Closed-Form and Explicit Analytical Model for Crosstalk in CMOS Photodiodes

Abstract

A closed-form and explicit 2-D analytical model for crosstalk (CTK) effects in p-n + CMOS photodiodes for pixel design optimization has been developed in this paper. This model complements and extends a previous development describing the photocurrent because of the active area illumination along with the lateral depletion region and lateral components owing to the diffused photocarriers from the surroundings of the junction. The model has very few fitting parameters because it is physically based. Similarly, it can be of great use for CMOS image sensors designers, especially to fulfill high resolution and small area requirements by pixel size reduction. The model was validated extensively through device simulations with ATLAS and experimental data, and describes the CTK dependencies on light conditions and physical, geometrical, and process parameters.

Analytical Model for Crosstalk in p-nwell Photodiodes

“…Each surface plot corresponds to a different value of λ, covering the visible range. Simulation and modeled results show a good agreement, revealing a response dependence on both the active and total PD areas, as previously observed for p-n + junctions [12], [13], [17]. I n increases as well regions grow and approach each other, and when the area surrounding the junction becomes smaller.…”

“…In comparison with the results found for the p-n + junction [12], [13], the introduction of the well modifies I aa , as the active area has now two different components linked to the diffusion and the well, and a double junction is formed in the device.…”

“…An analytical model for photoresponse and CTK in p-n + CMOS PDs has already been proposed and validated through device simulations and experimental results in [12]. In this paper, we step forward introducing a new model for p-n well junction PDs and the performance of both structures is compared.…”

“…Crosstalk Photocurrent, I n The CTK current due to the illumination of a neighbor PD, I n , is modeled as the sum of two terms: 1) the diode A reverse-bias saturation current, I o and 2) the CTK lateral current due to carriers generated in the surroundings of a zerobiased neighbor, B, under illumination, I CTK . As p-n well and p-n + junctions have the same substrate, which is the main source of photocarriers for the CTK current, the analysis for the p-n + can be applied to the p-n well PD and the details can be found in [12] …”

“…Recently, we have reported an analytical model for CTK estimation in p-n + CMOS PDs under normal incidence uniform illumination in the visible range [12]. It is a compact, closed-form, manageable expression in terms of light 0018-9383 © 2014 IEEE.…”