اسما مجردالمان اباد

Today, CMOS image sensors (CIS) have become leaders in the market due to their affordable price and high quality. Reducing pixel size as a method to enhance the performance of these sensors faces the challenge of managing the diffusion current in photodiodes, which requires a detailed study of carrier flow to improve image quality. In this thesis, the optimization of pinned photodiodes in CIS sensors is addressed, with a focus on analyzing diffusion current in photodiodes. Simulations were conducted using SILVACO software based on 0.18 µm technology. To thoroughly investigate carrier behavior in the epitaxy layer, a one-dimensional analytical model for diffusion current was initially developed, followed by the proposal of a new two-dimensional analytical model for diffusion current, which was separately eva‎luated for small and large pixels. The eva‎luation of this model for small pixels, compared to experimental data, yielded a mean absolute error of 5.0807×10⁻9 and a coefficient of determination (R²) of 0.93. The analysis of the proposed model for larger pixels indicates that it has a good accuracy in predicting diffusion current, with a mean absolute error of 1.26×10⁻8 and a coefficient of determination of 0.98. Additionally, electrical crosstalk was characterized based on substrate doping, the doping of the floating diffusion (FD) surrounding region, and diode depths. The simulation results showed that doping in the FD region affects the substrate potential and has a linear relationship with electrical crosstalk. Studies on the impact of substrate doping on crosstalk revealed that by properly selecting substrate doping, crosstalk can be improved by up to 55% at wavelengths greater than 0.6 µm compared to the reference. It was also observed that the effect of substrate doping on crosstalk increases as the diode depth increases.

حسگر‌هاي تصوير برداريCMOS , ديود‌هاي نوري , جريان انتشار , جريان انتشار جانبي , مدل‌سازي تحليلي

CMOS image sensors , photodiodes , diffusion current , lateral diffusion current , analytical modeling

Asma mojarrad alman abad

mohammad azim karami