Kotaro Satori

Solution-processed organic thin-film transistors with vertical nanophase separation

We have found that spin coating a solution of 6,13-bis(triisopropyl-silylethynyl)-pentacene (TIPS-pentacene) blended with poly(α-methylstyrene) (PαMS) induces vertical nanophase separation, which results in a trilayer film: a TIPS-pentacene layer, a mixed layer of TIPS-pentacene/PαMS, and a TIPS-pentacene layer. Organic thin-film transistors (TFTs) made from this TIPS-pentacene/PαMS solution have remarkably improved uniformity and thermal stability without degradation of electrical characteristics compared to organic TFTs with a conventional TIPS-pentacene sole channel layer.

Organic Thin-Film Transistors with Phase Separation of Polymer-Blend Small-Molecule Semiconductors: Dependence on Molecular Weight and Types of Polymer

We have investigated effect of polymer on solution-processed organic thin-film transistors (TFTs) with polymer-blend semiconductors. Organic TFTs made from a solution of 6,13-bis(triisopropylsilylethynyl)-pentacene with a poly(α-methylstyrene) (PaMS) molecular weight of 20 k or above, exhibited mobility around 0.1 cm2/(Vs). On the other hand, the organic TFTs with a PaMS molecular weight of 2 k or with a poly(isobutyl methacrylate), exhibited much lower mobility. This can be explained in terms of the structure and crystallinity of the films. The results of film structure can be explained by applying the Flory–Huggins theory.

Nitrogen depth profiling in ultrathin silicon oxynitride films with high-resolution rutherford backscattering spectroscopy

Nitrogen depth profiles in ultrathin silicon oxynitride films (2.5–8 nm) are measured by high-resolution Rutherford backscattering spectroscopy (HRBS). In order to reduce the large background due to the substrate silicon, HRBS spectra are measured under [111] channeling conditions. It is demonstrated that the HRBS/channeling technique provides the absolute concentration values and a depth resolution of sub-nm can be achieved. The nitrogen profiles are also measured by secondary ion mass spectroscopy (SIMS) and Auger electron spectroscopy (AES). The AES result roughly agrees with the HRBS result, while the SIMS result underestimates the nitrogen concentration.

Release of nitrogen from SiOxNy films during RBS measurement

We have found that nitrogen atoms are released very rapidly from ultrathin SiOxNy films (∼2.6 nm) during RBS measurement with 500 keV He+ ions. The release behavior strongly depends on the preparation technique of the SiOxNy films. There is no release from the film prepared by thermal nitridation of SiO2, while 80% of the nitrogen atoms are released from the film prepared by plasma nitridation at a fluence of 1×1016 cm−2. The release cross-section for plasma SiOxNy films is of the order of 10−16 cm2. This large cross-section cannot be explained by a simple recoil mechanism. The nitrogen release is also observed under irradiation with 5–10 keV electrons though the cross-section is of the order of 10−19 cm2. These findings suggest that the observed nitrogen release is an electronic excitation induced process.