Autofocus Pixel Isolation Structure for Photodiode Alignment
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Solution Overview
Problem
Image sensors face alignment errors and saturation issues due to misalignment of pixel internal isolation layers, which affect the autofocusing function and overall image quality.
Innovation Solution
The image sensor design includes a pixel array with a substrate, pixels, and a logic circuit, featuring a pixel internal isolation layer formed from a first surface similar to the pixel isolation layer, reducing alignment errors and minimizing light-receiving area differences between photodiodes, thereby enhancing autofocusing capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a pixel internal isolation layer is formed separately from the pixel isolation layer, then alignment errors between the isolation layer and photodiodes increase, but manufacturing process complexity decreases
Solution Approach 1:
The patent merges the formation of the pixel internal isolation layer with the pixel isolation layer into a single simultaneous process step. Both isolation layers are formed from the first surface of the substrate at the same time, ensuring they share the same alignment reference and reducing alignment errors between the isolation layer and photodiodes.
Solution Approach 2:
The isolation layer formation process is designed to serve multiple functions simultaneously: it creates both the pixel isolation layer that separates adjacent pixels and the pixel internal isolation layer that separates photodiodes within the same pixel. This multi-functional approach maintains alignment accuracy while simplifying the overall manufacturing process.
2Manufacturing precision
If the pixel internal isolation layer is misaligned, then the light-receiving area of photodiodes becomes uneven, but correcting alignment requires increased manufacturing complexity
Solution Approach 1:
By forming the pixel internal isolation layer and pixel isolation layer simultaneously from the first surface, the patent ensures both layers are aligned to the same reference features (such as the photodiode positions), resulting in uniform light-receiving areas for all photodiodes without requiring separate alignment control processes.
3Reliability
If photodiodes are not properly isolated, then saturation occurs in the photodiodes, but adding complex isolation structures increases device complexity
Solution Approach 1:
The patent achieves effective photodiode isolation and saturation prevention by forming both the pixel isolation layer and pixel internal isolation layer in a single simultaneous process. This merged approach provides adequate isolation functionality without requiring complex multi-step isolation structures, maintaining reliability while controlling 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 effectively reduces alignment errors and improves the autofocusing function by accurately aligning the pixel internal isolation layer, preventing photodiode saturation and enhancing image sensor resolution.
Implementation Method 1
reducing alignment errors and minimizing light-receiving area differences between photodiodes
Implementation Method 2
a microlens on the first photodiode and the second photodiode
Implementation Method 3
each of the plurality of pixels including at least one photodiode
Data Source
AI summary
An image sensor includes a pixel array and a logic circuit. The pixel array includes a pixel isolation layer between a plurality of pixels. Each of the plurality of pixels include a pixel circuit below at least one photodiode. The logic circuit acquires a pixel signal from the plurality of pixels. The pixel array includes at least one autofocusing pixel, which includes a first photodiode, a second photodiode, a pixel internal isolation layer between the first and second photodiodes, and a microlens on the first and second photodiodes. The pixel internal isolation layer includes a first pixel internal isolation layer and a second pixel internal isolation layer, separated from each other in a first direction, perpendicular to the upper surface of the substrate, and the first pixel internal isolation layer and the second pixel internal isolation layer include different materials.