• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.67 no.6
• /
• pp.799-803
• /
• 2018

We demonstrated memory thin-film transistors (MTFTs) with organic ferroelectric polymer poly(vinylidene fluoride-co-trifluoroethylene) and an amorphous oxide semiconducting indium gallium zinc oxide channel on the elastomeric substrate. The dielectric constant for the P(VDF-TrFE) thin film prepared on the elastomeric substrate was calculated to be 10 at a high frequency of 1 MHz. The voltage-dependent capacitance variations showed typical butterfly-shaped hysteresis behaviors owing to the polarization reversal in the film. The carrier mobility and memory on/off ratio of the MTFTs showed $15cm^2V^{-1}s^{-1}$ and $10^6$, respectively. This result indicates that the P(VDF-TrFE) film prepared on the elastomeric substrate exhibits ferroelectric natures. The fabricated MTFTs exhibited sufficiently encouraging device characteristics even on the elastomeric substrate to realize mechanically stretchable nonvolatile memory devices.

• Transactions on Electrical and Electronic Materials
• /
• v.12 no.6
• /
• pp.258-261
• /
• 2011

A ferroelectric $(Bi,La)_4Ti_3O_{12}$ (BLT) thin film fabricated by the pulsed-DC sputtering method was evaluated on a cell structure to check its compatibility to high density ferroelectric random access memory (FeRAM) devices. The BLT composition in the sputtering target was $Bi_{4.8}La_{1.0}Ti_{3.0}O_{12}$. Firstly, a BLT film was deposited on a buried Pt/$IrO_x$/Ir bottom electrode stack with W-plug connected to the transistor in a lower place. Then, the film was finally crystallized at $700^{\circ}C$ for 30 seconds in oxygen ambient. The annealed BLT layer was found to have randomly oriented and small ellipsoidal-shaped grains (long direction: ~100 nm, short direction: ~20 nm). The small and uniform-sized grains with random orientations were considered to be suitable for high density FeRAM devices.

• Korean Journal of Materials Research
• /
• v.18 no.4
• /
• pp.169-174
• /
• 2008

The structural and electrical properties of amorphous $BaSm_2Ti_4O_{12}$ (BSmT) films on a $TiN/SiO_2/Si$ substrate deposited using a RF magnetron sputtering method were investigated. The deposition of BSmT films was carried out at $300^{\circ}C$ in a mixed oxygen and argon ($O_2$ : Ar = 1 : 4) atmosphere with a total pressure of 8.0 mTorr. In particular, a 45 nm-thick amorphous BSmT film exhibited a high capacitance density and low dissipation factor of $7.60\;fF/{\mu}m2$ and 1.3%, respectively, with a dielectric constant of 38 at 100 kHz. Its capacitance showed very little change, even in GHz ranges from 1.0 GHz to 6.0 GHz. The quality factor of the BSmT film was as high as 67 at 6 GHz. The leakage current density of the BSmT film was also very low, at approximately $5.11\;nA/cm^2$ at 2 V; its conduction mechanism was explained by the the Poole-Frenkel emission. The quadratic voltage coefficient of capacitance of the BSmT film was approximately $698\;ppm/V^2$, which is higher than the required value (<$100\;ppm/V^2$) for RF application. This could be reduced by improving the process condition. The temperature coefficient of capacitance of the film was low at nearly $296\;ppm/^{\circ}C$ at 100 kHz. Therefore, amorphous BSmT grown on a TiN substrate is a viable candidate material for a metal-insulator-metal capacitor.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.37 no.4
• /
• pp.15-24
• /
• 2000

The dielectric relaxation of high-dielectric capacitors could be understood as a dynamic property of the capacitor in the time domain, which is regarded as a primarily important charge loss mechanism during the refresh time of DRAMs. Therefore, the equivalent circuit of the dielectric relaxation of the high-dielectric capacitor is essentially required to investigate its effects on DRAM. Nevertheless, There is not any theoretical method which is generally applied to realize the equivalent circuit of the dielectric relaxation. Recently, we have developed a novel procedure for the circuit modeling of the dielectric relaxation of high-dielectric capacitor utilizing the frequency domain. This procedure is a general method based on theoretical approach. We have also verified the feasibility of this procedure through experimental process. Finally, we successfully investigated the effect of dielectric relaxation on DRAM operation with the obtained equivalent circuit through this new method.

• Journal of the Korean Ceramic Society
• /
• v.40 no.9
• /
• pp.909-915
• /
• 2003

Anodic oxide films on aluminum play an important role as a dielectrics in aluminum electrolytic capacitor. In order to obtain the high capacitance, ZrO$_2$ films were coated on aluminum foils by sol-gel method and then, the properties of anodized films were studied. The coating and drying of the films were repeated 4-10 times and annealed at 300～$600^{\circ}C$ and the triple layer of ZrO$_2$/Al-ZrO$_{x}$ /Al$_2$O$_3$ was formed onto aluminum substrates after anodizing of ZrO$_2$/Al film. The thickness of $Al_2$O$_3$ layer was decreased with increasing the annealing temperature due to the densification of ZrO$_2$ film. The ZrO$_2$ films were crystallized even at 30$0^{\circ}C$ and showed nanocrystalline structure. The. capacitance of aluminum foil annealed at low temperature was higher than that at high temperature. The increase of capacitance was due to the high capacitance of ZrO$_2$ film annealed at low temperature. The capacitance of ZrO$_2$ coated aluminum increased about 3 times compared to that without a ZrO$_2$ layer after anodizing to 400 V. From these results, the aluminum foils with composite oxide layers are found to be applicable to the aluminum electrolytic capacitor.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2008.06a
• /
• pp.236-236
• /
• 2008

(Bi,La)$Ti_3O_{12}$(BLT) thin film is one of the most attractive materials for ferroelectric random access memory (FRAM) applications due to its some excellent properties such as high fatigue endurance, low processing temperature, and large remanent polarization [1-2]. The authors firstly investigated and reported the damascene process of chemical mechanical polishing (CMP) for BLT thin film capacitor on behalf of plasma etching process for fabrication of FRAM [3]. CMP process could prepare the BLT capacitors with the superior process efficiency to the plasma etching process without the well-known problems such as plasma damages and sloped sidewall, which was enough to apply to the fabrication of FRAM [2]. BLT-CMP characteristics showed the typical oxide-CMP characteristics which were related in both pressure and velocity according to Preston's equation and Hernandez's power law [2-4]. Good surface roughness was also obtained for the densification of multilevel memory structure by CMP process [3]. The well prepared BLT capacitors fabricated by CMP process should have the sufficient ferroelectric properties for FRAM; therefore, in this study the electrical properties of the BLT capacitor fabricated by CMP process were analyzed with the process parameters. Especially, the effects of CMP pressure, which had mainly affected the removal rate of BLT thin films [2], on the electrical properties were investigated. In order to check the influences of the pressure in eMP process on the ferroelectric properties of BLT thin films, the electrical test of the BLT capacitors was performed. The polarization-voltage (P-V) characteristics show a decreased the remanent polarization (Pr) value when CMP process was performed with the high pressure. The shape of the hysteresis loop is close to typical loop of BLT thin films in case of the specimen after CMP process with the pressures of 4.9 kPa; however, the shape of the hysteresis loop is not saturated due to high leakage current caused by structural and/or chemical damages in case of the specimen after CMP process with the pressures of 29.4 kPa. The leakage current density obtained with positive bias is one order lower than that with negative bias in case of 29.4 kPa, which was one or two order higher than in case of 4.9 kPa. The high pressure condition was not suitable for the damascene process of BLT thin films due to the defects in electrical properties although the better efficiency of process. by higher removal rate of BLT thin films was obtained with the high pressure of 29.4 kPa in the previous study [2].

• Journal of Surface Science and Engineering
• /
• v.34 no.5
• /
• pp.481-485
• /
• 2001

We investigated the structural and electrical properties of the Ba ($Zr_{x}$ $T_{il-x}$ )$O_3$ (BZT thin films with a mole fraction of x=0.2 and thickness 150 nm for the application in MLCC (Multilayer Ceramic Capacitor). BZT films were prepared on $Pt/SiO_2$/Si substrate at various substrate temperatures by the RF-magnetron sputtering system. When the substrate temperature was above $500^{\circ}C$, we could obtain multi-crystalline BZT films oriented at (110), (111), and (200) directions. The crystallization of the film and high dielectric constant were observed with the increase of substrate temperature. Capacitance of the film deposited at high temperature is more sensitive to the applied voltage than that of the film deposited at low temperature. This paper reports surface morphology, dielectric constant, dissipation factor, and C-V characteristics for BZT films deposited at three different temperatures. The BZT film deposited at 40$0^{\circ}C$ shows stable electrical properties but a little small dielectric constant for MLCC application.

• 한국신재생에너지학회:학술대회논문집
• /
• 2010.06a
• /
• pp.163.2-163.2
• /
• 2010

In this work, nano-flake shaped nickel oxide (NiO) films were synthesized by chemical bath deposition technique for electrochemical capacitors. The deposition was carried out for 1 and 2 h at room temperature using nickel foam as the substrate and the current collector. The structure and morphology of prepared NiO film were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). And, electrochemical properties were characterized by cyclic voltammetry, galvanostatic charge-discharge, and AC impedence measurement. It was found that the NiO film was constructed by many interconnected NiO nano-flakes which arranged vertically to the substrate, forming a net-like structure with large pores. The open macropores may facilitate the electrolyte penetration and ion migration, resulted in the utilization of nickel oxide due to the increased surface area for electrochemical reactions. Furthermore, it was found that the deposition onto nickel foam as substrate and curent collector led to decrease of the ion transfer resistance so that its specific capacitance of a NiO film had high value than NiO nano flake powder.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2001.07a
• /
• pp.263-266
• /
• 2001

In this paper, we investigated dielectric properies for BST thin films that was deposited on MgO/Si substrates using RF magnetron sputtering. In here, MgO film was used to perform that a diffusion b arrier between the BST film and Si substrate and a buffer layer to assist the BST film growth. A d eposition condition for MgO films was RF Power of 50W, substrate temperature of room temperature and the working gas ratio of Ar:O$_2$ were varied from 90:10 to 60:47. Finally we manufactured the cap acitor of Al/BST/MgO/Si/Al structure to know electrical properties of this capacitor through I-V, C-V measurement. In the results, C-V aha racteristic curves was shown a ferroelectric property so we measured P-E. A remanent poliazation and coerceive electric field was present 2$\mu$C/cm$^2$ and -27kV/cm respectively at Ar:O$_2$=90:10. And a va clue of dielectric constant was 86 at Ar:02=90:10.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2002.07b
• /
• pp.570-573
• /
• 2002

Pb(Zr0.52Ti0.48)O3 (PZT) thin films were deposited on the Pt/Ti bottom electrode by rf magnetron sputtering method from target containing 5%, 25% and 50% Pb excess for applying ferroelectric random access memory (FRAM). PZT films were deposited at $300^{\circ}C$ and then they were crystallized by rapid thermal annealing (RTA) at $700^{\circ}C$. After RTA treatment, our results showed that all PZT films indicated perovskite polycrystalline structure with preferred orientation (110) and no pyrochlore phase was observed by X-ray diffraction (XRD) and by Scanning electron microscopy (SEM). A well-fabricated PZT film of excess Pb 25% capacitor showed a leakage current density in the order of $2.63{\times}10^{-7}A/cm^2$ at 100kV/cm, a remanent polarization of $3.385{\mu}C/cm^2$ and a coercive field of 41.32 kV/cm. The results showed that Pb excess of target affects to electrical properties of PZT thin film.