Silicon Pixel Interface Geometry for Near-Infrared Light Trapping
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Solution Overview
Problem
Conventional image sensors using silicon pixels absorb limited near-infrared light, leading to defects and artifacts in captured images due to low absorption and subsequent light transmission to neighboring pixels.
Innovation Solution
The image sensor design incorporates silicon photoconversion regions surrounded by materials with a lower refractive index, featuring oblique surfaces that facilitate total reflections, increasing the optical path and absorption of near-infrared light within each pixel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional silicon photoconversion regions are used without special interface configuration, then the device structure is simple, but the absorption of near-infrared light is insufficient leading to image defects and artifacts
Solution Approach 1:
The patent applies curvature by configuring oblique surfaces at the interfaces of the silicon photoconversion region. These oblique surfaces create angled reflections that trap near-infrared light within the photoconversion region, increasing the optical path length and absorption efficiency. The curved/angled interface geometry transforms the flat interface into a light-trapping structure, resolving the contradiction between simple structure and high absorption efficiency.
Solution Approach 2:
The patent introduces dimensional complexity by adding oblique surfaces that extend the light path in multiple directions within the photoconversion region. Instead of a simple planar interface, the light undergoes successive reflections at angled surfaces, effectively increasing the interaction path length between light and silicon material without increasing the physical thickness of the photoconversion region.
2Reliability
If the photoconversion region thickness is increased to improve near-infrared absorption, then absorption efficiency improves, but the device dimensions increase and manufacturing complexity increases
Solution Approach 1:
The oblique surfaces create a light-trapping effect that extends the optical path length within the existing photoconversion region thickness. By configuring interfaces at angles greater than the critical angle for total internal reflection, the light undergoes multiple reflections, effectively increasing the absorption path length without increasing the physical thickness of the silicon layer, thus maintaining thin-device advantages while achieving high quantum efficiency.
Solution Approach 2:
The patent ensures continuous interaction between light and the photoconversion region by configuring oblique surfaces that guide light through multiple successive reflections. This continuous trapping and reflection of light within the photoconversion region maximizes the utilization of the existing silicon thickness, maintaining high absorption efficiency without requiring increased device dimensions.
3Reliability
If no light confinement structure is used, then the device structure is simple, but light transmits to neighboring pixels causing image artifacts
Solution Approach 1:
The oblique surfaces at the interfaces of the silicon photoconversion region act as built-in light confinement structures. By configuring these interfaces at angles greater than the critical angle, the patent achieves total internal reflection that directs light back into the photoconversion region, preventing light leakage to neighboring pixels. This geometric configuration provides effective light confinement without requiring additional external confinement structures.
4Reliability
If oblique surfaces with angles greater than the limiting angle are configured, then total reflection increases light absorption, but manufacturing precision requirements increase
Solution Approach 1:
The patent specifies that the oblique surfaces should have angles greater than the limiting angle for total internal reflection. By defining this angular parameter threshold rather than requiring precise control at a specific angle, the invention provides a parameter range that ensures light trapping effectiveness while relaxing manufacturing precision requirements. This parameter-based approach allows for manufacturing tolerance while maintaining the light confinement effect.
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 configuration enhances quantum efficiency and reduces image artifacts by confining light within the photoconversion region, improving image quality by increasing the absorption of near-infrared rays.
Implementation Method 1
The interface between the photoconversion region of the pixel and said material being configured so that at least one ray reaching the photoconversion region of the pixel undergoes a total reflection on this interface or a plurality of successive total reflections on this interface
Implementation Method 2
Sensors comprising pixels formed from a silicon wafer or substrate are known. In such sensors, each pixel comprises a silicon photoconversion region corresponding to a portion of the substrate
Data Source
AI summary
An image sensor is includes a plurality of pixels. Each of the pixels includes a silicon photoconversion region and a material that at least partially surrounds the photoconversion region. The material has a refraction index smaller than the refraction index of silicon, and the interface between the photoconversion region of the pixel and the material is configured so that at least one ray reaching the photoconversion region of the pixel undergoes a total reflection or a plurality of successive total reflections at the interface.