A Review of the Recent Developments in the Fabrication Processes of CMOS Image Sensors for Smartphones

CMOS Image Sensors are experiencing significant growth due to their capabilities to be integrated in smartphones with refined image quality. One of the major contributions to the growth of image sensors is the innovation brought about in their fabrication processes. This paper presents a detailed review of the different fabrication processes of the CMOS Image Sensors and its impact on the image quality of smartphone pictures. Fabrication of CMOS image sensors using wafer bonding technologies such as Through Silicon Vias and CuCu hybrid bonding along with their experimental results are discussed. A 2 layer architecture of photodiode and pixel transistors has adopted the 3D sequential integration, by which the wafers are bonded together one after the other in the fabrication process. Electrical characteristics and reliability test results are presented for the former two fabrication processes and the improvements in the pixels performance such as conversion gain, quantum efficiency, full well capacity and dynamic range for the 2 layer architecture are discussed.