Tokyo Institute of Technology · Engineering
Professor Kuniyuki Kakushima's research lab specializes in advanced semiconductor materials and nanostructured devices, with a focus on ferroelectric and high-k dielectric materials for next-generation electronic applications. The lab investigates the crystallographic and electronic properties of thin films—such as Sc-doped AlN and lanthanum silicates—using advanced characterization techniques like x-ray photoelectron spectroscopy and hard x-ray photoemission spectroscopy to probe band bending and interfacial chemistry. Their work spans ferroelectric memory devices, high-performance power transistors (e.g., 3D-scaled IGBTs), and interface engineering in metal-oxide-semiconductor systems, aiming to enable energy-efficient and high-density electronic technologies. The lab emphasizes the correlation between material microstructure, electronic band structure, and device performance at the nanoscale.
Figures are computed from collected data and may differ slightly.
Crystallographic characterization and the ferroelectric properties of 50 nm-thick sputter-deposited Al0.78Sc0.22N films deposited at room temperature (RT) and 400 °C are investigated. c-axis oriented growths were confirmed by x-ray diffraction patterns with rocking curve measurements for both samples. Al0.78Sc0.22N films were found to grow in the c-axis direction and showed poling-free ferroelectric properties, which are advantageous for practical memory and piezoelectric applications. Although
Band bendings of Si substrates have been observed using hard x-ray photoemission spectroscopy. With a capability of collecting photoelectrons generated as deep as 40 nm, the binding energy shift in a core level caused by the potential profile at the surface of the substrate results in a spectrum broadening. The broadening is found to be significant when heavily doped substrates are used owing to its steep potential profile. The surface potential of the substrate can be obtained by deconvolution
Three dimensionally (3D) scaled IGBTs that have a scaling factor of 3 (k=3) with respect to current commercial products (k=1) were fabricated for the first time. The scaling was applied to the lateral and vertical dimensions as well as the gate voltage. A significant decrease in ON resistance, - Vce(sat) reduction from 1.70 to 1.26 V - was experimentally confirmed for the 3D scaled IGBTs.
Oxygen bonding in La-silicate film with compositional gradient has been characterized by x-ray photoelectron spectroscopy. Based on an analytical model of bridging and nonbridging oxygen, the O 1s spectra arising from La-silicate layer have been deconvoluted with compositionally dependent parameters. For a composition ratio of 1:1 for SiO2 and LaO1.5 on the surface of the La-silicate layer, negative binding energy shifts of 0.35 and 0.10 eV for bridging and nonbridging oxygen, respectively, have
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