The presented results are obtained during the first steps taken in order to develop a set-up and measurement procedures which allow to compare properties of diverse samples of silicon photomultipliers. The response to 

low-intensity light was studied for silicon photomultipliers produced by CPTA (Russia), Hamamatsu(Japan), ITC-irst (Italy) and SensL (Ireland)

Bosio, C.

Gentile, S.

Kuznetsova, E.

Meddi, F.

English

Scientific Open-access Literature Archive and Repository

DOI 10.1393/ncc/i2008-10267-7IL NUOVO CIMENTO Vol. 30 C, N. 5 Settembre-Ottobre 2007First results of comparative studies of silicon photomultipliers(∗)C. Bosio(1), S. Gentile(2), E. Kuznetsova(1) and F. Meddi(2)(1) INFN, Sezione di Roma 1 - Rome, Italy(2) Universita` di Roma “La Sapienza” - Rome, Italy(ricevuto il 3 Marzo 2008; pubblicato online il 29 Aprile 2008)Summary. — The presented results are obtained during the first steps taken inorder to develop a set-up and measurement procedures which allow to compare prop-erties of diverse samples of silicon photomultipliers. The response to low-intensitylight was studied for silicon photomultipliers produced by CPTA (Russia), Hama-matsu (Japan), ITC-irst (Italy) and SensL (Ireland).PACS 85.60.Gz – Photodetectors (including infrared and CCD detectors).PACS 85.60.Ha – Photomultipliers; phototubes and photocathodes.1. – IntroductionFast development of the silicon photomultiplier technology results in a number ofdifferent SiPM types available on market and produced by different manufacturers. Sys-tematic studies done with various types of SiPM would provide start information foran optimal choice of the device appropriate for a given application. The results pre-sented here are obtained during the first steps taken in order to develop a set-up andmeasurement procedures which allow to compare properties of diverse SiPM samples.The measurements discussed here include current-voltage characteristics and studiesof the SiPM response to low-intensity light. While results of the former measurementsare mostly used to check the sample operability and to define the range of bias voltagesfor the latter studies, the measurements of the SiPM response to the light provide anumber of parameters suitable for the comparison of different samples.2. – Measurement set-upA principal scheme of the measurement set-up is shown in fig. 1. The bias voltageand current through a SiPM sample are monitored in the voltage circuit. The SiPM is(∗) Paper presented at the 1st Workshop on Photon Detection for High Energy Medical andSpace Applications; Perugia, June 13-14, 2007.c© Societa` Italiana di Fisica 529530 C. BOSIO, S. GENTILE, E. KUZNETSOVA and F. MEDDIFig. 1. – A principal scheme of the measurement set-up. The bias voltage and current througha SiPM sample are monitored in the voltage circuit. The SiPM is illuminated with light from aLight-Emitting Diode (LED) operated in a pulse mode. The signal from SiPM is read out witha charge-sensitive preamplifier (PA) and digitised with an integrating ADC. The LED pulse andADC gate are synchronised by means of a common trigger.illuminated with light from a light-emitting diode operated in a pulse mode. The LEDdrive developed by Institute of Physics ASCR (Prague) provides current pulses withtunable amplitude and duration and a sharp rise time down to 2 ns [1]. The signal fromSiPM is read out with a charge-sensitive preamplifier and digitised with an integratingADC. The LED pulse and ADC gate are synchronised by means of a common trigger.No temperature control is implemented yet; the measurements are done at roomtemperature. Temperature variation during the measurements done for one sample didnot exceed 2 ◦C, for all measurements discussed here the total variation was less than4 ◦C.3. – Measurement resultsFive samples of silicon photomultipliers have been studied. CPTA(1) producedsamples distributed by Obninsk University and Forimtech(2), HAMAMATSU producedMulti-Pixel Photon Counter S10362-11-025C [2], ITC-irst(3) and SensL(4) produced sam-ples were compared on the base of the measurement results.Figure 2 shows the current-voltage characteristics measured for the listed samples.Figure 3 shows an example of the SiPM response to low-intensity light measured withthe described set-up. The peaked structure indicates the number of cells fired duringone light pulse, starting with the pedestal for no cells fired. The distance between peakscorresponds to the SiPM gain.The spectrum is fitted as a sum of Gaussian distributions:(1)∑iG(Ni, μi, σi) =∑iG(Ni, μ0 + i · g, σi),where μ0 corresponds to the pedestal position and g is gain in units of ADC counts.(1) CPTA, Russia, http://www.zao-cpta.ru(2) Forimtech SA, http://www.forimtech.ch(3) ITC-irst, Italy, http://www.itc.it/irst(4) SensL, Ireland, http://www.sensl.comFIRST RESULTS OF COMPARATIVE STUDIES OF SILICON PHOTOMULTIPLIERS 531 [V]biasU10 20 30 40 50 60 70 80current [nA]-110110210310410HAMAMATSU         T=26.2 CIRST              T=24.8 CObninsk/CPTA      T=27.1 CFORIMTECH/CPTA    T=24.5 CSensL             T=24.5 CFig. 2. – The current-voltage characteristics measured for the studied samples.From statistical considerations the width of the i-th peak σi can be expressed as(2) σi =√σ20 + i · 〈σpx〉2,where σ0 is the pedestal width and 〈σpx〉 represents fluctuations of the one-cell responseaveraged over the active area of the sample.In order to check reproducibility of the measurements and fitting procedures, a seriesof spectra was taken for the same bias voltage but under different light intensities. Fig-ure 4 shows the fitted width of the i-th peak as a function of the peak number obtainedfrom different measurements (left) and the corresponding averaged values (right). Theright plot is fitted according to eq. (2).The gain as a function of the overvoltage Ubias − Ubrd was studied for several valuesof the bias voltage. The breakdown voltage Ubrd is defined here as the bias voltagecorresponding to the gain equal to one. Figure 5 shows the results obtained for themeasured samples.Fig. 3. – ADC spectrum of the SiPM response to the low-intensity pulsed light (dashed his-togram) fitted to a superposition of seven Gaussian peaks (gray line).532 C. BOSIO, S. GENTILE, E. KUZNETSOVA and F. MEDDIFig. 4. – Fit values for the width of the i-th peak as a function of the peak number (left).The results obtained from different measurements are shown with different markers. The cor-responding averaged values as a function of the peak number (right) are fitted according toeq. (2).Figure 6 shows gain normalised to the corresponding values of pedestal width (left)and 〈σpx〉 (right) as functions of the overvoltage. Being averaged over the active area ofSiPM, 〈σpx〉 contains statistical and systematic parts:(3) 〈σpx〉 ∼√N + σ2nu ,where N is the average number of charge carriers in the avalanche and σnu represents[V]brd-UbiasU0 0.5 1 1.5 2 2.5 3 3.5 4relative gain [ADC ch]0102030405060708090100HAMAMATSU      9.73IRST           24.7Obninsk/CPTA   11.4FORIMTECH/CPTA 15.2SensL          26.7Fig. 5. – Gain as a function of the overvoltage. Slope values obtained from the linear fit areshown on the top.FIRST RESULTS OF COMPARATIVE STUDIES OF SILICON PHOTOMULTIPLIERS 533Fig. 6. – The gain normalised to the corresponding values of pedestal width (left) and 〈σpx〉(right) as functions of the overvoltage.non-uniformity of the amplification over the SiPM active area. Since gain g ∼ N , theratio g/〈σpx〉 shown in fig. 6 (right) tends to a linear behaviour for the small gain valuesN  σ2nu. For the large gain values N  σ2nu the dependence would correspond to squareroot law g/〈σpx〉 ∼√N in the case of a constant σnu. As seen from fig. 6 (right) ratiog/〈σpx〉 ∼√N obtained for some of the samples indicate growth of the non-uniformityfactor σnu with the bias voltage.4. – ConclusionThe obtained results demonstrated operability and potential of the developed set-up.Further development and tune of the set-up, measurement procedure and data treatmentwill allow to obtain comparative characteristics of diverse types of silicon photomultipli-ers.∗ ∗ ∗We would like to thank Prof. R. Battiston (University and INFN of Perugia), Prof.V. Saveliev (Obninsk State University and DESY), Dr. I. Polak (Institute of Physicsof the ASCR, Prague) and Mr. N. D’Ascenzo for support and fruitful discussions.REFERENCES[1] CALICE Collaboration, Memorandum to DESY-PRC.[2] HAMAMATSU, Product catalogue (http://jp.hamamatsu.com/products/sensor-ssd/4010/index en.html).

First results of comparative studies of silicon photomultipliers

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First results of comparative studies of silicon photomultipliers

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