• Journal of the Institute of Electronics Engineers of Korea SD
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• v.45 no.11
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• pp.21-28
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• 2008

In this paper, we suggest an analytical model that can derive the I-V characteristics in the saturation region of a short channel GaAs MESFET. Instead of the pinch-off concept that has been used in the conventional models we can derive the two-dimensional potential in the depletion region in order that the velocity saturation region cannot be pinched-off and the current continuity condition can be satisfied. Obtained expression for the velocity saturation length is expressed in terms of the total channel length, channel doping density, gate voltage, and drain voltage. Compared with the conventional channel length shortening models, the present model seems to be considerably accurate and more reasonable in explaining the Early effect.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.257-257
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• 2016

최근에 메모리의 초고속화, 고집적화 및 초절전화가 요구되면서 resistive random access memory (ReRAM), ferroelectric RAM (FeRAM), phase change RAM (PRAM)등과 같은 차세대 메모리 기술이 활발히 연구되고 있다. 다양한 메모리 중에서 특히 resistive random access memory (ReRAM)는 빠른 동작 속도, 낮은 동작 전압, 대용량화와 비휘발성 등의 장점을 가진다. ReRAM 소자는 절연막의 저항 스위칭(resistance switching) 현상을 이용하여 동작하기 때문에 SiOx, AlOx, TaOx, ZrOx, NiOx, TiOx, 그리고 HfOx 등과 같은 금속 산화물에 대한 연구들이 활발하게 이루어지고 있다. 이와 같이 다양한 산화물 중에서 AlOx는 ReRAM의 절연막으로 적용되었을 때, 우수한 저항변화특성과 안정성을 가진다. 하지만, AlOx 박막을 형성하기 위하여 기존에 많이 사용되어지던 PVD (physical vapour deposition) 또는 CVD (chemical vapour deposition) 방법에서는 두께가 균일하고 막질이 우수한 박막을 얻을 수 있지만 고가의 진공장비 사용 및 대면적 공정이 곤란하다는 문제점이 있다. 한편, 용액 공정 방법은 공정과정이 간단하여 경제적이고 대면적화가 가능하며 저온에서 공정이 이루어지는 장점으로 많은 관심을 받고 있다. 본 연구에서는 sputtering 방법과 용액 공정 방법으로 형성한 AlOx 기반의 ReRAM에서 메모리 특성을 비교 및 평가하였다. 먼저, p-type Si 기판 위에 습식산화를 통하여 SiO2 300 nm를 성장시킨 후, electron beam evaporation으로 하부 전극을 형성하기 위하여 Ti와 Pt를 각각 10 nm와 100 nm의 두께로 증착하였다. 이후, 제작된 AlOx 용액을 spin coating 방법으로 1000 rpm 10 초, 6000 rpm 30 초의 조건으로 증착하였다. Solvent 및 불순물 제거를 위하여 $180^{\circ}C$의 온도에서 10 분 동안 열처리를 진행하였고, 상부 전극을 형성하기 위해 shadow mask를 이용하여 각각 50 nm, 100 nm 두께의 Ti와 Al을 electron beam evaporation 방법으로 증착하였다. 측정 결과, 용액 공정 방법으로 형성한 AlOx 기반의 ReRAM에서는 기존의 sputtering 방법으로 제작된 ReRAM에 비해서 저항 분포가 균일하지는 않았지만, 103 cycle 이상의 우수한 endurance 특성을 나타냈다. 또한, 1 V 내외로 동작 전압이 낮았으며 104 초 동안의 retention 측정에서도 메모리 특성이 일정하게 유지되었다. 결론적으로, 간단한 용액 공정 방법은 ReRAM 소자 제작에 많이 이용될 것으로 기대된다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.11
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• pp.1272-1280
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• 2008

In this paper, we have proposed a phase noise model of fast frequency hopping synthesizer with DDS Driven PLL architecture. To accurately model the phase noise contribution of noise sources in frequency hopping synthesizer, they were investigated using model of digital divider for PLL, DAC for DDS and Leeson's model for reference oscillator and VCO. Especially it was proposed that the noise component of low pass filter was considered together with the phase noise of VCO. Under assuming linear operation of a phase locked loop, the phase noise transfer functions from noise sources to the output of synthesizer was analyzed by superposition theory. The proposed phase noise prediction model was evaluated and its results were compared with measured data.

• Journal of Energy Engineering
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• v.29 no.3
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• pp.97-102
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• 2020

In this study, one-way fluid structure interaction analysis was adapted to verify the durability of the outdoor evacuation stair structure operated in the event of a fire when wind pressure caused by a typhoon was applied. To this end, flow analysis was performed with the flow field around the structure of the evacuation stair in a steady state, and the durability was analyzed through structural analysis such as structural stress, deformation, and fatigue life using these analysis results by fluid data input data for structural analysis. As a result of flow numerical analysis, the air flow was different according to the shape of the evacuation stair structure, and this flow velocity distribution generated by the total pressure on the structure surface. Through the structural analysis results calculated by this total pressure, the safety factor calculated as the maximum stress value was found to be more than the safety factor, and durability was proven by fatigue life and deformation analysis.

• Journal of the Korean Vacuum Society
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• v.14 no.1
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• pp.29-34
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• 2005

The degradation of the SiGe hetero-junction bipolar transistor(HBT) properties in SiGe BiCMOS process was investigated in this paper. The SiGe HBT prepaired by SiGe BiCMOS process, unlike the conventional one, showed the degraded DC characteristics such as the decreased Early voltage, the decreased collector-emitter breakdown voltage, and the highly increased base leakage current. Also, the cutoff frequency(f/sub T/) and the maximum oscillation frequency(f/sub max/) representing the AC characteristics are reduced to below 50%. These deteriorations are originated from the change of the locations of emitter-base and collector-base junctions, which is induced by the variation of the doping profile of boron in the SiGe base due to the high-temperature source-drain annealing. In the result, the junctions pushed out of SiGe region caused the parastic barrier formation and the current gain decrease on the SiGe HBT device.

• Journal of the Korean Magnetics Society
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• v.18 no.2
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• pp.79-83
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• 2008

We have investigated the effect of the formation of an initial oxide layer on the fabrication of the porous aluminium oxide. The porous aluminium oxide was fabricated by two-step anodization process with a electropolished aluminium foil. Before the first anodization step, the initial oxide layer with thickness of 10 nm was formed under the applied voltage of 1 V and later the anodization was continued under 40 V using oxalic acid solution. With the formation of the initial oxide layer, the anodization process was stable and the anodization current was constant throughout the process. In case of the absence of the initial oxide layer, the anodization was very unstable and the continuous increase in the anodization current was observed. This indicates the formation of the initial oxide layer on the aluminium surface prevents the burning of the surface due to the nonuniform distribution of the applied electric field, and allows the stable anodization process required for the porous aluminium oxide.

• Journal of Sensor Science and Technology
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• v.10 no.3
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• pp.196-206
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• 2001

Real temperature profiles of a planar chromel-alumel mutli-junction thermal converter(TC 1) were measured by thermal image. Temperature profiles as a function of input power of thermal converters(TC 1${\sim}$TC 6) were simulated by 3-dimensional ANSYS program based on finite element method. Temperature difference between the hot junction and the cold junction for TC 1 was smallest and largest for TC 6 and correspondingly, he voltage response for TC 1 and TC 6 showed the smallest value of 3.09 mV/mW and the largest value of 4.03 mV/mW, respectively.

• Journal of the Korean Institute of Gas
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• v.12 no.4
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• pp.63-68
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• 2008

This paper describes about the simulation and the experimental results of optical cavity with curved mirror surface and vertical mirror surface to improve the light intensity and efficiency of the optical sensors. When we use the vertical mirror surface, the distribution of light reached to the filter surface of detector shows an elliptical shape. Whereas, the curved mirror surface focuses the light into circular shape. Therefore, due to focusing effects in case of using curved mirror surface, the light intensity per unit area has been improved. Consequently, the output voltage of gas sensor has been expected to increase. Based upon the simulation, the experiment of gas sensor has been conducted with $CO_2$ gas from 0ppm to 2,500 ppm at 250 ppm step and $25^{\circ}C$, 45%R.H. ambient. The output voltage of gas sensor that has a curved mirror surface increases approximately 200 mV than that of vertical mirror surface.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.2
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• pp.75-80
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• 2006

In this paper, to detect and observation the void discharges pulse signal, AE signals and tree growth characteristics in case the high voltage is applied to a XLPE sample for a power cable. We also examined the partial discharge current pulse and AE signals with the increase of the applied voltage in XLPE insulation. The experimental results show that a branch-type tree grows in the presence of the voids, and a bush-type tree grows in the absence of the voids in both samples. A rate of tree growth increases abruptly in proportional to the deterioration time in the presence of the of the voids, but in the absence of the voids, a rate of tree growth decreases as time goes by and finally a breakdown occurs. The frequency band of AE signals that are generated from the partial discharges in a XLPE sample, one of solid dielectric materials, is about 1.0[MHz].

• Journal of Korean Society of Environmental Engineers
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• v.28 no.6
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• pp.634-639
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• 2006

The simulation of electric field distribution of discharge tube with globular $Al_2O_3$ and the removal characteristic of Escherichia coli by the discharge tube with globular $Al_2O_3$ were estimated. The removal characteristic of Escherichia coli was related to the input voltage because the electric field is increased according to input voltage. As the passing amount of test water in discharge tube is increased, the removal ratio of Escherichia coli was increased because passing numbers of electric field section is increased. As the particle size of globular $Al_2O_3$ increased, the removal time of Escherichia coli was shortened due to the dielectric polarization of globular dielectric $Al_2O_3$. Also, the removal efficiency of Escherichia coli for the discharge tube with globular dielectric $Al_2O_3$ was higher than that of the discharge tube without it.