• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.12
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• pp.996-1002
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• 2000

Ferroelectric (Ba, Sr) TiO$_3$(BST) thin films have attracted much attention for use in new capacitor materials of dynamic random access memories (DRAMs). In order to apply BST to the DRAMs, the etching process for BST thin film with high etch rate and vertical profile must be developed. However, the former studies have the problem of low etch rate. In this study, in order to increase the etch rate, BST thin films were etched with a magnetically enhanced inductively coupled plasma(MEICP) that have much higher plasma density than RIE (reactive ion etching) and ICP (inductively coupled plasma). Experiment was done by varying the etching parameters such as CF$_4$/(CF$_4$+Ar) gas mixing ratio, rf power, dc bias voltage and chamber pressure. The maximum etch rate of the BST films was 170nm/min under CF$_4$/CF$_4$+Ar) of 0.1, 600 W/-350 V and 5 mTorr. The selectivities of BST to Pt and PR were 0.6 and 0.7, respectively. Chemical reaction and residue of the etched surface were investigated with X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS).

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.6
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• pp.460-464
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• 2003

The barium strontium titannate ((Ba,Sr)TiO$_3$:BST) thin films were etched in an inductively coupled plasma (ICP) as a function of CF$_4$/Ar gas mixing ratio. Under CF$_4$(20%)/Ar(80%), the maximum etch rate of the BST films was 400 $\AA$/min. Etching products were redeposited on the surface of BST and then the nature of crystallinity were varied. Therefore, we investigated the etched surface of BST by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The plasma damages were evaluated in terms of leakage current density by Agilent 4145C and dielectric constant by HP 4192 impedance analyzer. After the BST thin films exposed in the plasma, the leakage current density and roughness increases. After annealing at 600 $^{\circ}C$ for 10 min in $O_2$ ambient, the leakage current density, roughness and nonvolatile etch byproducts reduced. From this results, the plasma induced damages were recovered by annealing process owing to the relaxation of lattice mismatches by Ar ions and the desorption of metal fluorides in high temperature.

• Korean Journal of Materials Research
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• v.5 no.7
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• pp.816-819
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• 1995

(Ba$_{1-x}$ , Sr$_{x}$)TiO/$_3$thin films on Pt/Ti/SiO$_2$/Si substrates were prepared by LP MOCVD(Low Pressure Metal-Organic Chemical Vapor Deposition). The crystalinity of BST deposit had a (100) preferred orientation with increasing deposition temperature due to surface diffusion. BST films deposited at 90$0^{\circ}C$ showed a dielectric constant of 365 and a dissipation factor of 0.052 at a frequency of 100kHz. The chance of capacitance of the films with applied voltage was small, showing paraelectric properties. BST film deposited at 90$0^{\circ}C$ had a charge storage density of 60 fc/${\mu}{\textrm}{m}$$^2$at a field of 0.2MV/cm and the leakage current density of 20 nA/$\textrm{cm}^2$ at a field of 0.15 MV/cm.cm.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.2
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• pp.114-121
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• 1996

Thin film Ba$^{0.7}Sr^{0.3}TiO^{3}$ (BST) capacitors were fabricated on SiO$_{2}$/Si substrates by RF magnetron sputtering method and characterized at microwave frequencies ranging from 40 MHz to 1GHz to examine the dielectric dispersion of the capacitors. The BST thin films were electrode material of BST thin films capacitor which is known as one of the best electrode materials for BST films. 50$\AA$-thick titanium (Ti) layers were introduced to increase adhesion between bottom Pt and SiO$_{2}$. The leakage current density of the capacitors was about 1.7${\times}10^{7}A/cm^{2}$ at 1.5V and the dielectric constant was about 140 at 1MHz. Microwave measurement patterns having a coplanar waveguide type were fabricated and their S parameters were measured using network analyzer. After de-embedding parasitic components in microwave measurement patterns nearly frequency-invariant dielectric constant of about 120 was extracted in the measurement range of 40 MHz to 1 GHz.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.60-60
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• 2008

We manufactured Liquid Crystal Polymer (LCP) and (1-x)$BaTiO_3-xSrTiO_3$(BST) ceramic composites and investigated dielectric properties to use as embedded capacitor in printed circuit boards and replace LTCC substrates. The dielectric properties of these composites are varied with volume fraction of BST and ratios of BT/ST. Dielectric constants are in the range of 3~28. In addition, we could get low TCC and High Q value that could not achieve in other ceramic-polymer composites. Especially, in composite with x=0.4 and 50vol% BST, the dieletric constant and Q-value are 27 and 300, respectively. And more TCC is -116~145ppm/$^{\circ}C$ in the temperature range of -55~$125^{\circ}C$. We think that this composites can be used high-Q substrate material like LTCC and embedded temperature compensation capacitor in printed circuit boards.

• Korean Journal of Materials Research
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• v.16 no.12
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• pp.747-753
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• 2006

(BaSr)$TiO_3$ (BST) thick films were prepared by tape casting method, using $BaTiO_3$ and $SrTiO_3$ powder slurry and their dielectric properties were investigated. With an additive, $Li_2CO_3$, the sintering temperature was lowered by $200^{\circ}C$. Sintering density was 5.7 g/$cm^3$ and the BST thick films exhibited a maximum dielectric constant, tunability at temperatures near phase transition point. Whilst their characteristics were deteriorated above the phase transition temperature, they were unchanged below the phase transition temperature, which is presumedly due to the acceleration of $90^{\circ}$ domain formation, its contribution to the relaxation of internal stress and the increase in sintering according to the replacement of Li.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.99-99
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• 2000

본 논문에서는 RF Magnetron Sputtering 방법으로 Ba0.5Sr0.5TiO3 박막을 Pt/Ti/SiO2/Si 기판위에 증착하였다. Ar과 O2의 가스비는 90:10부터 50:50까지 O2의 함유비율을 10씩 증가시켰으며, 모든 조건에서 증착온도는 실온으로 설정하였다. Ba0.5Sr0.5TiO3 박막의 증착후 각 가스비에 따른 동일한 샘플에 대해 RTA(Rapid Thermal Anneal) 장비를 이용하여 $600^{\circ}C$에서 열처리는 하여 열처리 효과에 대한 특성도 조사하였다. 최종적으로 제작한 BST 커패시터는 Pt/BST/Pt 구조를 갖는 MIM(Metal-Insulator-Metal) 구조의 커패시터였으며 상.하부 전극은 전기적 특성이 우수한 Pt를 사용하였다. 제작된 BST 커패시터를 대해 유전 특성을 조사하기 위해 C-V 측정을 한 결과 산소 함유량이 증가함에 따라 유전율의 증가를 보여주었으며, 제작된 샘플 중 산소 함유량이 30인 샘플은 300이상의 우수한 유전율을 나타내었다. 또한 누설 전류특성에서는 모든 샘플에 대해 1.0V의 인가전압에서 1.0$\times$106A/cm2 이하의 누설 전류 밀도 값을 가져 전기적으로도 안정된 커패시터 구조임을 확인하였다. 또한 막의 증착상태와 미세구조관찰을 위해 SEM 측정을 하였고 구성성분 결정 구조를 알기 위해 XRD 측정도 시행하였다. 결과적으로 본 논문에서 제작된 커패시터 중 Sr/O의 비율이 70:30인 샘플이 가장 우수한 유전특성을 나타내었고, 이 샘플의 유전특성과 누설 전류 특성은 차세대 메모리인 1GigaByte급 DRAM에 적용 가능한 조건들을 만족시켰다.

• The Korean Journal of Ceramics
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• v.1 no.4
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• pp.204-208
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• 1995

The microstructure and electrical propetries were investigated for polycrystalline $Ba^{1-x}Sr_xTiO_3$(BST) thin films deposited on Pt/Ti/$SiO_2$(PTSS) and Pt/MgO(PM) substrates by metalorganic chemical vapor deposition (MOCVD). BST films on PTSS have coulmnar and porous structures, while on PM have an equiaxied and dense structure. The dielectric constant and a dissipation factor of BST films on PTSS and 20 fC/$\mu \textrm{cm}^3$ on PTSS and 12fC/$\mu \textrm{cm}^2$ on PM was obtained at an applied electric field of 0.06 MV/cm. Leakage current density of BST films on PM was smaller than that on PTSS. The leakage current density level was about $8\times10^{-8}A/\textrm{cm}^2$ at 0.04MV/cm.

• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1550-1552
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• 1999

In this study, (Ba,Sr)$TiO_3$ thin films were etched with a magnetically enhanced inductively coupled plasma (MEICP) as a function $CF_4$/Ar gas mixing ratio. Experimental was done by varying the etching parameters such as rf power, dc bias and chamber pressure. The maximum etch rate of the BST films was $1700{\AA}$/min under $CF_4/(CF_4+Ar)$ of 0.1, 600W/350V and 5 mTorr. The selectivity of BST to Pt and PR was 0.6, 0.7, respectively. X-ray photoelectron spectroscopy (XPS) studies shows that there are surface reaction between Ba, Sr, Ti and C, F radicals during the (Ba,Sr)$TiO_3$ etching. To analysis the composition of surface residue remaining after the etching, films etched with different $CF_4$/Ar gas mixing ratio were investigated using XPS.

• Proceedings of the KIEE Conference
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• 2004.11a
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• pp.180-182
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• 2004

Polycrystalline $BaTiO_3/SrTiO_3$ powder was prepared by sol-gel process and the multilayered thick films were prepared on the $Al_2O_3$ substrates by screen printing method. The films were sintered at $1400^{\circ}C$ for 2 hours in the air. The structural and dielectric properties were investigated, The X-ray diffraction (XRD) patterns indicate that the BST phase and porocity were formed in the interface of $BaTiO_3/SrTiO_3$ multilayered thick films. The dielectric constant and the dielectric loss of the BT/ST/BT/ST multilayered thick films were about 247 and 0.84% at 1MHz.