Diffractive Lenses for Image Sensor Stray Light Control
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Solution Overview
Problem
Conventional image sensors with curved microlenses often fail to focus all incident light onto the photodiode, leading to optical cross-talk and performance limitations, and existing light blocking structures are large, difficult to manufacture, and have limited performance.
Innovation Solution
The use of diffractive lenses with varying refractive indices and thicknesses is introduced to redirect incident light effectively onto photodiodes, reducing optical cross-talk and improving image sensor performance by customizing the response to incident light through refractive index and dimensional adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional curved microlenses are used to focus light, then light focusing capability is provided, but optical cross-talk occurs because not all incident light is focused onto the intended photodiode
Solution Approach 1:
The patent changes the fundamental optical parameter from refraction-based focusing to diffraction-based focusing. The diffractive lens uses a planar surface with varying thickness to create phase delays that diffract light onto the intended photodiode, eliminating the optical cross-talk caused by conventional curved microlenses that cannot focus all incident light accurately.
Solution Approach 2:
The patent replaces the mechanical/refractive lens structure with a diffractive optical structure. Instead of using curved surfaces and refraction physics, the invention uses a planar diffractive lens that manipulates light through diffraction and interference patterns, substituting one optical mechanism for another to achieve better focusing accuracy.
2Object-generated harmful factors
If light blocking structures are used to prevent optical cross-talk, then cross-talk reduction is achieved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent extracts the light blocking function from separate physical structures and integrates it into the diffractive lens itself. The diffractive lens pattern is designed to inherently block stray light while maintaining the focusing function, eliminating the need for additional light blocking structures and reducing overall device complexity.
Solution Approach 2:
The diffractive lens serves multiple functions simultaneously: it focuses incident light onto the intended photodiode, blocks stray light that would cause optical cross-talk, and maintains a simple planar structure. This multi-functionality eliminates the need for separate light blocking components.
3Ease of manufacture
If conventional microlenses are used, then manufacturing process is simpler, but image sensor performance is limited due to incomplete light focusing
Solution Approach 1:
The patent inverts the conventional approach by using a planar (flat) surface instead of a curved surface. The diffractive lens has a planar upper surface with varying thickness, which is easier to manufacture using standard semiconductor fabrication techniques like spin coating and etching, while still achieving superior light focusing performance through diffraction effects.
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 implementation of diffractive lenses in image sensors enhances light focusing, reduces optical cross-talk, and improves overall image sensor performance by effectively directing light to the intended photodiodes, thereby enhancing image quality and reducing manufacturing complexities.
Implementation Method 1
Each image pixel in the array includes a diffractive lens that redirects incident light onto a photodiode
Implementation Method 2
Each image pixel in the array includes a photodiode that is coupled to a floating diffusion region via a transfer gate. Each pixel receives incident photons (light) and converts the photons into electrical signals.
Implementation Method 3
The microlenses of conventional image sensors typically have curved surfaces and use refraction to focus light on an underlying photodiode.
Data Source
AI summary
An image sensor may include an array of imaging pixels. Each imaging pixel may have a photosensitive area that is covered by a microlens and a diffractive lens that focuses light onto the photosensitive area. The diffractive lens may be interposed between the microlens and the photosensitive area. The diffractive lens may have a higher index of refraction than the surrounding materials. The diffractive lens may be formed as a portion of an anti-reflection coating. In some cases, multiple diffractive lenses may be formed over the imaging pixels. Focusing and defocusing diffractive lenses may be used to tune the response of the imaging pixels to incident light.