• Proceedings of the Korean Vacuum Society Conference
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• 2006.02a
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• pp.91-91
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• 2006

• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.3.1-3.1
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• 2010

Water splitting reaction using photocatalysts is of great interest in the utilization of solar energy [1]. In the present work, visible light-responsive $TiO_2$ thin films (Vis-$TiO_2$) were prepared by a radio frequency magnetron sputtering (RF-MS) deposition method and applied for the separate evolution of $H_2$ and $O_2$ from water as well as the photofuel cell. Special attentions will be focused on the effect of HF treatment of Vis-$TiO_2$ thin films on their photocatalytic activities. Vis-$TiO_2$ thin films were prepared by an RF-MS method using a calcined $TiO_2$ plate and Ar as the sputtering gas. The Vis-$TiO_2$ thin films were then deposited on the Ti foil substrate with the substrate temperature at 873 K (Vis-$TiO_2$/Ti). Vis-$TiO_2$/Ti thin films were immersed in a 0.045 vol% HF solution at room temperature. The effect of HF treatments on the activity of Vis-$TiO_2$/Ti thin films for the photocatalytic water splitting reaction have been investigated. Vis-$TiO_2$/Ti thin films treated with HF solution (HF-Vis-$TiO_2$/Ti) exhibited remarkable enhancement in the photocatalytic activity for $H_2$ evolution from a methanol aqueous solution as well as in the photoelectrochemical performance under visible light irradiation as compared with the untreated Vis-$TiO_2$/Ti thin films. Moreover, Pt-loaded HF-Vis-$TiO_2$/Ti thin films act as efficient and stable photocatalysts for the separate evolution of $H_2$ and $O_2$ from water under visible light irradiation in the presence of chemical bias. Thus, HF treatment was found to be an effective way to improve the photocatalytic activity of Vis-$TiO_2$/Ti thin films. Furthermore, unique separate type photofuel cell was fabricated using a Vis-$TiO_2$ thin film as an electrode, which can generate electrical power under solar light irradiation by using various kinds of biomass derivatives as fuel. It was found that the introduction of an iodine ($I^-/{I_3}^-$) redox solution at the cathode side enables the development of a highly efficient photofuel cell which can utilize a cost-efficient carbon electrode as an alternative to the Pt cathode.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.344-344
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• 2010

A capacitor with engineered tunnel barrier composed of High-k materials has been fabricated. Variable oxide thickness (VARIOT) barrier consisting of thin SiO2/HfO2/Al2O3 (2/1/3 nm) dielectric layers were used as engineered tunneling barrier. We studied the electrical characteristics of multi stacked tunnel layers for various RTA (Rapid Thermal Anneal) and FGA (Forming Gas Anneal) temperature.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.24-25
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• 2008

The effect of heat treatment in $HfO_2$ as charge trap with $SiO_2/Si_3N_4/SiO_2$ as tunnel oxide layer in capacitors has been investigated. Rapid thermal annealing (RTA) were carried out at the temperature range of 600 - $900^{\circ}C$. It is found that all devices carried out heat treatment have large threshold voltage shift Especially, device performed heat treatment at $900^{\circ}C$ has been confirmed the largest memory window. Also, Threshold voltage shift of device used conventional $SiO_2$ as tunnel oxide layer was smaller than that with $SiO_2/Si_3N_4/SiO_2$.

• Proceedings of the Korean Magnestics Society Conference
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• 2002.04a
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• pp.116-117
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• 2002

• Proceedings of the Materials Research Society of Korea Conference
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• 1996.05a
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• pp.75-75
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• 1996

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.80-80
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• 2009

Recently, multiferroics have attracted much attention due to their numorous potentials. In this work, we attemped to utilize the multiferroics as an alternative material for ferroelectrics. Ferroelectric materials have been stadied to ferroelectric random access memories, however, some inevitable problems prevent it from inplementation. multiferroics shows a ferroelectricity and has low process temperature $BiFeO_3$(BFO) films have good ferroelectric properties but poor leakage characterization. Thus we tried, in this work, to adopt $HfO_2$ insulating layer for metal-ferroelectric-insulator-semiconductor(MFMIS) structure to surpress to leakage current. $BiFeO_3$(BFO) thin films were fabricared by using a sol-gel method on $HfO_2/Si$ structure. Ferroelectric BFO films on a p-type Si(100)wafer with a $HfO_2$ buffer layer have been fabricated to form a metal-ferroelectric-insulator-semiconductor (MFIS) structure. The $HfO_2$ insulator were deposited by using a sol-gel method. Then, they were carried out a rapid thermal annealing(RTA) furnace at $750\;^{\circ}C$ for 10 min in $N_2$. BFO films on the $HfO_2/Si$ structures were deposited by sol-gel method and they were crystallized rapid thermal annealing in $N_2$ atomsphere at $550\;^{\circ}C$ for 5 min. They were characterized by atomic force microscopy(AFM) and Capacitance-voltage(C-V) curve.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.373-373
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• 2014

Resistive-change random access memory (ReRAM) device is one of the promising candidates owing to its simple structure, high scalability potential and low power operation. Many resistive switching devices using transition metal oxides materials such as NiO, Al2O3, ZnO, HfO2, $TiO_2$, have attracting increased attention in recent years as the next-generation nonvolatile memory. Among various transition metal oxides materials, HfO2 has been adopted as the gate dielectric in advanced Si devices. For this reason, it is advantageous to develop an HfO2-based ReRAM devices to leverage its compatibility with Si. However, the annealing temperature of these high-k thin films for a suitable resistive memory switching is high, so there are several reports for low temperature process including microwave irradiation. In this paper, we demonstrate the bipolar resistive switching characteristics in the microwave irradiation annealing processed Ag/HfO2/Pt ReRAM device. Compared to the as-deposited Ag/HfO2/Pt device, highly improved uniformity of resistance values and operating voltage were obtained from the micro wave annealing processed HfO2 ReRAM device. In addition, a stable DC endurance (>100 cycles) and a high data retention (>104 sec) were achieved.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.219-219
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• 2010

기존의 플로팅 타입의 메모리는 소자의 소형화에 따른 인접 셀 간의 커플링 현상과 전계에 따른 누설전류의 증가 등과 같은 문제가 발생한다. 이에 대한 해결책으로서 전하 저장 층을 폴리실리콘에서 유전체를 사용하는 SONOS 형태의 메모리와 NFGM (Nano-Floating Gate Memory)연구가 되고 있다. 그러나 높은 구동 전압, 느린 쓰기/지우기 속도 그리고 10년의 전하보존에 대한 리텐션 특성을 만족을 시키지 못하는 문제가 있다. 이러한 문제를 해결 하고자 터널베리어를 엔지니어링 하는 TBM (Tunnel Barrier Engineering Memory) 기술에 대한 연구가 활발히 진행 중이다. TBM 기술은 터널 층을 매우 얇은 다층의 유전체를 사용하여 전계에 따른 터널베리어의 민감도를 증가시킴으로써 빠른 쓰기/지우기 동작이 가능하며, 10년의 전하 보존 특성을 만족 시킬 수 있는 차세대 비휘발성 메모리 기술이다. 또한 고유전율 물질을 터널층으로 이용하면 메모리 특성을 향상 시킬 수가 있다. 일반적으로 TBM 기술에는 VARIOT 구조와 CRESTED 구조로 나눠지는데 본 연구에서는 두 구조의 장점을 가지는 Staggered tunnel barrier 구조를 $Si_3N_4$와 HfAlO을 이용하여 디자인 하였다. 이때 HfO2와 Al2O3의 조성비는 3:1의 조성을 갖는다. $Si_3N_4$와 HfAlO을 각각 3 nm로 적층하여 리세스(Recess) 구조의 트랜지스터를 제작하여 차세대 비휘발성 메모리로써의 가능성을 알아보았다.

• Journal of the Korean institute of surface engineering
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• v.29 no.1
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• pp.36-44
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• 1996

Fe-Cr-Al and Fe-Cr-Al-Hf alloys prepared either by arc melting or by single roll casting(melt spinning) were exposed to air isothermally at 900~$1100^{\circ}C$. Whisker-like alumina was observed on the surface of the specimens when oxidized at $900^{\circ}C$, but convoluted alumina above $1000^{\circ}C$. All the Hf-free specimens and Hf-added specimens produced by single roll casting formed only external scale mainly composed of $Al_2O_3$ after oxidation at 900~$1100^{\circ}C$ for 100 hours, but Hf-added specimen produced by arc melting formed Hf-rich internal oxides below the thin external $Al_2O_3$ scale except at $900^{\circ}C$. Most of the rapidly solidified Fe-Cr-Al alloys showed smaller weight gains than conventionally casted ones besides Hf-added one oxidized at $1100^{\circ}C$.