Positron Emission Tomography (PET) scanners provide functional three-dimensional images of the body that are extremely useful in cancer and brain research. The goal of this work is the modeling, design and characterization of a CMOS-based photodetector for PET. To this aim, first a model for the energy resolution and coincidence resolution time (CRT) for digital, SPAD-based detectors is developed. Then, a top-to-bottom detector architecture is proposed, containing an innovative in-pixel com-pression technique that allows for high fill-factor (FF) and efficient readout. At the top-level of the architecture, an integrated discriminator monitors the photon flux for incoming gamma events, enabling an event-based readout scheme. The first complete implementation of this archi-tecture is described, the SPADnet-I sensor, which is composed by an 8×16 pixel array, each of around 0.6 × 0.6 mm2 with 720 SPADs, resulting in a pixel FF of 42.6%. The sensor can obtain the discrete photon flux estimation at up to 100 Msamples/s, which are used by the discriminator and also output at real-time. The complete characterization of the sensor is presented, and the best sensor configuration was found to be at 84% of the SPADs enabled (disabled starting with the highest DCR one), with 2 V SPAD excess bias and 150 ns integration time. This configuration results in an energy resolution of 10.8% and a CRT of 288 ps, the latter which was obtained with a new, hardware-friendly time of arrival (ToA) estimation algorithm, also described in this thesis. Finally, the sensor model, validated by the experimental results, is used to predict the perfor-mance of possible modifications in the sensor, and some design improvements are suggested for a future implementation of the architecture.

This doctorate thesis is focused on the design, fabrication and characterization of Micro Electro Mechanical System (MEMS) Vibrational Energy Harvesters (VEHs). The targeted field of application of such devices is the emerging Internet of Things (IoT), in particular for Ultra Low Power (ULP) autonomous applications. In order to realize the ubiquitous paradigm remote and distributed nodes have to be small and in high number. The power requirement of such nodes is generally satisfied by means of batteries, which require periodic replacement and so are not desirable in an autonomous system. To overcome this limitation devices able to harvest energy from the surrounding environment have been investigated. Among the different sources of energy that could be harvested, the vibrational one results promising due to its high power density and its spreading in most environments of interest. The devices developed convert the vibrational energy scattered in the environment into electrical energy by means of a piezoelectric material. The thesis presents studies on both the mechanical and the electric design of a MEMS piezoelectric VEH, with particular attention on multi-modal design. The thesis presents a novel multi-modal device able to extract energy from multiple resonances in a wider bandwidth. Such a design presents two enabling features for IoT application, a wider working band and the compactness, making it more attractive with respect to cantilever like devices.

Automatic monitoring of environments, resouces and human processes are crucial and foundamental tasks to improve people's quality of life and to safeguard the natural environment. Today, new technologies give us the possibility to shape a greener and safer future. The more specialized is the kind of monitoring we want to achieve, more tight are the constraints in terms of reliability, low energy and maintenance-free autonomy. The challenge in case of tight energy constraints is to find new techniques to save as much power as possible or to retrieve it from the very same environment where the system operates, towards the realization of energy neutral embedded monitoring systems. Energy efficiency and battery autonomy of such devices are still the major problem impacting reliability and penetration of such systems in risk-related activities of our daily life. Energy management must not be optimized to the detriment of the quality of monitoring and sensors can not be operated without supply. In this thesis, I present different embedded system designs to bridge this gap, both from the hardware and software sides, considering specific resource constrained scenarios as case studies that have been used to develop solutions with much broader validity. Results achieved demonstrate that energy neutrality in monitoring under resource constrained conditions can be obtained without compromising efficiency and reliability of the outcomes.

In recent years, Silicon Photomultipliers (SiPMs) have been increasingly used as photo-detectors in Positron Emission Tomography (PET) application, which is a nuclear imaging tech-nique that is used to accurately image biochemical processes inside the human body. A SiPM is composed by an array of parallel connected micro-cells of Single Photon Avalanche Diodes (SPADs), and can be classified mainly into two categories Digital-SiPMs (D-SiPMs) and Analog-SiPMs (A-SiPMs). In A-SiPMs, all the microcells share the same bias voltage and have a common readout line. Through custom manufacturing process, the performance of A-SiPMs can be exten-sively optimized. With respect to A-SiPMs, D-SiPMs are composed by many SPAD pixels, each one containing one SPAD and local front-end circuitry. The digital SiPM takes advantage of CMOS technology to perform a 1-b direct A/D conversion per SPAD thus providing a fully digi-tal implementation. On the other hand, SPADs fabricated in CMOS process typically suffer high noise since the critical SPAD implants can hardly be optimized by using the standard CMOS process flow. The main activities carried out within this PhD thesis have been focused on two critical as-pects relevant for the optimization of PET systems performance: (I) the improvement of the per-formance of SPAD in D-SiPMs and (II) the development of high-performance A-SiPM readout application specific integrated circuit (ASIC). Concerning the first point, novel SPADs have been fabricated in CMOS 150-nm technology targeting at low noise, high sensitivity and excellent timing jitter. Three structures with different shapes, geometries and diameters, have been implemented in three test chips. Measurement re-sults of one p+/n-well SPAD array show a 0.4Hz/µm2 dark count noise, 0.85% afterpulsing for a dead time of 150ns at 3V excess bias. The photon detection probability is about 31% at 450nm wavelength at 5V excess bias. The SPAD exhibits a timing jitter of 82ps (FWHM) under a blue laser, which is potentially suitable for D-SiPMs in PET application. The second objective of this PhD work was to develop A-SiPM readout ASIC for PET appli-cation. To utilize the high intrinsic time resolution of A-SiPMs, the development of specialized, highly integrated readout electronics is required. Therefore, two ASICs, first chip with test struc-tures and 16 channels and the second chip with 32 channels, have been developed in 150-nm CMOS technology, with the aim of developing a compact A-SiPM module. The performance of the second chip has been validated by using 3 × 3 × 5 mm3 LYSO crystals coupled to 4 × 4 mm2 SiPMs (FBK-NUV-HD). The measurements show an energy resolution of 14.7% FWHM for the detection of 511 keV photons and the coincidence time resolution is 433ps (FWHM). To improve the timing resolution, part of the PhD work was carried on Stanford University, focused on char-acterization of A-SiPMs and analysis of noise contribution.

In the past few years, several interesting developments in microstructured solid-state thermal neutron detectors have been pursued. These devices feature high aspect-ratio cavities, filled with neutron converter materials, so as to improve the neutron detection efficiency with respect to coated planar sensors. In the framework of the INFN HYDE (HYbrid Detectors for neutrons) project, we have designed new microstructured sensors aimed at thermal and fast neutron detection. Owing to the different cross section, neutron imaging is complementary to X-ray imaging allowing for a high contrast in soft materials. To this purpose, the possibility to have pixelated neutron detectors compatible with existing read-out chips (e.g., those from the Medipix/Timepix family) is an important goal that was achieved in this thesis. In this thesis the entire workflow will be described in detail, covering the design, simulations, fabrication and characterization of 3D neutron detectors for imaging produced at FBK. As a related topic, new 3D sensors for the "Phase-2" upgrades at High Luminosity LHC have been developed, and some aspects relevant to the device simulation and characterization are also reported in this thesis.

Geiger-Mode avalanche photodiodes (GM-APDs) are diodes designed to operate at a reverse voltage that exceeds the breakdown voltage. Their ability to detect single photons combined with their excellent timing resolution make them ideal for applications in which low amplitude signals need to be detected with sub-ns timing resolution. In the research activity reported in this dissertation two different applications of Geiger-Mode Avalanche Photo Diode arrays have been analysed: a two-tier GM-APD array with in-pixel coincidence for particle tracking and a direct Time-of-Flight range meter with a SiPM-based receiver. The increasing complexity of particle tracking systems at collider experiments demands for high performance detectors with high granularity and position accuracy, low material budget and power consumption. Both Hybrid and monolithic detectors have been proposed as particle trackers. Hybrid detectors have the advantage of allowing an independent customization of sensors and readout electronics, but they exhibit a higher input capacitance that increases readout noise, thus limiting their minimum thickness (100 μm). Monolithic detectors have lower input capacitance, thus a better minimum detectable charge, with a charge time collection of few tens of ns. Thanks to their high gain, particle detectors based on GM-APDs have the potential for combining low material budget, low power consumption and an excellent timing resolution in the range of 100 ps. However, their use as particle tracking detectors has been prevented by their Dark Count Rate, since it is not possible to discriminate a particle-generated event from a dark event. To overcome this issue, the use of GM-APDs in coincidence has been proposed. The activity reported in this dissertation has been conducted in the framework of APiX2 and ASAP projects funded by Istituto Nazionale di Fisica Nucleare (INFN). A two-tier sensor based on avalanche detectors in coincidence has been designed and fabricated in standard 150 nm CMOS technology. A charged particle crossing both GM-APDs integrated in a pixel triggers an avalanche in both devices. The output signal from each detector reaches the coincidence electronics, that allows the device to discriminate the particle detection from dark events. The performance of the proposed detector has been evaluated in a complete electrical and functional characterization campaign. The feasibility to reduce the substrate thickness has been studied in some devices thinned down to 50 μm and 25 μm. The electronics for coincidence detection was also used to directly measure optical crosstalk, a phenomenon that is getting greater importance as stacked optical and image sensors are becoming common. The functional characterization of the APiX prototype was performed with a beta-source and an evaluation of the radiation hardness of the devices was carried out in an irradiation campaign with neutrons at the INFN Laboratori Nazionali di Legnaro (LNL). SiPMs take advantage of the characteristics of GM-APDs such as high sensitivity, high efficiency and very low time jitter, and overcome the problem related to the dead time connecting several sensitive elements in parallel, making them suitable for the simultaneous detection of more than one photon. The evaluation of a SiPM-based direct Time-of-Flight range meter has been performed at two different wavelengths: 405 nm and 810 nm. The set of measurement at 405 nm has been performed using a TCSPC module as acquisition system, while in the 810 nm measurements a low-cost FPGA-based TDC was used. The replacement of the TCSPC module with an FPGA-based TDC represents an important step towards the integration of a low-cost prototype thanks also to the low power consumption of the device. In order to evaluate the feasibility of a SiPM-based range meter in the NIR region, a collaboration with the Circuits and Systems Research Unit of the ITEE Faculty of the University of Oulu was established to set up a system with a GaAs/AlGaAs multiple quantum well laser diode with a spectral emission of 0.808 μm as transmitter and a NIR-HD SiPM with an enhanced efficiency for NIR photons recently developed at FBK as receiver. The evaluation was performed at high repetition rate (MHz range), for the perspective purpose to upgrade the system including a 2-axis scanning mirror to perform real-time 3D imaging.

A novel set up for Positronium Time Of Flight is proposed, using Silicon Photomultipliers (SiPMs) instead of Photomultiplier Tubes. The solution allows us to dramatically increase the compactness of the set up, thus improving the efficiency of 240%. Different configurations of SiPM+scintillators are characterized in order to find the best solution. Also, simulations are provided, together with preliminary tests in the particular application. A compact read-out board for the processing of up to 44 channels has been designed and tested.Further tests, expected in the near future, are needed in order to confirm the simulations and to build the final set up.

The introduction of the Brake By Wire is replacing the traditional mechanical control systems with ECUs and it is raising the need to reproduce feelings of eliminated static mechanical components (i.e. hydraulic fluids, pumps and cylinders). Thanks to electromechanical actuators and human-machine interfaces (i.e. active pedal) it is possible to reproduce such feelings and, therefore, arbitrarily change their features. In this way it will be possible to customize the pedal feelings and the vehicle deceleration needed depending on several factors (i.e. surrounding braking scenario, driver characteristics, race vs day-by-day driving condition). Since braking maneuvers are typically critical and involve the driver, the design and development of brake by wire system must start from the consideration of human factors in order to increase acceptance and braking effectiveness. The objective of this research was to redesign the pedal feelings, making them adaptable to the surrounding. Driver acceptance and braking effectiveness could be highly improved by means of adaptive pedal feelings. The starting points of this research were humans factors in the braking domain. Literature and relevant studies have been taken into consideration to put into evidence human mechanisms and behaviors during braking phases. On such basis, two main results have been found out: braking use cases and pedal feeling curves. With regard to the pedal feelings curves, 4 different pedal curves which describe both force on brake pedal travel and acceleration on brake pedal travel are designed. The pedal feeling depends on several factors like the pedal travel, the pedal idle travel, the effort, responsiveness, deceleration perceived, ease of balance (i.e. ease of modulation), gradual braking and so on. Regarding braking use cases, they are described by vehicle data as speed, acceleration, angles and relevant rates, engine rpm, gas and brake pedal position/speed and so on. These use cases have been clustered in order to meet the 4 pedal curves. The research continued on the implementation of a Matlab/Simulink/Stateflow model for the use case recognition. Basing on the vehicle data, the model is able to find out in which use case the vehicle is (parking, low speed maneuvers, emergency, downhill, and so on). Once it finds out the scenario, the model applies the most appropriate pedal feeling curve (both force feedback and deceleration needed). In the end, the model commands an EC brushless motor which is responsible of the changing of static springs force feedback of the pedal. The scenario recognition model has been validated through vehicle data on real road whereas the pedal feeling and relevant motor behaviors have been validate on bench tests.

Sustainable energy and energy harvesting has become a hot research area due to the shortage of fossil energy resources and burning fossil fuels release greenhouse gases in our environment, which is partaking in gradually increasing of surrounding temperature of our environment. Therefore, the penetration of various types of renewable/ distributed sources, onsite storage devices and DC powered appliances has recently focused attention towards DC power distribution in consumer grids to achieve the target of zero/positive energy buildings and communities. As compared to AC micro grid, many recent studies revealed that DC distribution has many advantages over the convectional AC distribution in term of high efficiency, integration of renewable/ distributed sources and storage locally. The objective of this dissertation is to propose reliable, cost-effective, sustainable, scalable DC consumer grid architecture which can integrate not only renewable/ distributed sources and storage, but also fully compatible with the convectional AC distribution network without any significant change or upgrade. In order to achieve this goal, we proposed the DC Transformer (DCT) enabled consumer grid model. The DC Transformer has been regarded as one of the most emerging technologies and it has many advantages over the convectional low frequency AC transformers such as high power density in small area, voltage regulation, reactive power compensation, fault detection and isolation etc. Apart from advantages, DCT required intelligent control algorithm and additional supervisory circuit makes it complicated and expensive. Therefore, in our proposed model we discussed the pros and cons of typical Solid-State transformer topologies already proposed and explained the topology used in the DCT transformer. Furthermore, in state of the art models, authors used three stages of grid operational modes, which is usually based on different factors such as the status of grid connections, State of charge of Battery storage and output power from locally available sources. However, we introduced four stages excluding buffering stage. All stages are depended upon the practical situations consumer grid may face during normal grid operations such as, DCT Isolation mode, if main grid and local generators are not available then how our proposed model would manage the locally available storage. Main grid interactive mode, we discussed the existing or convectional grid operational condition. In case of no local generator available and the AC main is the only source of power. Self-reliance grid operation, when the renewable energy sources are generating enough energy to fulfil demand side power requirements. Moreover, we explain the safest transition technique from grid connected mode to self-reliance mode without effecting overall grid stability and reliability, called buffer state. Power sharing mode, in this mode we discussed how the locally consumer grid would share surplus energy with adjacent consumer grids without effecting or compromising its own stability. The purpose of proposing critical operational modes and defining the rigid criteria between transitions of each mode is to operate whole grid flawlessly in any real time condition. Moreover, we introduced “Buffer stage†in between the grid connected and self-reliance mode to take into account that renewable sources are stochastic in nature and to avoid any grid stability issue. The operational modes are among key techniques of our proposed architecture and the detail contribution of our proposed model is mentioned in section $1.7.3$. Some practical issues related to the DC micro grid are also examined in detail, such as overall grid control algorithm, power management strategy, demand side management, fault isolation and rectification are highlighted and the solution of these issues also presented with detail simulation results. Furthermore, the state of art DC grid models are proposed for specific type of renewable source(s) such as PV, wind or combination of both. In our proposed architecture, we are not depending on any specific type of renewable and distributed source or storage. We proposed the standard interfaces for possible type of renewable /distributed sources, storage and grid connection. Therefore, by using the standard interface any type of the source and storage can be plug-n-play in PCmRC model. However, the main objectives are to maximize the exploitation of renewable-sources, to decrease reliance on fossil-fuel, to boost the overall efficiency of the grid by reducing the power-conversion losses and full management of end user demand in all possible forms. The simulation platform is designed in MATLAB/Simulink. Several types of case studies and simulation results show the effectiveness of the proposed power distribution and management model.

Terahertz gap corresponding to the frequency band of 0.3-3.0 THz is historically the last unexplored region of the electromagnetic spectrum left to be fully investigated. The major difficulty that has hampered the maturation of technologies operating in this region lies in the fact that much unlike its bordering millimeter and infrared regions, generation and detection of THz radiation is not trivial. Yet, such is the intriguing nature and properties of the terahertz radiations that the interest in this region has not faded. Infact, potential applications of THz based systems have emerged in various fields including biomedical imaging, safety and security, quality control and communication. Over the past decade, a lot of research work has been published with an aim to bridge this gap by both electronics and photonics based systems. While these attempts have succeeded to a certain extent, the available solutions either lack in terms of performance or are mostly bulky and difficult to integrate for portable and commercial purpose. This PhD dissertation focuses on the design and investigation of direct terahertz detectors which could be operated at room temperature and fabricated in standard silicon technologies, thereby making use of several advantages like high level of integration, low cost and small device size that these technologies have to offer. In particular, the emphasis is on developing and characterizing terahertz systems for imaging application by using field effect transistor devices as detectors. This objective is pursued in three parts. The first part (chapter 3) of the dissertation deals with the measurement and characterization challenges of terahertz systems. Unlike guided mode solutions, measurements of terahertz detectors and their systems require free space which presents several challenges due to atmospheric attenuation, spurious reflections and diffractions, beam shaping, and so on. Moreover, background noise is also significant considering that the detected signal is typically in the order of a few microvolts. In this regard, an overview of the most common techniques is given and a measurement methodology involving the use of a reference pyroelectric detector to measure the impinging input power and techniques for the evaluation of the detector under-test effective area is presented. The second part (chapter 4) is related to the investigation of variants of antenna-coupled field effect transistor and schottky barrier diode in standard 180 nm CMOS process as examples of direct detectors. During laboratory characterization, detection of terahertz radiation from schottky diode could not be achieved due to matching issues. Moreover, optimization of schottky diode by modifying its standard cell proved to be challenging as compared to field effect transistor, which can be optimized easily to enhance performance parameters and was therefore finally chosen as the preferred choice. The final part of the thesis (chapters 5 and 6) concerns with the implementation of analog readout interface to perform signal processing of detected terahertz signal. First, a single pixel consisting of on-chip antenna-coupled detector and a switched capacitor based filtering operation is designed and fabricated in 0.15Î1⁄4m process. The pixel is tested by performing both electrical and terahertz characterization, achieving high voltage responsivity value of 470 kV/W and a minimum NEP of 480 pW/sqrt (Hz). The interface architecture is highly repeatable and it can be used with any commercially terahertz source, even if its operation is limited by low modulation frequency. On the basis of the successful measurement results, an 8 x 6 terahertz array for real-time imaging application is fabricated in the same technology by modifying the interface architecture to make it power and area efficient.