Conventional CMOS image sensors equipped with global shutter function temporarily store charge signals in the memory area located next to the photodiode to resolve image distortion (focal plane distortion) caused by the time shift due to the row-by-row readout. In FSI CMOS sensors, there is a wiring layer on the silicon substrate forming the photodiode, and with such a structure, the benefit is that it is easy to form a light shield for protecting the charge signal temporarily stored in the memory area from leaked light. For this reason, conventional CMOS image sensors with global shutter function have adopted a FSI pixel structure. However, the wiring on top of the photodiode hinders the incident light, which creates an issue when attempting to miniaturize the pixels.
In response to this, Sony has developed a proprietary pixel structure that achieves the global shutter function on a BSI structure that has superior sensitivity characteristics. Normally, when pixels are miniaturized, the sensitivity and saturation characteristics deteriorate, but the new Sony technology enables a reduction in pixel size to 2.74 μm while maintaining performance of those characteristic, thereby achieving about 1.7 times higher resolution than conventional FSI CMOS sensors. Moreover, thanks to the high degree of freedom of the wiring layout of BSI pixel structures, a high speed of about 2.4 times that of conventional sensor can be achieved. In addition, the sensor’s stacked structure makes it possible to mount various signal processing circuits, whereby it is possible to realize smart functions such as signal processing only for the necessary part of the measurement and inspection images in a smaller size compared to conventional sensors.
Going forward, Sony will work to develop products equipped with this stacked CMOS sensor employing its proprietary global shutter function with BSI pixel structure for various industrial applications and intelligent transportation systems, including development of derivatives for signal processing circuits to be mounted. Sony plans to start shipping sample units in the summer of 2019 or later.
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