• Journal of the Korean Society of Radiology
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• v.5 no.2
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• pp.93-96
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• 2011

Currently, the development of direct conversion radiation detector using photoconductor materials is progressing in widely. Among of theses photoconductor materials, mercuric iodide compound than amorphous selenium has excellent absorption and sensitivity of high energy radiation. Also, the detection efficiency of signal generated in photoconductor film varies by electric filed and geometric distribution according to top-bottom electrode size. Therefore, in this work, the x-ray detection characteristics are investigated about the size of top electrode in $HgI_2$ photoconductor film. For sample fabrication, to solve the problem that is difficult to make a large area film, we used the spatial paste screen-print method. And the sample thickness is $150{\mu}m$ and an film area size is $3cm{\times}3cm$ on ITO-coated glass substrate. ITO(Indium-Tin-Oxide) electrode was used as top electrode using a magnetron sputtering system and each area is $3cm{\times}3cm$, $2cm{\times}2cm$ and $1cm{\times}1cm$. From experimental measurement, the dark current, sensitivity and SNR of the $HgI_2$ film are obtained from I-V test. From the experimental results, it shows that the sensitivity increases in accordance with the area of the electrode but the SNR is decreased because of the high dark current. Therefore, the optimized size of electrode is importance for the development of photoconductor based x-ray imaging detector.

• Korean Journal of Optics and Photonics
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• v.18 no.5
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• pp.351-361
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• 2007

The samples composed of a GST thin film and the protective layers of $ZnS-SiO_2$ or $Al_2O_3$ coated on c-Si substrate were prepared by using the magnetron sputtering method. Samples of three different structures were prepared, that is, i) the GST single film on c-Si substrate, ii) the GST film sandwiched by the protective $ZnS-SiO_2$ layers on c-Si substrate, and iii) the GST film sandwiched by $Al_2O_3$ protective layers on c-Si substrate. The ellipsometric constants in the temperature range from room temperature to $700^{\circ}C$ were obtained by using the in-situ ellipsometer equipped with a conventional heating chamber. The measured ellipsometric constants show strong variations versus temperature. The variation of ellipsometric constants at the temperature region higher than $300^{\circ}C$ shows different behaviors as the ambient medium is changed from in air to in vacuum or the protective layers are changed from $ZnS-SiO_2$ to $Al_2O_3$. Since the long heating time of 1-2 hours is believed to be the origin of the high temperature variation of ellipsometric constants upon the heating environment and the protective layers, a PRAM (Phase-Change Random Access Memory) recorder is introduced to reduce the heating time drastically. By using the PRAM recorder, the GST samples are heated up to $700^{\circ}C$ decomposed preventing its partial evaporation or chemical reactions with adjacent protective layers. The surface image obtained by SEM and the surface micro-roughness verified by AFM also confirmed that samples prepared by the PRAM recorder have smoother surface than the samples prepared by using the conventional heater.

• Journal of the Korean Magnetics Society
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• v.13 no.2
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• pp.53-58
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• 2003

Annealing effects of exchange bias fields ($H_{2ex}$(top), $H_{lex}$ (bottom)) on composite type NiFe/[FeMn/Mn]$_{80}$/NiFe multilayers have been studied. Three samples with ultra-thin Mn inserted layers on glass/Ta(50 $\AA$)/NiFe(150 $\AA$)/[F $e_{53}$M $n_{47}$(1.25 $\AA$)/Mn(0 $\AA$, 0.11 $\AA$, 0.3 $\AA$)]$_{80}$/NiFe(90 $\AA$)/Ta(50 $\AA$) were prepared by ion beam sputtering. The average x-ray diffraction peak ratios NiFe(111) of FeMn (111) fcc textures for the Mn inserted total thicknesses of 0 $\AA$, 9 $\AA$, and 24 $\AA$ were about 0.65, 0.90, and 1.5, respectively. For the sample without Mn inserted layer, the $H_{2ex}$ of 260 Oe up to 300 $^{\circ}C$ disappeared at 350 $^{\circ}C$. For two multilayer samples with ultra-thin Mn layers of 0.11 $\AA$ and 0.3 $\AA$, the $H_{2exs}$ of 310 Oe and 180 Oe up to 300 $^{\circ}C$ endured of 215 Oe and 180 Oe at 350 $^{\circ}C$, respectively. The $H_{ex}$ (bottom)s of three samples decreased from 100 Oe to 70 Oe up to 250 $^{\circ}C$, while these values increased beyond 300 $^{\circ}C$. This observation can be attributed to less diffusive path of Mn atoms in bottom NiFe than top NiFe layer. The top and bottom coercive fields slightly varied about 5 Oe∼10 Oe. From these results, we could obtain the enhancement of exchange coupling intensity and thermal stability by an ultra-thin Mn inserted layer on NiFe/[FeMn/Mn]$_{80}$/NiFe Multilayers.

• Applied Microscopy
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• v.38 no.4
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• pp.279-284
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• 2008

The phase change materials have been extensively used as an optical rewritable data storage media utilizing their phase change properties. Recently, the phase change materials have been spotlighted for the application of non-volatile memory device, such as the phase change random access memory. In this work, we have investigated the crystallization behavior and microstructure analysis of In-Sb-Te (IST) thin films deposited by RF magnetron sputtering. Transmission electron microscopy measurement was carried out after the annealing at $300^{\circ}C$, $350^{\circ}C$, $400^{\circ}C$ and $450^{\circ}C$ for 5 min. It was observed that InSb phases change into $In_3SbTe_2$ phases and InTe phases as the temperature increases. It was found that the thickness of thin films was decreased and the grain size was increased by the bright field transmission electron microscopy (BF TEM) images and the selected area electron diffraction (SAED) patterns. In a high resolution transmission electron microscopy (HRTEM) study, it shows that $350^{\circ}C$-annealed InSb phases have {111} facet because the surface energy of a {111} close-packed plane is the lowest in FCC crystals. When the film was heated up to $400^{\circ}C$, $In_3SbTe_2$ grains have coherent micro-twins with {111} mirror plane, and they are healed annealing at $450^{\circ}C$. From the HRTEM, InTe phase separation was occurred in this stage. It can be found that $In_3SbTe_2$ forms in the crystallization process as composition of the film near stoichiometric composition, while InTe phase separation may take place as the composition deviates from $In_3SbTe_2$.

• Journal of the Korean Electrochemical Society
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• v.13 no.2
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• pp.116-122
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• 2010

A $Cu_3Si$ film electrode is obtained by Si deposition on a Cu foil using DC magnetron sputtering, which is followed by annealing at $800^{\circ}C$ for 10 h. The Si component in $Cu_3Si$ is inactive for lithiation at ambient temperature. The linear sweep thermammetry (LSTA) and galvano-static charge/discharge cycling, however, consistently illustrate that $Cu_3Si$ becomes active for the conversion-type lithiation reaction at elevated temperatures (> $85^{\circ}C$). The $Cu_3Si$ electrode that is short-circuited with Li metal for one week is converted to a mixture of $Li_{21}Si_5$ and metallic Cu, implying that the Li-Si alloy phase generated at 0.0 V (vs. Li/$Li^+$) at the quasi-equilibrium condition is the most Li-rich $Li_{21}Si_5$. However, the lithiation is not extended to this phase in the constant-current charging (transient or dynamic condition). Upon de-lithiation, the metallic Cu and Si react to be restored back to $Cu_3Si$. The $Cu_3Si$ electrode shows a better cycle performance than an amorphous Si electrode at $120^{\circ}C$, which can be ascribed to the favorable roles provided by the Cu component in $Cu_3Si$. The inactive element (Cu) plays as a buffer against the volume change of Si component, which can minimize the electrode failure by suppressing the detachment of Si from the Cu substrate.

• Journal of Sensor Science and Technology
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• v.2 no.1
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• pp.101-108
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• 1993

$TiO_{2}$/Se : Te heterojunction for color sensor has been fabricated by RF reactive sputtering and thermal evaporation methods onto glass substrate. The optimum deposition condition of $TiO_{2}$ films was such that RF power was 120 W, substrate temperature was $100^{\circ}C$, oxygen concentration was 50%, working pressure was 50 mTorr for the $TiO_{2}$ film thickness of $1000{\AA}$. In this case, the optical transmittance of $TiO_{2}$ film at 550 nm-wavelength was 85%, resistivity was $2{\times}10^9{\Omega}{\cdot}cm$, refractive index was 2.3, and optical bandgap was 3.58 eV. The composition ratio of 0 to Ti by AES analysis was 1.7. When $TiO_{2}$ films were annealed at $400^{\circ}C$ for 30 min. in $O_{2}$ ambient, the optical transmittance of $TiO_{2}$ films at the wavelength range of $300{\sim}580$ nm was improved from 0 to 25%. When Se : Te films were annealed at $190^{\circ}C$ for 1 min., photosensitivity under illumination of 1000 lux was 0.75. The optical bandgap of Se : Te films was 1.7 eV. The structures of Se : Te films were the hexagonal with (100) and (110) orientation. The spectral response of a-Se was improved by the addition of Te, especially in the long wavelength region. The $TiO_{2}$/Se : Te heterojunction showed wide spectral response, and more improved one than that of a-Si film in the blue light region.