CMOS Image Sensor Layout for Wide Dynamic Range and High Sensitivity
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Solution Overview
Problem
CMOS image sensors face challenges in achieving both a wide dynamic range and high sensitivity due to the trade-off between enlarged capacitance of the storage capacitor, which reduces the photodiode fill factor and sensitivity, and the enlarged light receiving area of the photodiode, which reduces the dynamic range.
Innovation Solution
A solid-state imaging device is designed with a photoelectric conversion part having a first conductivity type semiconductor layer pinned between substrate surfaces, a transfer transistor, a floating diffusion, a storage transistor, and a storage capacitance element formed on the second substrate surface to spatially overlap with the photoelectric conversion part, allowing for both high sensitivity and wide dynamic range by optimizing the capacitance and light receiving area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the capacitance of the storage capacitor is enlarged to increase dynamic range, then the dynamic range is improved, but the photodiode fill factor is reduced leading to lower sensitivity
Solution Approach 1:
The storage capacitor is positioned on the opposite substrate surface, utilizing the third dimension (depth) rather than competing for planar space. This spatial separation in the vertical dimension allows both the photodiode and storage capacitor to achieve their required sizes without compromising each other's performance
2Measurement precision
If the light receiving area of the photodiode is enlarged to increase sensitivity, then the sensitivity is improved, but the area occupied by the storage capacitor is reduced leading to reduced dynamic range
Solution Approach 1:
By moving the storage capacitor to the opposite substrate surface, the invention utilizes the vertical dimension to resolve the area conflict. This allows the photodiode to maximize its light receiving area on the front surface while the storage capacitor is accommodated on the back surface, eliminating the zero-sum area competition
3Measurement precision
If the photodiode fill factor is increased to improve sensitivity, then the sensitivity is improved, but the dynamic range is reduced
Solution Approach 1:
The spatial separation of the storage capacitor to the opposite substrate surface removes the geometric constraint that forced a trade-off between fill factor and capacitor size. This dimensional reorganization allows both parameters to be optimized independently
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
The solution enables the CMOS image sensor to output both bright and dark signals with high conversion gain modes in a single reading period, effectively enhancing the dynamic range and sensitivity while preventing reduced fill factor and dynamic range issues.
Implementation Method 1
a photoelectric conversion part including a first conductivity type semiconductor layer pinned between the first substrate surface side and the second substrate surface side of the substrate, the photoelectric conversion part being configured to perform photoelectric conversion of received light and store charges
Data Source
AI summary
One object of the present invention is to provide a solid-state imaging device, a method for fabricating a solid-state imaging device, and an electronic apparatus that implement both a wide dynamic range and a high sensitivity. A storage capacitor serving as a storage capacitance element includes a first electrode and a second electrode on a second substrate surface side. The first electrode is formed of a p+ region (the second conductivity type semiconductor region) formed in the surface of a second substrate surface of a substrate, and the second electrode is formed above the second substrate surface so as to be opposed at a distance to the first electrode in the direction perpendicular to the substrate surface. The first electrode and the second electrode are arranged so as to spatially overlap with a photoelectric conversion part in the direction perpendicular to the substrate surface.