Studies on poly(methyl methacrylate) dielectric layer for field effect transistor: Influence of polymer tacticity

Electrical properties of three kinds of poly(methyl methacrylate) (PMMA) with different tacticity, i.e. isotactic(i), syndiotactic(s), and atatic(a), were investigated for the application in field effect transistor. Metal-insulator-silicon structures were fabricated via spin coating PMMA on heavily doped p-type silicon (p⁺-Si) followed by evaporating gold electrode. The electrical characteristics were remarkably improved by heat-treatment at temperatures 40 K above glass transition temperatures of PMMAs. Among the three PMMA isomers, i-PMMA was observed to possess the highest dielectric strength (1.1 MV/cm) with the lowest leakage current density, but also the lowest dielectric constant (k = 2.5). Top-contact thin film transistors fabricated with the configuration of NiO_x/pentacene/i-PMMA/p⁺-Si, where the NiO_x being used as a source/drain electrode, displayed relatively a decent field effect mobility of 0.042 cm²/V-s which is not that low with such a low dielectric capacitor as thick i-PMMA film.