Microlens Curvature Profile for Focus Detection and Low Pixel Crosstalk
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Solution Overview
Problem
Existing image sensors face challenges in suppressing crosstalk between pixels while maintaining focus detection performance, as the curvature of microlenses for improving pupil division and reducing crosstalk do not always match.
Innovation Solution
The image sensor design incorporates a microlens optical system with a principal curved surface where the first curvature at a shorter distance from the optical axis is larger than the second curvature at a farther distance, optimizing the focal points and curvature radii to minimize crosstalk while maintaining focus detection efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the curvature of microlens is increased to improve pupil division ability for focus detection, then focus detection performance is improved, but crosstalk between pixels increases
Solution Approach 1:
The microlens is designed with non-uniform curvature distribution across its surface. The curvature is higher at the center region and lower at the peripheral region, allowing different parts of the microlens to perform different functions: the central high-curvature region provides strong light gathering capability for focus detection, while the peripheral low-curvature region reduces light leakage to adjacent pixels, thereby suppressing crosstalk.
Solution Approach 2:
The invention changes the curvature parameter of the microlens from a uniform value to a spatially varying value. Specifically, the curvature radius is designed to be smaller (higher curvature) at the center and larger (lower curvature) at the periphery. This parameter variation allows the microlens to simultaneously achieve high focus detection performance through strong central curvature and low crosstalk through reduced peripheral curvature.
2Object-generated harmful factors
If the curvature of microlens is decreased to suppress crosstalk between pixels, then crosstalk is reduced, but focus detection performance deteriorates
Solution Approach 1:
The microlens employs local quality differentiation by assigning different curvature characteristics to different regions. The central region maintains high curvature for effective light convergence and focus detection, while the peripheral region uses low curvature to minimize light spill-over to neighboring pixels. This localized optimization resolves the contradiction between crosstalk suppression and focus detection performance.
Solution Approach 2:
The invention applies parameter changes by making the curvature radius a function of radial position from the optical axis. The curvature radius increases with distance from the center, creating a gradient structure. This parameter transformation enables the microlens to achieve both low crosstalk (through peripheral low curvature) and high focus detection performance (through central high curvature).
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 effectively suppresses crosstalk between pixels, enabling high-performance on-imaging plane phase difference focus detection and imaging performance simultaneously.
Implementation Method 1
a microlens optical system provided on a side on which light is incident with respect to the photoelectric conversion unit
Implementation Method 2
at least one photoelectric conversion unit
Data Source
AI summary
In an image sensor having a plurality of pixels including focus detection pixels that outputs signals from which a pair of focus detection signals having parallax can be obtained based on light flux passing through different pupil regions of an imaging optical system, each pixel comprises: at least one photoelectric conversion unit; and a microlens optical system provided on a side on which light is incident with respect to the photoelectric conversion unit, wherein a shape of a principal curved surface of the microlens optical system is such that a first curvature of the microlens optical system at a first distance from an optical axis of the microlens optical system is larger than a second curvature of the microlens optical system at a second distance which is farther from the optical axis of the microlens optical system than the first distance.