Half-Quad Photodiode Microlens Layout for Channel Balance
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Solution Overview
Problem
Image sensors often suffer from channel imbalance due to misaligned or offset microlenses, leading to non-uniform light sensitivity among subpixels, which affects the accuracy of photodiode light intensity readings.
Innovation Solution
The distribution of microlenses is spatially biased, with centrally located subpixels covered by centrally placed microlenses and peripherally located subpixels covered by offset microlenses, and smaller microlenses are used over individual photodiodes while larger microlenses cover entire subpixels, to achieve uniform quantum efficiency and reduce manufacturing complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If microlenses are placed centrally over each subpixel, then manufacturing alignment is simplified, but peripheral subpixels exhibit non-uniform light sensitivity
Solution Approach 1:
The patent applies local quality by differentiating microlens placement strategies between central and peripheral subpixels. Central subpixels receive centrally-aligned microlenses for manufacturing simplicity, while peripheral subpixels receive offset microlenses positioned toward the image sensor center to compensate for non-uniform light sensitivity. This localized differentiation resolves the contradiction by allowing each region to have optimized microlens placement.
Solution Approach 2:
The patent introduces asymmetry in microlens placement by offsetting peripheral microlenses from their subpixel centers toward the image sensor center, while maintaining symmetric central placement for central subpixels. This asymmetric approach compensates for the non-uniform light sensitivity distribution across the image sensor, resolving the contradiction between manufacturing ease and sensitivity uniformity.
2Manufacturing precision
If smaller microlenses are used over individual photodiodes, then channel imbalance is reduced, but device complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the image sensor into central and peripheral regions with different microlens configurations. This segmentation allows smaller microlenses to be used only where needed (over individual photodiodes in peripheral regions) rather than across the entire sensor, thereby reducing channel imbalance while limiting the increase in device complexity to specific regions only.
Solution Approach 2:
The patent implements partial action by applying the more complex smaller microlens configuration only to peripheral subpixels where it is most needed to correct channel imbalance, rather than uniformly across all subpixels. This partial application achieves the necessary precision improvement while minimizing the overall device complexity increase.
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 results in more uniform light sensitivity across the image sensor, improving the accuracy of photodiode light intensity readings and reducing manufacturing errors, while maintaining acceptable complexity and cost.
Implementation Method 1
Individual subpixels are covered with microlenses that may be misaligned, for example, through manufacturing errors that place the microlenses off-center with respect to the middle of the corresponding subpixel
Implementation Method 2
Half quad photodiode (QPD) to improve QPD channel imbalance
Data Source
AI summary
Half Quad Photodiode (QPD) for improving QPD channel imbalance. In one embodiment, an image sensor includes a plurality of pixels arranged in rows and columns of a pixel array that is disposed in a semiconductor material. Each pixel includes a plurality of subpixels. Each subpixel comprises a plurality of first photodiodes, a plurality of second photodiodes and a plurality of third photodiodes. The plurality of pixels are configured to receive incoming light through an illuminated surface of the semiconductor material. A plurality of small microlenses are individually distributed over individual first photodiodes and individual second photodiodes of each subpixel. A plurality of large microlenses are each distributed over a plurality of third photodiodes of each subpixel. A diameter of the small microlenses is smaller than a diameter of the large microlenses.