UC San Diego
Issues related to the characterization and fabrication of coiled carbon nanotube based inductors /
- Author(s): Faraby, Hasan Mohammad
- et al.
The superior inductive properties of coiled carbon nanotubes (CCNTs) have been demonstrated through numerical computations. It is shown, through computations, that a range of inductance values (in the pH to [mu]H range) operational at THz frequencies could be obtained through a variation of CCNT geometric parameters, which can be accomplished through rational synthesis. A comparison of the proposed inductor material to conventional inductor material e.g. copper (Cu), in terms of both component footprint and material volume, indicated a greater quality factor (Q) through the use of the CCNTs. Experimental characterization of these CCNT inductors require high quality ohmic contacts. Focused ion beam based metal deposition is one of the easiest ways to create contacts on those nanostructures. Metal deposition with focused ion beam (FIB) systems result in material composed of carbon, oxygen, gallium and the primary metal from the metallo- organic precursor. Four point probe measurements to determine the material resistivity and energy dispersive spectroscopy (EDS) to determine the relative chemical composition were conducted on a wide range of FIB deposited platinum (Pt) and tungsten (W) lines. It has been shown that the gallium (Ga) percentage in the metal line plays a significant role in reducing the electrical resistivity of the material. Effective media theory (EMT), specifically using Mc Lachlan's general effective medium (GEM) equation is used to describe the relationship between the chemical compositions of the FIB deposited metal lines and the corresponding electrical resistivity. The relation between the chemical elements and the resistivity of the FIB deposited metal lines will make possible the accurate estimation of their resistance without using conventional probe stations. Like metals insulators can also be deposited using the FIB system. Insulator deposition by FIB systems results in SiO₂ layers with impurities from gallium (Ga) and carbon (C). The electrical capacitance of focused ion beam (FIB) deposited SiO₂ is shown to be sensitive to the specific composition of the ion beam. The effect of Ga contamination can be identified by comparing the electrical properties of similar depositions by plasma FIB. In the plasma FIB xenon (Xe) ion plasma is used as the ion source instead of Ga. The presence of carbon, inevitably found as the product of the hydrocarbon precursor decomposition has been isolated as a major cause for an observed decrease in the capacitance/effective dielectric constant of the SiO₂. Our study has implications to the deposition of high quality insulator films through FIB based methodologies. In this way detailed investigation of the origin of the resistivity of FIB deposited metals and insulators provided significant insights on the contact resistance of the FIB contacts to the CCNTs , which was prohibiting the true experimental characterization of the inductive properties of CCNTs inductors