Image Sensor Pixel Structure With Dual Dielectric Walls for Low-Light QE
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Solution Overview
Problem
Existing image sensor designs face limitations in achieving high quantum efficiency due to practical constraints on substrate thickness, which affects the ability to collect and amplify low light levels, particularly in applications like night vision.
Innovation Solution
The design incorporates dielectric walls extending from both the top and bottom surfaces of the substrate to form a thicker pixel structure, combined with a doping profile that includes regions with varying dopant concentrations, enhancing light confinement and pathlength within the pixel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If substrate thickness is increased to improve quantum efficiency, then light collection capability is improved, but manufacturing complexity and structural stability deteriorate
Solution Approach 1:
The pixel structure is segmented into multiple functional layers including photodetector layer, charge collection layer, and readout circuit layer stacked vertically. This segmentation allows each layer to be optimized independently while maintaining overall structural integrity, enabling thicker substrates without proportionally increasing complexity
Solution Approach 2:
The patent transitions from planar pixel arrangements to three-dimensional stacked architectures, utilizing the vertical dimension to increase substrate thickness and light interaction pathlength. This dimensional change improves quantum efficiency without requiring proportional increases in lateral footprint or manufacturing complexity
2Reliability
If substrate thickness is increased to improve light collection, then quantum efficiency is improved, but structural stability and fabrication difficulty worsen
Solution Approach 1:
Dielectric walls are formed extending from both top and bottom surfaces of the substrate before photodetector fabrication. This preliminary structuring creates predefined light confinement regions that guide subsequent fabrication steps, simplifying the overall manufacturing process despite increased substrate thickness
Solution Approach 2:
Dielectric materials are introduced as intermediary structures between the substrate and photodetector layers. These dielectric walls serve as mediators that confine light paths and define pixel boundaries, enabling thicker substrates to be fabricated with standard processes by providing intermediate structural references
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 approach increases the quantum efficiency of the pixel by allowing for thicker substrates, improving light collection and amplification, particularly in low-light conditions.
Implementation Method 1
Light impinging upon a receiving end of the pixel reflects off of the inner walls of the dielectric barrier to remain within the pixel as it traverses through a thickness of the semiconductor substrate
Implementation Method 2
Each pixel includes a photodetector as well as a circuit to collect the charge from the photodetector in response to a light impinging on the photodetector
Data Source
AI summary
An image sensor includes a pixel array across a substrate, with at least one pixel of the array being defined by dielectric walls extending from both the top and bottom surfaces of the substrate. The dielectric walls contact each other within the substrate. The dielectric walls encircle around, or form a perimeter around, a volume of semiconductor material that defines the pixel. In this way, light entering through one end of the pixel is generally confined between the dielectric walls as it traverses through the height of the pixel. By using two different dielectric walls formed from the frontside and backside of the substrate, thicker substrates can be used which increases the quantum efficiency of the pixel.