First stacked SPAD ToF depth sensor for automotive LiDAR
Sony Semiconductor Solutions has developed what it says is the first stacked laser sensor using direct time of flight for automotive LiDAR.
The company has also developed a prototype system design of a mechanical LIDaR, taking on companies such as Velodyne directly.
The IMX459 sensor uses a stacked SPAD (single photon avalanche diode) depth sensor using direct Time-of-Flight (dToF). The 6.25mm sensor combines a 597 x 168 SPAD array on a 10 μm pitch with distance measuring processing circuit onto a single chip, making for a compact 1/2.9-type form factor.
Sony used various technologies such as a back-illuminated pixel structure, stacked configurations, and copper-to-copper connections from its CMOS image sensors to create the LiDAR sensor. This product employs a stacked configuration, where a Cu-Cu connection is used to achieve conduction for each pixel between the back-illuminated SPAD pixel chip and the logic chip equipped with distance measuring processing circuit. This allows for a configuration with circuit placed on the bottom of the pixel chip, maintaining a high aperture ratio while resulting in a small 10 μm square pixel size. This allows a sensor with a detection range from 15cm to 300m.
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The sensor also uses a light incidence plane with irregularities on its surface to refract incident light, thereby enhancing the absorption rate. These features result in a high 24 percent photon detection efficiency in the 905 nm wavelength commonly used in automotive LiDAR laser light sources. For example, it is possible to detect far-off objects with a low reflection rate at high resolution and distance resolution. Additionally, an active recharge circuit is included on the circuit section, which comes with a Cu-Cu connection for each pixel, allowing for a response speed that is approximately 6 nanoseconds at normal operation for each photon.
The sensor is undergoing AEC-Q100 Grade 2 automotive electronic component reliability tests and ony has also introduced a development process that complies with ISO 26262 automobile functional safety standards and supports functional safety requirement level ASIL- B(D) for functionalities such as failure detection, notification, and control.
The output is a MIPI CSI-2 serial (4 lane / 2 lane) interface, and the part is set to start smapling in March 2022.
Sony has also developed a mechanical scanning LiDAR reference design equipped with this new product, which is now being offered to customers and partners. Providing the design will help customers and partners save on man-hours in the LiDAR development process as well as reduce costs by optimizing device selection, it says.
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