Deep Device Isolation Layout for Low-Dark-Current Image Sensors
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Solution Overview
Problem
Existing image sensors face challenges in improving photosensitivity and minimizing dark current, which affects their overall performance and image quality.
Innovation Solution
The image sensor design incorporates a deep device isolation portion with specific conductive and insulating patterns, along with a transfer gate, to isolate unit pixels and reduce crosstalk, thereby enhancing photosensitivity and minimizing dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a deep device isolation portion is introduced to isolate unit pixels and reduce dark current, then photosensitivity is improved, but device complexity increases
Solution Approach 1:
The deep device isolation portion is divided into multiple conductive patterns (first conductive pattern, second conductive pattern) and insulating patterns arranged in alternating layers. This segmentation allows each layer to perform specific functions: the first conductive pattern provides initial isolation, the first insulating pattern provides electrical insulation, the second conductive pattern enhances isolation effectiveness, and the fixed charge layer minimizes dark current. By dividing the isolation structure into functional segments, the patent achieves superior photosensitivity and dark current reduction while maintaining manufacturability through standardized layering processes.
Solution Approach 2:
The deep device isolation portion employs a composite structure combining multiple materials with different properties: conductive materials (such as doped silicon or metal) for electrical isolation, insulating materials (such as silicon oxide or silicon nitride) for electrical insulation, and materials with fixed charges for dark current suppression. This composite approach leverages the complementary strengths of each material type to achieve comprehensive isolation performance that would be impossible with a single material, thereby improving photosensitivity without proportionally increasing complexity.
2Reliability
If the deep device isolation portion extends into the edge region with connection contacts, then isolation effectiveness is improved, but manufacturing complexity increases
Solution Approach 1:
The deep device isolation portion is formed to extend into the edge region before the connection contacts are created. This preliminary extension ensures that the isolation structure is already in place to prevent dark current and crosstalk at the critical edge regions where pixels meet the substrate boundary. By preparing the isolation structure in advance, subsequent connection contact formation becomes a simpler overlay process rather than requiring complex integration, thus improving isolation effectiveness while controlling manufacturing complexity.
Solution Approach 2:
The deep device isolation portion acts as an intermediary structure that bridges the pixel array region and the edge region. By extending into the edge region, it provides continuous isolation coverage across the transition zone, mediating between the isolated pixel environments and the substrate boundary. This intermediary extension ensures that connection contacts formed in the edge region do not compromise pixel isolation, as the isolation structure already occupies and protects the critical interface zone, simplifying the overall manufacturing sequence.
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 photosensitivity by increasing the amount of incident light and reduces dark current through effective isolation and bias voltage application, resulting in better image quality and reliability.
Implementation Method 1
a first fixed charge layer interposed between the second conductive pattern and the substrate
Implementation Method 2
The photodiode may convert incident light into an electrical signal
Data Source
AI summary
An image sensor includes a substrate including a first surface, a second surface opposite to the first surface, and unit pixels, a deep device isolation portion disposed in the substrate to isolate the unit pixels from each other, and a transfer gate disposed on the first surface and in each of the unit pixels. The deep device isolation portion includes a first conductive pattern extending from the first surface toward the second surface, a first insulating pattern interposed between the first conductive pattern and the substrate, a second conductive pattern extending from the second surface toward the first conductive pattern, and a first fixed charge layer interposed between the second conductive pattern and the substrate.