A Theoretical Study of Carbon Nanotubes in Electronic Packaging Applications

Doktorsavhandling, 2012

The continuous decrease in size of transistors has allowed more components to be integrated in a single unit area and brings a range of opportunities as well as problems to the electronic packaging industry. To meet these challenges, the introduction of Carbon Nanotubes (CNT), which display a series of extraordinary properties, have attracted great interest. CNTs pose great difficulties to direct experimental study, thus theoretical study becomes a valuable alternative. This thesis presents several examples of theoretical studies aiming at CNT-based applications. Classic Molecular dynamics simulation (MDS) and continuum modeling are adopted as key methodologies in these studies. Although it is a theoretical work, this thesis presents exciting findings that point to possible practical applications. Chapter 2 presents two direct applications of CNT in electronic packaging, i.e. thermal management and interconnection. The thermal management is related to the use of CNTs in a micro-channel cooler construction due to its excellent thermal conductivity. In this example, the thermal interface resistance between CNT and adhesive could influence the heat transfer between the heat generator and the CNT fins in the cooler. This influence shall be evaluated. Thus in section 2.1, the thermal conductivity of epoxy matrix for thermal conductive adhesive (TCA) is studied by MDS using the Nonequilibrium Molecular Dynamics Method (NEMD). The thermal resistivity at the interface between the carbon nanotube and the polymer is estimated to be 33.262×10-8 m2K/W, which is consistent with previous studies. Both thermal management and interconnection with CNTs requires peeling off the CNT forest from the metal catalysts where CNTs were grown. Therefore an investigation of the bonding strength between metal and SWNT is presented. Two kinds of metal, i.e. iron and nickel are studied. Simulation results reveal that to debond the joint, a force greater than 31.7 nN is needed for Fe-SWNT joint, and for Ni-SWNT joint the required force is 3.5 nN. Then buckling behaviors of CNT are investigated and its potential applications presented. These investigations can be used in the electronic packaging applications. It starts from formulation work on the radial buckling of CNT. The results of this work are then verified with MDS which predicts an enhanced critical pressure for buckling of CNT due to an inserted linear carbon chain. This is followed by a theoretical analysis on the boundary condition effect on axial bucking of chiral CNT with MDS. It finds that boundary conditions can influence critical bucking strain by 20%. Hereafter a molecular gun that utilizes bending buckling of a telescope CNT is studied, which shows the inner tube of the doublewalled carbon nanotube (DWNT) can be shot out with a speed up to 500 m/s. After that another study concerning the effects of mechanical manipulation of CNT is undertaken. In this study, forced transverse vibrations of a single wall carbon nanotube (SWNT) containing atomic-size particles inside has been looked at, and the inertial trapping phenomenon in CNT resonators is discovered with MDS. This work reveals that when standing wave occurs by applying driving oscillation, particles inside the SWNT will be trapped near the anti-nodes or tip of SWNT if there are either one or two anti-nodes. A brief theory based on Fokker-Planck equation is proposed to explain this phenomenon. This trapping phenomenon is found to be highly sensitive to the external driving frequency i.e. that even a very small change of driving frequency can strongly influence the probability of the particle location inside the CNT. This effect can be potentially employed to achieve the atomic scale control of a particle position inside the SWNT via the finite adjustment of the external driving frequency. The thesis proposes that the inertia trapping phenomenon can be used to realize the concept of matter manipulation. Although it is not a true full three-dimensional (3D) maneuvering matter at the atomic level, the work could still be valuable in fields such as synthetic biology and molecule level data storage and hopefully offer a valuable tool for the realization of true 3D nanotechnology.