• Journal of the Korean Ceramic Society
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• v.38 no.11
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• pp.962-966
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• 2001

Crystal structure of PbBi$_2$Nb$_2$$O_{9}$ and $Sr_{1.2}$$Bi_{1.8}$Ta$_2$$O_{9}$ were determined by Rietveld method using neutron diffraction data in the temperature range of 300 K~1273K. Phase transition temperature were measured from the dielectric permittivitytemperature curve. The PbBi$_2$Nb$_2$$O_{9}$ showed a phase transition at about 810 K. In the Sr-excess compound $Sr_{1.2}$$Bi_{1.8}$Ta$_2$$O_{9}$ the phase transition was suppressed down to room temperature. Several structural models were tested by the Rietiveld refinement. Based on the \`R\` values and the structural parameters, the B2cb model is judged to be the most feasible one for the high temperature phase at above 810 K of the PbBi$_2$Nb$_2$$O_{9}$. The $Sr_{1.2}$$Bi_{1.8}$Ta$_2$$O_{9}$ sample was refined to show the most reliable results by the Am2m model.sults by the Am2m model.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1997.04a
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• pp.217-221
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• 1997

We have investigated the ferroelectric properties of multi-layered SrBi$_2$Ta$_2$$O_{9}$Pb(Zr,Ti)O$_3$, SBT/PZT, thin film capacitors. Specimens were prepared onto Pt-coated Si wafer by sol-gel method. Ferroelectric properties of these finns could be obtained only for thin SBT layers below 50nm in thickness. The values of dielectric constant and remnant polarization depend mainly on the thickness of SBT layer, which arises from the paraelectric interface layer between SBT and PZT due to the thermal diffusion of Pb. The value of remnant poarization of PZT/SBT is greater than that of SBT, and the plarization fatigue behaviors of PZT/SBT/Pt capacitors are somewhat improved as compared with those of PZT/Pt.t.

• Journal of the Korean Ceramic Society
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• v.43 no.11 s.294
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• pp.680-687
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• 2006

An overview is given to optimize the solid state processes toward phase pure and well-crystallized fine particulates of mixed oxides, serving as electroceramic materials in various genres. Elevation of the reactivity and preservation of stoichiometry of the starting mixture are of universal importance. Mechanical activation is versatile for these purposes, particularly when an oxygen atom as a hinge promotes formation of hetero-bridging bonds between dissimilar cationic species prior to calcination. Case studies carried out recently in the author's laboratory are displayed and compared for ferroelectric materials, i.e. $PbMg_{1/3}Nb_{2/3}O_3$ $xPbTiO_3$(PMN-PT), $(1-y)Pb(Zn_xMg{1-x})_{1/3}$ $yNb_{2/3}O_3$ (PZN-PMN), $BaBi_2Ta_2O_9$ (BBT), $Ba(Mg_{1/3}Ta_{2/3})O_3$ (BMT), and ferromagnetics, i.e. M-, Y-, and Z-phases of Ba-hexaferrites.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.9
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• pp.555-560
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• 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 Institute of Electronics Engineers of Korea SD
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• v.37 no.4
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• pp.1-6
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• 2000

Recently, SrBi$_{2}$Ta$_{2}$ $O_{9}$(SBT) and Pb(Zr,Ti) $O_{3}$(PZT) were much attracted as materials of capacitor for ferroelectric random access memory(FRAM) with higher read/ write speed, lower power consumption and nonvolartility. SBT thin film has appeared as the most prominent fatigue free and low operation voltage. To highly integrate FRAM, SBT thin film has to be etched. A lot of papers have been reported over growth of SBT thin film and its characteristics. However, there are few reports about etching SBT thin film owing to difficult of etching ferroelectric materials. SBT thin film was etched in CF$_{4}$Ar plasma using magnetically enhanced inductively coupled plasma (MEICP) system. In order to investigate the chemical reaction on the etched surface of SBT thin films, X-ray Photoelecton spectrosocpy (XPS) and Secondary ion mass spectroscopy(SIMS) was performed.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.53 no.3
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• pp.128-132
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• 2004

The perovskite ferroelectric materials of the PZT, SBT and BST series will attract much attention for application to ULSI devices. Among these materials, the BST ($Ba_0.6$$Sr_0.4$/$TiO_3$) is widely considered the most promising for use as an insulator in the capacitors of DRAMS beyond 1 Gbit and high density FRAMS. Especially, BST thin films have a good thermal-chemical stability, insulating effect and variety of Phases. However, BST thin films have problems of the aging effect and mismatch between the BST thin film and electrode. Also, due to the high defect density and surface roughness at grain boundarys and in the grains, which degrades the device performances. In order to overcome these weakness, we first applied the chemical mechanical polishing (CMP) process to the polishing of ferroelectric film in order to obtain a good planarity of electrode/ferroelectric film interface. BST ferroelectric film was fabricated by the sol-gel method. And then, we compared the surface characteristics before and after CMP process of BST films. We expect that our results will be useful promise of global planarization for FRAM application in the near future.

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