Multi-Layer Amorphous Selenium Sensor Fusion for Avalanche Gain
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Solution Overview
Problem
Conventional x-ray detectors suffer from image degradation due to electronic noise, and existing methods to reduce noise increase costs, while amorphous selenium (a-Se) detectors face challenges in achieving avalanche gain without introducing electronic noise, especially in low photon flux applications.
Innovation Solution
The method involves forming a-Se-containing structures by delaying the formation of temperature-sensitive amorphous selenium layers until after the elevated temperature processing of charge blocking layers, allowing for the fusion of a-Se layers above the glass transition temperature but below the crystallization temperature, creating a multi-layer structure that can withstand high electric fields and reduce dark current injection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If amorphous selenium layers are formed before charge blocking layers, then the a-Se layers can be deposited at low temperature, but the subsequent elevated temperature processing of charge blocking layers causes degradation of the a-Se layers
Solution Approach 1:
The charge blocking layers are formed first on the substrates, and then the temperature-sensitive amorphous selenium layers are deposited afterward. This preliminary action of forming the charge blocking layers before the a-Se layers allows the a-Se layers to be protected from elevated temperature processing that would otherwise degrade them.
Solution Approach 2:
The conventional sequence of forming a-Se layers first and then charge blocking layers is inverted. Instead, the charge blocking layers are formed first, followed by the a-Se layers. This inversion resolves the contradiction by ensuring that the temperature-sensitive a-Se layers are not exposed to elevated temperatures during charge blocking layer processing.
2Manufacturing precision
If multiple a-Se layers are formed separately and then fused, then each layer can be optimized independently, but the fusion process requires precise temperature control between Tg and Tc
Solution Approach 1:
The fusion process utilizes the specific temperature parameters of amorphous selenium, heating the stacked a-Se layers to a temperature between the glass transition temperature (Tg) and crystallization temperature (Tc). This parameter change allows the layers to fuse together while maintaining their amorphous structure and optimized properties.
Solution Approach 2:
Multiple separately optimized amorphous selenium layers are combined into a composite multi-layer structure through thermal fusion. Each layer can have different compositions or properties optimized for specific functions, and the fusion process creates a unified structure that maintains the advantages of individual layer optimization.
3Device complexity
If conventional x-ray detectors are used, then the device structure is simple, but image degradation occurs due to electronic noise
Solution Approach 1:
The detector is segmented into multiple functional layers including charge blocking layers and multiple amorphous selenium layers. This segmentation allows for specialized functions in each layer, such as noise reduction in the charge blocking layers and signal generation in the a-Se layers, improving overall image quality.
Solution Approach 2:
The detector uses a composite structure combining charge blocking layers with multiple amorphous selenium layers. This composite material approach enables the integration of different material properties to reduce electronic noise while maintaining x-ray detection capability, thereby improving image quality.
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 enables improved signal amplification prior to electronic noise introduction, enhancing the performance of optical and x-ray sensors by forming efficient charge blocking layers and reducing image degradation, leading to more reliable and cost-effective detectors.
Implementation Method 1
a-Se with avalanche gain has also been proposed for use in an indirect x-ray detector. Advantages of a-Se over other photoconductors such as silicon, which may be used in both optical and x-ray sensing applications, and CdTe, which may be used to detect x-rays, include the capability for large area deposition, avalanche multiplication of holes at electric fields (ESe) greater than 70 V/um
Implementation Method 2
Fusion may be accomplished by heating to above the glass transition temperature (Tg) of amorphous selenium, but below its crystallization temperature (Tc)
Data Source
AI summary
A sensor including a layer of amorphous selenium (a-Se) and at least one charge blocking layer is formed by depositing the charge blocking layer over a substrate prior to depositing the amorphous selenium, enabling the charge blocking layer to be formed at elevated temperatures. Such a process is not limited by the crystallization temperature of a-Se, resulting in the formation of an efficient charge blocking layer, which enables improved signal amplification of the resulting device. The sensor can be fabricated by forming first and second amorphous selenium layers over separate substrates, and then fusing the a-Se layers at a relatively low temperature.