• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.05c
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• pp.93-96
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• 2002

In this study, PZT thin films were fabricated using sol-gel processing onto Si/$SiO_2$/Ti/Pt substrates. PZT sol with different Zr/Ti ratio(20/80, 30/70, 40/60, 52/48) were prepared, respectively. The films were fabricated by using the spin-coating method on substrates. The films were heat treated at $450^{\circ}C$, $650^{\circ}C$ by rapid thermal annealing(RTA). The preferred orientation of the PZT thin films were observed by X-ray diffraction(XRD), and Scanning electron microscopy(SEM). All of the resulting PZT thin films were crystallized with perovskite phase. The fine crystallinity of the films were fabricated. Also, we found that the ferroelectric properties from the dielectric constant of the PZT thin films were over 600 degrees, P-E hysteresis constant. And the leakage current densities of films were lower than $10^{-8}A/cm^2$. It is concluded that the PZT thin films by sol-gel process to be convinced of application for ferroelectric memory device.

• Analytical Science and Technology
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• v.33 no.2
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• pp.76-85
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• 2020

A stainless-steel needle (Hamilton 90022, 22 gauge, 718-㎛ o.d., 413-㎛ i.d., 51-mm length, bevel tip) with an electrochemically coated polyaniline layer having a microbore tunnel was newly prepared as a device for headspace in-needle microextraction. For designing the needle, the polyaniline layer length was optimized, and to evaluate the extraction efficiency for polycyclic aromatic hydrocarbons, numerous cyclic voltammetry scans were conducted. In addition, the optimization of the analytical conditions (including the adsorption and desorption parameters) and the validation of the analytical method were conducted. The optimized adsorption and desorption conditions were 40 ℃ for 30 min and 230 ℃ for 60 s, respectively. Finally, in this study, a polyaniline layer was electrochemically deposited on the in-needle surface, and it exhibited good thermal stability. The needle with the polyaniline layer was repeatedly used more than 200 times during this study. This method has some advantages in terms of the extraction time, extraction efficiency, and analysis cost.

• Journal of Electrical Engineering and information Science
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• v.2 no.6
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• pp.202-207
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• 1997

Design and fabrication issues for an L-band GaAs Monolithic Microwave Integrated Circuit(MMIC) Voltage Controlled Oscillator(VCO) as a component of Personal Communications Systems(PCS) Radio Frequency(RF) transceiver are discussed. An ion-implanted GaAs MESFET tailored toward low current and low noise with 0.5mm gate length and 300mm gate width has been used as an active device, while an FET with the drain shorted to the source has been used as the voltage variable capacitor. The principal design was based on a self-biased FET with capacitive feedback. A tuning range of 140MHz and 58MHz has been obtained by 3V change for a 600mm and a 300mm devices, respectively. The oscillator output power was 6.5dBm wth 14mA DC current supply at 3.6V. The phase noise without any buffer or PLL was 93dB/1Hz at 100KHz offset. Harmonic balance analysis was used for the non-linear simulation after a linear simulation. All layout induced parasitics were incorporated into the simulation with EEFET2 non-linear FET model. The fabricated circuits were measured using a coplanar-type probe for bare chips and test jigs with ceramic packages.

• New & Renewable Energy
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• v.5 no.2
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• pp.3-8
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• 2009

Tidal current power system is one of ocean renewable energies that can minimize the environmental impact with many advantages compared to other energy sources. Not like others, the produced energy can be precisely predicted without weather conditions and also the operation rate is very high. To convert the current into power, the first device encountered to the incoming flow is the rotor that can transform into rotational energy. The performance of rotor can be determined by various design parameters including numbers of blade, sectional shape, diameter, and etc. The stream lines near the rotating rotor is very complex and the interference effects around the system is also difficult to predict. The paper introduces the experiment of rotor performance and also the fundamental study on the characteristics of three different rotors and flow near the rotor by CFD.

• Journal of Life Science
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• v.19 no.6
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• pp.770-780
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• 2009

A new photosensitizer, 9-Hydroxypheophorbide-a (9-HpbD-a), was derived from Spirulina platensis. We conducted a series of experiments, in vitro and in vivo, to evaluate the anticancer effect and mechanism of photodynamic therapy using 9-HpbD-a and 660 nm diode lasers on a squamous carcinoma cell line. We studied the cytotoxic effects of pheophytin-a, 9-HpbD-a, 9-HpbD-a red and 660 nm diode lasers in a human head and neck cancer cell line (SNU-1041). Cell growth inhibition was determined by using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction assay. The effects of 9-HpbD was higher than those of 9-HpbD-a red or pheophytin-a in PDT. We then tested the cytotoxic effects of 9-hydroxypheophorbide-a (9-HpbD-a) in vitro. The cultured SNU-I041 cells were treated with serial concentrations of 9-HpbD-a followed by various energy doses (0, 0.1, 0.5, 3.2 J/$cm^{2}$) and by various interval times (0, 3, 6, 9, 12 hr) until laser irradiation, then MTT assay was applied to measure the relative inhibitory effects of photodynamic therapy (PDT). Optimal laser irradiation time was 30 minutes and the cytotoxic effects according to incubation time after 9-HpbD-a treatment increased until 6 hours, after which it then showed no increase. To observe the cell death mechanism after PDT, SUN-I041 cells were stained by Hoechst 33342 and propidium iodide after PDT, and observed under transmission electron microscopy (TEM). The principal mechanism of PDT at a low dose of 9-HpbD-a was apoptosis, and at a high dose of 9-HpbD-a it was necrosis. PDT effects were also observed in a xenografted nude mouse model. Group I (no 9-HpbD-a, no laser irradiation) and Group II (9-HpbD-a injection only) showed no response (4/4, 100%), and Group III (laser irradiation only) showed recurrence (1/4,25%) or no response (3/4, 75 %). Group IV (9-HpbD-a + laser irradiation) showed complete response (10/16, 62.5%), recurrence (4/16, 25%) or no response (2/16, 12.5%). Group IV showed a significant remission rate compared to other groups (p<0.05). These results suggest that 9-HpbD-a is a promising photosensitizer for the future and that further studies on biodistribution, toxicity and mechanism of action would be needed to use 9-HpbD-a as a photosensitizer in the clinical setting.

• Restorative Dentistry and Endodontics
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• v.29 no.6
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• pp.548-552
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• 2004

Intracanal disinfection of infected root canal is one of important treatment procedure. This in vitro study aimed to evaluate whether the surface polymers of controlled release drug (CRD) can effectively control the release rate of chlorhexidine for root canal disinfection. Four CRD prototypes were prepared: Group A (n=12); The core device (absorbent paper point) was loaded with 40% CHX solution as control. Group B (n=12); same as group A, but the device was coated with chitosan. Group C (n=12); same as group A and then coated three times with 5% PMMA. Group D (n=12); same as group A and then coated three times with 3% PLGA. All CRD prototypes were soaked in 3 mL distilled water for experimental periods and the concentrations of released CHX from each CRD prototype were determined using a UV spectrophotometer. Results showed that release rate of CHX were the greatest in the non-coated group (control group), followed by the chitosan-coated group, the PLGA-coated group, and the PMMA-coated group (P < 0.05). This data indicate that surface polymers can control the release rate of CHX from the CRD prototypes.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.101.1-101.1
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• 2016

Van der Waals (vdW) heterostructures built from two-dimensional layered materials provide an unprecedented opportunity in designing new material systems because the lack of dangling bonds on the vdW surfaces enables the creation of high-quality heterointerfaces without the constraint of atomically precise commensurability. In particular, the ability to build artificial heterostructures, combined with the recent advent of transition metal dichalcogenides, allows the fabrication of unique semiconductor heterostructures in an ultimate thickness limit for fundamental studies as well as novel device applications. In this talk, we will present the characterization of the electronic and optoelectronic properties of atomically thin p-n junctions consisting of vertically stacked WSe2 and MoS2 monolayers. We observed gate-tunable diode-like current rectification and a photovoltaic response across the p-n interface. Unlike conventional bulk p-n junctions, the tunneling-assisted interlayer recombination of the majority carriers is responsible for the tenability of the charge transport and the photovoltaic response. Furthermore, we will discuss the enhanced optoelectronic characteristics in graphene-sandwiched vdW p-n junctions.

• JSTS:Journal of Semiconductor Technology and Science
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• v.10 no.2
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• pp.130-133
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• 2010

This paper presents a study of the influence of variation of counter doping thickness on short channel effect in symmetric double-gate (DG) nano MOSFETs. Short channel effects are estimated from the computed values of current-voltage (I-V) characteristics. Two dimensional Quantum transport equations and Poisson equations are used to compute DG MOSFET characteristics. We found that the transconductance ($g_m$) and the drain conductance ($g_d$) increase with an increase in p-type counter-doping thickness ($T_c$). Very high value of transconductance ($g_m=38\;mS/{\mu}m$) is observed at 2.2 nm channel thickness. We have established that the threshold voltage of DG MOSFETs can be tuned by selecting the thickness of counter-doping in such device.

• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1858-1860
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• 1999

To fabricate superconducting multiplexers with narrow pass band characteristics and reduce the physical size of device, we have designed multiplexer using hair-pin type filters with the center frequency of 13.6 GHz. Multiplexers have been fabricated superconductor(HTS), because It has low surface resistance. The $YBa_2Cu_3O_{7-{\delta}}$(YBCO) films were deposited on MgO substrates$(20{\times}20{\times}0.5mm^3)$ by using pulsed laser deposition and conventional photo-lithographic methods were used to pattern the multiplexer. Epitaxial YBCO films were grown on(100) MgO substrates and showed strongly c_axis orientations observed by X-ray diffraction technique. Superconducting transition temperatures were measured to be about 89K. Simulated results of superconducting multiplexer consisting of hair-pin type filters show the insertion loss of about 1.2dB. The measured frequency response will be compared with the simulated results.

• Proceedings of the KIEE Conference
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• 2002.07b
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• pp.857-859
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• 2002

This paper describes an analysis of Magnetic actuator with permanent magnet using 2-D axisymmetric finite element method. Magnetic actuator is the machine to change electrical signal into mechanical signal, and fast switching device to be used for breaker and automation field etc. This magnetic actuator considered action for armature distance, external circuit, and nonlinear material characteristic and current. Also, comparative analysis is performed for 2 coil type and 1 coil type by coil type of actuator, then characteristic is grasped. It is Combined with external circuit for analyzing transient characteristic by variable time. According to the results, we analyzed action characteristic of Magnetic actuator.