In this paper we discuss the development of an indirect time-of-flight (ToF) pixel in the 0.11-µm CMOS image sensor technology. The pixel design is based on a pinnedphotodiode structure with a novel vertical overflow drain (VOD) shutter mechanism used for fast modulation. We present the second generation of the pixel, with a greatly improved VOD structure that enables a fast shutter efficiency better than 1:100 and a deeper photodiode collection depth for better quantum efficiency in the near-infrared wavelengths. We present a new 6.7-µm pixel design with four pinned storage diodes (SDs) that feature in-pixel complete charge transfer and enable correlateddouble-sampling readout as well as an almost simultaneous global shutter exposure of up to four interleaved frames to be used for the scene depth computation. The novel design features a low readout noise of 7.5e-and a full-well-capacity of 9500e-per SD (a total of 38 000e-per pixel).Index Terms-CMOS image sensor, time of flight (ToF) imaging, time resolved.
We developed a new 2.5 μm global shutter (GS) pixel using a 65 nm process with an advanced light pipe (LP) structure. This is the world’s smallest charge domain GS pixel reported so far. This new developed pixel platform is a key enabler for ultra-high resolution sensors, industrial cameras with wide aperture lenses, and low form factors optical modules for mobile applications. The 2.5 μm GS pixel showed excellent optical performances: 68% quantum efficiency (QE) at 530 nm, ±12.5 degrees angular response (AR), and quite low parasitic light sensitivity (PLS)—10,400 1/PLS with the F#2.8 lens. In addition, we achieved an extremely low memory node (MN) dark current 13 e−/s at 60 °C by fully pinned MN. Furthermore, we studied how the LP technology contributes to the improvement of the modulation transfer function (MTF) in near infrared (NIR) enhanced GS pixel. The 2.8 μm GS pixel using a p-substrate showed 109 lp/mm MTF@50% at 940 nm, which is 1.6 times better than that without an LP. The MTF can be more enhanced by the combination of the LP and the deep photodiode (PD) electrically isolated from the substrate. We demonstrated the advantage of using LP technology and our advanced stacked deep photodiode (SDP) technology together. This unique combination showed an improvement of more than 100% in NIR QE while maintaining an MTF that is close to the theoretical Nyquist limit (MTF @50% = 156 lp/mm).
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