Radiation Detector Charge Trapping via Remote Guiding Electrodes
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Solution Overview
Problem
In radiation-sensitive detectors, electric field lines often leave the detector crystal at gaps between electrode segments, causing charge trapping and reducing signal contribution, especially in direct conversion detectors like CZT or CdTe, where miniaturization or additional structuring may not be feasible, and steering electrodes can induce bias currents affecting noise properties.
Innovation Solution
The implementation of remote guiding electrodes, placed on a connecting layer or elsewhere, which are charged to push electric field lines back into the detector crystal, ensuring they end on collecting electrodes, thereby preventing charge trapping and enhancing signal contribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If electrode segments are placed close together to improve spatial resolution, then measurement precision is improved, but electric field lines leave the detector crystal at gaps between segments causing charge trapping and signal loss
Solution Approach 1:
A third electrode is introduced as an intermediary element positioned between the first and second electrodes. This third electrode modifies the electric field distribution in the gap region, preventing field lines from leaving the detector crystal and thereby preventing charge trapping while maintaining the segmented electrode configuration for spatial resolution
Solution Approach 2:
The third electrode is configured to preemptively counteract the harmful effect of electric field lines escaping at gap regions. By establishing a controlled electric field through the third electrode before charges can drift into gap regions, the design prevents charge trapping and signal loss that would otherwise occur at electrode segment boundaries
2Reliability
If steering electrodes are implemented to guide electric field lines, then charge trapping is reduced, but additional miniaturization or structuring is required which increases device complexity
Solution Approach 1:
The third electrode serves multiple functions: it acts as a charge collecting electrode like the first and second electrodes, while simultaneously functioning as a field-shaping element that prevents electric field lines from escaping at gap regions. This multi-functionality reduces the need for additional specialized steering electrodes, thereby limiting the increase in device complexity
3Reliability
If steering electrodes are used to guide electric field lines, then charge trapping is prevented, but the voltage required to drive the steering electrode induces bias currents which negatively affects noise properties
Solution Approach 1:
The electrical parameters (voltage, polarity) of the third electrode are optimized to achieve field line guidance with minimal bias current induction. By carefully selecting the voltage magnitude and polarity of the third electrode, the design prevents charge trapping while minimizing the induction of harmful bias currents that would increase noise, thereby improving the signal-to-noise ratio
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 solution improves imaging performance by ensuring more charges contribute to the output signal, maintaining mechanical stability and optimizing voltage application based on detector geometry, while minimizing bias currents and noise.
Implementation Method 1
remote guiding electrodes are provided and charged such that electric field lines which would commonly leave the detector crystal at the gap portions are pushed back to the detector crystal
Implementation Method 2
An incident photon creates a number of electron/hole pairs
Implementation Method 3
During the drift process, a current is capacitively induced on each electrode attached to the detector system according to the Shockley-Ramo theorem
Data Source
AI summary
In radiation-sensitive detector devices, such as direct conversion detectors, charges are drifting within an externally applied electric field towards collecting electrodes (4), which are segmented (e.g. representing a pixel array). At the gaps between segments, electrical field lines can leave the detector, and charges drifting along those field lines can be trapped within the gap. This can be avoided by external electrodes (8) which push electric field lines back into the direct conversion material.