KEYWORDS: Signal to noise ratio, Avalanche photodetectors, Optical amplifiers, Silicon, Interference (communication), Amplifiers, Silicon photomultipliers, Resistors, Information operations, Temperature metrology
We report on our Signal-to-Noise Ratio (SNR) measurements carried out, in the continuous wave regime, at different frequencies and at various temperatures, on a novel class of silicon photomultipliers (SiPMs) fabricated in planar technology on silicon p-type substrate. SNR of SiPMs is given by the ratio of the photogenerated current, filtered and averaged by a lock-in amplifier, and the Root Mean Square (RMS) deviation of the same current. In our measurements, we have employed a 10 Hz equivalent noise bandwidth, around the lock-in amplifier reference frequency. The measured noise takes into account the shot noise, resulting from the photocurrent and the dark current, while background light is not present in our setup. We have found that the SNR is independent from frequency in the evaluated range 1 - 100 kHz. Our measurements highlight a quasi-flat trend of the SiPM SNR up to an overvoltage of about 5 V (with respect to the breakdown voltage of 28.0 V). At higher overvoltages (OV), we have observed a SNR decrease, mainly because of the strong increase of the shot noise. We have also performed a comparison between the SiPM and the PhotoMultiplier Tube (PMT) SNR as a function of the temperature of the SiPM package and at different bias voltages. Our results show the outstanding performance of this novel class of SiPMs even without the need of any cooling system. Indeed, their SNR is only a few dBs below the PMT SNR at room temperature. Furthermore, cooling the SiPM at a package cell temperature of 3 °C, it reaches the PMT SNR values at room temperature despite the SiPM is biased in the range 28.7 – 33.5 V, while the PMT has a bias value up to 950 V.
We report on the design and the electro-optical characterization of a novel class of 4H-SiC vertical Schottky UV
detectors, based on the pinch-off surface effect and obtained employing Ni2Si interdigitated strips. We have measured, in
dark conditions, the forward and reverse I–V characteristics as a function of the temperature and the C–V characteristics.
Responsivity measurements of the devices, as a function of the wavelength (in the 200 – 400 nm range), of the package
temperature and of the applied reverse bias are reported. We compared devices featured by different strip pitch size, and
found that the 10 μm device pitch exhibits the best results, being the best compromise in terms of full depletion and
space-strip width ratio.
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.
We report the electrical and optical comparison, in continuous wave regime, of two novel classes of silicon
photomultipliers (SiPMs) fabricated in planar technology on silicon P-type and N-type substrate respectively.
Responsivity measurements have been performed with an incident optical power from tenths of picowatts to hundreds of
nanowatts and on a broad spectrum, ranging from ultraviolet to near infrared (340-820 nm).
For both classes of investigated SiPMs, responsivity shows flat response versus the optical incident power, when a preset
overvoltage and wavelength is applied . More in detail, this linear behavior extends up to about 10 nW for lower
overvoltages, while a shrink is observed when the reverse bias voltage increases. With regards to our responsivity
measurements, carried out in the abovementioned spectral range, we have found a peak around 669 nm for the N-on-P
and a peak at 417 nm for the P-on-N SiPM. A physical explanation of the all experimental results is also provided in the