• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.12
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• pp.1388-1398
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• 2012

SAR(Synthetic Aperture Radar) systems can provide images of wide coverage in day, night, and all-weather conditions. However wideband SAR systems are known to be vulnerable to interferences from other devices operating at in-band or adjacent spectrums and this may lead to image corruptions. In this paper, a SAR point target simulator is developed that provides performance analysis on image distortion caused by interferences from other devices. Interference signals are generated based on the experimental data observed from acquired SAR raw data. Simulation results include typical SAR performance measures such as spatial resolution, peak to sidelobe ratio and integrated sidelobe ratio. Finally, SAR target simulations are performed and shown to correspond to the image corruptions found in real SAR missions affected by RF interferences.

• Journal of the Microelectronics and Packaging Society
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• v.6 no.4
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• pp.49-53
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• 1999

In this study, the characteristics of the structure of buried type capacitor for RF multi- chip-module are investigated. We developed many kinds of structures to minimize the space of capacitor in module and the value of parastic series inductance without any loss in capacitance, and in this procedure the effect of vias especially position, size, number length are analyzed and optimized. This characteristics of structures are checked through HFSS(high frequency structure simulator) of HP, and the value of parastic series inductance is calculated by equivalent circuit analysis. And ensuing the result of simulation, we made buried type capacitors using LTCC (low temperature cofired ceramic) material. In measurement of this sample, we found out the effective and precise method can be applied to buried type and characteristics of vias and striplines added for measuring are quantified.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.2
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• pp.344-348
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• 2011

A layer of $TiO_2$ thin film less than ~200nm in thickness, as a blocking layer, was deposited by 13.56 MHz radio frequency magnetron sputtering method directly onto the anode electrode to be isolated from the electrolyte in dye-sensitized solar cells (DSCs). This is to prevent the electrons from back-transferring from the electrode to the electrolyte ($I^-/{I_3}^-$). The presented DSCs were fabricated with working electrode of F:$SnO_2$(FTO) glass coated with blocking $TiO_2$ layer, dye-attached nanoporous $TiO_2$ layer, gel electrolyte and counter electrode of Pt-deposited FTO glass. The effects of blocking layer were studied with respect to impedance and conversion efficiency of the cells. The, electrochemical impedances of DSCs using this electrode were $R_1$: 13.9, $R_2$: 15.0, $R_3$: 10.9 and $R_h$: $82{\Omega}$. The $R_2$ impedance related by electron movement from nanoporous $TiO_2$ to TCO showed lower than that of normal DSCs. The photo-conversion efficiency of prepared DSCs was 5.97% ($V_{oc}$: 0.75V, $J_{sc}$: 10.5 mA/$cm^2$, ff: 0.75) and approximately 1% higher than general DSCs sample.

• Journal of Navigation and Port Research
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• v.30 no.5 s.111
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• pp.351-356
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• 2006

In this paper, the high efficiency Doherty power amplifier has been designed and realized for microwave applications. The Doherty amplifier has been implemented using silicon MRF 281 LDMOS FET. The RF performances cf the Doherty power amplifier (a combination of a class AB carrier amplifier and a bias-tuned class C peaking amplifier) have been compared with those of a class AB amplifier alone. The realized Doherty power amplifier P1dB output power has 33dBm at 2.3GHz frequency. Also the Doherty power amplifier shows 11dB gain and -17.8dB input return loss at 2.3GHz to 2.4GHz. The designed Doherty amplifier has been improved the average PAE by 10% higher efficiency than a class AB amplifier alone. The Maximum PAE of designed Doherty power amplifier has been 39%.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37A no.12
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• pp.1013-1022
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• 2012

Tag collection is one of the major concerns in radio frequency identification(RFID) system. All tags in RFID reader's transmission range send response message back to the reader in response to collection request message on the given rf channel. When multiple tags respond simultaneously, tag-collision may occur. Tag-collision problem is one of the most important issues in active RFID performance. To mitigate this problem, frame slotted ALOHA(FSA) anti-collision protocol is widely used in active RFID system. Several studies show that the maximum system efficiency of FSA anti-collision protocol is 36.8%. In this paper, we propose an efficient slotted CSMA/CA protocol to improve tag collection performance. We compare our protocol to the FSA anti-collision protocol. For the experiment, an 433MHz active RFID system is implemented, which is composed of an RFID reader and multiple tags. We evaluated the tag collection performance using one RFID reader and 40 tags in the real test bed. The experimental result shows that proposed protocol improves the tag collection time, round and collision probability by 18%, 37.4% and 77.8%, respectively.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.48 no.5
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• pp.319-325
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• 1999

Direct current(d.c.)leakage current voltage characteristics of radio-frequencymagnetron sputtered BaTa\sub 2\O\sub 6\ film capacitors with aluminum(A1) top and indium tin oxide (ITO) bottom electrodes have been investigatedas a function of applied field and temperature. In order to study surfacetreatment effect on the electrical characteristics of as-deposited film weperformed exposure of oxygen plasma on $BaTa_2O_6$ surface. d. c.current-voltage (I-V), bipolar pulse charge-voltage (Q-V), d. c. current-time (I-t) andcapacitance-frequency (C-f) analysis were performed on films. All ofthe films exhibita low leakage current, a high breakdown field strength (3MV/cm-4.5MV/cm), and high dielectric constant (20-30). From the temperature dependence of leakage current,we can conclude that the dominant conduction mechanism is ascribed toSchottky emission at high electric field (>1MV/cm) and hopping conduction at lowelectric field (<1MV/cm). According to our results, the oxide plasma surfacetreatmenton as-deposited $BaTa_2O_6$ resulted in lowering interfacebarrier height and thus, leakage current when a negative voltage applied to the A1 electrode. This can be explained by reduction of surface contamination via etching surface and filling defects such as oxygen vacancies.

• Journal of Sensor Science and Technology
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• v.24 no.6
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• pp.379-384
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• 2015

An infrared image sensor is a core device in a thermal imaging system. The fabrication method of a focal plane array (FPA) is a key technology for a high resolution infrared image sensor. Each pixels in the FPA have $Si_3N_4/SiO_2$ membranes including legs to deposit bolometric materials and electrodes on Si readout circuits (ROIC). Instead of polyimide used to form a sacrificial layer, the feasibility of an amorphous silicon (${\alpha}-Si$) was verified experimentally in a $8{\times}8$ micro-bolometer array with a $50{\mu}m$ pitch. The elimination of the polyimide sacrificial layer hardened by a following plasma assisted deposition process is sometimes far from perfect, and thus requires longer plasma ashing times leading to the deformation of the membrane and leg. Since the amorphous Si could be removed in $XeF_2$ gas at room temperature, however, the fabricated micro-bolomertic structure was not damaged seriously. A radio frequency (RF) sputtered nickel oxide film was grown on a $Si_3N_4/SiO_2$ membrane fabricated using a low stress silicon nitride (LSSiN) technology with a LPCVD system. The deformation of the membrane was effectively reduced by a combining the ${\alpha}-Si$ and LSSiN process for a nickel oxide micro-bolometer.

• Journal of Sensor Science and Technology
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• v.20 no.2
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• pp.131-136
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• 2011

In this study, a compact wireless vibration measurement system was developed using a 3-axial accelerometer in order to evaluate the vibration stimulation system. A low power microprocessor chip integrated with 2.4 GHz RF transceiver was used for the wireless data communication. To evaluate the system, the frequencies and accelerations from the vibration stimulation system were measured using an LVDT sensor and a vibration measurement system. The average frequency difference by the measurement system was less than 0.1 Hz, and the standard deviation of frequencies estimated by the LVDT sensor and the accelerometer was below 0.08 Hz. The developed system was applied to access a vibration stimulation system for the future study. The average acceleration difference of the central and peripheral point of the stimulation system was less than 0.0005 g(1 g=9.8 $m/s^2$), and the standard deviation of the acceleration was below 0.004 g, which shows the usefulness of the wireless vibration measurement system.

• Journal of Electrical Engineering and Technology
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• v.9 no.5
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• pp.1654-1659
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• 2014

Tunneling field-effect transistors (TFETs) are very applicable to low standby-power application by their virtues of low off-current ($I_{off}$) and small subthreshold swing (S). However, low on-current ($I_{on}$) of silicon-based TFETs has been pointed out as a drawback. To improve $I_{on}$ of TFET, a gate-all-around (GAA) TFET based on III-V compound semiconductor with InAs/InGaAs/InP multiple-heterojunction structure is proposed and investigated. Its performances have been evaluated with the gallium (Ga) composition (x) for $In_{1-x}Ga_xAs$ in the channel region. According to the simulation results for $I_{on}$, $I_{off}$, S, and on/off current ratio ($I_{on}/I_{off}$), the device adopting $In_{0.53}Ga_{0.47}As$ channel showed the optimum direct-current (DC) performance, as a result of controlling the Ga fraction. By introducing an n-type InGaAs thin layer near the source end, improved DC characteristics and radio-frequency (RF) performances were obtained due to boosted band-to-band (BTB) tunneling efficiency.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2006.06b
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• pp.91-96
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• 2006

In this paper, the high efficiency Doherty power amplifier has been designed and realized for microwave applications. The Doherty amplifier has been implemented using silicon MRF 281 LOMOS FET. The RF performances of the Doherty power amplifier (a combination of a class AB carrier amplifier and a bias..tuned class C peaking amplifier) have been compared with those of a class AB amplifier alone. The realized Doherty power amplifier PldB output power has 33dBm at 2.3GHz frequency. Also the Doherty power amplifier shows 11dB gain and -17.8dB input return loss at 2.3GHz to 2.4GHz. The designed Doherty amplifier has been improved the average PAE by 10% higher efficiency than a class AB amplifier alone. The Maximum PAE of designed Doherty power amplifier has been 39%.