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A design modification to an existing 3D-trenched pixel detector is proposed, aimed at animproved fabrication yield. The device concept is studied and its performance is evaluatedby TCAD simulations, in comparison to the existing one. Although the modified designfeatures a less uniform electric field distribution, it is still expected to yield a very good timingperformance and high radiation tolerance, also exploiting charge multiplication effects.

The objective of the CERN RD50 Collaboration is the development of radiation hard semiconductor detectors for very high luminosity colliders, particularly to face the requirements of a possible upgrade scenario of the LHC.This document reports the status of research and main results obtained after the sixth year of activity of the collaboration.

3D Silicon sensors fabricated at FBK-irst with the Double-side Double Type Column (DDTC) approach and columnar electrodes only partially etched through p-type substrates were tested in laboratory and in a 1.35 Tesla magnetic field with a 180GeV pion beam at CERN SPS. The substrate thickness of the sensors is about 200um, and different column depths are available, with overlaps between junction columns (etched from the front side) and ohmic columns (etched from the back side) in the range from 110um to 150um. The devices under test were bump bonded to the ATLAS Pixel readout chip (FEI3) at SELEX SI (Rome, Italy). We report leakage current and noise measurements, results of functional tests with Am241 gamma-ray sources, charge collection tests with Sr90 beta-source and an overview of preliminary results from the CERN beam test., Comment: 8 pages, 8 figures, presented at RD09 - 9th International Conference on Large Scale Applications and Radiation Hardness of Semiconductor Detectors, 30 September - 2 October 2009, Florence, Italy

3D Si radiation sensors came along with extreme radiation hard properties, primarily owing to the geometrical advantages over planar sensors where electrodes are formed penetrating through the active substrate volume. Among them: reduction of the inter-electrode distance, lower depletion voltage requirement, inter-columnar high electric field distribution, lower trapping probability, faster charge collection capability, lower power dissipation, and lower inter-pitch charge sharing. Since several years, FBK has developed 3D sensors with a double-sided technology, that have also been installed in the ATLAS Insertable B-Layer at LHC. However, the future High-Luminosity LHC (HL-LHC) upgrades, aimed to be operational by 2024, impose a complete swap of current 3D detectors with more radiation hard sensor design, able to withstand very large particle fluences up to 2×1016 cm-2 1-MeV equivalent neutrons. The extreme luminosity conditions and related issues in occupancy and radiation hardness lead to very dense pixel granularity (50×50 or 25×100 µm2), thinner active region (~100 µm), narrower columnar electrodes (~5µm diameter) with reduced inter-electrode spacing (~30 µm), and very slim edges (~100 µm) into the 3D pixel sensor design. This thesis includes the development of this new generation of small-pitch and thin 3D radiation sensors aimed at the foreseen Inner Tracker (ITk) upgrades at HL-LHC.

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.

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.

Recent advancements in biomedical research and imaging applications have ignited an intense interest in single-photon detection. Along with single-photon resolution, nanosecond or sub-nanosecond timing resolution and high sensitivity of the device must be achieved at the same time. Single- Photon Avalanche Diodes (SPADs) have proved their prospectives in terms of shot-noise limited operation, excellent timing resolution and wide spec- tral range. Nonetheless, the performance of recently presented SPAD based arrays has an issue of low detection efficiency by reason of the area on the substrate occupied by additional processing electronics. This dissertation presents the design and experimental characteriza- tion of a few compact analog readout circuits for SPAD based arrays. Tar- geting the applications where the spatial resolution is the key requirement, the work is focused on the circuit compactness, that is, pixel fill factor re- finement. Consisting of only a few transistors, the proposed structures are remarkable for a small area occupation. This significant advancement has been achieved with the analog implementation of the additional circuitry instead of standard digital approach. Along with the compactness, the dis- tinguishing features of the circuits are low power consumption, low output non-linearity and pixel-to-pixel non-uniformity. In addition, experimental results on a time-gated operation have proved feasibility of a sub-nanosecond time window.

In the last several years, both scientific and industrial community have shown an increasing interest in range imaging due to its potential use in various application domains such as robotics, vehicle safety, gaming, mobile applications as well as many others. Among the diversity of techniques available for range detection, Time-of-Flight (TOF) offers advantages in terms of compact system realization, good performance and low required computational power. Recent works have shown a trend towards higher resolutions, with a consequent reduction of pixel size, higher modulation frequencies and demodulation contrast to allow a higher distance precision. In this thesis we propose a new concept of range camera exploiting linear-mode avalanche photodiodes as in-pixel demodulating detectors. Due to photocurrent gain modulation, avalanche photodiodes can combine optical sensing and light signal demodulation in a single device. The main advantage of the avalanche photodiode implementation is the possibility to operate at high frequencies due to its very wide bandwidth that, in turn, influences the precision in distance measurement. In a first stage, the concept was experimentally validated on single pixel structures. These measurement results encouraged the implementation of a time-of-flight image sensor. A 64x64 pixel array has been designed and fabricated in a 0.35um standard CMOS technology. The pixel pitch is 30um with a fill-factor of 25.7%. Demodulation contrast exceeds 85% at 25MHz modulation frequency. A 3D camera system demonstrates best precision of 1.9cm and a 3D frame rate of 200fps. Additional tests performed on single pixels have shown demodulation contrast as high as 80% measured at 200MHz modulation frequency.

Gamma-ray and Fluorescence Lifetime Spectroscopies are driving the development of non-imaging silicon photon sensors and, in this context, Silicon Photo-Multipliers (SiPM)s are leading the starring role. They are 2D array of optical diodes called Single Photon Avalanche Diodes (SPAD)s, and are normally fabricated with a dedicated silicon process. SPADs amplify the charge produced by the single absorbed photon in a way that recalls the avalanche amplification exploited in Photo-Multiplier Tubes (PMT)s. Recently 2D arrays of SPADs have been realized also in standard CMOS technology, paving the way to the realization of completely custom sensors that can host ancillary electronic and digital logic on-chip. The designs of scientific apparatus have been influenced for years by the bulky PMT-based detectors. An overwhelming interest in both SiPMs and CMOS SPADs lies in the possibility of displacing these small sensors realizing new detectors geometries. This thesis examines the potential deployment of SiPM-based detector in an apparatus built for the study of the Time-Of-Flight (TOF) of Positronium (Ps) and the displacement of 2D array of CMOS SPADs in a lab-on-chip apparatus for Fluorescence Lifetime Spectroscopy. The two design procedures are performed using Monte-Carlo simulations. Characterizations of the two sensor have been carried out, allowing for a performance evaluation and a validation of the two design procedures.

In this thesis we present a novel BJT (Bipolar Junction Transistor) detector that was developed and optimized for alpha particle and radon detection and monitoring. Using functional tests, we have shown that BJT detector operated with floating base can efficiently be used for the purpose of alpha-particle and, consequently, radon gas detection. Basing on these results, we have designed and fabricated a new batch of optimized BJT detectors. The results of electrical and functional characterization of newly fabricated detectors were presented in this work. Fabricated detectors observed high gain, low leakage currents and good detection properties. In parallel to the development of the detector, we successfully designed and implemented FPGA-based readout electronics ALPHADET. Design of the board and results of electrical tests of the board along with extensive data acquired by BJT detectors coupled to the board are presented in the thesis as well. The results of radon tests acquired using BJT detector confirmed that the detector can be successfully used in systems for radon monitoring.

Due to the increasing demand for 3D vision systems, many efforts have been recently concentrated to achieve complete 3D information analogous to human eyes. Scannerless optical range imaging systems are emerging as an interesting alternative to conventional intensity imaging in a variety of applications, including pedestrian security, biomedical appliances, robotics and industrial control etc. For this, several studies have reported to produce 3D images including stereovision, object distance from vision system and structured light source with high frame rate, accuracy, wide dynamic range, low power consumption and lower cost. Several types of optical techniques for 3D imaging range measurement are available in the literature, among them one of the most important is time-of-flight (TOF) principle that is intensively investigated. The third dimension, i.e. depth information, can be determined by correlating the reflected modulated light signal from the scene with a reference signal synchronous with the light source modulation signal. CMOS image sensors are capable of integrating the image processing circuitry on the same chip as the light sensitive elements. As compared to other imaging technologies, they have the advantages of lower power consumption and potentially lower price. The merits make this technology competent for the next-generation solid-state imaging applications. However, CMOS process technologies are developed for high-performance digital circuits. Different types of 3D photodetectors have been proposed for three-dimensional imaging. A major performance improvement has been found in the adoption of inherently mixing detectors that incorporate the role of detection and demodulation in a single device. Basically, these devices use a modulated electric field to guide the photo generated charge carriers to different collection sites in phase with a modulation signal. One very promising CMOS photonic demodulator based on substrate current modulation has recently been proposed. In this device the electric field penetrates deeper into the substrate, thus enhancing the charge separation and collection mechanism. A very good sensitivity and high demodulation efficiency can be achieved. The objective of this thesis has been the design and characterization of a Current Assisted Photo mixing Demodulator (CAPD) to be applied in a TOF based 3D CMOS sensing system. At first, the experimental investigation of the CAPD device is carried out. As a test vehicle, 10×10 pixel arrays have been fabricated in 0.18µm CMOS technology with 10×10 µm2 pixel size. The main properties of CAPD devices, such as the charge transfer characteristic, modulation contrast, noise performance and non-linearity problem, etc. have been simulated and experimentally evaluated. Experimental results demonstrate a good DC charge separation efficiency and good dynamic demodulation capabilities up to 45MHz. The influence of performance parameters such as wavelength, modulation frequency and voltage on this device is also discussed. This test device corresponds to the first step towards incorporating a high resolution TOF based 3D CMOS image sensor. The demodulator structure featuring a remarkably small pixel size 10 × 10 µm2 is used to realize a 120 × 160 pixel array of ranging sensor fabricated in standard 0.18µm CMOS technology. Initial results demonstrate that the demodulator structure is suitable for a real-time 3D image sensor. The prototype camera system is capable of providing real-time distance measurements of a scene through modulated-wave TOF measurements with a modulation frequency 20 MHz. In the distance measurement, the sensor array provides a linear distance range from 1.2m to 3.7m with maximum accuracy error 3.3% and maximum pixel noise 8.5% at 3.7m distance. Extensive testing of the device and prototype camera system has been carried out to gain insight into the characteristics of this device, which is a good candidate for integration in large arrays for time-of-flight based 3D CMOS image sensor in the near future.

Reliability of RF-MEMS devices is one of the main concerns of the engineers and scientists dealing with such type of devices. In particular, there are plenty of studies and investigations devoted to protection of devices from dierent kind of failures related to their operating conditions. The adhesion of movable parts of switches onto the actuation electrode, also referred to as stiction, due to accumulated charge or to micro-welding phenomenon, are the most common types of RF-MEMS failures. This work presents a novel effective heat-based mechanism that enables to release a stuck component. Such mechanism can be embedded within the switches of any topology and it has no influence on the normal behavior of the device.

Time-resolved fluorescence measurements enable the study of structure of molecular systems and dynamical processes inside them. This is possible because of a very high sensitivity of fluorescence lifetime to the physical and chemical properties of micro-environment in which fluorophores are situated. However, proper detection of the fluorescence lifetime is a challenging task, due to the fact that the fluorescence decay time of commonly used fluorophores lies in a nanosecond range. This puts strict requirements on the parameters of the fluorescence detectors. The features of single-photon avalanche diodes (SPAD) make these optical detectors a good alternative to conventional photomultiplier tubes and micro-channel plates. CMOS technology allows cointegration of a SPAD and electronic circuits on the same substrate and provides advantages in time resolution and noise characteristics. Monolithic integration of signal processing circuits and detectors on the same chip allows using such detectors without additional external hardware. New SPAD sensors with improved characteristics are produced every year. However, the designers consider various performance metrics while the importance of each particular detector characteristic depends on its application. Therefore, the validation and optimization of SPAD characteristics should be performed in a close connection with the analysis of a specific system, wherein this detector will be used. This work was aimed at developing of a model able to describe a typical fluorescence experiment with SPAD-based detector. The model simulates all essential parts of the fluorescence experiment starting from the light emission, through photo-physical processes occurring inside a bio-sample, to a detector itself and read-out electronics. The ability of the developed model to simulate various light sources (laser and micro-LED), fluorescence measurement techniques (time-correlated single photon counting and time-gating) was verified. The simulated results were in good agreement with the experimental data and the model proved its flexibility. Furthermore, the model provided the explanation of the distortions in experimental fluorescent curves measured under a very high ambient light when pile-up effects appear. Finally, a set of virtual experiments were established to investigate the influence of noisy pixels in SPAD array on a lifetime estimation and to study the feasibility of time-filtering instead of conventional optical filtering. Simulation results are in good agreement with data available in literature.