Abstract
Due to the CMOS technology scaling, the smaller imaging pixels provide higher resolution application. As doping concentration in a photodiode increases, the sensitivity of a pixel becomes lower. The cross-talk effect due to light scattering to adjacent cells is getting worse as pixel size reduces. Therefore, the optical issue should be considered carefully. In this work, two major subjects are investigated. First, modifying photodiode layout to achieve better pixel performance. From the experiments results, rounded corner photodiode can achieve lower dark current. In addition, a two-dimensional optical pixel model is proposed to study the micro-lens design and cross-talk effect due to light scattering. By optical and electrical simulation using MEDICI program, the pixel performance when micro-lens parameters and photodiode area design is discussed. Light Spot Color Filtering based on this model is proposed to replace Color Filter Array application. This model also allows for cross-talk simulation and cross-talk suppression effects as a result of different blocking materials. From simulation results, the metal can block the obliquely incident light efficiently. This study can help sensor designers not only to understand the ray trace in a sensor pixel but also serve as a reference for pixel and micro-lens design.