Versatile sputtering technology for Al2O3 gate insulators on graphene
  We report a novel fabrication method of graphene Al2O3 gate insulators based on sputtering. Electrical performance of dual-gated mono- and bilayer exfoliated graphene devices is presented. Sputtered Al2O3 layers possess comparable quality to oxides obtained by atomic layer deposition (ALD) with respect to a high relative dielectric constant of about 8, as well as low-hysteresis performance and high breakdown voltage. We observe a moderate carrier mobility of about 1000 cm2/Vs in graphene and 350 cm2/Vs in its bilayer due to increased resonant scattering on atomic scale defects. Most likely this originated from the thin Al precursor layer evaporated prior to sputtering the Al2O3 gate oxide. 
M. Friedemann, M. Woszczyna, A. M\"uller, S. Wundrack, T. Dziomba, Th.   Weimann, Th. Seyller, F. Ahlers
cond-mat.mes-hall cond-mat.mtrl-sci