7.3 A 189×600 Back-Illuminated Stacked SPAD Direct Time-of-Flight Depth Sensor for Automotive LiDAR Systems

SPADs and SiPMs Arrays for Long-Range High-Speed Light Detection and Ranging (LiDAR)

“…Detectors typically used in pulsed-LiDAR applications include Charge-coupled devices (CCDs), particularly electron-multiplying CCDs (EM-CCDs) [ 38 ] and intensified-CCDs (I-CCDs) [ 39 ], avalanche photodiodes (APDs) [ 40 ], single photon avalanche diodes (SPADs), and silicon photomultipliers (SiPMs), both analog (a-SiPM) and digital (d-SiPM) [ 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 ].…”

“…Recently, Sony (Tokyo, Japan) has presented a complete MEMS LiDAR system based on a 189 × 600 pixels SPAD array, in 3D-stacked technology, which includes a 90 nm BSI tier for SPADs and a 40 nm CMOS tier for digital logic [ 50 ]. The LiDAR system targets automotive applications with 300 m FSR and a micropixel logic for solar background rejection.…”

“…In Seo [ 57 ], a 1 × 36 SiPM is used for line scanning through MEMS and rotating polygon mirrors to achieve 2200 × 36 resolution and 120° × 8° FOV. In Kumagai [ 50 ], a blade illumination laser scanning with horizontally oscillating MEMS mirrors is used in combination with a staring 63 × 200 SPAD camera activated one column at a time, in a non-coaxial setup.…”

“…The general idea consists of triggering the TDC only when multiple photons are detected within a short coincidence time window, because laser photons are confined within the pulse width whereas background photons are usually equally distributed in time. For instance, in Niclass [ 41 ], Seo [ 57 ] and Kumagai [ 50 ], the macropixel triggers the TDC only when a coincidence event is detected, whereas in 2021 Padmanabhan [ 48 ] the TDC is triggered by the first detected photons but the conversion is validated only if a given number of coincident photons are detected within an adjustable (500 ps–2.2 ns) coincidence window. In Perenzoni [ 52 ], the SPAD output pulse is shrunk down to about 260 ps and all shrunk pulses of the same pixel are combined through an OR-tree into a single pulse train.…”

“…Nevertheless, 905 nm is commonly used in LiDAR application, mainly due to pulsed laser and detectors availability and because of the lower absorption by water (thus allowing LiDAR measurements even through fog and rain) compared to 1550 nm, which is the other standard wavelength employed in LiDAR. In fact, nowadays great efforts are focused on developing Silicon detectors with enhanced sensitivity at 905 nm [ 43 , 75 ] and high FF through 3D stacking (e.g., Ximenes [ 53 , 54 ] and Hutchings [ 46 ]) and on designing eye-safe certified LiDAR systems, such as Kumagai [ 50 ].…”