• JSTS:Journal of Semiconductor Technology and Science
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• v.8 no.1
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• pp.32-39
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• 2008

Tunnel oxide of non-volatile memory (NVM) devices would be very difficult to downscale if ten-year data retention were still needed. This requirement limits further improvement of device performance in terms of programming speed and operating voltages. Consequently, for low-power applications with Fowler-Nordheim programming such as NAND, program and erase voltages are essentially sustained at unacceptably high levels. A promising solution for tunnel oxide scaling is tunnel barrier engineering (TBE), which uses multiple dielectric stacks to enhance field-sensitivity. This allows for shorter writing/erasing times and/or lower operating voltages than single $SiO_2$ tunnel oxide without altering the ten-year data retention constraint. In this paper, two approaches for tunnel barrier engineering are compared: the crested barrier and variable oxide thickness. Key results of TBE and its applications for NVM are also addressed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.7-8
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• 2008

The memory characteristics of charge trap flash (CTF) with $HfO_2$ charge trap layer were investigated. Especially, we focused on the effects of tunnel barrier engineering consisted of $SiO_2/Si_3N_4/SiO_2$ (ONO) stack or $Si_3N_4/SiO_2/Si_3N_4$ (NON) stack. The programming and erasing characteristics were significantly enhanced by using ONO or NON tunnel barrier. These improvement are due to the increase of tunneling current by using engineered tunnel barrier. As a result, the engineered tunnel barrier is a promising technique for non-volatile flash memory applications.

• The Journal of Engineering Research
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• v.6 no.2
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• pp.33-38
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• 2004

To investigate the reliability of the MTJs on the roughness of insulating tunnel barrier, we prepared two MTJs with the different uniformity of barrier thickness. Namely, the one has uniform insulating barrier thickness; the other has non-uniform insulating barrier thickness as compared to different thing. As to depositing amorphous layer CoZrNb under the pinning layer IrMn, we achieved MTJ with uniform barrier thickness. Toinvestigate the reliability of the MTJs dependent on the bottom electrode, time-dependent dielectric breakdown (TDDB) measurements were carried out under constant voltage stress. The Weibull fit of out data shows clearly that $t_{BD}$ scales with the thickness uniformity of MTJs tunnel barrier. Assuming a linear dependence of log($t_{BD}$) on stress voltages, we obtained the lifetime of $10^4$years at a operating voltage of 0.4 V at MTJs comprising CoNbZr layers. This study shows that the reliabilityof new MTJs structure was improved due to the ultra smooth barrier, because the surface roughness of the bottom electrode influenced the uniformity of tunnel barrier.

• Korean Journal of Materials Research
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• v.12 no.3
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• pp.200-204
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• 2002

We fabricated TMR devices which have double oxidized tunnel barrier using plasma oxidation method to form homogeneously oxidized AlO tunnel barrier. We sputtered 10 $\AA$-bottom Al layer and oxidized it by varying oxidation time for 5, 10, 20 sec. Subsequent sputtering of 13 $\AA$ - Al was performed and the matallic layer was oxidized for 120 sec. The electrical resistance changed from 700$\Omega$ to 2700$\Omega$ with increase of oxidation time, while variation of MR ratio was little spreading 27~31% which is larger than that of TMR device of ordinary single tunnel barrier. We calculated effective barrier height and width by measuring I-V curves, from which we found the barrier height was 1.3~1.5 eV, sufficient for tunnel barrier, and the barrier width(<16.2 $\AA$) was smaller than that of directly measured value by the tunneling electron microscopy. Our results may be caused by insufficient oxidation of Al precursor into $Al_2O_3$. However, double oxidized tunnel barriers were superior to conventional single tunnel barrier in uniformity and density. We found that the external magnetic field to switch spin direction of ferromagnetic layer of pinned layer breaking ferro-antiferro exchange coupling was increased as bottom layer oxidation time increased. Our results imply that we were able to improve MR ratio and tune switching field by employing double oxidized tunnel barrier process.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.97-98
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• 2009

Tunneling barrier engineered charge trap flash (TBE-CTF) memory capacitor were fabricated using the tunneling barrier engineering technique. Variable oxide thickness (VARIOT) barrier and CRESTED barrier consisting of thin $SiO_2$ and $Si_3N_4$ dielectrics layers were used as engineered tunneling barrier. The charge trapping characteristic with different metal gates are also investigated. A larger memory window was achieved from the TBE-CTF memory with high workfunction metal gate.

• Wind and Structures
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• v.24 no.2
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• pp.171-184
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• 2017

The present study provides a deeper understanding of the flow fields of a full-scale railway wind barriers by means of a wind tunnel test. First, the drag forces of the three wind barriers were measured using a force sensor, and the drag force coefficients were compared with a similar scale model. On this basis, the mean wind velocity and turbulence upwind and downwind of the wind barriers were measured. The effects of pore size and opening forms of the wind barrier were discussed. The results show that the test of the scaled wind barrier model may be unsafe, and it is suitable to adopt the full-scale wind barrier model. The pore size and the opening forms of wind barriers have a slight influence on the flow fields upwind of the wind barrier but have some influences on the flow fields and power spectra downwind of the wind barrier. The smaller pore size generates a lower turbulence density and value of the power spectrum near the wind barrier, and the porous wind barriers clearly provide better shelter than the bar-type wind barriers.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.1014-1019
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• 2003

It seems inevitable for residential buildings to be high-rise and allocated near traffic roads due to the overcrowding in urban area. Acoustic environment in those area has been seriously deteriorated by the increase of traffic vehicles. Commonly used sound barriers have a limitation in controlling noise due to diffraction noise of sound barrier. Hence sound barrier is not effective to attenuate noise especially for the residential units in high level. This work aims at evaluating noise reduction according to the tunnel section shape by using 1/5 scale model. We carried out a number of field measurements for 1/5 scale model of Noise Barrier Tunnel with various sectional shape. The results from predictions and the measurement show generally good agreement.

• Wind and Structures
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• v.14 no.1
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• pp.55-70
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• 2011

This study investigates the design criteria required for wind barriers to protect vehicles running on an expressway under a high side wind. At the first stage of this study, the lateral deviations of vehicles in crosswinds were computed from the commercial software, CarSim and TruckSim, and the critical wind speeds for a car accident were then evaluated from a predefined car accident index. The critical wind speeds for driving stability were found to be 35 m/s for a small passenger car, yet 30 m/s for a truck and a bus. From the wind tunnel tests, the minimum height of a wind barrier required to reduce the wind speed by 50% was found to be 12.5% of the road width. In the case of parallel bridges, the placement of two edge wind barriers plus one wind barrier at center was recommended for a separation distance larger than 20 m (four lanes) and 10 m (six lanes) respectively, otherwise two wind barriers were recommended.

• Journal of Magnetics
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• v.10 no.4
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• pp.137-141
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• 2005

We confirmed that the improvement in properties of magnetic tunnel junctions prepared by radical oxidation after thermal treatment was mostly resulted from the redistribution of oxygen at the $AIOx/Co_{90}Fe_{10}$ interface. The as-deposited Al oxide barrier was oxygen-deficient but most of it re-oxidized into $Al_2O_3$, the thermodynamically stable stoichiometric phase, through thermal treatment. As a result, the effective barrier height was increased from 1.52 eV to 2.27 eV. On the other hand, the effective barrier width was decreased from 8.2 ${\AA}$ to 7.5 ${\AA}$. X-ray absorption spectra of Fe and Co clearly showed that the oxygen in the CoFe layer diffused back into the Al barrier and thereby enriched the barrier to close to a stoichiometirc $Al_2O_3$ phase. The oxygen bonded with Co and Fe diffused back by 6.8 ${\AA}$ and 4.5 ${\AA}$ after thermal treatment, respectively. Our results confirm that controlling the chemical structures of the interface is important to improve the properties of magnetic tunnel junctions.

• Wind and Structures
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• v.23 no.3
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• pp.171-189
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• 2016

An adjustable, louver-type wind barrier was introduced in this study for improving the running safety and ride comfort of train on the bridge under the undesirable wind environment. The aerodynamic characteristics of both train and bridge due to this novel wind barrier was systematically investigated based on the wind tunnel tests. It is suggested that rotation angles of the adjustable blade of the louver-type wind barrier should be controlled within $90^{\circ}$ to achieve an effective solution in terms of the overall aerodynamic performance of the train. Compared to the traditional grid-type wind barrier, the louver-type wind barrier generally presents better aerodynamic performance. Specifically, the larger decrease of the lift force and overturn moment of the train and the smaller increase of the drag force and torsional moment of the bridge resulting from the louver-type wind barrier were highlighted. Finally, the computational fluid dynamics (CFD) technique was applied to explore the underlying mechanism of aerodynamic control using the proposed wind barrier.