X-ray Detector Auxiliary Electrode Reverse Bias Lag Reduction
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Solution Overview
Problem
The image lag phenomenon in direct conversion type X-ray detectors, caused by trapped charges in the photoconductive layer, is not effectively reduced due to the nature of polycrystalline semiconductor materials and requires high voltage application which can damage the Schottky diode.
Innovation Solution
An X-ray detector with a lower electrode, an auxiliary electrode in the periphery, and a photoconductive layer, where the auxiliary electrode is applied with a reverse bias voltage after X-ray radiation to improve charge collection efficiency and reduce image lag, using specific voltage relationships and pulse forms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a reverse bias voltage is applied to the upper electrode after X-ray radiation to reduce lag signals, then the image lag phenomenon is improved, but the Schottky diode between the lower electrode and the CMOS substrate is damaged
Solution Approach 1:
The patent divides the electrode structure into three parts: lower electrode, auxiliary electrode, and upper electrode. The auxiliary electrode is positioned between the lower electrode and upper electrode, allowing the reverse bias voltage to be applied locally at the auxiliary electrode rather than globally across the entire detector structure. This segmentation enables lag signal reduction while protecting the Schottky diode at the lower electrode interface.
Solution Approach 2:
The auxiliary electrode acts as an intermediary element that mediates between the lower electrode (with Schottky diode) and the upper electrode. By applying the reverse bias voltage to the auxiliary electrode, trapped charges are cleared without directly subjecting the Schottky diode to high reverse bias stress, thus protecting the diode while achieving image lag reduction.
2Reliability
If a high voltage is applied in fast frequency to reduce lag signals, then the image lag phenomenon is improved, but the device reaches technical limits and causes Schottky diode damage
Solution Approach 1:
The patent segments the voltage application function by applying reverse bias voltage specifically to the auxiliary electrode rather than the entire detector. This localized approach reduces the overall power stress on the system while achieving the same lag signal reduction effect, avoiding the technical limits associated with global high voltage application.
3Ease of manufacture
If polycrystalline semiconductor material is used in the photoconductive layer, then the detector can be manufactured using vacuum thermal deposition, but trapped charges are generated during X-ray radiation causing image lag
Solution Approach 1:
The auxiliary electrode provides a self-service function by automatically clearing trapped charges from the photoconductive layer after X-ray radiation. This passive mechanism works continuously to reduce image lag without requiring complex material substitutions or manufacturing process changes, maintaining ease of manufacture while improving reliability.
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
Significantly increases charge collection efficiency and reduces the image lag phenomenon by applying a reverse bias voltage to the auxiliary electrode after X-ray radiation, enhancing the performance of the X-ray detector.
Implementation Method 1
in the direct conversion method, X-rays are directly converted into an electrical signal using a photoconductive layer
Implementation Method 2
a method that detrapped charges can be under recombination process by applying a reverse bias voltage to the upper electrode after the radiation of the X-rays
Data Source
AI summary
The objective of the present invention is to effectively improve an image lag phenomenon of a direct conversion detector. The present invention provides an X-ray detector comprising: a lower electrode, formed on a substrate, to which a first driving voltage V1 is applied; an auxiliary electrode, around the lower electrode, to which a third driving voltage V3 is applied; a photoconductive layer formed on the lower electrode and the auxiliary electrode; and an upper electrode, formed on the photoconductive layer, to which a second driving voltage V2 is applied, wherein the third driving voltage V3, right after the radiation of the X-rays is off, is a reverse bias voltage.