Solid-State Image Pickup Device OB Pixel Capacitance Matching
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Solution Overview
Problem
Conventional solid-state image pickup devices face challenges in achieving high S/N ratio due to reduced aperture ratio and increased costs and processes, particularly with the use of lightproof films and dummy pixels, which can degrade image quality and require complex configurations.
Innovation Solution
A multilayer solid-state image pickup device is designed with effective pixels and OB pixels, where the OB pixels are configured to obtain dark outputs without a lightproof film at the outer surface, using a common light receiving layer and signal read-out circuits with capacitors to match capacitance values, allowing for high-quality image signal acquisition without degrading the image due to step formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a lightproof film is stacked around the effective pixel area to form OB pixels, then the dark output can be obtained, but a step is formed between OB unit and light receiving unit which degrades image quality
Solution Approach 1:
The lightproof film is removed from the outer surface of the solid-state image pickup device. Instead, the lightproof layer is formed only on the semiconductor substrate side, extracting the lightproofing function from the surface level and relocating it to the substrate level, thereby eliminating the step formation while maintaining dark output detection capability
Solution Approach 2:
The lightproofing structure is shifted from a surface-level configuration (affecting the outer surface) to a substrate-level configuration (affecting only the semiconductor substrate side). This dimensional relocation allows the OB pixels to function without creating surface steps that would cause light diffusion and image degradation
2Measurement precision
If a lightproof film is stacked to form OB pixels, then dark output can be obtained, but the number of processes and cost are increased
Solution Approach 1:
The lightproof film stacking process is completely removed from the manufacturing sequence. The lightproof layer is integrated into the semiconductor substrate fabrication process itself, eliminating the need for separate film stacking operations and reducing manufacturing complexity and cost
Solution Approach 2:
The lightproof layer formation is merged with the semiconductor substrate fabrication process. By combining these functions into a single integrated process step, the number of manufacturing processes is reduced and production efficiency is improved while maintaining the ability to obtain dark output
3Device complexity
If photoelectric conversion unit and signal read-out circuit are formed on the same surface, then the device structure is simplified, but the aperture ratio cannot become 100% and S/N ratio is reduced
Solution Approach 1:
The photoelectric conversion layer is moved from the surface level to a stacked configuration above the semiconductor substrate. This dimensional relocation separates the photoelectric conversion function from the surface plane, allowing the aperture ratio to approach 100% while maintaining a relatively simple overall device structure
Solution Approach 2:
The device is segmented into distinct functional layers: the semiconductor substrate containing the signal read-out circuit, and the stacked photoelectric conversion layer above it. This segmentation allows each component to be optimized independently while maintaining overall structural simplicity
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 enables the acquisition of high-quality image signals with high S/N ratios while reducing manufacturing complexity and costs by eliminating the need for lightproof films and simplifying the process, thereby preventing image degradation from light diffusion.
Implementation Method 1
a photoelectric conversion unit (a photodiode) and a signal read-out circuit
Data Source
AI summary
A solid-state image pickup device includes a plurality of effective pixels each including a photoelectric conversion element and an OB pixel that is provided outside of an area where the effective pixels are formed and obtains the same output with a dark output of the effective pixel. Each of the effective pixels includes a first signal read-out circuit formed on a semiconductor substrate. The OB pixel includes a second signal read-out circuit formed on the semiconductor substrate and a capacitor connected to an input node of the second signal read-out circuit. The second signal read-out circuit has the same configuration as the first signal read-out circuit. A capacitance value of the capacitor is a value that renders the capacitance value at the input node of the first signal read-out circuit and the capacitance value at the input node of the second signal read-out circuit to be substantially equal to each other.