Large-Area Drift Detector Layout for Low-Noise Charge Collection
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Solution Overview
Problem
Current semiconductor drift detectors face challenges with low detection efficiency for energies above 20 keV and low electron mobility, leading to degraded charge collection efficiency, energy resolution, and count rate capacity, particularly due to the direct conversion nature of high-Z materials.
Innovation Solution
A large-area semiconductor drift detector using an amorphous selenium (a-Se) structure with a resistive charge division readout methodology, where drift microstrips and collecting electrodes are in separate planes to enhance charge collection and reduce electronic noise, enabling three-dimensional position sensing and simultaneous measurement of radiation energy, position, and timing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-Z materials are used for direct conversion of X-ray into electronic charge, then detection efficiency for high energy radiation is improved, but electron mobility is reduced leading to degraded charge collection efficiency
Solution Approach 1:
The detector is segmented into two distinct functional layers: a semiconductor layer for charge generation and a drift layer for charge transport. This segmentation allows each layer to be optimized independently - the semiconductor layer for high detection efficiency and the drift layer for high electron mobility, thereby resolving the contradiction between detection efficiency and charge collection efficiency.
Solution Approach 2:
The detector uses a composite structure combining semiconductor material (for X-ray absorption and charge generation) with drift layer material (for efficient charge transport). This composite approach allows the system to simultaneously achieve high detection efficiency from the semiconductor and high charge collection efficiency from the drift layer, overcoming the limitation of using单一 high-Z material.
2Area of stationary object
If the detection area is increased for large-area applications, then detection coverage is improved, but electronic noise increases due to larger collecting electrode area
Solution Approach 1:
The collecting electrode is segmented into two independent parts: a drift electrode and a collecting electrode. This segmentation allows the drift electrode to be optimized for charge collection from the large detection area while the collecting electrode can be optimized for low noise readout, thereby maintaining large detection area without proportionally increasing electronic noise.
Solution Approach 2:
The drift layer acts as an intermediary between the large-area semiconductor layer and the collecting electrode. It transports charges from the large detection area to the collecting electrode, allowing the collecting electrode area to be smaller than the detection area, thus reducing electronic noise while maintaining large detection coverage.
3Measurement precision
If segmented readout electrodes are used to achieve two-dimensional position sensitivity, then position resolution is improved, but device complexity increases
Solution Approach 1:
The patent achieves two-dimensional position sensitivity by utilizing the drift time dimension in addition to the spatial dimension. Charges drift through the drift layer and their arrival time at the collecting electrode provides the second position coordinate, eliminating the need for complex segmented readout electrodes while maintaining position sensitivity.
Solution Approach 2:
The drift layer structure itself provides the position encoding function through the drift time of charges. Instead of requiring external segmented readout electrodes to determine position, the system uses the inherent drift characteristics of the drift layer to encode position information in the charge arrival time, simplifying the overall device structure.
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 solution improves spatial resolution, energy resolution, and count rate capacity by minimizing the impact of slow charge carriers and reducing electronic noise, while allowing for cost-effective detection of higher energy radiation with reduced complexity in readout electronics.
Implementation Method 1
the set of drift microstrips shape an electric field and direct charges within the drift detector towards the set of collecting electrodes
Implementation Method 2
These materials are direct converters of X-ray into electronic charge
Implementation Method 3
the charge induced by an absorbed photon is divided along with the resistive layer or strip depending on the photon absorption location
Data Source
AI summary
The disclosure is directed at a large-area semiconductor drift detector that includes a set a substrate layer; a semiconductor layer; a set of drift microstrips positioned between the substrate layer and the semiconductor layer; and a set of collecting electrodes positioned between the substrate layer and the semiconductor layer and in a different plane than the set of drift microstrips; wherein the set of drift microstrips shape an electric field and direct charges within the drift detector towards the set of collecting electrodes.