Shinji Takayama

Effects of Y or Gd addition on the structures and resistivities of Al thin films

The addition of Y or Gd to Al thin films markedly decreases the grain size of the Al matrix and largely suppresses growth of hillocks at high temperatures (350–450 °C) associated with a large number of segregated metallic compounds, mostly at grain boundaries. The resistivities of the films after annealing at those high temperatures are less than 50 nΩ m. These tendencies also hold true for other Al rare‐earth alloy systems. The breakdown voltage of anodically oxidized films of Al–Y and Al–Gd alloys is higher than that of pure Al thin films.

Low resistivity Al–RE (RE=La, Pr, and Nd) alloy thin films with high thermal stability for thin‐film‐transistor interconnects

The addition of light rare‐earth (RE) metal elements (La, Pr, and Nd) to Al thin films with about 2–7 at. % markedly decreases the grain size of the Al matrix more than 50% compared with those of pure Al. Such addition largely suppresses growth of thermal defects of hillocks and whiskers at high temperatures (350–450 °C). A large number of fine metallic compounds of Al11RE3 and/or Al3RE (RE=La, Pr, and Nd) were segregated in an Al matrix, mostly at grain boundaries, after annealing at 350 °C. The resistivities of the films after annealing at the above temperatures show low values of less than 6 μΩ cm compared with those of current thin‐film‐transistor liquid‐crystal displays gate electrode materials (more than about 15 μΩ cm), without the salient formation of hillocks or whiskers on the surfaces.

Indium tin oxide films with low resistivity and low internal stress

Indium tin oxide (ITO) films prepared by dc magnetron sputtering were annealed in air, vacuum, and oxygen gas atmospheres. The electrical properties and internal stresses of these annealed ITO films were systematically investigated. It was found that, among the above postannealing treatments, oxygen gas annealing significantly reduced both the resistivity and the internal stress in ITO films at fairly low temperatures of 100–150 °C. Resistivities and internal stresses as low as 7×10−4 Ω cm and 38 MPa, respectively, were obtained by annealing in oxygen gas atmosphere at 100 °C. It was also revealed that the (111) crystal orientation becomes dominant and that whole grains grow dramatically as a result of postoxygen annealing, even at 100 °C.

Electronic structure calculations for a rare earth–transition metal amorphous alloy system

In order to clarify the origin of the Kerr effect for a rare earth–transition metal (RE‐TM) amorphous alloy system, electronic structure calculations were performed for the first time in an amorphous system including f orbitals. Tb20Fe80 and Nd20Fe80 amorphous alloy compositions were chosen for the present work. The electronic structures were calculated by using the most localized linear muffin‐tin orbital method based on atomic sphere approximation and the recursion method. To evaluate the first excited f states of rare‐earth metals, it was assumed that the occupied f electrons were sufficiently localized in the inner core of a RE atom to be treated as core electrons. The calculated density of states for a Tb20Fe80 amorphous alloy shows good agreement with reported experimental results measured by x‐ray photoelectron spectroscopy (XPS) and inverse XPS. In particular, the unoccupied f‐state level and the hybridization property between the Tb d state and the Fe d state were well reproduced. The calculated ...

Triple‐layered NdCo amorphous‐alloy films for magneto‐optical media

Magneto‐optical recording materials with high remanent Kerr rotation at a short wavelength were successfully obtained in a trilayer form. NdCo amorphous films with an in‐plane magnetization were sandwiched between TbFeCo amorphous films with strong perpendicular anisotropy and high coercivity. The thickness of the top layer of the TbFeCo film facing an incident laser beam is less than the light‐penetration depth. Triple‐layered films [Tb18Fe49Co33 (5 nm thickness)/Nd18Co82(10 nm)/Tb18Fe49Co33(200 nm)] thus obtained show a remanent Kerr rotation angle θKr = 0.37°–0.46° at wavelength λ=400–850 nm, coercivity Hc = 2 kOe, and good square loop (Mr/Ms = 1). The figure of merit √RθK, where R is reflectivity, is 0.24–0.31 at λ=400–850 nm, which is higher than that of conventional TbFeCo amorphous films (√RθK = 0.12–0.27 at λ=400–850 nm).

Effects of Oxygen Gas Annealing on Electrical Properties and Internal Stress in Indium Tin Oxide Films

Indium tin oxide (ITO) films prepared by d.c. magnetron sputtering were annealed in air, vacuum, and oxygen gas atmosphere. The electrical properties and internal stresses of these annealed ITO films were systematically investigated. It was found that, among the above post-annealing treatments, oxygen gas annealing significantly reduced both the resistivity and the internal stress in ITO films at fairly low temperatures of 100–150°C. Resistivities and internal stresses as low as 7×10-4 Ωcm and 38 MPa, respectively, were obtained by annealing in oxygen gas atmosphere at 100°C. It was also revealed that the (111) crystal orientation becomes dominant and that whole grains grow dramatically as a result of post-oxygen-annealing, even at 100°C.

Atomic Structure Analysis of Amorphous Tb-Fe1-xCox Film Systems

The atomic structure of sputtered amorphous Tb-Fe1-xCox thin film systems was studied by X-ray scattering. The composition fraction x was varied systematically, and the basic atomic structures of Tb-Fe1-xCox films were similar as a whole. The interatomic distances in Tb-Fe1-xCox films annealed at 200°C, overall, tend to decrease when the Co content is increased. These distances seem to change discontinuously at a composition of around x=0.5. The coordination numbers of the corresponding atoms did not show much correlation with Co concentration except in the case of transition metal atoms around a transition metal atom. In this case, the coordination number increases after annealing, but this increment tends to decrease as the Co concentration increases in Tb-Fe1-xCox films.

Electronic structure calculations for Gd32Co68 and Gd18Co82 amorphous alloys

The spin‐polarized electronic structures of Gd18Co82 and Gd32Co68 amorphous alloys are calculated self‐consistently in order to study their magnetic properties. The calculated electronic‐state densities of the Gd and Co d states do not have well‐resolved peaks; this is a characteristic of amorphous alloys. The magnetic moments of Co and Gd are 1.51 and 7.16 μB in Gd18Co82, and 1.38 and 7.14 μB in Gd32Co68, respectively. These values show good agreement with experimental data. The exchange splitting of Co d states in Gd32Co68 is smaller than in Gd18Co82, while the density of states at the Fermi level in the former is higher than that in the latter.

Electronic structure calculations for Gd sub 32 Co sub 68 and Gd sub 18 Co sub 82 amorphous alloys

The spin‐polarized electronic structures of Gd18Co82 and Gd32Co68 amorphous alloys are calculated self‐consistently in order to study their magnetic properties. The calculated electronic‐state densities of the Gd and Co d states do not have well‐resolved peaks; this is a characteristic of amorphous alloys. The magnetic moments of Co and Gd are 1.51 and 7.16 μB in Gd18Co82, and 1.38 and 7.14 μB in Gd32Co68, respectively. These values show good agreement with experimental data. The exchange splitting of Co d states in Gd32Co68 is smaller than in Gd18Co82, while the density of states at the Fermi level in the former is higher than that in the latter.

Structural Study of Thin Amorphous SiO2 and Si3N4 Films by the Grazing Incidence X-Ray Scattering (GIXS) Method

A method has been presented for determining a local atomic structure in an amorphous thin film of sub-micron thickness grown on a substrate by the grazing incidence x-ray scattering (GIXS) method. The capability of this method was demonstrated by analyzing amorphous Si02 and S13N4 films 200 and 70 nm thick, respectively. A network structure in the amorphous Si02 film consists of Si04 tetrahedra connecting each other by oxygen atoms at their vertices. This resembles that in a bulk amorphous Si02. The local ordering unit structure in the amorphous S13N4 film was found to be a SiN4 tetrahedron. A significant feature in the present amorphous Si3N4 film is the presence of two types of Si-Si pairs in the near neighbor region while only one type is present in the aSi3N4 crystal. This indicates that a part of the network structure formed by the SiN4 tetrahedra is quite different from that in its crystalline state. According to the coordination number of 3.8 for Si-N pairs, some nitrogen vacancies are quite likely involved in the film. Such nitrogen vacancies, then, are responsible for the modified network structure in the present amorphous Si3N4 film.