Low Temperature Atomic Layer Deposition of Thin HfO$_{2}$ Film as Top Gate Oxide in Graphene Field Effect Transistors

We explore the possibility of using HfO$_{2}$ as top gate oxide in graphene field effect transistors (FETs). Graphene flakes are obtained by mechanically exfoliating HOPG graphite on SiO$_ {2}$ (300nm)/doped Si substrates. We fabricate graphene FETs using e-beam lithography and metal electrodes deposition. A second e-beam writing is used to define the area of the HfO$_{2} $ over-layer. It is followed by an atomic layer deposition (ALD) of 30 nm HfO$_{2}$ film at low temperature without the use of an adhesion layer. This low-temperature recipe produces smooth HfO$_{2}$ films with RMS roughness of 2-3{\AA} over a 1x1 $\mu$m area. These films exhibit a dielectric constant of $\sim$12-15 and a breakdown field of $\sim$0.8 MV/cm. Carrier mobility in HfO$_{2}$-covered FETs is comparable to that of uncovered graphene. We report and discuss the influence of the HfO$_{2}$ over-layer on the transport properties of graphene.