Sony has developed a stacked direct Time of Flight (dToF) depth sensor for automotive LiDAR using single-photon avalanche diode (SPAD) pixels, an industry first.*1 This achievement was announced at the International Solid-State Circuits Conference (ISSCC), which opened on February 13, 2021.
The new technology employs a back-illuminated SPAD pixel structure that uses a Cu-Cu connection to achieve conduction for each pixel between the pixel chip (top) and the logic chip equipped with distance measuring processor circuits (bottom). This allows for a configuration with all circuits other than light-incorporating pixels to be placed on the bottom, resulting in a high aperture ratio and a high 22% photon detection efficiency rate. Even with its compact chip size, a high resolution of approximately 110,000 effective pixels (189 x 600 pixels) at a pixel size of 10 μm is achieved. This enables high-precision distance measuring at 15-centimeter range resolutions up to a distance of 300 meters, thereby contributing to improved LiDAR detection and recognition performance.
Sony has developed its original Time to Digital Converter (TDC), which converts the detected photon flight time into a digital value, and an original passive quenching/recharge circuit, and employed them along with a Cu-Cu connection for each pixel, making it possible to improve the response speed per photon to 6 nanoseconds under normal conditions. High-speed distance measuring processing contributes to safer driving by detecting and recognizing surrounding conditions in real time.