Front-Inner Lens for High Sensitivity of CMOS Image Sensors.

Area of Science:

• Optoelectronics
• Semiconductor device physics
• Optical engineering

Background:

• Advancements in camera technology necessitate high-resolution CMOS image sensors.
• Smaller pixel pitches (<1.0 μm) in limited sensor areas degrade optical performance due to increased aspect ratios.
• Shallow pixel depths exacerbate aspect ratio issues, while long-wavelength sensitivity is crucial for optical improvement.

Purpose of the Study:

• To propose and investigate a novel front-inner lens structure for enhancing sensitivity in small-sized and shallow-depth pixels.
• To improve light absorption in backside-illuminated CMOS image sensors.
• To analyze the impact of the front-inner lens on optical performance with varying pixel depths and materials.

Main Methods:

• 3D optical simulations were employed to investigate the proposed front-inner lens structures.
• The study focused on 1.0 μm pixel pitch designs with pixel depths of 3.0, 2.0, and 1.0 μm.
• Simulations compared the absorption rates of typical pixels with those incorporating the front-inner lens, using materials like air and magnesium fluoride (MgF₂).

Main Results:

• The proposed front-inner lens structure significantly enhanced light absorption in pixels.
• Absorption rate improvements were recorded as 7.27% for 3.0 μm, 10.47% for 2.0 μm, and 29.28% for 1.0 μm pixel depths.
• The front-inner lens effectively mitigated the negative effects of small pixel size and shallow depth on optical performance.

Conclusions:

• The front-inner lens structure is a viable solution for improving the sensitivity of high-resolution CMOS image sensors.
• This innovation addresses the optical challenges posed by shrinking pixel dimensions.
• The proposed structure offers a pathway to enhanced image quality in next-generation camera systems.