Image Sensor Pixel Structure for Full Well and Charge Transfer
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Solution Overview
Problem
Current image sensors face challenges in achieving improved electrical and optical characteristics, particularly in terms of reducing size while maintaining high resolution and full well capacity, and enhancing charge transfer efficiency.
Innovation Solution
The design incorporates a semiconductor substrate with a photoelectric conversion layer having regions of different thicknesses, overlapping with readout circuit transistors and a floating diffusion region, along with a pixel isolation layer, to increase the area for photocharge generation and improve charge transfer efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the image sensor size is reduced, then portability and integration are improved, but the area for photocharge generation is reduced and full well capacity decreases
Solution Approach 1:
The patent utilizes the vertical dimension by forming a photoelectric conversion layer with varying thickness in the depth direction. The first region has a greater thickness than the second region, creating a three-dimensional structure that increases photocharge generation volume without increasing the planar footprint, thus resolving the contradiction between reduced sensor size and maintained photocharge generation area.
Solution Approach 2:
The patent nests the photoelectric conversion layer within the semiconductor substrate, with the layer having different thickness regions that are vertically integrated into the substrate structure. This nesting approach allows the photoelectric conversion function to be embedded within the existing sensor architecture, maximizing space utilization without increasing overall sensor dimensions.
2Quantity of substance
If the photoelectric conversion layer thickness is increased to increase full well capacity, then charge storage capacity is improved, but charge transfer efficiency may be reduced due to longer transfer distance
Solution Approach 1:
The patent applies local quality by creating regions with different photoelectric conversion layer thicknesses within the same pixel structure. The first region has a greater thickness for enhanced charge storage, while the second region has a reduced thickness optimized for efficient charge transfer. This spatial differentiation of thickness allows simultaneous optimization of both full well capacity and charge transfer efficiency in different locations.
Solution Approach 2:
The photoelectric conversion layer is segmented into multiple regions with different thickness characteristics. The first region (greater thickness) is optimized for charge generation and storage, while the second region (reduced thickness) is optimized for charge transfer. This segmentation allows each region to perform its specific function optimally without compromising the other.
3Area of stationary object
If readout circuit transistors are positioned closer to the photoelectric conversion layer to reduce pixel size, then device integration is improved, but optical interference and electrical noise may increase
Solution Approach 1:
The patent positions readout circuit transistors in the horizontal plane while maintaining vertical separation through the layered structure. The photoelectric conversion layer and transistors operate in different vertical zones, allowing close horizontal integration for compact pixel size while the vertical stacking provides natural isolation that reduces optical interference and electrical noise coupling.
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 secures a larger area for photocharge generation, increases full well capacity, and enhances charge transfer efficiency, even in a reduced image sensor size, thereby addressing the limitations of existing technologies.
Implementation Method 1
a photoelectric conversion layer provided in the semiconductor substrate at a side of the transfer gate electrode and including dopants of a first conductivity type
Data Source
AI summary
An image sensor includes a semiconductor substrate having a first surface and a second surface opposite to the first surface, a transfer gate electrode provided on the first surface of the semiconductor substrate, readout circuit transistors spaced apart from the transfer gate electrode and provided on the first surface of the semiconductor substrate, and a photoelectric conversion layer provided in the semiconductor substrate at a side of the transfer gate electrode and including dopants of a first conductivity type. The photoelectric conversion layer includes a first region having a first thickness and a second region having a second thickness that is less than the first thickness. The second region overlaps with at least a portion of the readout circuit transistors in a direction perpendicular to the first surface of the semiconductor substrate.