CCD Dark Reference Light Shield Segmentation
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Solution Overview
Problem
Conventional CCD image sensors face challenges in accurately calibrating black levels due to varying dark signals between light-sensitive and dark reference pixels, leading to improper black clamp and gray appearance of black regions in images, primarily caused by inadequate passivation of unterminated bonds in dark reference regions.
Innovation Solution
The implementation of multiple stacked light shields with strategically placed openings above photosensitive areas and VCCDs in dark reference regions to facilitate hydrogen diffusion for passivation of unterminated bonds, while preventing stray light from entering, thereby minimizing dark current generation and ensuring accurate black level calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a solid metal light shield is used to block incoming light in dark reference regions, then light shielding effectiveness is improved, but dark signal uniformity deteriorates due to blocked hydrogen diffusion
Solution Approach 1:
The solid metal light shield is segmented into multiple light shield layers with light shield openings between them. This segmentation allows hydrogen to diffuse through the openings while the layers maintain light shielding effectiveness, resolving the contradiction between light blocking and hydrogen diffusion.
Solution Approach 2:
The light shield structure is transformed from a solid non-porous material to a porous structure with light shield openings. This allows hydrogen atoms to pass through the shield during diffusion while the metal material maintains its light-blocking properties.
2Measurement precision
If additional HCCD cycles are added to produce black reference, then calibration capability is improved, but dark current interference worsens
Solution Approach 1:
Dark reference pixels are prepared in advance during the imaging process, collecting dark signal during the exposure period. This preliminary collection of dark reference data allows for accurate black level calibration without requiring additional post-exposure HCCD cycles, thereby avoiding dark current interference.
3Measurement precision
If dark reference regions are used for black level calibration, then calibration functionality is improved, but dark step artifact worsens due to varying dark signals
Solution Approach 1:
Different regions of the sensor are given different local qualities: dark reference pixels lack the light-blocking layer to maximize hydrogen diffusion and dark signal generation, while imaging pixels have the light-blocking layer for normal operation. This local differentiation ensures dark signal consistency between reference and imaging regions.
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 effectively reduces dark current and stray light-induced signals, allowing for precise black level calibration and improved image contrast by ensuring sufficient hydrogen diffusion and light shielding, resulting in black regions appearing correctly as black rather than gray.
Implementation Method 1
openings are provided within the light shields, thus forming shorter paths for the diffusion of hydrogen for the passivation of unterminated interatomic bonds
Implementation Method 2
first and second substantially opaque light shields... preventing stray light from entering
Data Source
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Figure 3A
AI summary
In various embodiments, image sensors include an imaging array of optically active pixels, a dark-reference region of optically inactive pixels, and two light shields disposed over the dark-reference region and having openings therein. In a particular embodiment, an image sensor comprises: an imaging array of optically active pixels each comprising (i) a photosensitive area and (ii) a vertical CCD (VCCD) region associated therewith; proximate the imaging array, a dark-reference region of optically inactive pixels each comprising (i) a photosensitive area and (ii) a VCCD region associated therewith; a first substantially opaque light shield (i) disposed over the dark-reference region of optically inactive pixels and (ii) defining a plurality of openings therein; and a second substantially opaque light shield (i) defining a plurality of openings therein and (ii) disposed over the first light shield, wherein: within the dark-reference region, the openings in the first light shield are disposed over photosensitive areas or VCCD regions but not both, if the openings in the first light shield are disposed over photosensitive areas, then the openings in the second light shield are disposed over photosensitive areas but not VCCD regions, such that each photosensitive area in the dark-reference region has no more than one opening thereover, and if the openings in the first light shield are disposed over VCCD regions, then the openings in the second light shield are disposed over VCCD regions but not photosensitive areas, such that each VCCD region in the dark-reference region has no more than one opening thereover.