NUV-HD SiPMs with metal-filled trenches

In this paper we present the performance of a new SiPM that is sensitive to blue light and features narrow metal-filled trenches placed in the area around the single-photon avalanche diodes (SPADs) that allow an almost complete suppression the internal optical crosstalk. In particular, we show the benefits of this technological upgrade in terms of electro-optical SiPM performance when compared to the previous technology which had only a partial optical screening between the SPADs. The most relevant effect is the much higher bias voltage that can be applied to the new device before the noise diverges. This allows to optimize and improve both the photon detection efficiency and the single-photon time resolution. We also coupled the SiPMs to LYSO scintillators to verify the performance for possible application in Positron-Emission Tomography. Thanks to the better electro-optical features we were able to measure an improved coincidence time resolution. Furthermore, the optimal voltage operation region is substantially larger, making this SiPM more suitable for real system application where thousands of channels have to provide stable and reproducible performance

First Demonstration of the Use of LG-SiPMs for Optical Readout of a TPC

This paper describes a new method for optical readout of Time Projection Chambers (TPCs), based on the Linearly Graded Silicon Photomultiplier (LG-SiPM). This is a single photon-sensitive detector with excellent timing and 2D position resolution developed at Fondazione Bruno Kessler, Trento (FBK). The LG-SiPM produces time-varying voltage signals that are used to reconstruct the 3D position and energy of ionisation tracks generated inside the TPC. The TPC used in this work contained room-temperature CF$_4$ gas at a pressure of 100 mbar, with two THGEMs to produce secondary scintillation light. A collimated $^{241}$Am source (Q$_\alpha$ = 5.486 MeV) was used to produce the ionisation tracks. The successful reconstruction of these tracks is demonstrated, and the consistency of the methodology characterised through varying the geometry of the tracks within the TPC. Energy reconstruction and deposition studies are also described, demonstrating the feasibility of the LG-SiPM as a potential option for optical TPC readout.Comment: Various changes from previous version based on pre-publication revie

Characterization of Radiation Damage Effects of Protons and X-rays in FBK Silicon Photomultipliers

SiPMs have been employed in a growing number of applications, like medical imaging, LiDAR, etc. They are quickly replacing photomultiplier tubes and other detector technologies in high-energy physics (HEP) experiments, and for the readout of scintillators in gamma-ray detectors for space experiments. In such applications the SiPMs receive a significant dose of particles (such as protons and neutrons) as well as X and gamma rays. While the effect of radiation in silicon detectors biased below the voltage where avalanche multiplication becomes significant is well studied, the literature is not as much concerning Geiger-mode silicon-detector. In this work we studied in detail and with a systematic comparison, the effect of radiation on the performance of several SiPM technologies, produced by FBK. In particular we irradiated several chips with 74 MeV protons and with 40 keV X-rays, in two separate experiments. Each time we monitored their dark and light current-voltage curves after every irradiation step. We also studied the annealing after irradiations for few days at room temperature. Finally we characterized functionally the performance of irradiated device after irradiation and annealing, highlighting the differences between p-type silicon devices, n-type ones, and based on layout of the microcells

Radiation damage effects of protons and X-rays on silicon photomultipliers

Silicon photomultipliers (SiPMs) are highly-sensitive photodetectors emerging as the technology of choice for many applications. In high-energy physics experiments and as the detectors for space instruments they are often exposed to a large amount of irradiation. In recent years, there has been an increasing interest in assessing the performance deterioration of such detectors after ionizing and non-ionizing radiation, such as protons, neutrons and X or gamma rays. It is interesting to compare the radiation damage effects on several types of SiPMs, to assess the main deterioration mechanisms on SiPM performances. In this work we report on the irradiation by protons and X-rays of several types of small-area (1 mm2) SiPMs, produced in FBK with different technologies. We show and compare the most interesting results of the online measurements, taken just after each irradiation step, for both irradiations. We performed and monitored the current variation during a room temperature annealing. Finally we characterized all the main functional performance of the irradiated SiPMs, highlighting the most interesting variations

NUV-HD SiPMs with Metal-filled Trenches

In this contribution we would like to present a breakthrough improvement of the optical crosstalk between SPADs in SiPMs. In the framework of a collaboration between FBK and Broadcom we developed narrow metal-filled trenches that greatly suppress the optical crosstalk while maintaining a high fill factor and, in turn, photon detection efficiency. In particular, the new metal in trench detector (NUV-HD-MT) features an internal crosstalk almost 10 times lower than previous NUV-HD FBK SiPMs and can operate up to 17 V of excess bias voltages without any divergence of the correlated noise. The higher operating bias compensates the small loss in fill factor due to the insertion of the metal layer in the trenches and allows the NUV-HD-MT to reach PDE in excess of 60% with 40 μm cells. Together with a SiPM layout optimized for timing, the extended bias range allows to operate the detector with higher gain and low level of correlated noise, improving the CTR performance below 90 ps using 4x4 mm2 detectors coupled to 3x3x5 mm3 LYSO:Ce crystals and readout by a conventional front-end. The characteristics described above allow this detector to be considered as a good candidate for the upgrade of ToF-PET machines

Characterization of radiation damages on Silicon photomultipliers by X-rays up to 100 kGy

Silicon photomultipliers (SiPMs) are highly-sensitive photodetectors emerging as the technology of choice for many applications, including among the others, large high-energy physics experiments and detectors for space instruments, where they are often exposed to a large amount of radiation. In recent years, there has been an increasing interest in assessing the performance deterioration of such detectors after ionizing and non-ionizing radiation, such as protons, neutrons and X or gamma rays. It is therefore interesting to characterize the effect of irradiation on such Geiger-mode detectors, differentiating between the ionizing and non-ionizing energy-loss effects. Moreover, it is interesting to compare the radiation damage effects on several types of SiPMs, to assess the main phenomena and the deterioration mechanisms, aiming to a more radiation tolerant SiPM design. In this work we irradiated several types of SiPM structures, produced in FBK (Trento, Italy), with 40 keV X-rays, at several doses, up to 100 kGy (in silicon), performing both online measurements (after each irradiation step) and offline functional characterization, after one month of room temperature annealing. The SiPMs are made with many different technologies, in particular different layouts, junction polarities, internal structures and starting materials. We studied the variation in the reverse current–voltage curves, distinguishing the effects on multiplied and not-multiplied current components, the primary dark count rate, the correlated noise probabilities and photon detection efficiency. Comparing all the measurement results, knowing the internal structure and the fabrication processes, we were able to extract and distinguish different deterioration mechanisms, also supported by TCAD simulations on the different effects of ionizing radiation inside the microcells

On timing-optimized SiPMs for Cherenkov detection to boost low cost time-of-flight PET

Objective. Recent SiPM developments and improved front-end electronics have opened new doors in TOF-PET with a focus on prompt photon detection. For instance, the relatively high Cherenkov yield of bismuth-germanate (BGO) upon 511 keV gamma interaction has triggered a lot of interest, especially for its use in total body positron emission tomography (PET) scanners due to the crystal’s relatively low material and production costs. However, the electronic readout and timing optimization of the SiPMs still poses many questions. Lab experiments have shown the prospect of Cherenkov detection, with coincidence time resolutions (CTRs) of 200 ps FWHM achieved with small pixels, but lack system integration due to an unacceptable high power uptake of the used amplifiers. Approach. Following recent studies the most practical circuits with lower power uptake (<30 mW) have been implemented and the CTR performance with BGO of newly developed SiPMs from Fondazione Bruno Kessler tested. These novel SiPMs are optimized for highest single photon time resolution (SPTR). Main results. We achieved a best CTR FWHM of 123 ps for 2 × 2 × 3 mm3 and 243 ps for 3 × 3 × 20 mm3 BGO crystals. We further show that with these devices a CTR of 106 ps is possible using commercially available 3 × 3 × 20 mm3 LYSO:Ce,Mg crystals. To give an insight in the timing properties of these SiPMs, we measured the SPTR with black coated PbF2 of 2 × 2 × 3 mm3 size. We confirmed an SPTR of 68 ps FWHM published in literature for standard devices and show that the optimized SiPMs can improve this value to 42 ps. Pushing the SiPM bias and using 1 × 1 mm2 area devices we measured an SPTR of 28 ps FWHM. Significance. We have shown that advancements in readout electronics and SiPMs can lead to improved CTR with Cherenkov emitting crystals. Enabling time-of-flight with BGO will trigger a high interest for its use in low-cost and total-body PET scanners. Furthermore, owing to the prompt nature of Cherenkov emission, future CTR improvements are conceivable, for which a low-power electronic implementation is indispensable. In an extended discussion we will give a roadmap to best timing with prompt photons

Physical Considerations for Cherenkov Radiation Based Coincidence Time Resolution Measurements in BGO

Exploiting the Cherenkov luminescence from 511 keV photoelectric interactions is a potential solution to re-introduce BGO scintillators in time-of-flight positron emission tomography (TOF-PET). Recent improvements in vacuum- and near- ultra-violet high density (VUV- and NUV-HD) silicon photomultiplier (SiPM) technology combined with efficient data post-processing methods, make it possible to access timing information from the relatively few Cherenkov photons emitted. To achieve good coincidence time resolution (CTR) also requires low noise and fast readout electronics with small effective capacitance, which is possible by employing bootstrapping techniques.In this summary, we report the CTR evaluation of the new VUV-HD and NUV-HD enhanced SiPMs. Results using a (i) standard electronic board, and a (ii) custom designed board for timing measurements, are shown. After applying state-of-the-art correction methods, values below 400 ps CTR FWHM have been reported for 3×3 mm 2 BGO crystals with lengths ranging from 3 to 15 mm, thus indicating the excellent performance of new SiPM technology combined with our custom design board

Radiation damage on SiPMs for Spatial Applications

Silicon Photomultipliers are single-photon sensors working in Geiger mode. They are used in a wide range of applications, from high-energy physics to space and medical imaging. In some applications, they can be exposed to a significant amount of radiation, in the order of 1012−1014 neq/cm2 in high-energy physics or in the order of 109−1012 neq/cm2 in space for 5 years LEO orbits. In this contribution, we present an analysis of the main effects of the protons irradiation on the functional performance of several FBK SiPM technologies, with doses compatible with space missions along LEO orbits. In particular, we irradiated the SiPMs at the Protontherapy Center in Trento with proton fluences between 7.4×106 neq/cm2 and 6.4×1011 neq/cm2. During the irradiation test, reverse current-voltage (I-V) measurements were performed on the devices after each fluence step, and key parameter as Dark Count Rate and Photon Detection Efficiency were estimated. An annealing test was conducted at room temperature on all the devices for one month, performing reverse I-V measurements once a day. Lastly, results are showed and conclusions are drawn

Radiation damage on SiPMs for Space Applications

Silicon Photomultipliers (SiPMs) are very sensitive photo-detectors that experienced a big development in the last years in several applications, like LIDAR, astrophysics, medical imaging and high energy physics (HEP) experiments. In HEP experiments, in particular, they are often exposed to significant radiation doses. The main purpose of this manuscript is the characterization of several FBK SiPM technologies when exposed to 74 MeV protons with a total fluence comparable to the one that they would experience in space along circular Polar, Low Earth Orbits (LEO) during a five years mission. In this work, we estimated the expected proton fluences along the selected orbit, by means of the SPENVIS software. Several fluence steps were chosen to consider dense fluence intervals and have a more accurate sight on the whole damage process. We estimated a maximum fluence achieved during the tests of . Based on such simulations, we irradiated several SiPM technologies. We developed a custom experimental setup, which was used to perform online reverse voltage–current, right after each irradiation step, to minimize the effect of the annealing on the measurement. The results are then displayed, in particular the currents, the noise and the Photon Detection Efficiency. Also a 30-days study on the annealing of the devices was performed. Lastly, the conclusions are drawn on the basis of the Signal-to-Noise Ratio (SNR), taking into account the standard parameters of famous satellites using similar orbits as the ones considered into this work