A 0.64μm 4-Photodiode 1.28μm 50Mpixel CMOS Image Sensor with 0.98e- Temporal Noise and 20Ke- Full-Well Capacity Employing Quarter-Ring Source-Follower.

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 $1.0\mu\mathrm{m}$ -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].