• Transactions on Electrical and Electronic Materials
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• 제5권4호
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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.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 춘계학술대회 논문집 센서 박막재료 반도체재료 기술교육
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• pp.35-38
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• 2002

In this paper, for digital x-ray conversion receptor development studied by hybrid technology of based on CdZnTe. For this study, First searched fabricate method of CdZnTe x-ray receptor. Second, search the phosphor material & fabricate method for scintillator layer. Fabricated sample is analyzed with physical & electric measurement. This result is showed good SNR ratio hybrid thechnology with direct method & indirect method. 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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• 제4권3호
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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.

• 전자공학회논문지
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• 제51권12호
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• pp.189-194
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• 2014

본 연구에서는 새로운 구조의 X선 영상 검출기로써 광민감 $HgI_2$ 층이 포함된 CsI:Na 형광층의 구조를 설계하였다. 이러한 구조에서 X선은 두꺼운 CsI:Na 층에서 가시광선으로 변환된 후 하부의 얇은 $HgI_2$ 층에서 전하로 변환된다. CsI:Na와 $HgI_2$로 구성된 복합구조의 두께를 최적화하기 각 층의 두께를 변화시켜 X선에 대한 흡수효율을 시뮬레이션 하였다. 현재 상용화된 a-Se 단일층의 검출기는 수십 kV의 고전압이 요구되고, CsI:Na/a-Si 구조의 간접변환 방식은 낮은 변환효율을 가지는 단점이 있다. 본 연구의 결과로 제시된 새로운 형태의 CsI:Na/$HgI_2$ 복층 구조의 x-ray 검출기는 고전압이 필요한 직접 변환방식의 단점과 간접 변환방식의 낮은 효율을 보완할 수 있을 것으로 생각된다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 추계학술대회 논문집 Vol.15
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• pp.416-419
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• 2002

There are being two prominent studying for Digital Radiography. Direct and Indirect method of Digital Radiography are announced for producing high quality digital image. The one is using amorphous selenium as photoconductor and the other is using phosphor layer as a light conversion. But each two systems have strength and weakness such as high voltage and blurring effect. In this study, we investigated the electrical characteristic of $multi-layer\left(CaWO_{4}+a-Se \right)$ as a photoconductor according to the changing arsenic composition ratio. This is a basic research for developing of Hybrid digital radiography which is a new type X-ray detector. The arsenic composition ratio of a-Se compound is classified into 7 different kinds which have 0.1%, 0.3%, 0.5%, 1%, 1.5%, 5%, 10% and were made test sample throught thermo-evaporation. The phosphor layer of $CaWO_4$ was overlapped on a-Se using EFIRON optical adhesives. We measured the dark and photo current about the test sample and compared the electrical characteristic of the net charge and signal-to-noise ratio. Among other things, test sample of compound material of 0.3% arsenic showed good characteristic of $2.45nA/cm^2$ dark current and $357.19pC/cm^2/mR$ net charge at $3V/{\mu}m$.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2011년도 춘계학술발표대회
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• pp.5-5
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• 2011

The research and development of hybrid electric vehicle (HEV), plug-in hybrid electric vehicle (PHEV) and electric vehicle (EV) are intensified due to the energy crisis and environmental concerns. In order to meet the challenging requirements of powering HEV, PHEV and EV, the current lithium battery technology needs to be significantly improved in terms of the cost, safety, power and energy density, as well as the calendar and cycle life. One new technology being developed is the utilization of composite cathode by mixing two different types of insertion compounds [e.g., spinel $LiMn_2O_4$ and layered $LiMO_2$ (M=Ni, Co, and Mn)]. Recently, some studies on mixing two different types of cathode materials to make a composite cathode have been reported, which were aimed at reducing cost and improving self-discharge. Numata et al. reported that when stored in a sealed can together with electrolyte at $80^{\circ}C$ for 10 days, the concentrations of both HF and $Mn^{2+}$ were lower in the can containing $LiMn_2O_4$ blended with $LiNi_{0.8}Co_{0.2}O_2$ than that containing $LiMn_2O_4$ only. That reports clearly showed that this blending technique can prevent the decline in capacity caused by cycling or storage at elevated temperatures. However, not much work has been reported on the charge-discharge characteristics and related structural phase transitions for these composite cathodes. In this presentation, we will report our in situ x-ray diffraction studies on this mixed composite cathode material during charge-discharge cycling. The mixed cathodes were incorporated into in situ XRD cells with a Li foil anode, a Celgard separator, and a 1M $LiPF_6$ electrolyte in a 1 : 1 EC : DMC solvent (LP 30 from EM Industries, Inc.). For in situ XRD cell, Mylar windows were used as has been described in detail elsewhere. All of these in situ XRD spectra were collected on beam line X18A at National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory using two different detectors. One is a conventional scintillation detector with data collection at 0.02 degree in two theta angle for each step. The other is a wide angle position sensitive detector (PSD). The wavelengths used were 1.1950 ${\AA}$ for the scintillation detector and 0.9999 A for the PSD. The newly installed PSD at beam line X18A of NSLS can collect XRD patterns as short as a few minutes covering $90^{\circ}$ of two theta angles simultaneously with good signal to noise ratio. It significantly reduced the data collection time for each scan, giving us a great advantage in studying the phase transition in real time. The two theta angles of all the XRD spectra presented in this paper have been recalculated and converted to corresponding angles for ${\lambda}=1.54\;{\AA}$, which is the wavelength of conventional x-ray tube source with Cu-$k{\alpha}$ radiation, for easy comparison with data in other literatures. The structural changes of the composite cathode made by mixing spinel $LiMn_2O_4$ and layered $Li-Ni_{1/3}Co_{1/3}Mn_{1/3}O_2$ in 1 : 1 wt% in both Li-half and Li-ion cells during charge/discharge are studied by in situ XRD. During the first charge up to ~5.2 V vs. $Li/Li^+$, the in situ XRD spectra for the composite cathode in the Li-half cell track the structural changes of each component. At the early stage of charge, the lithium extraction takes place in the $LiNi_{1/3}Co_{1/3}Mn_{1/3}O_2$ component only. When the cell voltage reaches at ~4.0 V vs. $Li/Li^+$, lithium extraction from the spinel $LiMn_2O_4$ component starts and becomes the major contributor for the cell capacity due to the higher rate capability of $LiMn_2O_4$. When the voltage passed 4.3 V, the major structural changes are from the $LiNi_{1/3}Co_{1/3}Mn_{1/3}O_2$ component, while the $LiMn_2O_4$ component is almost unchanged. In the Li-ion cell using a MCMB anode and a composite cathode cycled between 2.5 V and 4.2 V, the structural changes are dominated by the spinel $LiMn_2O_4$ component, with much less changes in the layered $LiNi_{1/3}Co_{1/3}Mn_{1/3}O_2$ component, comparing with the Li-half cell results. These results give us valuable information about the structural changes relating to the contributions of each individual component to the cell capacity at certain charge/discharge state, which are helpful in designing and optimizing the composite cathode using spinel- and layered-type materials for Li-ion battery research. More detailed discussion will be presented at the meeting.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 추계학술대회 논문집 Vol.15
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• pp.432-435
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• 2002

The ultimate study of this research is to improve the properties of digital X-ray receptor based on amorphous selenium. There are being two prominent studying for Digital Radiography. Direct and Indirect method of Digital Radiography are announced for producing high quality digital image. But each two systems have strength and weakness. This is a basic research for developing of Hybrid digital radiography which is a new type X-ray detector. ln this study, we investigated the electrical characteristic of multi-layer$(CaWO_4+a-Se)$ as a photoconductor according to the changing iodine composition ratio. The iodine composition ratio of a-Se compound is classified into 5 different kinds which have 30ppm, 100ppm, 300ppm, 500ppm, 700ppm and were made test sample throught thermo-evaporation. The phosphor layer of $CaWO_4$ was overlapped on a-Se using EFIRON optical adhesives. We measured the dark and photo current about the test sample and compared the electrical characteristic of the net charge and signal-to-noise ratio. Among other things, test sample of compound material of 700ppm iodine showed good characteristic of $2.53nA/cm^2$ dark current and $479nC/cm^2{\cdot}mR$ net charge at $3V/{\mu}m$.