Device Architectures for Improved Temporal Response with Amorphous Selenium Radiation Detectors

dc.contributor.authorCamlica, Ahmet
dc.date.accessioned2019-07-29T19:45:52Z
dc.date.available2021-10-11T04:50:10Z
dc.date.issued2019-07-29
dc.date.submitted2019-07-25
dc.description.abstractAmorphous selenium (a-Se) is a commercially mature direct conversion photoconductor capable of very high spatial resolution that enables the early detection of small and subtle lesions in breast cancer screening and diagnostics. However, a-Se exhibits poor collection efficiency due to low carrier mobility and charge trapping related to its amorphous nature. Release of trapped electrons gives rise memory artifacts such as photocurrent lag, that can last for several seconds after the cessation of the X-ray pulse, thus making a-Se a challenging material for use in high spatial resolution dynamic imaging applications. In this research, the intrinsic causes of temporal behavior in a-Se photoconductor are investigated using lag, ghosting and pulse height spectroscopy (PHS) measurements on conventional a-Se detectors. The measured data is compared to the data obtained with alternative a-Se imaging device architectures for improved dynamic imaging performance. The alternative device architectures include: (1) use of a polyimide blocking layer that permits the operation of a-Se devices with higher electric fields, (2) a high field capable solid-state unipolar charge sensing detector that can achieve hole-mostly charge sensing and (3), small pixel geometries to obtain the small pixel effect (SPE). Theoretical and experimental results show that an image lag of less than 1.5% is achieved using the solid-state unipolar charge sensing detector for dynamic imaging which is in stark contrast to measurements performed on conventional a-Se imaging devices that exhibit a lag of up to 16%. PHS measurements are also presented that demonstrate, for the first time, a measured energy resolution of 8.3 keV at 59.5 keV was for the unipolar charge sensing device in contrast to 22 keV at 59.5 keV for conventional a-Se devices. Also, the photon counting ability of a-Se photoconductor was demonstrated by integrating a SPE capable a-Se detector with a CMOS pixel array having 11 x 11-μm pixels. Measured results on this CMOS array using a mono-energetic radioactive source are presented which indicate for the first time, that amorphous semiconductors can be used for photon-counting X-ray imaging applications. The research results indicate that mature large-area a-Se photoconductor, when incorporated with a single polarity charge sensing device design such as SPE or the solid-state unipolar charge sensing detector, can meet the requirements of high spatial resolution dynamic medical imaging applications such as spectral mammography or even micro-angiography without resorting to new sensor materials or crystalline semiconductors that are challenging to scale up to larger areas because of cost and yield issues associated with growth and bonding technology.en
dc.identifier.urihttp://hdl.handle.net/10012/14826
dc.language.isoenen
dc.pendingfalse
dc.publisherUniversity of Waterlooen
dc.subjectamorphous seleniumen
dc.subjectpulse-height spectroscopyen
dc.subjectunipolar charge sensingen
dc.subjectsmall pixel effecten
dc.subjectX-rayen
dc.subjectGamma-rayen
dc.subjectmedical imagingen
dc.subjectdetectoren
dc.titleDevice Architectures for Improved Temporal Response with Amorphous Selenium Radiation Detectorsen
dc.typeDoctoral Thesisen
uws-etd.degreeDoctor of Philosophyen
uws-etd.degree.departmentElectrical and Computer Engineeringen
uws-etd.degree.disciplineElectrical and Computer Engineeringen
uws-etd.degree.grantorUniversity of Waterlooen
uws-etd.embargo.terms1 year + another yearen
uws.comment.hiddenHello, As indicated on the email sent by the PhD administrative coordinator, the review process takes 3-5 business day. However, I need to submit my graduation letter to the government before July 30th. Otherwise, I need to pay back a huge amount of compensation. I kindly ask you to review my thesis at your earliest convenience and get back to me , if required, so that I can catch the due date. Your help on this is mostly appreciated. Kind Regards,en
uws.contributor.advisorKarim, Karim
uws.contributor.advisorLee, Denny
uws.contributor.affiliation1Faculty of Engineeringen
uws.peerReviewStatusUnrevieweden
uws.published.cityWaterlooen
uws.published.countryCanadaen
uws.published.provinceOntarioen
uws.scholarLevelGraduateen
uws.typeOfResourceTexten

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