Diffraction feature of microlens array with a small aperture size

With the development of a CMOS Image Sensor (CIS), the pixel size of a CIS is continuously decreasing. It makes the photo diode smaller and smaller in the unit pixel and, as a result, the sensitivity is reduced at the same time. A micro lens (ML) is added to improve the sensitivity of CIS. The size of ML is reduced with the pixel size and it almost arrived at the limitation of the size which is governed by diffraction. In this paper, we simulate the diffraction feature of a ML with an electro-magnetic wave simulation. The efficiency and the crosstalk of some ML which have a size near the diffraction limit are calculated and compared. From the simulation result, we suggest a guide line of the ML design.