• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.50-50
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• 2009

In this paper, the plasma doping is performed on p-type wafers using $PH_3$ gas(10 %) diluted with He gas(90 %). The wafer is placed in the plasma generated with 200 W and a negative DC bias (1 kV) is applied to the substrate for 60 sec under no substrate heating. the flow rate of the diluted $PH_3$ gas and the process pressure are 100 sccm and 10 mTorr, respectively. In order to diffuse and activate the dopant, annealing process such as rapid thermal annealing (RTA) is performed. RTA process is performed either in $N_2$, $O_2$ or $O_2+N_2$ ambient at $900{\sim}950^{\circ}C$ for 10 sec. The sheet resistance is measured using four point probe. The shallow n+/p doping profiles are investigated using secondary ion mass spectromtry (SIMS). The analysis of crystalline defect is also done using transmission electron microscopy (TEM) and double crystal X-ray diffraction (DXRD).

• JSTS:Journal of Semiconductor Technology and Science
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• v.14 no.5
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• pp.682-687
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• 2014

We have performed reverse gate bias stress tests on AlGaN/GaN-on-Si Heterostructure FETs (HFETs). The shift of threshold voltage ($V_{th}$) and the reduction of on-current were observed from the stressed devices. These changes of the device parameters were not permanent. We investigated the temporary behavior of the stressed devices by analyzing the temperature dependence of the instabilities and TCAD simulation. As the baseline temperature of the electrical stress tests increased, the changes of the $V_{th}$ and the on-current were decreased. The on-current reduction was caused by the positive shift of the $V_{th}$ and the increased resistance of the gate-to-source and the gate-to-drain access region. Our experimental results suggest that electron-trapping effect into the shallow traps in devices is the main cause of observed instabilities.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.05b
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• pp.7-11
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• 2002

In this study, Au thin films were etched with a $Cl_2/Ar$ gas combination in an in an inductively coupled plasma. The etch properties were measured for different gas mixing ratios of $Cl_2/(Cl_2+Ar)$ while the other process conditions were fixed at rf power (700 W), dc bias voltage (150 V), and chamber pressure (15 mTorr). The highest etch rate of the Au thin film was 3500 $\AA/min$ and the selectivity of Au to $SiO_2$ was 4.38 at a $Cl_2/(Cl_2+Ar)$ gas mixing ratio of 0.2. The surface reaction of the etched Au thin films was investigated using x-ray photoelectron spectroscopy (XPS) analysis. There is Au-Cl bonding by chemical reaction between Cl and Au. During the etching of Au thin films in $Cl_2/Ar$ plasma, Au-Cl bond is formed, and these products can be removed by the physical bombardment of Ar ions. In addition, Optical emission spectroscopy (OES) were investigated to analyze radical density of Cl and Ar in plasma. The profile of etched Au investigated with scanning electron microscopy (SEM).

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.40 no.10
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• pp.103-109
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• 2003

We have proposed the 4-Dimensional Multiple-Subcarrier Modulation with fixed bias in Optical Wireless Communications. Here, the 4-D signal vectors are derived from the optimization technique of signal waveforms maximizing the minimum distance between signal points in an n-dimensional Euclidean sphere. The resulting vectors are used in generating the output amplitude of impulse generator in a Multiple-Subcarrier Modulation scheme. We have achieved that the normalized power requirement of the proposed system is maximum 3 dB and 3.3 dB smaller than those of normal QPSK, Reserved Subcarrier, and Minimum Power scheme, respectively. Also, in the range of 1.125 ∼ 1.25 of the normalized bandwidth, the proposed system has maximum 3 dB, 2 ∼ 4 dB, 0 ∼ 3 dB smaller bandwidth requirement compare to normal QPSK, Res. Subcarrier, Min. Power schemes, respectively.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2004.06a
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• pp.32-42
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• 2004

Recently, plasma surface-cleaning or surface-etching techniques have been focused in respect of the decontamination of spent or used nuclear parts and equipment. In this study the removal rate of metallic cobalt surface is experimentally investigated via its surface etching rate with a $CF_4-o_2$mixed gas plasma. Experimental results reveal that a mixed etchant gas with about 80% $CF_4$-20% $O_2$ (molar) gives the highest reaction rate and the rate reaches 0.06 ${\mu}m$/min at $380^{\circ}C$ and ion-assisted etching dramatically enhances the surface reaction rate. With a negative 300 V DC bias voltage applied to the substrate, the surface reaction initiation temperature lowers and the rate increases about 20 times at $350^{\circ}C$ and up to 0.43 ${\mu}m$/min at $380^{\circ}C$, respectively. Surface morphology analysis confirms the etching rate measurements. Auger spectrum analysis clearly shows the adsorption of fluorine atoms on the reacted surface. From the current experimental findings and the results discussed in previous studies, mechanistic understanding of the surface reaction, fluorination and/or fluoro-carbonylation reaction, is provided.

• Korean Journal of Materials Research
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• v.25 no.9
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• pp.450-454
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• 2015

A simulation method to estimate microstructure dependent material properties and their influence on performance for a honeycomb structured SiC heating element has been established. Electrical and thermal conductivities of a porous SiC sample were calculated by solving a current continuity equation. Then, the results were used as input parameters for a finite element analysis package to predict temperature distribution when the heating element was subjected to a DC bias. Based on the simulation results, a direction of material development for better heating efficiency was found. In addition, a modified metal electrode scheme to decelerate corrosion kinetics was proposed, by which the durability of the water heating system was greatly improved.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1420-1421
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• 2011

비정질 IGZO 박막 트랜지스터에 포지티브 직류/교류 게이트 바이어스를 인가하여 신뢰성을 분석하고 비정질 IGZO 박막 트랜지스터의 신뢰성을 고려한 시프트 레지스터 회로를 설계하였다. 비정질 IGZO 박막 트랜지스터의 문턱전압은 바이어스 스트레스가 인가되었을 때 양의 방향으로 이동하였고, 전류가 감소하였다. 또한 문턱전압은 직류 바이어스 스트레스가 인가되었을 때 교류 바이어스 스트레스가 인가 되었을 때 보다 더 양의 방향으로 이동하였다. 총 8개의 박막 트랜지스터로 구성된 일반적인 시프트 레지스터 회로에서는 특정 박막 트랜지스터에 직류 바이어스 스트레스가 걸리기 때문에 비정질 IGZO 박막 트랜지스터를 이용하여 구동할 때 회로 오동작을 유발할 수 있다. 비정질 IGZO 박막 트랜지스터의 신뢰성 결과를 고려하여 총 9개의 박막 트랜지스터로 구성된 교류 동작하는 시프트 레지스터 회로를 설계하였다. 모든 소자에 직류 바이어스 스트레스가 걸리지 않도록 회로를 설계하였으며, 추가된 트랜지스터의 채널 너비가 매우 작기 때문에 트랜지스터가 하나 추가되어도 회로가 차지하는 면적에는 거의 변화가 없다. 바이어스 스트레스에 따른 소자 열화를 고려하여 시뮬레이션을 해 본 결과 일반적인 회로에서는 회로 오동작이 관측된 반면, 제안한 회로에서는 문제없이 동작하는 것을 확인하였다.

• Journal of electromagnetic engineering and science
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• v.16 no.4
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• pp.199-205
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• 2016

We present a novel schematic using a 3-dB coupler to transmit radiofrequency (RF) power to two receivers selectively. Whereas previous multiple receiver supporting schemes used hardware-switched methods, our scheme uses a soft power-allocating method, which has the advantage of variable power allocation in real time to each receiver. Using our scheme, we can split the charging area and focus the RF power on the targeted areas. We present our soft power-allocating method in three main points. First, we propose a new power distribution hardware structure using a FPGA (field-programmable gate array) and a 3-dB coupler. It can reconfigure the transmitting power to two receivers selectively using accurate FPGA-controlled signals with the aid of software. Second, we propose a power control method in our platform. We can variably control the total power of transmitter using the DC bias of the drain input of the amplifier. Third, we provide the possibility of expansion in multiple systems by extending these two wireless power transfer systems. We believe that this method is a new approach to controlling power amplifier output softly to support multiple receivers.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.3
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• pp.566-570
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• 2007

The specific electrical, optical and acoustic properties of Zinc Oxide (ZnO) are important for semiconductor process which has many various applications. Piezoelectric ZnO films has been widely used for such as transducers, bulk and surface acoustic-wave resonators, and acousto-optic devices. In this study, we investigated etch characteristics of ZnO thin films in inductively coupled plasma etch system with $BCl_3/Ar$ gas mixture. The etching characteristics of ZnO thin films were investigated in terms of etch rates and selectivities to $SiO_2$ as a function of $BCl_3/Ar$ gas mixing ratio, RF power, DC bias voltage and process pressure. The maximum ZnO etch rate of 172 nm/min was obtained for $BCl_3$ (80%)/Ar(20%) gas mixture. The chemical states on the etched surface were investigated with X-ray photoelectron spectroscopy (XPS).

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2000.11a
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• pp.40-44
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• 2000

In this paper, since the research on the etching of SrBi$_2$Ta$_2$O$_{9}$ (SBT) thin film was few (specially Cl$_2$-base ), we had studied the surface reaction of SBT thin films using the OES in high density plasma etching as a function of rf power, dc bias voltage, and Cl$_2$/(C1$_2$+Ar) gas mixing ratio. It had been found that the etch rate of SBT thin films appeared to be more affected by the physical sputtering between Ar ions and surface of the SBT compared to the chemical reaction in our previous papers$^{1.2}$ . The change of Cl radical density that is measured by the OES as a function of gas combination showed the change of the etch rate of SBT thin films. Therefore, the chemical reactions between Cl radical in plasma and components of the SBT enhance to increase the etch rates of SBT thin films and these results were confirmed by XPS analysis.