A MOS Image Sensor With a Digital-Microlens

We have developed a MOS image sensor with digital-microlenses (DMLs), each of which has an effective refractive index realized by variation of the subwavelength separations between the concentric SiO
₂
ring walls. The effective refractive index profiles are optimized for the location of each pixel. The light-collection efficiency of the image sensor is twice as high as that of a conventional image sensor because of the enhanced light acceptance in the periphery. A 2.2-mum pitch 3-megapixel MOS image sensor based on the DML technology exhibited excellent uniformity of the light-collection efficiency across the image area, even for light with a very large incident angle, i.e., over 45deg. The DML promises new levels of performance of image sensors.