Abstract
CMOS image sensors (CISs) have received great attention in high-end mobile devices equipped with multiple camera modules to obtain new functionality and advanced image quality. Even though the pixel size has gradually become smaller, this requires a high signal to noise ratio (SNR), and front-side deep-trench isolation (FDTI) is introduced to increase the full-well capacity (FWC) [1]. The FDTI demonstrated in a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1.0\mu\mathrm{m}$</tex> -pitch pixel showed 60% larger FWC compared to the partial DTI in the same pitch [2]. Nevertheless, FDTI and shallow-trench isolation (STI) limit the area of source-follower (SF) that deteriorate the dark temporal noise (TN) as pixel size decreases. In recent years, the emergence of submicron pixels over 50Mpixel has contributed to a major market for mobile-phone cameras by realizing high resolution and image quality [3]. In addition, phase-detection autofocus (PDAF) performance has also been required for providing precise imaging [4], [5]. Recently, horizontal-vertical (HV) dual pixels are reported to enable all-directional PDAF with accurate and fast AF at extremely low-level light conditions [6].
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