Thin-Film Photogate Pixel With Fixed Photodiode Bias for Near-Infrared Imaging

Abstract

This letter presents an organic thin-film photodiode (OPD) based photogate (PG) pixel for near-infrared image sensors with improved linearity and reduced dark current. The proposed image sensor is based on the conventional 3T pixel readout with an additional PG electrode below the photodiode structure. By including the PG below the OPD, which is being separated by a thin dielectric layer, the potential bias is kept constant during integration, allowing the photodiode to be biased with low potential. Compared to the conventional capacitive transimpedance amplifier pixel, which uses an in-pixel amplifier to fix the bias of the photodiode, the proposed pixel architecture provides an effective solution for affordable high-resolution, high-performance thin-film image sensors by keeping the simple pixel structure. The proposed image sensor is designed and processed using a 130nm complementary metal-oxide semiconductor process and an OPD process. The proposed pixel structure demonstrated a 72.01 % reduction in dark current while maintaining a 3.56 times higher conversion gain. In addition, the linearity error was reduced by 59.3 %.