Kuangwoo Nam

Fabrications and electrical properties of ferroelectric Bi3.25La0.75Ti3O12 thin films using a indium-tin-oxide conductive layer as the bottom electrode

Systematic effort was made to optimize the quality of ferroelectric Bi3.25La0.75Ti3O12 thin films, that were pulsed laser deposited onto indium–tin-oxide coated glass plates, by varying the conditions of laser fluence density, partial oxygen pressure and post-annealing temperature. Characterizations from the dielectric and ferroelectric measurements concluded that the films deposited with a laser power of 2.5 J cm−2, a deposition pressure of 200 mTorr and an annealing temperature of 650 °C showed the finest electrical properties, consisting of remnant polarization (2Pr) and coercive field (Ec) values of 28–32 µC cm−2 and 90–100 kV cm−1, respectively. No significant reduction in switching polarization magnitudes were observed until 1 × 1011 switching cycles, indicating that these electrical properties and the relevancy of the film with metallic-oxide ITO electrodes have satisfied the necessary requirements for applications in nonvolatile ferroelectric memory devices.

Inverse Capacitance-Voltage Characteristics of Bi3.25La0.75Ti3O12 Thin Film Pulsed Laser Deposited on Thermally Oxidized n-Type Si Substrates

Comparative studies on the electrical properties of a metal-ferroelectric-insulator-semiconductor field effect transistor were conducted using pulsed laser ablated ferroelectric Bi3.25La0.75Ti3O12 (BLT) thin films deposited on SiO2/Si substrates with different SiO2 thicknesses. The SiO2 layer was prepared on n-type Si substrates by dry oxidation at a temperature of 800°C. Small angle x-ray reflectivity studies were used to measure the SiO2 thickness. The capacitance-voltage (C-V) measurements revealed that the films showed good interfacial properties. Shifts in flatband voltages were observable, but were effectively reduced by deposition of the ferroelectric films. Au/BLT/SiO2/Si diodes with 8 nm SiO2 layer showed to be stable with relatively large memory window values of about 0.3 V, 2.5 V, 5.0 V, and 7.0 V, at increasing bias voltages of ±5 V, ±7 V, ±10 V, and ±12 V, respectively.

Unusual Switching Behavior Observed in Fatigue-Free Pb1.10Zr0.50Ti0.50O3 Thin Films Prepared on Conventional Pt/Ti/SiO2/Si Substrates

Pb(Zr,Ti)O 3 (PZT) thin films with Zr/Ti ratio of 50:50 were deposited on Pt/Ti/SiO 2 /Si substrates using the sol-gel method. Since controlling the conditions of heat-treatment is a great role in film growth, post-annealing processes were conducted under different environments. After standard processing, the films were annealed at 600°C under 3 different processes—(a) 30 min in air, (b) 30 min in O 2 ambient and (c) 2 step which was conducted first in air and then in O 2 atmosphere during 30 min respectively. Through electron microscopy and X-ray diffraction, we found that every film was crack-free and highly (111) oriented. Hysteresis measurements showed a generally large polarization value. The fatigue properties differ drastically for every process, showing an abnormal increase near the end of the measurement. The hysteresis loops before and after 1 × 10 10 switching cycles declined for the films annealed under a single-step, but as for the film by the two-step process, the hysteresis showed to increase in magnitude. Such abnormality and fatigue-free property is an unusual result for PZT films prepared on conventional Pt/Ti/SiO 2 /Si substrates.

Electrical properties induced by oxygen vacancies of CeO 2 thin films grown onp-Si(100)

We have deposited CeO2 thin films on p-Si(100) substrates to investigate their electrical properties originated from oxygen vacancies, using pulsed laser deposition(PLD) method. (111) preferential orientation was observed. Raman spectra revealed that a film deposited at 760deg C had the smallest distortion of the unit structure due to small quantities of oxygen vacancy. X-ray specular reflectivities were measured to investigate an electron density profile along the thickness. The profile was strongly correlated with oxygen vacancy because total net charges inside the dielectric film should be zero. As a result, oxide trapped-charge density rho(x) could be extracted from the electron-density profile. C-V curves depending on frequencies showed that and interface trapped-charge density is not high. Flat band voltage in C-V curves was slightly shifted because of the presence of oxide trapped charge. We will report on a decisive method calculating the shift of flat band voltage.

Ferroelectric properties of sol-gel derived Bi 4-x La x Ti 3 O 12 films prepared on Pt/Ti/SiO 2 /Si substrate

The ferroelectric properties of Bi4-xLaxTi3O12 (BLT) thin films deposited on Pt/Ti/SiO2/Si using sol-gel method have been studied. Their crystal structure, chemical composition and vibration modes were measured using x-ray thetas-2thetas scan, Electron probe micro-scope analyzer(EPMA), and Raman spectroscopy, respectively. Their orientations were domanantly (117) and (200). Various type of grains, lattice expansions and reductions are observed as a function of the content of La and the annealing temperature. The BLT0.25 had larger value of polarization and coercive field than other films, and showed poor fatigue property. However, BLT0.75 film kept a good fatigue property over 101 switching cycles. In this study, we have focused on understanding the features of polarization in terms of the microstructure and the distortion of the unit cell.

ELECTRICAL CHARACTERIZATIONS OF Bi3.25La0.75Ti3O12 THIN FILMS ON THERMALLY OXIDIZED p-Si SUBSTRATES

ABSTRACT A metal-ferroelectric-insulator-semiconductor (MFIS) diode was prepared using Bi3.25La0.75Ti3O12 thin films onto thermally oxidized Si substrates. Results on the electrical properties include capacitance-voltage (C-V), memory window effect and current-voltage (I-V) characteristics. C-V properties for the SiO2/Si structures showed an ideal switch from maximum to minimum capacitance exactly at zero voltage without any presence of flatband voltage difference. Such property ensures ohmic contacts of the electrodes and that the Au/SiO2/Si/Al diodes have fairly good interfacial properties. As for the MFIS-diodes, the flatband voltage difference enlarges at increasing voltages, exhibiting a memory window effect from ferroelectric polarization. The positive voltage sweep was measured to be identical at increasing bias voltages. Such unusual property may arise from the sudden increase in current density at about 0.9 V from I-V measurements.

Characteristics of Au/Bi3.25La0.75Ti3O12/Si3N4/Si Ferroelectric Field Effect Transistors

Pulsed laser deposition of ferroelectric Bi 3.25 La 0.75 Ti3 O 12 thin films was carried out for 5 mins at a substrate temperature of 400°C and a given partial oxygen pressure of 200 m Torr. Studies on the electrical properties of a metal-ferroelectric-insulator-semiconductor (MFIS) field effect transistor using Au/Bi 3.25 La 0.75 Ti 3 O 12 /Si3N 4 /Si have been conducted through measurements from capacitance-voltage and memory window characteristics for films prepared with different annealing temperatures and applied bias voltages. The films showed c-axis crystallizations at higher annealing temperatures but on the other hand, the memory window values had a tendency to decrease with respect to increasing temperatures. As the bias voltage was varied at 3 V, 5 V, 7 V, and 10 V for the film annealed at 700°C, the memory window values were measured to be 0.2 V, 0.36 V, 0.8 V, and 1 V, respectively.

Ferroelectric Properties of Au/Bi3.25La0.75Ti3O12/ITO Thin Film Capacitors

Characterizations on the crystallization, chemical composition and electrical property of pulsed laser deposited Bi 3.25 La 0.75 Ti 3 O 12 thin film with a thickness of 200 nm was investigated under various post-annealing treatments. Films annealed at 650°C showed a relatively large ferroelectric property compared to other films, consisting with remnant polarization and coercive field values of 14∼ 16 μ C/cm 2 and 90∼100 kV/cm, respectively. The films were found to be fatigue resistive but their hysteresis loops before and after undergoing 1 ×10 11 switching cycles showed a shift to the positive field. The n-type semiconducting property of the ITO electrode seems to be the main reason for concentrating the polarity to the positive electric field.