Conventional Ge2Sb2Te5 (GST) was modified by adding up a small amount of SiOx, using co-sputtering technique from multiple targets. The SiOx content was gradually increased by increasing the power applied to SiOx target, up to 8 volume percent. The sheet resistance of SiOx-containing GST exponentially increased, when the room-temperature-deposited samples were annealed at 300 °C. Transmission electron microscopy images revealed that no SiOx particulates were formed, which was confirmed by Gattan image filtering. It was indicated by x-ray diffraction patterns that the grain size of SiOx-containing GST is smaller than normal GST with lattice locally distorted at its crystalline state, suggesting that molecular SiOx is homogeneously distributed throughout the GST matrix. We observed that the crystallization temperature of SiOx-containing GST is gradually elevated by increasing the SiOx content, while the melting point decreased. These observations led to the reset current reduction, which is a critical requirement for the high density PRAM.

Effects of porosity on the microwave properties in dielectric ceramics were studied by the electromagnetic simulation. Scattering matrix S21 obtained from the network analyzer was compared to the S21 obtained from the simulation. From electric field distribution, the dominant resonant TE01 mode could be easily determined. The effects of the porosity inside the dielectrics on the microwave properties were investigated. Quality factor decreased with the porosity and the pore size.

The thermal activation energies for conduction of Nb-doped SrTiO3 grains and grain boundaries have been investigated by impedance spectroscopy. First, to observe the effect of electrode/SrTiO3 bulk interface, the varied impedances of SrTiO3 single crystal were measured with temperatures. The activation energy of an electrode/bulk interface was determined to be 1.3 eV, whereas that of bulk was 0.8 eV. When the impedances of Nb-doped SrTiO3 ceramics were measured, it was suggested that the more precise impedance values of a single grain and a single grain to grain junction be obtained using a microelectrode method. The activation energies for a grain, a grain boundary, and an electrode/bulk interface were determined to be about 0.8, 1.3, and 1.5 eV, respectively. From these measured results, it was suggested that the activation energy, 0.8 eV, measured in grain was originated from oxygen vacancies and the activation energy, 1.3 eV, in grain boundary was from strontium vacancies.

The effect of MnO on the electrical properties of Nb-doped SrTiO3 was investigated to understand the electronic states of grains and grain boundaries. Grain size and dielectric constant were decreased with increasing Mn-doped content from 0 to 0.07 mol%. However, it was observed that the non-linearity coefficient of Nb-doped SrTiO3 was changed from 5 to 43 with Mn-doped content increasing from 0 to 0.03 mol%. Current-voltage (I-V) characteristics, capacitance-voltage (C-V) measurement, complex plane analysis and impedance spectroscopy were performed to obtain the information about the electrical properties of grains and grain boundaries. The potential barrier height increased and the donor concentration decreased with increasing Mn-doped content. This phenomena, that the electrical properties of Nb-doped SrTiO3 were changed with the addition of Mn, would be determined by the effect which Mn-2-3 substituted for Ti sites. It was observed that the breakdown voltage of single grain boundary was changed from 3.8 V to 8.9 V when measured by micro-electrode method.

The dielectric temperature characteristics and microstructures of BaTiO3-based ceramics sintered with additives such as Sm2O3, CeO2, and Bi2O3:Nb2O5 were investigated using TEM, XRD, and EDS. For a Sm2O3-modified BaTiO3 ceramic whose additives were uniformly distributed in grains, the ferroelectric transition temperature (Tc) was shifted to a lower temperature, while the transition temperatures (T1 and T2) were shifted to a higher temperature. The additions of CeO2 and Bi2O3: PbO to BaTiO3 formed the chemical inhomogeneity which was composed of grain core, grain shell, and concentration gradient region. The dielectric curve versus temperature of CeO2-modified BaTiO3 has the shape of one strong peak, whereas BaTiO3 ceramics sintered with Bi2O3:Nb2O5 exhibit the broad dielectric constant at the low temperature region and 130 °C ferroelectric transition peak. The dielectric temperature characteristics of additives modified BaTiO3 were determined in terms of the chemical inhomogeneity and stress induced by the difference of the unit cell volume between grain core and grain shell.