Sony is planning to release a stacked SPAD depth sensor for automotive LiDAR. Enhanced Detection and Recognition Capabilities for Automotive LiDAR Applications Contributing to the Safety and Security of Future Mobility.
Atsugi, Japan — Sony Semiconductor Solutions Corporation today announced the upcoming release of the IMX459 stacked SPAD depth sensor for automotive LiDAR applications using direct Time-of-Flight (dToF) method, an industry first.
This product combines a single chip with tiny 10 m square single-photon avalanche diode (SPAD) pixels with a distance measuring processing circuit, resulting in a 1/2.9-type form factor that delivers high-precision, high-speed distance measurement.
The new sensor contributes to future mobility safety and security by enhancing automotive LiDAR detection and recognition performance, which is becoming more important as advanced driver assistance systems (ADAS) and autonomous driving become more widespread (AD).
|Model name||date (planned)||Sample price|
|IMX459 1/2.9-type (6.25 mm diagonal) approx.|
100,000 effective-pixel*3 SPAD ToF depth sensor
for automotive LiDAR applications
|March 2022||15,000 yen|
LiDAR is becoming increasingly essential as a technique of high-precision detection and recognition of road conditions, as well as the location and shape of objects such as cars and people, in addition to sensing devices such as automotive cameras and millimeter-wave radar. Meanwhile, technical hurdles remain in the way of LiDAR’s growth and penetration of the market, including the need for further improvements in distance measuring performance, delivery of greater safety and reliability regardless of usage environment and conditions, and a shift to a solid-state design to achieve a more compact form and lower cost. To address these issues, a number of initiatives are in the works.
SPAD pixels are used as a type of detector in a 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, among the various methods used for LiDAR distance measurement. Sony has achieved a unique device construction that includes SPAD pixels and a distance measuring processing circuit on a single chip by leveraging Sony’s technologies such as a back-illuminated pixel structure, stacked configurations, and Cu-Cu connections developed in the development of CMOS image sensors.
This design allows for a compact form and high resolution of roughly 100,000 effective pixels on a 1/2.9 type format, thanks to the minuscule 10 m square pixel size. It also has improved photon detection efficiency and responsiveness, allowing for high-speed, high-precision distance measurements with 15-centimeter range resolutions from long to short ranges. The product meets functional safety regulations for automotive applications, which improves LiDAR reliability, and the single-chip design allows for more compact, low-cost LiDAR.
Cu-Cu connections is a technology that provides electrical continuity via connected Cu (copper) pads when stacking the pixel section (top chip) and logic circuits (bottom chip). Compared with through-silicon via (TSV) wiring, where the connection is achieved by electrodes intruded around the circumference of the pixel area, this method gives more freedom in design, improves productivity, allows for a more compact size, and increases performance.
A layered structure with both 10 m square SPAD pixels and a distance measuring processing circuit allows for high-speed, high-precision distance measurement. A Cu-Cu connection is employed to achieve conduction for each pixel between the back-illuminated SPAD pixel chip (top) and the logic chip equipped with a distance measuring processing circuit in this device, which uses a stacked architecture (bottom). This enables for a layout with the circuit on the bottom of the pixel chip, resulting in a compact 10 m square pixel size while keeping a high aperture ratio. A light incidence plane having imperfections on its surface is also used to refract incident light, increasing the absorption rate. In the 905 nm wavelength widely utilized in automobile LiDAR laser light sources, these qualities result in a high photon detection effectiveness of 24 percent. For example, with a low reflection rate and high resolution and distance resolution, it is possible to identify far-off objects.
In addition, the circuit portion includes an active recharge circuit with a Cu-Cu connection for each pixel, allowing for a response time of roughly 6 nanoseconds for each photon in normal operation.
This unique stacked construction enables high-speed, high-precision distance measuring at 15-centimeter range resolutions from long-range to short-range distances, thereby contributing to improved automotive LiDAR detection and recognition performance.
This product will be certified as meeting the AEC-Q100 Grade 2 automotive electronic component reliability test standards. Sony has also implemented a development process that adheres to ISO 26262 automotive functional safety requirements and supports functional safety requirement level ASIL- B(D) for failure detection, reporting, and control. All of this will help to increase LiDAR accuracy.
Sony has also created a mechanical scanning LiDAR reference design that includes this new product and is now available to customers and partners. By providing the design, clients and partners will be able to save time and money during the LiDAR development process by optimizing device selection.
Mechanical Scanning is a method that provides horizontal scanning of a laser emitted from a laser diode by rotating a polygon mirror at high speeds.
|Effective pixels||597 x 168 pixels (H x V), approx. 100,000 pixels|
|Image size||Diagonal 6.25 mm (1/2.9-type)|
|Recommended light source wavelength||905 nm|
|SPAD unit cell size||10.08 μm x 10.08 μm (H x V)|
|Element size (ToF pixel unit)||3 x 3 (H x V)|
|Photon detection efficiency||24%|
|Response speed||Approx. 6 ns|
|Power supply||SPAD breakdown voltage||-20.5V|
|SPAD excess voltage||3.3V|
|Interface||MIPI CSI-2 serial output (4 lane / 2 lane)|
|Package||152-pin Plastic BGA|
|Package size||15.65 mm x 15.35 mm (H x V)|
|Max. detection distance||300 m|
|Distance precision at 300 m||3 x 3 pixels (H x V) additive mode: 30 cm|
6 x 6 pixels (H x V) additive mode: 15 cm