Hybrid X-ray Detector with Graded SiGe Buffer Layer
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Solution Overview
Problem
Radiation detectors using silicon sensors face significant radiation damage from X-rays and electrons, particularly at higher energies, leading to detector failure and limited performance, as existing materials like GaAs, CdZnTe, or CdTe are difficult to manufacture and process.
Innovation Solution
A hybrid radiation detector with an additional active layer of germanium or SiGe on a silicon substrate, where the buffer layer has a graded composition to minimize lattice mismatch, enhances X-ray absorption and reduces radiation damage by using a second sensor material layer with higher atomic number, allowing for better absorption and easier integration with conventional silicon processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a silicon sensor is used for X-ray detection, then the sensor is easy to manufacture and process, but the sensor suffers significant radiation damage at higher X-ray energies leading to detector failure
Solution Approach 1:
The patent employs a composite sensor structure with a silicon substrate and a deposited layer of germanium or silicon-germanium alloy. This composite material approach combines the manufacturing advantages of silicon with the superior X-ray absorption and radiation hardness of germanium, resolving the contradiction between ease of manufacture and radiation damage resistance.
Solution Approach 2:
The patent modifies the compositional parameters of the sensor by incorporating germanium or silicon-germanium alloys with varying germanium concentrations. This parameter change enhances the sensor's atomic number and X-ray absorption capability while maintaining compatibility with silicon processing techniques, thereby improving reliability without sacrificing manufacturability.
2Reliability
If materials like GaAs, CdZnTe, or CdTe are used to reduce radiation damage, then radiation damage is reduced, but the materials are difficult to manufacture and process
Solution Approach 1:
Instead of using purely exotic materials like GaAs or CdTe that are difficult to manufacture, the patent creates a composite structure where a thin layer of germanium or silicon-germanium is deposited on a standard silicon substrate. This allows the bulk of the sensor to remain silicon (easy to manufacture) while the germanium layer provides the radiation damage resistance.
Solution Approach 2:
The patent applies the high radiation-hardness property locally through a deposited germanium or silicon-germanium layer only where needed for X-ray absorption, rather than requiring the entire sensor to be made from difficult-to-process radiation-hard materials. This local application maintains ease of manufacture while achieving improved reliability.
3Device complexity
If a single layer sensor is used, then the sensor structure is simple, but the X-ray absorption is insufficient at higher energies
Solution Approach 1:
The patent uses a composite two-layer structure with silicon substrate and a germanium or silicon-germanium deposited layer. This composite approach increases X-ray absorption at higher energies by utilizing the higher atomic number of germanium, while keeping the overall structure relatively simple and compatible with existing manufacturing processes.
Solution Approach 2:
The patent enhances X-ray absorption by adding a dimensional layer (the germanium or silicon-germanium deposited layer) on top of the silicon substrate. This layered approach increases the effective absorption path length and material density without significantly complicating the device structure, thereby improving absorption capability while maintaining manufacturing simplicity.
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 multi-layer detector design significantly increases X-ray absorption, improves sensing efficiency, and reduces radiation damage, enabling effective operation at higher energies while maintaining ease of manufacturing and processing, thus extending the range of applications in X-ray diffraction and protein crystallography.
Implementation Method 1
When an X-ray is absorbed in a pixel of the sensor it interacts with an atom to produce a photoelectron that in turn excites a number of outer electrons from neighbouring atoms and hence creates a cloud of electrons (and holes)
Implementation Method 2
the buffer layer has a graded composition to minimize lattice mismatch
Data Source
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Figure 3~4
AI summary
A hybrid imaging detector is for detecting ionizing radiation such as X-rays or electron radiation. The detector has a sensor (10) on a read-out chip (20). The sensor (10) includes a plurality of sensor material layers (12,14) of different materials stacked on top of one another, having differing radiation absorbing properties. The materials may be Si and SiGe, Si and Ge, or Si and amorphous Se, for example. The read-out chip is a photon-counting read-out chip that records a single count when it detects a pulse above a threshold.