Solid-State Image Pickup Device Vertical Charge Transfer
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Solution Overview
Problem
The existing solid-state image pickup devices have a reduced light receiving efficiency due to the small area of photodiodes, which is exacerbated when the pitch of photodiodes is set at 1 micrometer or less, leading to a significant decrease in light receiving efficiency.
Innovation Solution
The design includes a semiconductor substrate with pixel circuits that feature a photoelectric conversion element, a first buried gate electrode adjacent to the element, a second buried gate electrode away from the first, and diffusion layers that overlap each other, allowing for efficient charge transfer and maximizing the area of the photoelectric conversion element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the pitch of photodiodes is reduced to 1 micrometer or less to increase pixel density, then the number of pixels per unit area increases, but the area of each photodiode becomes small which reduces light receiving efficiency
Solution Approach 1:
The patent introduces a vertical dimension by forming the first diffusion layer at a deeper position in the semiconductor substrate than the second diffusion layer. This stacked configuration in the depth direction allows charge storage functionality to be added without increasing the horizontal footprint, thereby maintaining small photodiode area while preserving charge transfer capability
Solution Approach 2:
The patent implements a nested structure where the first diffusion layer is positioned within the vertical projection area of the second diffusion layer. The first diffusion layer is formed in a region that overlaps with the second diffusion layer when viewed from the surface, creating a space-efficient nested arrangement that maximizes functional density
2Adaptability or versatility
If multiple diffusion layers are formed side by side in the light receiving area to enable charge transfer, then charge transfer functionality is achieved, but the photodiode area is reduced
Solution Approach 1:
Instead of arranging multiple diffusion layers horizontally side by side, the patent transitions to a vertical stacking arrangement where the first diffusion layer is positioned deeper in the substrate than the second diffusion layer. This vertical configuration enables charge transfer functionality while preserving horizontal photodiode area
Solution Approach 2:
The patent merges the charge storage and transfer functions into a vertically integrated structure where the first diffusion layer (deeper) and second diffusion layer (shallower) work together as a unified charge transfer pathway, eliminating the need for separate horizontal diffusion layer regions
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 enhances the functionality of the solid-state image pickup device while minimizing the reduction in photoelectric conversion element area, thereby maintaining high light receiving efficiency even at smaller pitches.
Implementation Method 1
a photoelectric conversion element; Electric charges accumulated in the photodiode conversion element are transferred
Data Source
AI summary
A solid-state image pickup device in which electric charges accumulated in a photodiode conversion element are transferred to a second diffusion layer through a first diffusion layer.