Young-Jin Lee

Deposition of ZnO Thin Films by the Ultrasonic Spray Pyrolysis Technique

This paper describes the design of an ultrasonic spray pyrolysis system and the determination of the optimal conditions for deposition of ZnO thin films. The film is desired to have strong piezoactivity, high resistivity, and good thickness uniformity. Zinc acetate is the source solution for the ZnO film on top of a SiO2/Si wafer. Controlled experiments show that the zinc acetate solution of 0.05 mol% doped with 30 at.% of LiCl can provide good ZnO films at the substrate temperature of 420°C. The optimal substrate rotation rate and nozzle tilting angle are also determined to improve the uniformity of the film. ZnO thin films deposited with these conditions show good c-axis orientation, and a resistivity higher than 107 Ωcm after annealing in oxygen, and good thickness uniformity across a 4 substrate wafer. Properties of the ZnO film developed in this study are comparable to those obtained with conventional techniques.

Development of Miniature Quad SAW filter bank based on PCB substrate

A miniaturization and integration are most important design factor in design of mobile handheld phone to enhance multi-function such as Bluetooth, camera and music so on. Especially in RF stage of multi-band GSM mobile phone, dozens of matching L, C passive components and several SAW filters occupy quite a little space, so phone makers partially use 7.0 times 3.5mm SAW filter bank instead of separate components. Current commercial filter bank is fabricated on PCB or LTCC base with 1.4 times 1.1 or 2.0 times 1.4(1.6)mm RF SAW end products, so the cost of this component is still similar to original one. This paper describes the development of a new 5.0 times 3.2 mm SAW filter bank which is consist of 12 L, C matching components and 4 SAW bare chips on PCB substrate with CSP technology. This technology can reduce the cost of materials down to 50% due to the elimination of 4 HTCC ceramic packages. We have investigated the multi-layered PCB substrate structures and raw materials to find out the optimal flip-bonding condition between the LiTaO3 wafer and PCB substrates. Also the optimal materials and processing conditions of epoxy laminating film were found out through the experiments which can reduce the bending moment caused by the difference of the thermal expansion between the PCB substrate and laminating film. The new PCB SAW filter bank shows good electrical and reliability performances with respect to the present one.

Effects of N2 on the Growth of Multiwalled Carbon Nanotubes Synthesized by Plasma-Enhanced Chemical Vapor Deposition

We have investigated the role of N2 in the synthesis of carbon nanotubes (CNTs) by dc hot-filament plasma-enhanced chemical vapor deposition. An NH3 and C2H2 gas mixture with a ratio of 4:1 was used as a precursor for the synthesis of CNTs on nickel-coated TiN/Si (100) substrates. N2 gas was introduced at a flow rate of 30–120 sccm with the precursor. The structure and composition of CNTs synthesized with/without N2 were investigated by scanning electron microscopy, transmission electron microscopy, X-ray photoemission spectroscopy (XPS), and Raman spectroscopy. The multiwalled carbon nanotubes (MWCNTs) synthesized with N2 were 2–5 times longer than those synthesized without N2, and the morphology of the MWCNTs was improved. An XPS core level spectrum shows that nitrogen is in the CNX and C–NH2 forms.

Platycodon grandiflorum root attenuates vascular endothelial cell injury by oxidized low-density lipoprotein and prevents high-fat diet–induced dyslipidemia in mice by up-regulating antioxidant proteins

We hypothesized that a Platycodon grandiflorum root (PG) ethyl acetate extract (PGEA) would help reduce the vascular cell injury caused by oxidized low-density lipoprotein (oxLDL) and prevent high-fat (HF) diet-induced dyslipidemia and oxidative stress by up-regulating antioxidant proteins. We investigated the protective effects of PGEA against vascular endothelial cell injury induced by oxLDL and dyslipidemia induced by an HF diet, and the mechanisms underlying these effects were studied. The protective effects of PGEA were investigated with respect to calf pulmonary arterial endothelial (CPAE) cell viability and the lactate dehydrogenase release during oxLDL treatment. The in vivo effects of PGEA were examined using C57BL/6 mice, which were fed an HF diet for 9 weeks. The HF diet was supplemented with 0, 25, or 75 mg/kg PGEA during the last 4 weeks of the experimental period. Histologic analyses of hepatic lipid accumulation were performed. The changes in antioxidant protein levels induced by PGEA, which protects against HF diet-induced oxidative stress, were measured using a proteomics approach. We found that PGEA exhibited antioxidant activity. In CPAE cells, PGEA inhibited both oxLDL-induced cell death and lactate dehydrogenase release. In the HF diet-induced obese mice that received PGEA, we observed significantly reduced plasma and hepatic lipid levels, demonstrating that PGEA has beneficial effects on hyperlipidemia. In addition, we found that PGEA caused the up-regulation of antioxidant proteins. These findings suggest that the antioxidant effects of PGEA may protect against oxidative stress-related diseases.

Nitrogen-incorporated multiwalled carbon nanotubes grown by direct current plasma-enhanced chemical vapor deposition

The nitrogen-incorporated multiwalled carbon nanotubes (N-MWCNTs) were synthesized by dc plasma-enhanced chemical vapor deposition with a gas mixture of C2H2, NH3, and N2. Nitrogens in the N-MWCNTs were pyridinic nitrogen and graphitic nitrogen. With increase in the flow rate of N2 gas during the synthesis of MWCNTs, the pyridinic nitrogen increased much more than graphitic nitrogen. The near-edge x-ray absorption fine structure spectra revealed that the density of states such as π*, σ*, and π*+σ* bands of the N-MWCNTs decreased with increase of concentration of pyridinic nitrogen incorporated in the MWCNTs. The intensity ratio of the D band to the G band of Raman spectrum increased with the incorporation of nitrogen into MWCNTs.

Ferroelectric and Piezoelectric Properties of 0.72Pb(Zr0.47Ti0.53)O3?0.28Pb[(Zn0.45Ni0.55)1/3Nb2/3]O3 Thick Films for Energy Harvesting Device Application

The Ferroelectric and piezoelectric properties of 0.72Pb(Zr0.47Ti0.53)O3–0.28Pb[(Zn0.45Ni0.55)1/3Nb2/3]O3 (PZT–PZNN) piezoelectric thick films were investigated for application to energy harvesting devices. The PZT–PZNN thick films were fabricated by a conventional tape casting process. The sintered PZT–PZNN thick film was highly dense and flat when the annealed temperature was 1100 °C. It exhibited substantial ferroelectric and piezoelectric properties of Pr = 20.6 µC/cm2, d33 = 370 pC/N, eT33/e0 = 1185, and kp = 0.44. Moreover, its d33g33, which can characterize high energy density material, is as large as approximately 13050×10-15 m2/N. Therefore, the PZT–PZNN thick film can be a potential piezoelectric material for application to energy harvesting devices.

A survival model for unthinned loblolly pine plantations that incorporates non-planted tree competition, site quality, and incidence of fusiform rust

Future biomass yields are functionally related to the number of trees surviving at a given age. A stand level survival model was developed that incorporates competition of non-planted trees, site quality, and the incidence of fusiform rust (Cronartium quercuum [Berk.] Miyabe ex Shirai f. sp. fusiforme). The model consists of a system of two equations, one of which represents the number of surviving trees infected by fusiform rust while the other represents the number of trees not infected by fusiform rust. Data from unthinned loblolly pine (Pinus taeda L.) plantations in East Texas were used to fit and evaluate the survival model and illustrate its use. The model successfully predicted that the number of surviving loblolly pine trees decreased as the number of non-planted trees increased. The model also successfully predicted the transition of loblolly pine trees from an uninfected to an infected status by fusiform rust.

Development of a New Design Technique for Surface Acoustic Wave Ladder Filters

Design of surface acoustic wave (SAW) ladder filters has been performed by trial and error, that is, by modifying the design variables step by step until performance of the filter satisfies given specifications. In this work, a new design method is developed that automatically determines the detailed pattern of a SAW ladder filter to meet all the given specifications. As a first step for the development, an analysis tool for the SAW ladder filter is produced by means of the Smith equivalent circuit analysis technique, and its validity is verified through comparison of calculated results with experimental data. With the analysis tool, we investigate variation of the filter performance in relation to the change in its design factors, and the results lead to the design algorithm. Validity and efficiency of the algorithm are illustrated with an exemplary design of a SAW ladder filter for cellular phones. The design scheme developed in this paper is so general that it can be applied to any other types of SAW filters too.

Design and fabrication of a dual-axial gyroscope with piezoelectric ceramics

Piezoelectric gyroscopes are devices for measuring the angular rotation of a system with respect to an inertial frame of reference by means of the Coriolis principle. Most current piezoelectric gyroscopes detect the angular velocity about a single axis of rotation. This paper describes the development of a new dual-axial gyroscope made out of the piezoelectric ceramic PZT, which can overcome the limitation of the current single-axial type. The validity of the new structure is checked through finite-element analysis. Based on the design, an experimental sample of the sensor is fabricated and its performance is discussed in comparison with the theoretical expectation. The results show that the present gyroscope is capable of measuring the rotational velocity over two orthogonal axes simultaneously with good enough sensitivity and distinction between the two axial components of the rotation.

Microstructure and Positive Temperature Coefficient of Resistivity Characteristics of Na 2 Ti 6 O 13 -Doped 0.94BaTiO3 3 -0.06(Bi 0.5 Na 0.5 )TiO 3 Ceramics

The microstructure and positive temperature coefficient of resistivity (PTCR) characteristics of 0.1 mol% doped (BBNT-NT001) ceramics sintered at various temperatures from to were investigated in order to develop eco-friendly PTCR thermistors with a high Curie temperature (). Resulting thermistors showed a perovskite structure with a tetragonal symmetry. When sintered at , the specimen had a uniform microstructure with small grains. However, abnormally grown grains started to appear at and a homogeneous microstructure with large grains was exhibited when the sintering temperature reached . When the temperature exceeded , the grain growth was inhibited due to the numerous nucleation sites generated at the extremely high temperature. It is considered that is responsible for the grain growth of the ) ceramics by forming a liquid phase during the sintering at around . The grain growth of the BBNT-NT001 ceramics was significantly correlated with a decrease of resistivity. All the specimens were observed to have PTCR characteristics except for the sample sintered at . The BBNT-NT001 ceramics had significantly decreased and increased resistivity jump with increasing sintering temperature at from to . Especially, the BBNT-NT001 ceramics sintered at exhibited superior PTCR characteristics of low resistivity at room temperature (), high resistivity jump (), high resistivity temperature factor (20.4%/), and a high Tc of .