Congratulations to Oleksandr Grynko on publishing a paper in IEEE Transactions on Electron Devices

Date: March 29, 2021

Oleksandr Grynko with co-authors: Tristen Thibault, Emma Pineau, and Alla Reznik
published a paper titled “Engineering of a Blocking Layer Structure for Low-Lag Operation of
the a-PbO-Based X-Ray Detector” in IEEE Transactions on Electron Devices (Volume: 68,
Issue: 5, May 2021). Congratulations on the published paper!


Direct conversion flat panel detectors are of great significance to the field of medical X-ray
imaging since they offer imaging performance and diagnostic capabilities not achievable with
other methods. Currently, mammographic direct conversion detectors employ a layer of
amorphous selenium (a-Se) photoconductor. Although its properties ideally fit the requirements
of mammography, where “soft” X-rays are used, a-Se cannot be used in high-energy X-ray
procedures. To extend the diagnostic capabilities of the direct conversion detectors, amorphous
lead oxide (a-PbO) is proposed as an alternative photoconductor. It is a high effective atomic
number material and thus has a higher X-ray stopping power over the wide X-ray energy range.
a-PbO is, therefore, a suitable candidate for applications in radiography, fluoroscopy, and digital
tomosynthesis. Here, we report on the development of a blocking structure with a polyimide (PI)
layer needed to maintain low dark current at high electric fields. We demonstrate that a 1- μm-
thick PI blocking layer allows the operation of the detector at strong electric fields (≥10 V/ μm)
while suppressing the dark current to an innocuous level (<; 1 pA/mm 2 ). It also improves
temporal performance by reducing signal lag. No ghosting effect was observed at exposure rates
up to 1 R/s; however, at high radiation levels, the detector's sensitivity degraded. This
degradation is not permanent as the detector restores its original sensitivity after several hours of
rest in the dark without bias applied.

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