BSI Pixel Structure With Shared Diffusion for Low Cross-Talk
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Solution Overview
Problem
Current back-side illuminated (BSI) image sensors face challenges in increasing sensitivity to radiation, full well capacity, reducing capacitance, and minimizing cross-talk between pixel structures while maintaining cost-effectiveness in manufacturing.
Innovation Solution
The implementation of dual radiation-sensing device (RSD)-based pixel structures with rectangular-shaped radiation-sensing surfaces, inter-pixel isolation structures, and shared floating diffusion regions and pixel transistor groups, along with a single metal line layer for electrical coupling, enhances radiation detection efficiency and reduces manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional single RSD pixel structures are used, then manufacturing is simpler, but radiation sensitivity and full well capacity are limited
Solution Approach 1:
The pixel structure is divided into multiple independent RSDs (first RSD, second RSD, third RSD, fourth RSD) within a single pixel unit. Each RSD can independently sense radiation, and their signals are combined through shared floating diffusion regions. This segmentation allows the pixel to achieve higher radiation sensitivity and full well capacity while maintaining a structured, manageable design through the use of shared components and systematic interconnect arrangements.
2Reliability
If more RSDs are added to increase sensitivity, then radiation detection capability improves, but manufacturing cost increases
Solution Approach 1:
Multiple pixel structures share common components including floating diffusion regions (first floating diffusion region, second floating diffusion region), interconnect layers, and metal line layers. For example, the first pixel structure and second pixel structure both connect to the same first floating diffusion region through the interconnect layer. This merging strategy reduces the total number of discrete components that need to be manufactured and assembled, thereby lowering manufacturing costs while still achieving high radiation sensitivity through the combined signal from multiple RSDs.
Solution Approach 2:
The shared floating diffusion regions and interconnect structures serve multiple functions: they collect signals from multiple RSDs, provide electrical connections to readout circuits, and enable signal combining from adjacent pixel structures. The first floating diffusion region receives signals from both the first RSD and second RSD, while the second floating diffusion region receives signals from the third RSD and fourth RSD. This multi-functionality reduces the overall component count and manufacturing complexity.
3Area of stationary object
If pixel structures are placed closer to increase density, then area efficiency improves, but cross-talk between pixels increases
Solution Approach 1:
Isolation structures are introduced as intermediary elements positioned between adjacent pixel structures. These isolation structures physically separate the RSDs and floating diffusion regions of neighboring pixels, preventing electrical and optical cross-talk while allowing the pixel structures to be densely packed. The isolation structures act as mediators that enable high pixel density without sacrificing signal integrity by blocking unwanted signal leakage between adjacent pixels.
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 radiation sensitivity and full well capacity while minimizing cross-talk and lowering production costs by utilizing dual RSD-based pixel structures and shared components in BSI image sensors.
Implementation Method 1
pixel structures that absorb (e.g., sense) an incoming radiation and convert it into electrical signals
Data Source
AI summary
An optical device and a method of fabricating the same are disclosed. The optical device includes a first die layer and a second die layer. The first die layer includes a first substrate having a first surface and a second surface opposite to the first surface, first and second pixel structures, an inter-pixel isolation structure disposed in the first substrate and surrounding the first and second pixel structures, and a floating diffusion region disposed in the first substrate and between the first and second pixel structures. The second die layer includes a second substrate having a third surface and a fourth surface opposite to the third surface and a pixel transistor group disposed on the third surface of the second substrate and electrically connected to the first and second pixel structures.