On-Chip Lens Slit Design for Image Sensor Light Leakage
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Solution Overview
Problem
Conventional solid-state image pickup elements face issues with light leakage and color mixture due to the use of photolithography for creating grooves in on-chip lenses, leading to reduced photosensitivity and increased refractive index differences when different materials are used, along with the degradation of sensitivity and oblique light incidence characteristics caused by planarization layers.
Innovation Solution
The introduction of a slit in the boundary between on-chip lens regions, formed using plasma etching to achieve a narrower width than traditional grooves, which is covered by the same material as the lens, enhancing total reflection and reducing light leakage, and the removal or reduction of planarization layers to minimize sensitivity degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If photolithography is used to form grooves in on-chip lenses, then light leakage prevention is improved, but manufacturing precision deteriorates due to position shifts
Solution Approach 1:
The patent replaces photolithography (chemical/mechanical process) with plasma etching (physical process) to form grooves in on-chip lenses. Plasma etching uses reactive ions to physically remove material, providing better control over groove dimensions and position, thereby preventing position shifts while maintaining light leakage prevention effectiveness.
Solution Approach 2:
The patent changes the formation method parameters from photolithography to plasma etching, which allows for more precise control of groove width and depth. This parameter change enables achieving the required groove dimensions with higher manufacturing precision and without position shifts.
2Object-affected harmful factors
If groove width is reduced to several hundreds nm, then light leakage prevention is improved, but on-chip lens area is reduced leading to concentration efficiency deterioration
Solution Approach 1:
The patent applies local quality by providing grooves only at the boundaries between pixel regions where light leakage occurs, rather than uniformly across the entire on-chip lens. This localized approach prevents light leakage at critical interfaces while preserving the light concentration area of the on-chip lenses, maintaining concentration efficiency.
Solution Approach 2:
The patent segments the on-chip lens structure by introducing grooves that divide adjacent pixel regions, creating optical isolation between pixels. This segmentation prevents light leakage between pixels while maintaining the integrity and concentration function of each individual on-chip lens.
3Adaptability or versatility
If different material is used for film on on-chip lens, then manufacturing flexibility is improved, but refractive index difference is reduced leading to light leakage prevention effectiveness deterioration
Solution Approach 1:
The patent uses the same material for both the on-chip lens and the film formed on it, ensuring homogeneity in refractive index. This material uniformity maintains the effectiveness of light leakage prevention by preserving the refractive index difference at the groove interfaces, while still allowing manufacturing flexibility through the plasma etching process.
4Shape
If planarization layer is provided, then surface flatness is improved, but distance between on-chip lens and sensor unit is increased leading to sensitivity degradation
Solution Approach 1:
The patent removes or reduces the planarization layer that was traditionally used to flatten the surface. By extracting this unnecessary layer, the distance between the on-chip lens and sensor unit is minimized, improving photoelectric conversion sensitivity while the groove structure itself provides the necessary optical isolation function.
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
The slit design improves photosensitivity and prevents color mixture by ensuring light is focused on the correct pixel, while the reduced planarization layer distance enhances light concentration efficiency and reduces defects and oblique light issues.
Implementation Method 1
light is totally reflected in a groove 21 in the boundary between the regions corresponding to the respective pixels of the on-chip lenses 11
Data Source
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AI summary
Provided is a solid-state image pickup element including: a sensor unit configured to generate an electrical signal in response to incident light; a color filter covering the sensor unit; and a lens configured to concentrate the incident light into the sensor unit via the color filter and formed by a laminated film made of a predetermined lens material. The lens is formed on the color filter without providing a planarization layer for removing a difference in level in the color filter.