Single-photon imaging in complementary metal oxide semiconductor processes

Abstract

This paper describes the basics of single-photon counting in complementary metal oxide semiconductors, through single-photon avalanche diodes (SPADs), and the making of miniaturized pixels with photon-counting capability based on SPADs. Some applications, which may take advantage of SPAD image sensors, are outlined, such as fluorescence-based microscopy, three-dimensional time-of-flight imaging and biomedical imaging, to name just a few. The paper focuses on architectures that are best suited to those applications and the trade-offs they generate. In this context, architectures are described that efficiently collect the output of single pixels when designed in large arrays. Off-chip readout circuit requirements are described for a variety of applications in physics, medicine and the life sciences. Owing to the dynamic nature of SPADs, designs featuring a large number of SPADs require careful analysis of the target application for an optimal use of silicon real estate and of limited readout bandwidth. The paper also describes the main trade-offs involved in architecting such chips and the solutions adopted with focus on scalability and miniaturization.

Wide-field TCSPC: methods and applications

“…In addition, the recent development of SPAD array detectors with picosecond timing capabilities hold great promise for the advancement of time-resolved fluorescence microscopy [57] as discussed below.…”

Ultra Low Noise CMOS Image Sensors

“…Such a signal level can be easily detected and quantized into two logic levels since the number of incident photons during the period of detection is assumed to be much less than one. But these devices present the following disadvantages [13]. First, they are limited to the case of single photon detection.…”

“…With a read noise below 0.3 e − rms , it becomes possible to count the photoelectrons with an accuracy of 90 %. The only commercial solid state semiconductor devices reaching this limit are electron multiplication CCDs (EMCCDs) [12], avalanche photodiodes (APDs) and single photon avalanche photo diodes (SPADs) [13]. All these devices introduce amplification at the early stage of the photoelectron generation by applying an electric field high enough to accelerate the photoelectron in order to multiply by impact ionisation or trigger an avalanche effect.…”

“…The conversion gain corresponds to the dc gain of the pixel transfer function H pix ( f ). It is given by This expression can be further detailed, by expressing the capacitances C GD and C GS as functions of the source follower gate size and oxide capacitance density per unit area, as 13) where C e is the extrinsic capacitance per unit width of the in-pixel source follower transistor. It includes the overlap and fringing capacitances as depicted in Fig.…”

“…10.6. The square magnitude of the frequency response of this filter is given by 13) where the quality factor Q is given by G m -C filter is given by…”