Solid-state imaging device with shallow trench isolation
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Solution Overview
Problem
As MOS image sensors miniaturize, the reduced area of photodiodes leads to decreased sensitivity and increased occurrence of dark current and white spots due to existing insulation and isolation systems, necessitating improved conversion efficiency and reduced capacitance in floating diffusion regions.
Innovation Solution
Implementing a shallow trench element isolation region for the floating diffusion portion and impurity diffusion isolation regions for other areas, reducing capacitance and suppressing dark current and white spots, while maintaining high conversion efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the pixel size is reduced to increase the number of pixels, then the resolution is improved, but the area of the photodiode is reduced, causing decreased sensitivity and reduced saturated electric charge amount
Solution Approach 1:
The patent applies different element isolation methods to different regions: shallow trench isolation (STI) is used specifically for element isolation regions bordering the floating diffusion portion to reduce capacitance and improve conversion efficiency, while other element isolation regions use impurity diffusion isolation. This localized differentiation allows the photodiode area to be minimized for high resolution while maintaining sensitivity through optimized capacitance management at critical interfaces.
2Reliability
If LOCOS or STI element isolation system is used, then element isolation is achieved, but dark current and white spots occur on the interface between the photodiode and the insulated and isolated area
Solution Approach 1:
The patent employs impurity diffusion isolation for element isolation regions not bordering the floating diffusion portion, which effectively suppresses dark current and white spot generation. Meanwhile, STI is used only where needed (at floating diffusion boundaries) for capacitance reduction. This selective application of different isolation techniques eliminates the harmful effects associated with LOCOS and STI while preserving their beneficial isolation properties.
3Productivity
If the photodiode area is reduced, then more pixels can be accommodated, but the conversion efficiency decreases and sensitivity is reduced
Solution Approach 1:
The patent changes the physical parameters of the element isolation regions by using STI with specific depth and material properties at critical locations (bordering floating diffusion). This reduces the junction capacitance of the floating diffusion portion, thereby improving conversion efficiency even when the photodiode area is reduced. The parameter optimization allows high pixel density to be achieved without sacrificing the electrical performance needed for sensitive detection.
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
Enhances sensitivity by improving conversion efficiency and preventing dark current and white spots, even with reduced pixel size and increased pixel count, making it suitable for miniaturized MOS image sensors.
Implementation Method 1
a photoelectric conversion element and a read transistor for reading electric charges photoelectrically-converted in the photoelectric conversion element
Data Source
AI summary
A solid-state imaging device including is provided. The solid-state imaging device includes: pixels arrayed; a photoelectric conversion element in each of the pixels; a read transistor for reading electric charges photoelectrically-converted in the photoelectric conversion elements to a floating diffusion portion; a shallow trench element isolation region bordering the floating diffusion portion; and an impurity diffusion isolation region for other element isolation regions than the shallow trench element isolation region.