Backside Diffuser Layout for Wide-Angle CMOS Image Sensing
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Solution Overview
Problem
CMOS image sensors face challenges in achieving high quantum efficiency across a broad range of angles of incidence due to the limitations of large diffusers in small pixel regions and the decreased absorption of near-infrared radiation as the angle of incidence increases.
Innovation Solution
The integration of a central diffuser with larger dimensions surrounded by peripheral diffusers of smaller size on the back-side of the silicon substrate, which are angled to redirect incident radiation and increase its path length within the substrate, enhancing absorption and quantum efficiency across various angles of incidence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large diffuser is used in a small pixel region, then quantum efficiency at small angles of incidence is improved, but the pixel region area is insufficient to accommodate the large diffuser
Solution Approach 1:
The diffuser structure is segmented into a central diffuser and multiple peripheral diffusers. The central diffuser has a larger size optimized for small angles of incidence, while the peripheral diffusers have smaller sizes and are positioned around the central diffuser to capture radiation at larger angles of incidence. This segmentation allows the pixel region to accommodate a comprehensive diffuser structure that addresses multiple angle ranges without requiring a single oversized diffuser.
Solution Approach 2:
Different regions of the pixel are assigned different diffuser sizes based on their functional requirements. The central region contains a larger diffuser for optimal small-angle performance, while the peripheral regions contain smaller diffusers for large-angle performance. This local differentiation of quality allows each region to be optimized for its specific angular range while collectively covering the full operational range within the constrained pixel area.
2Loss of energy
If the angle of incidence increases, then the absorption of near-infrared radiation decreases, but using larger diffusers to redirect radiation is limited by small pixel region size
Solution Approach 1:
The diffuser system is divided into central and peripheral components that work together to address the angle-dependent absorption problem. The central diffuser handles small-angle incident radiation effectively, while the peripheral diffusers are strategically positioned to intercept and redirect large-angle incident radiation toward the photodetector, compensating for the decreased absorption at larger angles without requiring excessive pixel area.
Solution Approach 2:
The solution extends the diffuser structure from a single-plane concept to a multi-dimensional arrangement with central and peripheral diffusers at different radial positions. This spatial distribution across multiple dimensions allows the system to capture radiation from a broader angular range by utilizing the vertical and radial dimensions of the pixel structure, effectively increasing the capture volume without proportionally increasing the pixel footprint.
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 significantly improves quantum efficiency, maintaining high performance between -10° and 10° angles and extending it to -20° to 20°, thereby optimizing image capture in both small and large angle conditions.
Implementation Method 1
enhancing absorption and quantum efficiency across various angles of incidence
Implementation Method 2
angled to redirect incident radiation and increase its path length 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.