Sub-Nanometer Interfacial Oxides on Highly Oriented Pyrolytic Graphite and Carbon Nanotubes Enabled by Lateral Oxide Growth

• Published in: ACS applied materials & interfaces Vol. 14; no. 9; pp. 11873 - 11882
• Main Authors: Zhang, Zichen, Passlack, Matthias, Pitner, Gregory, Kuo, Cheng-Hsuan, Ueda, Scott T, Huang, James, Kashyap, Harshil, Wang, Victor, Spiegelman, Jacob, Lam, Kai-Tak, Liang, Yu-Chia, Liew, San Lin, Hsu, Chen-Feng, Kummel, Andrew C, Bandaru, Prabhakar
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 09.03.2022
• Subjects: Surfaces, Interfaces, and Applications; effective oxide thickness; atomic layer deposition; carbon nanotubes; field effect transistor; metal oxide semiconductor capacitors
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/acsami.1c21743

A new generation of compact and high-speed electronic devices, based on carbon, would be enabled through the development of robust gate oxides with sub-nanometer effective oxide thickness (EOT) on carbon nanotubes or graphene nanoribbons. However, to date, the lack of dangling bonds on sp2 oriented graphene sheets has limited the high precursor nucleation density enabling atomic layer deposition of sub-1 nm EOT gate oxides. It is shown here that by deploying a low-temperature AlO x (LT AlO x ) process, involving atomic layer deposition (ALD) of Al2O3 at 50 °C with a chemical vapor deposition (CVD) component, a high nucleation density layer can be formed, which templates the growth of a high-k dielectric, such as HfO2. Atomic force microscopy (AFM) imaging shows that at 50 °C, the Al2O3 spontaneously forms a pinhole-free, sub-2 nm layer on graphene. Density functional theory (DFT) based simulations indicate that the spreading out of AlO x clusters on the carbon surface enables conformal oxide deposition. Device applications of the LT AlO x deposition scheme were investigated through electrical measurements on metal oxide semiconductor capacitors (MOSCAPs) with Al2O3/HfO2 bilayer gate oxides using both standard Ti/Pt metal gates as well as TiN/Ti/Pd gettering gates. In this study, LT AlO x was used to nucleate HfO2 and it was shown that bilayer gate oxide stacks of 2.85 and 3.15 nm were able to achieve continuous coverage on carbon nanotubes (CNTs). The robustness of the bilayer was tested through deployment in a CNT-based field-effect transistor (FET) configuration with a gate leakage of less than 10–8 A/μm per CNT.