Silicon Photomultipliers Gain Research Articles

Batch VUV4 characterization for the SBC-LAr10 scintillating bubble chamber

The Scintillating Bubble Chamber (SBC) collaboration purchased 32 Hamamatsu VUV4 silicon photomultipliers (SiPMs) for use in SBC-LAr10, a bubble chamber containing 10 kg of liquid argon. A dark-count characterization technique, which avoids the use of a single-photon source, was used at two temperatures to measure the VUV4 SiPMs breakdown voltage (VBD), the SiPM gain (g SiPM), the rate of change of g SiPM with respect to voltage (m), the dark count rate (DCR), and the probability of a correlated avalanche (PCA) as well as the temperature coefficients of these parameters. A Peltier-based chilled vacuum chamber was developed at Queen's University to cool down the Quads to 233.15 ± 0.2 K and 255.15 ± 0.2 K with average stability of ±20 mK. An analysis framework was developed to estimate VBD to tens of mV precision and DCR close to Poissonian error. The temperature dependence of VBD was found to be 56 ± 2 mV K-1, and m on average across all Quads was found to be (459 ± 3(stat.)±23(sys.))× 103 e- PE-1 V-1. The average DCR temperature coefficient was estimated to be 0.099 ± 0.008 K-1 corresponding to a reduction factor of 7 for every 20 K drop in temperature. The average temperature dependence of PCA was estimated to be 4000 ± 1000 ppm K-1. PCA estimated from the average across all SiPMs is a better estimator than the PCA calculated from individual SiPMs, for all of the other parameters, the opposite is true. All the estimated parameters were measured to the precision required for SBC-LAr10, and the Quads will be used in conditions to optimize the signal-to-noise ratio.

A 16-channel programmable SiPM bias supply system for Cherenkov telescope imaging camera

In recent years, the Silicon Photomultipliers (SiPMs) have emerged as a promising photodetector in various applications such as high energy physics, nuclear physics and medical instruments. One such application is in the pixelated camera of Imaging Atmospheric Cherenkov Telescopes (IACTs). IACTs are used to detect very high-energy celestial gamma rays using Atmospheric Cherenkov Technique. The SiPM gain is proportional to the overvoltage which is the difference between applied bias voltage and breakdown voltage. As the SiPM breakdown voltage increases with temperature, the overvoltage and hence the gain decreases proportionally (2-3%/°C) at a constant applied bias voltage. Also, the actual bias voltage across the SiPM changes with load current due to voltage drop across a series resistor in SiPM bias circuit, thus causing a change in overvoltage and gain. To maintain a constant gain of the SiPM, the applied bias voltage need to be adjusted to compensate for the changes in temperature and load. We are developing a 256-pixel imaging camera with SiPM as its photo-sensor. The camera will be placed at the focal point of telescope and will be operated during night in outdoor environment at Hanle, Ladakh, India. The night temperature at Hanle typically varies by ∼ 10°C overnight and ∼ 40°C (-20°C to +20°C) over the year. Thus, gain of SiPMs, exposed to the environment, may vary considerably during observations. A prototype 8-channel bias supply board with real time temperature & load compensation is developed to operate the camera SiPMs at fixed gain throughout the observation night.The voltage range of the bias supply for each channel is from 10 V to 80 V with 5 mV resolution and current upto 4 mA. The output voltage and current can be monitored with a resolution of ∼ 5 mV and ∼ 0.3 μA respectively. The single board computer, Raspberry Pi, is connected to the bias supply board over a 7-wire Customized Serial Peripheral Interface (CSPI) for control and monitoring. A multi-channel SiPM bias supply system is realized by daisy-chaining 8-channel boards through CSPI to cater bias voltage to all the pixels of the camera. The system is operated remotely using Ethernet interface of Raspberry-Pi. This paper discusses the design, development and performance of the prototype 16-channel closed-loop, programmable bias supply system with built-in compensation for changes in temperature and load.

A novel high dynamic-range SiPM for scintillator-based hadronic calorimetry

The Analog Hadronic Calorimeter (AHCAL) is one option of highly granular calorimeters optimised with the Particle Flow Algorithm (PFA) and considered for experiments at future lepton colliders. It consists of dense steel plates as absorber interleaved with plastic scintillator tiles, individually read out by Silicon Photomultipliers (SiPMs). A novel SiPM developed by the Novel Device Laboratory (NDL) with an active area of 1 mm2 and a pixel pitch of 12.5 micron[NDL-SiPM-12.5] has been mainly investigated. The characterisation studies include single photon calibration, dynamic range and performance of crosstalk as well as Minimum Ionising Particle (MIP) detection efficiency of a detector unit. Combined tests with a dedicated ASIC (SPIROC2E) for multi-channel SiPMs show that single photon spectra can be obtained, given the relatively small SiPM gain (∼2 × 105). The linearity of the SiPMs in response to incident photons of less than 10,000 (500 MIPs) is within 5% from measurements. Meanwhile, the dark count rate (DCR) is around 2×10-3 Hz at a threshold 0.5 MIP (10 p.e.) and the MIP detection efficiency of a detector unit can be near 95% from the MIP spectrum. These studies indicate the NDL-SiPM-12.5 can be a photosensor candidate for the future scintillator-based hadronic calorimeters.

Study on the FPGA-based Temperature Compensation for the SiPM of CEPC ECAL Prototype

Silicon photomultiplier (SiPM), with the advantages of high gain, low noise, small volumn, is used as the photoelectric converter in the detection unit of the electromagnetic calorimeter (ECAL) prototype of the Circular Electron Positron Collider (CEPC). However, the ambient temperature has influences on the SiPM gain, which will therefore affect the energy resolution of the calorimeter. To solve this problem, a temperature compensation strategy including the temperature field reconstruction and the high voltage control is proposed in this article. The compensation strategy is implemented in the Field Programmable Gate Array (FPGA) of ECAL prototype which can work real-timely and the LED test and the radiation source test both show good results. When using the temperature compensation, the variation of the system gain is less than 10% when temperature changes from 20̂C to 40̂C, compared with that of 35% without the compensation.

Radiation damage study of SensL J-series silicon photomultipliers using 101.4 MeV protons

Radiation damage of J-series silicon photomultipliers (SiPMs) has been studied in the context of using these photodetectors in future space-borne scintillation detectors. Several SiPM samples were exposed to 101.4 MeV protons, with 1 MeV neutron equivalent fluence ranging from 1.27×108 neq/cm2 to 1.23×1010 neq/cm2. After the irradiation, the SiPMs experienced a large increase in the dark current and noise, which may pose problems for long-running space missions in terms of power consumption, thermal control and detection of low-energy events. Measurements performed with a CeBr3 scintillator crystal showed that after exposure to 1.23×1010 neq/cm2 and following room-temperature annealing, the dark noise of a single 6 mm square SiPM at room temperature increased from 0.1 keV to 2 keV. Because of the large SiPM noise, the gamma-ray detection threshold increased to approximately 20 keV for a CeBr3 detector using a 4-SiPM array and 40 keV for a detector using a 16-SiPM array. Only a small effect of the proton irradiation on the average detector signal was observed, suggesting no or little change to the SiPM gain and photon detection efficiency.

Use of the Peak-Detector mode for gain calibration of SiPM sensors with ASIC CITIROC read-out

The ASIC CITIROC is a 32-channel fully analogue front-end ASIC dedicated to the read-out of silicon photo-multiplier (SiPM) sensors that can be used in a variety of experiments with different applications: nuclear physics, medical imaging, astrophysics, etc. For each channel, two parallel AC coupled voltage preamplifiers, one for the high gain and one for the low gain, ensure the read-out of the charge from 160 fC to 320 pC (i.e. from 1 to 2000 photo-electrons with SiPM gain = 106, with a photo-electron to noise ratio of 10). The signal in each of the two preamplifier chains is shaped and the maximum value is captured by activating the peak detector for an adjustable time interval. In this work, we illustrate the peak detector operation mode and, in particular, how this can be used to calibrate the SiPM gain without the need of external light sources. To demonstrate the validity of the method, we also present and discuss some laboratory measurements.

Characterisation of SiPM radiation hardness for application in hadron calorimeters at FAIR, CERN and NICA

Silicon PhotoMultipliers (SiPM) are an excellent choice for the scintillator light readout at hadron calorimeters due to their insensitivity to magnetic fields, low operating voltages, low cost, compactness and mechanical endurance. They are already successfully utilized in Projectile Spectator Detector (PSD) of NA61 at CERN, and will be utilized soon in PSD of CBM at FAIR and Forward Hadron CALorimeters (FHCAL) of BM@N at NICA heavy-ion collision experiments. The main issue of SiPM application is their degradation due to high neutron fluence that can reach up to 2×1011 neq/cm2 per year of the experiment operation. Multiple irradiation tests of SiPMs produced by Ketek, Zecotek, Hamamatsu and Sensl manufacturers were conducted at the cyclotron of NPI Řež with a broad neutron spectrum and total fluences in the wide range of 5×1010–6×1012 neq/cm2. Detailed characterisation of all SiPMs was performed based on dependencies of dark current on voltage, capacitance on voltage and frequency, and response to LED light on voltage. SiPM's breakdown voltage, quenching resistance, pixel capacitance, gain and signal to noise ratio were extracted from these measurements. Those parameters' dependence on neutron fluence and their variability are discussed. Performance of the PSD calorimeter module equipped with irradiated SiPMs in CERN during the beam scan with 2–80 GeV/c protons is briefly overviewed.

Gain stabilization of SiPMs with an adaptive power supply

The gain of silicon photomultipliers (SiPMs) increases with bias voltage and decreases with temperature. To operate SiPMs at stable gain, the bias voltage can be readjusted to compensate for temperature changes. We have tested this concept with 30 SiPMs from three manufacturers (Hamamatsu, KETEK and CPTA) operating in a climate chamber at CERN by varying temperatures between 1̂ C and 48̂ C. We built an adaptive power supply that uses a linear dependence of the bias voltage on temperature. We stabilized four SiPMs simultaneously with only one compensation parameter for the readjustment of the bias voltage of four SiPMs. For all tested Hamamatsu and CPTA SiPMs we achieved our goal of limiting gain changes to less than ± 0.5% in the 20–30̂C temperature range.

Study on SiPM breakdown voltage, dark current and gain from room down to liquid nitrogen temperature

Abstract Silicon Photo-Multipliers (SiPMs) at cryogenic temperatures are very promising for the realization of scintillation light detectors to be adopted in particle physics experiments dedicated to neutrino and Dark Matter searches. For these reasons, we tested several devices from different manufacturers with particular emphasis to breakdown voltage, dark current and gain changes at different temperatures. The system, based on a cryo-pump with a cold head, permits to scan the temperature from 300 K down to 50 K. A second system, based on a climatic chamber, was also used. We found that all devices can be operated at cryogenic temperatures. Furthermore, the thermal component of the noise decreases at low temperature, thus allowing the use of the device at higher overvoltage.

High-Resolution Gamma-Ray Spectroscopy With a SiPM-Based Detection Module for 1” and 2” LaBr3:Ce Readout

In this paper, we present a silicon photomultiplier (SiPM)-based photodetector module designed to readout large cerium-doped lanthanum bromide (LaBr3:Ce) scintillators (cylindrical 1” $\times$ 1” and 2” $\times$ 2”) for nuclear physics experiments. The detector prototype has a modular structure and implements a real-time stabilization of the SiPM gain to compensate for the gain drift with temperature. The SiPM module consists of an array of 5 by 6 near-ultraviolet high-density SiPMs (Fondazione Bruno Kessler, Italy), each one having an active area of 6 mm $\times$ 6 mm and 30- $\mu \text{m}$ microcells. The single array is used for the 1” crystal readout, and it is assembled in a $2{\times} 2$ format to read the 2” scintillator. Spectroscopic measurements were performed with both crystals. The 2” crystal was irradiated with different radioactive sources in an energy range between 122 keV and 1.3 MeV, and an energy resolution of 3.19 ± 0.01% full-width at half-maximum (FWHM) has been achieved at 662 keV. The result is very close to the 3.07 ± 0.03% FWHM measured with Super Bialkali photomultiplier tube (PMT) (Hamamatsu R6233-100) at the same energy with the same 2” crystal. In the framework of the comparison between SiPM and PMT for LaBr3:Ce readout, we provide an analysis of the energy resolution contributions based on the measurements performed with the developed gamma-ray detection system.

Temperature-compensated silicon photomultiplier

Silicon PhotoMultipliers (SiPM) have significant temperature dependence of important parameters such as gain, photon detection efficiency and optical crosstalk. Special temperature-controlled power supplies and off-line correction are typically used to mitigate this temperature dependence, though these methods are still not optimal for multichannel photodetectors exposed to significant temperature variations. We report on a design concept for a custom SiPM chip with an integrated thermo-compensation circuit that automatically adjusts an applied bias voltage thus maintaining a stable SiPM overvoltage value and gain over a wide range of temperatures. A prototype of the thermo-compensated SiPM chip was built using commercially available discrete components and tested in the temperature range from −30 to +30 °C. The measured temperature dependence of the thermo-compensated SiPM chip was reduced by factor 38 in comparison with the non-compensated device.

On reachable energy resolution of SiPM based scintillation counters for X-ray detection

Presently, silicon photomultipliers (SiPMs) are very attractive devices to replace photomultipliers for light detection in many different fields. For example, they could be used in detectors of photons with energies of 20–150 keV for medical and nondestructive testing applications. The small size and high electron gain of SiPMs make them very attractive candidates for pixelated X-ray detectors operating in a photon counting mode. In this research we evaluated the detector performance that can be reached with up-to-date Lu-based scintillators. Application of LYSO:Ce and LFS-3 scintillators provides high count rate capability because of a short scintillator decay time of ∼ 40 ns but enables reaching just a moderate energy resolution. Meanwhile, with a LuYAG:Pr scintillator of quite low non-proportionality one can attain much better energy resolution at a reduced rate.

Study of the breakdown voltage of SiPMs

The breakdown behaviour of SiPMs (Silicon PhotoMultiplier) with pixel sizes of 15×15,25×25,50×50, and 100×100μm2, manufactured by KETEK, has been investigated. From the current–voltage characteristics measured with and without illumination by LED light of 470nm wavelength, the current-breakdown voltage, VI, and from linear fits of the voltage dependence of the SiPM gain, measured by recording pulse-area spectra, the gain-breakdown voltage, VG, have been obtained. The voltage dependence of the Geiger-breakdown probability was determined from the fraction of zero photoelectron events with LED illumination. By comparing the results to a model calculation, the photodetection-breakdown voltage, VPD, has been determined. Within experimental uncertainties, VI and VPD are equal and independent of pixel size. For VG, a dependence on pixel size is observed. The difference VI−VG is about 1V for the SiPM with 15μm pixels, decreases with pixel size and is compatible with zero for the SiPM with 100μm pixels.

Gain compensation technique by bias correction in arrays of Silicon Photomultipliers using fully differential fast shaper

Proposed algorithm compensates the gain by changing the bias voltage of Silicon Photomultipliers (SiPM). The signal from SiPM is amplified in fully differential preamplifier then is formed in time by the fully differential fast shaper. The compensation method was tested with four channels common cathode multi-pixel photon counter from Hamamatsu. The measurement system requires only one high voltage power supply. The polarization voltage is adjusted individually in each channel indirectly by tuning the output common mode voltage (VOCM) of fully differential amplifier. The changes of VOCM affect the input voltage through the feedback network. Actual gain of the SiPM is calculated by measuring the mean amplitude of the signal resulting from detection of single photoelectron. The VOCM is adjusted by DAC so as to reach the desired value of gain by each channel individually. The advantage of the algorithm is the possibility to set the bias of each SiPM in the array independently so they all could operate in very similar conditions (have similar gain and dark count rate). The algorithm can compensate the variations of gain of SiPM by using thermally generated pulses. There is no need to use additional current to voltage conversion which could introduce extra noises.

Analog electro-optical readout of SiPMs achieves fast timing required for time-of-flight PET/MR

The design of combined positron emission tomography/magnetic resonance (PET/MR) systems presents a number of challenges to engineers, as it forces the PET system to acquire data in a space constrained environment that is sensitive to electro-magnetic interference and contains high static, radio frequency and gradient fields. In this work we validate fast timing performance of a PET scintillation detector using a potentially very compact, very low power, and MR compatible readout method in which analog silicon photomultipliers (SiPM) signals are transmitted optically away from the MR bore with little or even no additional readout electronics. This analog ‘electro-optial’ method could reduce the entire PET readout in the MR bore to two compact, low power components (SiPMs and lasers). Our experiments show fast timing performance from analog electro-optical readout with and without pre-amplification. With 3 mm × 3 mm × 20 mm lutetium–yttrium oxyorthosilicate (LYSO) crystals and Excelitas SiPMs the best two-sided fwhm coincident timing resolution achieved was 220 +/− 3 ps in electrical mode, 230 +/− 2 ps in electro-optical with preamp mode, and 253 +/− 2 ps in electro-optical without preamp mode. Timing measurements were also performed with Hamamatsu SiPMs and 3 mm × 3 mm × 5 mm crystals. In the future the timing degradation seen can be further reduced with lower laser noise or improvements SiPM rise time or gain.

An Active Compensation System for the Temperature Dependence of SiPM Gain

Silicon photo-multiplier (SiPM) gain drifts due to temperature variations and this issue can be a source of relevant errors, for instance when the application requires high accuracy in the evaluation of the photopeak position, especially at low signal levels. In this paper we describe a compensation system that exploits a SiPM as temperature sensor and is able to keep the detector gain constant by means of fine adjustment of its bias voltage. The system is based on a feedback loop which measures the average amplitude of the dark pulses generated by the detector and compares it with a fixed reference, thus automatically correcting the device bias voltage and achieving constant amplitude of the dark pulses in presence of temperature variations. The same bias correction can be also applied to compensate the gain fluctuations of a SiPM not involved in the feedback loop, characterized by the same temperature dependence. The experimental results prove the effectiveness of the compensation system: for the SiPM used in the measurements, considering a temperature span of 10 $^\circ$ C, the system is able to reduce the corresponding variation of the dark pulse amplitude from about 22% to only 0.78%.

Petiroc and Citiroc: front-end ASICs for SiPM read-out and ToF applications

Petiroc and Citiroc are the two latest ASIC from Weeroc dedicated to SiPM read-out.Petiroc is a 16-channel front-end ASIC designed to readout silicon photomultipliers (SiPMs) for particle time-of-flight measurement applications. It combines a very fast and low-jitter trigger with an accurate charge measurement.Citiroc is a 32-channel front-end ASIC designed to readout silicon photo-multipliers (SiPM). It allows triggering down to 1/3 pe and provides the charge measurement with a good noise rejection. Moreover, Citiroc outputs the 32-channel triggers with a high accuracy (100 ps).Each channel of both ASICs combines a trigger path with an accurate charge measurement path. An adjustment of the SiPM high voltage is possible using a channel-by-channel input DAC. That allows a fine SiPM gain and dark noise adjustment at the system level to correct for the non-uniformity of SiPMs.Timing measurement down to 16 ps RMS jitter for Petiroc and 100 ps RMS for Citiroc is possible along with 1% linearity energy measurement up to 2500 pe. The power consumption is around 3.5 mW/channel for Petiroc and 3 mW/channel for Citiroc, excluding ASICs outing buffer.

T3B — an experiment to measure the time structure of hadronic showers

The goal of the T3B experiment is the measurement of the time structure of hadronic showers with nanosecond precision and high spatial resolution together with the CALICE hadron calorimeter prototypes, with a focus on the use of tungsten as absorber medium. The detector consists of a strip of 15 scintillator cells individually read out by silicon photomultipliers (SiPMs) and fast oscilloscopes with a PC-controlled data acquisition system. The data reconstruction uses an iterative subtraction technique which provides a determination of the arrival time of each photon on the light sensor with sub-nanosecond precision. The calibration is based on single photon-equivalent dark pulses constantly recorded during data taking, automatically eliminating the temperature dependence of the SiPM gain. In addition, a statistical correction for SiPM afterpulsing is demonstrated. To provide the tools for a comparison of T3B data with GEANT4 simulations, a digitization routine, which accounts for the detector response to energy deposits in the detector, has been implemented.

A Novel Technique for the Stabilization of SiPM Gain Against Temperature Variations

In several applications of Silicon Photo-Multipliers (SiPM), drifts of the detector gain with the temperature represent a severe drawback which prevents from achieving optimal performance. We propose an original technique to address this issue, based upon the use of a SiPM not exposed to the light as a temperature sensor. The average amplitude of the dark pulses produced by this detector is measured and controlled to a constant reference value by means of a negative feedback loop, which automatically varies the bias voltage of the SiPM. The same bias voltage variations generated by the feedback loop are also applied to the sensitive SiPMs used in the specific application, thus making constant their gain. The effectiveness of the proposed compensation scheme has been experimentally demonstrated by using two SiPMs from FBK-irst (1 mm × 1 mm, 400 micro-cells, breakdown voltage Vbr ≅ 29 V), one as temperature sensor involved in the negative feedback loop and the other as light sensitive device. Both detectors have been enclosed in a thermally isolated box with temperature varied in the interval between 20 °C and 30 °C : the variation of the SiPM gain can be reduced from more than 20%, without compensation, to about 2%.

SPIROC: design and performances of a dedicated very front-end electronics for an ILC Analog Hadronic CALorimeter (AHCAL) prototype with SiPM read-out

For the future e+ e- International Linear Collider (ILC) the ASIC SPIROC (Silicon Photomultiplier Integrated Read-Out Chip) was designed to read out the Analog Hadronic Calorimeter (AHCAL) equipped with Silicon Photomultiplier (SiPM). It is an evolution of the FLC_SiPM chip designed by the OMEGA group in 2005. SPIROC2 [1] was realized in AMS SiGe 0.35 μm technology [2] and developed to match the requirements of large dynamic range, low noise, low consumption, high precision and large number of read-out channels. This ASIC is a very front-end read-out chip that integrates 36 self triggered channels with variable gain to achieve charge and time measurements. The charge measurement must be performed from 1 up to 2000 photo-electrons (p.e.) corresponding to 160 fC up to 320 pC for SiPM gain 106. The time measurement is performed with a coarse 12-bit counter related to the bunch crossing clock (up to 5 MHz) and a fine time ramp based on this clock (down to 200 ns) to achieve a resolution of 1 ns. An analog memory array with a depth of 16 for each channel is used to store the time information and the charge measurement. The analog memory content (time and charge) is digitized thanks to an internal 12-bit Wilkinson ADC. The data is then stored in a 4kbytes RAM. A complex digital part is necessary to manage all these features and to transfer the data to the DAQ. SPIROC2 is the second generation of the SPIROC ASIC family designed in 2008 by the OMEGA group. A very similar version (SPIROC2c) was submitted in February 2012 to improve the noise performance and also to integrate a new TDC (Time to Digital Converter) structure. This paper describes SPIROC2 and SPIROC2c ASICs and illustrates the main characteristics thank to a series of measurements.