C. Piemonte

Characterization of the First Prototypes of Silicon Photomultiplier Fabricated at ITC-irst

This paper reports on the electrical characterization of the first prototypes of Geiger-Mode Avalanche Photodiodes (GM-APDs) and Silicon Photomultipliers (SiPMs) produced at ITC-irst, Trento. Both static and functional measurements have been performed in dark condition. The static tests, consisting in reverse and forward IV measurements, have been performed on 20GM-APDs and 90 SiPMs. The breakdown voltage, the quenching resistance value and the current level have been proved to be very uniform. On the other hand, the analysis of the dark signals allowed the extraction of important properties such as the dark count rate, the gain, the after-pulse and optical cross-talk (in case of the SiPMs) rates. These parameters have been evaluated as a function of the bias voltage, showing trends perfectly compatible with the theory of the device

Double-Sided, Double-Type-Column 3-D Detectors: Design, Fabrication, and Technology Evaluation

We report on the latest results from the development of 3-D silicon radiation detectors at Fondazione Bruno Kessler of Trento (FBK), Italy (formerly ITC-IRST). Building on the results obtained from previous devices (3-D Single-Type-Column), a new detector concept has been defined, namely 3-D-DDTC (Double-sided Double-Type Column), which involves columnar electrodes of both doping types, etched from alternate wafer sides, stopping a short distance (d) from the opposite surface. Simulations prove that, if d is kept small with respect to the wafer thickness, this approach can yield charge collection properties comparable to those of standard 3-D detectors, with the advantage of a simpler fabrication process. Two wafer layouts have been designed with reference to this technology, and two fabrication runs have been performed. Technological and design aspects are reported in this paper, along with simulation results and initial results from the characterization of detectors and test structures belonging to the first 3-D-DDTC batch.

Characterization of a PET detector head based on continuous LYSO crystals and monolithic, 64-pixel silicon photomultiplier matrices

The characterization of a PET detector head based on continuous LYSO crystals and silicon photomultiplier (SiPM) arrays as photodetectors has been carried out for its use in the development of a small animal PET prototype. The detector heads are composed of a continuous crystal and a SiPM matrix with 64 pixels in a common substrate, fabricated specifically for this project. Three crystals of 12 mm × 12 mm × 5 mm size with different types of painting have been tested: white, black and black on the sides but white on the back of the crystal. The best energy resolution, obtained with the white crystal, is 16% FWHM. The detector response is linear up to 1275 keV. Tests with different position determination algorithms have been carried out with the three crystals. The spatial resolution obtained with the center of gravity algorithm is around 0.9 mm FWHM for the three crystals. As expected, the use of this algorithm results in the displacement of the reconstructed position toward the center of the crystal, more pronounced in the case of the white crystal. A maximum likelihood algorithm has been tested that can reconstruct correctly the interaction position of the photons also in the case of the white crystal.

Electrical Characterization of Silicon Photo-Multiplier Detectors for Optimal Front-End Design

Silicon Photo-Multiplier (SiPM) detectors represent an attractive solution for the detection of low energy photons in several fields of both high energy physics and medical imaging. We present here an accurate electrical model for this kind of detectors, which can be conveniently used to perform reliable simulations at circuit level. A suitable extraction procedure for the parameters involved in the model is also described, based on both static and dynamic measurements. The proposed model allows to reproduce accurately the waveform of the signal generated by the SiPM when coupled to the front-end electronics, as shown by excellent fittings obtained between simulations and measurements taken on real devices. This is particularly useful in order to choose the most suitable front-end architecture for SiPM detectors, since the performance of the whole detection system, especially in terms of dynamic range and timing resolution, can be correctly predicted as a function of the detector parameters and of the main characteristics of the coupled electronics.

Large area silicon drift detector for the ALICE experiment

AbstractTwohundredandsixtySiliconDriftDetectors(SDDs),eachwithanactiveareaof7:0 7:5cm 2 ; willequiptwoofthesixcylindricallayersofhighprecisionpositionsensitivedetectorsthatconstitutetheInnerTrackingSystem(ITS)oftheALICEexperimentatLHC.IndevelopingtheALICESDD,oneoftheobjectiveswastoworkoutarobustandredundantdesign.Unlikethecaseofsiliconmicrostriporpixeldetectors,asingledefectinaSDDmaybepropagatedthroughoutthewholedetector.Oneofthefeaturesofthedetectoristheoriginaldesignoftheintegratedvoltagedividerthatallowstoattenuateeffectivelysuchapropagationinthemostpracticalcases.Devicesimulationsandlaboratorymeasurementsarepresented.r 2002ElsevierScienceB.V.Allrightsreserved. 1. General detector characteristicsTheITSoftheALICEexperimentatLHCwillconsist of six cylindrical layers of high precisionposition-sensitive detectors. Two hundred andsixty identical SDDs will equip the 3rd and the4th layer, providingposition information in twodimensionsanddE(energy)sample[1,2].ThefinaldesignoftheALICESDD(calledALICE-D2)wascompleted in the year 2000 and up to now 40detectorshavebeenproduced.1.1. MaterialSpecial care was dedicated to the startingmaterial.Indeed,dopingfluctuationscausedistor-tions in the drift trajectories and deterioratesignificantly the detector position resolution inbothdirections[3–5].Thedetectorsarefabricatedon 5

Sub-100 ps coincidence time resolution for positron emission tomography with LSO:Ce codoped with Ca

The coincidence time resolution (CTR) becomes a key parameter of 511 keV gamma detection in time of flight positron emission tomography (TOF-PET). This is because additional information obtained through timing leads to a better noise suppression and therefore a better signal to noise ratio in the reconstructed image. In this paper we present the results of CTR measurements on two different SiPM technologies from FBK coupled to LSO:Ce codoped 0.4%Ca crystals. We compare the measurements performed at two separate test setups, i.e. at CERN and at FBK, showing that the obtained results agree within a few percent. We achieve a best CTR value of 85 ± 4 ps FWHM for 2 × 2 × 3 mm(3) LSO:Ce codoped 0.4%Ca crystals, thus breaking the 100 ps barrier with scintillators similar to LSO:Ce or LYSO:Ce. We also demonstrate that a CTR of 140 ± 5 ps can be achieved for longer 2 × 2 × 20 mm(3) crystals, which can readily be implemented in the current generation PET systems to achieve the desired increase in the signal to noise ratio.

Analog circuit for timing measurements with large area SiPMs coupled to LYSO crystals

The most common method for time pick-off from signals coming from SiPMs coupled to scintillator crystals in PET applications is the Leading Edge Triggering. In this work we propose a new filtering scheme to be applied before the discriminator. It implements a type of baseline compensation aimed at the reduction of the time jitter due to the dark counts of the detector and is based on a simple analog filter, which is well suited for an ASIC implementation. We describe a circuit, built with discrete components, that implements the filter. Finally we report on the Coincidence Resolving Time measurements performed coupling the circuit to the real detector, composed of a SiPM built at FBK and a LYSO crystal, for the detection of 511 keV photons. The results obtained are promising, showing that the method is quite effective in reducing the impact of the detector noise on the timing performance of the system.

Device simulations of isolation techniques for silicon microstrip detectors made on p-type substrates

Recent studies have shown that silicon particle detectors made on p-type substrates feature an improved radiation hardness compared to more conventional single-side n-type devices. In particular, they show an increased charge collection efficiency at very high irradiation levels. At present few devices have been fabricated on these substrates and there are still many doubts regarding the best type of isolation structure to be employed for the interruption of the inversion electron layer present between the n/sup +/ electrodes. In this paper, a description of the behavior of microstrip detectors featuring three isolation solution (p-spray, p-stop and a combination between the previous two) is presented. The analysis is based on device simulations and covers the breakdown and interstrip capacitance issues.

Characterization of new FBK SiPM technology for visible light detection

This paper presents the characterization of the new n-on-p SiPM technology developed at Fondazione Bruno Kessler (FBK, Trento-Italy). Several device aspects such as dark count rate, photo detection efficiency, breakdown voltage uniformity, and temperature stability have been significantly improved with respect to the original FBK SiPM technology. The modifications introduced involve the internal device structure and are based on an electric-field engineering approach. We report on the dark characterization, the visible light detection efficiency and 511 keV gamma ray energy resolution, when reading out small LYSO or Ce:GAGG crystals, of the new devices. In parallel, a comparison to the original SiPMs is done in order to underline the main advancements that have been obtained. We refer this new technology to as RGB-SiPMs because of the high detection efficiency for the whole red, green, and blue part of the spectrum.

SiPM based preclinical PET/MR insert for a human 3T MR: first imaging experiments

Simultaneous PET/MRI is a hybrid imaging modality which promises to play an important role in the field of molecular imaging, as it combines the outstanding soft-tissue contrast of MRI with the metabolic and functional information of PET and MRI. In addition, the possibility for true simultaneous acquisition allows for improved 4D registration which in due course may lead to enhanced image quality and image quantification. The main technical challenges of simultaneous PET/MR are the MR-based attenuation correction and the development of an MR-compatible PET detector technology. Avalanche photo diode based detectors have been already successfully integrated into preclinical as well as human systems [1,2]. Low but noticeable interferences between PET and MRI have been reported so far. Unfortunately, these implementations do not offer the measurement of time of flight (TOF) information in the sub-ns range, which is one of the drivers for high quality clinical PET and has been state-of-the-art in clinical PET/CT for the last 5 years.