Grated Interface Pixel Cell Reducing Light Reflection
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Solution Overview
Problem
Conventional pixel cells suffer from significant light reflection due to the abrupt transition in refractive indices between the oxide layer and the silicon substrate, resulting in approximately 18% of incident light being lost, which is undesirable for efficient light capture.
Innovation Solution
A pixel cell design featuring a grated interface between the oxide layer and the silicon substrate, where the oxide layer is provided within and over trenches in the substrate, creating a hybrid refractive index that reduces light reflection by smoothing the transition, allowing a greater percentage of incident light to be captured.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If an oxide layer is provided over the silicon substrate in a conventional pixel cell, then the structural integrity and electrical isolation are maintained, but approximately 18% of incident light is reflected due to the abrupt transition in refractive indices
Solution Approach 1:
The oxide layer is segmented into a grated structure with multiple trenches, dividing the abrupt interface into multiple smaller interfaces. This segmentation creates a progressive transition in refractive index, reducing light reflection from 18% to significantly lower levels while maintaining the electrical isolation function of the oxide layer.
Solution Approach 2:
The oxide layer is modified locally by creating trenches only in specific regions where light incidence occurs, while maintaining the continuous oxide structure in areas needed for electrical isolation. This local modification reduces reflection at the light-entry points without compromising the overall structural integrity.
2Productivity
If a grated interface with trenches is created in the oxide layer, then light reflection is significantly reduced and light capture efficiency is improved, but the manufacturing process complexity increases
Solution Approach 1:
The trenches are formed in the oxide layer before subsequent processing steps, allowing the grated structure to be established early in the fabrication sequence. This preliminary action enables the use of standard photolithography and etching techniques to create the light-capture-enhancing structure before other pixel cell components are added.
Solution Approach 2:
The grated oxide layer acts as an intermediary structure between the air/silicon interface and the underlying photosensor, providing a progressive refractive index transition. This intermediary structure enables improved light capture while using conventional materials and processes, avoiding the need for exotic fabrication techniques.
3Reliability
If the oxide layer is made continuous over the substrate, then electrical isolation and structural stability are ensured, but light reflection increases and reduces photosensor efficiency
Solution Approach 1:
The oxide layer is segmented into a grated pattern where trenches are distributed across the surface, creating multiple small discontinuities rather than one large gap. This segmentation maintains electrical isolation between adjacent pixel elements while reducing the overall reflective surface area and improving light capture efficiency.
Solution Approach 2:
The grated oxide structure creates a composite interface combining oxide material and substrate material in a controlled pattern. This composite structure provides both the electrical isolation properties of the continuous oxide layer and the light-capture enhancement of a disrupted interface, achieving dual functionality through material arrangement.
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 grated interface significantly reduces light reflection, enabling a higher percentage of incident light to be captured by the photosensor, improving the efficiency of light conversion into electrical signals compared to conventional pixel cells.
Implementation Method 1
the oxide layer has a grated interface with the silicon substrate... creating a hybrid refractive index that reduces light reflection by smoothing the transition
Implementation Method 2
Conventional pixel cells suffer from significant light reflection due to the abrupt transition in refractive indices between the oxide layer and the silicon substrate
Data Source
AI summary
A pixel cell having a photosensor within a silicon substrate; and an oxide layer provided over the photosensor, the oxide layer having a grated interface with said silicon substrate, and a method of fabricating the pixel cell having a grated interface.