Experiment and device simulation for photo-electron overflow characteristics on a pixel-shared CMOS image sensor using lateral overflow gate

A wide dynamic range CMOS image sensor with lateral overflow integration capacitor sharing two pixels by using lateral overflow gate (LO-gate) which directly connect the photodiode and the overflow photoelectron integration capacitor (Cs) has been developed. In this paper, the characteristics of the saturated-photoelectrons overflowing to the floating diffusion (FD) and to the Cs have been discussed through the comparison of the results of experiments and device simulations. It is possible to integrate all the saturated photoelectrons in the Cs without leaking to the shared FD by controlling the voltages of the gate electrodes of the transfer transistor and the LO-gate in the pixel which strong light irradiates. The CMOS image sensor consisting of 1/3.3 inch optical format, 3 μm pixel pitch and 1280^(H) × 960^(V) pixels was fabricated by a 0.18 μm 2P3M CMOS technology with a buried pinned photodiode process and has achieved 84 μV/e- photo-electric conversion gain, 6.9 × 104 e^- full well capacity and 90 dB dynamic range in one exposure.