A novel CIS pixel structure design and simulation for DNA fluorescence sequencing

Miniaturization of DNA fluorescence sequencing is important to reduce costs and promote audiences. Among them, CMOS image sensor (CIS) is an effective method for fluorescence detection. In order to solve the problems of large pixel area and low throughput in CIS chip sequencing technology, we have designed a new CIS pixel structure with special hexagonal topology, reduced floating diffusion (FD) capacitance, improved conversion gain, and applied neighborhood-dark-current-cancellation technology. Simulations using sentaurus and lumerical FDTD software show that the capacitance of FD node is 0.48fF and 0.496fF for different PDs respectively, meaning the whole conversion gain is about 320 uV/e- before the back-end process. The relationship between the sensitivity efficiency of hexagon pixel structure and the edge length of the photodiode (PD) shape and the micro lens (ML) shape was investigated. The optimal design conditions were determined, that is, 1.8 um hexagon PD edge length, or 1.6 um octagon PD edge length, with 2.3 um ML thickness and 2.5 um curvature radius.