• 한국결정성장학회지
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• 제8권2호
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• pp.221-226
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• 1998

$RuO_2$ 하부전극 상에 형성된 $(Ba, Sr)TiO_3$[BST] 박막의 물성을 향상시키기 위하여 비정질 BST층(30, 70nm)을 $RuO_2$와 BST사이에 증착하여 2중 BST구조를 형성시켰다. 비정질 BST층의 도입을 통해, BST박막의 평균 입도가 증가하고, 표면 거칠기가 감소하여 전체 BST 박막의 미세구조와 표면 mophology가 단일 BST박막에 비해 상당한 변화가 발생함을 확인하였다. 30nm의 비정질측이 적용된 BST박막의 경우, 하부기판의 영향으로부터 비교적 자유로운 미세구조를 갖는 BST 박막이 형성되었다. 2중 BST 박막의 경우 유전상수는 340, 누설전류는 $6.85{\times}10^{-7}A/{\textrm}{cm}^2$로서 비정질층을 갖지 않는 단일 BST 박막에 비하여(유전상수: 152, 누설전류: $1.25{\times}10^{-5}A/{\textrm}{cm}^2$)놀라운 전기적 특성의 향상이 이루어짐을 확인하였다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 하계학술대회 논문집 Vol.5 No.2
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• pp.794-797
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• 2004

The object of investigation is represented by PbxSrl-xTiO3(PST) thin films, which were fabricated by the alkoxide-based sol-gel method on Pt/Ti/SiO2/Si substrate. We have investigated both structural and dielectric properties of PST thin films aimed to tunable microwave device applications as a function of Pb/Sr ratio. PST thin films showedtypical polycrystalline structure with a dense microstructure without secondary phase formation. Dielectric properties of PST films were found as strongly dependent on Pb/Sr composition ratio. Increasing of Pb content leads to simultaneous increasing of both dielectric constant and dielectric loss characteristics of PST films. The figure of merit (FOM) Parameter (FOM : (%) tunability / tan (%)) reached a maximal value of 27.5 corresponding to Pb/Sr ratio of 40/60. The tunability increased with increasing Pb content. The dielectric constants, dielectric loss and tunability of the PST thin films at Pb/sr ratio of 40/60 measured at 100 kHz were 335, 0.0174 and 47.89 %, respectively.

• 한국재료학회지
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• 제17권7호
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• pp.386-389
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• 2007

The dielectric properties of $(Ba_{0.5}Sr_{0.5})TiO_3$ ferroelectric thin films have been investigated according to the substrates in order to optimize the their properties. MgO, r-plane sapphire, and poly-crystalline sapphire (Alumina) substrates have been used to deposite $(Ba_{0.5}Sr_{0.5})TiO_3$ ferroelectric thin films by RF magnetron sputtering. The BST thin films deposited on the single crystal (100)MgO substrates have high tunability and low dielectric loss. These results are caused by a low misfit between the lattice parameters of the BST films and the substrate. The BST films deposited on r-plane sapphire have relatively high misfit, and the tunability of 17% and dielectric loss of 0.0007. To improve the dielectric properties of the BST films, the post-annealing methods has been introduced. The BST films deposited on (100)MgO, (1102)r-plane sapphire, and poly-crystalline sapphire substrates have best properties in post-annealing conditions of $1050^{\circ}C$, $1100^{\circ}C$, and $1150^{\circ}C$, respectively. The different optimal post-annealing conditions have been found according to the different misfits between the films and substrates, and thermal expansion coefficients. Moreover, the films deposited on alumina substrate which is relatively cheap have a good tunability properties of 23% by the post-annealing.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 Techno-Fair 및 추계학술대회 논문집 전기물성,응용부문
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• pp.173-174
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• 2008

페로브스카이트 구조의 (Ba,Sr,Ca)$TiO_3$ 분말에 $Dy_2O_3$ 불순물을 첨가하여 첨가량에 따른 영향을 연구하였다. 시편의 제작은 Screen-printing을 이용하여 후막으로 제작하였으며, 구조적인 특성과 전기적인 특성을 관찰하였다. XRD 회절 분석을 통하여 $Dy_2O_3$가 첨가된 모든 시편에서 이차상이 없는 전형적인 페로브스카이트 구조를 나타내었다. 시편의 미세구조를 관찰한 결과 grain size는 $Dy_2O_3$ 첨가량이 증가 할수록 감소하였으며, 기공은 증가하는 것을 알 수 있었다. 후막의 두께는 $Dy_2O_3$ 첨가량에 영향을 받지 않았으며 평균 두께는 $69{\mu}m$이었다. 큐리 온도는 $Dy_2O_3$ 첨가량에 따라 감소하였으며, 유전 손실은 상온 이상에서 1%이하로 크게 감소하였다.

• The Korean Journal of Ceramics
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• 제3권4호
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• pp.274-278
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• 1997

(Ba, Sr) TiO$_3$(BST) thin films were prepared on RuO$_2$/Si substrates by rf magnetron sputtering and annealing was followed at temperatures ranging from 550 to 80$0^{\circ}C$ in $N_2$or $O_2$atmosphere. The effects of annealing conditions on the properties of BST film deposited on RuO$_2$bottom electrodes were investigated. It was found that the crystallinity. surface roughness, and grain size of BST films vary with the annealing temperature but they are not dependent upon the annealing atmosphere. The flat region in the current-voltage (I-V) curves of BST capacitors shortened with increasing annealing temperature under both atmospheres. This is believed to be due to the lowering of potential barrier caused by unstable interface and the increase of charge The shortening of the flat region by $O_2$annealing was more severe than that by $N_2$-annealing. As a result, there was no flat region when the films were annealed at 700 and 80$0^{\circ}C$ in $O_2$atmosphere. The dielectric properties of BST films were improved by annealing in either atmosphere. however, a degradation with frequency was observed when the films were annealed at relatively high temperature under $O_2$atmosphere.

• 한국재료학회지
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• 제5권1호
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• pp.3-11
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• 1995

Titanium oxide$(TiO_{2})$ 박막을 금속 알콕사이드 물질인 $(Ti(OC_3H_7)_4$(titanium isopropoxide)를 이용하여 p-Si(100) 기판위에 상압 화학 기상 증착법으로 증착시켰다. $(TiO_{2})$ 박막의 증착기구는 단순경 계층 이론으로 잘 설명되었으며, 화학반응 지배 기구 영역에서 겉보기 활성화 에너지는 18.2kcal/mol이었다. 증착된 박막은 $250^{\circ}C$이상에서 anatase상의 결정질 박막이었으며, 고온에서 열처리를 했을 경우에 rutile상으로 전이하였다. 박막의 상전이에는 열처리 온도외에도 열처리 시간과 박막의 두께가 영향을 미쳤다. 정전용량-전압특성을 조사해 본 결과 전형적인 MOS 다이오드구조의 특성을 보였으며, 비유전율 상수는 약 80정도였다. 제조한 $(TiO_{2})$ 박막의 열처리 공정 후에는 정전용량이 감소하였으며, 첨가물을 사용한 박막은 열처리 전과 같았다. 이때 $V_{FB}$는 -0.5 ~ 1.5V였다. 전기전도 특성을 알아보기 위하여 전류-전압특성을 조사하였으며 증착된 박막의 전도기구는 hopping mechanism이었다. 전기적 특성을 개선하기 위해서 후열처리 방법과 박막 증착시 Nb, Sr을 첨가하였으며, 모두 누설전류의 감소와 정전파괴전압의 증가를 가져왔다.

• 한국결정학회지
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• 제11권2호
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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.

• 한국재료학회지
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• 제7권2호
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• pp.107-113
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• 1997

플라즈마를 이용한 유기금속 화학증착법에 의해 $Pt/Ti/SiO_{2}/Si$기판위에 $SrBi_{2}Ta_{2}O_{9}(SBT)$박막이 제조되었다. X-ray회절패턴, 미세구조 및 조성분석으로부터 Sr과 Ta bubbling 온도는 $120^{\circ}C$로 고정되었으며 Bi bubbling온도가 변화되었다. Bi bubbling 온도 $130^{\circ}C$에서 얻어진 SBT 박막의 유전상수 및 유전손실은 100kHz에서 각각 150과 0.02이며 누설전류 밀도는 20kV/cm 에서 약 $1.0{\times}10^{-8}A/cm^2$이었다. 이 조건에서 얻어진 SBT박막의 누설전류 특성은 poole-Frenkel기구에 의해서 지배된다. $550^{\circ}C$에서 annealing된 SBT박막의 잔류분극($_{2}P_{r}$)은 $9{\mu}C/cm^2$이며 항전계는 70kV/cm이었다.

• 한국전기전자재료학회논문지
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• 제11권6호
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• pp.436-441
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• 1998

$Pt/SrTiO_3/Pb_x(Zr_{0.52}, Ti_{0.48})O_3/SrTiO_3/Si$ structure was prepared by rf-magnetron sputtering method for use in nondestructive read out ferroelectric RAM(NDRO-FEAM). PBx(Zr_{0.52}Ti_{0.48})O_3}$(PZT) and $SrTiO_3$(STO) films were deposited respectively at the temperatures of $300^{\circ}C and 500^{\circ}C$on p-Si(100) substrate. The role of the STO film as a buffer layer between the PZT film and the Si substrate was studied using X-ray diffraction (XRD), Auger electron spectroscopy (ASE), and scanning electron microscope(SEM). Structural analysis on the interfaces was carried out using a cross sectional transmission electron microscope(TEM). For PZT/Si structure, mostly Pb deficient pyrochlore phase was formed due to the serious diffusion of Pb into the Si substrate. On the other hand, for STO/PZT/STO/Si structure, the PZT film had perovskite phase and larger grain size with a little Pb interdiffusion. the interfaces of the PZT and the STO film, of the STO film and the interface layer and $SiO_2$, and of the $SiO_2$ and the Si substate had a good flatness. Across sectional TEM image showed the existence of an amorphous layer and $SiO_2$ with 7nm thickness between the STO film and the Si substrate. The electrical properties of MIFIS structure was characterized by C-V and I-V measurements. By 1MHz C-V characteristics Pt/STO(25nm)/PZT(160nm)/STO(25nm)/Si structure, memory window was about 1.2 V for and applied voltage of 5 V. Memory window increased by increasing the applied voltage and maximum voltage of memory window was 2 V for V applied. Memory window decreased by decreasing PZT film thickness to 110nm. Typical leakage current was abour $10{-8}$ A/cm for an applied voltage of 5 V.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 하계학술대회 논문집 Vol.8
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• pp.200-201
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• 2007

The SBT($SrBi_2Ta_2O_9$) thin films with $Bi_2O_3$ buffer layer were deposited on Pt/Ti/$SiO_2$/Si substrate by R.F. magnetron sputtering method in order to improve the ferroelectric characteristics. In SBT thin films, the deficiency of bismuth during the process due to its volatility results in an obvious non stoichiometry of the films and the presence of secondary phases. $Bi_2O_3$ buffer layer was found to be effective to achieve the low temperature crystallization and improve the ferroelectric properties of SBT thin films. Ferroelectric properties and crystallinities of SBT thin films with various post annealing of $Bi_2O_3$ buffer layer were observed as various annealing temperature, using X-Ray Diffraction (XRD), scanning electron microscopy (SEM), Keithley 237 and HP 4192A Impedance Analyzer.