Amplifying Transistor Gate Area Noise Reduction CMOS Sensor
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Solution Overview
Problem
CMOS image sensors face challenges in reducing random noise, particularly due to defects at the silicon/gate insulation film interface, which affects image quality, especially under low light conditions, and existing methods to mitigate this noise are either ineffective or require significant changes to the semiconductor forming process, impacting device reliability.
Innovation Solution
A solid-state image capturing apparatus is designed with a pixel array where the amplifying transistor has a larger gate area than other transistors, and adjacent pixels share reset or selection transistors, reducing noise without relying on the semiconductor forming process, by configuring the source follower transistor to have a gate area 135% or more of other transistors, thereby minimizing noise influence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the gate insulation film is formed without nitrogen atoms to reduce defect level density, then random noise is reduced, but the film quality changes and device reliability may be affected
Solution Approach 1:
The invention changes the physical parameter of the gate insulation film by forming a low-temperature oxide film (thickness 5-15 nm) with different dielectric properties and thermal characteristics compared to conventional high-temperature oxide films. This parameter change reduces defect level density at the silicon interface, thereby reducing random noise while maintaining device reliability through controlled film quality
Solution Approach 2:
The invention uses a composite gate insulation film structure consisting of a low-temperature oxide film layer and a nitrogen-containing oxide film layer. The low-temperature oxide film provides low defect density for noise reduction, while the nitrogen-containing layer maintains appropriate film quality and device characteristics, creating a composite structure that resolves the contradiction between noise reduction and reliability
2Object-affected harmful factors
If the gate insulation film structure is changed to reduce random noise, then noise control improves, but the complexity of the forming process increases
Solution Approach 1:
The gate insulation film is segmented into multiple functional layers: a low-temperature oxide film layer (5-15 nm) for noise reduction and a nitrogen-containing oxide film layer for maintaining film quality. This segmentation allows each layer to perform its specific function independently, reducing random noise while keeping the overall process manageable through modular construction
3Manufacturing precision
If pixel size is reduced to several times the wavelength of light, then resolution improves, but random noise increases due to crystal defects
Solution Approach 1:
The invention changes the physical parameter of the gate insulation film by forming a low-temperature oxide film (thickness 5-15 nm) with different dielectric properties and thermal characteristics compared to conventional high-temperature oxide films. This parameter change reduces defect level density at the silicon interface, thereby reducing random noise while maintaining device reliability through controlled film quality
Solution Approach 2:
The invention applies local quality improvement by specifically treating the gate insulation film region with a low-temperature oxide film to reduce defect level density at the silicon interface. This localized treatment targets the specific area where random noise originates (the source follower transistor gate interface) without affecting other parts of the pixel structure, enabling noise reduction in miniaturized pixels
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 effectively reduces random noise by half, improving the signal-to-noise ratio and maintaining device reliability without altering the semiconductor forming process, thus providing a simple and effective method for noise reduction.
Implementation Method 1
a photodiode for obtaining a signal charge by a photoelectric conversion of an incident light
Data Source
AI summary
A solid-state image capturing apparatus includes a pixel array in which a plurality of pixels are arranged in a matrix, where each of the pixels includes: a photodiode for obtaining a signal charge by a photoelectric conversion of an incident light; and an amplifying transistor for the signal charge obtained at the photodiode, and where the amplifying transistor is configured in such a manner that a gate area of the amplifying transistor is defined to be larger than a gate area of other transistors that configure the pixel.