IEDM 2021: Canon Presents 3.2MP SPAD Sensor for Low-Light Imaging

IEDM publishes few pictures from Canon's IEDM paper #20.2, “3.2 Megapixel 3D-Stacked Charge Focusing SPAD for Low-Light Imaging and Depth Sensing,” K. Morimoto/J. Iwata et al.

3D Backside-Illuminated SPAD Imager Sensors: Unlike the CMOS image sensors found in smartphones, which measure the amount of light reaching a sensor’s pixels in a given timeframe, single photon avalanche diode (SPAD) image sensors detect each photon that reaches the pixel. Each photon is converted into an electric charge, and the electrons that result are eventually multiplied in avalanche fashion until they form an output signal. SPAD image sensors hold great promise for high-performance, low-light imaging applications, for depth sensing, and for fully digital system architectures.

However, until now their performance has been limited by tradeoffs in pixel detection efficiency vs. pixel size, and by poor signal-to-noise ratios. Recently a charge-focusing approach was proposed to overcome these issues, but until now it remained to be implemented. In a late-news paper, Canon researchers will discuss how they did so, with the industry’s first 3D-stacked backside-illuminated (BSI) charge-focusing SPADs. The devices featured the largest array size ever reported for a SPAD image sensor (3.2 megapixels) and demonstrated a photon detection efficiency of 24.4%, and timing jitter below 100ps at 940 nm.

From the images below:

(a) is a full-resolution color intensity image captured by the 3.2megapixel SPAD image sensor at a high light level.

(b) is a monochrome intensity image captured by the device under a scene illumination of 2mlux (without post-processing)

(c) is a monochrome intensity image captured by the device under a scene illumination of 0.3mlux (without post-processing)

a full-resolution color intensity image captured
by the 3.2megapixel SPAD image sensor
at a high light level.

a monochrome intensity image captured
 by the device under a scene illumination
 of 2mlux (without post-processing)

a monochrome intensity image captured
by the device under a scene illumination
 of 0.3mlux (without post-processing)