Electric-field-induced band gap of bilayer graphene in ionic liquid

Ionic liquid-gated graphene field-effect-transistors (G-FETs) were fabricated to generate a band gap in bilayer graphene. The transfer characteristics of the G-FETs revealed that the transconductance when using the ionic-liquid gate was significantly higher than that when using the back gate, because an electrical double layer formed in the ionic liquid with 200-fold the capacitance of a 300-nm-thick SiO2 layer. The results indicate that the ionic-liquid-gate structure enables application of an effective electric field. Moreover, an increase in the resistance of the bilayer graphene was clearly observed as the magnitude of the electric-field intensity was increased, owing to the creation of the band gap. From measurements of electrical characteristics as a function of temperature, a band gap of 235 meV was created in bilayer graphene at an ionic-liquid-gate voltage of −3.0 V.