X-ray Image Sensor Pixel Isolation via Reverse Biased Well
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Solution Overview
Problem
In x-ray imaging, the absorption of x-ray photons by the image sensor generates significant noise, which is difficult to filter without degrading image resolution, and existing solutions like fiberoptic plates are costly and increase system thickness and weight.
Innovation Solution
A pixel structure for the image sensor based on a doped substrate with a lightly doped epitaxial layer, where a photosensitive structure is encapsulated in a reversely biased well to reduce x-ray interaction and isolate noise to a single pixel, maintaining sufficient depth for visible photon absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the image sensor depth is increased to improve visible photon absorption, then the absorption efficiency of visible photons is improved, but the noise from x-ray photon absorption increases
Solution Approach 1:
The image sensor is segmented into multiple pixels, each with its own isolated photosensitive structure. This segmentation prevents noise from spreading between pixels, allowing each pixel to have optimized depth characteristics that reduce x-ray noise while maintaining visible photon absorption efficiency.
Solution Approach 2:
Each pixel is given locally optimized properties through the reversely biased well structure, which creates a localized electric field configuration. This allows the photosensitive structure to have sufficient depth for visible photon absorption while the local electric field configuration reduces x-ray interaction probability, achieving different quality requirements in different spatial regions of the same pixel.
2Object-generated harmful factors
If a fiberoptic plate is added to reduce x-ray noise, then the noise from x-ray photons is reduced, but the system cost and thickness increase
Solution Approach 1:
The noise reduction function is extracted from a separate external component (fiberoptic plate) and integrated directly into the image sensor structure itself. The reversely biased well is formed within the sensor substrate, eliminating the need for additional external noise-reducing components and their associated costs and thickness.
Solution Approach 2:
The noise reduction function is merged with the image sensor structure by forming the reversely biased well directly in the sensor substrate. This combines the image sensing function and the x-ray noise reduction function into a single integrated structure, eliminating the need for separate fiberoptic plates.
3Object-generated harmful factors
If the photosensitive structure depth is reduced to reduce x-ray interaction, then the noise from x-ray photons is reduced, but the absorption of visible photons decreases
Solution Approach 1:
The electric field distribution parameters are changed by applying reverse bias to the well structure. This creates a non-uniform electric field configuration that enhances the collection efficiency of visible photon-generated carriers while reducing the interaction probability with x-ray photons, effectively decoupling the two absorption processes through parameter optimization.
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 reduces x-ray noise while maintaining high resolution and image quality, achieving results similar to fiberoptic plates without increasing system weight or cost, and is applicable in dental, industrial, and scientific x-ray applications.
Implementation Method 1
the probability of x-ray interaction will be reduced, while maintaining enough depth for sufficient absorption of visible photons
Implementation Method 2
a scintillator and a pixelated image sensor are used in combination to capture an x-ray image
Implementation Method 3
Some of these x-ray photons are absorbed in the image sensor
Data Source
Figure 1A~1B
Figure 2A~2D
Figure 3A~3B
AI summary
There is provided a pixel (100) for an image sensor, wherein the pixel (100) is based on a doped substrate (110) on which a lightly doped epitaxial layer (120) is provided. A photosensitive structure (130) and an isolating reversely biased well (140) are defined in the epitaxial layer, and the photosensitive structure (130) is encapsulated in the reversely biased well (140). Alternatively, or as a complement, the pixel (100) comprises isolating wells extending on respective sides of the photosensitive structure (130) throughout the entire or at least a major part of the epitaxial layer to provide isolation from neighboring pixels of the image sensor.