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Hybrid Approach of Top Down and Bottom Up to Achieve Nanofabrication of Carbon Nanotube Devices. Maggie Zhang. A Dielectrophoretic Method for High Yield Deposition of Suspended, Individual Carbon Nanotubes with four-Point Electrode Contact.
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Hybrid Approach of Top Down and Bottom Up to Achieve Nanofabrication of Carbon Nanotube Devices Maggie Zhang
A Dielectrophoretic Method for High Yield Deposition of Suspended, Individual Carbon Nanotubes with four-Point Electrode Contact • Manufacture four-point contacted suspended, individual multiwalled carbon nanotubes by dielectrophoresis • DEP (dielectrophoresis) force is exerted on a dielectric particle when it is subjected to a non-uniform electric field • Bulk Carbon Nanotube Self Assembly (Chinese U of HK) • Avoid time-consuming in-situ manipulation: AFM etc. • Theory: • 2D chip design • Structures fab by focused-ion beam (FIB) treatment • Pt electrodes by light lithography, physical vapor deposition, and subsequent lift-off Tomb Shwarmb et al, Nanoletter 2007, 3
3D chip design • Manufacturing process of 3-D chips: (I) first layer of Pt structures : photolithography, physical vapor deposition and lift off (II + III) layer of SiN evaporated on the first layer of Pt isolates both Pt layers (IV + V) definition of electrodes by cutting out trenches by FIB milling in two steps (V) final 3-D design and a SEM picture of 3-D chip. DEP manipulation parameters: f = 5MHz Yielding of the process dependent on • Chip design • Solution. SDS (sodium dodecyl sulfate) reduce the bundled CNT attached on the electrode • Electrode material • Gap distance
Resistive Heating to achieve localized carbon nanotube synthesis • CMOS integration of nano structures (carbon nanotubes (CNTs)) • Local and selective synthesis using silicon microstructures (MEMS) • Device applications to nano sensors and nano electronics • In-situ controlled growth of CNT • Assembly of single CNT • CNT/silicon contact discussed
Electric field assisted synthesis Temperature C2H2/Ar gas Synthesis pressure 850 ~ 900C 60 / 55 sccm 250 Torr Gaps between Si structures Bias between Si (V2 ) Electric field (V2 / gaps) 5 ~ 10 mm 2 ~ 5 V 0.2 ~ 1 V/mm Experimental Procedure Local synthesis of CNT
CNT :Work function of CNT Si: Electron affinity of silicon Eg-Si : Band gap of silicon Ei -EF : Fermi level for silicon Bp: Barrier height Bp=(S+Eg-Si ) -CNT = 0.37~0.67 eV CNT: multiwall CNT (root and tip growth) Si: p+type, conc. 1019/cm3 Contact resistance Specific contact resistivity C: 10-5~10-4W-cm2 [1] • Barrier height Bp:0.4 eV • Concentration of Silicon:1019 /cm3(p-type) Contact area A: 2 10 -11 cm2 • Diameter of CNT : 50nm Contact resistance = 0.5 ~ 5MW [1] K. K. Ng and R. Liu, IEEE Trans. ED, 37, 1535 (1990) CNT-Silicon Heterojunction
Conclusion • Top down approach: Photolithography and FIB, SOI standard process • Bottom up: DEP manipulation (micro to nano scale) to CNT synthesis • Localized heating: Better control of synthesis, higher yielding and capatibility for post-processing • Contact Resistance Issue