57th AVS 4568 MN-ThP11 (Poster) Modeling of Diffusion, Nucleation and Growth in the Chemical Vapor Infiltration of Vertically-Aligned Carbon Nanotube Forests for MEMS. A.M. Konneker, D.D. Allred, R.C. Davis, Brigham Young University

 

We present preliminary results using computer simulation of chemical vapor deposition into vertically aligned carbon nanotube (VACNT) forests.  The model is based upon deposition processes used in the carbon nanotube templated microfabrication (CNT-M) process. It utilizes VACNT arrays as a framework into which matter is infiltrated via a chemical vapor deposition (CVD)-type process to create solid microstructures and microelectromechanical systems (MEMS). These can have large aspect ratios (200:1) and startling heights (to date up to a mm).  Long nozzles with narrow ID and other structures have been made that would be difficult by subtractive techniques.  One of the biggest advantages of CNT-M is the promise of being able to prepare MEMS from any desired solid material that can be deposited by CVD, though to date this has only been amorphous and polycrystalline Si, SiO2, SiC, silicon nitride and amorphous carbon.   

This work was inspired by the desire to understand how the gas diffusion, reaction and nucleation and growth models used to describe, mostly 2-D, thin-film CVD can be applied to understanding growth on the individual carbon nanotubes and nanotube bundles that make up a VACNT structure.  This scaffolding is 3-dimensional, but “rarified”- that is > 99% empty and geometrically complex, and is vital for use of the CNT-M process. How it changes from mostly emptiness to a filled structure was a puzzle. Without optimized growth parameters, deposition is limited to the exterior of the VACNT forests and the structural integrity of the MEMS is poor. In addition, the adhesion of the MEMS devices to the substrate is often inadequate, which leads to low yields and frequent device failure.

Our model explores how the deposition rate, VACNT geometry, and VACNT forest density affects the filling of the forest. We base the parameters in our model on data from the TEM analysis of MEMS devices fabricated using the CNT-M process with CVD-deposited polysilicon, amorphous carbon, and silicon nitride.

 

Alternate title: A Simulation of the Thin-Film Coating of Vertically Aligned Carbon Nanotubes