Atomic-Layer-Deposited Al2O3 as Gate Dielectrics for Graphene-Based Devices

Abstract

We present a facile route to deposit a uniform Al2O3 layer on a highly oriented pyrolytic graphite (HOPG) surface using atomic layer deposition (ALD). Al2O3 layers deposited from TMA (trimethylaluminum)/ H2O chemistry showed selective deposition only on step edges. However, TMA/O3 chemistry resulted in the deposition of Al2O3 layers on basal planes of HOPG, which has a chemically inert surface. An O3-pretreatement followed by Al2O3 deposition using TMA/O3 chemistry produced conformal and uniform Al2O3 dielectric layers with a small RMS roughness of ~ 0.2 nm. This suggests that O3-pretreatement prior to ALD deposition makes the chemically inert HOPG surface reactive toward ALD precursors, which leads to the desired two-dimensional growth mode. High-resolution transmission electron microscopy (HR-TEM) and Raman spectroscopy revealed that this O3 process used for Al2O3 deposition does not introduce a significant defect concentration to the top graphene layer. The dielectric constant of the deposited Al2O3 film on top of the HOPG surface was found to be ~ 9 from C-V measurements.

Nucleation and Growth of the HfO2 Dielectric Layer for Graphene-Based Devices

“…In earlier studies, ALD dielectrics such as Al 2 O 3 and HfO 2 were attempted on graphite surfaces which have chemically identical surface properties to those of graphene. − Selective growth of ALD dielectrics along the step edge sites of highly ordered pyrolytic graphite (HOPG) was observed since the step edge sites are chemically more reactive than the basal planes. − In the following studies, dielectric deposition by ALD on graphene prepared from the exfoliation of HOPG shows similar results to previous reports about ALD on HOPG since there was no chemically available adsorption site on graphene surfaces. − In other research, interestingly, on graphene synthesized by CVD, there was no selectivity in the growth of ALD dielectrics rather island growth over all the surface. − Different growth behaviors of ALD dielectrics on graphene surfaces are probably affected by nonideal surface properties of graphene originating from different synthesis methods and preparation processes. Although exfoliated graphene from HOPG and CVD-grown graphene have been widely used to prepare graphene, however, there has been no systematic and comprehensive study on surface reactions between ALD precursors and graphene synthesized by various ways.…”

Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems

“…7 There is some anecdotal evidence that the presence of residue has a beneficial effect on the nucleation of ALD dielectrics, such as Al 2 O 3 . 1035 However, this approach to prepare the graphene surface for ALD is not ideal, since the residues have uncontrolled chemical nature and are not uniform. Ref.…”

Dioxygen molecule adsorption and oxygen atom diffusion on clean and defective aluminum(111) surface using first principles calculations

“…Aluminum oxides have been subject to wide number of studies focused on growth mechanisms, thermal and diffusion barrier coating properties, insulating interfaces, surface reactivity as catalysis among others [1][2][3] because they are of major interest for highly applicative fields such as corrosion of aluminum-based alloys, surface preparation through thermally grown oxides, high-k oxides integration in microelectronics [4,5]. Knowing the high potential breakthroughs and reduced domestic and technological costs that could arise from the mastering and tailoring of aluminum oxide growth, this topic is still of concern.…”