• ETRI Journal
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• v.35 no.4
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• pp.734-737
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• 2013

Nonvolatile ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) memory based on an organic thin-film transistor with inkjet-printed dodecyl-substituted thienylenevinylene-thiophene copolymer (PC12TV12T) as the active layer is developed. The memory window is 4.5 V with a gate voltage sweep of -12.5 V to 12.5 V. The field effect mobility, on/off ratio, and gate leakage current are 0.1 $cm^2/Vs$, $10^5$, and $10^{-10}$ A, respectively. Although the retention behaviors should be improved and optimized, the obtained characteristics are very promising for future flexible electronics.

• Journal of the Korean Physical Society
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• v.73 no.11
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• pp.1712-1715
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• 2018

To study the applications for ferroelectric non-volatile memory and ferroelectric memristor, etc., deposition pressure dependent electric the properties of $(Hf,\;Zr)O_2$ thin films by RF sputtering deposition method were investigated. The bottom electrode was TiN thin film to produce stress effect on the formation of orthorhombic phase and top electrode was Pt thin film by DC sputtering deposition. Deposition pressure was varied along with the same other deposition conditions, for example, sputtering power, target to substrate distance, post-annealing temperature, annealing gas, annealing time, etc. The structural and electric properties of the above thin films were investigated. As a result, it is confirmed that the electric properties of the $(Hf,\;Zr)O_2$ thin films depend on the deposition pressure which affects structural properties of the thin films, such as, structural phase, ratio of the constituents, etc.

• 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.

• Korean Journal of Materials Research
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• v.13 no.2
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• pp.69-73
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• 2003

In this work, $IrO_2$thin films as bottom electrode of ferroelectric capacitors were deposited and characterized. The $IrO_2$films deposited in the conditions of 25, 40 and 50% oxygen ambient by sputtering method were annealed at 600, 700 and $800^{\circ}C$, respectively. It was found that the crystallinity and the surface morphology of $IrO_2$films affected the surface properties and electrical properties of SBT thin films prepared by the MOD method. With increasing temperature, the crystallinity and the roughness of $IrO_2$films were also increasing. This increasing of roughness degraded the surface properties and electrical properties of SBT films. We found an optimum condition of $IrO_2$films as bottom electrode for ferroelectric capacitor at 50% oxygen ambient and $600^{\circ}C$ annealing temperature. Electrical characterizations were performed by using$ IrO_2$bottom electrodes grown at an optimum conditions. The remanent polarization ($P_{r}$) of the Pt/SBT/$IrO_2$/$SiO_2$/Si structure was 2.75 $\mu$C/$\textrm{cm}^2$ at an applied voltage of 3 V. The leakage current density was $1.06${\times}$10^{-3}$ A/$\textrm{cm}^2$ at an applied voltage of 3 V.

• Journal of the Korean Ceramic Society
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• v.44 no.8
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• pp.403-406
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• 2007

Ferroelectric Ce-doped $Bi_4Ti_3O_{12}$ (BCT) thin films were deposited by liquid delivery metal organic chemical vapor deposition (MOCVD) onto a $Pt(111)/Ti/SiO_2/Si(100)$ substrate. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to identify the crystal structure, the surface, and the cross-section morphology of the deposited ferroelectric flims. After annealing above $640^{\circ}C$, the BCT films exhibited a polycrystalline structure with preferred (001) and (117) orientations. The BCT lam capacitor with a top Pt electrode showed a large remnant polarization ($2P_r$) of $44.56{\mu}C/cm^2$ at an applied voltage of 5 V and exhibited fatigue-free behavior up to $1.0{\times}10^{11}$ switching cycles at a frequency of 1 MHz. This study clearly reveals that BCT thin film has potential for application in non-volatile ferroelectric random access memories and dynamic random access memories.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.180-180
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• 2003

FRAM (Ferroelectric Random Access Memory)은 DRAM(Dynamic Random Access Memory)in 커패시터 재료을 상유전체 물질에서 강유전체 물질로 대체하여 전원 공급이 차단되어도 정보를 기억할 수 있고, 데이터의 고속처리가 가능하고 저소비전력과 집적화가 뛰어난 차세대 메모리 소자이다. 본 연구에서는 n-Well/P-Si(100) 기판위에 $Y_2$O$_3$ 박막을 중간층 (buffer layer)으로 사용하여 (Bi,La) Ti$_3$O$_{12}$ (BLT) 강유전체 박막을 졸-겔 방법으로 형성하여 MFM(I)S(Metal Ferroelectric Metal (Insulation) Silicon) 구조의 커패시터 및 전계효과형 트랜지스터(Field Effect Transistor) 소자를 제작하였다. 제작된 소자에 대해 형상학적, 전기적 특성을 조사, 분석하였다.

• JSTS:Journal of Semiconductor Technology and Science
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• v.3 no.3
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• pp.132-138
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• 2003

We investigated the polarization retention characteristics of ferroelectric capacitors with $Pb(Zr,Ti)O_3$ (PZT) thin films which were fabricated by different deposition methods. In thermally-accelerated retention tests, PZT films which were prepared by a chemical solution deposition (CSD) method showed rapid decay of retained polarization charges as the thickness of the films decreased down to 100 nm, while the films which were grown by metal organic chemical vapor deposition (MOCVD) retained relatively large non-volatile charges at the corresponding thickness. We concluded that in the CSD-grown films, the thicker interfacial passive layer compared with the MOCVD-grown films had an unfavorable effect on retention behavior. We observed the existence of such interfacial layers by extrapolation of the total capacitance with thickness of the films and the capacitance of these layers was larger in MOCVD-grown films than in CSD-grown films. Due to incomplete compensation of surface polarization charges by the free charges in the metal electrodes, the interfacial field activated the space charges inside the interfacial layers and deposited them at the boundary between the ferroelectric layer and the interfacial layer. Such space charges built up an internal field inside the films, which interfered with domain wall motion, so that retention property at last became degraded. We observed less imprint which was a result of less internal field in MOCVD-grown films while large imprint was observed in CSD-grown films.

• Transactions on Electrical and Electronic Materials
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• v.12 no.2
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• pp.64-67
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• 2011

The effect of Ta substitution on the crystal structure, ferroelectric, and piezoelectric properties of $Bi_{0.5}(Na_{0.82}K_{0.18})_{0.5}Ti_{1-x}Ta_xO_3$ ceramics has been investigated. The Ta doping resulted in a transition from coexistence of ferroelectric tetragonal and rhombohedral phases to an electrostrictive pseudocubic phase, leading to degradations of the remnant polarization, coercive field, and piezoelectric coefficient $d_{33}$. However, the electricfield-induced strain was significantly enhanced by the Ta substitution-induced phase transition and reached a highest value of $S_{max}/E_{max}$ = 566 pm/V under an applied electric field 6 kV/mm when 2% Ta was substituted on Ti sites. The abnormal enhancement in strain was attributed to the pseudocubic phase with high electrostrictive constants.

• JSTS:Journal of Semiconductor Technology and Science
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• v.2 no.3
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• pp.205-212
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• 2002

The growth characteristics of metal-organic chemical vapor deposition (MOCVD) $Pb(Zr_xTi_{1-x})O_3 (PZT) thin films were investigated for the application of high-density ferroelectric random access memories (FRAM) devices beyond 64Mbit density. The supply control of Pb precursor plays the most critical role in order to achieve a reliable process for PZT thin film deposition. We have monitored the changes in the microstructure and electrical properties of films on increasing the Pb precursor supply into the reaction chamber. Under optimized conditions, $Ir/IrO_2/PZT(100nm)/Ir capacitor shows well-saturated hysteresis loops with a remanent polarization (Pr) of $~28{\mu}C/textrm{cm}^2$ and coercive voltage of 0.8V at 2.5V. Other issues such as step coverage, compositional uniformity and low temperature deposition was discussed in viewpoint of actual device application.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.12 no.3
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• pp.161-164
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• 2002

Polycrystalline and epitaxial heterostructure films of $La_{0.5}Sr_{0.5}CoO_{3}/Pb(Nb_{0.04}Zr_{0.28}Ti_{0.68})O_{3}/La_{0.5}Sr_{0.5}CoO_{3}$ (LSCO/PNZT/LSCO) capacitors were evaluated in terms of low voltage and high speed operation in high density memory, using TiN/Pt conducting barrier combination. Structural studies for a high density ferroelectric memory process flow, which requires the integration of conducting barrier layers to connect the drain of the pass-gate transistor to the bottom electrode of the ferroelectric stack, indicate complete phase purity (i.e. fully perovskite) in both epitaxial and polycrystalline materials. The polycrystalline capacitors show lower remnant polarization and coercive voltages. However, the retention, and high-speed characteristics are similar, indicating minimal influence of crystalline quality on the ferroelectric properties.