CMOS integrated SPAD detectors for LiDAR
Through the progressive development of driving assistance systems up to autonomous vehicles there is an increasing need for highly dynamic, efficient and reliable sensors for three-dimensional capturing of the environment. The CSPAD detectors developed by Fraunhofer IMS unite highly sensitive 3D imaging with secure algorithms for the efficient use in LiDAR applications. The central goal is to achieve a maximal range, even in high sunlight intensity, while also having low system costs. The CSPAD technology is based on the integration of the SPAD detectors (Single Photon Avalanche Diodes) in a 0.35 µm CMOS process certified for the automotive industry and optimized for optoelectronic applications. This allows SPAD detectors and evaluation electronics to be accommodated on the same chip. An example of this is the double line sensor SPADeye2 with 2x192 pixels and one time-to-digital converter per pixel. In addition, 3D integration in wafer-to-wafer and chip-to-wafer bonding processes allows the realization of back-lit CSPAD detectors. The stacked arrangement of image receiver and evaluation electronics makes the detector even more efficient and compact. In this way, CSPAD area sensors with thousands of pixels can be realized for use in solid-state LiDAR systems with high resolution.
The CSPAD detectors developed at the Fraunhofer IMS are characterized in particular by the adaptive photon coincidence circuits integrated into the pixels for background light suppression. This is the only way to increase the range in high sunlight and to ensure reliable distance measurement even under changing weather conditions.
In addition to the development and production of new 3D sensors, also customized, the Fraunhofer IMS offers a wide range of services in the field of LiDAR. Evaluation boards for CSPAD chips as well as complete LiDAR cameras with corresponding software are offered, with which the sensors can be evaluated in realistic measurement scenarios. Furthermore, system simulations are carried out at the Fraunhofer IMS and new methods for signal processing are constantly being investigated to achieve an additional increase in range.