Friday, March 29, 2019

Front Side Microlens for BSI Pixel

MDPI paper "Front-Inner Lens for High Sensitivity of CMOS Image Sensors" by Godeun Seok and Yunkyung Kim from Dong-A University, Busan, Korea propose dual-side microlens for small pixels:

"Due to the continuing improvements in camera technology, a high-resolution CMOS image sensor is required. However, a high-resolution camera requires that the pixel pitch is smaller than 1.0 μm in the limited sensor area. Accordingly, the optical performance of the pixel deteriorates with the aspect ratio. If the pixel depth is shallow, the aspect ratio is enhanced. Also, optical performance can improve if the sensitivity in the long wavelengths is guaranteed. In this current work, we propose a front-inner lens structure that enhances the sensitivity to the small pixel size and the shallow pixel depth. The front-inner lens was located on the front side of the backside illuminated pixel for enhancement of the absorption. The proposed structures in the 1.0 μm pixel pitch were investigated with 3D optical simulation. The pixel depths were 3.0, 2.0, and 1.0 μm. The materials of the front-inner lens were varied, including air and magnesium fluoride (MgF2). For analysis of the sensitivity enhancement, we compared the typical pixel with the suggested pixel and confirmed that the absorption rate of the suggested pixel was improved by a maximum of 7.27%, 10.47%, and 29.28% for 3.0, 2.0, and 1.0 μm pixel depths, respectively."


  1. Initially I was thinking this was an early April Fools joke, but after I closer look I realized it's not because what they are describing as a lens, the rest of the world would call a mirror.

    They're using a low refractive index (MgF2 or air) to high refractive index interface. This means it's reflecting light. In other words it's a mirror.

  2. How would they get the air inside? Which deposition method for the ILD would they like to use?

    You can simulate a lot, but that doesn't make it feasible...


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