Nan-Chung Wu

Dielectric properties of Ba(ZrxTi1−x)O3 thin films prepared using radio frequency magnetron sputtering

Pt/Ba(ZrxTi1−x)O3/Pt/Ti/SiO2/Si capacitors were fabricated using radio frequency (rf) magnetron sputtering. The deposition parameter effects on the dielectric constant, capacitance, and leakage current density of the capacitors were investigated. Amorphous Ba(ZrxTi1−x)O3 (BZxT1−x) thin films were sputtered onto a substrate with a temperature of 300 °C, rf power of 130 W, and in a no-oxygen atmosphere. BZxT1−x thin films deposited onto Pt-coated Si substrates show a preferred orientation in the (100) reflection. The dielectric constants of the BZxT1−x thin films increased with increasing Zr content and deposition temperature. The diffuse phase transition behavior of the BZxT1−x thin films became more pronounced at high Zr content films. The leakage current density of the Pt/Ba(ZrxTi1−x)O3/Pt/Ti/SiO2/Si capacitors at 1 kV/cm was about 1.0×10−7 A/cm2. This increased with increasing deposition temperature but decreased with increasing O2/(O2+Ar) ratio. From the films, P–E hysteresis loops, the BZ0.1T0.9 thin ...

Structural and dielectric characterization of the (Ba1-xSrx)(Ti0.9Sn0.1)O3 thin films deposited on Pt/Ti/SiO2/Si substrate by radio frequency magnetron sputtering

(Ba1−xSrx)(Ti0.9Sn0.1)O3 (BSxTS) thin films prepared by rf magnetron sputtering have been characterized as a function of temperature, applied voltage, and electric field. The BSxTS thin films have been confirmed with x-ray diffraction and electron diffraction analysis. The BSxTS thin films show a strong (111) preferred orientation for Sr content 0.1≦x≦0.3. Grain size increases with increasing deposition temperature and is correlated to high dielectric constants. Leakage current density at 1 kV/cm varies from below 10−7 to mid 10−9 A/cm2 for the O2/(O2+Ar) ratio varying from 5/(5+5) to 1/(1+9). A large and clear hysteresis shows ferroelectricity at 25 °C for all BSxTS thin films. The remnant polarization increases with increasing Sr content, which is preseemably caused by the lattice mismatch between BSxTS thin films and Pt layers.

Dielectric Properties of Nanocrystalline Barium Titanate Thin Films Deposited by RF Magnetron Sputtering

The nanocrystalline thin films of BaTiO3 have been deposited on the Pt/Ti/SiO2/Si substrates by RF magnetron sputtering at 500°C. The film deposited at 500°C has a thickness of 450.0 nm and is composed of granular crystallites of about 45.0 nm size. The crystallite size decreases with decreasing film thickness. The dielectric constant of the nanocrystalline BaTiO3 thin films increases with increasing film thickness. For the film thicknesses of 150.0 and 450.0 nm, the leakage current density is below 1.0×10-9 A/cm2 for the applied voltage of less than 5 V.

Effect of process parameters on synthesis of aluminum nitride powder prepared by chemical vapor deposition

Ultrafine aluminum nitride (AlN) powders were obtained by the chemical vapor deposition (CVD) process via the AlCl3-N2-NH3 system operated at various temperatures and different mixing modes of AlCl3 and NH3 gases. X-ray diffraction (XRD), Fourier transform infrared spectroscope (FTIR), transmission electron microscope (TEM) and electron diffraction (ED) were utilized to study the effect of process parameters on the synthesis and characterization of the AlN powders. It had been shown that all of the obtained powders were exclusively identified to be the single phase AlN and were indifferent to the different mixing modes AlCl3 and NH3 gases. The yield of synthesized AlN powder was affected by the entries mixing position of the reacting gases of AlCl3 and NH3.The yield increased from 13% to 82% where the mixed position was shifted from the front edge to middle point of the quartz tube. On the other hand, the yield increased from 5% to 82% as the reaction temperature increased from 600°C to 1050°C. The morphology of the AlN powders was affected by the diameter of a feeding nozzle and mixing mode of AlCl3 and NH3 gases.

Reproducibility ofTc in a Bi2Sr2CaCu208 superconductor

The reproducibility ofTc in superconductive Bi2Sr2CaCu2O8 is known to be very poor. In our study, the reproducibility was found to depend greatly on preparation conditions. DTA, TGA and powder X-ray diffraction methods were used to study the Bi2Sr2CaCu2O8 superconductors prepared by different routes. Resistivity and diamagnetic susceptibility were taken as the measure of superconductivity. It was found that those superconductors prepared from the oxides/carbonates (one-step) process resulted in scatteredTc data which were less reproducible. The two-step synthesis from precalcined precursors of Bi-Sr-O and Sr-Ca-Cu-0 containing mixtures, resulted in a much improved reproducibility with the predominantTc = 80 K superconducting phase (more than 95%). It was also found that the amount ofTc = 115 K phase tends to decrease after repeated pulverization and sintering, leading to a single 80 K phase state. Compaction of the pulverized powder at a pressure > 4.5 ton cm−2 was found to induce a preferred (00L) orientation during sintering.

Sintering and piezoelectric properties of Pb(Ni1/3Sb2/3)O3-PbZrO3-PbTiO3 ceramics

The sintering and piezoelectric properties of Pb(Ni1/3Sb2/3)O3-PbZrO3-PbTiO3 ceramics have been investigated. When the powders contain 48 mol% PbTiO3 and less than 10 mol% Pb(Ni1/3Sb2/3)O3 followed by calcination at 850°C for 2 h, the calcine only contains the perovskite structure; but if the Pb(Ni1/3Sb2/3)O3 content is between 12 mol% and 14 mol%, both tetragonal and rhombohedral phases are obtained. The composition of the morphotropic phase boundary(MPB) in the Pb(Ni1/3Sb2/3)O3-PbZrO3-PbTiO3 system is Pb(Ni1/3Sb2/3)O3 = 12 mol%, PbZrO3 = 40 mol% and PbTiO3 = 48 mol%. As the composition at the MPB is sintered at 1260°C and 1280°C for 2 h, respectively, the maximum density (7.8 g/cm3) is obtained. The SEM micrographs indicate that a decrease in porosity with increasing sintering temperature is attained at 1280°C, which is due to a decrease in the number and size of pores. When the sintering temperature is higher than 1280°C, the porosity increases due to PbO evaporation leading to an increase of the number of pore sites and in enlargement of the pore diameter. When the compact composition at MPB is sintered at 1280°C for 2 h, the planar coupling coefficient (Kp) and mechanical quality coefficient (Qm) tend to approach the maximum (0.488) and minimum values (292.5), respectively.

Effect of CaCN2 Addition on the Densification Behavior and Electric Properties of AlN Ceramics

Calcium cyanamide (CaCN2) has been used as a sintering aid as well as a dopant for AlN. The effect of CaCN2 addition on the densification behavior and electric properties of liquid-phase sintered AlN ceramics was investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM), dielectric and electric resistance measurements. Dense sintered specimens (relative density > 97.0%) were obtained using 1.0 to 2.0 wt% CaCN2 additives. With 0.5 to 3.0 wt% added CaCN2 and sintering at 1600 to 1700°C, only the AlN phase was observed in the XRD patterns. In the TEM and electron diffraction (ED) patterns, the minor phase, 3CaOAl2O3, appeared around the AlN grain boundaries. Based on the SEM observation, the well-faceted grain morphology was considered to be due to a predominant intergranular fracture. The dielectric constant of the AlN specimens were about 8.6 and 8.2 for 150 kHz to 10 MHz, respectively, when the samples were sintered at 1650°C for 1, 3 and 6 h. The electric resistance of the AlN specimens approached 3.87×1012 Ω. The trend of the electric resistance variation in the specimens was the same as that of the linear shrinkage and relative density of the specimens.

The formation of superconducting YBa2Cu3O7−x through solid state reaction

DTA, TGA and X-ray diffractometry (XRD) were utilized to study the formation of the high Tc superconducting YBa2Cu3O7-x (Y123) phase through solid state reaction of a mixture of Y2O3:BaCO3:CuO, in the molar ratio of 0.5:2:3. For continuous heating at 10°C/min, it was found that the Y123 phase exists at 820–996°C and gradually disappears at higher temperatures. The insulating Y2BaCuO5 (Y211) phase exists over the temperature range 987 through 1190°C, while the semiconducting YBa3Cu2O7−y (Y132) phase coexists with the Y123 phase. For isothermal heating, it was found that the most appropriate conditions for the formation of the Y123 phase is isothermal heating at 907°C for more than 16 h. The pure Y123 phase is obtainable since the Y132 and the Y211 phases disappear after prolonged soaking at 907°C. Semiquantitative analyses on the amount of existing phases during continuous heating, including the intermediate binary phases, are also given. The high temperature superconductor can be synthesized reproducibly with a Tc of around 93 K by the calcining process based on this study.

Dielectric Properties and Leakage Current Characterization of the Ba(SnxTi1-x)O3 Thin Films Prepared by Radio Frequency Magnetron Sputtering

Ba(SnxTi1-x)O3 (BSxT1-x, 0≤x≤0.15) thin films deposited by rf magnetron sputtering with platinum (Pt) top and silver (Ag) bottom electrodes have been characterized with respect to the dielectric properties and leakage current density as a function of composition and rf power. BSxT1-x thin films are amorphous when deposited at rf powers of 100 and 125 W, 5×10-3 Torr working pressure, an O2/(O2+Ar) ratio of 1/(1+9) and room temperature. The XRD result shows the presence of a single perovskite phase of BaTiO3, operated at a range of rf power increasing from 125 to 175 W. The maximum capacitance of Pt/BSxT1-x/Si/Ag capacitors increases with increasing Sn content. The ferroelectric characteristics of the capacitance–voltage hystersis loop in the BSxT1-x thin films are observed. The leakage current density of the Pt/BS0.15T0.85/Si/Ag capacitors at 100 kV/cm varies from mid 10-6 to about 10-8 A/cm2 with the rf power decreasing from 175 to 125 W. The dominant conduction mechanism of the BS0.15T0.85 thin films has shown to be related to Schottky emission (SE) and Poole–Frenkel (PF) mechanisms. The remnant polarization (Pr) and coercive electric field (Ec) of the above device appear to decrease with increasing Sn content.