Search

The 3D vertical integration of SPAD and readout electronics is a promising avenue to high performance photodetectors. This approach will minimize most limitations of current SiPM and lead to better performances in terms of effective PDE, timing and added functionalities. In this paper, we present a new integrated digital SiPM electronic architecture. This specific architecture aims to replace conventional analog SiPM with the added benefits of a significantly lower and constant output capacitance as well as immunity to SPAD to SPAD gain variation on the single photon resolution while providing an analog-like output signal waveform representing the sum of all triggered SPADs. This electronic architecture also offers options to turn off noisy SPADs, to reduce afterpulsing through a programmable hold-off time and to adjust the dynamic range of the output depending on the photon flux. While the 3D integration process development is underway, we realized a 2D version as a proof of principle of the electronic architecture. The 2D detector presented in this article is composed of an array of 242 pixels for a size of $1.1\times 1.1$ mm2. The output capacitance of the device is 5.6 pF/mm2, the timing jitter associated to the quenching circuit is about 40 ps FWHM and the maximum timing skew within the array is about 70 ps, which could still be optimized.

Single Photon Avalanche Diodes (SPAD) are known for their excellent timing performance which enables Time of Flight capabilities in positron emission tomography (PET). However, current array architectures juxtapose the SPAD with its ancillary electronics at the expense of a poor fill factor of the SPAD array. The 3D vertical integration of SPADs and readout electronics represents a solution to the aforementioned problem. Compared to systems with external electronics readout, 3D vertical integration reduces the SPAD interconnect parasitic capacitance while greatly increasing the photosensitive area and improving overall performances. This paper presents the implementation of two SPAD structures designed for PET. The SPAD structures are designed using Teledyne DALSA high voltage (HV) CMOS technology targeted for a 3-dimensional single photon counting module (3DSPCM). SPAD with two types of guard ring (diffusion-based and virtual guard ring) are designed, fabricated and characterized. All structures are based on a $p + $ anode in an $n$ -well cathode and are implemented along with active quenching circuits for proper characterization. The results show that the contact distribution and the anode-cathode spacing impact the dark count rate (DCR). The design of SPADs with a diffusion guard ring have a DCR down to $3~\hbox{s}^{- 1}\mu \hbox{m}^{-2}$ at room temperature, afterpulsing probability of $ , timing resolution of 27 ps FWHM and PDE of 49% at 480 nm.

We developed a configurable model of single photon avalanche diodes (SPAD) array photodetectors with intelligent control and active quenching. In this model individual components can be simulated independently and subsequently linked to provide the overall detector response. The model enables the simulation of the entire detector and analysis of performance, including photon detection efficiency, timing and energy resolution. It can be used to optimize detector performance for specific applications, such as positron emission tomography (PET). The simulator consists of multiple configurable and interchangeable modules to model the array geometry as well as physical and optical characteristics based on physical models and statistical equations. Readout electronics are also simulated in an algorithmic form. Monte Carlo simulations are used to model the 511 keV annihilation photon interactions and the optical photon transport in the scintillator, as well as carrier random walk in the silicon. Different methods to extract information from the digital output signal can be investigated. The simulator paves the way to the developement of new algorithms to extract relevant information in PET, but also for other applications such as Cerenkov radiation and fluorescence microscopy. Simulation results for photon detection efficiency, energy resolution and timing resolution are reported, showing the functionality of the simulator.