Angle-Selective CMOS Color Sensor Waveguide
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Solution Overview
Problem
Existing optical colour sensors face challenges in achieving high measurement accuracy due to the angle-dependent shift in filter characteristics, which is exacerbated by the use of plasmonic filters, and the difficulty in integrating angle-selective structures in semiconductor technology for large-area photosensitive elements without increasing the sensor height.
Innovation Solution
The implementation of an array of angle-selective passageways within the CMOS layer stack, using structured metallic layers and dielectric layers to limit the angle of incidence, allowing only radiation within a specific range to reach the photosensitive surface, thereby reducing the height of the angle-selective structure and maintaining high accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an additional mechanical assembly with a duct is used to limit the angle of incidence, then measurement accuracy is improved, but the device size and complexity increase significantly
Solution Approach 1:
The patent replaces the mechanical duct assembly with an optical waveguide structure that is integrated into the semiconductor layer stack. The waveguide uses total internal reflection and evanescent wave coupling to limit the angle of incidence, substituting mechanical angle selection with optical physics-based filtering. This eliminates the need for separate mechanical assemblies while maintaining measurement accuracy.
Solution Approach 2:
The angle-selective waveguide structure is merged with the CMOS layer stack, combining the angle-limiting function with the existing sensor structure. The waveguide is formed using the same semiconductor fabrication processes that create the photodiode and color filter layers, integrating multiple functions into a single unified structure rather than adding separate components.
2Measurement precision
If a mechanical duct assembly is used to define the maximum angle of incidence, then angle selectivity is improved, but the height of the structure increases to about 1 mm
Solution Approach 1:
The patent replaces the tall mechanical duct with a planar optical waveguide that achieves angle selectivity through its optical properties rather than its physical height. The waveguide's evanescent field extends only a short distance into the surrounding medium, providing effective angle filtering within a thickness of less than 10 μm, matching the CMOS layer stack height.
Solution Approach 2:
The patent transitions from a three-dimensional mechanical duct structure to a two-dimensional planar waveguide structure integrated into the layer stack. The angle-selective function is achieved through in-plane waveguide geometry and optical mode confinement rather than through vertical duct height, effectively moving the solution to a different dimensional approach.
3Measurement precision
If the CMOS layer stack is made thicker to integrate angle-selective structures, then angle filtering is improved, but the photosensitive surface area and sensitivity are reduced
Solution Approach 1:
The patent merges the angle-selective waveguide function with the existing CMOS layer stack structure. The waveguide is formed using the same semiconductor layers and fabrication processes that create the photodiode and color filter, so no additional thickness is required. The angle filtering and photosensitive functions coexist in the same integrated structure without compromising either performance.
4Length of stationary object
If an array of angle-selective passageways is integrated in the CMOS layer stack, then the sensor height is reduced and manufacturing is simplified, but the angle of incidence control must be achieved within a thinner structure
Solution Approach 1:
The patent uses optical physics principles (total internal reflection, evanescent wave coupling, and waveguide mode confinement) to achieve angle selectivity without relying on mechanical geometry. This allows precise angle control to be achieved through optical design parameters rather than mechanical dimensions, enabling accurate angle filtering within the thin CMOS layer stack.
Solution Approach 2:
The patent controls the angle-selective properties by adjusting optical parameters such as the waveguide layer refractive index, thickness, and lateral dimensions. By changing these optical parameters during semiconductor fabrication, the angle of incidence control is precisely tuned without requiring mechanical adjustments or thicker structures.
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 enables the creation of a thin, accurate colour sensor that can be fully produced in semiconductor technology, allowing for precise spectral filtering without the need for external mechanical assemblies, thus enhancing measurement accuracy and reducing crosstalk while maintaining a low profile.
Implementation Method 1
an array of angle-selective passageways is used for the optical radiation between the light input side and the photosensitive surface, which limit the angle of incidence
Implementation Method 2
The suggested variant with a smaller number of through-connections has the advantage that fewer diffraction effects occur
Implementation Method 3
They use interference filters or plasmonic filters as colour filters in front of the photosensitive element
Implementation Method 4
In plasmonic filters, this effect is more pronounced than with interference filters
Implementation Method 5
optical colour sensors are used for example in colorimeters for colour recognition in printing machines and in the textile industry
Data Source
AI summary
The present invention relates to a color sensor having at least one photosensitive element, in front of which a layer stack of dielectric layers and structured metal layers is constructed, and at least one color filter, through which optical radiation incident on a light input side of the color sensor is filtered before it reaches a photosensitive surface of the photosensitive element. In the suggested color sensor, an array of angle-selective passageways is provided for the optical radiation between the light input side and the photosensitive surface, and each passageway only allows parts of the optical radiation incident on the light input side of the color sensor within a limited angle of incidence range relative to an axis extending perpendicularly to the colour filter to pass through to the photosensitive surface. When the color sensor is manufactured with semiconductor technology, it enables the angle-selective structures to be integrated in the CMOS layer stack. In this way, ultra-flat color sensors can be made.