Timing and probability of crosstalk in a dense CMOS SPAD array in pulsed TOF applications

Abstract

As the distance between neighboring devices in large CMOS single-photon avalanche diode (SPAD) arrays is reduced for improving the density, increased crosstalk becomes an important issue, limiting the maximum practical fill factor of the array. In this study, the temporal correlation of crosstalk events, as well as the crosstalk probability, and their dependence on parameters, such as the illumination wavelength and intensity, and the distance between SPADs, are investigated via measurement of a ~45%-fill factor CMOS SPAD array fabricated using 0.35-µm high-voltage CMOS technology. The SPADs have 24 µm × 24 µm square-shaped active areas, and all devices share a common deep-N-well cathode. On-chip time-to-digital converters with 65-ps resolution are used to measure the timing of crosstalk events in "coincidence measurements." For the crosstalk measurements, the internal noise in one SPAD is used to produce crosstalk events in the neighboring devices. The measurement results indicate both optical and electrical crosstalk with the crosstalk events, having a specific temporal distribution. The crosstalk probability in the first two adjacent pixels is found to be 0.3% and 0.01%, with a distribution having full widths at half maximum (FWHMs) of 700 and 400 ps, respectively. In pulsed time-of-flight measurements, when one SPAD is triggered with external short-pulsed (FWHM of approximately 200 ps) illumination, extra correlated noise in the adjacent SPADs added to the crosstalk noise, increasing the correlated noise considerably. This additional noise was a secondary effect of the absorbed laser photons deep in the substrate.

Quantum correlation measurement with single photon avalanche diode arrays

“…The probability for a false detection pair is (1.45±0.16)×10 −3 for nearest neighbor pixel pairs, while the corresponding value for next nearest neighbors is lower by a factor of ∼ 6. Note that these values are well below the typical values reported in the literature for SPAD arrays (∼ 1%) [6,20,28,60], while conventional SiPM detectors usually have higher probabilities of 4 − 20% [43]. Compared to SiPMs, SPAD arrays usually have a smaller capacitance and consequently a smaller charge flowing through the SPAD.…”

“…For the detector used here we estimated the photon detection efficiency (PDE), by comparison with an independent EMCCD measurement, to be 42% at 515 nm and 7 V excess bias. While PDE, DCR, dynamic range and afterpulsing are often depicted in the literature, only few works discuss the issue of inter-pixel crosstalk [6,20,28,44,60]. While both afterpulsing and crosstalk generate artificial correlations, afterpulsing artifacts are avoided here altogether by disregarding the autocorrelation of any single detector, as typically done in HBT experiments.…”

Single Photon Lidar in Mobile Laser Scanning: The Sampling Rate Problem and Initial Solutions via Spatial Correlations

“…Recent advances in SPAD technology have yielded high pixel count imagers which enable fast acquisition rates and sensitivity to individual photons (Gyongy et al, 2018). Since there are multiple smallsize receivers close to one another, measures have been taken to reduce the crosstalk between the neighboring receivers (Jahromi, Kostamovaara, 2018).…”

Design and Measurement of Ring-Gate Single Photon Avalanche Diode with Low Dark Count Rate

“…Jahromi, S et al analyzed the crosstalk problem in SPAD arrays. In order to improve the fill factor in the array, a SPAD array was fabricated using a 0.35 μm CMOS process, and it was found that the photon noise absorbed by the substrate would significantly increase the crosstalk noise [4]. Mahmoudi, H et al proposed a fiber receiver based on a single photon avalanche diode.…”

“…Because the dead time caused by the quenching circuit of the single photon avalanche diode will seriously affect the performance of the system, Wang, C et al considered the effect of the dead time and proposed a fast blind union detection (FBUD) algorithm, and the test results show that the algorithm is significantly better than the traditional algorithm [6]. It can be found that various researches on various applications of SPAD have been carried out in [4]- [6]. However, the design of high-performance SPAD devices can fundamentally improve the characteristics of the system.…”