Masaaki Takata

Proposal of New Nonvolatile Memory with Magnetic Nano-Dots

In this study, a new nonvolatile memory with magnetic nano-dots (MNDs) was proposed. A relatively large anisotropic change of gate current–voltage characteristics by the magnetization in magnetic non-volatile memory with Co nano floating gate and Ni-Fe control gate was obtained. A Co magnetic nano-dot film with very high dot density of 2×1013 cm-2 was successfully formed by sputtering with optimized target composition. A small anisotropic change of gate current–voltage characteristics by the magnetization in MND memory with Co MNDs and Ni-Fe control gate was observed.

Proposal of New Non-Volatile Memory with Magnetic Nano-Dots

We proposed a new non-volatile memory with magnetic nano-dots (MND) dispersed in an insulating film as charge retention layer. We evaluated fundamental characteristics of FePt magnetic nano-dot film which is employed in such new magnetic nano-dot memory. We successfully formed a highly ordered L1 0 phase face-centered tetragonal structured FePt nano-dot ( < 4.2nm) films on Si 3 N 4 (5nm)/SiO 2 (10nm)/silicon substrates and SiO 2 (10nm)/ silicon substrate by using SAND method. The uniformity of FePt particle size is dramatically improved by introducing a Si 3 N 4 buffer layer on SiO 2 /Si substrate. In addition, it is found that FePt nano-dot film formed on Si3N4(5nm)/Si02(10nm)/Si substrate has a large coerce-ivity of ∼22 kOe at room temperature.

Homogeneity improvement of TiO2-SiO2 glass synthesized by the soot method and its evaluation using the ultrasonic measurement system

TiO2-SiO2 glass is one of the leading candidates for optical elements of extreme ultraviolet lithography. TiO2-SiO2 glass synthesized by the soot method has shown striae related to inhomogeneity of TiO2 concentration formed in the planes perpendicular to soot growth direction in the synthesis process. It can induce CTE variation and localized surface roughness. Striae were characterized in three modes by polarization microscope. Such striae were improved with an improved gas condition and developing a modified material gas supply system. Specimen prepared from the improved TiO2-SiO2 glass was evaluated by a line-focus-beam ultrasonic material characterization system, using a surface-acoustic-wave mode. Improved glass had 43% striae level compared to conventional glass by birefringence measurement, 31% compared to conventional glass by the ultrasonic measurement. It was found that improved glass had good homogeneity to both directions perpendicular and parallel to striae plane.