EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

In the recent years, a shift from rigid to flexible electronics was observed where the latter enables new degrees of freedom in the design of consumer products like displays, wearable sensors, solar cells, among others. Unlike in rigid electronics, thin film materials used in flexible electronics are deposited on thin compliant polymer substrates and they have to withstand various static and dynamic mechanical loading conditions in order to ensure that the flexible electronic devices remain operational for a sufficiently long period of time. Among these loading conditions are also tribological exposures and, hence, suitable characterisation methods and strategies are needed to analyse friction and wear for a variety of tribological contact situations. In the present work, thin Mo films were deposited by high power impulse magnetron sputtering on polyimide substrates and tested in a ball-on-disk test configuration against a series of counterpart materials. The latter included polymers, steel, ceramics, rubber and glass to establish different tribological contact situations. The obtained results provided a basis for tests where the tribological exposure was combined with stretching. Here, pre-conditioned films were prepared by straining to different strain levels including the crack onset strain and strains within the crack saturation regime. Subsequently, these samples were tribologically tested using the same parameters. A comparison of the results from both experiments revealed information about how straining of the films and crack formation influence the tribological behaviour of the deposited Mo films. This knowledge is intended to aid establishing design rules for the synthesis of thin films on polymer substrates that can be used in flexible and wearable electronics.