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Nanocrystalline diamond for nano-electro-mechanical systems

Thomas, Evan L. H. 2017. Nanocrystalline diamond for nano-electro-mechanical systems. PhD Thesis, Cardiff University.
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Abstract

Micro and Nano-Electro-Mechanical Systems (MEMS/NEMS) incorporating micro- and nano-scale mechanical elements into electronic circuits are of increasing interest in both fundamental physics and technological applications, with uses ranging from atomic resolution mass spectrometers to low cost gravimeters and RF filtering. For applications reliant on the perturbation of mechanical elements, a high resonant frequency (f) with minimal dissipation (Q−1) is desired to increase device response, while for filtering within the RF high Q enables the selection of individual channels. With the resonant frequency of devices proportional to the acoustic value of the material, diamond’s unrivalled value of 18 000ms−1 makes it ideal for high frequency devices with minimal dissipation from scaling induced loss. However, the use of Nanocrystalline Diamond (NCD) for smaller scale NEMS is inhibited by the quality of the resulting films, in particular the non-diamond carbon content, and the considerable surface roughness resulting from the competitive growth of randomly orientated crystallites. Within Chapter 4 spectroscopy ellipsometry, a powerful technique capable of probing the variation in the optical properties with depth, and hence microstructure, of thin films is therefore applied to the characterisation of 25– 75 nm thick NCD films. The model developed is able to discern the point of coalescence of the film, with the indicated surface roughness and composition verified by AFM and Raman spectroscopy. Chapter 5 then details the adaption of chemical mechanical polishing, a technique routinely used within the IC fabrication industry, to the polishing of diamond. Using a soft polymer polishing pad and an alkaline colloidal silica polishing fluid a reduction in roughness is observed for NCD films from 18.3 to 1.7 nm RMS over 25 μm2 after 4 hours. Finally, the polishing technique is used to aid in the construction of NEMS devices within Chapter 6 with the aim of improving the Q factor.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Physics and Astronomy
Subjects: Q Science > QC Physics
Uncontrolled Keywords: Diamond, Nanocrystalline, NCD, CMP, polishing, ellipsometry, MEMS, NEMS
Funders: EPSRC
Date of First Compliant Deposit: 30 March 2017
Last Modified: 04 Jun 2017 09:46
URI: http://orca.cf.ac.uk/id/eprint/99464

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