Sub-wavelength Lens Protrusions for Image Sensor Light Condensation
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Solution Overview
Problem
The miniaturization of solid-state image pickup devices poses challenges in accurately fabricating on-chip micro convex lenses with small focal lengths and large curvatures, and existing sub-wavelength lenses face difficulties in maintaining light-condensing performance due to complex scattering and reflection, especially when the refractive index varies significantly with electromagnetic wave polarization.
Innovation Solution
A two-dimensional solid-state image pickup device incorporating a sub-wavelength lens with protrusions or recesses having rounded edges, where the refractive index varies smoothly, reducing reflection components and enhancing light condensation efficiency by using a filler substance with a different refractive index and optimizing the spatial distribution of protrusions or recesses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the pixel size is reduced to increase the number of pixels, then the resolution is improved, but the manufacturing precision of the light-condensing element deteriorates
Solution Approach 1:
The light-condensing element is divided into multiple protrusions arranged in a periodic pattern, where each protrusion has a size smaller than the wavelength of incident light. This segmentation allows the overall structure to achieve sub-wavelength light control while individual components remain within manufacturable dimensions
Solution Approach 2:
The protrusions are designed with specific local geometric characteristics (size, shape, spacing) that differ from conventional lenses. Each protrusion has dimensions optimized for sub-wavelength operation, creating localized optical effects that collectively achieve the desired light condensing function at reduced pixel scales
2Use of energy by moving object
If a conventional on-chip micro convex lens is used, then the light condensing function is provided, but the light-condensing efficiency for obliquely incident light deteriorates
Solution Approach 1:
The optical parameters of the light-condensing element are fundamentally changed from conventional lens geometry to a periodic array of sub-wavelength protrusions. This parameter change enables the structure to maintain effective light condensing across a wide range of incidence angles, including oblique incidence, by exploiting sub-wavelength diffraction effects rather than geometric optics
3Reliability
If a sub-wavelength lens with complex structure is used, then the light condensing performance is enhanced, but the manufacturing complexity increases
Solution Approach 1:
The light-condensing element employs a periodic array of identical or similar protrusions with uniform geometric parameters. This homogeneity in structure simplifies manufacturing processes compared to complex asymmetric designs, while the collective periodic structure maintains sub-wavelength light condensing 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
The solution effectively reduces reflection and enhances light condensation efficiency, allowing for precise guidance of obliquely incident electromagnetic waves to the light-receiving element, even at smaller pixel sizes, by smoothing the refractive index variation and reducing scattering.
Implementation Method 1
A light-condensing element formed of a sub-wavelength lens (SWLL) having a periodic structure at a physical scale, which is smaller than a wavelength of an electromagnetic wave (for example, visible light) incident on a light-receiving element
Implementation Method 2
A sub-wavelength lens has a high light-condensing characteristic within a large incidence angle range
Implementation Method 3
Each of the protrusions (column portions) has a rounded edge... to prevent a light-condensing performance from being degraded... complex scattering and reflection may occur
Implementation Method 4
complex scattering and reflection may occur... by smoothing the refractive index variation and reducing scattering
Data Source
AI summary
A two-dimensional solid-state image pickup device includes a plurality of pixel regions arranged in a two-dimensional matrix in X and Y directions. Each of the pixel regions includes at least a light-receiving element, and a light-condensing element. The light-condensing element is a sub-wavelength lens including protrusions each having a size equivalent to or smaller than a wavelength of an electromagnetic wave incident on the light-receiving element. Each of the protrusions has a rounded edge.