THE SILICON PHOTOMULTIPLIER:AN IN-DEPTH ANALYSIS IN THE CONTINUOUS WAVE REGIME

The Silicon Photomultiplier (SiPM) is a novel solid state photon counting detector consisting of a parallel array of avalanche photodiodes biased beyond their breakdown voltage. It has known a fast development in the last few years as a possible alternative to vacuum photomultiplier tubes (PMTs) and conventional avalanche photodiodes (APDs). Indeed, current research in photodetectors is directed toward an increasing miniaturization of the pixel size, thus both improving the spatial resolution and reducing the device dimensions. SiPMs show high photon detection efficiency in the visible and near infrared range, low power consumption, high gain, ruggedness, compact size, excellent single-photon response, fast rise time and reduced sensitivity with temperature, voltage fluctuations, and magnetic fields. Furthermore, solid-state technology owns the typical advantages of the planar integration process, therefore, they can be manufactured at low costs and with high reproducibility. SiPMs performances in photon counting regime have been deeply investigated in literature, using picosecond pulsed lasers. In this regime, they can be used in applications like positron emission tomography, magnetic resonance imaging, nuclear physics instrumentation, high energy physics. An optical characterization performed via continuous wave (CW) sources has seldom been reported even though this kind of excitation seems to be very useful in several fields such as low power measurements, near-infrared spectroscopy and immunoassay tests. In this Thesis, I perform an electrical and optical analysis of two novel classes of SiPMs in the CW regime. After a brief introduction about the SiPM operating principle, parameters and properties (Chapter 1), I describe my responsivity measurements made with an incident optical power down to tenths of picowatts, monitoring the temperature of the device packages, and on a spectrum ranging from ultraviolet to near infrared (Chapter 2). These measurements allowed to define an innovative criterion to establish the conditions necessary for the device to be usable in CW regime. Chapter 3 continues with an investigation of the SiPM signal-to-noise ratio. Measurements employed a 10 Hz equivalent noise bandwidth, around a tunable reference frequency in the range 1 - 100 kHz, and were performed varying the applied bias and the temperature of the SiPM package. These results were compared with similar measurements performed on a PMT. Once the SiPM is characterized, Chapter 4 reports an innovative application: an optical characterization of a class of photonic crystals infiltrated with a new ethanol responsive hydrogel employing the SiPM as a reference photodetector. This activity shows innovative developments for the ethanol sensing to be applied into inexpensive and minimally invasive breathalyzers. Finally, Appendix A shows an electro-optical characterization of a novel class of Silicon Carbide (SiC) vertical Schottky UV detectors. I performed responsivity measurements as a function of the wavelength and the applied bias, varying the temperature of the SiC package, in the 200 - 400 nm range. The results of this work show a new approach to investigate the SiPM capabilities, the CW regime, demonstrating its outstanding performances and innovative applications. This Thesis was made in collaboration with the "Advanced Sensors Development Group" of STMicroelectronics and partially supported by the Project HIGH PROFILE (HIGH-throughput PROduction of FunctIonaL 3D imagEs of the brain), which is funded by the European Community under the ARTEMIS Joint Undertaking scheme.