Image Sensor Contact Plug Placement for Dark Current Noise Reduction
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Solution Overview
Problem
The existing image pickup apparatuses face challenges in reducing noise caused by well contact plugs, which affect image quality and focus detection accuracy due to variations in dark current among photoelectric conversion units, especially when these units are adjacent and receive light of the same wavelength.
Innovation Solution
The image pickup apparatus is designed with a reduced number of well contact plugs, where each plug is strategically located closer to potential barriers between same-color photoelectric conversion units, minimizing the difference in noise between adjacent units and reducing dark current impact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the number of contact plugs is reduced, then device complexity is reduced, but noise from dark current variations among photoelectric conversion units increases
Solution Approach 1:
The patent applies local quality by positioning contact plugs at specific locations within the image sensing area that are closer to certain photoelectric conversion units than others. This non-uniform distribution creates different electrical characteristics for different units, allowing strategic placement to minimize dark current noise impact on same-color units while maintaining reduced overall plug count.
Solution Approach 2:
The patent achieves equipotentiality by ensuring that same-color photoelectric conversion units (e.g., all red or all blue units) have equal electrical characteristics through symmetric positioning relative to contact plugs. This equalizes dark current levels across same-color units, reducing noise variations that would otherwise degrade image quality and focus detection accuracy.
2Measurement precision
If contact plugs are positioned closer to same-color photoelectric conversion units, then noise equalization is improved, but distance to other units increases
Solution Approach 1:
The patent implements local quality by creating non-uniform distance relationships between contact plugs and different photoelectric conversion units. Same-color units are positioned at equal distances from contact plugs to equalize their electrical characteristics, while other units accept varying distances. This localized optimization improves focus detection accuracy by reducing noise variations among same-color units without requiring uniform positioning for all units.
3Reliability
If well contact plugs are disposed in image sensing area, then voltage supply to semiconductor regions is improved, but dark current noise affects image quality
Solution Approach 1:
The patent applies parameter changes by strategically positioning contact plugs to alter the electrical parameters (resistance, capacitance, dark current levels) of adjacent photoelectric conversion units. By changing the spatial arrangement and electrical characteristics, the patent reduces dark current noise impact on same-color units while maintaining reliable voltage supply to all semiconductor regions through the reduced set of contact plugs.
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 image quality by equalizing dark current across same-color photoelectric conversion units and improves focus detection accuracy by minimizing noise variations, thereby improving overall performance.
Implementation Method 1
a plurality of photoelectric conversion units each including a first-conductivity-type first semiconductor region configured to accumulate a signal charge
Implementation Method 2
a potential barrier formed between photoelectric conversion units included in the plurality of photoelectric conversion units
Data Source
AI summary
An image pickup apparatus includes photoelectric conversion units each including a first semiconductor region of a first conductivity type and a semiconductor region of a second conductivity type disposed in contact with the first semiconductor region, a potential barrier formed between photoelectric conversion units, and a contact plug disposed in an image sensing area. The number of contact plugs is smaller than the number of photoelectric conversion units. The photoelectric conversion units include first and second photoelectric conversion units and are arranged such that at least two first photoelectric conversion units are adjacent in a first direction. The potential barrier includes a first part formed between the two first photoelectric conversion units disposed adjacently and a second part formed between first and second photoelectric conversion units adjacent to each other. The contact plug is located closer to the first part than to the second part.