theoretically and ex- perimentally that interfaces in the image can be visualized by imaging the so-called nonlinear partial volume effect. The results suggest that the studied silicon-strip detector is a promising candidate for photon-counting CT.

The activities carried out within the present work were aimed at the preparation for heavy quarks measurements, thus including the construction and commissioning of the SPD. More in detail, they can be summarised in the following: • Assembly of the silicon pixel sensors on the carbon fibre support. Given its role as a precision tracker, the assembly of the SPD requires the use of specific procedures to ensure a high degree of accuracy. • Tuning and maintenance of the cooling system of the SPD. The SPD power dissipation is of about 1.5 kW. This means that, without cooling, the temperature of the sensors would rise at about 1°C/s. The cooling system is thus of vital importance for the operation of the detector. • Development of a set of tools for the monitoring of the alignment procedures of the ITS and, in particular of the SPD. The misalignment of the detector must be accounted for in the software description of the geometry in order to optimize the spatial resolution. The matching of the geometry with the data is done using software procedures. A dedicated set of tools has been developed to control the results of this phase and to evaluate the resolution of the detector. • Study of the possibility of using semi-electronic decays of beauty particles for the investigation of the QGP, with an emphasis on the specific issues of the first LHC runs (electron PID and misalignment). The simulation studies reported here are devoted to assess ALICE performance in measuring the nuclear modification factor and the elliptic flow of electrons from beauty decays. Moreover, using previous studies on the charm production measurement, it has been possible to estimate the sensitivity to the mass dependence of the partonic energy loss.
L'attività svolta nell’ambito della presente tesi è stata mirata alla preparazione per lo studio della produzione di beauty. Ha perciò incluso la costruzione dei settori, il tuning dell'impianto di raffreddamento ed il commissioning dell’SPD. Più in dettaglio: • Assemblaggio dei sensori a pixel sul supporto di fibra di carbonio. Dato il suo ruolo come tracciatore, l'assemblaggio dell'SPD richiede l'impiego di specifiche procedure per assicurare un’alta precisione. • Tuning e funzionamento del sistema di raffreddamento dell'SPD. La dissipazione dell'SPD è di circa 1.5 kW. Questo vuol dire che, senza raffreddamento, la temperatura dei sensori aumenterebbe alla velocità di circa 1°C/s. L’impianto di raffreddamento è quindi di vitale importanza per il funzionamento del rivelatore. • Sviluppo di un set di strumenti per il monitoraggio dell'allineamento dell'ITS ed, in particolare, dell'SPD. Il misallineamento del rivelatore dev'essere valutato e riportato nel software della geometria per ottimizzare la risoluzione spaziale. Questa operazione viene fatta utilizzando dei programmi dedicati. Per controllare i risultati ottenuti da questi programmi e per valutare la risoluzione spaziale del rivelatore, è stato sviluppato uno strumento software apposito. • Valutazione sulla possibilità di usare i decadimenti semi-elettronici del beauty per lo studio del QGP, con particolare riferimento alle problematiche inerenti ai primi run ad LHC (identificazione degli elettroni e misallineamento). Gli studi di simulazione riportati qui sono mirati alla valutazione delle performance di ALICE per la misura del fattore di modifica nucleare (RAA) e dell'anisotropia azimutale (v2) degli elettroni provenienti da decadimenti del beauty. Inoltre, sfruttando precedenti studi sulla produzione del charm, è stato possibile stimare la sensitività per la dipendenza dalla massa della perdita d'energia partonica.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2012.
"June 2012." Cataloged from PDF version of thesis.
Includes bibliographical references (p. 45).
In high energy physics experiments, very high precision tracking of charged particles is needed. Solid state detectors achieve the high precision necessary to provide track and vertex reconstruction of the particles that traverse them, but tracking performance begins to deteriorate at fluxes of radiation around 10¹⁴ - 10¹⁵ hadrons/cm 2. These radiation levels are congruent with those experienced by the ATLAS pixel detector, the inner most part of the ATLAS tracking system, which is vital to track and vertex reconstruction. During the planned shut-down of the Large Hadron Collider (LHC) in 2013-2014, the energy and luminosity of the LHC will both be increased. The current pixel detector has begun to suffer deterioration of performance, so the ATLAS Collaboration has initiated an upgrade to take place during the scheduled shut-down beginning in 2013, the Insertable B-Layer (IBL). The IBL will be assembled and placed in between a reduced diameter beam pipe and the current pixel detector, acting as the fourth layer of the ATLAS inner detector. The pixel sensors of the IBL will have to sustain a radiation dose of 5 * 10¹⁵neq/cm². Two sensor technologies are being considered for the IBL upgrade: planar n-in-p silicon pixel sensors and 3D double sided n-in-p pixel sensors. Research of both these technologies is being done by the IFAE in collaboration with CNM-Barcelona. To cope with the increased data rate after the LHC upgrade, a new front-end chip has also been produced, the FE-14 front-end chip. Test results and data analysis from five different 3D pixel sensor devices, all fabricated at CNM-Barcelona were done. Evaluation of these technologies and the test results of irradiated 3D pixel sensor devices are carried out in this thesis.
by Matthew R. Chapa.
S.B.

Prévue pour 2024, une série d’améliorations doit être apportée au grand collisionneur d’hadrons du CERN (LHC) de manière à élargir son potentiel de découverte de nouvelle physique. Cette thèse se situe dans la perspective des études d’amélioration du détecteur ATLAS dans ce nouvel environnement, et concerne une nouvelle technologie monolithique HV/HR CMOS qui pourrait être utilisée pour les détecteurs de traces centraux pixélisés. Cette technologie a le potentiel de permettre la réduction de l’épaisseur des détecteurs, d'augmenter la granularité ainsi que de réduire les couts de production.Au sein de la collaboration HV/HR CMOS d’ATLAS, divers prototypes ont été développés en utilisant les technologies de différents partenaires industriels : GlobalFoundries (GF) BCDlite 130 nm et LFoundry (LF) 150 nm entre autres. Pour comprendre le comportement électrique et la capacité de détection de telles technologies, des simulations TCAD -Technology Computer Aided Design- en 2D et 3D ont été réalisées pour extraire le profil de la zone déplétée, la tension de claquage, la capacitance ainsi que la collection de charges ionisées des prototypes. Le développement de systèmes de test complexes et la caractérisation des prototypes HV/HR CMOS ont aussi été une partie du travail fourni pour cette thèse. Les programmes d’acquisition, en particulier pour ce qui concerne les tests sous protons ou auprès d’irradiateurs à rayons X, ainsi que les programmes de réglages de seuil ont été implémenté dans divers systèmes de test. Plusieurs versions des prototypes développés dans 3 technologies HV/HR CMOS différentes (AMS 0.18 μm HV, GF BCDlite 130nm et LF 150nm) ont été caractérisées
A major upgrade to the Large Hadron Collider (LHC), scheduled for 2024 will be brought to the machine so as to extend its discovery potential. This PhD is part of the ATLAS program and aims at studying a new monolithic technology in the framework of the design of an upgraded ATLAS inner tracker. This new type of sensor is based on a HV/HR CMOS technology, which would potentially offer lower material budget, reduced pixel pitch and lower cost with respect to the traditional hybrid pixel detector concept.Various prototypes have been developed using different HV/HR CMOS technologies from several industrial partners, within the ATLAS HV/HR collaboration, for instance Global Foundry (GF) BCDlite 130 nm and LFoundry (LF) 150 nm. In order to understand the electric behavior and the detection capabilities of these technologies, 3D and 2D Technology Computer Aided Design (TCAD) simulations have been performed to extract the depletion zone profile, the breakdown voltage, the leakage current, the capacitance as well as the charge collection of the prototypes. Test setup developments and characterizations of the HV/HR CMOS prototypes were also part of this thesis. The data acquisition programs, in particular dedicated to the proton test beams, X-ray sources and threshold tuning, have been implemented into various test setups. Several HV/HR CMOS prototypes developed in three HV/HR technologies, AMS 0.18 µm HV, GF BCDlite 130 nm and LF 150 nm, have been characterized

This thesis concerns the development and characterisation of X-ray imaging systems based on single photon processing. “Colour” X-ray imaging opens up new perspectives within the fields of medical X-ray diagnosis and also in industrial X-ray quality control. The difference in absorption for different “colours” can be used to discern materials in the object. For instance, this information might be used to identify diseases such as brittle-bone disease. The “colour” of the X-rays can be identified if the detector system can process each X-ray photon individually. Such a detector system is called a “single photon processing” system or, less precise, a “photon counting system”. With modern technology it is possible to construct photon counting detector systems that can resolve details to a level of approximately 50 µm. However with such small pixels a problem will occur. In a semiconductor detector each absorbed X-ray photon creates a cloud of charge which contributes to the image. For high photon energies the size of the charge cloud is comparable to 50 µm and might be distributed between several pixels in the image. Charge sharing is a key problem since, not only is the resolution degenerated, but it also destroys the “colour” information in the image. This thesis presents characterisation and simulations to provide a detailed understanding of the physical processes concerning charge sharing in detectors from the MEDIPIX collaboration. Charge summing schemes utilising pixel to pixel communications are proposed. Charge sharing can also be suppressed by introducing 3D-detector structures. In the next generation of the MEDIPIX system, Medipix3, charge summing will be implemented. This system, equipped with a 3D-silicon detector, or a thin planar high-Z detector of good quality, has the potential to become a commercial product for medical imaging. This would be beneficial to the public health within the entire European Union.
Denna avhandling berör utveckling och karaktärisering av fotonräknande röntgensystem. ”Färgröntgen” öppnar nya perspektiv för medicinsk röntgendiagnostik och även för materialröntgen inom industrin. Skillnaden i absorption av olika ”färger” kan användas för att särskilja olika material i ett objekt. Färginformationen kan till exempel användas i sjukvården för att identifiera benskörhet. Färgen på röntgenfotonen kan identifieras om detektorsystemet kan detektera varje foton individuellt. Sådana detektorsystem kallas ”fotonräknande” system. Med modern teknik är det möjligt att konstruera fotonräknande detektorsystem som kan urskilja detaljer ner till en upplösning på circa 50 µm. Med så små pixlar kommer ett problem att uppstå. I en halvledardetektor ger varje absorberad foton upphov till ett laddningsmoln som bidrar till den erhållna bilden. För höga fotonenergier är storleken på laddningsmolnet jämförbar med 50 µm och molnet kan därför fördelas över flera pixlar i bilden. Laddningsdelning är ett centralt problem delvis på grund av att bildens upplösning försämras, men framför allt för att färginformationen i bilden förstörs. Denna avhandling presenterar karaktärisering och simulering för att ge en mer detaljerad förståelse för fysikaliska processer som bidrar till laddningsdelning i detektorer från MEDIPIX-projekter. Designstrategier för summering av laddning genom kommunikation från pixel till pixel föreslås. Laddningsdelning kan också begränsas genom att introducera detektorkonstruktioner i 3D-struktur. I nästa generation av MEDIPIX-systemet, Medipix3, kommer summering av laddning att vara implementerat. Detta system, utrustat med en 3D-detektor i kisel, eller en tunn plan detektor av högabsorberande material med god kvalitet, har potentialen att kunna kommersialiseras för medicinska röntgensystem. Detta skulle bidra till bättre folkhälsa inom hela Europeiska Unionen.

Le Large Hadron Collider (LHC), située au CERN, Genève, produit des collisions de protons accélérés à une énergie de 3.5 TeV depuis le 23 Novembre 2009. L'expérience ATLAS enregistre depuis des données et poursuit sa recherche de nouvelle physique à travers l'analyse de la cinématique des événements issues des collisions. L'augmentation prévue de la luminosité sur la période s'étalant de 2011 2020 apportera de nouveaux défis pour le détecteur qui doivent être considérés pour maintenir les bonnes performance de la configuration actuelle. Le détecteur interne sera le sous-détecteur le plus affecté par l'augmentation de la luminosité qui se traduira par une augmentation des dommages occasionnés par la forte radiation et par la multiplication du nombre de traces associées à chaque croisement de faisceau. Les dommages causés par l'irradiation intense entrainera une perte d'efficacité de détection et une réduction du nombre de canaux actifs. Un intense effort de Recherche et Développement (R&D) est présentement en cours pour concevoir un nouveau détecteur pixel plus tolérant aux radiations et au cumul des événements générant un grand nombre de traces à reconstruire. Un premier projet de mise-à-jour du détecteur interne, nommé Insertable B-Layer (IBL) consiste à ajouter un couche de détection entre le tube à vide du faisceau et la première couche de silicium. Le projet SLHC prévoit de remplacer l'ensemble du détecteur interne par une version améliorée plus tolérante aux radiations et aux cumuls des événements. Dans cet ouvrage, je présente une étude utilisant la simulation technologique assisté par ordinateur (TCAD) portant sur les méthodes de conception des détecteurs pixels planaires permettant de réduire les zones inactives des détecteurs et d'augmenter leurs tolérances aux radiations. Les différents modèles physiques disponible ont étés étudiés pour développer un modèle cohérent capablede prédire le fonctionnement des détecteurs pixels planaires après irradiation. La structure d'anneaux de gardes utilisée dans le détecteur interne actuel a été étudié pour obtenir de l'information sur les possible méthodes permettant de réduire l'étendu de la surface occupée par cette structure tout en conservant un fonctionnement stable tout au long de la vie du détecteur dans l'expérience ATLAS. Une campagne de mesures sur des structures pixels fut organisée pour comparer les résultats obtenue grâce à la simulation avec le comportement des structures réelles. Les paramètres de fabrication ainsi que le comportement électrique ont été mesurés et comparés aux simulations pour valider et calibrer le modèle de simulation TCAD. Un modèle a été développé pour expliquer la collection de charge excessive observée dans les détecteurs planaires en silicium lors de leur exposition a une dose extrême de radiations. Finalement, un modèle simple de digitalisation à utiliser pour la simulation de performances détecteurs pixels individuels exposés à des faisceau de haute énergie ou bien de l'ensemble du détecteur interne est présenté. Ce modèle simple permets la comparaison entre les données obtenue en faisceau test aux modèle de transport de charge inclut dans ladigitalisation. Le dommage dû à la radiation , l'amincissement et l'utilisation de structures à bords minces sont autant de structures dont les effets sur la collecte de charges affectent les performance du détecteur. Le modèle de digititalisation fut validé pour un détecteur non-irradié en comparant les résultats obtenues avec les données acquises en test faisceau de haut énergie. Le modèle validé sera utilisé pour produire la première simulation de l'IBL incluant les effets d'amincissement du substrat, de dommages dûes aux radiations et de structure dotés de bords fins.

碩士
國立清華大學
物理學系
85
Four kinds of the silicon pixel sensors with integrated coupling capacitors and polysilicon bias resistors have been designed and fabricated. The pixel sensors were processed on n- type silicon wafers with the thickness of 280 μm and the orientation of <111>. Each sensor with area of 1.2 × 1.2 c㎡ includes 30 × 30 diodes. A 80 nm gate oxide thickness was chosen to provide a coupling capacitance of 53.3 nF/c㎡. A full depletion voltage of 70 V and the leakage currents of 0.0975, 0.0585, 40.279, and 0.1078 μA/c㎡ for the sensors areas of12475 × 12480, 12475 × 12480, 12450 × 12480, and 12450 × 12455 μ ㎡ respectively were measured. The electrical tests indicate that the leakage current and the junction capacitance of the silicon pixel sensors are smaller than that of the silicon microstrip detector in this study. The characteristic measurements show that the developed pixel sensors can work except a defective one.

The Large Hadron Collider (LHC) is the largest circular accelerator ever build, allowing collisions at a center-of-mass energy of 13 TeV. The Phase-2 of the LHC, known as High Luminosity LHC (HL-LHC), is going to start in 2027. With HL-LHC, the Compact Muon Solenoid (CMS) experiment will gather an integrated luminosity up to 4000 fb^{-1} in 10 years, making it possible to study rare events of the Standard Model (SM) or to search for processes beyond it. The CMS experiment will be upgraded between 2025 and 2027 to cope with the higher luminosity: especially in the regions near the collision point, unprecedented requirements in terms of radiation resistance and granularity need to be met. The first part of this Thesis focuses on the upgrade of the CMS silicon tracker, whose inner section will be made of pixel detectors. The characteristics of the new tracker will be extremely important in the future analysis to be carried out in CMS during Phase-2. For the new Phase, pixel sensors of new conception have been considered, in which the electrodes (p+ and n+) penetrate deep into the silicon from the same side of the sensor: these new pixels are referred as `3D' for their characteristic of having columnar implants as deep as the active thickness of the sensor, while the more conventional planar `2D' pixels have superficial implants of small thickness. Thanks to this structure, 3D sensors can have excellent performance even with high radiation damage, making them suitable for the use in the inner layers of the future CMS tracker. Due to the cutting edge technology needed to produce these sensors, their use for a large scale experiment has only recently become feasible. However, the production processes are more complex than those of planar sensors, and this affects costs and production effciency. Therefore, 3D sensors have been taken into consideration only for the inner layers of the tracker, while planar sensors will be used in the other layers. In this Thesis, a complete characterisation of 3D and planar pixel detectors is presented. The studies are performed at the INFN and CERN laboratories and in several test beam experiments at DESY. My work was crucial for the characterisation of the detectors both before and after irradiation, to verify that both the sensor and the readout chip are able to resist the high fuences expected at the HL-LHC with a minimum loss of performance. The studies I made demonstrated that planar pixel detectors reach a hit detection effciency of over 99% at a bias voltage of 600 V after an irradiation corresponding the fuence expected after ten years of operations of HL-LHC. 3D pixel detectors have not been tested to these fuences yet (new test beams in the near future will target their characterisation), but are expected to reach similar effciencies with far lower bias voltages, around 150 V. Having high efficiencies at relatively low bias voltages leads to a lower power consumption and reduces the susceptibility to sparking issues with respect to planar sensors. Both of these features are invaluable in the inner tracker environment. Among the studies presented in this Thesis, the spatial resolution of 3D and planar pixel detectors was thoroughly evaluated. Non-irradiated 3D and planar pixel detectors have shown remarkable spatial resolution, down to 2 µm or 5 µm depending on the pixel pitch. The results presented in this Thesis will contribute significantly to the choice of the pixel sensors to be used in the future CMS Inner Tracker. The second part of this Thesis focuses on the measurement of the Vector Boson Fusion (VBF) Higgs production mechanism in the H->WW decay channel. A particle consistent with the SM Higgs boson was observed in 2012 by the CMS and ATLAS collaborations at the LHC. After the discovery, precision on the measure- ment of this new particle properties and interactions has progressed as more data were collected. Currently, all production processes have been observed in one or more decay channels or via combination of several decay channels, with no significant deviations with respect to the SM prediction. However, the VBF mechanism, being at the heart of the electroweak symmetry breaking, needs to be studied with ever-improving analysis techniques while waiting for additional data to reduce the statistical uncertainty. Such a rare process is sensitive to new physics phenomena and allows to set stringent constraints on the compatibility of the Higgs boson itself with the SM. The cross section for the VBF mechanism in proton-proton collisions at a center of mass energy of 13 TeV has been measured by CMS in several Higgs decay channels. The H->WW decay, thanks to its large branching ratio, is ideal for the observation of this production process. The most recent CMS analysis in the H ! WW decay channel, however, mainly focused on the measurement of the global production cross section: the analysis was not optimized with respect to the VBF production mode. In this Thesis, a multivariate analysis was implemented in order to enhance the sensitivity of the measurement of the VBF mechanism in the H->WW decay channel. In particular, a Deep Neural Network (DNN) was developed in order to isolate the signal events from the background, which is mainly composed by top quarks events, non-resonant WW and gluon fusion Higgs boson production mechanism. The DNN yields four scores for each event, corresponding to the degree of compatibility either with the signal or one of the main backgrounds. These scores are then combined and used in the fitting procedure. This innovative approach was necessary because one of the main backgrounds of this analysis is another Higgs production process, therefore making it diffcult to tackle this analysis in a simple signal versus background paradigm. This study is based on the whole Run-2 dataset, collected from 2016 to 2018 with the CMS experiment. The VBF Higgs production mechanism is observed with a significance of 3.6 standard deviations, resulting in the first evidence of this production mechanism in the WW decay channel with the CMS experiment. Moreover, the measured cross section is compatible with the Standard Model within one standard deviation. This work established an analysis strategy that will be used for the LHC Run-3 and possibly beyond it.

For the X-ray astronomy project Advanced Telescope for High ENergy Astrophysics (Athena) wafer-scale DEpleted P-channel Field Effect Transistor (DEPFET) detectors are proposed as Focal Plane Array (FPA) for the Wide Field Imager (WFI). Prototype structures with different pixel layouts, each consisting of 64 x 64 pixels, were fabricated to study four different DEPFET designs. This thesis reports on the results of the electrical and spectroscopic characterization of the different DEPFET designs. With the electrical qualification measurements the transistor properties of the DEPFET structures are investigated in order to determine whether the design intentions are reflected in the transistor characteristics. In addition, yield and homogeneity of the prototypes can be studied on die, wafer and batch level for further improvement of the production technology with regard to wafer-scale devices. These electrical characterization measurements prove to be a reliable tool to preselect the best detector dies for further integration into full detector systems. The spectroscopic measurements test the dynamic behavior of the designs as well as their spectroscopic performance. In addition, it is revealed how the transistor behavior translates into the detector performance. This thesis, as the first systematic study of different DEPFET designs on die and detector level, shows the limitations of the current DEPFET assessment methods. Thus, it suggests a new concise characterization procedure for DEPFET detectors as well as guidelines for expanded testing in order to increase the general knowledge of the DEPFET. With this study of four different DEPFET variants not only designs suitable for Athena mission have been found but also improvement impulses for the starting wafer-scale device production are provided.

碩士
國立清華大學
工程與系統科學系
102
From the early times of the electron microscopy, film has been used for recording the electron images in TEM. A standard detector option commonly used instead of film is the charged coupled device (CCD), which was first used in electron microscopy in the late 1980s. The CCD systems have enabled the immediate access to images in real-time, and have significantly increased throughput in the electron microscopy field. The CCD camera system is an indirect imaging detection system because the CCD will suffer from radiation damage and charge saturation during direct exposure of electron beam in TEM. A scintillator is thus needed to convert the electron image to a photonic image, which is then relayed to the CCD cameras for image acquisition. Hence, indirect imaging detection system have some inherent restrictions, including spatial and temporal resolution, efficiency and frame rate. In order to improve performance of electron detection systems, the application of silicon strip detector in TEM as a direct imaging systems was proposed. The application of silicon strip detector in TEM can meet the requirements for two-dimensional position sensitivity, spatial resolution and frame rate with direct sensing. Compared to pixel detector like CCD, silicon strip detector has advantages of simple structure, less number of readout circuits and lower manufacturing complexity. But silicon strip detector has one major issue, ghost images, which is unavoidable. If more than one particle hits the silicon strip detector, the measured particles position is no longer unambiguous and ghost hits appear. In this work, we proposed a direct electron detector with unique readout metal strip arrangement, called silicon strip-pixel detector, to relieve multi-hits induced ghost image problems and greatly reduce the number of readout circuits compared with pixel detector. Owing to characteristics integration of silicon strip detector and pixel detector, it was called silicon strip-pixel detector. The silicon strip-pixel detector is fabricated by single-sided process on high resistivity n-doped 4 inch diameter silicon wafer with a thickness of 250 μm. The pitch of strips determines the spatial resolution of the detector. The performance of P-N junction can be obtained by fine-tuning of implantation energy, dose and annealing parameters. The guard rings are designed around the active area to reduce leakage current. The dark current of silicon strip-pixel detector is 0.3 pA, breakdown voltage is -120 V and leakage current is 2.3 μA. The detector with guard rings design can greatly reduce leakage current with 3.48 times and increase breakdown voltage of 75 V compared with detector without guard ring. The threshold energy of detector sensitivity is 5 keV, minimum signal current is 15.1 pA and signal to noise ratio (in full depletion) is 3.12. According to theoretical calculations, charge collection efficiency is 0.703, DQE is 0.016 and theoretical frame rate is 0.7 ms per frame. The strip-pixel detector can meet the generic requirements for direct electron imaging system and has great potential to be used as imaging sensor in TEM.

The high luminosity phase of the LHC, poised to start taking data in 2027, aims to increase the instantaneous luminosity of the machine to 7.5 x 10³⁴ cm^-2 s^-1. This will make it possible for experiments at CERN to make higher precision measurements on known physics phenomenon as well as to search for “new physics”. However, this motivates the need for hardware upgrades at the various experiments in order to ensure compatibility with the HL-LHC. This thesis describes some of the efforts to upgrade the inner-most layers of the Compact Muon Solenoid, namely the CMS silicon pixel tracking detector.

Silicon sensors used to track particles are installed in the detector as part of a pixel sensor module. Modules consist of a silicon sensor-readout chip assembly that is wire-bonded to an HDI, or High Density Interconnects to provide power and signals.

As part of the upgrade, 2,541 modules need to be assembled delicately and identically with alignment error margins as low as 10 microns. Assembly will be across three production sites in clean rooms to avoid dust and humidity contamination.

In addition, the modules need to survive high magnetic fields and extended close-range radiation as part of the HL-LHC.

In line with this effort, new materials and assembly procedures able to sustain such damage are investigated. Techniques to assemble modules are explored, specifically precision placing of parts with a robotic gantry and techniques to protect wirebonds. This is followed by a discussion of the accuracy and repeatability.