Micro-structured Color Filter Waveguide Image Sensor
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Solution Overview
Problem
Decreasing pixel size in camera modules to increase resolution leads to reduced light capture, resulting in increased noise and diminishing the effectiveness of microlenses when pixel size approaches the wavelength of light, thereby limiting image quality.
Innovation Solution
Incorporating a two-dimensional photodiode-array with a waveguide and a non-planar color-filter structure, where the waveguide is aligned above the substrate surface and the color filter has a non-uniform thickness, eliminating the need for microlenses and enhancing light capture by optimizing coupling efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pixel size is decreased to increase pixel density and resolution, then resolution is improved, but light capture is reduced resulting in increased noise
Solution Approach 1:
The patent employs curved surfaces including microlenses with spherical or aspherical shapes to focus and concentrate incident light onto the photodiode active area. The curved microlens surfaces enable efficient light collection and focusing, maximizing light capture at each pixel location while maintaining small pixel dimensions for high resolution.
Solution Approach 2:
The patent introduces vertical dimensionality through stacked photodiodes arranged at different depths within the semiconductor substrate. This three-dimensional arrangement allows multiple photodiodes to capture light simultaneously at different wavelengths or angles, increasing overall light capture efficiency without increasing the lateral pixel footprint, thereby maintaining high resolution.
2Quantity of substance
If pixel size is decreased to increase pixel density, then pixel density is improved, but microlenses become ineffective when pixel size approaches the wavelength of light
Solution Approach 1:
The patent modifies the microlens parameters including curvature radius, aperture size, and focal length to optimize performance at sub-wavelength pixel dimensions. By adjusting these geometric parameters, the microlenses remain effective even when pixel sizes approach the wavelength of light, maintaining reliable light focusing capability across high-density pixel arrays.
Solution Approach 2:
The patent employs composite structures combining microlenses made from materials with different refractive indices, such as silicon nitride, silicon oxide, or polymer materials, to enhance light focusing efficiency at small scales. The composite material approach allows optimization of optical properties independent of the underlying pixel structure, maintaining microlens effectiveness at high pixel densities.
3Illumination intensity
If non-planar color-filter structures are used to enhance light capture, then light capture is improved, but manufacturing complexity increases
Solution Approach 1:
The patent implements curved or domed color filter structures with spherical or aspherical surfaces that follow the contour of the underlying microlenses. This curvature enables the color filters to effectively modulate light across the entire microlens aperture, enhancing light capture efficiency. The curved geometry can be fabricated using standard semiconductor processing techniques such as spin-coating followed by reflow or direct deposition on curved substrates.
Solution Approach 2:
The patent employs a stacked architecture where color filters are positioned in vertical layers nested within or above the microlens structures. This nested arrangement allows multiple color filter layers to be integrated without significantly increasing lateral footprint or manufacturing complexity, as each layer can be deposited using sequential processing steps in a vertical configuration.
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 configuration improves light capture and signal-to-noise ratios, maintaining image quality without the limitations of microlenses at smaller pixel sizes, effectively balancing resolution and noise levels.
Implementation Method 1
A waveguide may be positioned above the pixel array, and a color-filter array may be positioned on the waveguide. The color filters may have a non-uniform height above the waveguide core.
Implementation Method 2
A pixel array's pixel density is the number of pixels per unit area on the image sensor. In operation, the lens of a camera module forms an image, on the image sensor, of an object in its field of view.
Implementation Method 3
The color filters may have a non-uniform height above the waveguide core.
Data Source
AI summary
An image sensor includes a two-dimensional photodiode-array formed in a semiconductor substrate, a first waveguide, and a first color filter. The first waveguide is aligned to a first photodiode of the photodiode-array, located above a top substrate surface of the semiconductor substrate. A first core of the first waveguide has a first core width that is less than a pitch of the photodiode-array in a first direction and a second direction corresponding to respective orthogonal dimensions of the photodiode-array. The first color filter is on a top waveguide surface of the first waveguide and has a first non-uniform thickness above the first core. The first waveguide is between the top substrate surface and the first color filter.