Mutsunori Uenuma

Temperature-independent silicon waveguide optical filter.

We have proposed a new design for temperature-independent silicon optical filters utilizing a combination of wide and narrow waveguides. The waveguide structure was optimized to minimize the spectral shift of the filter owing to the environmental temperature change. Based on this new waveguide design, we fabricated Mach-Zehnder interferometer optical filters on silicon-on-insulator substrates. The measured spectrum showed substantially small temperature dependence being in good agreement with the theoretical estimation.

Guided filament formation in NiO-resistive random access memory by embedding gold nanoparticles

Controllable positioning of conductive filament in resistive memory is demonstrated using gold nanoparticles (GNPs). A GNP of 15u2009nm diameter is encapsulated by the porter protein and delivered to the designated positions. The restricted nanoscale filament formation by the GNP was observed by conductive atomic force microscopy, and writing and erasing were achieved in a defined area on the nanometer scale. The GNPs act as defect creators and assist the formation of nanoscale filaments with a low voltage.

Resistive random access memory utilizing ferritin protein with Pt nanoparticles

This study reports controlled single conductive paths found in resistive random access memory (ReRAM) formed by embedding Pt nanoparticles (Pt NPs) in NiO film. Homogeneous Pt NPs produced and placed by ferritin protein produce electric field convergence which leads to controlled conductive path formation. The ReRAM with Pt NPs shows stable switching behavior. A Pt NP density decrease results in an increase of OFF state resistance and decrease of forming voltage, whereas ON resistance was independent of the Pt NP density, which indicates that a single metal NP in a memory cell will achieve low power and stable operation.

Site-directed delivery of ferritin-encapsulated gold nanoparticles

Newly designed porter proteins, which catch gold nanoparticles and deliver the nanoparticles selectively to a silicon dioxide (SiO(2)) surface under the specific conditions were reported. Recombinant apoferritin subunits, each of which has gold-binding peptide and titanium-binding peptide at the C- and N-terminus, respectively, can efficiently encapsulate a gold nanoparticle. The bio-conjugate, a nanogold and surrounding mutant protein subunits, had a property which can deliver itself to the SiO(2) surface through the interaction. In theory, our genetically manipulated apoferritin subunits can encapsulate gold nanoparticles of various sizes, which is a promising property for applications involving surface plasmon resonance.

Memristive nanoparticles formed using a biotemplate

We demonstrated a novel biological process based on the use of a supramolecular protein as a reaction cage, in which a memristive element is formed. We showed that ferritin can be used to generate memristive nanoparticles by biomineralization. Magnetite (Fe3O4) nanoparticles with a size of 6 nm were prepared using a biotemplate. After a fine monolayer of NPs was formed on the electrode, the protein shells were removed in order to improve the electrical contact between NP and electrode. The synthesized nanoparticles exhibit clear bipolar resistive switching behaviors in metal/oxide/metal structure. From c-AFM measurements, even a single NP exhibits the memory behavior, leading to their promising potential application in nanoscale resistive memory.

Three-Dimensional Nanodot-Type Floating Gate Memory Fabricated by Bio-Layer-by-Layer Method

The properties of a nanodot-type floating gate memory with a multilayered nanodot array were investigated. High-density and uniform cobalt bio-nanodot (Co-BND) arrays were stacked on a SiO2 tunnel oxide layer by a bio-layer-by-layer method (Bio-LBL). Memory properties, such as hysteresis width, charge retention, charging speed, and reliability, were improved by increasing the number of Co-BND arrays in a floating gate memory. This research confirmed that the proposed memory is promising for application in next-generation memory devices.

Controlled charged amino acids of Ti-binding peptide for surfactant-free selective adsorption.

The adsorption mechanism of titanium-binding peptide (TBP) on metal oxide substrates was investigated by evaluating the adsorption behavior of ferritins with various alanine-substituted TBPs. Results revealed that (a) a positively charged amino acid, lysine (K) or arginine (R), in TBP can anchor ferritin to negative zeta-potential substrates, (b) the adsorption force of K is stronger than R, and (c) local electrostatic interactions and flexibility of TBP directly affect adsorption. Based on these findings, selective ferritin adsorption on SiO2 with TiOX patterned surfaces in a surfactant-free condition was demonstrated. Alanine-substituted TBP with one positively charged amino acid (K) and one negatively charged amino acid (D), achieved ferritin-selective adsorption without a surfactant. The importance of controlled electrostatic forces between TBP and a substrate for selective adsorption without a surfactant was clearly demonstrated.

Floating gate memory with charge storage dots array formed by Dps protein modified with site-specific binding peptides

We report a nanodot (ND) floating gate memory (NFGM) with a high-density ND array formed by a biological nano process. We utilized two kinds of cage-shaped proteins displaying SiO2 binding peptide (minTBP-1) on their outer surfaces: ferritin and Dps, which accommodate cobalt oxide NDs in their cavities. The diameters of the cobalt NDs were regulated by the cavity sizes of the proteins. Because minTBP-1 is strongly adsorbed on the SiO2 surface, high-density cobalt oxide ND arrays were obtained by a simple spin coating process. The densities of cobalt oxide ND arrays based on ferritin and Dps were 6.8xa0×xa010(11) dots cm(-2) and 1.2xa0×xa010(12) dots cm(-2), respectively. After selective protein elimination and embedding in a metal-oxide-semiconductor (MOS) capacitor, the charge capacities of both ND arrays were evaluated by measuring their C-V characteristics. The MOS capacitor embedded with the Dps ND array showed a wider memory window than the device embedded with the ferritin ND array. Finally, we fabricated an NFGM with a high-density ND array based on Dps, and confirmed its competent writing/erasing characteristics and long retention time.

Joule heating effect in nonpolar and bipolar resistive random access memory

The position of the conductive filament (CF) and the heating behaviour during a switching process in nonpolar and bipolar resistive random access memories (ReRAMs) were evaluated using thermal analysis. The position of the CF was clearly observed from Joule heating at the surface of the electrode on the CF. The position of the CF did not change during the switching cycle, except in the case of an unstable CF. In the nonpolar ReRAM, spike-shaped temperature increments were observed during both the forming and the set processes because of the overshoot current. However, the behaviour of the temperature increment in the bipolar ReRAM was virtually consistent with the profile of the electrical power.

Analysis of thermoelectric properties of amorphous InGaZnO thin film by controlling carrier concentration

We have investigated the thermoelectric properties of amorphous InGaZnO (a-IGZO) thin films optimized by adjusting the carrier concentration. The a-IGZO films were produced under various oxygen flow ratios. The Seebeck coefficient and the electrical conductivity were measured from 100 to 400 K. We found that the power factor (PF) at 300 K had a maximum value of 82 × 10−6 W/mK2, where the carrier density was 7.7 × 1019 cm−3. Moreover, the obtained data was analyzed by fitting the percolation model. Theoretical analysis revealed that the Fermi level was located approximately above the potential barrier when the PF became maximal. The thermoelectric properties were controlled by the relationship between the position of Fermi level and the height of potential energy barriers.