Silicon hybrid SPAD with high-NIR-sensitivity for TOF applications

This paper proposes a single-photon avalanche diode (SPAD) sensor array comprised of a hybrid structure which can maximize the fill factor of the active area and be compatible with the other detector layer optimized for various demands. In order to implement the hybrid structure, a 100μm pitch through silicon via (TSV) implementation method has been developed to access the back surface of the sensor layer. The achieved fill factor is up to 60%, thus, photon detection efficiency can be reached 35%. A 32×32 SPAD array and a dedicated application specific IC has been designed. We have proved the concept structure can work successfully through the characterization of the hybridized chip. On the other hand, we realized multi-event detection capability should be considered when we apply the photon counting image sensor to a time-of-flight application in high background intensity, and the new concept of a SiPM-based pixel structure has been considered. In order to prove the concept, fundamental experiments have been performed by using the new SiPMs which have extended sensitivity in the near infrared region, and a current mode front-end ROIC which can mark a time-of-arrival and distinguish a photon quantity. A walk error has been studied and found the plot of the time-of-arrival and the photon quantity can be utilized for the measurement compensation.