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.

[1]  J. Hauser,et al.  Minority carrier reflecting properties of semiconductor high-low junctions , 1975 .

[2]  J. Gunn.  On Carrier Accumulation, and the Properties of Certain Semiconductor Junctions† , 1958 .

[3]  J.A. del Alamo,et al.  Measurement of hole mobility in heavily doped n-type silicon , 1986, IEEE Electron Device Letters.

[4]  R. M. Swanson,et al.  Simultaneous measurement of hole lifetime, hole mobility and bandgap narrowing in heavily doped n-type silicon , 1985, 1985 International Electron Devices Meeting.

[5]  R. M. Swanson,et al.  Measurement of electron lifetime, electron mobility and band-gap narrowing in heavily doped p-type silicon , 1986, 1986 International Electron Devices Meeting.

[6]  D. H. Seib,et al.  Carrier diffusion degradation of modulation transfer function in charge coupled imagers , 1974 .

[7]  D. Robinson,et al.  A method for improving the spatial resolution of frontside-illuminated CCD's , 1981, IEEE Transactions on Electron Devices.

[8]  J. Janesick,et al.  Scientific Charge-Coupled Devices , 2001 .

[9]  J.A. del Alamo,et al.  The physics and modeling of heavily doped emitters , 1984, IEEE Transactions on Electron Devices.

[10]  Yuan Taur,et al.  Fundamentals of Modern VLSI Devices , 1998 .

[11]  M. H. Crowell,et al.  The silicon diode array camera tube , 1969 .

[12]  Eric G. Stevens,et al.  An analytical, aperture, and two-layer carrier diffusion MTF and quantum efficiency model for solid-state image sensors , 1994 .

[13]  Eric G. Stevens,et al.  A unified model of carrier diffusion and sampling aperture effects on MTF in solid-state image sensors , 1992 .