Design, Fabrication and Characterization of a Unipolar Charge Sensing Amorphous Selenium X-ray Detector
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Date
2023-06-19
Authors
Warsi, Zain Hussain
Journal Title
Journal ISSN
Volume Title
Publisher
University of Waterloo
Abstract
Amorphous Selenium is a direct conversion photoconductor that has been widely used
in X-ray imaging applications. Due to its high spatial resolution A-Se plays an important
role in breast cancer screening and diagnostics, allowing for the detection of small and
subtle lesions. However, a-Se has poor collection efficiency due to low carrier mobility and
charge trapping resulting from its amorphous structure. The trapped charges can cause
memory artifacts, including photocurrent lag, which can persist for several seconds after
the X-ray pulse has ended. As a result, a-Se is a challenging material for dynamic imaging
applications that require high spatial resolution.
The research discussed in this thesis aims to investigate and address the temporal
behavior of a-Se photoconductors, specifically the issue of lag, which can lead to image
artifacts and degradation of image quality in dynamic imaging applications. The research
involves the design of unipolar charge sensing detectors with pixel sizes of 20, 40, 80
and 150 microns to improve energy resolution and the temporal response compared to
conventional a-Se detectors. Theoretical analysis and simulations are presented for the
unipolar charge sensing detector including weighting potential, charge collection efficiency,
pulse height spectroscopy and energy resolution which range from 5% to 2% . The work
further discusses the fabrication process of the designed detector in the G2N lab at the
university of Waterloo. It discusses the experimental results obtained and the challenges
that were faced while fabricating the detector and how they can be overcome in the future
Description
Keywords
Amorphous Selenium, X-ray Detector, Unipolar Charge Sensing