Wen Cheng Tzou

Low Temperature Method for Enhancing Ferroelectric Thin Films in Non-Volatile Random Access Memory Devices

In this study, the electrical properties of as-deposited Sr0.4Ba0.6Nb2O6 (SBN) ferroelectric thin films on SiO2/Si(100) substrates were improved by low temperature supercritical carbon dioxide fluid (SCF) process treatment. The as-deposited SBN ferroelectric thin films were treated by SCF process which mixed with pure H2O and propyl alcohol. After SCF process treatment, the memory windows increased in C-V curves, and the passivation of oxygen vacancy and defect in leakage current density curves were obtained. In addition, the improvement properties of as-deposited SBN thin films after SCF process treatment were found by XPS, C-V, and J-E measurement. Finally, the mechanism concerning the dependence of electrical properties of the SBN ferroelectric thin films on the SCF process was discussed.

Synthesis of Fe-Core/Au-Shell Nanoparticles under Ambient Pressure

Pure metal iron nanoparticles are unstable in the air. By a coating iron on nanoparticle surface with gold, these air-stable nanoparticles are protected from the oxidation and retain most of the favorable magnetic properties. However, it is difficult to prepare Fe-core/Au-shell (Fe@Au) nanoparticles under ambient pressure because iron nanoparticles are very easily to be oxidized in the air. In this study, we synthesized Fe@Au nanoparticles by modified reverse micelle method under ambient pressure and investigated them by X-ray diffraction, transmission electron microscopy (TEM), ultraviolet-visible absorption spectra, and magnetic susceptibility measurements. X-ray diffraction analysis shows that the pattern of iron is hidden under the pattern of gold. TEM image reveals that the core-shell structure is obviously observed and the average size of Fe@Au nanoparticles is about 12 nm, with about 8 nm diameter core and 2 nm shell. The absorption band of the Fe@Au nanoparticles shifts to a longer wavelength and broadens relative to that of the pure gold. The magnetic susceptibility of Fe@Au nanoparticles is measured with a SQUID magnetometer and found to be superparamagnetic with a blocking temperature Tb ~25 K.

Investigate the Characteristics of 0.65(K0.5Bi0.5TiO3)-0.35BaTiO3 Films at Various Deposition Temperatures

0.65(K0.5Bi0.5)TiO30.35BaTiO3 (KBT-BT3) ceramics were synthesized using a two-step calcination process that combined hydrothermal and conventional calcination processes. After sintered into ceramic target, KBT-BT3 films were deposited on Pt/Ti/Si and SiO2/Si/Al substrates by radio frequency magnetron (RF) sputtering at various temperatures. The surface morphologies and thicknesses of KBT-BT3 films were characterized by field emission scanning electron microscopy, and the thickness increased with increasing deposition temperature. XRD patterns showed that all KBT-BT3 films were amorphous and higher deposition temperature had no apparent effects to improve the crystalline orientation. The effects of deposition temperatures on the properties of the current-electric filed, polarization-applied electric field, and capacitance-voltage curves were also investigated. As deposition temperatures of KBT-BT3 films increased from room temperature to 400°C, the leakage current density had no apparent variation but the threshold voltage was shifted to lower value. The theorems for the effects of deposition temperature on the properties of KBT-BT3 films were also investigated.

The Influences of Post-annealing Temperature on the Properties of Sr0.6Ba0.4Nb2O6 Thin Films

In this study, Sr0.6Ba0.4Nb2O6 (SBN) thin films were prepared by radio-frequency (RF) magnetron sputtering. After finding the optimal deposition parameters, the deposited SBN thin films were annealed in a conventional furnace. In comparisons of XRD patterns, the annealing process had improved the crystallization and also had large effects on the crystalline orientation of SBN thin films. As the annealing temperature was risen from 600 to 700 °C, the diffraction intensities of (410) and (001) peaks really increased. Annealed at 800 °C, SBN thin films showed a highly c-axis crystalline orientation in (001) peak. Effects of annealing temperature on the electrical characteristics were recorded and analyzed, including the polarization-applied electric field curves, the capacitance-voltage curves, and the leakage current density-electric field curves. As the annealing process was used to treat on the as-deposited SBN thin films, the Pr, Ps, and Ec values were really improved. The theorems to cause the drastic variations in the capacitances, the memory windows, and the flat-band shift voltages of SBN thin films were also discussed.

Effects of Deposition Parameters and Annealing Temperatures on the Characteristics of the Sr0.6Ba0.4Nb2O6 Thin Films

Sr0.6Ba0.4Nb2O6 (SBN) thin films were prepared by radio frequency (RF) sputtering onto the SiO2/Si/Al and Pt/Ti/Si substrates to form the MFIS and MFM structures. Their deposition rates increased with decreasing oxygen concentration and with increasing RF power. Their optimal deposition parameters were the substrate temperature of 500°C, chamber pressure of 10 mTorr, oxygen concentration of 40%, and RF power of 120W, respectively. The rapid temperature annealing (RTA) process had large effects on the grain growth of the SBN thin films. The effects of different RTA temperatures on the leakage current density - electrical field curves and the capacitance - voltage curves of the SBN thin films were also investigated.

The Influences of Annealing Temperatures on the Properties of the Sol-Gel Deposition SrBi4Ti4O15 Thin Films

In this study, SrBi4Ti4O15 (SBT) thin films were deposited onto the SiO2/p-Si(100) and Pt/Ti/SiO2/p-Si(100) substrates by using sol-gel method. After deposition, the SBT thin films were then heated by a rapid thermal annealing (RTA) process conducted in air for 1min at 600-800°C. The surface morphologies and the crystalline structures of the SBT thin films were investigated by using SEM and XRD patterns. The grain sizes increased and the pores decreased with rising RTA temperature. In addition, the coercive field decreased and the remanent polarization and saturation polarization increased with rising RTA temperature. The lnJ-E1/2 curves of the SBT thin films were also investigated to find the leakage current mechanisms correspond either to the Schottky emission or to the Poole-Frenkel emission.

Developing the Crystalline Structures and Dielectric Properties of Excess Bi2O3-Added 0.95(Na0.5Bi0.5)TiO3-0.05BaTiO3 Ceramics

0.95 (Na0.5Bi0.5)TiO3-0.05 BaTiO3 (NBT-BT3) compositions with excess x wt% Bi2O3 (NBT-BT3-x, with x=0, 1, 2, and 3) are sintered at 1200°C. When excess Bi2O3 is added, the NBT-BT3-1 ceramic displays the largest grain sizes, after which the grain sizes apparently decrease as more excess Bi2O3 is added. The lattice constants of calcined NBT-BT3 powder and NBT-BT3-x ceramics are calculated by the Rietveld full-pattern refinement method using the XRD standard pattern of ICSD-154041 and the measured XRD patterns of NBT-BT3-x ceramics. The refined values are compared with the measured XRD patterns to determine the cause of the distortion in the NBT-BT3-x ceramics. We show that NBT-BT3-1 ceramic has the minimum lattice constant a and maximum lattice constant c. The effects of excess Bi2O3 content on the dielectric properties of NBT-BT3-x ceramics are also discussed.

The Influence of Annealing Treatment on Physics and Electrical Characteristics of Ba(Zr0.1Ti0.9)O3 Ferroelectric Films on ITO/Glass Substrate

Perovskite Ba(Zr0.1Ti0.9)O3 (BZ1T9) ferroelectric thin films well deposited on ITO/glass substrates for applications in system-on-panel (SOP) devices are produced and investigated. The sputtering parameters of as-deposited BZ1T9 thin films were rf power of 160 W, chamber pressure of 10 mTorr, substrate temperature of 550oC, and an oxygen concentration of 40%. From the SEM cross- sectional observation, the deposition rate were about 2.5 nm/min. Additionally, the maximum dielectric constant and leakage current density of annealed BZT films under the rapid temperature annealing would be increased, as the temperature increased to 6500C. Further, the maximum remnant polarization and coercive field of BZT films were found and calculated from the p-E curves.

Memory Properties of SrBi2Ta2O9/ Ba(Zr0.1Ti0.9)O3 Thin Films Prepared on Si Substrate

In this study, ferroelectric thin films of SrBi2Ta2O9 (SBT) or bilayered SrBi2Ta2O9/ Ba(Zr0.1Ti0.9)O3 (SBT/BZT) are successfully deposited on Si substrate under the optimal RF magnetron sputtering conditions, and their electrical and ferroelectric characteristics are discussed. Ferroelectric thin films are deposited on Si substrate under the RF power of 80 W, chamber pressure of 10 mTorr, substrate temperature of 550oC, and different oxygen concentrations. The surface morphology of deposited thin films is observed from the FESEM images, and the memory windows and leakage current of the Al/SBT/BZT/Si (MFS) structure are measured by an impendence phase analyzer and a semiconductor parameter analyzer, respectively. The memory window, capacitance and leakage current density of MFS structures under different oxygen concentrations are also reported. We find that the memory window of bilayered SBT/BZT structure shows larger than one of single layer SBT structure.

Dielectric Characteristics of the Lead-free Piezoelectric Ceramics K0.50Na0.50Nb0.95Ta0.05O3

In order to improve the sintering density and dielectric properties of the lead-free K0.5Na0.5NbO3-based ceramics, by the use of solid-state reaction, part of the Nb atoms are substituted by the Ta atoms to form K0.5Na0.5Nb0.95Ta0.05O3 ceramics and the dielectric characteristics are detail investigated in this letter. It is found that the phases of K0.5Na0.5Nb0.95Ta0.05O3 ceramics are pure perovskite with typical orthorhombic symmetry, in addition, no other secondary phases could be certified. For pure K0.5Na0.5Nb0.95Ta0.05O3 ceramics, the shapes of the grains are quadrate and which would due to the increase of the porosity and can not be eliminated easily. Because of the phase stability of pure K0.5Na0.5Nb0.95Ta0.05O3 ceramics is limited to 1140 °C in this study, higher sintering temperature (over than 1140 °C) is not suitable for the fabrication of K0.5Na0.5Nb0.95Ta0.05O3 ceramics. Moreover, the Ta atoms in the K0.5Na0.5NbO3-based ceramics could be used to improve the dielectric properties effectively, and it also reveals lower Curie temperature and lower phase transition temperature than the pure K0.5Na0.5NbO3 ceramics. In this letter, for 1120°C-sintered K0.5Na0.5Nb0.95Ta0.05O3 ceramics, the optimum bulk density is 95.6 % of the theorical density, the Curie temperature is 380 °C, and the optimum relative dielectric constant is 6107 at 10 kHz.