Experimental method to monitor temperature stability of SiPMs operating in conditions of extremely high dark count rate

The use of Silicon Photomultipliers (SiPMs) in high radiation environments (e.g. detectors at collider experiments) or in outdoor conditions (e.g. LIDAR applications), requires to deal with a high level of dark count noise. An undesired effect emerging under these conditions is the self-heating of the SiPM due to a large power dissipation that causes variations of the breakdown voltage and thus affects operating parameters such as gain and PDE. A method to evaluate the heat dissipation properties of different SiPM packages and the temperature stability of SiPMs during operation under extremely high dark count rates (larger than 30 GHz) is presented in this paper. Starting from a condition in which the SiPM is at thermal equilibrium with the environment, a change in the current measured under intense illumination with a LED can be attributed to a temperature variation of the SiPM due to self-heating. Under certain assumptions, a quantitative estimate of the local change of temperature can be obtained if certain parameters of the SiPM are known: gain, photon detection efficiency, equivalent charge factor and drift of the SiPM breakdown voltage with temperature. The method is applied to evaluate the thermal conductivity of different SiPM package configurations, which is a key requirement for reliable operation in conditions of extremely high dark count rate. Among the SiPM package configurations tested, the one consisting of a ceramic substrate coupled to a copper heat sink provided the best performance in terms of good heat dissipation with less than 0.5 °C temperature variation for 100 mW dissipated power.