• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.10
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• pp.2237-2246
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• 2012

A bias circuit required for an oral sensor is manufactured inside the oral sensor chip to reduce its size and cost. The proposed DC-DC converter supplies the required reference and bias currents for their corresponding regulators by using IREF of the reference current generator. Their target voltages of the voltage regulators are regulated by the negative mechanism by generating their reference voltages required for their corresponding regulators. In addition, a constant current IB0/IB1 is supplied by being mirrored by a current mirror ratio and then VREF is generated. It is confirmed by measurements that the average volatge, ${\sigma}$, and $4{\sigma}$ of the designed DC-DC converter for intra oral sensors with a $0.18{\mu}m$ X-ray CMOS process are within their required ranges. And the line-pair pattern image shows a high-resolution characteristic without blurring. Also, a good oral image can be obtained.

• Journal of the Korean Vacuum Society
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• v.8 no.3B
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• pp.346-352
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• 1999

Diamond-like carbon (DLC) lims were deposited by using end hall type ion gun. Benzene gas was used for the generation of carbon ions. In order to systematically control the ion energy, we applied to the substrate DC, pulsed DC or 250 kHz medium frequency bias voltage, DLC films of superior mechanical properties of hardness 39$\pm$4 GPa and elastic mudulus 290$\pm$50GPa (2 to 6 times better than those of the films deposited by plasma assisted CVD method) could be obtained. Deposition rate was much higher than when using Kaufman type ion source, which results from higher ion beam current of end hall type ion gun. The mechanical properties and atomic bond structure were independent of the bias voltage type ion gun. The mechanical properties and atomic bond structure were independent of the bias voltage type but intimately related with the magnitude of the bias voltage. With increasing the negative bias voltage, the structure of the films changed to graphitic one resulting in decreased content of three dimensional inter-links. Degradation of the mechanical properties with increasing bias voltage could be thus understood in terms of the content odf three dimensional inter-links.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2002.02a
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• pp.109-110
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• 2002

The purpose of a superconductive DC/SFQ circuit is to produce a controlled number of picosecond single flux quantum pulses at the output when a slowly changing DC current is applied to the input. In this work, we have designed and simulated a DC/SFQ circuit based on Nb/Al$O_{x}$/Nb Josephson junction technology. From the simulation, we could obtain the margins for various circuit parameters. And also we have successfully operated a DC/SFQ circuit which was fabricated with the same design. The margin for the input bias current of the circuit was observed to be of $\pm$60%, which was very close to the simulated value.

• Transactions on Electrical and Electronic Materials
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• v.9 no.6
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• pp.260-264
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• 2008

The operational characteristics of superconducting amplifier using vortex flux flow were analyzed from an equivalent circuit in which its current-voltage characteristics for the vortex motion in YBCO microbridge were reflected. For the analysis of operation as an amplifier, dc bias operational point for the superconducting amplifier is determined and then ac operational characteristics for the designed superconducting amplifier were investigated. The variation of transresistance, which describes the operational characteristics of superconducting amplifier, was estimated with respect to conditions of dc bias. The current and the voltage gains, which can be derived from the circuit for small signal analysis, were calculated at each operational point and compared with the results obtained from the numerical analysis for the small signal circuit. From our paper, the characteristics of amplification for superconducting flux flow transistor (SFFT) could be confirmed. The development of the superconducting amplifier applicable to various devices is expected.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2018.10a
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• pp.35-38
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• 2018

This paper describes a low-power MPPT interface for DC-type energy harvesting sources. The proposed circuit consists of an MPPT controller, a bias generator, and a voltage detector. The MPPT controller consists of an MPG (MPPT Pulse Generator) with a schmitt trigger, a logic gate operating according to energy type (light, heat), and a sample/hold circuit. The bias generator is designed by employing a beta multiplier structure, and the voltage detector is implemented using a bulk-driven comparator and a two-stage buffer. The proposed circuit is designed with $0.35{\mu}m$ CMOS process. The simulation results show that the designed circuit consumes less than 100nA of current at an input voltage of less than 3V and the maximum power efficiency is 99.7%. The chip area of the designed circuit is $1151{\mu}m{\times}940{\mu}m$.

• Progress in Superconductivity and Cryogenics
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• v.14 no.4
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• pp.36-40
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• 2012

This paper presents an experimental and numerical study on current limiting characteristics of a fault current controller (FCC). The FCC consists of an AC/DC power converter, a superconducting coil, and a control unit. Even though some previous researches proved that the FCC could adjust the fault current level, the current limiting characteristics by the superconducting coil should be investigated for design of the coil. In this paper, four kinds of model coils were tested; 1) air core, 2) iron core without any bias, 3) reversely magnetized core (RMC) using permanent magnets, and 4) RMC using an electromagnet. Based on a comparative study, it is confirmed that a RMC by an electromagnet (EM) could increase the effective inductance of the coil. In this paper, a numerical code to simulate the HTS coil with RMC was developed. This code can be applied to design the HTS coil with active reversely magnetized bias coil.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2002.02a
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• pp.127-130
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• 2002

Step-edge dc SQUID magnetometers have been fabricated on sapphire substrate. Ce$O_{2}$ buffer layer and $YBa_{2}$$Cu_{3}$ $O_{7}$(YBCO) films were deposited in-situ on the low angle (~$35^{\circ}$)steps formed on the substrates. Typical 5-$\mu$m-wide junction has $R_{N}$ of 4 $\Omega$ and $I_{c}$ of 60 $\mu$A with $I_{c}$$R_{N}$ product of 240 $\mu$V at 77 K. According to applied bias current, depth of voltage modulation was changed and maximum voltage was measured 100~300 fT/$\checkmark$ Hz at 100 Hz, and about 1.5 pT/$\checkmark$ Hz at 1 Hz. For ac bias reversal method, field noise was decreased in the 1/f region. The QRS peak of magneto-cardiogram was measured 50 pT in the magnetically shielded room.

• Proceedings of the KIEE Conference
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• 1995.07c
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• pp.1078-1080
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• 1995

The pulsed electro-acoustic method was used as a nondestructive measurement technique of spare charge distribution in dielectric materials. In our work presented here, we measured simultaneously the space charge distribution and conduction current in the low-density polyethylene samples with elevated temperatures up to $80^{\circ}C$ and electric field up to 20kV/mm. In the temperature less than $50^{\circ}C$, homocharges are mainly accumulated close to the electrodes under DC bias and after grounding. At the temperature exeeds $50^{\circ}C$, heterocharges are accumulated near the opposite electrode under DC bias. However after grounding the upper electrode, this charges immediately disappeared. The conduction current in LDPE at $20^{\circ}C$ and $30^{\circ}C$ was reduced slowly with increasing interval of applied voltage. But as temperature increased, the conduction current tended to increase slowly with the time and the degree of increase is enlarged.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.4
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• pp.367-372
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• 2002

The vertically well-aligned carbon nanotubes(CNTs) were successfully grown on Ni coated silicon wafer substrate by DC bias-assisted PECVD(Plasma Enhanced Chemical Vapor Deposition). As a catalyst, Ni thin film of thickness ranging from 15~30nm was prepared by electron beam evaporator method. In order to find the optimum growth condition, the type of gas mixture such as $C_2H_2-NH_3$ was systematically investigated by adjusting the gas mixing ratio at $570^{\circ}C$ under 0.4Torr. The diameter of the grown CNTs was 40~200nm and the diameter of the CNTs increased with increasing the Ni particles size. TEM images clearly showed carbon nanotubes to be multiwalled. The measured turn-on field was $3.9V/\mu\textrm{m}$ and an emission current of $1.4{\times}10^4A/\textrm{cm}^2$ was $7V/\mu\textrm{m}$. The CNTs grown by bias-assisted PECVD was able to demonstrate high quality in terms of vertical alignment, crystallization of graphite and the processing technique at low temperature of $570^{\circ}C$ and this can be applied for the emitter tip of FEDs.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.102-102
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• 2016

본 연구에서는 직류 전원(direct current; DC)을 이용한 스퍼터링과 고전력펄스 마그네트론 스퍼터링(high-power impulse magentron sputtering; HIPIMS)의 두 가지 방법과 빗각 증착을 적용하여 제조한 티타늄 질화물(TiN) 박막의 미세구조 변화가 물성에 미치는 영향을 확인하였다. TiN 박막은 99.5%의 Ti 타겟을 사용하고, Ar가스와 $N_2$ 분위기에서 스테인리스(SUS304)와 초경(cdmented carbide; WC-10wt.%Co) 기판위에 코팅하였다. 기판은 알코올과 아세톤으로 초음파 세척을 실시한 후 진공용기에 장착하고 기본 진공도인 ${\sim}2.0{\times}10^{-5}Torr$ 까지 진공배기를 실시하였다. 기판과 타겟 간의 거리는 DC 스퍼터링은 10 cm, HIPIMS 스퍼터링은 8.5 cm 이었다. 진공용기의 압력이 기본 진공도까지 배기되면 Ar 가스를 ${\sim}10^{-2}Torr$로 주입한 후 기판에 라디오 주파수(radio frequency; RF) 전원으로 약 -800 V의 전압을 인가하여 글로우 방전을 발생시키고 약 30 분간 청정을 실시하였다. 기판의 청정이 끝난 후 기본 진공도까지 배기한 후 Ar와 $N_2$ 가스를 ${\sim}10^{-3}Torr$로 주입하여 TiN 코팅을 실시하였다. 빗각의 크기는 $45^{\circ}$와 $-45^{\circ}$이며, TiN 박막의 총 두께는 약 $2.5{\sim}4.0{\mu}m$ 로 유지하였다. 공정조건에 따라 TiN 박막의 주상정은 형태와 기울어진 각도가 다른 것을 확인하였다. DC 스퍼터링으로 제조된 TiN 박막은 기판홀더에 약 -100 V 의 bias 전압을 인가하면 인가하지 않은 박막에 비해 치밀한 박막의 성장과 경도 값도 증가하는 사실을 확인하였다. 또한 빗각을 적용하고 bias 전압을 인가하지 않은 시편에서 박리현상이 일어났다. HIPIMS로 제조한 TiN 박막은 bias 전압을 인가한 박막과 인가하지 않은 박막의 주상정 형상과 경도 값에 큰 차이가 없었으며, 박막의 박리현상은 모든 시편에서 일어나지 않았다. DC 스퍼터링으로 제조한 TiN 박막은 bias 전압을 인가하지 않으면 색상이 노란색이 아닌 갈색으로 나타났으며, HIPIMS으로 제조한 박막은 bias 전압 인가 유무에 상관없이 노란색 색상을 나타냈다. 앞서 설명한 DC 스퍼터링과 HIPIMS의 공정조건에 따라 나타난 박막의 경도, 색상, 물성변화 차이는 DC 스퍼터링보다 높은 HIPIMS의 이온화율에서 기인한 것으로 생각된다. 본 연구결과를 이용하면 다양한 형태의 박막 구조 제어가 가능하고 이러한 미세구조 제어를 통해서 박막의 물성도 제어가 가능할 것으로 판단된다.