Nano-scratch, nanoindentation and fretting tests of 5–80nm ta-C films on Si(100)

Abstract

Wear and stiction forces limit the reliability of Silicon-based micro-systems when mechanical contact occurs. Ultra-thin filtered cathodic vacuum arc (FCVA) ta-C films are being considered as protective overcoats for Si-based MEMS devices. Fretting, nano-scratch and nanoindentation of different thickness (5, 20 and 80 nm) ta-C films deposited on Si(100) has been performed using spherical indenters to investigate the role of film thickness, tangential loading, contact pressure and deformation mechanism in the different contact situations. The influence of the mechanical properties and phase transformation behaviour of the silicon substrate in determining the tribological performance (critical loads, damage mechanism) of 2 the ta-C film coated samples has been evaluated by comparison with previously published data on uncoated Silicon. The small scale fretting wear occurs at significantly lower contact pressure than is required for plastic deformation and phase transformation in nanoindentation and nano-scratch testing. There is a clear correlation between the fretting and nano-scratch test results despite the differences in contact pressure and failure mechanism in the two tests.In both cases increasing film thickness provides more load support and protection of the Si substrate. Thinner films offer significantly less protection, failing at lower load in the scratch test and more rapidly and/or at lower load in the fretting test.

Development of DLC coating architectures for demanding functional surface applications through nano- and micro-mechanical testing

“…The friction coefficient at yield is commonly reported to be ~0.05-0.1 for carbon films when sliding against spherical diamond probes [9,42]. Differences in elastic deformation and plastic ploughing have a marked influence on the evolution of the friction vs. load in the nano-scratch test.…”

“…The authors of this paper have also performed a more complete characterisation of carbon coatings by combining the results of the nanoindentation tests with additional nanomechanical and nano-tribological test capability, namely nano-scratch, nano-impact and nano-wear [9][10][11]. These tests provided complementary information about the durability of DLC films in these more complex mechanical loading situations.…”

Deformation, failure and removal mechanisms of thin film structures in abrasive machining

“…Recent nanoscratch studies revealed that film thickness had great effect on the critical normal load that induced interfacial failure [67,[74][75][76]. Beake et al [74] characterized the nanoscratch induced surface damages in Ta-C films of different thicknesses deposited on a Si substrate.…”

“…Beake et al [74] characterized the nanoscratch induced surface damages in Ta-C films of different thicknesses deposited on a Si substrate. The scratching results shown in Fig.…”

Advanced Nanomechanical Test Techniques

“…Beake and co-workers have reported nanomechanical and nanotribological (nano-scratch and nano-wear) characterisation of a wide range of thin films on Si, with thicknesses from 5 nm (ta-C) to 1500 nm (TiN) performing nanoindentation with Berkovich indenters combined with nano-scratch testing with spherical indenters [49,[54][55][56][57]. A key motivation for studying several of these was to understand the interplay between film thickness and interfacial toughness for MEMS and protective thin film applications.…”