Wang, Zhongnan (2016) Tribological investigation for next-generation polymeric micro-systems. PhD thesis, University of Warwick.

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Abstract

The development of micro-fabrication processes for 3D microstructures has led to the production of low-cost, low-energy devices at millimeter scales known as MEMS for a wide range of electronic, mechanical, mechatronic and biomedical applications. As surface-to-volume ratio increases drastically with decreasing dimension, surface properties of the materials are the prominent factor at the interface between two solids and consequent tribological issues such as adhesion, friction and wear will arise in MEMS devices when surfaces are in, or have the potential for, sliding contact. Measurement techniques and principles used in micro-tribology are quite different from those in macro-tribology. Various specialized micro-tribometers have attracted recent attention in attempts to obtain consistent, accurate tribological measurements that could provide information for the design of MEMS components. However, even these have operational parameters quite different to those in the regime typical of MEMS devices. For example, the thermal properties of polymers might mean that they are especially sensitivity to the speeds and reciprocating scan frequencies of measurements. This is a serious concern because the selection of appropriate materials for such applications is very important in order to reduce not only friction and wear, but also the stiction of the parts. The immediate challenge is that there is very little reliable information about the properties of this new generation of engineering materials because of insufficient understanding and characterization of their behaviour at the microscale under a wide range of experimental conditions.

With these points in mind, this thesis aims to prompt wide study of the micro-tribological properties of polymers for MEMS applications, providing preliminary new data on them while exploring in some detail possible uncertainty effects that could arise from the testing regimes of most micro-tribometers. It starts by re-commissioning and characterizing a unique, wide-bandwidth prototype micro-tribometer developed at Warwick, establishing good operating procedures by comparing measurements on materials widely discussed in the literature. New data has been collected on an acrylate resin typically used for micro-stereo-lithography, PTFE and oxide-coated silicon. It suggests that deviations from Amonton’s law in the ten millinewton range might be less severe than previously reported. Observing that the skill and time required for such testing makes it unattractive for a production control environment, the thesis then explores, via contact modelling, whether there is a useful correlation between Berkovich tip nano-hardness and the micro-friction of the polymeric samples: several plausible modelling assumptions are shown to lead to inconsistencies. Final discussions and recommendations consider how to move on from these experimental scoping studies to acquire detailed evaluations of the properties of the best candidates under typical usage conditions prior to designers of potential products taking these materials and processes at all seriously.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	T Technology > TK Electrical engineering. Electronics Nuclear engineering
Library of Congress Subject Headings (LCSH):	Microelectromechanical systems, Microfabrication, Tribology, Friction, Polymers -- Thermal properties
Official Date:	October 2016
Dates:	Date Event October 2016 Submitted
Institution:	University of Warwick
Theses Department:	School of Engineering
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Chetwynd, D. G. (Derek G.), 1948- ; Mao, Ken
Format of File:	pdf
Extent:	xxiii, 206 leaves : illustrations, charts
Language:	eng

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