Characterization of large TSV MPPC arrays (4×4ch and 8×8 ch) in scintillation spectrometry

The main objective of this work was to characterize the new multi-pixel photon counter (MPPC) arrays with a 12×12mm2 and a 24×24mm2 active area, made using through-silicon via (TSV) technology and with trenches introduced between the cells, in gamma-ray spectrometry with five different scintillators: CsI:Tl, NaI:Tl, LSO/LYSO, BGO, and LaBr3. The results of the study are compared to those obtained previously with the older sample of the 12×12mm2 MPPC array made as a monolithic device. TSV MPPC array with the size of 24×24mm2 is one of the first commercially available SiPM with such a large active area and with the dead space between channels minimized to only 0.2 mm. Moreover, in these devices, Hamamatsu introduced trenches between cells to reduce cross-talk. Hence excess noise factor (ENF) was also reduced from a value of 1.7 to 1.2 in comparison to the “old” monolithic sample (data for the same overvoltage of 1.3V). Whereby for the new MPPCs, the optimum operating voltage is higher by about 0.6V. In consequence, this higher optimal overvoltage means a higher photon detection efficiency (PDE) and number of photoelectrons, and leads to improved energy resolution. Energy resolution measured for the 662keV full energy peak in a 137Csγ-source spectrum recorded with 12×12mm2 TSV MPPC and two CsI:Tl scintillators (12×12×12mm3 and 1×1in) equals to 5.8% and 6.8%, respectively. For the “old” MPPC with the same CsI:Tl scintillators energy resolution is equal to 6.4% and 7.1%, respectively. These improved TSV MPPC arrays can be commercially used for scintillation light readout of “large” crystals with a diameter of 1×1in or 2×2in, suitable for gamma spectrometry in a wide range of applications. The combination of new 8×8ch (24×24mm2) TSV MPPC and 2×2in NaI:Tl gives an excellent energy resolution below 8%, despite the incomplete match of the scintillator surface to the active area of MPPC and loss of the part of the light.