3D Stacked Image Sensor Pixels for Sensitivity
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Solution Overview
Problem
As CMOS image sensors have become smaller, their sensitivity has decreased due to the reduction in size of photo-electric conversion elements, leading to lower photo sensitivity.
Innovation Solution
The design includes multiple pixels with photoelectric conversion elements at different depths in a semiconductor substrate, where some elements are partially overlapped to increase the effective size and sensitivity, and sharing of floating diffusion nodes to enhance charge transfer efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the pixel size is reduced to make the CMOS image sensor smaller, then the device size is reduced, but the sensitivity of the photoelectric conversion element decreases
Solution Approach 1:
The patent transitions from two-dimensional planar photoelectric conversion elements to three-dimensional vertically stacked photoelectric conversion elements at different depths. This allows multiple conversion elements to occupy the same horizontal footprint while increasing total light capture volume, thereby maintaining sensitivity while reducing device area.
Solution Approach 2:
The patent implements nested photoelectric conversion elements where deeper elements are positioned within the vertical projection of upper elements. This nesting arrangement allows multiple conversion elements to share the same horizontal space at different depths, effectively increasing the total photoelectric conversion area without increasing the device footprint.
2Reliability
If multiple photoelectric conversion elements are stacked vertically to increase sensitivity, then the sensitivity improves, but the device complexity increases
Solution Approach 1:
The patent divides the photoelectric conversion function into multiple segmented elements positioned at different depths, each responsible for converting light to electrical signals. This segmentation allows the system to maintain high sensitivity through multiple conversion elements while managing complexity by distributing the conversion function across discrete, modular units.
Solution Approach 2:
The patent creates multi-functional pixel structures where each pixel contains multiple photoelectric conversion elements that can collectively perform light detection across different intensities and wavelengths. This universality allows a single pixel structure to handle various lighting conditions, reducing the need for separate specialized components and thereby managing overall system complexity.
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 enhances the sensitivity and full-well capacity of the image sensor, improving its performance without the light loss associated with color filters, thereby addressing the sensitivity decline in smaller pixel sizes.
Implementation Method 1
the first photoelectric conversion element is configured to convert a first visible light spectrum into a first photo charge, and the second photoelectric conversion element is configured to convert a second visible light spectrum into a second photo charge
Data Source
AI summary
An image sensor according to an example embodiment of includes a first pixel and a second pixel in a first row. The first pixel includes a first photoelectric conversion element at a first depth in a semiconductor substrate and the first photoelectric conversion element is configured to convert a first visible light spectrum into a first photo charge, and the second pixel includes a second photoelectric conversion element at a second depth from the first depth in the semiconductor substrate, the second photoelectric conversion element is at least partially overlapped by the first photoelectric conversion element in a vertical direction, and the second photoelectric conversion element is configured to convert a second visible light spectrum into a second photo charge.