Modeling and measurements of MTF and quantum efficiency in CCD and CMOS image sensors

Sensitivity and image quality are two of the most important characteristics for all image sensing systems. The Quantum Efficiency (QE) and the Modulation Transfer Function (MTF) are respectively the common metrics used to quantify them, but inter-pixel crosstalk analysis is also of interest. Because of an important number of parameters influencing MTF, its analytical calculation and crosstalk predetermination are not an easy task for an image sensor, particularly in the case of CMOS Image Sensor (CIS). Classical models used to calculate the MTF of an image sensor generally solve the steady-state continuity equation in the case of a sinusoidal type of illumination to determine the MTF value by a contrast calculation. One of the major drawbacks of this approach is the difficulty to evaluate analytically the crosstalk. This paper describes a new theoretical three-dimensional model of the diffusion and the collection of photo-carriers created by a point-source illumination. The model can take into account lightly-doped EPI layers which are grown on highly-doped substrates. It allows us to evaluate with accuracy the crosstalk distribution, the quantum efficiency and the MTF at every needed wavelengths. This model is compared with QE, MTF measurements realized on different pixel types.