Backside-Illuminated Pixel Light Guide Reduces Ghosting
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Solution Overview
Problem
Backside-illuminated image sensors experience light reflection at interfaces between substrate and dielectric layers and conductive lines, leading to reduced light collection efficiency, particularly at longer wavelengths like red, causing unwanted 'ghosting' in captured images.
Innovation Solution
Incorporating a front-side light guide with a refractive index equal to or greater than the substrate, made of materials like optical grade acrylics or glass, to reduce reflections at these interfaces, ensuring light passes through without being reflected back.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a BSI pixel structure is used to allow light to reach photosensitive area without traversing front-side conductive lines, then light collection efficiency is improved, but light reflection at substrate-dielectric interfaces and conductive lines causes ghosting in captured images
Solution Approach 1:
The patent introduces a light guide as an intermediary component between the incident light and the photosensitive area. This light guide modifies the light path and reduces direct reflection at problematic interfaces, thereby maintaining high light collection efficiency while minimizing ghosting effects. The light guide acts as a mediator that controls light propagation without requiring the light to directly traverse through reflective interfaces.
Solution Approach 2:
The patent modifies optical parameters by introducing a light guide with specific refractive index properties. By changing the optical path and refractive index distribution within the pixel structure, the light guide reduces reflection losses and ghosting while maintaining efficient light collection. This parameter change approach allows optimization of both light collection efficiency and reduction of harmful reflections.
2Illumination intensity
If light travels through substrate and dielectric layers in BSI pixels, then photosensitive area can be accessed, but reflections at these interfaces reduce light collection efficiency particularly at longer wavelengths
Solution Approach 1:
The light guide serves as an intermediary that optimizes light transmission through the substrate and dielectric layers. It reduces interface reflections by controlling the light path and refractive index distribution, ensuring maximum light intensity reaches the photosensitive area while minimizing energy loss through reflections, particularly at longer wavelengths.
Solution Approach 2:
The patent changes optical parameters by introducing a light guide with specific refractive index characteristics. This modification optimizes light transmission through multiple interfaces, reducing reflection losses and maintaining high illumination intensity at the photosensitive area across different wavelengths, especially improving performance at longer wavelengths where reflection is more pronounced.
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 light guide significantly enhances light collection efficiency by minimizing reflections, particularly at longer wavelengths, resulting in improved image quality by reducing unwanted 'ghosting' and increasing signal generation in backside-illuminated pixels.
Implementation Method 1
Incorporating a front-side light guide with a refractive index equal to or greater than the substrate, made of materials like optical grade acrylics or glass, to reduce reflections at these interfaces
Data Source
AI summary
Implementations of a pixel including a substrate having a front side, a back side, and a photosensitive region formed on or near the front side, a dielectric layer formed on the front side, and a metal stack having a bottom side and a top side, the bottom side being on the dielectric layer. A light guide is formed in the dielectric layer and the metal stack and extending from the front side of the substrate to the top side of the metal stack, the light guide having a refractive index equal to or greater than the refractive index of the substrate. Other implementations are disclosed and claimed.