Sony stacks SPAD sensor and logic in single chip for automotive lidar - Embedded.com

Sony stacks SPAD sensor and logic in single chip for automotive lidar

Sony said its new IMX459 is the industry’s first stacked SPAD depth sensor for automotive lidar applications that includes SPAD pixels and distance measuring processing circuit on a single chip.

In addition to sensing devices such as automotive cameras and millimeter wave radar, lidar is becoming increasingly an essential part of high-precision detection and recognition of road conditions, and the location and shape of objects such as cars and pedestrians. However, lidar does have some technical hurdles remaining, including the need for further improvements in distance measuring performance, delivery of greater safety and reliability regardless of the usage environment and conditions, and shifting to a solid-state design to achieve a more compact form and lower cost. There are various initiatives underway to address these challenges.

Out of various methods used for lidar distance measurement, single-photon avalanche diode (SPAD) pixels are used as a type of detector in a direct time-of-flight (dToF) sensor, which measures the distance to an object by detecting the time of flight (time difference) of light emitted from a source until it returns to the sensor after being reflected by the object.

Sony said it has succeeded in creating a unique device construction that includes SPAD pixels and distance measuring processing circuit on a single chip, which it claims is an industry first for automotive lidar, with its new IMX459 SPAD depth sensor, scheduled to start sampling from March 2022. The new sensor will help contribute to safe, secure future mobility by improving automotive lidar detection and recognition performance required for advanced driver assistance systems (ADAS) and autonomous driving (AD).

Sony stacked SPAD sensor
The new IMX459 packs a tiny 10 μm square single-photon avalanche diode (SPAD) pixels and distance measuring processing circuit onto a single chip, making for a compact 1/2.9-type form factor delivering high-precision, high-speed distance measurement. (Source: Sony)

The new IMX459 leverages Sony’s technologies created in the development of CMOS image sensors, such as a back-illuminated pixel structure, stacked configurations, and Cu-Cu connections. This design helps achieve a tiny, 10 μm square pixel size, allowing for a compact form and high-resolution of approximately 100,000 effective pixels on a 1/2.9 type format. It also delivers enhanced photon detection efficiency and improved responsiveness, enabling high-speed, high-precision distance measuring at 15-centimeter range resolutions from long-range to short-range distances. The product complies with functional safety standards for automobile applications, which help improve lidar reliability, and the single chip construction contributes to more compact, low-cost lidar.

The 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 (top) and the logic chip equipped with distance measuring processing circuit (bottom). 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. The product also employs 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% 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 product is also set to be certified for meeting the requirements of AEC-Q100 Grade 2 automotive electronic component reliability tests. Sony 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. All this will contribute to improved lidar reliability.

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.

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