New Research


Control of material structures, electrical properties and functions for next-generation nanoelectron

- Detection of structural fluctuation on the nano- to micro- meter scale in the direct silicon bondi

Prof. Akira Sakai, Associate Prof. Yoshiaki Nakamura, Assistant Prof. Jun Kikkawa

In crystalline materials, atoms are regularly arranged, and each line of atoms forms three-dimensional lattices. Lattice strains and defects of the regular atomic arrangements give critical impacts on electrical properties of the materials. By controlling these strains and defects, it is possible to bring out various novel and interesting properties from the materials. Peculiar atomic arrangements are formed especially at the interfaces between different materials and between the same materials with different crystallographic orientations due to lattice mismatches. These local structures influence the crystallinity around the interfaces on the nano- to micro-meter scale. Clarifying structural properties in local areas is important to correlate them with electrical properties. For instance, it is a key issue for Direct Silicon Bonding (DSB) substrates which are hybrid substrates of directly-bonded Si substrates with different crystallographic orientations and used as potential substrates for high-performance complementary MOS transistors.
Recently, we have successfully detected tiny tilting of lattice planes in the DSB substrates, using a leading-edge X-ray micro-diffraction system at SPring-8 (Super Photon ring, 8 GeV). This method enables imaging the fluctuation of lattice plane tilting on a submicron scale, by scanning a fine X-ray micro-beam (0.7 x 1.9 μm2 in size) across samples. The figure (top) shows the fluctuation of lattice plane tilting in the DSB substrate. Furthermore, observing the arrangement of silicon atoms by transmission electron microscopy as shown in the figure (bottom), we have found the correlation between the submicron-scale structural fluctuation and the peculiar atomic arrangements at the interface.
Our group is interested in the synthesis of advanced semiconductor and oxide materials, characterization of their physical properties and controlling their functions for next-generation nanoelectronics devices with an emphasis on deep understanding of structural properties.

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