Solid-State Imaging Device Floating Diffusion Leakage Current
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Solution Overview
Problem
CMOS solid-state imaging devices suffer from high leakage current in the floating diffusion region due to crystal defects and uneven depletion layers, leading to increased dark current, especially at higher temperatures, which affects image quality.
Innovation Solution
The formation of a p-type semiconductor region at the edge of the isolation dielectric region to hole-pin the field edge, reducing the area of the depletion layer and minimizing defects, along with applying a prescribed bias voltage or using an insulating film with negative fixed charges between the floating diffusion region and the isolation dielectric region to control the depletion layer width.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the floating diffusion region is formed near the isolation dielectric region to increase pixel density, then the area utilization is improved, but the leakage current increases due to crystal defects and uneven depletion layers
Solution Approach 1:
An insulating film with negative fixed charges is introduced as an intermediary layer between the floating diffusion region and the isolation dielectric region. This intermediary film modifies the electric field distribution and reduces the depletion layer width at the field edge, thereby suppressing leakage current while maintaining the compact pixel layout.
Solution Approach 2:
The invention changes the electrical parameters at the field edge by applying negative fixed charges through the insulating film. This parameter change reduces the depletion layer width and modifies the electric field intensity, effectively suppressing the TAT mechanism that causes leakage current in high-density pixel structures.
2Reliability
If the depletion layer area is increased to improve charge collection, then the charge collection efficiency is improved, but the dark current increases due to more defect sites
Solution Approach 1:
The invention applies local quality modification by concentrating the negative fixed charges specifically at the field edge region near the isolation dielectric. This localized charge distribution reduces the depletion layer width only where defects are concentrated, without affecting the charge collection area in the bulk region, thereby suppressing dark current while maintaining charge collection efficiency.
3Ease of manufacture
If the pixel structure is simplified to reduce manufacturing complexity, then the manufacturing cost is reduced, but the leakage current control capability deteriorates
Solution Approach 1:
The insulating film with negative fixed charges is merged with the existing isolation dielectric structure, forming an integrated solution that addresses leakage current without requiring separate complex structures. This merging approach maintains manufacturing simplicity while effectively controlling leakage current through the combined electric field effects.
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 reduces leakage current in the floating diffusion region and minimizes variation among pixels, resulting in improved image quality and reduced dark current, even at elevated temperatures.
Implementation Method 1
an insulating film with negative fixed charges, which modifies an electric field at a field edge
Implementation Method 2
reduces a width of the depletion layer
Implementation Method 3
photoelectric conversion elements (photodiodes) arranged in an array
Data Source
AI summary
Disclosed herein is a solid-state imaging device including, a first semiconductor region of the first conduction type, a photoelectric conversion part having a second semiconductor region of the second conduction type formed in the region separated by the isolation dielectric region of the first semiconductor region, pixel transistors formed in the first semiconductor region, a floating diffusion region of the second conduction type which is formed in the region separated by the isolation dielectric region of the first semiconductor region, and an electrode formed on the first semiconductor region existing between the floating diffusion region and the isolation dielectric region and is given a prescribed bias voltage.