Silicon Photomultiplier Response Research Articles

Understanding the Nonlinear Response of SiPMs.

A systematic study of the nonlinear response of Silicon Photomultipliers (SiPMs) was conducted through Monte Carlo (MC) simulations. The MC code was validated against experimental data for two different SiPMs. Nonlinearity mainly depends on the balance between the photon rate and the pixel recovery time. Additionally, nonlinearity has been found to depend on the light pulse shape, the correlated noise, the overvoltage dependence of the photon detection efficiency, and the impedance of the readout circuit. Correlated noise has been shown to have a minor impact on nonlinearity, but it can significantly affect the shape of the SiPM output current. Considering these dependencies and a previous statistical analysis of the nonlinear response of SiPMs, two phenomenological fitting models were proposed for exponential-like and finite light pulses, explaining the roles of their various terms and parameters. These models provide an accurate description of the nonlinear responses of SiPMs at the level of a few percentages for a wide range of situations.

Correcting the Non-Linear Response of Silicon Photomultipliers.

The finite number of pixels in a silicon photomultiplier (SiPM) limits its dynamic range to light pulses up to typically 80% of the total number of pixels in a device. Correcting the non-linear response is essential to extend the SiPM's dynamic range. One challenge in determining the non-linear response correction is providing a reference linear light source. Instead, the single-step method used to calibrate PMTs is applied, based on the difference in responses to two light sources. With this method, the response of an HPK SiPM (S14160-1315PS) is corrected to linearity within 5% while extending the linear dynamic range by a factor larger than ten. The study shows that the response function does not vary by more than 5% for a variation in the operating voltage between 2 and 5 V overvoltage in the gate length between 20 and 100 ns and for a time delay between the primary and secondary light of up to 40 ns.

Measurements of the Cherenkov effect in direct detection of charged particles with SiPMs

In this paper, different Silicon PhotoMultiplier (SiPM) sensors have been tested with charged particles to characterize the Cherenkov light produced in the sensor protection layer. A careful position scan of the SiPM response has been performed with different prototypes, confirming the large number of firing cells and proving almost full efficiency, with the SiPM filling factor essentially negligible. This study also allowed us to study the time resolution of such devices as a function of the number of firing cells, reaching values below 20 ps. These measurements provide significant insight into the capabilities of SiPM sensors in direct detection of charged particles and their potential for several applications.

Test beam results of the fiber-sampling dual-readout calorimeter

The dual-readout calorimetric technique reconstructs the event-by-event electromagnetic fraction of the hadronic shower through the simultaneous measurement of scintillating (S) and Cherenkov (C) light produced by the shower development. The new generation of prototypes, based on Silicon Photomultipliers (SiPMs) readout, adds unprecedented granularity to the well-known high-energy resolution. A highly granular prototype (10×10×100cm3), designed to fully contain electromagnetic showers, was recently built and qualified on beam. It consists of 9 modules, each made of 320 brass capillaries equipped with both scintillating and clear fibers. All the fibers of the central module are coupled with SiPMs, while the PMTs are used for the others. Furthermore, the new FERS-System, designed by Caen to exploit the CITIROC1A ASICs performances, is at the core of the SiPM readout.The recent test beam at DESY allowed us to qualify the readout system and define a procedure to calibrate the SiPM response from ADC to ph-e in a wide dynamic range. We measured the number of ph-e per GeV for scintillating and Cherenkov light together with the calorimetric performances in the energy range of 1–6 GeV. This work reports the system qualification and the test beam results regarding SiPM calibration.

Monte Carlo simulation of a scintillation crystal read by a SiPM with GATE

Silicon photomultipliers (SiPMs) have recently emerged as a replacement for photomultiplier tubes (PMTs) for light detection in many applications, including high-energy physics and medical imaging. Recently, detailed Monte Carlo simulation of SiPMs has been implemented in GATE to quantify the impact of SiPM specifications on the linearity, energy and time resolution of a scintillation crystal read by a SiPM. In this paper, GATE simulations of a LYSO crystal coupled to a SiPM are compared to measurements. The energy spectra of the 241Am and 22Na radioactive sources are found to agree with less than 2% difference. The linearity of the SiPM response is duly affected by the SiPM saturation and, as seen above 511 keV with our configuration, it is slightly enhanced by the generation of crosstalk. Furthermore, with an over-voltage close to that recommended by the manufacturer, all sources of SiPM noise contribute about equally to the degradation of the energy resolution at low energies, which is downgraded by more than 15% at 60keV, but have less impact at higher energies. In addition, the GATE simulations show that crosstalk plays an important role on the time resolution of the installation.

Study on the Optimized Energy Resolution of Scintillator Detectors Based on SiPMs and LYSO:Ce

The cerium-doped lutetium yttrium silicate (LYSO:Ce) crystal has many advantages such as high light output and fast decay time, showing great potential to improve the performance of scintillation detectors. Silicon photomultipliers (SiPMs) are high-performance semiconductor photodetectors, which generally have a higher photon detection efficiency than photomultiplier tubes (PMTs) and are beneficial to realize a better energy resolution. The energy resolution and detected light output of SiPM-coupled LYSO:Ce crystals were studied by optimizing the photon detection efficiency (PDE), the operating voltage, the wrapper, the surface finish and the coupling method between the SiPM and crystal. Considering the output saturation of SiPMs in high light intensity, a preliminary correction method was applied to the saturation response of SiPMs and energy resolution of 662 keV gamma-rays from 137Cs was obtained after correction. The results show that the optimized energy resolution at 662 keV measured by the SiPM of 50 μm microcells can reach 7.6%. The light output of the polished and rough crystal detected by a SiPM of 10 μm microcells were also measured, which can reach 27000 ± 3200 photons/MeV and 36000 ± 3700 photons/MeV, respectively.

SiPM dynamic range for CEPC scintillator-based electromagnetic calorimeter

A high-granularity scintillator calorimeter readout with silicon photomultipliers (SiPMs) is an electromagnetic calorimeter (ECAL) candidate for experiments at the Circular Electron Positron Collider (CEPC). A critical design parameter of this ECAL candidate is the dynamic range of the SiPMs. This study investigates the SiPM dynamic range required for the CEPC scintillator ECAL. A model is developed on the basis of the operation principles of SiPMs to describe the response of an SiPM to light pulses within one recovery period by considering the cross-talk effect, photon detection efficiency, and number of pixels. The response curve of a 10000-pixel SiPM predicted by the model is consistent with the measured curve within 2% for an incident light pulse of up to 12000 photons. The intrinsic fluctuations of the SiPM response naturally exist in this model, and the correction of the saturation effect in the SiPM response is investigated. Monte Carlo (MC) simulation shows that the algorithm can restore the response linearity of an SiPM for an incident light pulse in which the number of photons is up to around six times the number of SiPM pixels. The model and correction program are implemented for full simulation of the ZH production Z → νν, H → γγ channel to evaluate the impact of the SiPM dynamic range of the CEPC scintillator ECAL on the reconstructed Higgs boson mass and the sensitivity to the Higgs signal in this channel. The results show that the CEPC scintillator ECAL equipped with no less than 4000 SiPM pixels and operated with a light yield of 20 photon-electrons per channel for a single minimum ionizing particle can meet the requirements for Higgs boson precision measurement in the di-photon channel at the CEPC.

Novel Model for Analysis and Optimization of Silicon Photomultiplier-Based Scintillation Systems

Nowadays, silicon photomultipliers (SiPMs) are extensively used for absorption of scintillation light in all types of scintillators in high-energy physics. Fast spread of SiPMs resulted in a rapid development of both analytical and Monte Carlo models. Models describe the response of these silicon integrated circuits. We introduce a novel Monte Carlo model of SiPM with a scintillator module that enables modeling the response of SiPM to dynamic scintillation processes. The model introduces several improvements over other models. This article focuses on the analysis of pulse shape discrimination (PSD) performance of SiPM-based scintillation systems since such techniques are often used to discriminate between incident particles of ionizing radiation. The algorithms for PSD are sensitive to the shape of the pulse and SiPMs have several mechanisms that influence the shape of the output pulse, such as bandwidth of the system, the presence of fast decay components, and the recovery time of individual microcells. Some of these mechanisms are not present in a classical photomultiplier, for instance, a recovery time or the fast decay component. We have analyzed the performance of three different PSD algorithms with three SiPMs (MicroFC-30020, MicroFC-30035, and MicroFC-30050) coupled with scintillators EJ-301 and EJ-276. Several conclusions are drawn from the analysis. The two most important ones are that optimized systems need to finetune their bandwidth and that scintillators with fast decay signals are better suited for photomultipliers with lower recovery time and vice versa. It is also shown that the classical charge comparison algorithm does not reach the performance of modern algorithms, for instance, frequency gradient analysis.

A 3.45 Gigabits/s SiPM-Based OOK VLC Receiver

A relationship between irradiance and the current needed to maintain the bias voltage applied to a silicon photomultiplier (SiPM) is shown to agree with experimental data. In addition to showing the saturation of the SiPMs response this relationship can be used to determine the power consumed by an SiPM. In addition, results are presented which show that, because of its higher maximum photon count rate, a 30020 SiPM can achieve a bit error rate (BER) of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> at a data rate of 3.45 Gbits/s.

On the use of silicon photomultipliers for thermoluminescence measurements

Abstract: In this work, we evaluate the use of silicon photomultipliers (SiPMs) as a suitable candidate for use as a photodetector for thermoluminescence measurements. The measurements were based on the Hamamatsu S13360-series with a pixel area of 3 × 3 mm2 and microcell pitches of 25 μm, 50 μm, and 75 μm, which were mounted on a Riso TL/OSL reader system with LiF:Mg,Cu,Si chosen as the reference TL material. Through the experiment, we showed that the typical TL glow curves can be obtained with SiPMs, despite their lower geometric efficiencies. We also demonstrated the dose response of SiPMs ranging from 6 to 66 mGy for three different photon threshold levels. The detection limit was approximately equal to 0.2 mSv, 0.08 mSv, and 0.17 mSv for 25 μm, 50 μm, and 75 μm SiPMs, respectively. More importantly, a sensitivity change and sensor temperature depending on a TL reading up to 260 °C was monitored on a sequential readout. Lastly, we discuss some of the possible benefits and limitations of SiPM-based TL measurements in comparison to PMT-based TL measurements.

Evaluation of a PET detector based on SiPMs and FPGA-only MVT digitizers

Silicon photomultipliers (SiPMs) are considered among the most promising sensors for positron emission tomography (PET) applications. To fully utilize the fast response of SiPMs, a 1-to-1 coupling configuration for scintillators and sensors is applied in SiPM-based detectors, leading to a vast number of channels to process. Previously, we have proposed a multi-voltage threshold (MVT) sampling method that can digitize scintillation pulses by means of simplified circuits. The feasibility of implementing MVT digitizers with only field programmable gate arrays (FPGAs) was proven, and hence, a digital PET detector module based on SiPMs was developed. In this work, we report the performance of our upgraded detector modules based on an evaluation of a fully functional demonstrator system. The system has the form of a 12-sided ring with a 108 mm diameter and a 25 mm axial length composed of 6 detector modules. Our measurements show an energy resolution of 18.9% at 511 keV and a coincidence timing resolution of 354 ps. With an energy window of 450–650 keV, the absolute sensitivity at the center of the scanner is 1.11%. The spatial resolutions are 2.08, 2.19 and 2.24 mm in the radial, tangential and axial directions, respectively. Since inter-crystal scatter (ICS) can cause count loss in the system, a recovery scheme is employed for the same data. As a result, the sensitivity and signal-to-noise ratio in the uniform region for an image quality phantom increase by 83% and 19%, respectively. However, we observe a compromised time resolution of 419 ps and a deterioration of 7–12% in spatial resolution.

Current status of an optically-segmented single-volume scatter camera for neutron imaging

The Single-Volume Scatter Camera (SVSC) approach to kinematic neutron imaging, in which an incident neutron’s direction is reconstructed via multiple neutron-proton scattering events, potentially offers much greater efficiency and portability than current systems. In our first design of an Optically-Segmented (OS) SVSC, the detector consists of an 8 × 8 array of 5 × 5 × 200 mm3 bars of EJ-204 scintillator wrapped in Teflon tape, optically coupled with SensL J-series 6 × 6 mm Silicon Photomultiplier (SiPM) arrays, all inside an aluminum frame that serves as a dark box. The SiPMs are read out using custom (multi-GSPS) waveform sampling electronics. In this work, construction, characterization, and electronics updates are reported. The position, time, and energy resolutions of individual bars were obtained by measuring different scintillators with different reflectors. This work was carried out in parallel at the University of Hawaii and at Sandia National Laboratories and resulted in the preliminary design of the camera. Monte-Carlo simulations using the Geant4 toolkit were carried out for individual scintillator bars, as well as the array setup. A custom analysis using ROOT libraries in C++ simulated the SiPM response from Geant4 photon hits. This analysis framework is under development and will allow for seamless comparisons between experimental and simulated data.

Feasibility assessment of an SiPM for implementation in an OSL reader

In this work, we report on the feasibility of a silicon photomultiplier (SiPM) for optically stimulated luminescence dosimeter (OSLD) application. In particular, to assess SiPMs as a viable technology for OSLD, we investigated the SiPM response to OSL detection in terms of microcell size, excess voltage (Vex), and photon threshold-levels. Furthermore, the dose response was explored to highlight some of the benefits and limitations of relying on SiPMs in OSL detection compared to using the conventional reader based on photomultiplier tubes (PMTs). SiPMs tested in this work were based on the Hamamatsu S13360-series with the pixel area of 3 × 3 mm2 and microcell pitches of 25μm, 50μm, and 75μm. The material used for the OSL detection is based on Al2O3:C and the measurements were carried out using a Risø TL/OSL reader system with the existing PMT replaced with a customized SiPM readout module. The results showed that SiPMs exhibit optimal performances at Vex of 5 V, 3 V, and 3 V for 25μm, 50μm, and 75μm, respectively. We also demonstrated that the dose responses in three SiPMs are nearly linear for doses below 1 Gy and found the minimal detectable doses as 23 mGy, 20 mGy, and 11 mGy for 25μm, 50μm, and 75μm, respectively. Finally, it was shown that the detection sensitivity in the OSL signal fluctuates by nearly 5% for a temperature change of about 0.5 °C in an SiPM.

Energy calibration using scintillator background radiation for high-resolution PET detectors

Nowadays more and more positron emission tomography (PET) detectors are constructed with a LYSO crystal array coupled to a silicon photomultiplier (SiPM) array. Due to the non-linearity of readout electronics and SiPM response, the energy calibration is needed to obtain the correct 511 keV photopeak position, energy resolution and precise γ photon interaction position. Different with conventional energy calibration methods involving extra multiple sources of different radioactive energies, this paper proposes to use the intrinsic 176Lu radiation of LYSO crystal for energy calibration. The isotope 176Lu in the crystal decays into 176Hf and emits a beta particle with maximum energy 589 keV, and a cascade of gamma rays of energies 307 keV, 202 keV and 88 keV. This uniformly distributed multi-energy radioactivity makes the crystal itself an idea radiation source for in situ calibration. Applying the calibration method to PET detectors with 1:1, 4:1, and 9:1 couplings between the crystal array and SiPM array respectively, the effect on improving spatial resolution is also presented, which demonstrates the energy calibration is particularly necessary for light-sharing based PET detectors.

Development of Silicon Photomultiplier sensors using a 180 nm custom CMOS process technology

Silicon Photomultiplier (SiPM) sensors with different pixel sizes and active areas were designed. The fabrication technology was developed using a 8′′ silicon wafer foundry supporting 180 nm CMOS process technology. A simulation study using process and device simulators was carried out to study the effect of critical process parameters on the device characteristics. A custom process based on CMOS process flow was developed by optimizing critical process parameters for the fabrication of SiPMs. The sensors were characterized using various techniques for the measurement of dark current, breakdown voltage, dark count rate and cross talk, response to external light at different operating voltages and light intensities. The SiPMs were demonstrated to have desired performance in terms of dark current, geometric efficiency, and dark count rate. The developed SiPMs have low dark currents ({<}5 nA/cm2) and breakdown voltage of 22 V . Initial measurements with LED light shows good linearity of SiPM response with light intensity.

Scanning a Silicon Photomultiplier with a Laser Beam

The Silicon Photomultiplier (SiPM) is a novel semiconducting photodetector which can detect single photons. It consists of many microcells (pixels) operating in the so-called Geiger mode. At present, there are two principal designs among such devices: surface pixel and deeply buried pixel (microwell) structures. The cellular structure decreases the device’s effective photosensitive area, expressed in terms of the geometrical fill factor. It is very important to take it into account when developing new constructions with high pixel densities that are necessary for increasing the dynamic range. It is believed that the fill factor of deep microwell SiPMs is close to unity. In this work, the technique and results of studying the zonal response of different SiPMs by scanning (moving) with micron laser spot are presented. It is shown that the geometrical fill factor of the deep microwell SiPM is less than 100% when detecting the red light (λ = 632 nm).

Direct detection of high intensity X-ray fluxes with silicon photomultipliers

Silicon Photomultipliers (SiPM) are photodetectors optimized for the detection of infrared to ultraviolet photons and employed in a wide range of fast timing applications for medical imaging and particle detectors. SiPMs are used to detect the passage of ionizing radiation into matter via the collection of secondary photons emitted by the radiator material. In this work, we have investigated the possibility to detect high intensity X-ray fluxes using the DC current produced by SiPMs exposed directly to the X-ray beam, in absence of any passive converter material, to demonstrate the possibility to measure intense radiation fluxes without saturation of the SiPM response. In our application, the signal-to-noise ratio of the SiPM current during the direct exposition to X-rays is typically larger than 100, providing a robust indication of a positive detection. We show that, for a wide range of operational parameters and X-ray flux intensities, the SiPM current can be correlated to the X-ray beam intensity using a parametrization that describes the data with an accuracy of the order or better than 1%. We also show that the SiPM signal current to dark current ratio is maximum for hundreds of mV above the breakdown voltage, with a weak dependence on temperature. These results open the prospects for interesting applications for monitoring intense X-ray beams, for example beam spatial profiling, and possibly real time dosimetry both in medical and industrial applications.

Measurement of the response of Silicon Photomultipliers from single photon detection to saturation

The development of Silicon Photomultipliers (SiPM) is very dynamic and a large variety of types exists. Important SiPM characteristics include the size and number of pixels, the gain, the photon detection efficiency (PDE), the recovery time, and correlated noise. SiPMs are particularly suitable for single-photon detection and low-intensity exposures. For photon numbers (PDE corrected) reaching the number of pixels, however, the sensors saturate. In this work, we present comprehensive response measurements for state-of-the-art SiPMs using an experimental setup based on a tunable picosecond laser. Several models are applied to the measured response curves, taking particularly correlated noise and saturation effects into account. Sensors with different numbers of pixels and different design are compared, some of which exhibit an over-saturation behavior. The results are discussed in the context of high-granularity calorimeters developed for future particle physics experiments employing millions of SiPMs. For these projects the full dynamic range of the sensors has to be exploited, thus an understanding and calibration of the saturation behavior is crucial. • Experimental method to compare the response of different SiPMs using the same setup. • Observation of over-saturation for certain SiPM models. • SiPMs with many small pixels (here 2668 pixels with 25 μ m pitch) and trenches are best suitable for calorimeter applications.

Reconstruction and initial calibration of silicon photomultipliers response in the DANSS experiment

The specific features of silicon photomultiplier (SiPM) signal reconstruction in the DANSS experiment are discussed. A technique for calibration of SiPM response using its noise spectrum parameters is described. The method allows one to calculate the number of detected photoelectrons. The results of practical application of the developed procedure to the adjustment of SiPM operating voltages are presented. It is shown that the achieved precision of such hardware calibration is better than 2%.

New method for evaluating effective recovery time and single photoelectron response in silicon photomultipliers

The linearity of a silicon photomultiplier (SiPM) response depends on the number of APD cells and its effective recovery time and it is related to the intensity and duration of the detected light pulses. The aim of this study was to determine the effective recovery time on the basis of the measured SiPM response to light pulses of different durations. A closer analysis of the SiPM response to the light pulses shorter than the effective recovery time of APD cells led to a method for the evaluation of the single photoelectron response of the devices where the single photoelectron peak cannot be clearly measured. This is necessary in the evaluation of the number of fired APD cells (or the number of photoelectrons) in measurements with light pulses of various durations. Measurements were done with SiPMs manufactured by two companies: Hamamatsu and SensL.