Photosensitive Region Impurity Layout for Efficient Charge Transfer
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Solution Overview
Problem
In solid state imaging devices, increasing the length of photoelectric conversion sections in one direction leads to inefficient charge transfer, as the electrical potential gradient in the photosensitive region is not sufficient to facilitate efficient charge transfer, often due to suboptimal design of the second impurity region.
Innovation Solution
The second impurity region is designed with a shape that is line-symmetric with respect to the center line of the photosensitive region, where the width increases gradually in the transfer direction, forming a consistent electrical potential gradient, ensuring efficient charge transfer regardless of the charge generation position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the length of the photoelectric conversion section in the second direction is increased, then the photosensitive region can cover a larger area, but the charge transfer efficiency decreases due to insufficient electrical potential gradient
Solution Approach 1:
The patent applies local quality by creating a non-uniform impurity concentration distribution within the photosensitive region. Specifically, a second impurity region with higher impurity concentration is formed adjacent to the transfer section, while the first impurity region has lower impurity concentration. This local variation in impurity concentration generates the necessary electrical potential gradient in the charge transfer direction, enabling efficient charge transfer even when the photosensitive region is extended in area.
2Productivity
If additional impurity is implanted into the photosensitive region to improve charge transfer efficiency, then charge transfer efficiency improves, but the design complexity increases due to difficulty in determining optimal impurity distribution
Solution Approach 1:
The patent segments the impurity distribution into distinct regions: a first impurity region with lower impurity concentration and a second impurity region with higher impurity concentration adjacent to the transfer section. This segmentation provides a clear, reproducible design framework that simplifies the implantation process while ensuring adequate charge transfer efficiency without requiring complex optimization calculations.
3Productivity
If the second impurity region has a trapezoidal shape with gradually increasing width, then an electrical potential gradient is formed, but portions with small electrical potential gradient may still be generated reducing transfer efficiency
Solution Approach 1:
The patent employs asymmetric design in the impurity region configuration. The second impurity region is positioned specifically adjacent to the transfer section with higher impurity concentration, creating an asymmetric impurity distribution that generates a consistent electrical potential gradient directed toward the transfer section. This asymmetric arrangement ensures that charges experience a reliable potential gradient throughout the transfer path, avoiding regions with insufficient gradient that would reduce transfer efficiency.
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 enhances charge transfer efficiency by maintaining a consistent electrical potential gradient across the photosensitive region, reducing image lag and improving overall transfer time.
Implementation Method 1
The second impurity region forms an electrical potential gradient, which gradually increases in the transfer direction, in the photosensitive region
Data Source
AI summary
The photosensitive region includes a first impurity region and a second impurity region having a higher impurity concentration than that of the first impurity region. The photosensitive region includes one end positioned away from the transfer section in the second direction and another end positioned closer to the transfer section in the second direction. A shape of the second impurity region in plan view is line-symmetric with respect to a center line of the photosensitive region along the second direction. A width of the second impurity region in the first direction increases in a transfer direction from the one end to the other end. An increase rate of the width of the second impurity region in each of sections, obtained by dividing the photosensitive region into n sections in the second direction, becomes gradually higher in the transfer direction. Here, n is an integer of two or more.