Effect on MIM structured parallel quenching capacitor of SiPMs

Abstract A SiPM is an array of several thousand micro-Geiger-mode APDs (GAPD), and a GAPD generally consists of a PN diode ( C d ), a quenching resistor ( R q ) and any parasitic capacitor ( C q ) in parallel to the quenching resistor. The single-photon pulse shape is determined by a RC decay time, a product of C total ( C d + C q ) and R q . A large fraction of current in the long tailed single-photon pulse shape causes Scintillation detectors with SiPM to exhibit a poor timing resolution compared to PMTs, which have very narrow Gaussian single-photon pulse shape. In this paper, a ∼40 fF Metal–Insulator–Metal (MIM) quenching capacitor ( C q-MIM ) parallel to a quenching resistor in a Geiger mode APD is proposed to modify the single-photon pulse shape of a SiPM, in order to improve the timing performance of PET detectors. A single-photon pulse shape with C q-MIM has a very fast pulse with a low slow tail, consequently the increasing initial current.