• Advances in nano research
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• 제1권3호
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• pp.125-131
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• 2013

This study is aimed to calculate the radiative lifetime of Wannier-Mott excitons in nanoclusters of a narrow-bandgap semiconductor embedded in a wide-bandgap one. The nanocluster linear dimensions are assumed to be much larger than the radius of the exciton so that the latter is not destructed by the confinement potential as it takes place in small quantum dots. The calculations were carried out for an example of InAs nanoclusters put into the GaAs matrix. It is shown that the radiative lifetime of Wannier-Mott excitons in such clusters increases with the decrease of the cluster dimensions, this tendency being more pronounced at low temperatures. So, the creation of excitons in nanoclusters of a narrow-bandgap material embedded in a wide-bandgap one can be used to significantly prolong their radiative lifetime in comparison with that of excitons in a bulk semiconductor.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.100-100
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• 2013

Among recently discovered 2-dimensional materials, molybdenum disulfide has fascinating physical properties. It is atomically thin and is a semiconductor with with a similar level of bandgap with silicon. Especially, its properties get interesting when it becomes thinner. Its bandgap goes through bandgap transition from indirect to direct gap. Also its gap size increases as its thickness decreases. In this talk, I am going to present our recent work on characterization of its electrical and optical properties. We used Raman and PL spectroscopy to observe its property dependence on thickness. We fabricated electrical devices to study optimal condition for MoS2 devices. Also we synthesized large-area MoS2 films for devices applications.

• 한국정보통신학회논문지
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• 제11권8호
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• pp.1552-1557
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• 2007

본 논문에서는 밴드갭 기준전압을 이용하여 동작온도에 무관한 PWM(Pulse Width Modulation) 제어 회로를 설계 하였다. 동작온도에 무관한 PWM 제어기는 BiCMOS 기술을 이용하여 동작온도에 무관한 기준전압과 동작온도에 따라 변화하는 두개의 기준 전압을 이용하였다. 설계되어진 회로는 공급전압 3.3volt를 사용하였으며, 출력 주파수는 1MHz이다. 회로의 시뮬레이션 결과 동작 온도가 $0^{\circ}C$에서 $70^{\circ}C$까지 변화할 때, PWM 제어기의 출력 펄스폭의 변화는 상온에 비하여 +0.86%에서 -0.38%였다.

• 한국정보기술학회 영문논문지
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• 제8권2호
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• pp.59-67
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• 2018

The minimum power supply voltage of a typical bandgap current reference (BGCR) is limited by operating temperature and input common mode range (ICMR) of a feedback amplifier. A new BGCR using a bandgap voltage generator (BGVG) is proposed to minimize the effect of temperature, supply voltage, and process variation. The BGVG is designed with proportional to absolute temperature (PTAT) characteristic, and a feedback amplifier is designed with weak-inversion transistors for low voltage operation. It is verified with a $0.18-{\mu}m$ CMOS process with five corners for MOS transistors and three corners for BJTs. The proposed circuit is superior to other reported current references under temperature variation from $-40^{\circ}C$ to $120^{\circ}C$ and power supply variation from 1.2 V to 1.8 V. The total power consumption is $126{\mu}W$ under the conditions that the power supply voltage is 1.2 V, the output current is $10{\mu}A$, and the operating temperature is $20^{\circ}C$.

• 한국전자파학회:학술대회논문집
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• 한국전자파학회 2002년도 종합학술발표회 논문집 Vol.12 No.1
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• pp.380-383
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• 2002

본 논문에서는 20㎓~50㎓ 대역에서 2 차원 PBG(Photonic-Bandgap) 구조의 투과 특성을 RCWA(Rigorous coupled-wave analysis)방법에 의한 Transfer matrix로 해석하였다. Square lattice의 PBG 구조에 대하여 TE 편파에서 유전율의 변화와 결함(defect)의 유무에 대한 투과 특성을 고찰하였다.

• 대한전자공학회논문지SD
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• 제41권12호
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• pp.59-65
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• 2004

적외선 소자로부터 생성되는 신호의 잡음 특성의 향상, 즉 좋은 영상을 얻기 위해서 적외선 영상신호 취득회로(ROIC)에서는 안정적인 기준 전압원이 필요하다. 본 논문은 극저온인 77K에서 동작하는 적외선 영상신호 취득회로(readout integrated circuit)를 위한 밴드갭 회로를 처음으로 제작한 후 측정, 평가하여 그 실용 가능성을 입증하고 있다. 밴드갭 회로는 대표적인 전압 기준회로로서 기존에 발표된 대부분의 밴드갭 회로는 실온에서 동작하는 것이며, 액체질소 온도 77K에서는 그 특성이 적합하지 않다. 본 논문에서는 극저온에서 동작하는 밴드갭 회로 설계를 위하여, 그에 맞는 회로를 선택하여 온도변화에 따른 사용되는 소자들의 파라미터에 대한 이론정립을 통한 그것의 특성을 살펴보고, 이러한 특성들을 고려하여 저온동작에 적합도록 하였다. 이 회로는 Hynix 0.6um standard CMOS 공정을 통해서 제작되었으며, 측정된 출력전압($V_{out}$)은 60K에서 110K까지 1.0396$\pm$0.0015V로서 기존의 실온에 동작하던 밴드갭 회로보다 더 높은 안정도를 보여주었다.

• Transactions on Electrical and Electronic Materials
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• 제13권2호
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• pp.64-68
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• 2012

We have successfully demonstrated a bandgap alteration of transparent zinc oxide (ZnO) thin film with Mg dopant by using sol-gel spin coating technique. By increasing the dopant from 0 to 30 atomic percent (at.%), a decrement value in the cutoff is observed, where the absorption edge shifts continuously to the shorter wavelength side, towards 300 nm. This resulted in a significant bandgap increment from 3.28 to 3.57 eV. However, the transmittance of the thin film at 350-800 nm gradually downgraded, from 93 to 80 % which is most probably due to the grain size that becomes bigger, and it also affected the electrical properties. The decrement from 45 to 0.05 mA at +10 V was observed in the I-V characteristics, concluding the significant relationship; where higher optical bandgap materials will exhibit lower conductivity. These findings may be useful in optoelectronics devices.

• 정보통신설비학회논문지
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• 제9권4호
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• pp.141-146
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• 2010

In this paper, bandgap reference PTAT(Proportional to Absolute Temperature) circuit and flexible gain control of LNA(Low Noise Amplifier) which is usable in Zigbee system of 2.4GHz band are designed by TSMC $0.18{\mu}m$ CMOS library. PTAT bandgap reference circuit is proposed to minimize the instability of CMOS circuit which may be unstable in temperature changes. This circuit is designed such that output voltage remains within 1.3V even when the temperature varies from $-40^{\circ}C$ to $-50^{\circ}C$ when applied to the gate bias voltage of LNA. In addition, the LNA is designed to be operated on 2.4GHz which is applicable to Zigbee system and able to select gains by changing output impedance using 4 NMOS operated switches. The simulation result shows that achieved gain is 14.3~17.6dB and NF (Noise Figure) 1.008~1.032dB.

• JSTS:Journal of Semiconductor Technology and Science
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• 제3권3호
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• pp.145-152
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• 2003

Electrical gate and drain characteristics of double heterostructure InAlAs/InGaAs pseudomorphic HEMTs have been investigated under sub-bandgap photonic excitation ($hv). Drain $(V_{DS})-,{\;}gate($V_{DS})-$, and optical power($P_{opt}$)-dependent variation of the abnormal gate leakage current and associated physical mechanisms in the PHEMTs have been characterized. Peak gate voltage ($V_{GS,P}$) and the onset voltage for the impact ionization ($V_{GS.II}$) have been extracted and empirical model for their dependence on the $V_{DS}$ and $P_{opt} have been proposed. Anomalous gate and drain current, both under dark and under sub-bandgap photonic excitation, have been modeled as a parallel connection of high performance PHEMT with a poor satellite FET as a parasitic channel. Sub-bandgap photonic characterization, as a function of the optical power with $h\nu=0.799eV$, has been comparatively combined with those under dark condition for characterizing the bell-shaped negative humps in the gate current and subthreshold drain leakage under a large drain bias.

• Advances in aircraft and spacecraft science
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• 제6권6호
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• pp.479-495
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• 2019

Periodic cellular core structures included in sandwich panels possess good stiffness while saving weight and only lately their potential to act as passive vibration filters is increasingly being studied. Classical homogeneous honeycombs show poor vibracoustic performance and only by varying certain geometrical features, a shift and/or variation in bandgap frequency range occurs. This work aims to investigate the vibration filtering properties of the AUXHEX "hybrid" core, which is a cellular structure containing cells of different shapes. Numerical simulations are carried out using two different approaches. The first technique used is the harmonic analysis with commercially available software, and the second one, which has been proved to be computationally more efficient, consists in the Wave Finite Element Method (WFEM), which still makes use of finite elements (FEM) packages, but instead of working with large models, it exploits the periodicity of the structure by analysing only the unit cell, thanks to the Floquet-Bloch theorem. Both techniques allow to produce graphs such as frequency response plots (FRF's) and dispersion curves, which are powerful tools used to identify the spectral bandgap signature of the considered structure. The hybrid cellular core pattern AUXHEX is analysed and results are discussed, focusing the investigation on the possible spectral bandgap signature heritage that a hybrid core experiences from their "parents" homogeneous cell cores.