AVS 65th International Symposium & Exhibition
    Thin Films Division Thursday Sessions
       Session TF+PS-ThM

Paper TF+PS-ThM4
Tungsten Atomic Layer Deposition on Vertically Aligned Carbon Nanotube Structures

Thursday, October 25, 2018, 9:00 am, Room 104B

Session: Deposition Processes for 3D and Extreme Geometries
Presenter: Ryan Vanfleet, Brigham Young University
Authors: R. Vanfleet, Brigham Young University
R.C. Davis, Brigham Young University
D.D. Allred, Brigham Young University
R.R. Vanfleet, Brigham Young University
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Carbon Nanotubes (CNTs) can be grown from 2D patterns into high aspect ratio, 3D MEMS structures. These porous structures can then be filled solid with different materials in order to impart specific and unique properties to the MEMS device. Tungsten, with its conductivity, high density and high temperature resistance, could be of special interest for many MEMs devices. Due to the high packing density and high aspect ratios of vertically aligned CNT forests, it is difficult to uniformly deposit films throughout the entirety of the structure. Atomic Layer Deposition (ALD) has been shown to uniformly coat structures with extreme geometries using sequential, self-limiting surface reactions. This in an inherently slow process, especially on geometries where the deposition is diffusion-limited such as in CNT forests. Approximately 50 nm of tungsten is required to fill a CNT-patterned structure solid where the individual CNTs grow roughly 100 nm apart. The tungsten ALD process has been shown to be able to deposit more than a single atomic layer per cycle so that the necessary number of cycles to fill the CNT structure is reduced. The process parameters that facilitate this increased deposition rate will be discussed. Tungsten-filled CNT beams were subjected to three-point bending tests to determine material properties of the composite structures. Preliminary tests on beams with about 35 nm of as-deposited tungsten give an ultimate strength of 11 MPa and a Young's Modulus of 1.7 GPa. The microstructure of the as-deposited tungsten is extremely fine and annealing studies will also be addressed.