• 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.

• Journal of the Korean Ceramic Society
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• v.38 no.5
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• pp.492-498
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• 2001

Ba$_{0.5}$Sr$_{0.5}$TiO$_3$타겟을 이용 Pt/Ti/SiO/Si 기판 위에 R.F magnetron sputtering 방법으로 BST 박막을 증착하여 다양한 열처리 조건에 따른 BST 박막의 전기적 성질(정전용량, 누설전류)에 대해 박막의 결정성과 미세구조의 연관성에 대하여 연구하였다. BST 박막의 유전상수는 grain size에 영향 받으며, 열처리 온도가 증가할수록 유전상수는 증가함을 보였고 온도에 따른 누설전류는 저전압 영역에서는 Hopping conduction, 고전압 영역에서는 Schottky conduction mechanism을 따르는 것으로 나타났다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.05b
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• pp.16-19
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• 2002

(Ba,Sr)TiO3(BST) thin film is an attractive material for the application in high-density dynamic random access memories (DRAMs) because of the high relative dielectric constant and small variation in dielectric properties with frequency. In this study, (Ba0.6,Sr0.4)TiO3 thin films on Pt/Ti/SiO2/Si substrates were deposited by a sol-gel method and the CF4/Ar inductively coupled plasma (ICP) etching behavior of BST thin films had been investigatedby varying the process parameters such as chamber pressure, ICP power, and substrate bias voltage. To analysis the composition of surface residue following etching BST films etched with different Ar/CF4 gas mixing ratio were investigated using x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometer (SIMS).

• Korean Journal of Materials Research
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• v.4 no.4
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• pp.453-458
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• 1994

$(Ba_{0.5}Sr_{0.5)/TiO_3$(BST) thin films were prepared for the application of 256 Mb DRAM by RF magnetron sputtering. The crystallinity of BST thin films increased with increasing deposition tempera lure. The composition of thin films was $(Ba_{0.48}Sr_{0.48)/TiO_{2.93}$ Pt/Ti barrier layer suppressed the diffusion of Si into BST layer. The films showed a dielectric constant of 320 and a dissipation factor of 0.022 at 100 kHz. the change of capacitance of the films with applied voltage was small, showing paraelectric property. The charge storage density and leakage current density were 40fC/$\mu \textrm{m}^{2}$ and 0.8$\mu A/\textrm{cm}^2$, respectively at a field of 0.15 MV/cm. The BST films obtained by RF magnetron sputtering appeared to be potential thin film capacitors for 256 Mb DRAM application.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.51-54
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• 2000

In this paper, $Ba_{0.5}$Sr$_{0.5}$TiO$_3$ thin films were prepared on Pt/Ti/SiO$_2$/Si substrate by RF magnetron sputtering method. We investigated effect of deposition conditions (especially RF input power) on structural properties of BST thin films. Deposit conditions of BST films were set working gas ratio, Ar:O$_2$= 70 : 30, working pressure 10mTorr, and RF input power 25W, 50W, 75W and 100W. Post-annealing using rapid thermal annealing(RTA) performed at 45$0^{\circ}C$, 55$0^{\circ}C$, $650^{\circ}C$, and 75$0^{\circ}C$ in oxigen ambient for 60 sec, respectively. The structural properties of BST films on Pt/Ti/SiO$_2$/Si substrate analysed by X-ray diffraction(XRD).).).

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.54 no.1
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• pp.13-17
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• 2005

The Pb(Zr/sub 0.52/Ti/sub 0.48/)O₃/(Ba/sub 0.6/Sr/sub 0.4/)TiO₃[PZT/BST] heterolayered thin films were deposited on Pt/Ti/SiO₂/Si substrates by using the RF sputtering method with different RF power. The PZT/BST heterolayered thin films had the tetragonal structure of the PZT phase and BST phase. Increasing the RF power. the intensity of the PZT (100), (110) peaks and BST (111) peaks were decreased and the intensity of the BST (100), (110) peaks were increased. The thickness ratio of the top layered BST thin film and the bottom layered PZT thin film was 2 to1. The atomic concentration of the Ba, Sr, Pb. Zr, Ti atoms were constant in the PZT thin films and BST thin films, respectively. The Pt atom was diffused to the PZT region in the PZT/BST heterolayered thin films deposited at condition of 60[W] RF power. Increasing the frequency, dielectric constant and loss of the PZT/BST heterolayered thin films were decreased. The dielectric constant and loss of the PZT/BST heterolayered thin films deposited with RF power of 90[W] were 406 and 3%, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.607-610
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• 2004

The Pb $(Zr_{0.52}Ti_{0.48})O_3/(Ba_{0.6}Sr_{0.4}TiO_3$ [PZT(52/48)/BST(60/40)] heterolayered thin films were fabricated on the Pt/Ti/$SiO_2$/Si by RF sputtering method. The structural properties of the PZT(52/48)/BST(60/40) heterolayered thin films were investigated with Ar/$O_2$ ratio condition. All the PZT(52/48)/BST(60/40) heterolayered thin films had shown the PZT(111), (200) and BST(200) Peaks of the tetragonal structure. Increasing the Ar/$O_2$ ratio, the average roughness was increased. The thickness ratio of the to the PZT and BST thin film was 1:2. In the case of the PZT(52/48)/BST(60/40) heterolayered thin films with Ar/$O_2$ ratio of 80/20, the average roughness was 3.4 [nm].

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.04b
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• pp.157-160
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• 2004

Ferroelectric $(Ba_xSr_{1-x})TiO_3$ (BST) thin films have been deposited on (001) MgO single crystals by a pulsed laser deposition (PLD) method. The structure of deposited BST thin films were investigated by an x-ray diffractometer. Calculated c-axis lattice parameters of the BST films exhibit a strong lattice distortion, which was not observed in ceramic BST at room temperature. This lattice distortion of BST has been attributed to strains caused by lattice constant difference between film and substrate, oxygen vacancies in BST film, and thermal expansion difference between film and substrate. Ferroelectric properties at 10 GHz have been measured using a HP 8510C vector network analyzer. Dielectric properties, capacitance tunability and quality factor, of the interdigitaed capacitors fabricated on BST films were calculated from the measured s-parameters. Two distinct behaviors in structural, opitical, and microwave properties of BST films were observed; below and above 200 mTorr of oxygen pressure in the deposition chmber.

• Korean Journal of Materials Research
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• v.17 no.7
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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.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11b
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• pp.455-458
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• 2001

The thin films of high pemitivity in ferroelectric materials using a capacitor are applied to DRAMs and FRAMs. (Ba, Sr)$TiO_3$ thin films as ferroelectric materials were prepared by the sol-gel method and made by spin-coating on the Pt/Ti/$SiO_2/Si$ substrate at 4,000 [rpm] for 10 seconds. The devices of BST thin films to composite $(Ba_{0.7},Sr_{0.3})TiO_3$ were fabricated by changing of the depositing layer number on $Pt/Ti/SiO_2/Si$ substrate. The thin film capacitor to be ferroelectric devices was investigated by structural and electrical properties. The thickness of BST thin films at each coating numbers 3, 4 and 5 times was $2500[\AA]$, $3500[\AA]$, $3800[\AA]$. The dielectric factor of thin film when the coating numbers were 3, 4 and 5 times was 190, 400 and 460 on frequency l[MHz]. The dielectric loss of BST thin film was linearly increased by increasing of the specimen area.