• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 추계학술대회 논문집 Vol.14 No.1
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• pp.17-20
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• 2001

Nonvolatile semiconductor memory devices with reoxidized nitrided oxide(RONO) gate dielectrics were fabricated, and nitrogen distribution and bonding species which contribute to memory characteristics were analyzed. Also, memory characteristics of devices depending on the anneal temperatures were investigated. The devices were fabricated by retrograde twin well CMOS processes with $0.35{\mu}m$ Nonvolatile semiconductor memory devices with reoxidized nitrided oxide(RONO) gate dielectric were fabricated, and nitrogen distribution and bonding species which contributing memory characteristics were analyzed. Also, memory characteristics of devices according to anneal temperatures were investigated. The devices were fabricated by $0.35{\mu}m$ retrograde twin well CMOS processes. The processes could be simple by in-situ process of nitridation anneal and reoxidation. The nitrogen distribution and bonding state of gate dielectric were investigated by Dynamic Secondary Ion Mass Spectrometry(D-SIMS), Time-of-Flight Secondary Ion Mass Spectrometry(ToF-SIMS), and X-ray Photoelectron Spectroscopy(XPS). Nitrogen concentrations are proportional to nitridation anneal temperatures and the more time was required to form the same reoxidized layer thickness. ToF-SIMS results show that SiON species are detected at the initial oxide interface and $Si_{2}NO$ species near the new $Si-SiO_{2}$ interface that formed after reoxidation. As the anneal temperatures increased, the device showed worse retention and degradation properties. These could be said that nitrogen concentration near initial interface is limited to a certain quantity, so excess nitrogen are redistributed near the $Si-SiO_{2}$ interface and contributed to electron trap generation.

• 한국산학기술학회논문지
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• 제5권3호
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• pp.197-203
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• 2004

나노미터 크기의 임의형상 패턴을 새기기 위하여 노광기술이 사용된다. 광노광에서 자외선과 엑스레이 같은 전자기파가 나노미터 크기로 형상을 새긴 마스크 위에 조사되면 회절현상은 필연적으로 발생하며 마스크의 상이 불명확하게 웨이퍼 위에 맺히도록 한다. 볼록렌즈만이 프리어변환기 역할을 한다고 알려져 있으며 마스크 위에 패턴의 크기가 전자기파의 파장에 비교하여 매우 클 때에도 볼록렌즈를 사용하면 프리어변환시키는 것이 가능하다. 본 논문에서 설명하는 방법으로 마스크를 준비하여 렌즈 앞에 놓고 레이저 빔으로 조사하면 프리어 평면이라 알려진 평면 위에서만 나노미터 크기의 패턴이 형성된다. 이 방법은 매우 단순한 장치로 구성되어 있고, 현재 혹은 차세대 노광인 자외선/극자외선 및 전자투사노광으로 제작한 최소선폭과 비교해 볼 때 손색이 없다. 여기서는 프리어광학을 이용하여 이론적인 연구결과를 보이고 있지만 가까운 장래에 실험결과로 이론적인 접근을 증명할 수 있을 것이다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.243-243
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• 2010

Low-temperature grown (LTG) InGaAs epilayers were grown by MBE technique for studying a correlation between terahertz (THz) emission and the intrinsic defects. The 1.2-um-thick Be-compensated LTG-InGaAs epilayers were prepared on SI-InP:Fe substrate at $200-250^{\circ}C$, and subsequently in-situ annealed under As environment at $550^{\circ}C$ for 5-30 minutes. The carrier concentration/mobility and the crystalline structure were analyzed by the Hall effect and the x-ray diffraction (XRD), respectively, and the carrier lifetime were determined by the fs time-resolved pump-probe spectroscopy. THz generation from LTG-InGaAs was carried out by a Ti-sapphire laser (800 nm) of a pulse width of 190 fs at a repetition of 76 MHz. Figure shows the spectral amplitude of generated waves in the THz region. As the growth temperature of epilayer increases, the amplitude is enhanced. However, two samples grown at $200^{\circ}C$, as-grown and annealed, show almost no difference in the spectral amplitude. This suggests that the growth temperature is critical in the formation of defect states involved in THz emission. We are now investigating the correlations between the XRD band attributed to defects, the Hall parameter, and the spectral amplitude of generated THz wave.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 추계학술대회 초록집
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• pp.57.2-57.2
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• 2011

Dye-sensitized solar cells (DSSC) have recently been developed as a cost-effective photovoltaic system due to their low-cost materials and facile processing. The production of DSSC involves chemical and thermal processes but no vacuum is involved. Therefore, DSSC can be fabricated without using expensive equipment. The use of dyes and nanocrystalline $TiO_2$ is one of the most promising approaches to realize both high performance and low cost. The efficiency of the DSSC changes consequently in the particle size, morphology, crystallization and surface state of the $TiO_2$. Nanocrystalline $TiO_2$ materials have been widely used as a photo catalyst and an electron collector in DSSC. Front electrode in DSSC are required to have an extremely high porosity and surface area such that the dyes can be sufficiently adsorbed and be electronically interconnected, resulting in the efficient generation of photocurrent within cells. In this study, DSSC were fabricated by an screen printing for the $TiO_2$ thin film. $TiO_2$ nanoparticles characterized by X-ray diffractometer (XRD) and scanning electron microscope (SEM) and scanning auger microscopy (SAM) and zeta potential and electrochemical impedance spectroscopy(EIS).In addition, DSSC module was modeled and simulated using the SILVACO TCAD software program. Improve the efficiency of DSSC, the effect of $TiO_2$ thin film thickness and $TiO_2$ nanoparticle size was investigated by SILVACO TCAD software program.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.468-468
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• 2011

Carbon nanotubes (CNTs) have been considered as one of the promising candidate for next-generation field emitters because of their unique properties, such as high field enhancement factor, good mechanical strength, and excellent chemical stability. So far, a lot of researchers have been interested in field emission properties of CNT itself. However, it is necessary to study proper field emitter shapes, as well as the fundamental properties of CNTs, to apply CNTs to real devices. For example, specific applications, such as x-ray sources, e-beam sources, and microwave amplifiers, need to get a focused electron beam from the field emitters. If we use planar-typed CNT emitters, it will need several focal lenses to reduce a size of electron beam. On the other hand, the point-typed CNT emitters can be an effective way to get a focused electron beam using a simple technique. Here, we introduce a fabrication of CNT fibers with nanoscale point tips which can be used as a point-typed emitter. The emitter made by the CNT fibers showed very low turn-on electric field, high current density, and large enhancement factor. In addition, it showed stable emission current during long operation period. The high performance of CNT point emitter indicated the potential e-beam source candidate for the applications requiring small electron beam size.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.167-167
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• 2011

Magnetic random access memory (MRAM) is one of the prospective semiconductor memories for next generation. It has the excellent features including nonvolatility, fast access time, unlimited read/write endurance, low operating voltage, and high storage density. MRAM consists of magnetic tunnel junction (MTJ) stack and complementary metal-oxide semiconductor (CMOS). The MTJ stack is composed of various magnetic materials, metals, and a tunneling barrier layer. For the successful realization of high density MRAM, the etching process of magnetic materials should be developed. Among various magnetic materials, FePt has been used for pinned layer of MTJ stack. The previous etch study of FePt magnetic thin films was carried out using $CH_4/O_2/NH_3$. It reported only the etch characteristics with respect to the variation of RF bias powers. In this study, the etch characteristics of FePt thin films have been investigated using an inductively coupled plasma reactive ion etcher in various etch chemistries containing $CH_4$/Ar and $CH_4/O_2/Ar$ gas mixes. TiN thin film was employed as a hard mask. FePt thin films are etched by varying the gas concentration. The etch characteristics have been investigated in terms of etch rate, etch selectivity and etch profile. Furthermore, x-ray photoelectron spectroscopy is applied to elucidate the etch mechanism of FePt thin films in $CH_4$/Ar and $CH_4/O_2/Ar$ chemistries.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.390-390
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• 2012

Information technology industries has grown rapidly and demanded alternative memories for the next generation. The most popular random access memory, dynamic random-access memory (DRAM), has many advantages as a memory, but it could not meet the demands from the current of developed industries. One of highlighted alternative memories is magnetic random-access memory (MRAM). It has many advantages like low power consumption, huge storage, high operating speed, and non-volatile properties. MRAM consists of magnetic-tunnel-junction (MTJ) stack which is a key part of it and has various magnetic thin films like CoFeB, FePt, IrMn, and so on. Each magnetic thin film is difficult to be etched without any damages and react with chemical species in plasma. For improving the etching process, a high density plasma etching process was employed. Moreover, the previous etching gases were highly corrosive and dangerous. Therefore, the safety etching gases are needed to be developed. In this research, the etch characteristics of CoFeB magnetic thin films were studied by using an inductively coupled plasma reactive ion etching in $CH_4/O_2/Ar$ gas mixes. TiN thin films were used as a hardmask on CoFeB thin films. The concentrations of $O_2$ in $CH_4/O_2/Ar$ gas mix were varied, and then, the rf coil power, gas pressure, and dc-bias voltage. The etch rates and the selectivity were obtained by a surface profiler and the etch profiles were observed by a field emission scanning electron microscopy. X-ray photoelectron spectroscopy was employed to reveal the etch mechanism.

• 한국세라믹학회지
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• 제42권11호
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• pp.729-736
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• 2005

HTGR (High Temperature Gas-cooled Reactor) is spotlighted to next generation nuclear power plant for producing the clean hydrogen gas and the electricity. In this study, the spherical $UO_3$ gel particles were prepared by the external gelation process, and the characteristics of these particles were analyzed the particle shape, composition of precipitate, and thermal decomposition characteristics with the Streoscope, FT-IR, and X-ray diffractometer. Raw material of the ADUN (Acid Deficient Uranyl Nitrate) solution, which has [$NO_3$]/[U] mole ratio = 1.75, was obtained from dissolution of the $U_{3}O_{8}$ powder with concentrated $HNO_3$, and its concentration is 3.5 M-U/l. The broth solution is prepared with the ADUN, urea, PVA, and THFA solution. The droplets of the broth solution was made through a nozzle system. From this study, we obtained the following results; 1) an externel chemical gelation process is a suitable method in the spherical $UO_3$ particle production, 2) the particle shape are changed by an urea mixing time, THFA volume, and the viscosity of the broth solution, 3) the amorphous $UO_3$ particles obtained from these experiments was converted to $U_{3}O_{8}$ and then $UO_2$ by heat treatment in hydrogen atmosphere at $600^{\circ}C$.

• Bulletin of the Korean Chemical Society
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• 제35권2호
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• pp.357-364
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• 2014

Size controlled, $LiNi_{0.8}Co_{0.15}Al_{0.05}O_2$ cathode powders were prepared by co-precipitation method followed by heat treatment at temperatures between 750 and $850^{\circ}C$. The synthesized samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical performance. The synthesized $LiNi_{0.8}Co_{0.15}Al_{0.05}O_2$ after calcined at $750^{\circ}C$ has a good electrochemical performance with an initial discharge capacity of $190mAhg^{-1}$ and good capacity retention of 100% after 30 cycles at 0.1C ($17mAg^{-1}$). The capacity retention of $LiNi_{0.8}Co_{0.15}Al_{0.05}O_2$ after calcined at $750^{\circ}C$ is better than that at 800 and $850^{\circ}C$ without capacity loss at various high C rates. This is ascribed to the minimized cation disorder, a higher conductivity, and higher lithium ion diffusion coefficient ($D_{Li}$) observed in this material. In the differential scanning calorimetry DSC profile of the charged sample, the generation of heat by exothermic reaction was decreased by calcined at high temperature, and this decrease is especially at $850^{\circ}C$. This behavior implies that the high temperature calcinations of $LiNi_{0.8}Co_{0.15}Al_{0.05}O_2$ prevent phase transitions with the release of oxygen.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.208-208
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• 2013

Graphene has emerged as a fascinating material for next-generation nanoelectronics due to its outstanding electronic properties. In particular, graphene-based field effect transistors (GFETs) have been a promising research subject due to their superior response times, which are due to extremely high electron mobility at room temperature. The biggest challenges in GFET applications are control of carrier concentration and opening the bandgap of graphene. To overcome these problems, three approaches to doping graphene have been developed. Here we demonstrate the decoration of Ni nanoparticles (NPs) on graphene films by simple annealing for p-type doping of graphene. Ni NPs/graphene films were fabricated by coating a $NiCl2{\cdot}6H2O$ solution onto graphene followedby annealing. Scanning electron microscopy and atomic force microscopy revealed that high-density, uniformly sized Ni NPs were formed on the graphene films and the density of the Ni NPs increased gradually with increasing $NiCl2{\cdot}6H2O$ concentration. The formation of Ni NPs on graphene films was explained by heat-driven dechlorination and subsequent particlization, as investigated by X-ray photoelectron spectroscopy. The doping effect of Ni NPs onto graphene films was verified by Raman spectroscopy and electrical transport measurements.