Effect on MIM structured parallel quenching capacitor of SiPMs

A SiPM is an array of several thousand micro-Geiger-mode APDs (GAPD), and a GAPD generally consists of a PN diode (Cd), a quenching resistor (Rq) and any parasitic capacitor (Cq) in parallel to the quenching resistor. The single-photon pulse shape is determined by a RC decay time, a product of Ctotal (Cd+Cq) and Rq. 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 ∼40fF Metal–Insulator–Metal (MIM) quenching capacitor (Cq-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 Cq-MIM has a very fast pulse with a low slow tail, consequently the increasing initial current.