• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.3.1-3.1
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• 2011

Over the past decade, the major efforts for lowering the cost of electronics has been devoted to increasing the packaging efficiency of the integrated circuits (ICs), which is defined by the ratio of all devices on system-level board compared to the area of the board, and to working on a larger but cheaper substrates. Especially, in flexible electronics, the latter has been the favorable way along with using novel nanomaterials that have excellent mechanical flexibility and electrical properties as active channel materials and conductive films. Here, the tool for achieving large area patterning is by printing methods. Although diverse printing methods have been investigated to produce highly-aligned structures of the nanomaterials with desired patterns, many require laborious processes that need to be further optimized for practical applications, showing a clear limit to the design of the nanomaterial patterns in a large scale assembly. Here, we demonstrate the alignment of highly ordered and dense silicon (Si) NW arrays to anisotropically etched micro-engraved structures using a simple evaporation process. During evaporation, entropic attraction combined with the internal flow of the NW solution induced the alignment of NWs at the corners of pre-defined structures. The assembly characteristics of the NWs were highly dependent on the polarity of the NW solutions. After complete evaporation, the aligned NW arrays were subsequently transferred onto a flexible substrate with 95% selectivity using a direct gravure printing technique. As proof-of-concept, flexible back-gated NW field effect transistors (FETs) were fabricated. The fabricated FETs had an effective hole mobility of 0.17 $cm2/V{\cdot}s$ and an on/off ratio of ${\sim}1.4{\times}104$. These results demonstrate that our NW gravure printing technique is a simple and effective method that can be used to fabricate high-performance flexible electronics based on inorganic materials.

• Journal of the Korean Vacuum Society
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• v.21 no.2
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• pp.99-105
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• 2012

We fabricated the textured silicon (Si) surface on Si substrates by the electrochemical etching using gold (Au) nanoparticle catalysts. The antireflective property of the fabricated Si nanostructures was improved. The Au nanoparticles of ~20-150 nm were formed by the rapid thermal annealing using thermally evaporated Au films on Si. In the chemical etching, the aqueous solution containing $H_2O_2$ and HF was used. In order to investigate the effect of electrochemical etching on the etching depth and reflectance characteristics, the sample was immersed in the aqueous etching solution for 1 min with and without applied cathodic voltages of -1 V and -2 V. As a result, the solar weighted reflectance, i.e., the averaged reflectance with considering solar spectrum (air mass 1.5), could be efficiently reduced for the electrochemically etched Si by applying the cathodic voltage of -2 V, which is expected to be useful for Si solar cell applications.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.7
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• pp.42-49
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• 1999

In this paper, we proposed a simple measurement method to find the behaviors of the fiber-to-waveguide coupler. The polished fiber blocks and planar waveguides on silicon dioxide were fabricated independently and then optically coupled by physical pressure. Several kinds of polymer with different refractive indices were used for waveguide films. The proposed method makes it possible to measure the center wavelength, bandwidth, extinction ratio, and polarization dependence of the coupler during fabrication procedure. The wavelength sensitivity increased with refractive index of polymer. The symmetric planar waveguide structure and isotropic property of guiding materials reduced polarization dependent property. Insertion loss of the coupler was less than 0.5dB. It is expected that our measurement method is useful for developing various optical devices using evanescent coupling between polished fiber and planar waveguide such as optical modulators and filters etc.

• Journal of the Microelectronics and Packaging Society
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• v.11 no.2 s.31
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• pp.29-35
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• 2004

Hafnium-oxide gate dielectric films deposited by a metal organic chemical vapor deposition technique on a $N_2-plasma$ treated SiNx and a hydrogen-terminated Si substrate have been investigated. In the case of $HfO_2$ film deposited on a hydrogen-terminated Si substrate, suppressed crystallization with effective carbon impurity reduction was obtained at $450^{\circ}C$. X-ray photoelectron spectroscopy indicated that the interface layer was Hf-silicate rather than phase separated Hf-silicide and silicon oxide structure. Capacitance-voltage measurements show equivalent oxide thickness of about 2.6nm for a 5.0 nm $HfO_2/Si$ single layer capacitor and of about 2.7 nm for a 5.7 nm $HfO_2/SiNx/Si$ stack capacitor. TEM shows that the interface of the stack capacitor is stable up to $900^{\circ}C$ for 30 sec.

• JSTS:Journal of Semiconductor Technology and Science
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• v.8 no.1
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• pp.21-26
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• 2008

We fabricated nano-particles of ZnO, $In_2O_3$ and $SnO_2$ by using the chemical reaction between metal thin films and polyamic acid. The average size and density of these ZnO, $In_2O_3$ and $SnO_2$ nano-particles was approximately 10, 7, and 15 nm, and $2{\times}10^{11},\;6{\times}10^{11},\;2.4{\times}10^{11}cm^{-2}$, respectively. Then, we fabricated nano-floating gate memory (NFGM) devices with ZnO and $In_2O_3$ nano-particles embedded in the devices' polyimide dielectrics and silicon dioxide layers as control and tunnel oxides, respectively. We measured the current-voltage characteristics, endurance properties and retention times of the memory devices using a semiconductor parameter analyzer. In the $In_2O_3$ NFGM, the threshold voltage shift (${\Delta}V_T$) was approximately 5 V at the initial state of programming and erasing operations. However, the memory window rapidly decreased after 1000 s from 5 to 1.5 V. The ${\Delta}V_T$ of the NFGM containing ZnO was approximately 2 V at the initial state, but the memory window decreased after 1000 s from 2 to 0.4 V. These results mean that metal-oxide nano-particles have feasibility to apply NFGM devices.

• Journal of the Korean Magnetics Society
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• v.13 no.3
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• pp.115-120
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• 2003

We have developed laser micro-machining technology for fabrication of the micro thin-film inductors. After the thin layers of FM/M/FM films were coated to the silicon substrate by using the conventional sputtering method, the new laser machining was applied to the patterning process that used to be carried out by the semiconductor lithography procedure. A CW Nd:YAG laser operating in TEM$\sub$00/ mode was actively Q-switched to obtain the very short pulse of 200 ns. The laser micro-machining process with pulse energy and repetition rate have been optimized as 5 mJ/pulse and 5 kHz, respectively, to obtain the line resolution as fine as 20 $\mu\textrm{m}$.

• Transactions on Electrical and Electronic Materials
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• v.18 no.1
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• pp.55-57
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• 2017

Amorphous oxide thin film transistors (TFTs) were fabricated with 0.5 wt% silicon doped zinc tin oxide (a-0.5SZTO) thin film deposited by radio frequency (RF) magnetron sputtering. In order to investigate the effect of annealing treatment on the electrical properties of TFTs, a-0.5SZTO thin films were annealed at three different temperatures ($300^{\circ}C$, $500^{\circ}C$, and $700^{\circ}C$ for 2 hours in a air atmosphere. The structural and electrical properties of a-0.5SZTO TFTs were measured using X-ray diffraction and a semiconductor analyzer. As annealing temperature increased from $300^{\circ}C$ to $500^{\circ}C$, no peak was observed. This provided crystalline properties indicating that the amorphous phase was observed up to $500^{\circ}C$. The electrical properties of a-0.5SZTO TFTs, such as the field effect mobility (${\mu}_{FE}$) of $24.31cm^2/Vs$, on current ($I_{ON}$) of $2.38{\times}10^{-4}A$, and subthreshold swing (S.S) of 0.59 V/decade improved with the thermal annealing treatment. This improvement was mainly due to the increased carrier concentration and decreased structural defects by rearranged atoms. However, when a-0.5SZTO TFTs were annealed at $700^{\circ}C$, a crystalline peak was observed. As a result, electrical properties degraded. ${\mu}_{FE}$ was $0.06cm^2/Vs$, $I_{ON}$ was $5.27{\times}10^{-7}A$, and S.S was 2.09 V/decade. This degradation of electrical properties was mainly due to increased interfacial and bulk trap densities of forming grain boundaries caused by the annealing treatment.

• Progress in Medical Physics
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• v.27 no.4
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• pp.213-219
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• 2016

The position verification of the radiation source utilized in brachytherapy forms a critical factor in determining the therapeutic efficiency. Currently, films are used to verify the source position; however, this method is encumbered by the lengthy time interval required from film scanning to analysis, which makes real-time position verification difficult. In general, the source position accuracy is usually tested in a monthly quality assurance check. In this context, this study investigates the feasibility of the real-time position verification of the radiation source in high dose rate (HDR) brachytherapy with the use of scintillating fibers. To this end, we construct a system consisting of scintillating fibers and a silicon photomultiplier (SiPM), optimize the dosimetric software setup and radiation system characteristics to obtain maximum measurement accuracy, and determine the relative ratio of the measured signals dependent upon the position of the scintillating fiber. According to the dosimetric results based on a treatment plan, in which the dwell time is set at 30 and 60 s at two dwell positions, the number of signals is 31.5 and 83, respectively. In other words, the signal rate roughly doubles in proportion to the dwell time. The source position can also be confirmed at the same time. With further improvements in the spatial resolution and scintillating fiber array, the source position can be verified in real-time in clinical settings with the use of a scintillating fiber-based system.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.158-158
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• 2017

Titanium and its alloys have been used in the field dental and orthopedic implants because of their excellent mechanical properties and biocompatibility. Despite these attractive properties, their passive films were somewhat bioinert in nature so that sufficient adhesion of bone cells to implant surface was delayed after surgical treatment. Recently, plasma electrolyte oxidation (PEO) of titanium metal has attracted a great deal of attention is a comparatively convenient and effective technique and good adhesion to substrates and it enhances wear and corrosion resistances and produces thick, hard, and strong oxide coatings. Silicon(Si), Zinc(Zn), and Manganese(Mn) have a beneficial effect on bone. Si in particular has been found to be essential for normal bone and cartilage growth and development. And, Zn has been shown to be responsible for variations in body weight, bone length and bone biomechanical properties. Also, Mn influences regulation of bone remodeling because its low content in body is connected with the rise of the concentration of calcium, phosphates and phosphatase out of cells. The objective of this work was research on bone-like apatite morphology on Si-Zn-Mn-hydroxyapatite coating on Ti-6Al-4V alloy by plasma electrolytic oxidation. Anodized alloys were prepared at 280V voltage in the solution containing Si, Zn, and Mn ions. The surface characteristics of PEO treated Ti-6Al-4V alloy were investigated using XRD, FE-SEM, and EDS.

• Journal of the Korean Vacuum Society
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• v.9 no.4
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• pp.373-378
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• 2000

There was a great difference in the formation kinetics of $TiO_2$ and $Bi_2O_3$ on silicon, but the growth of bismuth titanate (BIT) thin film was mainly limited by the formation of $TiO_2$. As a result, the BIT film was easy to be lack of bismuth. The pulse injection metalorganic chemical vapor deposition (MOCVD) process was introduced in order to overcome this problem by recovering the insufficient bismuth content in the film. By this pulse injection method, bismuth content was increased and also the uniform in-depth composition of the film was attained with a abrupt $Bi_4Ti_3O_{12}/Si$ interface. In addition, the crystallinity of $Bi_4Ti_3O_{12}$ thin film prepared by pulse injection process was greatly improved and the leakage current density was lowered by 1/2~1/3 of magnitude. Clockwise hysteresis of C-V was observed and the ferroelectric switching was confirmed for $Bi_4Ti_3O_{12}$ film deposited by pulse injection method.