CMOS Image Sensor Pixel Arrays with Symmetric Metallization
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Solution Overview
Problem
Conventional CMOS active pixel sensors have lower fill factors due to active circuits and interconnects, leading to degraded performance in terms of sensitivity, quantum efficiency, and dynamic range, and require additional light shielding layers that further reduce sensitivity and increase noise, resulting in non-uniform pixel response across the array.
Innovation Solution
The use of symmetrically patterned lower-level metallization layers that provide both BEOL interconnections and act as light shielding layers, balancing incident light distribution across the pixel array without the need for an additional light shielding layer, thereby maintaining uniform pixel-to-pixel sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If additional light shielding layers are added to block incident light from active circuits, then pixel response uniformity is improved, but sensitivity and quantum efficiency are reduced
Solution Approach 1:
The patent combines the light shielding function with the existing lower-level metallization layers that provide BEOL interconnections. By integrating light blocking capability into the interconnect structure through symmetric patterning, the design eliminates the need for additional dedicated light shielding layers, thereby maintaining sensitivity while achieving uniform pixel response.
Solution Approach 2:
The lower-level metallization layers are designed to serve dual purposes: providing electrical interconnections (BEOL) and acting as light shielding structures. This multi-functional approach allows the same structural elements to fulfill both electrical and optical requirements, avoiding the sensitivity penalty associated with adding separate light shielding layers.
2Manufacturing precision
If additional light shielding layers are added to block incident light, then pixel response uniformity is improved, but device complexity increases
Solution Approach 1:
The patent merges the light shielding function with the existing lower-level metallization layers that provide BEOL interconnections. By integrating light blocking capability into the interconnect structure through symmetric patterning, the design eliminates the need for additional dedicated light shielding layers, thereby maintaining sensitivity while achieving uniform pixel response.
3Object-affected harmful factors
If additional light shielding layers are added, then light blocking is improved, but noise increases
Solution Approach 1:
The patent combines the light shielding function with the existing lower-level metallization layers that provide BEOL interconnections. By integrating light blocking capability into the interconnect structure through symmetric patterning, the design eliminates the need for additional dedicated light shielding layers, thereby maintaining sensitivity while achieving uniform pixel response.
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 increases the fill factor and sensitivity of CMOS active pixel sensors by evenly distributing light across the photosensitive regions, reducing noise and variability, and eliminating the need for additional light shielding layers, which enhances the overall performance and uniformity of the pixel array.
Implementation Method 1
the first wiring layer is an optical blocking layer to block incident light in each unit pixel to maintain substantially the same sensitivity for each light receiving element of the pixel array
Implementation Method 2
CCD and CMOS image sensors operate based on the 'photoelectric effect ', which occurs when silicon is exposed to light. In particular, CCD and CMOS image sensors include pixel arrays where each unit pixel includes a light receiving region including one or more photo detector elements (such as photodiodes)
Data Source
AI summary
Solid state CMOS active pixel sensor devices having unit pixels that are structured to provide improved uniformity of pixel-to-pixel sensitivity across a pixel array without the need for an additional light shielding layer. For example, unit pixels with symmetrical layout patterns are formed whereby one or more lower-level BEOL metallization layers are designed operate as light shielding layers which are symmetrically patterned and arranged to balance the amount of incident light reaching the photosensitive regions.