C. Marzocca

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.

Defect level evaluation in an IC design environment

The purpose of this paper is to present a methodology for the evaluation of the Defect Level in an IC design environment. The methodology is based on the extension of Williams-Brown formula to nonequiprobable faults, which are collected from the IC layout, using the information on a typical IC process line defect statistics. The concept of weighted fault coverage is introduced, and the Defect Level (DL) evaluated for the Poisson and the negative binomial yield models. It is shown that DL depends on the critical areas associated with undetected faults, and their correspondent defect densities. Simulation results are presented, which highlight that the classic single Line Stuck-At (LSA) fault coverage is a unreliable metric of test quality. Moreover, results show that the efficiency of a given set of test patterns strongly depends on the physical design and defect statistics.

Novel Silicon Photomultipliers for PET Applications

Silicon photomultipliers (SiPMs) with quantum efficiency maximized for a wavelength between 420 and 470 nm have been developed at ITC-irst Trento (Italy), and are being tested for their application in the construction of a ultra high resolution small animal PET tomograph. The devices have an area of 1 mm times 1 mm and 625 microcells. The breakdown voltage is around 30 V, and the gain of the order of 106. The intrinsic timing resolution is 70 ps rms at the single photoelectron level. The first tests as readout for scintillators show an energy resolution of 21% FWHM with Na-22 employing LSO crystals. The first matrices of SiPMs have been produced and are being tested.

BASIC: An 8-channel front-end ASIC for Silicon Photomultiplier detectors

Multi-channel, integrated front-end electronics suitable for Silicon Photomultiplier detectors and mainly intended for medical imaging applications has been developed in a CMOS standard technology, according to a current-mode approach. Full exploitation of the good performance of the detector in terms of fast response and gain has been made possible by this design approach. An 8-channel, self-triggered prototype with an on-chip ADC has been designed and realized, also featuring a good degree of programmability and sparse read-out capabilities. Characterization measurements, carried out by coupling the circuit to both an injection capacitance and a SiPM manufactured from FBK-irst, confirm the expected results in terms of overall charge to voltage gain, dynamic range (more than 70pC at 1% non-linearity error), equivalent input noise charge (about 50fC) and timing accuracy.

ASIC development for SiPM readout

The design of CMOS front-end electronics suitable for Silicon Photo-Multipliers (SiPM) is described in this paper, starting with the specification of an accurate electrical model of the detector and its experimental validation. A novel current-mode solution is proposed for the preamplifier and the discriminator, to cope with the large dynamic range and the extremely fast rise time of the detector signal. Experimental results achieved from front-end prototypes designed according to this current-mode approach demonstrate its effectiveness: dynamic range of the order of 50 pC and timing accuracy of the electronics alone of about 30 ps have been measured.

Preliminary results from a current mode CMOS front-end circuit for silicon photomultiplier detectors

We propose a CMOS front-end circuit suitable for Silicon Photomultiplier detectors (SiPM) based on a current buffer, as input stage, which features small input impedance and large bandwidth, thanks to the application of current feedback techniques. The current mode approach enhances the dynamic range of the front-end and does not suffer from possible voltage limitations due to deep-submicron CMOS implementation. We report the first measurement results obtained by coupling the circuit prototype to a SiPM detector excited by a blue LED light source. The measurements confirm the effectiveness of the proposed front-end approach and demonstrate its capability of managing large current signals with good linearity.

Mixed-signal circuit classification in a pseudorandom testing scheme

Pseudo-random testing techniques for mixed-signal circuits offer several advantages compared to explicit time-domain and frequency-domain test methods, especially in a BIST structure. To fully exploit these advantages a suitable choice of the pseudo-random input parameters should be done and an investigation on the accuracy of the circuit response samples needed to reduce the risk of misclassification should be carried out. Here these issues have been addressed for a testing scheme based on the estimation of the impulse response of the device under test (DUT) by means of input-output cross-correlation. Moreover, new acceptance criteria for the DUT are suggested which solve some ambiguity problems arising if the classification of the DUT as good or bad is based on a few samples of the cross-correlation function. Examples of application of the proposed techniques to real cases are also shown in order to assess the impact of the measurement system inaccuracies on the reliability of the test.

Steps towards the use of silicon drift detectors in heavy ion collisions at LHC

Abstract The inner tracking system of the ALICE detector for PbPb collisions at the LHC require a very good granularity in the innermost planes, due to the high particle density, up to 8000 particles per unit of rapidity. The silicon drift detectors are a very good candidate for this application, but up to now no large system using this technology has been industrially produced and operated in experiments. One of the first steps towards large scale production is the study of the doping uniformity in commercially available Si wafers. The understanding of doping fluctuations is of fundamental importance since they introduce deviations of the electron trajectories from the expected ones. In addition, it is also necessary to know the changes possibly introduced by different processing steps in the resistivity profiles. We report here the results of measurements of resistivity profiles for NTD silicon wafers both before and after processing.

Designing a linear silicon drift detector

The design and 2D simulation results of a Silicon Drift Chamber with a rectangular configuration are presented. The proposed structure is intended to allow a test of the technology used in the production of the device and serve as a basis to verify different solutions in the design of drift detectors. >

An innovative detection module concept for PET

The design of a Positron Emission Tomography detection module capable of working inside a Magnetic Resonant Imaging system is the main objective of the 4D-MPET project. Combining the two imaging technologies offers better soft tissue contrast and lower radiation doses by providing both functional and morphological information at the same time. The proposed detector will feature a three-dimensional architecture based on two tiles of Silicon Photomultipliers coupled to a single LYSO scintillator on both its faces. Silicon Photomultipliers are magnetic-field compatible photo-detectors with a very small size enabling novel detector geometries that allow the measurement of the Depth of Interaction as well as a high detector packing fraction to maximize system sensitivity. Furthermore they can be fabricated using standard silicon technology, have a large gain in the order of 106 and are very fast thus allowing evaluating the Time of Flight. Among the other features of the proposed detection system, the architecture of the innovative readout electronics will be also described which plays a relevant role for the achievement of the desired performance and is based on custom integrated circuits. Simulation results of the whole system show good performance in terms of time and spatial resolution: a timestamp of 100 ps is the ultimate performance achievable with the use of a double threshold technique along with fast electronics. Time over threshold is exploited to provide the energy information with a bin size of 400 ps. Moreover, a z resolution of 1.4 mm Full Width at Half Maximum can be achieved. The proposed detector can also be exploited in other tracking applications, such as High Energy Physics and Astrophysics.