• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.31 no.7
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• pp.462-468
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• 2018

The piezoelectric energy harvesting characteristics of a trapezoidal cantilever generator with lead zirconate titanate (PZT) laminate were investigated with various Ag inner electrodes. The piezoelectric mode of operation was a transverse mode by using a planar electrode pattern. The piezoelectric cantilever generator was fabricated using trapezoidal cofired-PZT/Ag laminates by five specimens of 2, 3, 4, 7, and 13 layers of Ag. As the number of Ag electrodes increased, impedance and output voltage at resonant frequency significantly decreased, and capacitance and output current showed an increasing tendency. A maximum output power density of $7.60mW/cm^3$ was realized for the specimen with seven Ag layers in the optimal condition of acceleration (1.2 g) and resistive load ($600{\Omega}$), which corresponds to a normalized power factor of $5.28mW/g^2{\cdot}cm^3$.

• JSTS:Journal of Semiconductor Technology and Science
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• v.14 no.1
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• pp.109-116
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• 2014

This paper presents a high-efficiency digital class-D audio amplifier using a composite interpolation filter for portable audio devices. The proposed audio amplifier is composed of an interpolation filter, a delta-sigma modulator, and a class-D output stage. To reduce power consumption, the designed interpolation filter has an optimized composite structure that uses a direct-form symmetric and Lagrange FIR filters. Compared to the filters with homogeneous structures, the hardware cost and complexity are reduced by about half by the optimization. The coefficients of the digital delta-sigma modulator are also optimized for low power consumption. The class-D output stage has gate driver circuits to reduce shoot-through current. The implemented class-D audio amplifier exhibited a high efficiency of 87.8 % with an output power of 57 mW at a load impedance of $16{\Omega}$ and a power supply voltage of 1.8 V. An outstanding signal-to-noise ratio of 90 dB and a total harmonic distortion plus noise of 0.03 % are achieved for a single-tone input signal with a frequency of 1 kHz.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.33-33
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• 2007

SoP-L 공정은 유전율이 상이한 재료를 이용하여 PCB 공정이 가능하고 다른 packaging 방법에 비해 공정 시간과 비용이 절약되는 잠정이 있다. 본 연구에서는 SoP-L 기술을 이용하여 Si 기판의 함몰에 판한 공정의 안정도와 함몰 시 제작된 때턴의 특성의 변화에 대해 관찰 하였다. Si 기판의 함몰에 Active device를 이용하여 특성의 변화를 살펴보고 공정의 안정도를 확립하려 했지만 Active device는 측정 시 bias의 확보와 특성의 민감한 변화로 인해 비교적 측정이 용이하고 공정의 test 지표를 삼기 위해 passive device 를 구현하여 함몰해 보았다. Passive device 의 제작 과정은 Si 기판 위에 spin coating을 통해 PI(Poly Imide)를 10um로 적층한 후에 Cr과 Au를 seed layer로 증착을 하였다. 그리고 photo lithography 공정을 통하여 photo resister patterning 후에 전해 Cu 도금을 거쳐 CPW 구조로 $50{\Omega}$ line 과 inductor를 형성하였다. 제작 된 passive device의 함몰 전 특성 추출 data와 SoP-L공정을 통한 함몰 후 추출 data 비교를 통해 특성의 변화와 공정의 안정도를 확립하였다. 차후 안정된 SoP-L 공정을 이용하여 Active device를 함몰 한다면 특성의 변화 없이 size 룰 줄이는 효과와 외부 자극에 신뢰도가 강한 기판이 제작 될 것으로 예상된다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.12
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• pp.809-814
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• 2014

Spinel thin films were prepared by the spin spray technique to develop new thermal imaging materials annealed at low temperature for uncooled microbolometer applications. The spinel thin films were deposited from $[(Ni_{0.30}Co_{0.33}Mn_{0.37})_{1-x}Cu_x]_3O_4$ ($0.1{\leq}x{\leq}0.2$) solutions and then annealed at $400^{\circ}C$ for 1 h in argon. Effects of Cu content (x) and deposition time on the electrical properties of the annealed films were investigated. With increasing deposition time, the resistivity of the annealed films increased. For the annealed films deposited for 1 min, the resistivity of x=0.15 films was lower than that of x=0.1 films due to the different grain sizes. The high temperature coefficient of resistance (TCR) of the annealed films could be obtained at temperature below $50^{\circ}C$. Typically, the resistivity of $127{\Omega}{\cdot}cm$ and TCR of -5.69%/K at $30^{\circ}C$ were obtained for x=0.1 films with deposition time of 1 min annealed at $400^{\circ}C$ for 1 h in argon.

• Korean Journal of Materials Research
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• v.18 no.1
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• pp.32-37
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• 2008

The electrical, optical, structural and surface properties of an indium tin oxide (ITO) film grown on a flexible PET substrate using a specially designed roll-to-roll (R2R) sputtering system as a function of the DC power, $Ar/O_2$ flow ratio, and rolling speed is reported. It was observed that both the electrical and optical properties of the ITO film on the PET substrate were critically dependent on the $Ar/O_2$ flow ratio. In addition, x-ray diffraction examination results showed that the structure of the ITO film on the PET substrate was an amorphous structure regardless of the DC power and the $Ar/O_2$ flow ratio due to a low substrate temperature, which was maintained constant by a main cooling drum. Under optimized conditions, ITO film with resistivity of $6.44{\times}10^{-4}{\Omega}-cm$ and transparency of 86% were obtained, even when prepared at room temperature. Furthermore, bending test results exhibited that R2R-grown ITO film had good flexibility which would be applicable to flexible displays and solar cells.

• Journal of the Korean Ceramic Society
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• v.43 no.2 s.285
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• pp.79-84
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• 2006

We studied the microstructure and magnetic property of the pulsed DC magnetron sputtered $Zn_{\0.8}Co_{0.2}O$ film as a function of substrate temperatures. The X-ray patterns of the $Zn_{\0.8}Co_{0.2}O$ film showed a strong (002) preferential orientation at $500^{\circ}C$. The films with a crystallite size of 23-35 nm were grown in the form of nano-sized structure and this tendency was remarkable with increasing substrate temperature. The UV-visible result showed that the $Zn_{\0.8}Co_{0.2}O$ film prepared above $300^{\circ}C$ has a high optical transmittance of over $80\%$ in the visible region. The absorption bands were observed due to sp-d interchange action by $Co^{2+}$ complex ion and dd transition in the region from 500 to 700nm. The resistivity of the film was below $10^{-1}\;\Omega-cm\;above\;300^{\circ}C$. The AGM analysis results for the all films showed the magnetic hysteresis curves of ferromagnetic nature. The low electrical resistivity and room temperature ferromagnetism of ZnCoO thin films 'deposited above $300^{\circ}C$ suggested the possibility for the application to Diluted Magnetic Semiconductors (DMSs).

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1425_1426
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• 2009

In this study, commercially available polyethylene terephthalate(PET), which is widely used as a substrate of flexible electronic devices, was modified by dielectric barrier discharge(DBD) method in an air condition at atmospheric pressure, and aluminium - doped zinc oxide (ZnO:Al) transparent conducting film was deposited on PET substrate by r. f. magnetron sputtering method. Surface analysis and characterization of the plasma-treated PET substrate was carried out using contact angle measurements, X-ray Photoelectron Spectroscopy(XPS) and Atomic Force Microscopy (AFM). Especially the effect of surface state of PET substrate on some important properties of ZnO:Al transparent conducting film such as electrical and morphological properties and deposition rate of the film, was studied experimentally. The results showed that the contact angle of water on PET film was reduced significantly from $62^{\circ}$ to $43^{\circ}$ by DBD surface treatment at 20 min. of treatment time. The plasma treatment also improved the deposition rate and electrical properties. The deposition rate was increased almost linearly with surface treatment time. The lowest electrical resistivity as low as $4.97{\times}10^{-3}[\Omega-cm]$ and the highest deposition rate of 234[${\AA}m$/min] were obtained in ZnO:Al film with surface treatment time of 5min. and 20min., respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.261-262
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• 2006

$CuInS_2$ thin films were synthesized by sulpurization of Cu/In Stacked elemental layer deposited onto glass Substrates by vacuum furance annealing at temperature 200[$^{\circ}C$]. And structural and electrical properties were measured in order to certify optimum conditions for growth of the ternary compound semiconductor $CuInS_2$ thin films with non-stoichiometry composition. $CuInS_2$ thin film was well made at the heat treatment 200[$^{\circ}C$] of SLG/Cu/In/S stacked elemental layer which was prepared by thermal evaporator, and chemical composition of the thin film was analyzed nearly as the proportion of 1:1:2. Physical properties of the thin film were investigated at various fabrication conditions substrate temperature, annealing and temperature, annealing time by XRD, FE-SEM and hall measurement system. At the same time, carrier concentration, hall mobility and resistivity of the thin films was $9.10568{\times}10^{17}[cm^{-3}]$, 312.502 [$cm^2/V{\cdot}s$] and $2.36{\times}10^{-2}[{\Omega}{\cdot}cm]$, respectively.

• Journal of the Korean Ceramic Society
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• v.44 no.12
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• pp.710-714
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• 2007

LSGM$(La_{0.8}Sr_{0.2}Ga_{0.8}Mg_{0.2}O_{3-{\delta}})$ is the very promising electrolyte material for lower-temperature operation of SOFCs, especially when realized in anode-supported cells. But it is notorious for reacting with other cell components and resulting in the highly resistive reaction phases detrimental to cell performance. LDC$(La_{0.4}Ce_{0.6}O_{1.8})$, which is known to keep the interfacial stability between LSGM electrolyte and anode, was adopted in the anode-supported cell, and its effect on the interfacial reactivity and electrochemical performance of the cell was investigated. No severe interfacial reaction and corresponding resistive secondary phase was found in the cell with LDC buffer layer, and this is due to its ability to sustain the La chemical potential in LSGM. The cell exhibited the open circuit voltage of 0.64V, the maximum power density of 223 $mW/cm^2$, and the ohmic resistance of $0.17{\Omega}cm^2$ at $700^{\circ}C$. These values were much improved compared with those from the cell without any buffer layer, which implies that formation of the resistive reaction phases in LSGM and then deterioration of the cell performance is resulted mainly from the La diffusion from LSGM electrolyte to anode.

• The Korean Journal of Ceramics
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• v.3 no.4
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• pp.263-268
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• 1997

RuO$_3$ thin films were deposited on Si(100) substrate at low temperatures by hot-wall metalorganic chemical vapor deposition. Bis(cyclopentadienyl) ruthenium, Ru$(C_5H_5)_2$, was used as the precursor RuO$_2$single phase was obtained at a low deposition temperature of 25$0^{\circ}C$ and the crystallinity of RuO$_2$thin films improved with increasing deposition temperature. RuO$_2$thin films grow perpendicularly to the substrate and show the columnar structure. The grain size of RuO$_2$films drastically increases with increasing the deposition temperature. The resistivity of the 180 nm-thick RuO$_2$thin films deposited at 27$0^{\circ}C$ was 136 $\mu$$\Omega$-cm and increased with decreasing film thickness. SrBi$_2Ta_2O_4$ thin films deposited by rf magnetron sputtering on the RuO$_2$bottom electrodes showed a fatigue-free characteristics up to ~10$^10$ cycles under 5 V bipolar square pulses and the remanent polarization, 2 P$_r$ and the coercive field, 2 E, were 5.2$\mu$C/$\textrm{cm}^2$ and 76.0 kV/cm, respectively, for an applied voltage of 5 V The leakage current density was about 7.0$\times$10$^{-6}$ A/$\textrm{cm}^2$ at 150 kV/cm.