• Journal of the Microelectronics and Packaging Society
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• v.8 no.4
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• pp.11-15
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• 2001

In this paper, hermetic sealing technology was studied for wafer level packaging of the RF-MEMS devices. With the flip-chip bonding method. this non-conductive B-stage epoxy sealing will be profit to the MEMS device sealing. It will be particularly profit to the RF-MEMS device sealing. B-stage epoxy can be cured by 2-step and hermetic sealing can be obtained. After defining 500 $\mu\textrm{m}$-width seal-lines on the glass cap substrate by screen printing, it was pre-baked at $90^{\circ}C$ for about 30 minutes. It was, then, aligned and bonded with device substrate followed by post-baked at $175^{\circ}C$ for about 30 minutes. By using this 2-step baking characteristic, the width and the height of the seal-line could be maintained during the sealing process. The height of the seal-line was controlled within $\pm$0.6 $\mu\textrm{m}$ in the 4 inches wafer and the bonding strength was measured to about 20MPa by pull test. The leak rate, that is sealing characteristic of the B-stage epoxy, was about $10^{-7}$ cc/sec from the leak test.

• Korean Journal of Crystallography
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• v.12 no.2
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• pp.70-75
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• 2001

The purpose of this study is to investigate the effect of V₂O/sub 5/ addition on physical and magnetic properties of NiCuZn ferrite for multi-layer chip inductors. NiCuZn ferrite pastes doped with 0, 0.1, 0.3 and 0.5 wt% V₂O/sub 5/ were prepared and samples of ferrite sheets were prepared by the screen printing method. They were sintered at 870, 880, 890 and 900℃, and then their physical and magnetic properties were analyzed. After sintering at 870℃, the sintered density of the ferrite sheet doped with 0.5wt% V₂O/sub 5/ showed the highest value to 5.08g/cm³due to the best densification by the liquid phase sintering, while the microstructures of ferrite sheets doped with 0.1 and 0.3 wt% V₂O/sub 5/ showed and inhibited grain growth. Irrespective of the sintering temperature, the initial permeability of ferrite sheet doped with 0.5 wt% V₂O/sub 5/ was highest and after sintering beyond 880℃, the quality factor of 0.3 wt% V₂O/sub 5/-doped sample appeared to be highest.

• Journal of the Korean Institute of Gas
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• v.11 no.1 s.34
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• pp.29-33
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• 2007

This study investigates the use of $TiO_{2},\;Pd,\;Pt$, and In which greatly improves a sensitivity to trimethylamine gas. The metal-$SnO_{2}$ thick films were prepared by screen-printing method onto $Al_{2}O_{3}$ substrates with platinum electrode. The sensing characteristics were investigated by measuring the electrical resistance of each sensor in a test box as a function of detecting gas concentration. This was then used to detect trimethylamine, dimethylamine, and ammonia vapours within the concentration range of 100-1000ppm. The gas sensing properties of metal-$SnO_{2}$ mixed thick films depended on the content and variety of metal. It was found that sensitivity and selectivity of the films dopped with 1 wt% Pd and 10 wt% $TiO_{2}$ for trimethylamin gas showed the best result at $250^{\circ}C$.

• Journal of the Microelectronics and Packaging Society
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• v.25 no.4
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• pp.149-154
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• 2018

This paper describes the fabrication and heat transfer property of 50 watts rated LED array module where multiple chips are mounted on chip-on-board type ceramic-metal hybrid substrate with high heat dissipation property for high power street and anti-explosive lighting system. The high heat transfer ceramic-metal hybrid substrate was fabricated by conformal coating of thick film glass-ceramic and silver pastes to form insulation and conductor layers, using thick film screen printing method on top of the high thermal conductivity aluminum alloy heat-spreading panel, then co-fired at $515^{\circ}C$. A comparative LED array module with the same configuration using epoxy resin based FR-4 PCB with thermalvia type was also fabricated, then the thermal properties were measured with multichannel temperature sensors and thermal resistance measuring system. As a result, the thermal resistance of the ceramic-metal hybrid substrate in the $4{\times}9$ type LEDs array module exhibited about one third to the value as that of FR-4 substrate, implying that at least triple performance of heat transfer property as that of FR-4 substrate was realized.

• Journal of Sensor Science and Technology
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• v.11 no.1
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• pp.18-27
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• 2002

$LaFeO_3$-based thick films with 2wt.%, 5wt.% and 10wt.% $Al_2O_3$ additives were fabricated by screen printing method on $Al_2O_3$ substrates. Structural, electrical and ammonia gas sensing characteristics of the thick films with different heat treatment temperatures were examined. From XRD results, the compound of $LaFeO_3$ and $Al_2O_3$ was not found until the heat treatment at $1200^{\circ}C$. SEM microphotograph showed similar grain growth despite the amount of $Al_2O_3$ additives with the heat treatment. Thick films with high activation energy and low resistance in the electrical properties showed high sensitivity for gases. Thick films with 2wt % $Al_2O_3$ additives heat-treated at $1200^{\circ}C$ showed the sensitivities of 210% for 100 ppm $NH_3$ gas at the working temperature of $350^{\circ}C$. The thick films showed food selectivity to $NH_3$ gas.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.9
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• pp.581-588
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• 2016

Piezoelectric thick films of a soft $Pb(Zr,Ti)O_3$ (PZT) based commercial material were produced by a conventional tape casting method. Thereafter, the interdigitated (IDT) Ag-Pd electrode pattern was printed on the $25{\mu}m$ thick piezoelectric film at room temperature. Co-firing of the 10-layer laminated piezoelectric thick films was conducted at $1,100^{\circ}C$ and $1,150^{\circ}C$ for 1 h, respectively. Piezoelectric cantilever energy harvesters were successfully fabricated using the IDT electrode pattern embedded piezoelectric laminates for 3-3 operation mode. Their energy harvesting characteristics were investigated with an excitation of 120 Hz and 1 g under various resistive loads (ranging from $10k{\Omega}$ to $200k{\Omega}$). A parabolic increase of voltage and a linear decrease of current were shown with an increase of resistive load for all the energy harvesters. In particular, a high output power of 3.64 mW at $100k{\Omega}$ was obtained from the energy harvester (sintered at $1,150^{\circ}C$).

• Journal of Sensor Science and Technology
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• v.11 no.2
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• pp.77-83
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• 2002

In order to get low cost and portability, semiconductor gas sensor need to have low operating temperature and high sensitivity. $Fe_2O_3$ based sensors which were doped with metal oxide catalysts($MoO_3$, $V_2O_5$, $TiO_2$, and CdO) were fabricated by screen printing method. To improve electrical stability of sensors, the $Fe_2O_3$ sensors were annealed in $N_2$ at $700^{\circ}C$ for 2 hours. The $V_2O_5$ doped $Fe_2O_3$ sensor showed about $80{\sim}90%$ sensitivity at alcohol 1,000 ppm and have good selectivity to hydrocarbon gas and tobacco odors. The fabricated sensor and PIC-chip were employed for portable alarm system.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.346-346
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• 2007

압전세라믹 재료는 현재 압전 변압기, actuator, transducer, sensor, speaker 등에 광범위하게 이용이 되고 있다. 이 중에서 압전세라믹 소결체를 이용한 스피커의 제조는 가공이 까다롭고, 대형의 크기로 제작 시 소자가 깨지는 등의 많은 제약을 받고 있으며, 저음 특성이 떨어져 응용 범위가 한정되어 있다. 따라서 최근에는 이러한 단점을 극복하기 위하여 세라믹/고분자 복합체를 이용한 필름 스피커를 제작하고자 시도하고 있다. 이러한 세라믹/고분자 0-3형 압전 복합체를 이용할 경우, 제품의 경량화를 실현할 수 있고, 크기나 환경의 영향을 거의 받지 않으므로, 고기능성 스피커로의 응용에 적합할 것으로 보인다. 따라서 본 연구에서는 PZT계의 세라믹와 PVDF, PVDF-TrFE, Polyester, acrylic resin 등의 여러 고분자 물질과의 복합체를 제조하여 압전특성을 평가하였다. 본 실험은 먼저 $(Pb_{1-a-b}Ba_aCd_b)(Zr_xTi_{1-x})_{1-c-d}(Ni_{1/3}Nb_{2/3})_c(Zn_{1/3}Nb_{2/3})_dO_3$ (이하 PZT라 표기)의 최적화 조성을 선택하여, $1050^{\circ}C$에서 소결된 분말을 48시간 ball milling방법 로 약 $1{\mu}m$ 크기로 분쇄하였다. 고분자 물질들은 알맞은 용제들을 선택하여 녹였다. 그 다음 소결된 PZT분말과 고분자를 50:50, 60:40, 65:35, 70:30등의 무게 분율로 혼합하고, 분산제, 소포제 등을 첨가하여 3단 roll mill을 이용하여 충분히 분산시켜 페이스트 (Paste)를 제조하였다. 제조된 페이스트를 ITO가 코팅된 PET필름 위에 스크린 프린팅 법을 사용하여 인쇄하여 $120^{\circ}C$에서 5분간 건조하였다. 코팅된 복합체의 두께는 약 $80{\mu}m$ 정도로 측정되었다. Ag 페이스트를 이용한 상부 전극 형성에도 스크린 프린팅 법을 적용하였다. 이를 $120^{\circ}C$에서 4 kV/mm의 DC 전계로 분극 공정을 수행한 후 전기적 특성을 평가하였다. 유전특성을 조사하기 위해서 LCR meter (EDC-1620)를 사용하였고, 시편의 결정구조는 XRD (Rigaku; D/MAX-2500H)을 통해 분석하였으며, 전자현미경(SEM)을 이용하여 미세구조를 분석하였다. 압전 전하상수$(d_{33})$ 값은 APC 8000 모델을 이용하여 측정하였다. PZT의 혼합비가 증가할수록 비유전율 및 압전 전하 상수 등의 전기적 특성이 증가되었다. 또 여러 고분자 물질 중에서 PVDF-TrFE 수지가 가장 우수한 특성을 보였다. 이는 PVDF-TrFE 수지가 압전성을 나타내기 때문인 것으로 판단되었다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.375-375
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• 2010

CdTe as an absorber material is widely used in thin film solar cells with the heterostructure due to its almost ideal band gap energy of 1.45 eV, high photovoltaic conversion efficiency, low cost and stable performance. The deposition methods and preparation conditions for the fabrication of CdTe are very important for the achievement of high solar cell conversion efficiency. There are some rearranged reports about the deposition methods available for the preparation of CdTe thin films such as close spaced sublimation (CSS), physical vapor deposition (PVD), vacuum evaporation, vapor transport deposition (VTD), closed space vapor transport, electrodeposition, screen printing, spray pyrolysis, metalorganic chemical vapor deposition (MOCVD), and RF sputtering. The RF sputtering method for the preparation of CdTe thin films has important advantages in that the thin films can be prepared at low growth temperatures with large-area deposition suitable for mass-production. The authors reported that the optical and electrical properties of CdTe thin film were closely connected by the thickness-uniformity of the film in the previous study [1], which means that the better optical absorbance and the higher carrier concentration could be obtained in the better condition of thickness-uniformity for CdTe thin film. The thickness-uniformity could be controlled and improved by the some process parameters such as vacuum level and RF power in the sputtering process of CdTe thin films. However, there is a limitation to improve the thickness-uniformity only in the preparation process [1]. So it is necessary to introduce the external or additional method for improving the thickness-uniformity of CdTe thin film because the cell size of thin film solar cell will be enlarged. Therefore, the authors firstly applied the chemical mechanical polishing (CMP) process to improving the thickness-uniformity of CdTe thin films with a G&P POLI-450 CMP polisher [2]. CMP process is the most important process in semiconductor manufacturing processes in order to planarize the surface of the wafer even over 300 mm and to form the copper interconnects with damascene process. Some important CMP characteristics for CdTe were obtained including removal rate (RR), WIWNU%, RMS roughness, and peak-to-valley roughness [2]. With these important results, the CMP process for CdTe thin films was performed to improve the thickness-uniformity of the sputtering-deposited CdTe thin film which had the worst two thickness-uniformities of them. Some optical properties including optical transmittance and absorbance of the CdTe thin films were measured by using a UV-Visible spectrophotometer (Varian Techtron, Cary500scan) in the range of 400 - 800 nm. After CMP process, the thickness-uniformities became better than that of the best condition in the previous sputtering process of CdTe thin films. Consequently, the optical properties were directly affected by the thickness-uniformity of CdTe thin film. The absorbance of CdTe thin films was improved although the thickness of CdTe thin film was not changed.

• Journal of the Korean Electrochemical Society
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• v.6 no.1
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• pp.59-64
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• 2003

We fabricated mixed ionic-electronic conducting membranes, $CH_4\;Using\;{0.7}Sr_{0.3}Ga_{0.6}Fe_{0.4}O_{3-\delta}$, by solid state reaction method for solid oxide fuel cell. The membranes consisted of single perovskite phase and exhibited high relative density, $>95\%$. We coated $La_{0.6}Sr_{0.4}CoO_{3-\delta}$ layer using screen printing method in order to improve surface reactivity of the $La_{0.7}Sr_{0.3}Ga_{0.6}Fe_{0.4}O_{3-\delta}$. As a result, the oxygen permeation flux of the coated $La_{0.7}Sr_{0.3}Ga_{0.6}Fe_{0.4}O_{3-\delta}$ showed higher value, $0.5ml/min{\cdot}cm^2\;at\;950^{\circ}C$ than the uncoated one. Higher oxygen permeation was observed in the porously coated Lao $La_{0.7}Sr_{0.3}Ga_{0.6}Fe_{0.4}O_{3-\delta}$membranes with larger grain sizes. Syngas, $CO+H_2$, was successfully obtained from methane gas, $CH_4$, using the $La_{0.6}Sr_{0.4}CoO_{3-\delta}$ coated $La_{0.7}Sr_{0.3}Ga_{0.6}Fe_{0.4}O_{3-\delta}$, with over $40\%\;of\;CH_4$ conversion and syngas yield. $La_{0.7}Sr_{0.3}Ga_{0.6}Fe_{0.4}O_{3-\delta}$ membrane was stable even when it was exposed to the reducing environment, methane, for 600 hrs at $950^{\circ}C$.