PDAF Pixel With Plasmonic Nanostructures

The sub micrometer pixel pitch of CMOS image sensors improves the resolution and functionality of image sensors. To achieve the high optical performance of sensors, optical characteristics, such as sensitivity and crosstalk, should be satisfied. However, due to the tradeoffs between resolution and sensitivity, it is necessary to enhance the aspect ratio of pixel structures. In this study, we propose a phase detection autofocus (PDAF) pixel with a plasmonic nanostructure. Not only the wavelength selectivity but also the incident angle dependency of the proposed structure is adapted for the PDAF function. We fabricated the metal-insulator-metal (MIM) structure above the photodetector for red and near-infrared (NIR) pixels. Sensitivity was measured, and the angular response for the autofocus (AF) function was confirmed. Moreover, the AF contrast, which verifies the performance of the AF pixel, was calculated to be 2.2 at the red pixel and 2.7 at the NIR pixel. The experimental results confirmed that the suggested MIM structure is effective for PDAF pixels.