  We demonstrate the atomic layer deposition of high-quality HfO2 film on
graphene and report the magnitude of remote oxide phonon (ROP) scattering in
dual-oxide graphene transistors. Top gates with 30 nm HfO2 oxide layer exhibit
excellent doping capacity of greater than 1.5x10^(13)/cm^(2). The carrier
mobility in HfO2-covered graphene reaches 20,000 cm^(2)/Vs at low temperature,
which is the highest among oxide-covered graphene and compares to that of
pristine samples. The temperature-dependent resistivity exhibits the effect of
ROP scattering from both the SiO2 substrate and the HfO2 over-layer. At room
temperature, surface phonon modes of the HfO2 film centered at 54 meV dominate
and limit the carrier mobility to ~20,000 cm^(2)/Vs. Our results highlight the
important choice of oxide in graphene devices.
