Kentaro Kyuno

Moisture-absorption-induced permittivity deterioration and surface roughness enhancement of lanthanum oxide films on silicon

Effects of moisture absorption on permittivity and surface roughness of lanthanum oxide (La2O3) films were investigated. It was found that the moisture absorption deteriorates the permittivity (k) of La2O3 films on silicon because of the formation of hexagonal La(OH)3 with a low permittivity after films were exposed to the air. Therefore, the moisture absorption should be a very possible reason for the permittivity variation of La2O3 film in literatures reported, so far. Furthermore, a roughness enhancement was also observed after La2O3 films were exposed to the air for several hours. This observation should be another concern of hygroscopic La2O3 film application.

Permittivity increase of yttrium-doped HfO2 through structural phase transformation

An approach to control the dielectric properties of hafnium-based oxide films with an intentional structural phase transformation was proposed and demonstrated. Yttrium serves effectively as a dopant to induce a phase transformation from the monoclinic to the cubic phase even at 600°C. The yttrium-doped HfO2 films show higher permittivity than undoped HfO2, and the permittivity as high as 27 is obtained by 4at.% yttrium doping. The permittivity enhancement by yttrium doping can be explained by the shrinkage of molar volume due to the structural phase transformation. The advantage of yttrium doping is more pronounced at higher temperatures, since the permittivity of undoped HfO2 is reduced significantly, whereas that of 17at.% yttrium-doped film shows no change even at 1000°C.

In-plane mobility anisotropy and universality under uni-axial strains in nand p-MOS inversion layers on (100), [110], and (111) Si

An investigation of the inversion layer mobility characteristics on conditions with systematic combinations of three key parameters: surface orientations, in-plane channel directions, and uni-axial strains, was performed. A guiding principle for an optimum combination of above three key parameters in terms of electron and hole mobility enhancement is presented. In addition, it is found experimentally that the definition of the mobility universality should be changed with surface orientations and applied uni-axial strains.

Structural and electrical properties of HfLaOx films for an amorphous high-k gate insulator

Thin HfLaOx films on Si(100) have been investigated as an alternative gate insulator. The introduction of La2O3 into HfO2 causes an increase of crystallization temperature. Furthermore, unlike other Hf-based amorphous materials such as HfSiOx or HfAlOx, the permittivity of HfLaOx keeps a high value (>20). The capacitance-voltage curve of metal oxide semiconductor capacitor using the HfLaOx dielectric film has shown a negligible hysteresis and no frequency dispersion, indicating very small degradations of both interface and bulk properties. In addition, a very low fixed charge density in HfLaOx films is demonstrated from a very small film thickness dependence of the flatband voltage.

Study of La-induced flat band voltage shift in Metal/HfLaOx/SiO2/Si capacitors

The flat band voltage in metal/HfLaOx/SiO2/Si capacitors has been investigated as a function of La concentration in HfLaOx. We have found that with an increase of La concentration, the flat band voltage shifts to the negative direction. Furthermore, we demonstrate that the flat band voltage in this system is determined by the La concentration at HfLaOx/SiO2 interface. This result suggests that the flat band voltage shift is due to the dipole layer formed at the HfLaOx/SiO2 interface rather than the Fermi-level pinning at the metal/HfLaOx interface.

Growth Mechanism Difference of Sputtered HfO2 on Ge and on Si

HfO2 films were deposited by the reactive sputtering on Ge and Si substrates simultaneously, and we found both the interface layer and the HfO2 film were thinner on Ge substrate than those on Si substrate. A metallic Hf layer has a crucial role for the thickness differences of both interface layer and HfO2 film, since those thickness differences were observed only when an ultrathin metallic Hf layer was predeposited before the reactive sputtering process. The role of metallic Hf in these phenomena is understandable by assuming the formation of a volatile Hf–Ge–O ternary compound at the early stage of the film growth. This result shows that the HfO2∕Ge system has an advantage over the HfO2∕Si system from the viewpoint of further reduction of the gate oxide film thickness.

Higher-k LaYOx films with strong moisture resistance

The permittivities and the moisture resistance of LaYOx films annealed at 600°C with different Y concentrations are investigated. The permittivities of 40%Y–LaYOx and 70%Y–LaYOx films are higher than 25. The high permittivities come from the well crystallized hexagonal phase of LaYOx films, since the hexagonal phase rare earth oxides show higher permittivity than the cubic phase ones due to the smaller molar volume of the hexagonal phase. Furthermore, the high permittivity LaYOx films (40%Y–LaYOx and 70%Y–LaYOx) show a strong resistance to the moisture due to the introduction of Y2O3.

Growth and the diffusion of platinum atoms and dimers on Pt (111)

Abstract The diffusion of platinum adatoms and dimers on Pt(111) has been measured at different temperatures by direct observation in a low-temperature field ion microscope. The activation energy for single atom motion is found to be 0.260 ± 0.003 eV, while for dimers it is 0.37 ± 0.02 eV. Comparison with previous results obtained in STM studies of the density of islands after deposition from the vapor as well as with theoretical estimates are now possible. The former are in excellent agreement, the latter less so, but empirical extrapolation from the neighboring iridium proves useful. Contributions from dimer diffusion to growth at low temperatures can also be assessed, and are found to be minor.

Band gap enhancement and electrical properties of La2O3 films doped with Y2O3 as high-k gate insulators

In this study, we prepare the well crystallized La2O3 films by doping Y2O3 with different contents (La2−xYxO3) and examine the dielectric and electrical properties of La2−xYxO3 films experimentally. It is found that the optical band gap of La2−xYxO3 film increases with the increase in Y content (x) monotonically. Furthermore, a low leakage current of about 10−5 A/cm2 (equivalent oxide thickness: 1 nm) when the gate voltage is 1 V larger than the flat band voltage, and good capacitance-voltage characteristics in Au/La2−xYxO3/Si metal-insulator-semiconductor capacitors are observed. Our results also indicate that Pt/La2−xYxO3/Au metal-insulator-metal capacitor shows a low leakage current and a small voltage dependence of the capacitance.

Theoretical Study on the Magnetocrystalline Anisotropy of X/Co (X=Pd, Pt, Cu, Ag, Au) Multilayers

The magnetocrystalline anisotropy energies of X(2ML)/Co(1ML) (ML: monolayer) (X=Pd, Pt, Cu, Ag, Au) multilayers have been calculated from first principles within the local-spin-density approximation using the linear muffin-tin orbitals method. The easy axis of Pd/Co, Pt/Co and Au/Co are found to be perpendicular to the film plane, which are in good agreement with experiments.