Rectangular Image Sensor Pixel Asymmetry
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Solution Overview
Problem
The reduction in pixel size to less than 1.7 µm leads to reduced sensitivity due to smaller pixel area and narrower openings between metal wires, which block excessive light, resulting in poor quantum efficiency, especially when light rays are incident at angles.
Innovation Solution
Increasing the area of openings above photodiodes by using rectangular pixels with a greater height than width, reducing the number of vertical wires, and eliminating or combining certain horizontal wires, such as the row select transistor, to allow more light to reach the photodiodes, while summing pixels in low resolution imaging modes for improved sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pixel size is reduced to less than 1.7 µm to increase resolution, then the number of pixels per area increases, but the opening between metal wires becomes narrower and blocks too much light, reducing sensitivity and quantum efficiency
Solution Approach 1:
The patent changes the pixel shape from square to rectangular with aspect ratios such as 4:3, 16:9, or other non-1:1 ratios. This asymmetric shape allows the opening between metal wires to be elongated in one direction, increasing the effective light transmission area while maintaining the same pixel footprint. The rectangular geometry optimizes the wire spacing arrangement to maximize the opening area for light passage.
Solution Approach 2:
The patent utilizes the vertical dimension by stacking multiple metal wire layers (3 or more layers) to carry signal lines. By moving wires to different vertical levels, the opening in any single horizontal plane can be enlarged, as wires that would otherwise block light in the same plane are distributed across multiple layers, allowing light to pass through the gaps between layers.
2Area of stationary object
If 3 or more layers of metal wires are used to increase opening area, then the opening area increases, but light rays incident at 25 degrees from normal are blocked by the tall stack of metal wires
Solution Approach 1:
The rectangular pixel shape with optimized aspect ratio creates an asymmetric opening geometry that is elongated in the direction most affected by angled light incidence. This asymmetric configuration ensures that even when light arrives at 25 degrees from normal, there is sufficient vertical or horizontal clearance in the opening to allow light transmission without being blocked by the multi-layer wire stack.
3Illumination intensity
If rectangular pixels with greater height than width are used, then the opening area increases and sensitivity improves, but the pixel geometry becomes more complex
Solution Approach 1:
The rectangular pixel design serves multiple functions: it increases the opening area for light transmission, optimizes wire spacing to reduce metal coverage, and maintains compatibility with standard manufacturing processes. The same rectangular geometry works for various aspect ratios (4:3, 16:9, etc.) and can be adapted to different wire layer configurations, making it a universal solution for improving sensitivity across different device specifications.
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 approach significantly increases the opening area for light, enhancing the sensitivity of the image sensor by more than doubling the prior art metal opening, resulting in higher quantum efficiency and improved light capture, even for angled light incidence.
Implementation Method 1
photodiode for converting light into electrical charge
Data Source
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Figure 7~8
AI summary
An image sensor includes a unit cell (204) of four pixels. The unit cell includes four photosensitive regions (211, 212, 213, 214) that collect charge in response to light; four transfer transistors (207, 208, 209, 210) that respectively pass the charge from each of the four photosensitive regions to one common charge-to-voltage conversion mechanism (203); three control wires (TG1, TG2, TG3) in which a first control wire (TG) controls two (208, 210) of the transfer transistors and a second control wire (TG1) controls one (207) of the transfer transistors and a third control wire (TG3) controls one (209) of the transfer transistors; an amplifier (205) connected to the common charge-to-voltage conversion mechanism that outputs an output signal in response to a signal from the charge-to-voltage conversion mechanism; and a reset transistor (206) connected to the common charge-to-voltage conversion mechanism for resetting the charge-to-voltage conversion mechanism to a predetermined signal level (VDD).