Image Sensor Transfer Gate Projections and Spacers
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Solution Overview
Problem
Existing image sensors face interferences between adjacent charge transfer regions in pixel blocks, leading to reduced light-to-charge conversion gain and blooming issues.
Innovation Solution
The image sensor design includes transfer gates with projections and spacers on sidewalls, allowing for self-alignment in forming a floating diffusion region, which prevents interferences and enhances conversion gain by aligning diffusion region interfaces with spacers and maintaining uniform channel lengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If transfer gates are positioned close to each other in pixel blocks, then device area is reduced, but interference between adjacent charge transfer regions increases leading to reduced conversion gain and blooming issues
Solution Approach 1:
The transfer gate is divided into a first transfer gate and a second transfer gate positioned adjacent to each other. Each transfer gate has its own separate charge transfer region, physically segmenting the charge transfer paths to prevent interference while maintaining compact pixel block area.
Solution Approach 2:
A dummy pattern is introduced as an intermediary structure positioned between the first and second transfer gates. This dummy pattern acts as a mediator that prevents direct interference between adjacent charge transfer regions while allowing the transfer gates to remain close together, thus maintaining small pixel area without sacrificing conversion gain.
2Area of stationary object
If transfer gates are positioned close to each other in pixel blocks, then device area is reduced, but blooming issues occur due to interference between adjacent charge transfer regions
Solution Approach 1:
By dividing the transfer gate structure into separate first and second transfer gates with distinct charge transfer regions, the patent segments the potential blooming paths. This segmentation prevents charge overflow from spreading between adjacent regions, eliminating blooming while maintaining compact pixel area.
Solution Approach 2:
The dummy pattern positioned between the transfer gates serves as an intermediary barrier that blocks the propagation of blooming effects. This intermediary structure physically separates the charge transfer regions, preventing harmful charge overflow from affecting adjacent pixels while keeping the overall pixel block area small.
3Manufacturing precision
If spacers are formed on sidewalls of transfer gates, then self-alignment precision is improved, but device complexity increases
Solution Approach 1:
The spacers are formed to extend along the sidewalls of the transfer gates, and the charge transfer regions are self-aligned to the spacer positions. This self-service mechanism allows the structure itself to define the alignment, eliminating the need for additional complex alignment steps while achieving high manufacturing precision.
Solution Approach 2:
The spacers act as intermediary alignment references between the transfer gates and the charge transfer regions. By using the spacers as a mediating structure, the patent achieves precise self-alignment without requiring complex external alignment processes, thus improving manufacturing precision without proportionally increasing device 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 design improves the operational characteristics of image sensors by preventing unnecessary impurity implantation and reducing blooming, thereby enhancing optical sensitivity and uniformity across pixel blocks.
Implementation Method 1
different photoelectric conversion elements formed adjacent to one another in a substrate and structured to generate photocharges in response to an incident light
Implementation Method 2
different transfer gates formed over the different photoelectric conversion elements, respectively, one transfer gate for one photoelectric conversion element, and structured to transfer the photocharges from the photoelectric conversion elements to the floating diffusion region
Data Source
AI summary
An image sensor includes a first transfer gate formed over a substrate, and including a first projection; a second transfer gate formed over the substrate, neighboring the first transfer gate, and including a second projection; and a floating diffusion formed in the substrate, and partially overlapping with the first transfer gate and the second transfer gate, wherein the first projection and the second projection face each other.