Buried Photodiode Detector Layout for Radiation Dark Current
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Solution Overview
Problem
Detectors with CMOS sensors experience increased dark current noise due to radiation exposure, primarily because defects in the insulating film lead to a larger contact area between the depletion layer and the insulating film, causing noise and reducing image quality.
Innovation Solution
A detector design with a substrate featuring a buried photodiode structure where the charge generation region is surrounded by a P-type semiconductor region and an insulator region, reducing the contact area between the depletion layer and the insulating film, thereby minimizing dark current noise. This design includes a charge collection region with higher impurity concentration and a P-type semiconductor region with a lower concentration, separated by an insulator region to prevent depletion layer spread and defect-induced dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the semiconductor region and electrode region are adjacent on the substrate surface to enable charge collection, then the detection function is achieved, but the depletion layer contacts the insulating film causing dark current increase under radiation exposure
Solution Approach 1:
The patent introduces an insulator region as an intermediary element positioned between the first semiconductor region and the second semiconductor region. This insulator region acts as a mediator that prevents the depletion layer from spreading to the insulating film, thereby blocking the harmful interaction between radiation-induced defects and the depletion layer that causes dark current increase.
Solution Approach 2:
The patent extracts the problematic interface between the depletion layer and insulating film by introducing the insulator region as a separator. This removes the direct contact path that allows radiation-induced defects to generate dark current, effectively taking out the harmful interaction from the system.
2Reliability
If the insulator region is introduced to reduce depletion layer contact with insulating film, then dark current noise is reduced, but the device structure becomes more complex
Solution Approach 1:
The insulator region is merged with the existing semiconductor regions to form an integrated structure. Rather than adding a separate, independent component, the insulator region is combined with the first and second semiconductor regions in a unified substrate design, reducing overall structural complexity while maintaining the noise reduction function.
Solution Approach 2:
The insulator region serves multiple functions: it acts as an electrical isolator to prevent depletion layer spread, provides structural support, and helps define the boundaries of the semiconductor regions. This multi-functionality reduces the need for additional components, thereby simplifying the overall device structure despite the added functional capability.
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 proposed detector effectively reduces dark current noise and maintains image quality by minimizing the contact area between the depletion layer and the insulating film, even under radiation exposure, thereby enhancing the dynamic range and reducing the occurrence of white flaws.
Implementation Method 1
a conversion element portion configured to convert an energy ray into a signal charge
Data Source
AI summary
A detector includes a substrate and an insulating film formed over a main surface of the substrate. The substrate includes a conversion element portion and an insulator region disposed in a recess portion of the main surface. The conversion element portion includes a first semiconductor region that is formed on the main surface and is of a first conductivity type, a second semiconductor region that is formed on the main surface and is of a second conductivity type, and a third semiconductor region that is formed under the first semiconductor region and the second semiconductor region and is of the first conductivity type. In a plan view with respect to the main surface, the insulator region is located between the first semiconductor region and the second semiconductor region in at least one direction.