Scaling of HfO2 dielectric on CVD graphene

The deposition of ultra-thin metal oxides on graphene is challenging due to the inert nature of the sp2 bonded graphene lattice. The feasibility of e-beam deposition of hafnium and hafnium oxide layers as seeds for further growth by atomic layer deposition on graphene CVD graphene is presented here. It is shown that metallic hafnium deposited in an ultra high vacuum environment readily reacts with graphene, forming a metal-carbide, rendering it unsuitable as a seed layer for the deposition of gate oxide materials. The deposition of HfO2 by reactive e-beam under an O2 partial pressure on the other hand eliminates the reaction with the underlying graphene. The uniformity of the e-beam HfO2 seed layers is found to control the uniformity of the subsequent films deposited by atomic layer deposition. Contrary to previous studies on graphite and exfoliated graphene substrates it is found that the uniformity and thickness scalability of atomic layer deposited thin films is limited on CVD graphene, most likely due to transfer induced residues on the graphene surface.