• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.11
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• pp.855-858
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• 2011

In this paper, in order to suppress unwanted current paths originating from adjacent cells in a passive crossbar array based on resistive random access memory (RRAM) without extrinsic switching devices, 1-diode type RRAM which consists of a 0.2% chromium-doped strontium titanate (Cr-$SrTiO_3$) film deposited on a silicon substrate, was proposed for high packing density, and intrinsic rectifying characteristics from the current versus voltage characteristics were successfully demonstrated.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.95-95
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• 2011

비정질 산화물 반도체(Amorphous oxide semiconductors: AOSs)는 대면적화에도 불구하고 높은 이동도를 가지고, 상온에서도 제작할 수 있고, 투명 플렉시블 디스플레이 소자에 사용할 수 있기 때문에 최근 들어 각광받고 있는 연구 분야이다. 본 연구에서는 스퍼터링을 이용하여 활성층을 Amorphous indium gallium zinc oxide(a-IGZO)로 증착할 시에 스퍼터의 파워와 챔버내의 Ar/O2 비율을 다르게 했을 때 소자에 미치는 영향을 MIS구조를 이용하여 분석했다. 또한 같은 조건의 a-IGZO 활성층을 사용한 박막트랜지스터(TFT) 소자의 절연막의 종류를 바꿔가며 제작했을때의 소자의 특성 변화에 대해서도 분석하였다. 먼저 60 nm 두께의 a-IGZO층을 Heavily doped된 N형 실리콘 기판위에 스퍼터링 파워와 가스 분압비를 달리하여 증착하였다. 그 후 30 nm두께의 SiO2, Al2O3, SiNx 절연막을 증착하고, 마지막으로 열 증발 증착장비(Thermal Evaporator)를 이용하여 Al 전극을 150nm 증착하였다. 소자의 전기적 특성 분석은 HP4145와 Boonton 720을 사용하여 I-V와 C-V를 측정하였다. 위의 실험으로부터 스퍼터에서의 증착 rf파워가 증가할수록 a-IGZO 박막 트랜지스터에서의 캐리어 이동도가 감소하는 것을 볼 수 있었고, 챔버내의 가스분압비와 소자의 절연막의 종류가 변하면 a-IGZO 박막 트랜지스터의 전기적 특성이 변하는 것을 볼 수 있었다. 이러한 캐리어 이동도의 감소와 전기적 특성의 변화의 이유는 a-IGZO 활성층의 bulk trap과 절연막, 활성층 사이의 interface trap에 의한 것으로 보여진다.

• Journal of the Korean Ceramic Society
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• v.41 no.11
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• pp.826-833
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• 2004

In this study, photosensitivity dynamics in SiO$_2$ glass with the composition similar to that of silica Planar Lightwave Circuit (PLC) devices was investigated as a fundamental study prior to the device fabrication. Silica bulk glasses with similar composition to the core layer of PLC devices were prepared with variable composition of B$_2$O$_3$. The photosensitivity in boron and germanium co-doped SiO$_2$ glass yields refractive index change $\Delta$n as high as 10$\^$-3/. However such index modulation disappeared after annealing. From the result of annealing experiment and W absorption / Raman spectra, we conclude the compaction model is applicable to our glass system.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.5
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• pp.175-182
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• 2022

Rare-earth elements were doped with Mg to enhance the temperature stability of dielectric properties of BaTiO₃ for its application to MLCC (Multi-Layer Ceramic Capacitor). The additives strongly affect both grain growth and densification behaviors during sintering, and hence dielectric properties. The additive effects therefore should be examined in each system with different additives. This study investigated the crystal structure, grain growth and densification behaviors and related variations in dielectric constant with respect to sintering temperature. Dielectric constant appears to be varied with grain size in a temperature range between 1200 and 1300℃, suggesting the importance of grain size control. The temperature dependence of grain size variation was well explained by an established theory correlating the grain growth behavior with grain boundary structure. This accordance provides a basis for sintering technique to control grain growth thus to improve dielectric constant in rare-earth doped BaTiO₃.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1996.06a
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• pp.519-521
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• 1996

Emerald (3BeO.Al2O3.6SiO2 : Cr3+) single crystals were crystals were grown by reflux method of temperature gradient in the flux solution of Li2O-MoO3-V2O5 system. The composition of flux materials were 3 mole ratio of MoO3-V2O5/Li2O, subtituted 0.2 mole% of K2O, Na2O, Nb2O5 etc to Li2O content, solved 10-15% of beryl to flux quantity and doped 1% of Cr2O3 to emerald amount. Those of mixing were melted at 110$0^{\circ}C$ in Pt containers of the 3 zone furnace of melt-growth-return to circulate continniously, specially it has been grown large emerald single crystal when thermal fluctuation was treated for 2hrs of once time a day at 1050-95$0^{\circ}C$ in growth zone, substitutional solid solution effect of Cr+3 ion for Al+3 to the growth of emerald single crystal was good. Emerald single crystals were c(0001) hexagonal crystal face of preferencial growth direction and m(1010) post side. When it had been durated for 5 months emerald single crystals of the firet size of 0.6mm thickness of seed crystal were grown 32$\times$65mm(c x m) of maximum size and 6.2mm thickness.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.187-187
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• 2012

Solution-processed metal-alloy oxides such as indium zinc oxide (IZO), indium gallium zinc oxide (IGZO) has been extensively researched due to their high electron mobility, environmental stability, optical transparency, and solution-processibility. In spite of their excellent material properties, however, there remains a challenging problem for utilizing IZO or IGZO in electronic devices: the supply shortage of indium (In). The cost of indium is high, what is more, indium is becoming more expensive and scarce and thus strategically important. Therefore, developing an alternative route to improve carrier mobility of solution-processable ZnO is critical and essential. Here, we introduce a simple route to achieve high-performance and low-temperature solution-processed ZnO thin film transistors (TFTs) by employing alkali-metal doping such as Li, Na, K or Rb. Li-doped ZnO TFTs exhibited excellent device performance with a field-effect mobility of $7.3cm^2{\cdot}V-1{\cdot}s-1$ and an on/off current ratio of more than 107. Also, in case of higher drain voltage operation (VD=60V), the field effect mobility increased up to $11.45cm^2{\cdot}V-1{\cdot}s-1$. These all alkali metal doped ZnO TFTs were fabricated at maximum process temperature as low as $300^{\circ}C$. Moreover, low-voltage operating ZnO TFTs was fabricated with the ion gel gate dielectrics. The ultra high capacitance of the ion gel gate dielectrics allowed high on-current operation at low voltage. These devices also showed excellent operational stability.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.115-115
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• 2007

PRAM (Phase Change Random Access Memory)은 상변화 물질의 비저항 차이를 이용한 메모리 소자로 차세대 비휘발성 메모리로 주목받고 있다. 현재 상변화 물질로 사용되고 있는 $Ge_2Sb_2Te_5$ 박막은 결정질 상태에서 저항이 낮아 RESET 동작에서 많은 전력이 소비되고 메모리의 고집적의 어려움이 있다. 이러한 문제를 해결하기 위해 상변화 물질의 개선과 소자 구조의 개선 등의 새로운 접근이 시도되고 있다. 본 연구에서는 $Ge_2Sb_2Te_5$ 박막의 전기적 특성을 개선하기 위해서 이종 원소인 질소를 첨가한 N-doped $Ge_2Sb_2Te_5$ 박막에 대한 특성을 살펴 보았다. $SiO_2$/Si 기판 위에 100 nm 두께의 박막을 D.C. magnetron sputter 방법으로 증착하여, 질소 분위기 $100^{\circ}C{\sim}300^{\circ}C$온도 구간에서 열처리하였다. 열처리에 따른 박막 특성을 관찰하기 위해 면저항 측정, XRD, TEM 분석을 통해 박막 특성을 관찰하였다. 면저항 측정과 XRD peak 분석을 통해 $Ge_2Sb_2Te_5$ 시스템에 비하여 N-doped $Ge_2Sb_2Te_5$ 시스템의 결정화 온도가 상승하였음을 확인하였다. 면저항은 첨가된 질소의 조성이 증가할수록 증가하였고, FCC 상에서 HCP 상으로의 상변화 온도 역시 증가하였다. 첨가된 질소가 $Ge_2Sb_2Te_5$, 박막의 결정 성장을 억제하였고, 상대적으로 높은 저항을 가지고 안정한 FCC상을 고온 열처리 이후에도 유지하였다. 질소 첨가를 이용한 상변화 물질의 열안정성 향상과 저소비전력 구동을 통해 향후 고집적 상변화 메모리에의 적용이 가능하다.

• Journal of the Korean Ceramic Society
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• v.31 no.8
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• pp.861-868
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• 1994

CaO-Al2O3 glass is a good candidate as optical fiber amplifier and laser. In this study, optical properties for 4I13/2longrightarrow4I15/2 transition of Er3+ ions doped in CaO-Al2O3 glasses were investigated. Optical absorptions, radiative transition probabilities and lifetimes for 4I13/2 level were evaluated by using Judd-Ofelt theory. Also, induced- emmision cross-sections of 4I13/2longrightarrow4I15/2 transition were calculated. Radiative transition probability and lifetime of 4I13/2 level were 144.6s-1, 690$mutextrm{s}$ respectively for 60CaO.40Al2O3 glass(FS0) and 152.6s-1, 660 $mutextrm{s}$ for 54 CaO.36Al2O3.10SiO2 glass (FS10). Each induced-emission cross sections for FS0 and FS10 was 0.749$\times$10-20 $\textrm{cm}^2$, 0.892$\times$10-20 $\textrm{cm}^2$. Obtained values were comparable with those of ZBLA glass studied as optical fiber amplifier and laser material.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.319.1-319.1
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• 2016

Recently, the Al-doped ZnO (ZnO:Al) films are intensively used in thin film a-Si solar cell applications due to their high transmittance and good conductivity. The textured ZnO:Al films are used to enhance the light trapping in thin film solar cells. The wet etch process is used to texture ZnO:Al films by dipping in diluted acidic solutions like HCl or HF. During that process the glass substrate could be damaged by the acidic solution and it may be difficult to apply it for the inline mass production process since it has to be done outside the chamber. In this paper we report a new technique to control the surface morphology of RF-sputtered ZnO:Al films. The ZnO:Al films are textured with vaporized HF formed by the mixture of HF and H2SiO3 solution. Even though the surface of textured ZnO:Al films by vapor etching process showed smaller and sharper surface structures compared to that of the films textured by wet etching, the haze value was dramatically improved. We achieved the high haze value of 78% at the wavelength of 540 nm by increasing etching time and HF concentration. The haze value of about 58% was achieved at the wavelength of 800 nm when vapor texturing was used. The ZnO:Al film texture by HCl had haze ratio of about 9.5 % at 800 nm and less than 40 % at 540 nm. In addition to low haze ratio, the texturing by HCl was very difficult to control etching and to keep reproducibility due to its very fast etching speed.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.3
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• pp.147-151
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• 2016

Graphene has a monolayer crystal structure formed with C-atoms and has been used as a base layer of HETs (hot electron transistors). Graphene HETs have exhibited the operation at THz frequencies and higher current on/off ratio than that of Graphene FETs. In this article, we report on the preliminary results of current characteristics from the HETs which are fabricated utilizing highly doped Si collector, graphene base, and 5 nm thin $Al_2O_3$ tunnel layers between the base and Ti emitter. We have observed E-B forward currents are inherited to tunneling through $Al_2O_3$ layers, but have not noticed the Schottky barrier blocking effect on B-C forward current at the base/collector interface. At the common-emitter configuration, under a constant $V_{BE}$ between 0~1.2V, $I_C$ has increased linearly with $V_{CE}$ for $V_{CE}$ < $V_{BE}$ indicating the saturation region. As the $V_{CE}$ increases further, a plateau of $I_C$ vs. $V_{CE}$ has appeared slightly at $V_{CE}{\simeq}V_{BE}$, denoting forward-active region. With further increase of $V_{CE}$, $I_C$ has kept increasing probably due to tunneling through thin Schottky barrier between B/C. Thus the current on/off ration has exhibited to be 50. To improve hot electron effects, we propose the usage of low doped Si substrate, insertion of barrier layer between B/C, or substrates with low electron affinity.