Back-Illuminated Image Sensor With Magnetic Layer for Dark Current Control
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Solution Overview
Problem
Image sensors face deterioration due to dark current, which acts as noise and degrades their characteristics, particularly caused by charges generated on the back side of the substrate.
Innovation Solution
Incorporating a magnetic layer on the back side of the substrate with a ferromagnetic substance like titanium dioxide (TiO2) or indium-tin oxide (ITO) to generate a horizontal magnetic field, which applies an electric force perpendicular to the substrate, controlling charges and preventing dark current and noise generation, along with an impurity barrier region and color filters/microlenses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If photoelectric conversion regions are formed on the back side of the substrate, then light sensitivity is improved, but dark current increases causing noise
Solution Approach 1:
A magnetic layer is introduced as an intermediary component between the photoelectric conversion regions and the external environment. This magnetic layer generates a magnetic field that acts as a mediator to control charge carrier behavior, specifically preventing minority carrier generation that causes dark current, while allowing the photoelectric conversion regions to maintain high light sensitivity.
Solution Approach 2:
The invention changes the physical parameter of the operating environment by introducing a magnetic field. By applying a magnetic field through the magnetic layer, the behavior of charge carriers is modified - specifically, the magnetic field suppresses the generation of minority carriers that would otherwise create dark current noise, thereby improving the signal-to-noise ratio while maintaining photoelectric conversion efficiency.
2Productivity
If the substrate structure is simplified for manufacturing, then manufacturing precision may be compromised, but production efficiency is improved
Solution Approach 1:
The invention segments the functional layers into distinct components: photoelectric conversion regions, a separate magnetic layer, color filters, and microlenses. This segmentation allows each layer to be optimized and manufactured independently, then assembled together. The magnetic layer can be formed as a separate entity with standardized processes, reducing overall manufacturing complexity while maintaining precise control over sensor characteristics.
3Device complexity
If color filters and microlenses are disposed directly on the substrate, then device complexity is reduced, but dark current control is insufficient
Solution Approach 1:
The magnetic layer serves as an intermediary layer between the substrate and the color filters/microlenses assembly. This intermediate magnetic layer provides a functional buffer that generates magnetic field effects to control dark current, while still allowing the color filters and microlenses to be positioned for optimal optical performance. The magnetic layer's presence does not significantly increase device complexity as it can be integrated into existing manufacturing processes.
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
The magnetic field effectively reduces dark current and noise, enhancing image sensor performance by controlling charge transfer and improving lag effects, thus maintaining sensor characteristics.
Implementation Method 1
The magnetic layer may generate the magnetic field in a direction horizontal to the back side of the substrate by applying an electric field in a direction perpendicular to the substrate
Implementation Method 2
The magnetic layer may generate the magnetic field in a direction horizontal to the back side of the substrate by applying an electric field in a direction perpendicular to the substrate, which controls charges and prevents dark current and noise generation
Data Source
AI summary
An image sensor includes a substrate including photoelectric conversion regions, a magnetic layer disposed on a back side of the substrate and suitable for generating a magnetic field, and color filters and microlenses disposed on the magnetic layer.