First stacked SPAD ToF depth sensor for automotive LiDAR

September 06, 2021 // By Nick Flaherty
First stacked SPAD ToF depth sensor for automotive LiDAR
Sony has developed a stacked laser sensor for automotive LiDAR using direct time of flight (dToF) and a prototype system design

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.

www.sony-semicon.co.jp/e

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