Silicon Pixel Structure for Near-Infrared Light Confinement
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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 efficiency 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 configured for total reflections, increasing the optical path and absorption of near-infrared light within each pixel to enhance quantum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional silicon photoconversion regions are used, then the sensor structure is simple, but the absorption of near-infrared light is insufficient leading to image defects
Solution Approach 1:
The patent applies curvature by replacing flat photoconversion region surfaces with oblique (slanted) surfaces. These oblique surfaces cause incident near-infrared light rays to reflect at angles that increase the optical path length within the silicon, thereby improving absorption efficiency without requiring additional materials or complex structures
Solution Approach 2:
The patent changes the geometric parameters of the photoconversion regions by introducing oblique surfaces with specific angles. This parameter modification increases the interaction between near-infrared light and the silicon material, enhancing absorption while maintaining structural simplicity
2Reliability
If the photoconversion region thickness is increased to improve absorption, then light absorption improves, but the optical path for total reflection decreases
Solution Approach 1:
By introducing oblique surfaces, the patent creates a longer optical path for light rays within the same physical thickness. The slanted geometry causes multiple internal reflections, effectively increasing the distance light travels through the silicon photoconversion region without increasing the vertical thickness
3Reliability
If conventional flat photoconversion regions are used, then manufacturing is simple, but light rays transmit to neighboring pixels causing artifacts
Solution Approach 1:
The oblique surfaces are integrated into the standard CMOS fabrication process using conventional photolithography and etching techniques. The slanted geometry is achieved through controlled etching steps that create the desired angles, maintaining compatibility with existing manufacturing processes while improving light confinement
Solution Approach 2:
The patent applies the oblique surface modification locally to the photoconversion regions where light confinement is needed, while leaving other parts of the sensor structure unchanged. This localized approach maintains manufacturing simplicity while achieving the desired optical performance
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 significantly increases the absorption of near-infrared light, reducing artifacts and improving image quality by confining light rays within the photoconversion region, thereby enhancing the quantum efficiency of the sensor.
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.