1.4-$\mu\hbox{m}$-Pitch 50% Fill-Factor 1T Charge-Modulation Pixel for CMOS Image Sensors

Ring-gate implementation of single-transistor charge modulation pixel structure obviates the need to employ shallow trench isolation for pixel isolation. This enables achievements of smaller pixel size and/or higher fill factor. It also reduces dark current by minimizing surface component contribution and band-to-band tunneling effect. Characteristics of a ring-gate 1.4-pitch 50% fill-factor pixel are compared with those of a rectangular-gate 2.2-pitch 46% fill-factor pixel, both being in a 0.13- complementary metal-oxide-semiconductor process. The 1.4-pitch ring-gate pixel has an improved conversion gain and a degraded full well capacity (FWC), as can be roughly predicted according to scaling law. It also shows substantial reductions on dark current, temporal noise, and fixed pattern noise. The resulting signal-to-noise ratio outweighs degradation of FWC, which allows a larger dynamic range.