A 32x24 pixel SPAD detector system for LiDAR and quantum imaging

We have developed a 32x24 pixel sensor array based on single-photon avalanche diodes (SPADs). Beside conventional 2- dimensional imaging, this sensor allows for precise timing of single-photon arrival times which can be exploited in a variety of technical and scientific approaches like 3D image acquisition, quantum imaging and quantum random number generation. Thus, such a sensor is eligible for many fields of application such as autonomous driving, remote and non-lineof- sight sensing, safety, robotics and more recently random number generation for statistical applications or data encryption. The novel sensor contains CMOS integrated backside illuminated SPADs which are connected to an underlying read-out IC by wafer-to-wafer bonding. Their single-photon sensitivity (quantum efficiency QE=60 % @ 580 nm) and high-speed performance (readout frequency 𝑓 = 25 kHz, temporal resolution 𝑡_TDC = 312.5 ps) make the sensor a promising choice for, e.g. quantum imaging with photon-pairs where a 2-dimensional spatial and temporal resolution are as crucial as a low noise level. SPADs also offer exciting opportunities for random number generation by using the randomness of photon generation paired with time-resolved detection and post-processing. Another potential application of the sensor is light detection and ranging for which we integrated the sensor into a demonstrator system for direct time-of-flight measurements. It is capable of coincidence detection using 4 SPADs in each pixel, which allows for background light suppression in outdoor situations. This combination of single-photon sensitivity, precise photon arrival timing and our recent developments in wafer-to-wafer bonding technology gives access to a new generation of optical sensors for a variety of applications.