• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2008.11a
• /
• pp.205-205
• /
• 2008

PZT 세라믹은 우수한 유전 및 압전특성을 갖고 있어 변압기, 센서 및 엑츄에이터 등에 널리 응용되고 있다. 그러나, 우수한 특성에도 불구하고 PZT세라믹스의 소결시 PbO의 높은 유독성 및 휘발로 인하여 환경오염을 야기 시킨다. 그러므로 PbO로 구성된 세라믹을 대체하기 위한 우수한 압전특성을 가진 비납계 세라믹스 개발이 연구의 주류를 이루고 있다. 그 중 비납계 NKN와 BZT는 대체물질로 많이 관심을 받고 있다. 이는 일반적인 NKN조성은 우수한 압전성과 높은 큐리온도를 가지고 있을 뿐만 아니라, BZT조성의 Zr성분이 큐리온도를 낮추거나 유전특성을 졸게 하여 유전율 곡선을 완화하게 하는 특징이 있다. 하지만 NKN은 $1140^{\circ}C$이상의 소결온도에서 K의 휘발특성으로 인해 소성 후에도 주변의 수분을 흡수하는 조해성이 발생하는 문제가 발생한다. 그래서 본 연구에서는 낮은 온도에서 NKN계 세라믹스의 밀도를 증가시킬 뿐만 아니라, 우수한 유전 및 압전특성을 갖는 세라믹스를 제조하고자 비납계 $0.94(K_{0.5}Na_{0.5})NbO_3-0.06Ba(Zr_{0.05}Ti_{0.95})O_3$ (NKN-BZT)의 조성을 사용하였고 소결조제로는 $MnO_2$, NiO, $Bi_2O_3$, ZnO, $Li_2CO_3$, CuO등을 변화주어 유전 및 압전 특성을 알아보았다.

• Proceedings of the KWS Conference
• /
• 2009.11a
• /
• pp.76-76
• /
• 2009

눈부신 전자산업의 발달로 대부분의 전자제품이 다기능/경박단소화 되고 있어, 고밀도 실장 기술인 양면 표면실장과 고집적 패키징 기술인 패키지 적층 공정의 적용이 점차 확대되고 있다. 따라서 양면 표면실장 및 패키지 적층 공정에 사용되는 저온 접합용 무연 솔더 즉, $183^{\circ}C$(Sn-37Pb 공정 솔더 융점) 이하의 융점을 가지는 저온 무연 솔더에 대한 관심이 높아지고 있다. 한편, 미세피치 적용 분야에 있어 ACF/P를 이용한 COG 접속 분야 외에도 최근 저온 접합용 무연 솔더를 이용한 접속 분야가 각광을 받고 있다. 따라서, 접속피치 미세화에 대응하기 위해 스크린 인쇄성을 향상시킬 수 있는 저온 무연 솔더 paste 제조 및 공정 기술의 개발이 필요한 실정이다. 현재 대표적인 저온 무연 솔더 조성은 Sn-Bi계($138^{\circ}C$ 융점)와 Sn-In계($120^{\circ}C$ 융점)이다. 하지만, 이들 조성의 신뢰성 등에 있어 개선의 여지가 있으므로 이를 해결하기 위한 무연솔더 조성의 개발이 필요하다. 이와 같은 관점에서, 본 연구는 $137^{\circ}C$의 융점을 갖는 Sn-57.6Ag-0.4Ag 저온 무연 솔더 paste를 $217^{\circ}C$의 융점을 갖는 Sn-3.0Ag-0.5Cu 솔더 paste와 비교하여 인쇄성, reflow 특성, void inspection, 미세조직 관찰 및 underfill 적용 등의 실험을 실시하였다.

• Economic and Environmental Geology
• /
• v.26 no.4
• /
• pp.445-454
• /
• 1993

The Keumseongsan caldera is composed of the Cretaceous sedimentary rocks of the Gyeonesang Supergroup, volcanic rocks of the Yucheon Group and basic dykes. The Keumseongsan caldera is formed by subsidence of volcanic rocks, and arc fault developed late. Also, synistral strike-slip fault ($N60^{\circ}W$) developed. Volcanic rocks belong to subalkaline rocks and calcalkaline magma series. First tuffaceous breccia erupted before 71.4 Ma and cavity of magma chamber caused subsidence, which formed arc fault. Basaltic lava erupted at 71.4 Ma and residual fluids containing Fe, As, Pb, Zn and Cu metal elements built the Ohto deposits, which are dated to be 70.5 Ma based on K-Ar age for sericite. Tuffaceous breccia and tuff erupted between 70.5 and 67 Ma. When volcanic eruption became weakened, cavity in site of magma chamber brought subsidence. Rhyolite intruded and erupted at 67 Ma, and intrusive rhyolite intruded according to arc faults, also. Hydrothermal fluids containing Fe, As, Pb, Zn, Cu, Sb, Bi, Au and Ag formed the Tohyeon deposits. K-Ar age for sericite from the Tohyeon mine gives 66.0 Ma. Results of field exploration, geochemical analyses of volcanic rocks support mineralization possibility by volcanism. Especially, age of volcanism and mineralization are well in coincidence with results of K-Ar age dating. By these results, Ohto Cu mineralization is regarded to be associcated with basaltic rocks, while Tohyeon Cu mineralization with rhyolitic rocks.

• The Journal of Korean Academy of Prosthodontics
• /
• v.42 no.1
• /
• pp.30-40
• /
• 2004

Purpose : The purpose of this study was aimed to compare the shear bond strength on dentin of three dentin bonding agents and two resin cements used in conjunction with self-cured composite resin core material. Material and method : Control group and six experimental groups were divided for this study. Control group was designated as specimens bonded with Tenure$ A&B^{(R)}$. Experimental groups were as follows : PB-BL group : specimens bonded with Prime&Bond $NT^{(R)}$, $BondLink^{(R)}$ SB-BL group : specimens bonded with $^{(R)}$, BondLink$SingleBond^{(R)}$ PB group : specimens bonded with Prime&Bond $NT^{(R)}$ SB group : specimens bonded with $SingleBond^{(R)}$ PF group : specimens bonded with $Panavia-F^{(R)}$ BI group specimens bonded with Bistite $II^{(R)}$ All specimens were stored in $37^{\circ}C$ distilled water for 24 hours, followed by the shear bond strength was tested by universal testing machine. The data was analysed statistically by Mann-Whitney test. Results : 1. For Prime&Bond $NT^{(R)}$ and $SingleBonde^{(R)}$, the shear bond strength was 0.24 MPa and 7.19 MPa each by each, while Tenure $A&B^{(R)}$ group control was measured at 13.93 MPa (p<0.05). Especially for Prime&Bond $NT^{(R)}$ it did not get conjunction with dentin. 2. For Prime&Bond $NT^{(R)}$ and $SingleBond^{(R)}$ using $BondLink^{(R)}$, there was no significant difference as a result of 11.73 MPa and 14.00 MPa each by each (p<0.05). 3. For $Panavia-F^{(R)}$ and Bistite $II^{(R)}$, they showed the highest shear bond strength as measured by 18.24 MPa and 16.09 MPa each (p<0.05).

• Journal of the Korean Solar Energy Society
• /
• v.38 no.1
• /
• pp.45-55
• /
• 2018

Environmentally benign lead-free solder coated ribbon (e. g. SnCu, SnZn, SnBi${\cdots}$) has been intensively studied to interconnect cells without lead mixed ribbon (e. g. SnPb) in the crystalline silicon(c-Si) photovoltaic modules. However, high melting point (> $200^{\circ}C$) of non-lead based solder provokes increased thermo-mechanical stress during its soldering process, which causes early degradation of PV module with it. Hence, we proposed low-temperature conductive paste (CP) based tabbing method for lead-free ribbon. Modules, interconnected by the lead-free solder (SnCu) employing CP approach, exhibits similar output without increased resistivity losses at initial condition, in comparison with traditional high temperature soldering method. Moreover, 400 cycles (2,000 hour) of thermal cycle test reveals that the module integrated by CP approach withstands thermo-mechanical stress. Furthermore, this approach guarantees strong mechanical adhesion (peel strength of ~ 2 N) between cell and lead-free ribbons. Therefore, the CP based tabbing process for lead free ribbons enables to interconnect cells in c-Si PV module, without deteriorating its performance.

• Transactions on Electrical and Electronic Materials
• /
• v.1 no.2
• /
• pp.32-37
• /
• 2000

Effect of alloying element additions to Ag on thermal conductivity and electrical conductivity of sheath materials for Bi-Pb-Sr-Ca-Cu-O(BSCCO) tapes has been characterized. The thermal conductivity at low temperature range (10~300K) of Ag and Ag alloys were evaluated by both direct and indirect measurement techniqueas and compared with each other, It was observed that the thermal conductivity decreases with increasing the content of alloying element such as Au, Pd and Mg. Thermal conductivity of pure Ag at 3 0K was measured to be 994.0 W(m.K) on the other hand, the corresponding values of $Ag_{0.9995}Mg_{0.0005}$, $Ag_{0.974}$, $Au_{0.025}$, $Mg_{0.001}$, $Ab_{0.973}$, $Au_{0.025}$, $Mg_{0.002}$ and $Ag_{0.92}$, $Pb_{0.06}$, $Mg_{0.02}$ were 342.6, 62.1, 59.2 and 28.9 W(m.K), respectively, indicating 3 to 30 times lower than that of pure Ag. In addition, the thermal conductivity of pure Ag measured by direct and indirect measurement techniques was 303.2 and 363.8 W(m.K) The difference in this study is considered to be within an acceptable error range compared to the reference data.

• Journal of Radiation Protection and Research
• /
• v.47 no.4
• /
• pp.214-225
• /
• 2022

Background: The conventional cerium-doped Gd₂Al₂Ga₃O₁₂ (GAGG(Ce)) scintillator-based gamma-ray imager has a bulky detector, which can lead to incorrect positioning of the gammaray source if the shielding against background radiation is not appropriately designed. In addition, portability is important in complex environments such as inside nuclear power plants, yet existing gamma-ray imager based on a tungsten mask tends to be weighty and therefore difficult to handle. Motivated by the need to develop a system that is not sensitive to background radiation and is portable, we changed the material of the scintillator and the coded aperture. Materials and Methods: The existing GAGG(Ce) was replaced with Bi₄Ge₃O₁₂ (BGO), a scintillator with high gamma-ray detection efficiency but low energy resolution, and replaced the tungsten (W) used in the existing coded aperture with lead (Pb). Each BGO scintillator is pixelated with 144 elements (12 × 12), and each pixel has an area of 4 mm × 4 mm and the scintillator thickness ranges from 5 to 20 mm (5, 10, and 20 mm). A coded aperture consisting of Pb with a thickness of 20 mm was applied to the BGO scintillators of all thicknesses. Results and Discussion: Spectroscopic characterization, imaging performance, and image quality evaluation revealed the 10 mm-thick BGO scintillators enabled the portable gamma-ray imager to deliver optimal performance. Although its performance is slightly inferior to that of existing GAGG(Ce)-based gamma-ray imager, the results confirmed that the manufacturing cost and the system's overall weight can be reduced. Conclusion: Despite the spectral characteristics, imaging system performance, and image quality is slightly lower than that of GAGG(Ce), the results show that BGO scintillators are preferable for gamma-ray imaging systems in terms of cost and ease of deployment, and the proposed design is well worth applying to systems intended for use in areas that do not require high precision.

• Proceedings of the KIEE Conference
• /
• 1999.07d
• /
• pp.1553-1555
• /
• 1999

Recently, $SrBi_2Ta_2O_9$(SBT) and $Pb(ZrTi)O_3$(PZT) were much attracted as materials of capacitor for ferroelectric random access memory(FRAM) showing higher read/write speed, lower power consumption and nonvolartility. Bi-layered SBT thin film has appeared as the most prominent fatigue free and low operation voltage for use in nonvolatile memory. To highly integrate FRAM, SBT thin film should be etched. A lot of papers on SBT thin film and its characteristics have been studied. However, there are few reports about SBT thin film due to difficulty of etching. In order to investigate properties of etching of SBT thin film, SBT thin film was etched in $CF_4$/Ar gas plasma using magnetically enhanced inductively coupled plasma (MEICP) system. When $CF_4/(CF_4+Ar)$ is 0.1, etch rate of SBT thin film was $3300{\AA}/min$, and etch rate of Pt was $2495{\AA}/min$. Selectivities of SBT to Pt. $SiO_2$ and photoresist(PR) were 1.35, 0.6 and 0.89, respectively. With increasing $CF_4$ gas, etch rate of SBT thin film and $P_t$ decreased.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.27 no.9
• /
• pp.555-560
• /
• 2014

In this paper, in order to develop outstanding Pb-free composition ceramics, the $Fe_2O_3$-doped ($Na_{0.525}K_{0.443}Li_{0.037}$)($Nb_{0.883}Sb_{0.08}Ta_{0.037}$)$O_3$ + 0.3 wt% $Bi_2O_3$ + x wt% $Fe_2O_3$ (x= 0~1.0 wt%)(abbreviated as NKL-NST) lead-free piezoelectric ceramics have been synthesized using the ordinary solid state reaction method. The effect of $Fe_2O_3$-doping on their microstructure and electrical properties were investigated. XRD diffraction pattern studies confirm that $Fe_2O_3$ completely diffused into the NKL-NST lattice to form a new stable soild solution with $Fe^{3+}$ entering the $Nb^{5+}$, $Sb^{5+}$ and $Ta^{5+}$ of B-site. And, phase structure of all the ceramics exhibited pure perovskite phase and no secondary phase was found in the ceramics. The ceramics doped with 0.6 wt% $Fe_2O_3$ have the optimum values of piezoelectric constant($d_{33}$), planar piezoelectric coupling coefficient($k_p$) and mechanical quality factor($Q_m$) : $d_{33}$ = 233 [pC/N], $k_p$= 0.44, $Q_m$= 95. These results indicate that the ($Na_{0.525}K_{0.443}Li_{0.037}$)($Nb_{0.883}Sb_{0.08}Ta_{0.037}$)$O_3$ +0.3 wt% $Bi_2O_3$ + 0.6 wt% $Fe_2O_3$ ceramic is a promising candidate for lead-free piezoelectric ceramics.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.29 no.2
• /
• pp.90-94
• /
• 2016

In this work, [$Pb(Mg_{1/2}W_{1/2})_{0.03}(Ni_{1/3}Nb_{2/3})_x(Zr_{0.5}Ti_{0.5})_{0.97-x}O_3-BiFeO_3$] (x=0.02 to 0.12) composition ceramics were fabricated by the conventional soild state reaction method and their microstructure and piezoelectric properties were investigated according to PNN substitution. The addition of small amount of $BiFeO_3$, $Li_2CO_3$, and $CaCO_3$ were used in order to decrease the sintering temperature of the ceramics. The XRD (x-ray diffraction patterns) of all ceramics exhibited a perovskite structure. The sinterability of PMW-PNN-PZT-BF ceramics was remarkably improved using liquid phase sintering of $CaCO_3$, $Li_2CO_3$. However, it was identified from of the X-ray diffraction patterns that the secondary phase formed in grain boundaries decreased the piezoelectric properties. According to the substitution of PNN, the crystal structure of ceramics is transformed gradually from a tetragonal to rhombohedral phase. The x=0.10 mol PNN-substituted PMW-PNN-PZT-BF ceramics sintered at $920^{\circ}C$ showed the optimum values of piezoelectric constant($d_{33}$), piezoelectric figure of merit($d_{33{\cdot}}g_{33}$), planar piezoelectric coupling coefficient($k_p$) and density : $d_{33}=566$ [pC/N], $g_{33}=29.28[10^{-3}mV/N]$, $d_{33{\cdot}}g_{33}=16.57[pm^2/N]$, $k_p=0.61$, density=7.82 [$g/cm^3$], suitable for duplex ultrasonic sensor application.