Yumiko Kaji

Air-assisted High-performance Field-effect Transistor with Thin Films of Picene

A field-effect transistor (FET) with thin films of picene has been fabricated on SiO2 gate dielectric. The FET showed p-channel enhancement-type FET characteristics with the field-effect mobility, mu, of 1.1 cm2 V-1 s-1 and the on-off ratio of >10(5). This excellent device performance was realized under atmospheric conditions. The mu increased with an increase in temperature, and the FET performance was improved by exposure to air or O2 for a long time. This result implies that this device is an air (O2)-assisted FET. The FET characteristics are discussed on the basis of structural topography and the energy diagram of picene thin films.

Metal-intercalated aromatic hydrocarbons: a new class of carbon-based superconductors

New carbon-based superconductors are synthesized by intercalating metal atoms into the solid-phase hydrocarbons picene and coronene. The highest reported superconducting transition temperature, T(c), of a hydrocarbon superconductor is 18 K for K(3)picene. The physics and chemistry of the hydrocarbon superconductors are extensively described for A(x)picene (A: alkali and alkali earth-metal atoms) for x = 0-5. The theoretical picture of their electronic structure is also reviewed. Future prospects for hydrocarbon superconductors are discussed from the viewpoint of combining electronics with condensed-matter physics: modification of the physical properties of hydrocarbon solids is explored by building them into a field-effect transistor. The features of other carbon-based superconductors are compared to clarify the nature of hydrocarbon superconductors.

Characteristics of [6]phenacene thin film field-effect transistor

Transistor characteristics are studied for field-effect transistors (FETs) with thin films of [6]phenacene, which has six benzene rings and W-shape structure. The molecular alignment preferable for FET transport is found to be formed in [6]phenacene thin films. The transistor shows clear p-channel FET characteristics with field-effect mobility μ as high as 3.7 cm2 V−1 s−1. The similar O2 sensing properties to picene FET are observed in [6]phenacene thin film FET. The bias stress properties are observed in [6]phenacene thin film FET. The pulse-voltage application suppresses the bias-stress effect and it enables a continuous O2 sensing in [6]phenacene FET.

Flexible picene thin film field-effect transistors with parylene gate dielectric and their physical properties

Flexible picene thin film field-effect transistors (FETs) have been fabricated with parylene gate dielectric on polyethylene terephthalate substrates. The picene thin film FETs show p-channel output/transfer characteristics and the field-effect mobility μ reaches ∼1 cm2 V−1 s−1 in vacuum. The FET shows a clear O2 gas sensing effect and negligible hysteresis in the transfer curves, indicating a possible application of the transistor as O2 selective gas sensor. Furthermore, it has been found that the parylene gate dielectric can eliminate a reduction in on-state drain current caused by continuous bias-voltage application which is observed if a SiO2 gate dielectric is used.

Characteristics of field-effect transistors using the one-dimensional extended hydrocarbon [7]phenacene

Field-effect transistors (FETs) with solid gate dielectrics are fabricated with thin films of the one-dimensional (1D) extended hydrocarbon [7]phenacene, which contains seven benzene rings. p-channel FET characteristics are observed for these FETs, with a mobility of 0.75 cm2 V−1 s−1 at 100 Torr of O2. The O2 gas-sensing effect is examined for the [7]phenacene FET and for the 1D hydrocarbon picene FET. These FETs’ trap density and contact resistance are investigated with the multiple shallow trap and release model and the transfer line method. Unlike picene FETs, [7]phenacene FETs have few charge traps and are therefore air-stable.

Low voltage operation in picene thin film field-effect transistor and its physical characteristics

Low voltage operation of picene thin film field-effect transistor (FET) has been realized with 40 nm thick SiO2 gate dielectrics coated by two polymers, Cytop™ and polystyrene. The picene FETs operated in low absolute gate voltage |VG| below 15 V for Cytop™ coated SiO2 and 30 V for polystyrene coated SiO2 gate dielectrics, and they showed a significant O2 gas sensing effect down to ∼10 ppm. Photoemission spectrum clarified that O2 molecules penetrate into the thin films at O2/picene mole ratio of 1: 1. X-ray diffraction pattern of picene thin films showed highly oriented growth on the polymer-coated SiO2.

Allelic characterization of the leaf-variegated mutation var2 identifies the conserved amino acid residues of FtsH that are important for ATP hydrolysis and proteolysis.

Arabidopsis var1 and var2 mutants exhibit leaf variegation. VAR1 and VAR2 encode similar FtsH metalloproteases (FtsH5 and FtsH2, respectively). We have previously found many variegated mutants to be allelic to var2. Each mutant was shown to express a different degree of variegation, and the formation of white sectors was enhanced in severely variegated alleles when these alleles were grown at low temperature. VAR1/FtsH5 and VAR2/FtsH2 levels were mutually affected even in the weak alleles, confirming our previous observation that the two proteins form a hetero complex. In this study, the sites of the mutations in these var2 alleles were determined. We isolated eight point mutations. Five alleles resulted in an amino acid substitution. Three of the five amino acid substitutions occurred in Walker A and B motifs of the ATP-binding site, and one occurred in the central pore motif. These mutations were considered to profoundly suppress the ATPase and protease activities. In contrast, one mutation was found in a region that contained no obvious signature motifs, but a neighboring sequence, Gly–Ala–Asp, was highly conserved among the members of the AAA protein family. Site-directed mutagenesis of the corresponding residue in E. coli FtsH indeed showed that this residue is necessary for proper ATP hydrolysis and proteolysis. Based on these results, we propose that the conserved Gly–Ala–Asp motif plays an important role in FtsH activity. Thus, characterization of the var2 alleles could help to identify the physiologically important domain of FtsH.