Piero Giorgio Fallica

Preliminary radiation hardness tests of single photon Si detectors

Single photon Si detectors were fabricated by STMicroelectronics and fully characterized in standard operation conditions and after irradiations. Both single cells and arrays, of dimensions ranging from 5x5 up to 64x64, were electrically tested. The devices operation was studied as a function of the temperature from -25°C to 65°C varying the voltage over breakdown, from 5% up to 20% of the breakdown voltage before and after irradiation using both light ions, 10 MeV B ions to doses in the range 3×107 - 5×1010 cm-2, and X-rays irradiations in the range 0.5 - 20 krad(Si). Optical characterization was performed using a laser at 659 nm and opportunely chosen filters to vary the optical power. A strong difference in the radiation damage effect is observed for the two different irradiation sources. Ion irradiation, or better implantation, produces a damage preferentially sitting in the active device region, hence even at the lowest irradiation dose the device functionality is compromised, while at the highest dose the device is completely blind. On the other hand, X-rays produce damage in a low concentration, in fact it does not significantly affect the device dark current, only an increase in the leakage current under breakdown is observed. Hence the device functionality is preserved to doses up to 20 Krad(Si).

Potentialities of Silicon Photomultiplier.

The Silicon Photomultiplier (SiPM) is a novel pixelated photon detector able to detect single photon arrival with good timing resolution and high gain. In this work we present a complete study of the performances of different SiPMs produced by STMicroelectronics. Their potentialities and limits were identified using experimental measurements and electrical simulations performed both on single pixel and SiPM having up to ∼4000 pixels. SiPM was tested in different experiments such as photoluminescence emission measurement, lifetime measurement of semiconductor materials and light diffusion in highly scattering material in the near infrared spectrum showing its aptitude to replace PMT in those applications.

Solid state photodetectors for nuclear medical imaging applications

One of the most important challenges facing the entire globe is the trend towards an aging population. By 2045, there will be more people over 60 years old than younger than 15, thus raising from 600mln to 2bln worldwide. This will raise the number of patients with age-specific, chronic and degenerative diseases (e.g. cardio-vascular, cancer, diabetes, Alzheimers, Parkinsons). Minimally-invasive imaging technologies such as PET (Positron Emission Tomography) and MPI (Magnetic Resonance Imaging) play a vital role in detecting and tracking the evolution of the above mentioned illnesses and determining the strategy and the effectiveness of the prescribed therapies. So far the detection unit of PET equipment has been implemented using photomultipliers tubes (PMTs). A novel solid state photo-detector, the Silicon photomultiplier (SiPM), can replace the PMT, offering, among many other advantages, the possibility of PET/MRI combo equipment.