Image Sensor Waveguide Reduces Petal Flare
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Solution Overview
Problem
Image sensors suffer from petal flare due to light leakage through the buffer layer to neighboring pixels, which is exacerbated by high angle light reflections and diffraction patterns, leading to image quality degradation, especially in large photodiode/small photodiode (LPD/SPD) sensors.
Innovation Solution
Incorporating a clear waveguide between the buffer layer and microlenses increases the distance and height of spacers, reducing light leakage without significantly reducing sensor sensitivity, and guiding incoming light into the corresponding pixel, thereby minimizing petal flare.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the height of spacers and distance between microlenses and buffer layer are increased to reduce light leakage, then petal flare is reduced, but sensor sensitivity may be reduced
Solution Approach 1:
A clear waveguide layer is introduced as an intermediary component between the buffer layer and microlenses. This waveguide has a higher refractive index than the surrounding spacer material, creating optical confinement that guides light laterally to the correct pixel. The waveguide acts as a mediator that redirects straying light without requiring increased spacer height, thus reducing light leakage while preserving sensor sensitivity.
2Object-affected harmful factors
If spacer height is increased to block high angle light, then petal flare is reduced, but manufacturing complexity increases
Solution Approach 1:
The patent replaces the purely mechanical approach of using tall spacers to block light with an optical solution. The clear waveguide layer uses refractive index differences to optically confine and guide light, substituting the mechanical blocking function with an optical guiding mechanism. This reduces the need for mechanically complex tall spacers while effectively blocking high angle light.
3Object-affected harmful factors
If the distance between microlenses and buffer layer is increased to reduce light leakage, then petal flare is reduced, but light gathering efficiency decreases
Solution Approach 1:
The clear waveguide layer serves as an intermediary that maintains optical coupling between the microlenses and photodiodes even when the physical distance is increased. The waveguide's higher refractive index creates total internal reflection at its boundaries, confining light within the waveguide and ensuring efficient light transport over the increased distance, thus preventing light leakage while maintaining gathering efficiency.
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 light leakage to neighboring pixels, maintaining image sensor sensitivity and improving image quality by confining incident light within the spacers and directing it through the waveguide and color filters to the photodiodes, thus minimizing petal flare.
Implementation Method 1
The array of waveguides is disposed between the buffer layer and the array of color filters
Implementation Method 2
Each microlens is disposed above and aligned with one of the waveguides
Implementation Method 3
The array of color filters is disposed between the array of waveguides and the array of photodiodes
Data Source
AI summary
An image sensor includes a substrate material, an array of the color filters, an array of waveguides and spacers. The substrate material includes a plurality of photodiodes disposed therein. The array of color filters are disposed over the substrate material. The array of waveguides are disposed over the substrate material. The buffer layer is disposed between the substrate material and the arrays of color filters and waveguides. The spacers are disposed between the color filters in the array of color filters. The spacers are disposed between the waveguides in the array of waveguides. Incident light is adapted to be confined between the spacers. The incident light is adapted to be directed through one of the waveguides and through one of the color filters prior to being directed through the buffer layer into one of the photodiodes in the substrate material.