Triple-Dielectric ARC Structure for Image Sensor Quantum Efficiency
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Solution Overview
Problem
CMOS image sensors face challenges with reflection of incident radiation away from underlying image sensor elements due to insufficient bending of light caused by a small difference in refractive indices between dielectric layers, leading to decreased quantum efficiency and increased cross-talk.
Innovation Solution
An anti-reflective coating (ARC) structure comprising a first dielectric layer with a higher refractive index, a second dielectric layer with an even higher refractive index, and a third dielectric layer with a lower refractive index is applied over the image sensor element, where the second and third indices have a large difference to effectively direct incident light towards the image sensor element, reducing reflection and cross-talk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single dielectric layer is used over the image sensor element, then the device complexity is reduced, but the quantum efficiency decreases due to insufficient light bending and increased reflection
Solution Approach 1:
The anti-reflective coating is divided into three separate dielectric layers (first, second, and third dielectric layers) with different refractive indices. This segmentation allows each layer to contribute differently to light management, with the second layer having the highest refractive index to maximize light bending toward the image sensor element, thereby resolving the contradiction between simplicity and quantum efficiency.
Solution Approach 2:
The patent employs a composite dielectric structure combining three materials with distinct refractive index characteristics. The second dielectric layer is specifically selected to have a refractive index higher than both the first and third layers, creating an optimized optical path that enhances quantum efficiency while maintaining a relatively compact overall structure.
2Manufacturing precision
If dielectric layers with similar refractive indices are used, then the manufacturing precision requirements are reduced, but cross-talk increases due to insufficient light direction
Solution Approach 1:
The second dielectric layer is designed with a locally optimized high refractive index specifically at the interface where light bending is most critical. This localized quality enhancement ensures that light is effectively directed toward the image sensor element without requiring extreme precision across the entire multi-layer structure, thereby reducing manufacturing complexity while minimizing cross-talk.
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 ARC structure enhances quantum efficiency and reduces cross-talk by ensuring incident light is directed towards the image sensor element, thereby improving the overall performance of the pixel sensor.
Implementation Method 1
The second index of refraction is greater than a third index of refraction of the third dielectric layer. Incident light that passes from the third dielectric layer to the second dielectric layer is bent towards a line that is normal to an upper surface of the second dielectric layer
Data Source
AI summary
Various embodiments of the present disclosure are directed towards a pixel sensor. The pixel sensor includes a substrate having a front-side opposite a back-side. An image sensor element comprises an active layer disposed within the substrate, where the active layer comprises germanium. An anti-reflective coating (ARC) structure overlies the back-side of the substrate. The ARC structure includes a first dielectric layer overlying the back-side of the substrate, a second dielectric layer overlying the first dielectric layer, and a third dielectric layer overlying the second dielectric layer. A first index of refraction of the first dielectric layer is less than a second index of refraction of the second dielectric layer, and a third index of refraction of the third dielectric layer is less than the first index of refraction.