• Proceedings of the KIEE Conference
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• 1999.11d
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• pp.867-869
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• 1999

In this study, $SrBi_{2}Ta_{2}O_{9}$(SBT) thin films were etched as a function of $SF_6$/Ar gas mixing ratio in magnetically enhanced inductively coupled plasma(MEICP) system fer a fixed rf power, dc-bias voltage, and chamber pressure. The etch rate of SBT thin film was $1500{\AA}/min$ and the selectivities of photoresist (PR) and $SiO_2$ to SBT thin film were 0.48 and 0.62, respectively when the samples were etched at a rf power of 600W, a dc-bias voltage of -150V, a chamber pressure of 10 mTorr and a gas mixing ratio of $SF_6/(SF_6+A)$=0.1. In order to examine the chemical reactions on the etched surface, X-ray photoelectron spectroscopy(XPS) and secondary ion mass spectrometry(SIMS) were done.

• Korean Journal of Crystallography
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• v.11 no.2
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• pp.95-101
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• 2000

Ferroelectric SrBi2Ta2O9 (SBT) thin films of Pt/Ti/SiO2 electrode were fabricated using a sintered SBT target with various Bi2O3 content by rf magnetron sputtering. Good hysteresis loop characteristics were observed in the SBT thin films deposited with 50mol% excess Bi target. SBT thin films crystallized from 650℃ however, good hysteresis loop can be obtained in the film annealed above 700℃. pt/TiO2/SiO2 and Pt/SiO2 electrodes were also used to investigate the Pt electrode dependence of SBT thin films. SBT thin films showed random oriented polycrystalline structure and similar morphology regardless of electrodes with quite different surface morphology. A 0.2㎛ thick SBT film annealed at 750℃ exhibited the remanent polarization (2Pr) of μC/㎠ and coercive voltage(Vc) of 1V at an applied voltage of 5V.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.2
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• pp.143-150
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• 2000

Ferroelectric SrxBi2+yTa2O9+$\alpha$ thin films with various compositions(x=0.7, 0.8, 1, y=0.3, 0.4) were prepared by sol-gel method. The film with moled ratio of 0.8:2.3:2.0 in Sr/Bi/Ta, which was deposited on Pt/SiO2/Si (100), showed better ferroelectric properties than other films. To investigate substrate effects, the same compositions were spin coated on Pt/Ti/SiO2/Si (100) substrates. At an applied voltage of 5V, the dielectric constant($\varepsilon$r), remanent polarization (2Pr) and coercive field (Ec) of the Sr0.8Bi2.3Ta2O9+$\alpha$ thin film prepared on Pt/Ti/SiO2/Si (100) were about 296, 24$\mu$C/$\textrm{cm}^2$ and Ec of 49kV/cm respectively. Both SBT films firred at 80$0^{\circ}C$ revealed no fatigue up to 1010 cycles. Retention characteristics of these capacitors showed no degradation up to 104 sec.

• Electrical & Electronic Materials
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• v.16 no.9
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• pp.64.1-64
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• 2003

A metal-ferroelectric [SrBi$_2$Ta$_2$O$\_$9/ (SBT)-high-k-insulator(PrOx)-semiconductor(Si) structure has been fabricated and evaluated as a key part of metal-ferroelectric-insulator-semiconductor-field-effect-transistor MFIS-FET memory, aiming to improve the memory retention characteristics by increasing the dielectric constant in the insulator layer and suppressing the depolarization field in the SBT layer. A 20-nm PrOx film grown on Si(100) showed both a high of about 12 and a low leakage current density of less than 1${\times}$ 10e-8 A/$\textrm{cm}^2$ at 105 MV/cm. A 400-nm SBT film prepared on PrOx/Si shows a preferentially oriented (105) crystalline structure, grain size of about 130 nm and subface roughness of 3.2 nm. A capacitance-voltage hysteresis is confirmed on the Pt/SBT/PrOx/Si diode with a memory window of 0.3V at a sweep voltage width of 12 V. The memory retention time was about 1 104s, comparable to the conventional Pt/SBT/SiO$\_$x/N$\_$y/(SiO$\_$N/)/Si. The gradual change of the capacitance indicates that some memory degradation mechanism is different from that in the Pt/SBT/SiON/Si structure.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.39 no.6
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• pp.10-10
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• 2002

This paper introduces the high-resolution channel estimation technique which are used to estimate the first arrival multipath delay component. The proposed technique yields the precise estimate of the first time arrival which is directly related to the performance of TDOA-based position location. The proposed technique utilizes the transformed auto-correlation function of received common pilot signal in frequency domain, its samples compose the hermitian Toeplitz matrix at sequel. Then the time delay components could be estimated with precision by the analysis of eigen-structure of corresponding matrix. In this paper, obeying the modified CODIT model, the performance of the PR-IPDL(Pseudo Random-Idle Period Downlink) and TA-IPDL(Time Aligned-Idle Period Downlink considered as 3GPP position location technique will be exploited systematically through the computer simulations with applying the proposed technique.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.39 no.6
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• pp.268-276
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• 2002

This paper introduces the high-resolution channel estimation technique which are used to estimate the first arrival multipath delay component. The proposed technique yields the precise estimate of the first time arrival which is directly related to the performance of TDOA-based position location. The proposed technique utilizes the transformed auto-correlation function of received common pilot signal in frequency domain, its samples compose the hermitian Toeplitz matrix at sequel. Then the time delay components could be estimated with precision by the analysis of eigen-structure of corresponding matrix. In this paper, obeying the modified CODIT model, the performance of the PR-IPDL(Pseudo Random-Idle Period Downlink) and TA-IPDL(Time Aligned-Idle Period Downlink considered as 3GPP position location technique will be exploited systematically through the computer simulations with applying the proposed technique.

• Journal of the Korean Ceramic Society
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• v.41 no.1
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• pp.13-18
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• 2004

$La_{0.5}Sr_{0.5}CoO_3$ (LSCO) electrodes were prepared on ferroelectric $Sr_{0.9}Bi_{2.1}Ta_2O_9$(SBT) thin films by spin coating method using photosensitive sol-gel solution. Self-patterning technique of photosensitive sol-gel solution has advantages such as simple manufacturing process compared to photoresist/dry etching process. Lanthanum(III) 2-methoxyethoxide, Stronitium diethoxide. Cobalu(II)2-methoxyethoxide were used as starting materials for LSCO electrode. UV irradiation on LSCO thin films lead to decrease solubility by M-O-M bond formation and the solubility difference allows us to obtain self-patternine. There was little composition change of the LSCO thin films between before leaching and after leaching in 2-methoxyethanol. The lowest resistivity of LSCO thin films deposited on $SiO_2$/Si substrate was $1.1{\times}10^{-2}{\Omega}cm$ when the thin film was ennealed at $740^{\circ}C$. The values of Pr/Ps and 2Pr of LSCO/SBT/Pt capacitor on the applied voltage of 5V were 0.51, 8.89 ${\mu}C/cm^2$, respectively.

• The Korean Journal of Ceramics
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• v.6 no.3
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• pp.276-279
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• 2000

Ferroelectric properties of $SrBi_2TaNbO_9$ (SBTN) thin films were changed by the amount of Bi content in SBTN. We suggested that the addition of excess Bi into the films could be accomplished by heat-treating $SBTN/Bi_2O_3/SBTN$ heterostructure fabricated by r.f. magnetron sputtering method. Excess Bi composition was controlled by the thickness of the sandwiched $Bi_2O_3$ from 0 to $400\;\AA$. When the SBTN thin films were inserted by $400\;{\AA}\;Bi_2O_3$ layer, $Bi_2Pt$ phase was formed as a second phase in SBTN films, resulting in poor ferroelectric properties. The onset temperature for hysteresis loop can be reduced by heat treating $SBTN/Bi_2O_3/SBTN$ heterostructure. The films with $SBTN/Bi_2O_3(100\;{\AA})/SBTN$ hetero-structure followed by annealing at $650^{\circ}C$ for 30 min show 2Pr and Ec of $5.66\;{\mu}C/\textrm{cm}^2$ and 54 kV/cm, respectively.

• Journal of the Microelectronics and Packaging Society
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• v.6 no.2
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• pp.51-61
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• 1999

$SrBi_2Ta_2O_9$ thin films were prepared on $Pt/SiO_2$/Si p-tyPp (100) substrate by r.f. magnetron sputtering method. The films were annealed at $800^{\circ}C$ and characterized in terms of micro-structures and electrical properties depending on film deposition conditions. XRD patterns of SBT films annealed at $800^{\circ}C$ indicated the typical SBT phase of (006), (111), and (200) with BiPt additional peaks. SEM images show that crystal gram become to grow with increasing the substrate temperature and decreasing the gas pressure. The remanant polarization(2Pr) and the coercive field(Ec) of 200nm thickness SBT film which was deposited at 10$0^{\circ}C$ under 50mtorr gas pressure and annealed at $800^{\circ}C$ were 20.07$\mu$C/$\textrm {cm}^2$ and 79kV/cm, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.11a
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• pp.41-43
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• 1999

Among the feffoelectric thin films that have been widely investigated for ferroelectric random access memory (FRAM) applications, SrBi$_2$Ta$_2$$O_{9}$ thin film is appropriate to memory capacitor materials for its excellent fatigue endurance. However, very few studies on etch properties of SBT thin film have been reported although dry etching is an area that demands a great deal of attention in the very large scale integrations. In this study, the a SrBi$_2$Ta$_2$$O_{9}$ thin films were etched by using magnetically enhanced inductively coupled Ar/CHF$_3$ plasma. Etch properties, such as etch rate, selectivity, and etched profile, were measured according to gas mixing ratio of CHF$_3$(Ar$_{7}$+CHF$_3$) and the other process conditions were fixed at RF power of 600 W, dc bias voltage of 150 V, chamber pressure of 10 mTorr. Maximum etch rate of SBT thin films was 1750 A77in, under CHF$_3$(Ar+CHF$_3$) of 0.1. The selectivities of SBT to Pt and PR were 1.35 and 0.94 respectively. The chemical reaction of etched surface were investigated by X-ray photoelectron spectroscopy (XPS) analysis. The Sr and Ta atoms of SBT film react with fluorine and then Sr-F and Ta-F were removed by the physical sputtering of Ar ion. The surface of etched SBT film with CHF$_3$(Ar+CHF$_3$) of 0.1 was analyzed by secondary ion mass spectrometer (SIMS). Scanning electron microscopy (SEM) was used for examination of etched profile of SBT film under CHF$_3$(Ar+CHF$_3$) of 0.1 was about 85˚.85˚.˚.