B. Carbone

Silicon Photomultiplier Technology at STMicroelectronics

In this paper we present the results of the first electrical and optical characterization performed on 1 mm2 total area Silicon Photomultipliers (SiPM) fabricated in standard silicon planar technology at the STMicroelectronics Catania R&D clean room facility. The device consists of 289 microcells and has a geometrical fill factor of 48%. Breakdown voltage, gain, dark noise rate, crosstalk, photon detection efficiency and linearity have been measured in our laboratories. The optical characterization has been performed by varying the temperature applied to the device. The results shown in the manuscript demonstrate that the device already exhibits relevant features in terms of low dark noise rate and inter-pixel crosstalk probability, high photon detection efficiency, good linearity and single photoelectron resolution. These characteristics can be considered really promising in view of the final application of the photodetector in the Positron Emission Tomography (PET).

Timing Performances of Large Area Silicon Photomultipliers Fabricated at STMicroelectronics

In this paper the results of charge and timing resolution characterization realized at Fermi National Accelerator Laboratory (Fermilab) on 3.5 × 3.5 mm2 Silicon PhotoMultipliers fabricated at STMicroelectronics Catania R&D clean room facilities are presented. The device consists of 4900 microcells and has a geometrical fill factor of 36%. Timing measurements were realized at different wavelengths by varying the overvoltage and the temperature applied to the photodetector. The results shown in this manuscript demonstrate that the device, in spite of its large area, exhibits relevant features in terms of low dark current density, fast timing and very good single photoelectron resolution. All these characteristics can be considered very appealing in view of the utilization of this technology in applications requiring detectors with high timing and energy resolution performances.

Electro-Optical Performances of p-on-n and n-on-p Silicon Photomultipliers

Silicon photomultipliers (SiPMs) are fabricated in two different configurations: p-on-n and n-on-p junctions. p-on-n SiPMs turn out to be more suitable for application in positron emission tomography (PET), due to their higher sensitivity in blue wavelength range where common PET scintillators have their emission spectrum. In this paper, we report on the electro-optical performances of the first p-on-n SiPMs manufactured at STMicroelectronics, Catania. The results obtained on these devices are compared with those measured on the standard n-on-p technology.

A large area cosmic ray detector for the inspection of hidden high-Z materials inside containers

Traditional inspection methods are of limited use to detect the presence of fissile (U, Pu) samples inside containers. To overcome such limitations, prototypes of detection systems based on cosmic muon scattering from high-Z materials are being tested worldwide. This technique does not introduce additional radiation levels, and each event contributes to the tomographic image, since the scattering process is sensitive to the charge of the atomic nuclei being traversed. A new Project, started by the Muon Portal Collaboration, plans to build a large area muon detector able to reconstruct muon tracks with good spatial and angular resolution. Experimental tests of the individual detection modules are already in progress. The design and operational parameters of the muon portal under construction are here described, together with the preliminary simulation and test results. Due to the large acceptance of the detector for cosmic rays, coupled to the good angular reconstruction of the muon tracks, it is also planned to employ such detector for cosmic ray studies, complementing its detection capabilities with a set of trigger detectors located some distance apart, in order to measure multiple muon events associated to extensive air showers.

Thin Metal Film Ni 2 Si/4H—SiC Vertical Schottky Photodiodes

Photodetection in the ultraviolet (UV) region has drawn extensive attention owing to its various applications in industrial, environmental, and even biological fields. In this letter, we report on the morphological and electro-optical characteristics of continuous thin metal film Ni2Si/4H-SiC photodiodes properly designed for the realization of an extremely compact digital sensor suited to measure the total sun UV radiation for environmental UV light monitoring.

Silicon Photomultipliers for nuclear medical imaging applications

In this contribution we present the results of the first morphological and electro-optical characterization of Silicon Photomultipliers (SiPM) for nuclear medical imaging applications fabricated in standard silicon planar technology at the STMicroelectronics Catania R&D clean room facility. We have improved our previous Geiger Mode Avalanche Photodiodes (GMAP) technology in order to realize a photodetector with relevant features in terms of single-photoelectron resolution, timing and photon detection efficiency. The performances of our devices, investigated in several experimental conditions and here reported make ST-SiPM suitable in many applications like for example PET (Positron Emission Tomography).

Design and development of a fNIRS system prototype based on SiPM detectors

Functional Near Infrared Spectroscopy (fNIRS) uses near infrared sources and detectors to measure changes in absorption due to neurovascular dynamics in response to brain activation. The use of Silicon Photomultipliers (SiPMs) in a fNIRS system has been estimated potentially able to increase the spatial resolution. Dedicated SiPM sensors have been designed and fabricated by using an optimized process. Electrical and optical characterizations are presented. The design and implementation of a portable fNIRS embedded system, hosting up to 64 IR-LED sources and 128 SiPM sensors, has been carried out. The system has been based on a scalable architecture whose elementary leaf is a flexible board with 16 SiPMs and 4 couples of LEDs each operating at two wavelengths. An ARM based microcontroller has been joined with a multiplexing interface, able to control power supply for the LEDs and collect data from the SiPMs in a time-sharing fashion and with configurable temporal slots. The system will be validated by using a phantom made by materials of different scattering and absorption indices layered to mimic a human head. A preliminary characterization of the optical properties of the single material composing the phantom has been performed using the SiPM in the diffuse radial reflectance measurement technique. The first obtained results confirm the high sensitivity of such kind of detector in the detection of weak light signal even at large distance between the light source and the detector.

Design of a large area tomograph to search for high-Z materials inside containers by cosmic muons

In recent years the need to have a better control of potentially dangerous materials across the borders has raised the opportunity to search for alternative detection techniques. In particular, to detect the presence of hidden high-Z materials inside containers, traditional techniques based on X-rays or neutron scattering are of limited use, and prototypes of detection systems based on cosmic muon scattering from high-Z materials are being tested worldwide to overcome these limitations. The use of this method is particularly suited to this aim, since it does not introduce additional radiation levels to the already existing natural dose. Since the technique is based on the scattering process of muons and not on their absorption, each event may in principle contribute to produce the tomographic image. A new Project has recently started by the Muon Portal Collaboration, which plans to build a large area muon detector, able to reconstruct muon tracks with good spatial and angular resolution. The design and operational parameters of the tomograph under construction are here described, together with preliminary simulation and test results of the individual detection modules. Due to the large acceptance of the detector for cosmic rays, coupled to the good angular reconstruction of the muon tracks, it is also planned to employ such detector in the future for cosmic ray studies, complementing its detection capabilities with a set of trigger detectors located some distance apart, in order to measure multiple muon events associated to extensive air showers.

The Muon Portal Project: Development of an innovative scanning portal based on muon tomography

The Muon Portal is a recent Project [1] which aims at the construction of a 18 m2 tracking detector for cosmic muons. This apparatus has been designed as a real-size prototype to inspect containers using the muon tomography technique, i.e. by measuring the deflection of muons when traversing high-Z materials. The detection setup is based on eight position-sensitive X-Y planes, four placed below and four above the volume to be inspected, with good tracking capabilities for charged particles. The detection planes are segmented into strips of extruded plastic scintillators with WLS fibres to transport the light produced in the scintillator material to the photo-sensors (SiPMs) at one of the fibre ends. Detailed GEANT4 simulations have been carried out under different scenarios to investigate the response of the apparatus. The tomographic images are reconstructed by tracking algorithms and suitable imaging software tools. Simulations have demonstrated the possibility to reconstruct a 3D image of the volume to be inspected in a reasonable amount of time, compatible with the requirement of a fast inspection technique. The first two of the 48 detection modules are presently under construction.

Enhanced blue-light sensitivity P on N Silicon Photomultipliers

Silicon Photomultipliers (SiPMs) have known a fast development in recent years, due to their excellent single photon detection capability and very fast timing response. In this paper we present the results of the electro-optical characterization performed on the first STMicroelectronics P on N SiPMs prototypes properly designed for their possible application in Positron Emission Tomography (PET). We will show that the performances of the new devices are extremely promising in terms of high photon detection efficiency and fast timing response in blue wavelength range.