Top-Gate Graphene-on-UNCD Transistors with Enhanced Performance
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Top-Gate Graphene-on-UNCD Transistors with Enhanced Performance Jie Yu1, Guanxiong Liu1, Anirudha V. Sumant2 and Alexander A. Balandin1 1
Nano-Device Laboratory, Department of Electrical Engineering and Materials Science and Engineering Program, University of California, Riverside, California 92521 USA 2
Center for Nanoscale Materials, Argonne National Laboratory, IL, 60439 USA
ABSTRACT We fabricated a number of top-gate graphene field-effect transistors on the ultrananocrystalline diamond (UNCD) – Si composite substrates. Raman spectroscopy, scanning electron microscopy and atomic force microscopy were used to verify the quality of UNCD and graphene device channels. The thermal measurements were carried out with the “hot disk” and “laser flash” methods. It was found that graphene on UNCD devices have increased breakdown current density by ~50% compared to the reference devices fabricated on Si/SiO2. The relatively smooth surface of UNCD, as compared to other synthetic diamond films, allowed us to fabricate top gate graphene devices with the drift mobility of up to ~ 2587 cm2V-1s-1.
INTRODUCTION In order to improve the electrical properties and thermal management of graphene devices we examined a possibility of graphene device fabrication on synthetic diamond. It is expected that replacement of silicon oxide with synthetic diamond can improve heat conduction and reduce leakage current in the substrate. We studied graphene on several composite substrates including ultrananocrystalline (UNCD), microcrystalline diamond (MCD) thin films on silicon. The diamond thin films were grown by the microwave plasma chemical vapor deposition (MPCVD) at Argon National Laboratory and characterized using optical microscopy, Raman spectroscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The SEM and TEM inspection revealed that the average grain size of UNCD films is in the range 3 - 5 nm. The UNCD films were polished using CMP process and the average surface roughness for UNCD is on the order of 1 nm measured by AFM. The graphene layers were prepared by the mechanical exfoliation from the bulk highly oriented pyrolytic graphite. The quality of graphene was verified using the micro-Raman spectroscopy by analyzing the G peak and 2D band. In this paper, we discuss the issues of resolving graphene peaks on the Raman spectrum background from UNCD. After the number of layers and quality of graphene-on-diamond were confirmed, the fabrication steps were implemented [1]. The current-voltage (I-V) characteristics of the resulting graphene-on-diamond devices were measured using the semiconductor parameter analyzer. The obtained devices had the carrier
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mobility ~ 2354 cm2V-1S-1 for holes and ~1293 cm2V-1S-1 for electrons. The breakdown current density of the graphene-on-diamond devices was significantly improved as compared to grapheneon-oxide. It is expected that further improvements in synthetic diamond growth technology will lead to higher mobility and breakdown current density in graphene-on-diamond FETs.
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