Abstract
Polycrystalline Lead Oxide (poly-PbO) was considered one of the most promising photoconductors for the direct conversion X-ray medical imaging detectors due to its previous success in optical imaging, i.e., as an optical target in so-called Plumbicon video pick-up tubes. However, a signal lag which accompanies X-ray excitation, makes poly-PbO inapplicable as an X-ray-to-charge transducer in real-time X-ray imaging. In contrast, the recently synthesized Amorphous Lead Oxide (a-PbO) photoconductor is essentially lag-free. Here, we report on our approach to a PbO detector where a thin layer of a-PbO is combined with a thick layer of poly-PbO for lag-free operation. In the presented a-PbO/poly-PbO bilayer structure, the poly-PbO layer serves as an X-ray-to-charge transducer while the a-PbO acts as a lag prevention layer. The hole mobility in the a-PbO/poly-PbO bilayer structure was measured by photo-Charge Extraction by Linearly Increasing Voltage technique at different temperatures and electric fields to investigate charge transport properties. It was found that the hole mobility is similar to that in a-Se—currently the only commercially viable photoconductor for the direct conversion X-ray detectors. Evaluation of the X-ray temporal performance demonstrated complete suppression of signal lag, allowing operation of the a-PbO/poly-PbO detector in real-time imaging.
Highlights
Polycrystalline Lead Oxide was considered one of the most promising photoconductors for the direct conversion X-ray medical imaging detectors due to its previous success in optical imaging, i.e., as an optical target in so-called Plumbicon video pick-up tubes
The first commercial mammographic direct conversion detectors based on amorphous selenium (a-Se) photoconductor to directly convert incident X-rays to charge, which is subsequently electronically read out by a two-dimensional array of a-Si:H thin film transistors (TFTs), made a breakthrough in the breast imaging field due to the excellent detectability of small breast lesions[1]
The performance of a-PbO/poly-PbO bilayer structure has been investigated in terms of whether combining these PbO polymorphs into a multilayer structure allows to consolidate the adequate hole mobility inherent in poly-PbO with the excellent X-ray temporal response inherent in a-PbO layers
Summary
Polycrystalline Lead Oxide (poly-PbO) was considered one of the most promising photoconductors for the direct conversion X-ray medical imaging detectors due to its previous success in optical imaging, i.e., as an optical target in so-called Plumbicon video pick-up tubes. A signal lag which accompanies X-ray excitation, makes poly-PbO inapplicable as an X-ray-to-charge transducer in real-time X-ray imaging. Evaluation of the X-ray temporal performance demonstrated complete suppression of signal lag, allowing operation of the a-PbO/poly-PbO detector in real-time imaging. The X- ray-to-charge conversion rate of these materials is 3–8 times larger than that of a-Se and they are capable of X-ray quantum noise limited operation at low exposures, since the X-ray quantum noise can prevail over the electronic noise. The performance of these polycrystalline photoconductors is far Scientific Reports | (2020) 10:20117
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