• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.254-254
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• 2011

The memories with nano-particles are very attractive because they are promising candidates for low operating voltage, long retention time and fast program/erase speed. In recent, various nano-floating gate memories with metal-oxide nanocrystals embedded in organic and inorganic layers have been reported. Because of the carrier generation in semiconductor, induced photon pulse enhanced the program/erase speed of memory device. We studied photo-induced electrical properties of these metal-oxide nanocrystal memory devices. At first, 2~10-nm-thick Sn and In metals were deposited by using thermal evaporation onto Si wafer including a channel with $n^+$ poly-Si source/drain in which the length and width are 10 ${\mu}m$ each. Then, a poly-amic-acid (PAA) was spin coated on the deposited Sn film. The PAA precursor used in this study was prepared by dissolving biphenyl-tetracarboxylic dianhydride-phenylene diamine (BPDA-PDA) commercial polyamic acid in N-methyl-2-pyrrolidon (NMP). Then the samples were cured at 400$^{\circ}C$ for 1 hour in N atmosphere after drying at 135$^{\circ}C$ for 30 min through rapid thermal annealing. The deposition of aluminum layer with thickness of 200 nm was followed by using a thermal evaporator, and then the gate electrode was defined by photolithography and etching. The electrical properties were measured at room temperature using an HP4156a precision semiconductor parameter analyzer and an Agilent 81101A pulse generator. Also, the optical pulse for the study on photo-induced electrical properties was applied by Xeon lamp light source and a monochromator system.

• Proceedings of the KIEE Conference
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• 2006.07c
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• pp.1341-1342
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• 2006

Electrical characteristics of field-effect thin film transistors (TFTs) with p-channels of CdTe/CdHgTe core-shell nanocrystals are investigated in this paper. For the fabrication of bottom- and top-gate TFTs, CdTe/CrHgTe nanocrystals synthesized by colloidal method are first dispersed on oxidized p+ Si substrates by spin-coating, the dispersed nanoparticles are sintered at $150^{\circ}C$ to form the channels for the TFTs, and $Al_{2}O_{3}$ layers are deposited on the channels. A representative bottom-gate field-effect TFT with a bottom-gate $SiO_2$ layer exhibits a mobility of $0.21cm^2$/ Vs and an Ion/Ioff ratio of $1.5{\times}10^2$ and a representative top-gate field-effect TFT with a top-gate $Al_{2}O_{3}$ layer provides a field-effect mobility of $0.026cm^2$/ Vs and an Ion/Ioff ratio of $2.5{\times}10^2$. $Al_{2}O_{3}$ was deposited for passivation of CdTe/CdHgTe core-shell nanocrystal layer, resulting in enhanced hole mobility, Ior/Ioff ratio by 0.25, $3{\times}10^3$, respectively. The CdTe/CdHgTe nanocrystal-based TFTs with bottom- and top gate geometries are compared in this paper.

• Journal of the Korean Vacuum Society
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• v.9 no.3
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• pp.216-220
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• 2000

Photoluminescence (PL) results of $Si^+$-implanted $SiO_2$films on crystalline silicon are reported. Visible and infrared PL are observed for all the samples. The PL spectrums have about 7000 $\AA$, 7400 $\AA$ and 8400 $\AA$ peak positions. As amount of $Si^+$ ion dose changed, the PL peak positions and intensity are changed. In particular, the PL spectrum has three peaks and more intensity than the other $Si^+$ ion implantation samples for $1{\times}10^{17}/cm^2$ $Si^+$ ion implantation. Not nanocrystal but defects that $Si^+$ ions treated are contributed to the PL spectrum. For the changes of $Si^+$ ion dose and annealing time, O rich radiative defects, Si rich radiative defects, and nonradiative defects control the PL spectrum. We confirmed that more radiative defects can be created by control of $Si^+$ ion dose.

• Journal of Magnetics
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• v.8 no.4
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• pp.157-159
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• 2003

The strengths of the inter-grain exchange interaction were evaluated for nanocrystalline $Nd_{2.33}Fe_{14}B_{1.06}Si_{0.21}$ magnets of different grain size by comparing the $_{i}H_{c}$ calculated by micromagnetics with the experiments. With increase of the grain boundary thickness to that of the magnet of grain diameter 12.4, 24.8, 37.2 and 49.6 nm, the strengh of the interaction in reference to that without the grain boundary phase decreases to 83％, 69％, 54％ and 42％.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.54 no.10
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• pp.438-442
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• 2005

Si nanocrystal (Si NC) memory device has several advantages such as better retention, lower operating voltage, reduced punch-through and consequently a smaller cell area, suppressed leakage current. However, the physical and electrical reasons for this behavior are not completely understood but could be related to interface states of Si NCs. In order to find out this effect, we characterized electrical properties of Si NCs embedded in a SiO$_{2}$ layer by scanning probe microscopy (SPM). The Si NCs were generated by the laser ablation method with compressed Si powder and followed by a sharpening oxidation. In this step Si NCs are capped with a thin oxide layer with the thickness of 1$\~$2 nm for isolation and the size control. The size of 51 NCs is in the range of 10$\~$50 m and the density around 10$^{11}$/cm$^{2}$ It also affects the interface states of Si NCs, resulting in the change of electrical properties. Using a conducting tip, the charge was injected directly into each Si NC, and the image contrast change and dC/dV curve shift due to the trapped charges were monitored. The results were compared with C-V characteristics of the conventional MOS capacitor structure.

• Tribology and Lubricants
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• v.31 no.4
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• pp.157-162
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• 2015

In this study, an ultrasonic nanocrystalline surface modification (UNSM) technique is applied to tungsten carbide-cobalt (WC-Co) to extend the service life of carbide parts used in press mold. The UNSM technique modifies the structure, reduces the surface roughness, increases the surface hardness, induces the compressive residual stress, and increases the wear resistance of materials by introducing severe plastic deformation. The surface roughness, hardness, and compressive residual stress of WC after UNSM treatment improve by about 42, 10, and 71%, respectively. A wear test under dry conditions is used to assess the effectiveness of the UNSM technique on the friction and wear behavior of WC. The UNSM technique is found to reduce the WC friction coefficient by approximately 21% and enhance the wear resistance by approximately 85%. The improved friction and wear behavior of WC may be mainly attributed to the increased hardness and compressive residual stress. Moreover, the WC specimen is treated by UNSM technique using three different WC, silicon nitride (Si₃N₄) and stainless steel (STS304) balls. The surface treated by WC balls shows the highest hardness when compared with treatment by stainless steel and silicon nitride balls. According to the obtained results, the UNSM technique is believed to increase the durability of the carbide component by improving the friction and wear behavior.

• Journal of Integrative Natural Science
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• v.2 no.1
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• pp.37-40
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• 2009

Synthesis and characterization of alkyl-capped nanocrystalline silicon (R-n-Si) have been achieved from the reaction of silicontetrachloride with magnesiumsilicide. Surface of silicon nanocrystal has been derivatized with various alkyl groups (R=methyl, n-butyl, etc.). Silicon nanoparticles have been also obtained by the sonication of luminescent porous silicon. Former exhibits an emission band at 360 nm, but latter exhibits an emission band at 680 nm. In this study very sensitive detection of TNT (2,4,6-trinitrotoluene), DNT (2,4-dinitrotoluene), NB (nitrobenzene), and PA (picric acid) has been achieved in gas phase with porous silicon using photoluminescence quenching of the silicon crystallites as a transduction mode. Porous silicon are electrochemically etched from crystalline silicon wafers in an aqueous solution of hydrofluoric acid. We have characterized these silicon nanoparticles by Luminescence Spectrometer (LS 55).

• Proceedings of the KIEE Conference
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• 2004.11a
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• pp.95-97
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• 2004

본 연구에서는 Scanning Capacitance Microscopy (SCM)와 Electrostatic Force Microscopy (EFM)을 이용하여 국소영역에서 실리콘나노 크리스탈의 전기적 특성을 분석하였다. 실리콘 나노 크리스탈은 에어로솔 방식으로 P-type 실리콘웨이퍼 위에 $10{\sim}40\;nm$의 크기와 약 $10^{11}/cm^2$의 밀도를 갖도록 제작하였다. 실리콘 나노 크리스탈에서 전자와 정공의 trapping 현상은 EFM, SCM 이미지를 통하여 관찰하였고 이러한 나노 크리스탈의 국소영역 특성을 MOS 캐패시터 구조의 C-V 특성을 비교 분석하였다. 또한, 나노 크리스탈에 trapping된 전하의 detrapping 과정을 스트레스 조건에 따라 분석하였다.

• Journal of the Korean Vacuum Society
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• v.21 no.5
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• pp.273-278
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• 2012

Over the last decade, the hafnium-based gate dielectric materials have been studied for many application fields. Because these materials had excellent behaviors for suppressing the quantum-mechanical tunneling through the thinner dielectric layer with higher dielectric constant (high-K) than $SiO_2$ gate oxides. Although high-K materials compensated the deterioration of electrical properties for decreasing the thickness of dielectric layer in MOSFET structure, their nano-mechanical properties of $HfO_2$ thin film features were hardly known. Thus, we examined nano-mechanical properties of the Hafnium oxide ($HfO_2$) thin film in order to optimize the gate dielectric layer. The $HfO_2$ thin films were deposited by rf magnetron sputter using hafnium (99.99%) target according to various oxygen gas flows. After deposition, the $HfO_2$ thin films were annealed after annealing at $400^{\circ}C$, $600^{\circ}C$ and $800^{\circ}C$ for 20 min in nitrogen ambient. From the results, the current density of $HfO_2$ thin film for 8 sccm oxygen gas flow became better performance with increasing annealing temperature. The nano-indenter and Weibull distribution were measured by a quantitative calculation of the thin film stress. The $HfO_2$ thin film after annealing at $400^{\circ}C$ had tensile stress. However, the $HfO_2$ thin film with increasing the annealing temperature up to $800^{\circ}C$ had changed compressive stress. This could be due to the nanocrystal of the $HfO_2$ thin film. In particular, the $HfO_2$ thin film after annealing at $400^{\circ}C$ had lower tensile stress, such as 5.35 GPa for the oxygen gas flow of 4 sccm and 5.54 GPa for the oxygen gas flow of 8 sccm. While the $HfO_2$ thin film after annealing at $800^{\circ}C$ had increased the stress value, such as 9.09 GPa for the oxygen gas flow of 4 sccm and 8.17 GPa for the oxygen gas flow of 8 sccm. From these results, the temperature dependence of stress state of $HfO_2$ thin films were understood.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.282.1-282.1
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• 2016

The remarkable physical properties of two-dimensional (2D) semiconducting materials such as molybdenum disulfide ($MoS_2$) and tungsten disulfide ($WS_2$) etc. have attracted considerable attentions for future high-performance electronic and optoelectronic devices. The ongoing studies of $MoS_2$ based nonvolatile memories have been demonstrated by worldwide researchers. The opening hysteresis in transfer characteristics have been revealed by different charge confining layer, for instance, few-layer graphene, $MoS_2$, metallic nanocrystal, hafnium oxide, and guanine. However, limited works built their nonvolatile memories using entirely of assembled 2D crystals. This is important in aspect view of large-scale manufacture and vertical integration for future memory device engineering. We report $WS_2$ based nonvolatile memories utilizing functional van der Waals heterostructure in which multi-layered graphene is encapsulated between $SiO_2$ and hexagonal boron nitride (hBN). We experimentally observed that, large memory window (20 V) allows to reveal high on-/off-state ratio (>$10^3$). Moreover, the devices manifest perfect retention of 13% charge loss after 10 years due to large graphene/hBN barrier height. Interestingly, the performance of our memories is drastically better than ever published work related to $MoS_2$ and black phosphorus flash memory technology.