Backside Diffuser Layout for Wide-Angle NIR Image Sensing
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Solution Overview
Problem
Image sensor integrated chips (ICs) face challenges in achieving high quantum efficiency for near-infrared (NIR) radiation detection due to the absorption coefficient of silicon decreasing with increasing wavelength, and existing diffuser configurations either limit efficiency at small angles or fail to maintain it at larger angles of incidence.
Innovation Solution
The integration of a central diffuser surrounded by peripheral diffusers on the back-side of the silicon substrate, where the central diffuser is larger than the peripheral ones, allows for improved absorption of NIR radiation across a broad range of angles by altering the path length of incident radiation within the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single uniform diffuser configuration is used, then the structure is simple, but quantum efficiency cannot be maintained across a broad range of angles of incidence
Solution Approach 1:
The diffuser structure is segmented into multiple regions with different characteristics: a first diffuser region with a first angle and a second diffuser region with a second angle. This segmentation allows each region to handle different angles of incidence optimally, resolving the contradiction between maintaining quantum efficiency across angles and keeping the structure simple.
Solution Approach 2:
Different regions of the diffuser are assigned different local properties (different angles) to optimize performance for specific angular ranges. The first diffuser region is optimized for certain angles while the second diffuser region is optimized for other angles, allowing the overall structure to maintain high quantum efficiency across a broad angular range without excessive complexity.
2Reliability
If the silicon substrate thickness is increased to improve NIR absorption, then quantum efficiency improves, but the device size and manufacturing complexity increase
Solution Approach 1:
The diffuser regions are configured with angled surfaces that create curved/reflected paths for incident radiation. This curvature allows radiation to traverse a longer effective path length through the silicon substrate without increasing the physical thickness, thereby improving NIR absorption and quantum efficiency while maintaining a compact device form factor.
Solution Approach 2:
The angled diffuser surfaces continuously reflect and redirect radiation through the substrate multiple times, extending the interaction path length. This continuous useful action of radiation-substrate interaction enhances absorption efficiency without requiring increased substrate thickness, resolving the contradiction between detection efficiency and device dimensions.
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 to greater than 50% for angles between -10° and 10° and maintains efficiency above 45% for angles between -20° and 20°, effectively addressing the limitations of previous diffuser designs.
Implementation Method 1
the absorption coefficient of silicon decreasing with increasing wavelength
Implementation Method 2
altering the path length of incident radiation within the substrate
Data Source
AI summary
The present disclosure relates to an integrated chip. The integrated chip includes an image sensing element disposed within a substrate. A gate structure is disposed along a front-side of the substrate. A back-side of the substrate includes one or more first angled surfaces defining a central diffuser disposed over the image sensing element. The back-side of the substrate further includes second angled surfaces defining a plurality of peripheral diffusers laterally surrounding the central diffuser. The plurality of peripheral diffusers are a smaller size than the central diffuser.