Near-Infrared Metalens Structure for CMOS Angular Response
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Solution Overview
Problem
Manufacturing constraints limit the focal length for microlenses in CMOS image sensors, leading to worsened angular response due to increased optical path length, which affects the range of angles of incidence for incoming electromagnetic radiation.
Innovation Solution
A metalens is interposed between the microlens and the photosensitive structure, combining with the microlens to reduce focal length and potentially eliminate the spacer, using an array of nanostructures that vary in width, shape, or spacing to focus electromagnetic radiation effectively on the photosensitive structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the focal length for microlenses is reduced due to manufacturing constraints, then the device can be manufactured, but the angular response worsens
Solution Approach 1:
The patent divides the single microlens function into two separate components: a microlens for initial light collection and a metalens with nanostructures for precise focal length control. This segmentation allows each component to be optimized independently - the microlens for manufacturability and the metalens for angular response performance.
Solution Approach 2:
The patent changes the optical parameters by introducing a metalens with specifically designed nanostructures that have different focal length characteristics than conventional microlenses. The metalens compensates for the short focal length of the microlens, effectively extending the optical path length and improving angular response without requiring a physically longer spacer.
2Productivity
If the pixel size is made smaller, then the power consumption and manufacturing cost are reduced, but the manufacturing difficulty and crosstalk increase
Solution Approach 1:
By segmenting the focusing function into microlens and metalens components, the patent enables better control over light confinement in smaller pixels. The metalens's precise focal control reduces light spill between adjacent pixels, addressing crosstalk issues that become more severe at smaller pixel sizes.
Solution Approach 2:
The metalens introduces local optical quality enhancement through nanostructures that precisely control light focusing at each pixel location. This localized control improves light confinement efficiency, allowing smaller pixels to maintain effective light collection without increased crosstalk or manufacturing complexity.
3Length of stationary object
If the spacer height is increased to extend optical path length, then the focal length constraint is satisfied, but the angular response worsens
Solution Approach 1:
The patent replaces the mechanical approach of increasing spacer height with an optical approach using a metalens. Instead of physically extending the optical path through a taller spacer, the metalens uses nanostructures to create the equivalent optical path extension, achieving the same focal length effect without the negative angular response consequences.
Solution Approach 2:
The patent changes the optical path parameters by introducing a metalens with specific focal length properties. The metalens effectively increases the optical path length through its optical design rather than physical distance, allowing the system to achieve the required focal length while maintaining optimal angular response characteristics.
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 metalens reduces the focal length, allowing for improved angular response and increased efficiency in capturing electromagnetic radiation, enhancing the performance of CMOS image sensors by focusing incident radiation within the focal length constraint.
Implementation Method 1
A metalens is interposed between the microlens and the photosensitive structure, combining with the microlens to reduce focal length... using an array of nanostructures that vary in width, shape, or spacing to focus electromagnetic radiation effectively on the photosensitive structure
Data Source
AI summary
An image sensing device includes a germanium sensor within a semiconductor body and a metalens formed in the back side of the semiconductor body. The metalens is structured to focus infrared light on the germanium sensor and may have a lower profile than an equivalent microlens. Optionally, the metalens is combined with a microlens to achieve a desired focal length. The metalens, or the metalens in combination with a microlens, overcomes a manufacturing process limitation on the focal length of the microlens, which in turn eliminates the need for, or reduces the thickness of, a spacer between the microlens and the germanium sensor. Eliminating the spacer or reducing its thickness improves the angular response of the image sensing device.