Stacked Image Sensor Pixel Layout for Accurate Focus Detection
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Solution Overview
Problem
Existing image sensors face challenges in maintaining focus detection accuracy, especially when dealing with objects having luminance fluctuations or low light conditions, due to insufficient light reception areas and inadequate pupil division configurations.
Innovation Solution
The image sensor is designed with a stacked structure featuring PDIC-side and MEMIC-side pixels, where photoelectric conversion units are arranged in both horizontal and vertical directions within each pixel, allowing for simultaneous signal readout and global shutter functionality, enhancing focus detection accuracy across different pupil division directions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If photoelectric conversion units are arranged in only one direction (horizontal) within a pixel for pupil division, then the device complexity is reduced, but focus detection accuracy deteriorates when the subject has horizontal stripes due to insufficient parallax
Solution Approach 1:
The patent applies dimensionality change by arranging photoelectric conversion units not only in the horizontal direction but also in the vertical direction within pixels. Specifically, some pixels have photoelectric conversion units arranged horizontally while other pixels have them arranged vertically, creating two-dimensional pupil division capability. This resolves the contradiction by adding vertical arrangement dimension to complement the horizontal arrangement, enabling accurate focus detection for both horizontal and vertical stripe patterns without significantly increasing overall device complexity.
2Reliability
If the isolation region in each pixel is enlarged to separate phase difference detection pixels with vertical and horizontal division directions, then cross-talk between adjacent photoelectric conversion units is reduced, but the light reception area decreases leading to reduced focus detection accuracy in dark conditions
Solution Approach 1:
The patent applies local quality by making the isolation region configuration selective rather than uniform across all pixels. Specifically, the isolation region is provided between photoelectric conversion units of different pupil division directions (horizontal vs vertical) where needed to prevent cross-talk, but is minimized or omitted in other configurations. This localized approach to isolation maintains signal integrity where required while preserving maximum light reception area in low light conditions.
3Adaptability or versatility
If a stacked structure with separate semiconductor substrates for pixel circuits and signal accumulation is used to achieve global shutter function, then the global shutter capability is improved, but the manufacturing complexity and device structure become more complex
Solution Approach 1:
The patent applies multi-functionality by designing the stacked structure so that the first semiconductor substrate serves dual purposes: it contains both the pixel circuits and functions as the signal accumulation layer through the photoelectric conversion units. The second substrate provides support and additional circuitry. This integration of multiple functions into the first substrate reduces the need for separate dedicated accumulation layers, simplifying the overall laminated structure while maintaining global shutter capability.
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 focus detection accuracy by ensuring sufficient light reception and consistent timing across all pixels, reducing the impact of luminance fluctuations and low light conditions, thereby enhancing the overall focus detection precision.
Implementation Method 1
a plurality of photoelectric conversion units that convert incident light into charge and accumulate the charge
Data Source
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AI summary
An image sensor includes a plurality of pixels, and each pixel comprises: a microlens; a plurality of photoelectric conversion units that convert incident light into charge and accumulate the charge; a plurality of holding units that hold signals corresponding to the charge; control means configured to control timings of accumulating the charge converted by the plurality of photoelectric conversion units and timings of causing the plurality of holding units to hold the signals corresponding to the charge; and output means configured to output the signals held in the plurality of holding units in units of one row. The plurality of pixels include a plurality of first pixels having the plurality of photoelectric conversion units arranged in a first direction and a plurality of second pixels having the plurality of photoelectric conversion units arranged in a second direction which is perpendicular to the first direction.