Solid-State Image Sensor Light-Shielding Sections for Global Shutter Noise
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Solution Overview
Problem
Global shutter type image sensors face challenges in maintaining sensitivity and preventing optical noise due to the need for charge retention regions within pixels, which can lead to reduced aperture ratios and increased risk of light leakage, causing image distortion.
Innovation Solution
A solid-state image sensor design incorporating light-shielding sections on either side of the memory unit to prevent light from entering the charge retention region, formed by trenching the substrate and embedding light-shielding material, ensuring effective light shielding and maintaining sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a charge retention region is formed inside a pixel to enable global shutter operation, then image distortion is prevented, but the aperture ratio decreases and sensitivity deteriorates
Solution Approach 1:
The patent moves the charge retention region from the front surface (2D plane) to the deep interior of the substrate (3D space), utilizing the depth dimension to resolve the conflict between needing charge retention space and maintaining front surface aperture ratio. This allows the photodiode to occupy the entire front surface while charge retention occurs in the substrate depth.
Solution Approach 2:
Instead of placing the charge retention region adjacent to or overlapping with the photodiode on the front surface, the patent inverts the spatial relationship by positioning the charge retention region deep inside the substrate beneath the photodiode, effectively reversing the conventional layout approach.
2Object-affected harmful factors
If the charge retention region is made smaller to reduce optical noise, then light leakage is suppressed, but the saturation capacity of the charge retention region deteriorates
Solution Approach 1:
The patent utilizes the depth dimension of the substrate to create a vertically extended charge retention region. By forming the charge retention region deep inside the substrate rather than laterally expanding it on the surface, the design achieves both reduced optical noise (by isolating from surface light paths) and maintained saturation capacity (by extending in the depth direction).
3Manufacturing precision
If the charge retention region is formed deep inside the substrate to maintain aperture ratio, then sensitivity is improved, but light leakage into the charge retention region increases
Solution Approach 1:
The patent introduces light-shielding sections as intermediary structures between the photodiode and the deep charge retention region. These light-shielding sections act as mediators that block stray light paths while allowing the charge retention region to remain deep inside the substrate for maintaining aperture ratio and sensitivity.
Solution Approach 2:
The patent extracts the light-shielding function from the charge retention region itself and implements it through separate dedicated light-shielding sections. This allows the charge retention region to be optimized for capacity (deep in substrate) while the light-shielding sections handle the optical isolation function.
4Object-affected harmful factors
If light-shielding sections are added to prevent light leakage, then optical noise is suppressed, but device complexity increases
Solution Approach 1:
The patent merges the light-shielding sections with the existing pixel structure by forming them within the same substrate using similar fabrication processes. The light-shielding sections are integrated into the pixel layout and share processing steps with other pixel components, reducing the overall complexity increase.
Solution Approach 2:
The light-shielding sections serve multiple functions: they block stray light from reaching the charge retention region, define pixel boundaries, and can be integrated with color filter structures. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in 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 effectively suppresses optical noise and maintains high sensitivity by preventing light leakage into the charge retention region, thereby reducing image distortion and enhancing the saturation capacity of the charge retention region.
Implementation Method 1
a photoelectric conversion element disposed therein, the photoelectric conversion element converting an amount of incident light into a charge amount
Data Source
AI summary
A solid-state image sensor including a substrate having a photoelectric conversion element disposed therein, the photoelectric conversion element converting an amount of incident light into a charge amount, a memory unit disposed at a side of the photoelectric conversion element, the memory unit receiving the charge amount from the photoelectric conversion element, a first light-shielding section formed at a first side of the memory unit and disposed between the charge accumulation region and the photoelectric conversion element, and a second light-shielding section formed at a second side of the memory unit such that the second side is opposite the first side.