| AVS 60th International Symposium and Exhibition | |
| Graphene and Other 2D Materials Focus Topic | Thursday Sessions |
| Session GR-ThP |
| Session: | Graphene and Other 2D Materials Poster Session |
| Presenter: | A.M. Pascon, University of Campinas, Brazil |
| Authors: | A.M. Pascon, University of Campinas, Brazil J.A. Diniz, University of Campinas, Brazil L.R.C. Fonseca, University of Campinas, Brazil J.F. de Souza, University of Campinas, Brazil |
| Correspondent: | Click to Email |
For devices based on graphene, non-refractory metallic electrodes of Ti/Au or Ti/Pd are frequently used. However, to reduce the contact resistance between metal electrodes and graphene, an annealing step in vacuum at a temperature of 700º C is generally required, which is incompatible with non-refractory metals [1]. On the other hand, refractory metal electrodes, such as tantalum nitride (TaN), can tolerate the annealing step but are less studied. Furthermore, the many techniques established to obtain graphene and to build high quality devices based on graphene are severely limited for large scale integration (LSI). Here we attempt a new approach to reach LSI. In our approach, graphene was obtained in large quantity from dielectrophoretic (DEP) assembly [2] of a few layers of insulating graphene oxide followed by thermal reduction at 450ºC. Next, for the metal contacts with graphene we used tantalum nitride (TaN) electrodes deposited by DC reactive sputtering in N2/Ar environment. FET devices were obtained with the graphene sheets deposited between TaN electrodes, which are employed as source and drain, and laying on top of a TaOx high-k gate dielectric deposited on an n+ silicon substrate used as the back electrode. To improve the contacts between graphene and TaN, ac signals were applied between electrodes, followed by annealing at 700° C in high vacuum to prevent electrode oxidation.
Scanning electronic microscopy and current-voltage (I-V) measurements were carried out to obtain the physical and electrical characteristics of our devices, respectively. The resistance values measured before and after annealing differ by five orders of magnitude, in agreement with [2], resulting in good contact characteristics.
In parallel, ab initio calculations were performed to investigate the nature of graphene/TaN interface employing two models for the interface. While this simulation effort is still ongoing, we have found that for the Ta/N-rich TaN surface and for the Ta-rich TaN surface the absence of the Dirac cone in the BL for each case is not due the BL roughness caused by the strong interaction with the TaN surface, especially for the Ta/N-rich surface, but due to metal surface states induced in the BL. Because in graphene the inter-layer separation is large, the electronic properties of the second graphene sheet are graphene-like, displaying a clear linear dispersion near the Dirac point.
[1] Souza, J. F., Development of Materials and Methods of Fabrication of Chemical/Biochemical Sensors based on Silicion and Carbon Nanostructures (ISFET, CNTFET and GraFET), PhD, University of Campinas, 2012;
[2] Burg B R et al, Appl. Phys, Lett. 94 053110 (2009);