Improved One-dimensional Analysis of CMOS Photodiode Including Epitaxial-Substrate Junction

An improved one-dimensional analysis of CMOS photodiode has been derived in which the effect of the substrate, which forms a high-low junction with the epitaxial layer, has been included. The fully analytical solution was verified with numerical simulations based on parameters extracted from a standard 0.35 μm CMOS process. The parameter availability and the degree of accuracy for photoresponse modeling are briefly discussed. Two empirical parameters are suggested to offset the unavoidable inaccuracies in the employed parameters. The derived semi-empirical expression exhibits a good agreement with the measured spectral response of npepi photodiodes fabricated using a standard 0.35 μm CMOS process. The simplicity and the accuracy of the model makes it a suitable candidate for implementation in circuit-level simulation of npepi CMOS photodiodes. The applicability of one-dimensional approximation of the peripheral photoresponse in linearand two-dimensional arrays is also discussed with measurements based on linear photodiode arrays.