• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.33 no.2
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• pp.155-160
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• 2020

Ga₂O₃/n-type 4H-SiC heterojunction diodes were fabricated by RF magnetron sputtering. The optical properties of Ga₂O₃ and electrical properties of diodes were investigated. I-V characteristics were compared with simulation data from the Atlas software. The band gap of Ga₂O₃ was changed from 5.01 eV to 4.88 eV through oxygen annealing. The doping concentration of Ga₂O₃ was extracted from C-V characteristics. The annealed oxygen exhibited twice higher doping concentration. The annealed diodes showed improved turn-on voltage (0.99 V) and lower leakage current (3 pA). Furthermore, the oxygen-annealed diodes exhibited a temperature cross-point when temperature increased, and its ideality factor was lower than that of as-grown diodes.

• The Transactions of the Korean Institute of Power Electronics
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• v.22 no.4
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• pp.297-304
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• 2017

The purpose of this paper is to analyze losses because of switching devices and the secondary side circuit diodes of 500 W full bridge dc-dc converter by applying gallium nitride (GaN) field-effect transistor (FET), which is one of the wide band gap devices. For the detailed device analysis, we translate the specific resistance relation caused by the GaN FET material property into algebraic expression, and investigate the influence of the GaN FET structure and characteristic on efficiency and system specifications. In addition, we mathematically compare the diode rectifier circuit loss, which is a full bridge dc-dc converter secondary side circuit, with the synchronous rectifier circuit loss using silicon metal-oxide semiconductor (Si MOSFET) or GaN FET, which produce the full bridge dc-dc converter analytical value validity to derive the final efficiency and loss. We also design the heat sink based on the mathematically derived loss value, and suggest the heat sink size by purpose and the heat divergence degree through simulation.

• Progress in Superconductivity and Cryogenics
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• v.16 no.2
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• pp.64-69
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• 2014

Measuring an exact amount of remaining cryogenic liquid propellant under microgravity condition is one of the important issues of rocket vehicle. A Pressure-Volume-Temperature (PVT) gauging method is attractive due to its minimal additional hardware and simple gauging process. In this paper, PVT gauging method using liquid nitrogen is investigated under microgravity condition with parabolic flight. A 9.2 litre metal cryogenic liquid storage tank containing approximately 30% of liquid nitrogen is pressurized by ambient temperature helium gas. During microgravity condition, the inside of the liquid tank becomes near-isothermal condition within 1 K difference indicated by 6 silicon diode sensors vertically distributed in the middle of the liquid tank. Helium injection with higher mass flow rate after 10 seconds of the waiting time results in successful measurements of helium partial pressure in the tank. Average liquid volume measurement error is within 11% of the whole liquid tank volume and standard deviation of errors is 11.9. As a result, the applicability of PVT gauging method to liquid propellant stored in space is proven with good measurement accuracy.

• Journal of the Korean institute of surface engineering
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• v.53 no.5
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• pp.201-206
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• 2020

A SiOxCy(-H) thin film was synthesized by atmospheric pressure dielectric barrier discharge(APDBD), and a SiO₂-like layer was formed on the surface of the film by oxidation treatment using oxygen plasma. Hexamethylcyclotrisiloxane was used as a precursor for the SiOxCy(-H) synthesis, and He gas was used for stabilizing APDBD. Oxygen permeability was evaluated by forming an oxidized SiOxCy(-H) thin film on a PET film. When the single-layer oxidized SiOxCy(-H) film was coated on the PET, the oxygen gas permeability decreased by 46% compared with bare PET. In case of three-layer oxidized SiOxCy(-H) film, the oxygen gas permeability decreased by 73%. The oxygen permeability was affected by the thickness of the SiO₂-like layer formed by oxidation treatment rather than the thickness of the SiOxCy(-H) film. The excellent corrosion resistance was demonstrated by coating an oxidized SiOxCy(-H) thin film on the silver-coated aluminum PCB for light emitting diode (LED).

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.7
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• pp.1281-1286
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• 2006

We have used the silicon-carbide(4H-SiC) instead of conventional silicon materials to develope of the planar junction barrier schottky rectifier for ultra high breakdown voltage(1,200 V grade). The substrate size is 2 inch wafer, Its concentration is $3*10^{18}/cm^{3}$ of $n^{+}-$type, thickness of epitaxial layer $12{\mu}m$ conentration is $5*10^{15}cm^{-3}$ of n-type. The fabticated devices are junction barrier schottky rectifier, The guard ring for improvement of breakdown voltage is designed by the box-like impurity of boron, the width and space of guard ring was designed by variation. The contact metals to rectify were used by the $Ni(3,000\:{\AA})/Au(2,000\:{\AA})$. As a results, the on-state voltage is 1.26 V, on-state resistance is $45m{\Omega}/cm^{3}$, maximum value of improved reverse breakdown voltage is 1180V, reverse leakage current density is $2.26*10^{-5}A/CM^{3}$. We had improved the measureme nt results of the electrical parameters.

• The Journal of Korean Society for Radiation Therapy
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• v.17 no.1
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• pp.19-31
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• 2005

Purpose : To supply the information of EPID system and to analyze the possibility of substitution EPID for film dosimetry. Materials & Methods : With amorphous silicon(aSi) type EPID and liquid filled lonization chamber(LC) type EPID, the reproducibility according to focus detector distance(FDD) change and gantry rotation was analyzed, and also the possible range of image acquisition was analyzed with Alderson Rando phantom. The resolution and the contrast of aSi type EPID image were analyzed through Las Vegas phantom and water phantom. DMLC image was analyzed with X-Omat V film and EPID to see wether it could be applied to the qualify assurance(QA) of IMRT. Results : The reproducibility of FDD position was within 1mm, but the reproducibility of gantry rotation was ${\pm}2,\;{\pm}3mm$ respectively. The resolution and the contrast of EPID image were affected by dose rate, image acquisition time, image acquisition method and frame number. According to the possible range of image acquisition of EPID, it is verified that the EPID is easier to use than film. There is no difference between X-Omat V film and EPID images for the QA of IMRT. Conclusion : Through various evaluation, we could obtain lots of useful information about the EPID. Because the EPID has digital data, also we found that the EPID is more useful than film dosimerty for the periodical Qualify Assurance of IMRT. Especially when it is difficult to do point dose measurement with diode or ionization chamber, the EPID could be very useful substitute. And we found that the diode and ionization chamber are difficult to evaluate the sliding window images of IMRT, but the EPID was more useful to do it.

• Progress in Medical Physics
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• v.25 no.4
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• pp.255-263
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• 2014

The dosimetry of very small fields is challenging for several reasons including a lack of lateral electronic equilibrium, large dose gradients, and the size of detector in respect to the field size. The objective of this work was to evaluate the suitability of a new commercial synthetic diamond detector, namely, the PTW 60019 microDiamond, for the small field dosimetry in cyberknife photon beams of 6 different collimator size (from 5 mm to 30 mm). Measurements included dose linearity, dose rate dependence, output factors (OF), percentage depth doses (PDD) and off center ratio (OCR). The results were compared to those of pinpoint ionization chamber, diamond detector, microLion liquid Ionization chamber and diode detector. The dose linearity results for the microDiamond detector showed good linearly proportional to dose. The microDiamond detector showed little dose rate dependency throughout the range of 100~600 MU/min, while microLion liquid Ionization chamber showed a significant discrepancy of approximately 5.8%. The OF measured with microDiamond detector agreed within 3.8% with those measured with diode. PDD curves measured with silicon diode and diamond detector agreed well for all the field sizes. In particular, slightly sharper penumbras are obtained by the microDiamond detector, indicating a good spatial resolution. The results obtained confirm that the new PTW 60019 microDiamond detector is suitable candidate for application in small radiation fields dosimetry.

• Journal of the Korean Society of Radiology
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• v.7 no.1
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• pp.81-84
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• 2013

The use of the dosimetry have been increasingly recognized as high radiation energy and radiation treatment planning(RTP) have rapidly developed in radiotherapy. There are many types of detectors for the dosimetry such as ionization chamber, film, TLD, diode, and etc. Among such detectors, the diode detector uses a photoconductor materials that generate electrical signals by the incident radiation energy. Though many research groups are recently interested in such materials, there is few experimental results except for silicon in the radiation therapy field. In this study, the feasibility of photoconductor materials was verified as a dosimeter through the evaluation of response properties at a high radiation energy. For the fabricated detectors based on $HgI_2$ and $PbI_2$, reproducibility, linearity, and pulse-rate response were analyzed. Such evaluations are essential factors for the use of dosimeter. From results, linearity and reproducibility of the fabricated $HgI_2$ detector indicated about 7% error. The fabricated $PbI_2$ detector showed 1.7% error in linearity, and 12.2% error in reproducibility.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.58.1-58.1
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• 2010

In solar cell module manufacturing, single solar cells has to be joined electrically to strings. Copper stripes coated with tin-silver-copper alloy are joined on screen printed silver of solar cells which is called busbar. The bus bar collects the electrons generated in solar cell and it is connected to the next cell in the conventional module manufacturing by a metal stringer using conventional hot air or infrared lamp soldering systems. For thin solar cells, both soldering methods have disadvantages, which heats up the whole cell to high temperatures. Because of the different thermal expansion coefficient, mechanical stresses are induced in the solar cell. Recently, the trend of solar cell is toward thinner thickness below 180um and thus the risk of breakage of solar cells is increasing. This has led to the demand for new joining processes with high productivity and reduced error rates. In our project, we have developed a new method to solder solar cells with a laser heating source. The soldering process using diode laser with wavelength of 980nm was examined. The diode laser used has a maximum power of 60W and a scanner system is used to solder dimension of 6" solar cell and the beam travel speed is optimized. For clamping copper stripe to solar cell, zirconia(ZrO)coated iron pin-spring system is used to clamp both joining parts during a scanner system is traveled. The hot plate temperature that solar cell is positioned during lasersoldering process is optimized. Also, conventional solder joints after $180^{\circ}C$ peel tests are compared to the laser soldering methods. Microstructures in welded zone shows that the diffusion zone between solar cell and metal stripes is better formed than inIR soldering method. It is analyzed that the laser solder joints show no damages to the silicon wafer and no cracks beneath the contact. Peel strength between 4N and 5N are measured, with much shorter joining time than IR solder joints and it is shown that the use of laser soldering reduced the degree of bending of solar cell much less than IR soldering.

• Journal of Radiation Protection and Research
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• v.31 no.4
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• pp.181-186
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• 2006

A radiophotoluminescent glass rod detector (GRD) system has recently become commercially available. We investigate the dosimetric properties of the GRD regarding the reproducibility of signal, dose linearity and energy dependence. The reproducibility of five measurements for 50 GRDs is presented by an average of one standard deviation of each GRD and it is ${\pm}1.2%$. It is found to be linear in response to doses of $^{60}Co$ beam in the range 0.5 to 50 Gy with a coefficient of linearity of 0.9998. The energy dependence of the GRD is determined by comparing the dose obtained using cylindrical chamber to that by using the GRD. The GRD response for each beam is normalized to the response for a $^{60}Co$ beam. The responses for 6 and 15 MV x-ray beams are within ${\pm}1.5%$ (1SD). The energy response of GRD for high-energy photon is almost the same as the energy dependence of LiF:Mg:Ti (TLD-100)and shows little energy dependence unlike p-type silicon diode detector. The GRDs have advantages over other detectors such diode detector, and TLD: linearity, reproducibility and energy dependency. It has been verified to be an effective device for small field dosimetry for stereotactic radiosurgery.