CMOS Compatible Growth of Carbon Nanotubes and Their Application in Field-Effect Transistors
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CMOS Compatible Growth of Carbon Nanotubes and Their Application in Field-Effect Transistors T. Uchino1,2, G. N. Ayre3, D. C. Smith3, J. L. Hutchison4, C. H. de Groot2, and P. Ashburn2 1
Department of Electronics and Intelligent Systems, Tohoku Institute of Technology, Sendai,
982-8577, Japan 2
School of Electronics and Computer Science, University of Southampton, Southampton SO17
1BJ, U.K. 3
School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, U.K.
4
Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, U.K.
ABSTRACT The metal-catalyst-free growth of carbon nanotubes (CNTs) using chemical vapor deposition and the application in field-effect transistors (FETs) is presented. The CNT growth process used a 3-nm-thick Ge layer on SiO2 that was subsequently annealed to produce Ge nanoparticles. Raman measurements show the presence of radial breathing mode (RBM) peaks and the absence of the disorder induced D-band, indicating single walled CNTs (SWNTs) with a low defect density. The synthesized CNTs are used to fabricate CNTFETs and the best device has a state-of-the-art on/off current ratio of 3×108 and a steep sub-threshold slope of 110 mV/decade. INTRODUCTION The excellent electrical, optical, thermal, and mechanical properties of carbon nanotubes (CNTs) have spurred research into many practical applications including nanoelectronic devices [1], biosensors [2], and via interconnects [3]. For applications such as CNT sensors, integration of the sensors with Si complementary metal-oxide-semiconductor (CMOS) circuits is highly desirable. One approach towards smart sensors is to fabricate the CMOS circuits before the CNT sensor fabrication [4]. However, metal catalyzed CNT growth is typically carried out around 800°C [5], which is not compatible with the requirement to keep the CNT growth temperature below 500°C to avoid degradation of CMOS performance. An alternative approach is to grow the CNTs before the CMOS circuit fabrication. However, in this case the integration of metal catalyzed CNT growth with a CMOS manufacturing process is problematic due to the metal contamination. CNT growth traditionally involves the use of metal nanoparticles as a catalyst. Transition metals such as Fe and Ni create deep levels in the Si bandgap which act as recombination centers just like Au. In this paper, the metal-catalyst-free growth of CNTs is investigated and applied to the fabrication of CNT field-effect transistors (FETs). Several different metal-catalyst-free growth methods of CNTs have been reported [6-12], including our earlier work on CNT growth from Ge nanoparticles [8, 10]. However to date, no
device results have been reported for CNTFETs produced by any of the metal-catalyst-free CNT growth methods, mainly because it has not been possible to grow CNTs on a suitable insulator without a metal catalyst. EXPERIMENTAL A p+ Si substrate (0.005 Ω·cm) was employed as a back gate and a 45-nm-thick thermally grown SiO2 layer was employed as a gate dielectric. A 3-nm-thick Ge
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