Graphene-based field effect transistor with ion-gel film gate

Abstract

Graphene is a kind of two-dimensional material with high light transmittance, high mechanical properties and high carrier mobility. The energy band of graphene can be turned by doping and electric field. Researches on the application of graphene to electronic devices focused on field effect transistors. For improving the performance, one generally improves the fabrication process and device structure, but many researchers chose to change the material or structure of dielectric layer. Ion-gel is a kind of mixture of organic polymer mesh structure with good thermal stability and high dielectric value, prepared by macromolecule organic polymer and ionic salt electrolyte material. With the effect of electric field, cations and anions in ion-gel diffuse to form a double charge layer distribution with a charge layer on the surface of material. This capacitance characteristic is similar to that of traditional capacitor. In this paper, ion-gel (PVDF-[EMIM]TF2N) film is used as a dielectric layer material to prepare the bottom-gate graphene-based field effect transistor (GFET), which is compared with the GFET with SiO₂ bottom-gate, according to electrical characteristic curves. The effect of the ion-gel film on the transconductance, switching ratio and Dirac voltage of the GFET are analyzed. The effect of the vacuum environment and temperature on the GFET performance with ion-gel film gate are also investigated. The results show that in the room-temperature environment, the switching ratio and transconductance of the ion-gel film gate GFET device increase to 6.95 and 3.68 × 10^–2 mS, respectively, compared with those of the SiO₂ gate GFET, while the Dirac voltage decreases to 1.3 V. The increase in transconductance and switching ratio of ion-gel film gate GFETs are mainly due to the high capacitance of ion-gel film compared with those of conventional SiO₂ gate dielectrics. There will be more carriers inside the graphene while in the carrier accumulation region of GFET transfer characteristic curve, which makes graphene more conductive. The Dirac voltage of ion-gel film gate GFET can be reduced to 0.4 V in the vacuum environment; as the temperature increases, the transconductance of GFET can increase up to 6.11×10^–2 mS. The results indicate that the ion-gel film-based graphene field effect transistor shows good electrical properties in serving as high dielectric constant organic dielectric materials.