A CMOS Digital SiPM With Focal-Plane Light-Spot Statistics for DOI Computation

Abstract

Silicon photomultipliers can be used to infer the depth-of-interaction (DOI) in scintillator crystals. DOI can help to improve the quality of the positron emission tomography images affected by the parallax error. This paper contemplates the computation of DOI based on the standard deviation of the light distribution. The simulations have been carried out by GAMOS. The design of the proposed digital silicon photomultiplier (d-SiPM) with focal plane detection of the center of mass position and dispersion of the scintillation light is presented. The d-SiPM shares the same off-chip time-to-digital converter such that each pixel can be individually connected to it. A miniature d-SiPM 8×8 single-photon avalanche-diode (SPAD) array has been fabricated as a proof of concept. The SPADs along each row and column are connected through an OR combination technique. It has 256×256µm 2 without peripherals circuits and pads. The fill factor is about 11%. The average dark count rate of the mini d-SiPM is of 240kHz. The average photon detection efficiency is 5% at 480nm wavelength, room temperature and 0.9V excess voltage. The dynamic range is of 96dB. The sensor array features a time resolution of 212ps. The photon-timing SNR is 81dB. The focal plane statistics of the lightspot has been proved as well by measurements. Index Terms-single photon avalanche diode (SPAD), digital silicon photomultiplier (d-SiPM), time-of-flight (ToF), focal-plane processing, scintillation light spot dispersion

Application of CMOS Technology to Silicon Photomultiplier Sensors

“…As reported in Table 1 , the result is consistent with a similar SiPM obtained at the 180 nm CMOS technology node [ 49 ]. Breakdown voltages ranging from 10 V to 14 V are usually obtained at a scale lower than 180 nm, as in 90 nm [ 56 , 57 ] and 180 nm [ 20 ] CMOS nodes.…”

“…This physics mechanism, together with the presence of STI and lower annealing temperature used at smaller scales, increases the amount of free electrons, which reach the conduction band spontaneously, deteriorating the noise performance of the SiPM sensor. The dark rate obtained in this study is compatible with the results at the 180 nm CMOS technology node [ 49 ].…”

“…This result is below the expectation and is consistent with similar studies in standard CMOS technology processes. We observe in Table 1 that a photon detection efficiency lower than 4% at 420 nm due to the absence of an optical window and to the presence of a passivation layer are reported in the development of CMOS SiPM at the 350 nm HV AMS [ 41 ] and 180 nm [ 49 ] nodes.…”

“…The CMOS technology offers few possibilities of implementing such guard rings [ 19 , 20 , 21 , 22 ]. By way of example, SPAD, SPAD arrays, and SiPM detection structures with several possible layout techniques for the implementation of guard rings were successfully implemented in 800 nm [ 10 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ], 700 nm [ 31 ], 500 nm [ 32 , 33 ], 350 nm [ 18 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 ], 180 nm [ 47 , 48 , 49 ], 150 nm [ 50 ], 130 nm [ 15 , 51 , 52 , 53 , 54 , 55 ], and 90 nm [ 56 , 57 ] CMOS nodes, and were used to detect single photon signals on the basis of the avalanche breakdown process. Two main limitations of the CMOS technology remain; namely, the higher dark rate and the lower photon detection efficiency with respect to the custom-technology-based conventional SiPMs.…”

Spatial resolution improvement for point light source detection in scintillator cube using SPAD array with multi pinholes

“…Therefore this type of scintillation detector usually generates SPAD data within a certain measuring time and resets the SPADs, then the output data are added to estimate the position of scintillation [10,11]. In each case, this type of scintillation detector can only provide spatial resolution about 1 mm even utilizing depth-of-interaction (DOI) method [12], which cannot afford the demands for higher resolution in medical applications.…”