• Journal of the Korean Society of Radiology
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• v.17 no.6
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• pp.897-902
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• 2023

The purpose of this paper is to analyze the characteristics of Silicon Photomultiplier (SiPM) for the realization of high-sensitivity radiation detection in portable detectors. Portable X-ray detectors offer the advantage of quickly accessing the patient's location and obtaining real-time images, allowing physicians to perform rapid diagnoses. However, this mobility comes with challenges in achieving accurate radiation detection. In existing detectors, SiPM is used for a simple purpose of detecting X-ray triggers. To verify the feasibility of high-sensitivity X-ray detection through SiPM, seven types of SiPM sensors were compared and selected, and their characteristics were analyzed. The SiPM used in the final test demonstrated the ability to distinguish signals at the ultra-low radiation level of 10 nGy, and it was observed that the slope of the signal rise curve varies with the X-ray tube voltage. Utilizing the characteristics of SiPM, which exhibits changes in signal level and duration with X-ray dose, it appears possible to achieve high-sensitivity measurements for X-ray detection.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.05b
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• pp.31-34
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• 2002

In this paper, the electric properties of amophous selenium multilayer samples has been investigated. In order to develop the hybrid flat-panel digital· X-ray image detector, we measured and analyzed their performance parameters such as the X -ray sensitivity and dark-current for a amophous selenium multilayers X-ray detector with a phosphor layer, The hybrid digital X-ray image detector can be constructed by integrating a phosphor layer (or a scintillative layer) that convert X-ray to a light on a-Se photoconduction mulilayers that convert a light to electrical signal. As results, the dielectric materials such as parylene between the phosphor layer and the top electrode may reduce the dark-current of the samples. Amorphous selenium multilayers having dielectric layer(parylene) has characteristics of low dark-current, high X-ray sensitivity. So we can acquired a enhanced signal to noise ratio. In this paper offer the method can reduce the dark-current in the hybrid X-ray detector.

• Transactions on Electrical and Electronic Materials
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• v.3 no.4
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• pp.16-20
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• 2002

The high bias voltage associated with the thick layer (typically 500-1000 ㎛) of selenium required to have an acceptable x-ray absorption in radiography and fluoroscopy applications may have some practical inconvenience. A hybrid x-ray detector with zinc sulfide-amorphous selenium structure has been developed to improve the x-ray sensitivity of a a-Se based flat-panel digital imaging detector. Photoluminescence(PL) characteristic of a ZnS:Ag phosphor layer showed a light emission peak centered at about 450 nm, which matches the sensitivity spectrum of selenium. The dark current of the hybrid detector showed similar characteristics with that of a a-Se detector. The x-ray sensitivity of hybrid and a-Se x-ray detector was 345 pC/㎠/mR and 295 pC/㎠/mR at an applied voltage of 10 V/㎛, respectively. The purpose of this study was to evaluate the pertinence of a solution using a thin selenium layer, as a photosensitive converter, with a thick coating of silver doped zinc sulfide phosphor.

• Transactions on Electrical and Electronic Materials
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• v.4 no.3
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• pp.10-14
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• 2003

In this paper, we have introduced the x-ray detector built with a CsI:Na scintillation layer deposited on amorphous selenium. To determine the thickness of the CsI:Na layer, we have estimated the transmission spectra and the absorption of continuous x-rays in diagnostic range by using computer simulation (MCNP 4C). A x-ray detector with 65 ${\mu}m$-CsI:Na/30 ${\mu}m$-Se layer has been fabricated by a thermal evaporation technique. SEM and PL measurements have been performed. The dark current and x-ray sensitivity of the fabricated detector has been compared with that of the conventional a-Se detector with 100 ${\mu}m$ thickness. Experimental results show that both detectors exhibit a similar dark current, which was of a low value below $400 pA/cm^2$ at 10 V/${\mu}m$. However, the CsI:Na-Se detector indicates high x-ray sensitivity, roughly 1.3 times that of a conventional a-Se detector. Furthermore, a CsI:Na-Se detector with an aluminium reflective layer shows a 1.8 times higher x-ray sensitivity than an a-Se detector. The hybrid type detector proposed in this work exhibits a low dark current and high x-ray sensitivity, and, in particular, excellent linearity to the x-ray exposure dose.

• Transactions on Electrical and Electronic Materials
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• v.5 no.4
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• pp.133-137
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• 2004

The development of digital x-ray detector has been extensively progressed for the application of various medical modalities. In this study, we introduce a new hybrid-type x-ray detector to improve problems of a conventional direct or indirect digital x-ray image technology, which composed of multi-layer structure using a CaWO$_4$ phosphor and amorphous selenium (a-Se) photoconductor. The leakage current of our detector was found to be ∼180 pA/cm$^2$ at 10 V/m, which was significantly reduced than that of a single a-Se detector. The x-ray sensitivity was measured as the value of 4230 pC/cm$^2$/mR at 10 V/m. We found that the parylene thin film between a CaWO$_4$ phosphor and an a-Se layer acts as an insulator to prevent charge injection from indium thin oxide (ITO) electrode into an a-Se layer under applied bias.

• Transactions on Electrical and Electronic Materials
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• v.4 no.5
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• pp.15-18
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• 2003

The Cd$\_$1-x/Zn$\_$x/Te film was produced by thermal evaporation for the flat-panel X-ray detector. The crystal structure and the surface morphology of poly crystalline Cd$\_$1-x/Zn$\_$x/Te film were examined using XRD and SEM, respectively. The leakage current and X-ray sensitivity of the fabricated films were measured to analyze the X-ray response characteristic of Zn in a polycrystalline CdZnTe thin film. The leakage current and the output charge density of Cd$\_$0.7/Zn$\_$0.3/Te thin film were measured to 0.3 1nA/$\textrm{cm}^2$ and 260 pC/$\textrm{cm}^2$ at an applied voltage of 2.5 V/$\mu\textrm{m}$, respectively. Experimental results showed that the increase of Zn doping rates in Cd$\_$1-x/Zn$\_$x/Te detectors reduced the leakage current and improved the X-ray sensitivity significantly. The leakage current was drastically diminished by the formation of thin parylene layer in the Cd$\_$0.7/Zn$\_$0.3/Te detector.

• Proceedings of the KIEE Conference
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• 2005.05a
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• pp.281-283
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• 2005

Processing Plasmas are very sensitive to a variation in process parameters, To maintain process quality and device field, plasma malfunction should be tightly monitored with high sensitivity. A new monitoring method is presented and this was accomplished by applying discrete wavelet transformation to X-ray photoelectron spectroscopy. XPS data were collected during a plasma etching of silicon carbide. Various effects of DWT factor on fault sensitivity were optimized experimentally. Compared to raw data, total percent sensitivity for DWT data demonstrated a significantly improved sensitivity to plasma faults induced by bias power.

• Transactions on Electrical and Electronic Materials
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• v.3 no.2
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• pp.28-31
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• 2002

The Cdl-xZnxTe film was fabricated by thermal evaporation for the flat-panel X-ray detector. The stoichimetric ratio and the crystal structure of a polycrystalline Cd$_{1-x}$ Zn$_{x}$Te were investigated by EPMA and XRD, respectively. The leakage current and X-ray sensitivity of the fabricated films were measured to analyze the X-ray response characteristic of Zn in the polycrystalline CdZnTe thin film. The leakage current and the output charge density of Cd$_{0.7}$Zn$_{0.3}$Te thin film were measured to 0.37 nA/cm$^2$ and 260 pc/cm$^2$ at an applied voltage of 2.5 V/${\mu}{\textrm}{m}$, respectively. Experimental results showed that the increase of Zn doping rates in Cd$_{1-x}$ Zn$_{x}$Te detectors reduced the leakage current and improved the signal to noise ratio significantly.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.52.3-52.3
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• 2021

Timing analysis에서 pulsar 또는 magnetar의 pulsation 측정은 background 또는 주변의 다른 source의 영향으로 매우 세밀하게 측정을 진행해야 할 수 있다. 하지만 gamma-ray 영역에서는 instrument의 낮은 imaging resolution으로 인해 likeihood 분석법을 사용하며, pulsation측정의 sensitivity를 향상시키기 위해 weighted H-test를 적용하고 있다. weighted H-test는 Instrument의 responses와 source, background의 radiational properties를 이용하여 각 photon의 probability를 계산하고 이를 weight하여 pulsation detection의 sensitivity를 향상시키는 방법으로 이번 연구를 통해 이를 X-ray에서 적용할 수 있도록 확장하였다. 이번 발표에서는 X-ray 데이터 중 상대적으로 낮은 imaging resolution을 갖는 XMM-Newton data에 weighted H-test를 적용하여 기존의 H-test와의 차이를 비교해보고, weighted H-test가 갖는 이점에 대하여 논의하고자 한다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.305-306
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• 2005

The effects of As addition In amorphous selenium (a-Se) films for digital X-ray conversion material have been studied using the moving photocarrier grating (MPG) technique We have found an increase in hole drift mobility and recombination lifetime, especially when 0.3% As is added into a-Se film, whereas electron mobility decreases with As addition due to the defect density. The transport properties for As doped a-Se films obtained by using MPG technique have been compared with X-ray sensitivity for a-Se:As X-ray device. The fabricated a-Se (0.3%As) based X-ray detector exhibited the highest X-ray sensitivity of 5 samples.