CMOS Image Sensor Floating Diffusion Capacitor Dynamic Range
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Solution Overview
Problem
CMOS image sensors face limitations in dynamic range due to the saturation of the floating diffusion node, which restricts their performance in both low light and high light conditions, especially as pixel size decreases.
Innovation Solution
A CMOS image sensor design that incorporates a physical capacitor in the floating diffusion area, where the gate electrode of the drive transistor serves as the lower capacitor electrode, connected to the floating diffusion area, enhancing electron storage capacity without increasing pixel size through the use of a dielectric layer and an upper capacitor electrode, and optionally a polysilicon or metal pattern for the upper electrode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the pixel size is decreased to reduce space, then the area occupied by the image sensor is reduced, but the electron storing capacity of the floating diffusion node is reduced, leading to reduced dynamic range
Solution Approach 1:
The patent introduces a capacitor structure with upper and lower electrodes stacked vertically above the floating diffusion node. By utilizing the vertical dimension (third dimension) rather than only horizontal expansion, the electron storing capacity is increased without increasing the pixel area. The lower electrode is formed on the floating diffusion node and the upper electrode is formed above it with a dielectric layer in between, creating a three-dimensional capacitor structure that maximizes storage capacity within the constrained pixel area.
2Quantity of substance
If the floating diffusion area is enlarged to increase electron storing capacity, then the dynamic range is improved, but the pixel size must be increased
Solution Approach 1:
The patent resolves this contradiction by transitioning from a two-dimensional planar expansion to a three-dimensional vertical structure. The capacitor is formed with the lower electrode on the floating diffusion node and the upper electrode above it, separated by a dielectric layer. This vertical stacking allows the electron storing capacity to be increased without requiring additional horizontal space, thus maintaining the same pixel size while improving dynamic range.
Solution Approach 2:
The capacitor structure is nested within the existing pixel architecture. The lower capacitor electrode is formed on the floating diffusion node, and the upper capacitor electrode is formed above it, effectively nesting the capacitor structure within the vertical space of the pixel. This nested arrangement allows the capacitor to be integrated without increasing the overall pixel footprint.
3Quantity of substance
If a physical capacitor is added to increase electron storing capacity, then the dynamic range is improved, but the device complexity increases
Solution Approach 1:
The patent merges the capacitor structure with the existing drive transistor gate electrode. The lower capacitor electrode is formed using the same conductive material and process as the drive transistor gate electrode, and the gate electrode is extended to serve as the lower electrode. This merging approach allows the capacitor to be formed using existing transistor fabrication processes, reducing the need for additional complex manufacturing steps and integrating the capacitor seamlessly into the pixel structure.
Solution Approach 2:
The drive transistor gate electrode serves dual functions: as the control electrode for the drive transistor and as the lower electrode of the capacitor. This multi-functionality reduces the number of separate components and simplifies the overall device structure. The gate electrode material and formation process are utilized for both transistor operation and capacitor formation, reducing device complexity.
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 increases the electron storing capacity of the floating diffusion node, thereby improving the dynamic range of the image sensor, ensuring effective output response across varying light conditions without enlarging the pixel size.
Implementation Method 1
the image sensor is a semiconductor device converting an optical image into an electrical signal
Implementation Method 2
a capacitor comprising a lower capacitor electrode connected to the floating diffusion area, a dielectric layer on the lower capacitor electrode, and an upper capacitor electrode
Data Source
AI summary
The embodiment relates to a complementary metal oxide semiconductor (CMOS) image sensor and more particularly, to a CMOS image sensor and a manufacturing method thereof capable of improving electron storing capacity in a floating diffusion area. The CMOS image sensor includes a first gate electrode on a semiconductor substrate; a photodiode in the semiconductor substrate on one side of the first gate electrode; a floating diffusion area in the semiconductor substrate on an opposite side of the first gate electrode; a capacitor including a lower capacitor electrode connected to the floating diffusion area, a dielectric layer on the lower capacitor electrode, and an upper capacitor electrode; a drive capacitor coupled to the lower capacitor electrode and having a second gate electrode connected to the floating diffusion area. The electron storing capacity of the floating diffusion node is increased, making it possible to improve the dynamic range of the image sensor.