• Nanomaterials
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• v.11 no.2
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• pp.494-503
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• 2021

Interface traps between a gate insulator and beta-gallium oxide (β-Ga₂O₃) channel are extensively studied because of the interface trap charge-induced instability and hysteresis. In this work, their effects on mobility degradation at low temperature and hysteresis at high temperature are investigated by characterizing electrical properties of the device in a temperature range of 20-300 K. As acceptor-like traps at the interface are frozen below 230 K, the hysteresis becomes negligible but simultaneously the channel mobility significantly degrades because the inactive neutral traps allow additional collisions of electrons at the interface. This is confirmed by the fact that a gate bias adversely affects the channel mobility. An activation energy of such traps is estimated as 170 meV. The activated trap charges' trapping and de-trapping processes in response to the gate pulse bias reveal that the time constants for the slow and fast processes decrease due to additionally activated traps as the temperature increases.

• Journal of the Korea Institute of Military Science and Technology
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• v.7 no.1
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• pp.34-46
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• 2004

Copper films were prepared by using ECR-MOCVD(Electron Cyclotron Resonance Metal Organic Chemical Vapor Deposition) coupled with a DC bias system. The DC bias is connected to the electrode which placed 1∼3cm above the polymer substrate. The pulse electrical field around the electrode attracts the positive charged copper ions generated from the dissociation of copper precursor, $Cu(hfac)_2$, under ECR plasma. Condensation of supersaturated copper ions in the space between the electrode and substrate, makes it possible to deposit copper film on the polymer substrate even at room temperature. In this study, optimization of the electrode configuration was carried out in order to obtain the uniform films. The uniformity of the deposited films were closely related to the parameters of electrode geometry such as electrode shape, thickness, grid size and the spacing between electrodes. The most uniform copper film was observed with the electrode that enabled uniform electrical field distribution across the whole dimension of electrode.

• Journal of Astronomy and Space Sciences
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• v.25 no.4
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• pp.481-490
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• 2008

Reaction wheel is one of the actuators for spacecraft attitude control, which generates torque by changing an inertial rotor speed inside of the wheel. In order to generate required torque accurately and estimate an accurate angular momentum, wheel speed should be measured as close to the actual speed as possible. In this study, two conventional speed detection methods for high speed motor with digital tacho pulse (Elapsed-time method and Pulse-count method) and their resolutions are analyzed. For satellite attitude maneuvering and control, reaction wheel shall be operated in bi directional and low speed operation is sometimes needed for emergency case. Thus the bias error at low speed with constant acceleration (or deceleration) is also analysed. As a result, the speed detection error of elapsed-time method is largely influenced upon the high-speed clock frequency at high speed and largely effected on the number of tacho pulses used in elapsed time calculation at low speed, respectively.

• Korean Journal of Materials Research
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• v.25 no.11
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• pp.616-621
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• 2015

Atmospheric pressure plasma is used in the biological and medical fields. Miniaturization and safety are important in the application of apply atmospheric plasma to bio devices. In this study, we made a small, pocket-sized inverter for the discharge of atmospheric plasma. We used pulse power to control the neutral gas temperature at which the, when plasma was discharged. We used direct current of 5 V of bias(voltage). The output voltage is about 1 to 2 kilo volts the frequency is about 80 kilo hertz. We analyzsed the characteristics of the atmospheric plasma using OES(Optical emission spectroscopy) and the Current-Voltage characteristic of pulse power. By calculating of the current voltage characteristics, we were able to determine that, when the duty ratio increased, the power that actually effects the plasma discharge also increased. To apply atmospheric plasma to human organisms, the temperature is the most important factor, we were able to control the temperature by modulating the pulse power duty ratio. This means we can use atmospheric plasma on the human body or in other areas of the medical field.

• 전기의세계
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• v.26 no.3
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• pp.76-83
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• 1977

The choice of control method and circuit must be decided after a broad inspection with the characteristics of load and control elements as well as that of electric and mechanical nature. In the present study, Pulse width modulated(PWM) SCR chopper was chosen and for the electric commutation, Jones' forced method was taken bacause of its having enough reverse bias energy. Objectives of experimentation by this system are; 1) the condition of SCR as a gate trigger pulse. 2) the observation of phenomena at the time of forced commutation 3) the experimentation on characteristics of speed control by PWM chopper. Above experimentation shows good characteristics, however, in the limit of narrow gap between the ON and OFF pulses, a complete control was not possible. So, that must be the point to be studied further alone with the harmonics influence.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.1947-1950
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• 2008

Printing technology is a very useful method in the several process of industrial fabrication due to noncontact and fast pattern generation. To make micro pattern, we investigate the electrostatic induced inkjet printer head for micro droplet generation and drop-on-demand jetting. In order to achieve the drop-on-demand micro droplet ejection by the electrostatic induced inkjet printer head, the pulsed DC voltage is supplied. In order to find optimal pulse conditions, we tested jetting performance for various bias and pulse voltages for drop-on-demand ejection. In this result, we have successful drop-on-demand operation and micro patterning. Therefore, our novel electrostatic induced inkjet head printing system will be applied industrial area comparing conventional printing technology.

• Nuclear Engineering and Technology
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• v.46 no.3
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• pp.387-394
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• 2014

A Slowing Down Time Spectrometer (SDTS) system is a highly efficient technique for isotopic nuclear material content analysis. SDTS technology has been used to analyze spent nuclear fuel and the pyro-processing of spent fuel. SDTS requires an external neutron source to induce the isotopic fissile fission. A high intensity neutron source is required to ensure a high for a good fissile fission. The electron linear accelerator system was selected to generate proper source neutrons efficiently. As a first step, the electron generator of an 80-keV electron gun was manufactured. In order to produce the high beam power from electron linear accelerator, a proper beam current is required form the electron generator. In this study, the beam current was measured by evaluating the performance of the electron generator. The beam current was determined by five parameters: high voltage at the electron gun, cathode voltage, pulse width, pulse amplitude, and bias voltage at the grid. From the experimental results under optimal conditions, the high voltage was determined to be 80 kV, the pulse width was 500 ns, and the cathode voltage was from 4.2 V to 4.6 V. The beam current was measured as 1.9 A at maximum. These results satisfy the beam current required for the operation of an electron linear accelerator.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.12
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• pp.2173-2178
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• 2007

Dynamics of plasma sheath was analyzed using simple ion fluid model with poison equation. Incident ion current, energy, potential distribution and space charge density profile were calculated as a function of time. The effects of initial floating sheath on the evolution of biased sheath were compared with ideal matrix sheath. The effects of finite rising time of pulse bias voltage on the ion current and energy was studied. The influence of surface charging on the evolution of sheath was also investigated

• Journal of the Korean Institute of Telematics and Electronics
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• v.27 no.4
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• pp.612-619
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• 1990

In this paper, a design method of optical FSK transmitter is described using LD-FM circuit model. In the design of optical FSK transmitter, an optimum bias current was chosen using LD-FM circuit model, and an unequalized FM transfer function was determined at this current. The equalizers that can make this transfer function uniform were designed by use of a simple passive network. For the designed optical FSK transmitter, the pulse-transient and small-signal frequency-deviation responses were simulated and discussed.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.307-307
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• 2013

초고집적 회로에 적용되는 반도체 소자의critical dimension (CD)이 수 nano 사이즈로 줄어들고 있기 때문에, 다양한 물질의 식각을 할 때, 건식식각의 중요성이 더 강조되고 있다. 특히 $SiO_2$와 같은 유전체 물질을 식각할 때, plasma process induced damages (P2IDs)가 관찰되어 왔고, 이러한 P2IDs를 줄이기 위해, pulsed-time modulation plasma가 광범위하게 연구되어 왔다. Pulsed plasma는 정기적으로 radio frequency (RF) power on과 off를 반복하여 rf power가 off된 동안, 평균전자 온도를 낮춤으로써, 웨이퍼로 입사되는 전하 축적을 효과적으로 줄일 수 있다. 또한 fluorocarbon plasmas를 사용하여 $SiO_2$를 식각하기 위해 Dual-Frequency Capacitive coupled plasma (DF-CCP)도 널리 연구되어 왔는데, 이것은 기존의 방법과는 다르게 plasma 밀도와 ion bombardment energy를 독립적으로 조절 가능하다는 장점이 있어서 미세 패턴을 식각할 때 효과적이다. 본 연구에서는 Source power에는 60 MHz pulsed radio frequency (RF)를, bias power에는 2 MHz continuous wave (CW) rf power가 사용된 system에서 Ar/$C_4$ F8/$O_2$ 가스 조합으로, amorphous carbon layer (ACL)가 hard mask로 사용된 $SiO_2$를 식각했다. 그리고 source pulse의 duty ratio와 pulse frequency의 효과에 따른 $SiO_2$의 식각특성을 연구하였다. 그 결과, duty ratio의 감소에 따라 $SiO_2$, ACL의 etch rate이 감소했지만, $SiO_2$/ACL의 etch selectivity는 증가하였다. 반면에 pulse frequency의 변화에 따른 두 물질의 etch selectivity는 크게 변화가 없었다. 그 이유는 pulse 조건인 duty ratio의 감소가 전자 온도 및 전자 에너지를 낮춰 $C_2F8$가스의 분해를 감소시켰으며, 이로 인해 식각된 $SiO_2$의 surface와 sidewall에 fluorocarbon polymer의 형성이 증가하였기 때문이다. 또한 duty ratio의 감소에 따라 etch selectivity뿐만 아니라 etch profile까지 향상되는 것을 확인할 수 있었다.