• Proceedings of the Korean Magnestics Society Conference
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• 2002.04a
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• pp.42-43
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• 2002

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.11
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• pp.934-940
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• 2001

Magnetic properties were investigated for Si/SiO$_2$/NiFe(300 )/A1$_2$O$_3$(t)/Co(200 ) junction related with the parameters of $Al_2$O$_3$. Insulating $Al_2$O$_3$ layer was formed by depositing a 5~40 thick Al layer, followed by a 90~120s RF plasma oxidation in an $O_2$ atmosphere. Magnetoresistance was not observed for tunnel junction with 5~10 thick Al layer, but magnetoresistance was observed large for tunnel junction with 15~40 thick Al layer. Oxidation time did not largely influence magnetoresistance. Tunnel magnetoresistance effect depended on magnetization behavior of two ferromagnetic layers. Tunneling junction was confirmed through nonlinear I-V curve. In this work, tunneling magnetoresistance(TMR) up to 30 % was observed. This apparent TMR is an artifact of the nonuniform current flow over the junction in the cross geometry of the electrodes.

• 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.

• 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 Magnestics Society Conference
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• 2003.06a
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• pp.21-21
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• 2003

Microstructure and magnetic transport phenomina in rf sputtered AlN/Co type ten-layered discontinuous films of nanoscaled [AlN (3 nm)/Co (t nm)]...$\sub$10/ with t$\sub$Co/=1.0∼2.0 nm have been investigated. The microstructure and tunneling magnetic resistance of the samples are strongly dependent on the thickness of Co layer. Negative tunneling magneto-resistance due to the spin-dependent transport has been observed along the current-in-plane configuration in the samples having the Co layers below 1.6 nm thick. When the thickness of Co layer was less than 1,2 nm, randomly oriented granular Co particles were completely isolated and embedded in amorphous AlN matrix, and the films showed the superparamagnetic behavior with a high MR value of Δ$\rho$/$\rho$$\sub$0/=1.8 %. As t$\sub$Co/ increases, a transition from the regime of co-existence of superparamagnetic and ferromagnetic behaviors to ferromagnetic behavior was observed. Tunneling barrier called "decay length for tunneling" for the films having the thickness of Co layer from 1.4 to 1.6 nm was measured to be ranged from 0.004 to 0.021 ${\AA}$$\^$-1/.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.127-128
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• 2008

The electrical characteristics of VARIOT (variable oxide thickness) with various $HfO_2$ thicknesses on thin $SiO_2$ or $Al_2O_3$ layer were investigated. Especially, the charge trapping characteristics of $HfO_2$ layer were intensively studied. The thin $HfO_2$ layer has small charge trapping characteristics while the thick $HfO_2$ layer has large memory window. Therefore, the $HfO_2$ layer is superior material and can be applied to charge storage as well as tunneling barrier of the non-volatile memory applications.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.8
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• pp.688-693
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• 2001

A series of Fe/CeO$_2$/Fe$_{75}$Co$_{25}$ tunnel junctions (Magnetic Tunnel Junction, MTJ) having CeO$_2$ barrier layers from 30 to 90$\AA$ in thickness were prepared by ion beam sputtering (IBS) method. In order to compare the properties of MTJs, Fe/Al oxide/Fe-Co tunnel junctions were also prepared. Some junctions with a CeO$_2$ barrier layer showed the ferromagnetic tunneling effect and the highest MR ratio at room temperature was 5%. The electric resistance of junctions with a CeO$_2$ barrier layer was higher that that of junctions with an Al oxide barrier. On the other hand, The interface analysis of the Fe/CeO$_2$ bilayer was conducted by means of X-ray photoelectron spectroscopy (XPS). It was found that CeO$_2$ was decomposed to Ce and $O_2$ during sputtering, and Fe was oxidized with these decomposed $O_2$ molecules. The reduction of both electric resistance and MR ratio may be associated with the decomposed Ce in the barrier layer.r.r.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.5
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• pp.386-389
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• 2009

The electrical characteristics and annealing effects of tunneling dielectrics stacked with $SiO_2$ and $Si_{3}N_{4}$ were investigated. I-V characteristics of band gap engineered tunneling gate stacks consisted of $Si_{3}N_{4}/SiO_2/Si_{3}N_{4}$ (NON), $SiO_2/Si_{3}N_{4}/SiO_2$ (ONO) dielectrics were evaluated and compared with $SiO_2$ single layer using the MOS (metal-oxide-semiconductor) capacitor structure. The leakage currents of engineered tunneling barriers (ONO, NON stacks) are lower than that of the conventional $SiO_2$ single layer at low electrical field. Meanwhile, the engineered tunneling barriers have larger tunneling current at high electrical field. Furthermore, the increased tunneling current through engineered tunneling barriers related to high speed operation can be achieved by annealing processes.

• Journal of Magnetics
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• v.8 no.2
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• pp.98-102
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• 2003

Microstructure and magnetic transport phenomina in rf sputtered AIN/CO type ten- layered discontinuous films of nanoscaled [AIN(3 nm)/Co(t nm)]…$_10$ with t$_Co$=1.0∼2.0 nm have been investigated. The microstructure and tunneling magnetic resistance of the samples are strongly dependent on the thickness of Co layer, Negative tunneling magneto-resistance due to the spin-dependent transport has been observed along the current-in-plane configuration in the samples having the Co layers below 1.6 nm thick. When the thickness of Co layer was less than 1.2 nm, randomly oriented granular Co particles were completely isolated and embedded in amorphous AIN matrix, and the films showed the superparamagnetic behavior with a high MR value of ${\Delta}p/p_0$=1.8%. As t$_Co$ increases, a transition from the regime of co-existence of superparamagnetic and ferromagnetic behaviors to ferromagnetic behavior was observed. funneling barrier called “decay length far tunneling” fur the films haying the thickness of Co layer from 1.4 to 1.6 nm was measured to be ranged from 0.004 to 0.021 ${\AA}$$^{-1}$.

• Journal of the Korean Magnetics Society
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• v.10 no.3
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• pp.118-122
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• 2000

MR characteristics of $Al_2$ $O_3$ based magnetic tunneling juction with various $Al_2$ $O_3$ thicknesses were investigated. Spin-dependent tunneling junctions, in which the tunneling barrier $Al_2$ $O_3$ is formed by depositing a 1-3 nm thick Al layer, followed by thermal oxidation at room temperature in an $O_2$atmosphere, were fabricated on 4$^{\circ}$tilt(111)Si substrate in 3-gun magnetron sputtering system. The top and bottom ferromagnetic electrodes were Ni$_{80}$Fe$_{20}$ and Co. A maximum Tunneling MR ratio of 14% was obtained in the junction of which insulating barrier thickness was 2 nm. By increasing the tunneling voltage across the junction, maximum MR ratio reduced and finally showed no MR characteristics.s.