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/GaN stacks for high-quality GaN-based metal-oxide-semiconductor devices with improved gate dielectric reliabilityYamada, Takahiro*; Watanabe, Kenta*; Nozaki, Mikito*; Yamada, Hisashi*; Takahashi, Tokio*; Shimizu, Mitsuaki*; Yoshigoe, Akitaka; Hosoi, Takuji*; Shimura, Takayoshi*; Watanabe, Heiji*
Applied Physics Express, 11(1), p.015701_1 - 015701_4, 2018/01
Times Cited Count：39 Percentile：84.89(Physics, Applied)A simple and feasible method for fabricating high-quality and highly reliable GaN-based metal-oxide-semiconductor (MOS) devices was developed on the basis of systematic physical and electrical characterizations. Chemical vapor deposition of SiO films directly onto GaN substrates forming Ga-oxide interlayers was used to fabricate SiO/GaO
/GaN stacked structures. Although well-behaved hysteresis-free GaN-MOS capacitors with extremely low interface state density below 10
cm
eV
were obtained by post-deposition annealing, Ga diffusion into overlying SiO layers severely degraded the insulating property and dielectric breakdown characteristics of the MOS devices. However, this problem was found to be solved by employing rapid thermal processing, leading to superior performance of the GaN-MOS devices in terms of interface quality, insulating property and gate dielectric reliability.
Takahashi, Shuichi*; Okonogi, Hiroyuki*; Hagiwara, Tokio*; Maekawa, Yasunari
Journal of Membrane Science, 324(1-2), p.173 - 180, 2008/10
Times Cited Count：37 Percentile：72.79(Engineering, Chemical)Polymer electrolyte membranes (PEM) consisting of alkylsulfonic acid were successfully synthesized by radiation-induced graft polymerization of methyl acrylate (MA) into a poly(ethylene-co-tetrafluoroethylene) (ETFE) film, followed by sulfonation at an 
-carbonyl carbon of the MA units in the grafting chain using an equimolar complex of chlorosulfonic acid and dioxane (ClSO
H-Complex). The ion exchange capacity and ion conductivity of the MA-grafted PEM were controlled in the respective ranges of 0.54-1.47 mmol/g and 0.014-0.14 S/cm by changing the grafting degree. It has been confirmed by titrimetric and gravimetric analyses of sulfonic and carboxylic acids in the film that the sulfonation reaction is accompanied with decarboxylation of the MA units equimolar to the substituted sulfonic acids (substitution of carboxylic acid with sulfonic acid), that the sulfonation degree was about 30%.
Takahashi, Shuichi; Maekawa, Yasunari; Hagiwara, Tokio*; Okonogi, Hiroyuki*
no journal, ,
Aliphatic vinyl monomers, like acrylatic acid derivatives or vinyl ketones, were grafted by 
-ray irradiation on a poly(ethylene-co-tetrafluoroethylene) (ETFE) film. Then, novel electrolyte membranes, which possess alkyl sulfonic acids on grafted chain, were synthesized by polymeric transformation of functional groups. The electrolyte membranes prepared by the above approach showed higher heat-stability in the wet condition compared to the electrolyte membranes with sulfonated styrene grafted membranes.
Takahashi, Shuichi; Maekawa, Yasunari; Hagiwara, Tokio*; Okonogi, Hiroyuki*
no journal, ,
Methyl acrylate monomer was grafted by -ray irradiation on a poly(ethylene-co-tetrafluoroethylene)(ETFE) film. Then, the novel polymer electrolyte membranes (PEM), which possess alkyl sulfonic acids on grafted chain, were synthesized by polymeric transformation of functional groups. The PEM prepared by the above approach were analyzed structurally and characterized well.
Maekawa, Yasunari; Takahashi, Shuichi; Hanh, T. T.*; Okonogi, Hiroyuki*; Hagiwara, Tokio*
no journal, ,
Polymer electrolyte membranes (PEMs) consisting of alkylsulfonic acid in grafting chains can be prepared by radiation-induced graft polymerization of methyl acrylate (MA) onto a poly(ethylene-co-tetrafluoroethylene) (ETFE) film, followed by the sulfonation of MA units in the grafting chains using an equimolar complex of chlorosulfonic acid and dioxane. The sulfonation reaction accompanied equimolar decarboxylation of the MA unit (substitution of carboxylic acid with sulfonic acid) to give the PEMs with conductivity of 0.01-0.11 S/cm. Furthermore, the replacement of the MA unit with methyl metacrylate (MMA) as a comonomer in grafting chains enhances the stability of the PEM at higher temperatures.
