Conventional CMOS image sensors widely used in products currently on the market are mainly equipped with a rolling exposure function. This rolling exposure causes so-called "Jell-o effect" distortion when capturing a moving target. CMOS image sensors with a global-shutter function are one of the solutions to avoid this distortion. An in-pixel storage node is required to create a global-shutter CMOS image sensor. A floating diffusion and an additional capacitor can be used as an in-pixel storage node [1,2]. The light sensitivity of the in-pixel storage node is specified by the parasitic light sensitivity (PLS), which is the ratio of the light sensitivity of an in-pixel storage node and the light sensitivity of a photodiode. The PLS should be small enough so that the in-pixel storage is not lightsensitive. Artifacts are captured in an image from bright moving objects during read-out if the PLS is not small enough. The PLS of reported global-shutter CMOS image sensors is around -100dB. That would be small enough to use those image sensors in fields where the light source can be controlled. However, for DSC usage, users can easily encounter scenes with bright objects (e.g. sunlight or car headlights). Even if the in-pixel storage node is light-shielded, it is difficult to perfectly protect the in-pixel storage node from photo-generated carriers, as long as the in-pixel storage node and a photodiode are on the same silicon substrate. Meanwhile, 3D stacking technologies have been introduced for image sensors to give them more functionality and improved performance [3,4]. The reported minimum interconnection pitches for image sensors are over 20μm. These technologies do not fit the smaller pixel pitches of the image sensors in recent DSCs. In this paper, we report a rolling-shutter distortion-free 3D stacked image sensor with an in-pixel storage node of -160dB parasitic light sensitivity. The image sensor virtually achieves a global-shutter function using a 4times frame-shutter operation. The image sensor has 2 semiconductor substrates, where 1 substrate has a backside-illuminated photodiode array and the other a storage-node array. The image sensor achieves a PLS level of -160dB. The image sensor has 8.6μm pitched interconnections, and an interconnection yield of over 99.9% is achieved.

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This means there are four million micro bumps in the pixel array area for 16 million effective pixels. The signals from readout circuit on the bottom substrate are transferred to the top substrate with micro bumps which are arrayed outside a pixel array area and readout to the outside of the chip through bonding pads in the bottom Abstract We have developed a 3D stacked 16Mpixel 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 in a 7.6µm pitch. Each signal of the photodiodes is transferred to the corresponding storage node on the bottom substrate via the interconnection to achieve a global-shutter function. The ratio of the parasitic light sensitivity of an in-pixel storage node and the light sensitivity of a photodiode is -180dB with a 3.8µm pixel. In addition, we discuss further improvement to reduce noise figure in global-shutter image sensors.

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We demonstrated multiband imaging with a multi-storied photodiode CMOS image sensor (CIS), which comprises two individually functioning layered devices that achieve optimized images in different substrates bonded by 3D technology. The sensor is able to capture a wide variety of multiband images, which is not limited to conventional visible RGB (Red Green Blue) images taken with a Bayer filter or to invisible infrared (IR) images, at the same time without any color or image degradation even with an extra IR light source. Its wide range sensitivity enables us to select the specific narrow band light wave with specific optical filter in addition to visible RGB images. This wide selection of specific wavelengths of light is useful for specific applications like medical systems to identify pathological lesions and also enables additional functions on the same sensor to make such systems smarter, smaller, and cheaper than the conventional combination of IR imaging sensors with RGB image ones. A wide selection of multiband images is also possible with our device by modifying the top semiconductor layer thickness or changing the characteristics of a color filter on the top substrate to cover a wide range of application needs.Introduction: