A 3D stacked global-shutter image sensor with pixel-level interconnection technology for high-speed image capturing

We have developed a 3D stacked 16M-pixel, 3.8-mu m pixel pitch, global-shutter CMOS image sensor with pixel level interconnections using four million micro bumps. The four photodiodes in the unit pixel circuit on the top substrate share one micro-bump interconnection at a 7.6-mu m pitch. Each signal of the photodiodes is transferred to the corresponding storage node on the bottom substrate via the micro bump. This 3D architecture gives the image sensor not only a 16M-pixel global-shutter function but also a 2M-pixel 10K-fps high-speed image capturing mode with a burst of eight images. In this paper, we report on the improvement in the high-speed image capturing mode to operate at up to 100K fps by optimizing the timing for the higher-speed | image capturing with 2M-pixel resolution. In addition, we estimated the further potential of the 3D image sensor for high-speed image capturing to make the most of the 3D structure, which comprised one photodiode in the pixel unit circuit on the top substrate and electrically connected multiple storage nodes on the bottom substrate. This enables the image sensor to capture a burst of as many frames as the number of storage nodes in the pixel unit without sacrificing a photodiode and have better sensitivity with photodiodes fully occupying the chip surface with bigger photodiodes than when using conventional sensors. These results demonstrate that our 3D stacking technology pushes the envelope of capturing high-speed images with monolithic sensors.