Hafnium Oxide Anti-Reflective Layers for CMOS Image Sensors
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Solution Overview
Problem
The existing fabrication process for CMOS image sensors is complex and expensive due to the different structures and processes required for active and optical black pixel arrays, leading to inefficiencies in black level compensation and increased costs.
Innovation Solution
The use of hafnium oxide layers with varying transmittance properties is implemented, where a high transmittance layer is formed over the active pixel array and a low transmittance layer over the optical black pixel array, allowing for the same fabrication process while improving black level compensation and reducing fabrication costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If different structures and processes are used for active and optical black pixel arrays, then black level compensation characteristics are improved, but fabrication complexity and cost increase
Solution Approach 1:
The patent applies local quality by forming a first anti-reflective layer with high light transmittance over the active pixel array and a second anti-reflective layer with low light transmittance over the optical black pixel array. This allows each region to have optimized optical properties tailored to its specific function, improving black level compensation while maintaining a unified fabrication process.
2Reliability
If different anti-reflective layers are formed over active and optical black pixel arrays, then optical characteristics are optimized, but fabrication time and cost increase
Solution Approach 1:
The patent merges the fabrication processes for forming anti-reflective layers over both active and optical black pixel arrays into a single unified process. By using the same fabrication steps to form both the first and second anti-reflective layers, the patent reduces fabrication time and cost while still achieving optimized optical characteristics for each pixel array type.
3Ease of manufacture
If uniform anti-reflective layers are used over both pixel arrays, then fabrication is simplified, but black level compensation performance deteriorates
Solution Approach 1:
The patent resolves this contradiction by implementing local quality through region-specific anti-reflective layers. The first anti-reflective layer over the active pixel array has high light transmittance to maximize light sensing, while the second anti-reflective layer over the optical black pixel array has low light transmittance to minimize interference. This localized optimization maintains fabrication simplicity while significantly improving black level compensation performance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the black level compensation characteristics, reduces the time and cost of image sensor fabrication, and improves reliability by ensuring consistent out diffusion and field effect characteristics across both pixel array types.
Implementation Method 1
a first anti-reflective layer which is formed over the active pixel array, and including a hafnium oxide layer with a high transmittance; and a second anti-reflective layer which is formed over the optical black pixel array, and including a hafnium oxide layer with a low transmittance
Data Source
AI summary
An image sensor includes a pixel layer in which an active pixel array and an optical black pixel array are formed; a first anti-reflective layer which is formed over the active pixel array, and including a hafnium oxide layer with a high transmittance; and a second anti-reflective layer which is formed over the optical black pixel array, and including a hafnium oxide layer with a low transmittance.