• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.140-140
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• 2009

The Metal-ferroelectric-semiconductor (MFS) structure has superior advantages such as high density integration and non-destructive read-out operation. However, to obtain the desired electrical characteristics of an MFS structure is difficult because of interfacial reactions between ferroelectric thin film and Si substrate. As an alternative solution, the MFS structure with buffer insulating layer, i.e. metal-ferroelectric-insulator-semiconductor (MFIS), has been proposed to improve the interfacial properties. Insulators investigated as a buffer insulator in a MFIS structure, include $Ta_2O_5$, $HfO_2$, and $ZrO_2$ which are mainly high-k dielectrics. In this study, we prepared the Dy-doped $La_2O_3$ solution buffer layer as an insulator. To form a Dy-doped $La_2O_3$ buffer layer, the solution was spin-coated on p-type Si(100) wafer. The coated Dy-doped $La_2O_3$ films were annealed at various temperatures by rapid thermal annealing (RTA). To evaluate electrical properties, Au electrodes were thermally evaporated onto the surface of the samples. Finally, we observed the surface morphology and crystallization quality of the Dy-doped $La_2O_3$ on Si using atomic force microscopy (AFM) and x-ray diffractometer (XRD), respectively. To evaluate electrical properties, the capacitance-voltage (C-V) and current density-voltage (J-V) characteristics of Au/Dy-doped La2O3/Si structure were measured.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.7
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• pp.599-603
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• 2003

Ferroelectric B $i_4$$_{-x}$N $d_{x}$ $Ti_3$ $O_{12}$ (BNdT) thin films with the composition(x=0.75) were prepared on Pt/Ti/ $SiO_2$(100) substrate by metal-organic deposition. The films were annealed by various temperatures from 550 to $650^{\circ}C$ and then the electrical and structural characteristics of BNdT films were investigated for the application of FRAM. Electrical properties such as dielectric constant, 2Pr and capacitance were quite dependent on the thermal heat treatment. The measured 2Pr value on the BNdT capacitor annealed at $650^{\circ}C$ was 56$\mu$C/$\textrm{cm}^2$ at an applied voltage of 5V. In fatigue characteristics value remained constant up to 8$\times$10$^{10}$ read/write switching cycles at a frequency of 1Mhz regardless of annealing temperatures.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.171-172
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• 2007

We fabricated the metal-ferroelectric-insulator-semiconductor filed-effect transistors (MFIS-FETs) using the $(Bi,La)_4Ti_3O_{12}\;and\;LaZrO_x$ thin films. The $LaZrO_x$ thin film had a equivalent oxide thickness (EOT) value of 8.7 nm. From the capacitance-voltage (C-V) measurements for an Au/$(Bi,La)_4Ti_3O_{12}/LaZrO_x$/Si MFIS capacitor, a hysteric shift with a clockwise direction was observed and the memory window width was about 1.4 V for the bias voltage sweeping of ${\pm}9V$. From drain current-gate voltage $(I_D-V_G)$ characteristics of the fabricated Fe-FETs, the obtained threshold voltage shift (memory window) was about 1 V due to ferroelectric nature of BLT film. The drain current-drain voltage $(I_D-V_D)$ characteristics of the fabricated Fe-FETs showed typical n-channel FETs current-voltage characteristics.

• Journal of the Korean Applied Science and Technology
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• v.35 no.4
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• pp.1206-1212
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• 2018

In this study, the polarization reversal characteristics of thin film capacitors with a thickness of 100 nm or less fabricated with ferroelectric polymer were measured and analyzed. For the fixed film thickness, polarization reversal occurred at higher coercive fields as the applied maximum electric field increased. For the fixed maximum electric field, polarization reversal occurred at the same coercive field irrespective of the thickness of the thin film. The proportional constant values between the logarithmic electric field and the logarithmic scale frequency were $0.12{\pm}0.01$ for all measurements. As a result, the ferroelectric polymer capacitors consistently exhibited polarization reversal characteristics without any size effects up to a thickness of 40 nm. This study shows the possibility of a polymer memory device that can operate at low voltage, which is useful for predicting the behavior of a low-voltage operating polymer memory device.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.10a
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• pp.537-541
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• 2003

The a-Si:H TFTs using ferroelectric of SrTiO$_3$, as a gate insulator is fabricated on glass. Dielectric characteristics of ferroelectric is better than SiO$_2$, SiN. Ferroelectric increases ON-current, decreases threshold voltage of TFT and also breakdown characteristics. The a-Si:H deposited by PECVD shows absorption band peaks at wavenumber 2,000 $cm^{-1}$ /, 635 $cm^{-1}$ / and 876 $cm^{-1}$ / according to FTIR measurement. Wavenumber 2,000 $cm^{-1}$ /, 635 $cm^{-1}$ / are caused by stretching and rocking mode SiH1. The wavenumber of weaker band, 876 $cm^{-1}$ / is due to SiH$_2$ vibration mode. The a-SiN:H has optical bandgap of 2.61 eV, refractive index of 1.8 - 2.0 and resistivity of 10$^{11}$ - 10$^{15}$ aim respectively. Insulating characteristics of ferroelectric is excellent because dielectric constant of ferroelectric is about 60 - 100 and breakdown strength is over 1 MV/cm. TFT using ferroelectric has channel length of 8 - 20 $\mu$m and channel width of 80 - 200 $\mu$m. And it shows drain current of 3 $\mu$A at 20 gate voltages, Ion/Ioff ratio of 10$^{5}$ - 10$^{6}$ and Vth of 4 - 5 volts.

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

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.135-136
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• 2006

Bismuth titanate ($Bi_4Ti_3O_{12}$, BIT) thin film has been studied intensively in the past decade due to its large remanent polarization, low crystallization temperature, and high Curie temperature. Substitution of various trivalent rare-earth cations (such as $La^{3+}$, $Nd^{3+}$, $Sm^{3+}$ and $Pr^{3+}$) in the BIT structure is known to improve its ferroelectric properties, such as remanent polarization and fatigue characteristics. Among them, neodymuim-substituted bismuth titanate, ((Bi, Nd)$_4Ti_3O_{12}$, BNT) has been receiving much attention due to its larger ferroelectricity. In this study, Ferroelectric $Bi_{3.3}Nd_{0.7}Ti_3O_{12}$ thin films were successfully fabricated by liquid delivery MOCVD process onto Pt(111)/Ti/$SiO_2$/Si(l00) substrates. Fabricated polycrystailine BNT thin films were found to be random orientations, which were confirmed by X-ray diffraction and scanning electron microscope analyses. The remanent polarization of these films increased with increase in annealing temperature. And the film also demonstrated fatigue-free behavior up to $10^{11}$ read/write switching cycles. These results indicate that the randomly oriented BNT thin film is a promising candidate among ferroelectric materials useful for lead-free nonvolatile ferroelectric random access memory applications.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.427-427
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• 2012

Ferroelectric-gate field effect transistor based memory using a nanowire as a conducting channel offers exceptional advantages over conventional memory devices, like small cell size, low-voltage operation, low power consumption, fast programming/erase speed and non-volatility. We successfully fabricated ferroelectric nonvolatile memory devices using both n-type and p-type Si nanowires coated with organic ferroelectric poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] via a low temperature fabrication process. The devices performance was carefully characterized in terms of their electrical transport, retention time and endurance test. Our p-type Si NW ferroelectric memory devices exhibit excellent memory characteristics with a large modulation in channel conductance between ON and OFF states exceeding $10^5$; long retention time of over $5{\times}10^4$ sec and high endurance of over 105 programming cycles while maintaining ON/OFF ratio higher $10^3$. This result offers a viable way to fabricate a high performance high-density nonvolatile memory device using a low temperature fabrication processing technique, which makes it suitable for flexible electronics.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07b
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• pp.861-864
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• 2002

Ferroelectric $Bi_{4-x}Nd_xTi_3O_{12}$(BNdT) thin films with the composition(x=0.75) were prepared on pt/Ti/$SiO_2$/Si(100) substrate by metal-organic deposition. The electrical and structural characteristics of BNdT thin films were investigated to develop ferroelectric thin films for capacitor layers of FRAM. After spin coating, thin films were annealed at $650^{\circ}C$ for 1hour in oxygen atmosphere. Scanning electron micrographs showed uniform surfaces composed of rod-like grains. The $Bi_{4-x}Nd_xTi_3O_{12}$(X=0.75) thin film capacitors with a Pt top electrode showed better ferroelectric properties. At the applied voltage of 5V, the dielectric constant$(\varepsilon_r)$, dissipation factor$(tan{\delta})$, remanent polarization(2Pr) and nonvolatile swiching charge of the $Bi_{4-x}Nd_xTi_3O_{12}$(x=0.75)thin films were about 346.7, 0.095, $56{\mu}C/cm^2$ and $38{\mu}C/cm^2$ respectively. Also the capacitor did not show any significant fatigue up to $8{\times}10^{10}$ read/write switching cycles at a frequency of 1MHz.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11b
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• pp.463-466
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• 2001

In recent year, Ferroelectric $BLT(Bi_{4-x}La_{x}Ti_{3}O_{12})$ is a promising candidate materials. This study was practiced to make good conditions of BL T targets. In this study, calcination and sintering temperature were kept at $750^{\circ}C$, $1100^{\circ}C$ for 2 hour respectively. the density obtained 7.612, 7.98, $7.877g/cm^{3}$ as $La_{2}O_{3}$ contents were 0.0mol%, 0.25mol%, 0.5mol%. Especially, the lanthanum content of 0.5 mol% measured C-axis (117) preferred orientation more than the others targets in the XRD. In $\varepsilon_{r}-f$ relationship using by HP 4194 A impedance analyzer, the 0.5 mol% observed above 200 relative dielectric constant. but the dissipation factor was higher than others targets at 100Hz~13MHz range. SEM photograph with the content of $La_{2}O_{3}$ was observed like rod and plate types.