Hiroshi Suga

Performance Enhancement of Thin-Film Transistors by Using High-Purity Semiconducting Single-Wall Carbon Nanotubes

Thin-film transistors (TFTs) using a random network of semiconductor-enriched single-wall carbon nanotubes (SWCNTs) were fabricated on a SiO2/Si substrate. Semiconductor-enriched SWCNTs were extracted from a pristine sample by centrifugation using agarose gel. Prior to depositing the SWCNTs, the substrate surface was modified by self-assembly of a monolayer of aminosilanes to produce an ideal two-dimensional network structure. As a result, all the TFTs fabricated on the substrate had on/off current ratios higher than 104 without electrical breakdown, while TFTs fabricated using pristine SWCNTs had a broad distribution of on/off ratios from 101 to 104. This improvement in transfer characteristics demonstrates a major advantage of using semiconductor-enriched SWCNTs.

Non-volatile Resistance Switching using Single-Wall Carbon Nanotube Encapsulating Fullerene Molecules

A resistance switching effect was found for a nanogap junction that has electrodes composed of single-wall carbon nanotubes (SWCNTs) that encapsulate fullerenes. A clear negative differential resistance effect and repeated on–off cycles were observed in the current–voltage characteristics of the nanogap junctions. The results suggest that the resistance switch effect is due to gap size changes that result in the migration of fullerene molecules. This implied that the electrode areas of a resistance switch could be miniaturized to true nanoscale size.

Influence of electrode size on resistance switching effect in nanogap junctions

The size dependence of the resistance switching effect in nanogap junctions was investigated to determine the nature of the local structural changes responsible for the effect. The maximum current, during resistance switching, decreased with the total emission area across the nanogap to an average of 146u2002μA at a linewidth of 45 nm. This implies that the resistance switching effect stems from changes in the gap width at multiple local sites on the metal surface.

Non-Volatile Resistance Switching Using Silicon Nanogap Junction

We have investigated the resistance switching effect of a silicon nanogap structure when pulse bias voltages are applied. Silicon nanogap junctions were prepared by applying large-bias voltages across a Si wire and their electrical properties were measured in a vacuum chamber. The measured current–voltage characteristics exhibited a clear negative differential resistance effect and repeated on-off cycles with a large on-off ratio of over 103. The results suggest that resistance switching effects can be generated in a nanogap junction that is composed of a covalently bonded material such as silicon.

4kb nonvolatile nanogap memory (NGpM) with 1 ns programming capability

A 4k bits nonvolatile high-speed nanogap memory device was fabricated with a newly developed vertical nanogap structure and its memory characteristics were evaluated. The newly developed vertical nanogap structures realized controllable electrode gap and higher yield compared to the initial phase lateral type nanogap structure. The structures were integrated on a CMOS chip. The specially embedded measurement circuit revealed programming speed from a low resistance state to a high resistance state (from on to off state) to be 1 ns.

Single-molecule behaviors of conjugated 2,2'-bipyridine derivative inserted in matrix layer using dendrimer-based template

Single-molecule immobilization of phenylene-ethynylene derivatives having a 2,2-bipyridine unit was performed by inserting them into an alkanethiol monolayer on Au using a dendrimer-based template. Scanning tunneling microscope (STM)-based statistical analysis of the resulting surface was performed before and after protonation of the bipyridine moiety in terms of the apparent height of the conjugated bipyridine derivative. As a result, it was found that the average height of the isolated bipyridines became smaller after protonation, and the height distributions were narrower than those of the mixture of single and bundled bipyridines, overall.

Nonvolatile memories with controllable nanogap structures

As one of the candidates of a next-generation memory, we study the memory element using resistance change of the metal nanogap. Since this element has many advantages, for example, quite simple structure, wide material selectivity, highspeed operation, and high temperature tolerance. In this report, miniaturization and mass production, vertical type nanogap elements were developed. As a result of measurements, the characteristic of vertical type is better than the element of lateral type. Moreover, we discuss switching speed of the elements. We confirmed that the switching speed is at least below 50 ns. This is certain progress towards practical use.

Memory Effect in Simple Cu Nanogap Junction

We have investigated the resistance switching effect in Cu nanogap junction. Nanogap structures were created by means of electromigration and their electrical properties were measured in a high vacuum chamber. The measured current-voltage characteristics exhibited a clear negative resistance and memory effect with a large on-off ratio of over 10 5 . The estimation from I-V curves indicates that the resistance switching was caused by the gap size change, which implies that the nanogap switching (NGS) effect also occurs in Cu electrodes, a popular wiring material in an integrated circuit.