Abstract
Strain-dependent cracking behaviors in thin titanium (Ti) films on polydimethylsiloxane (PDMS) substrates were systematically investigated for their application to sensitive, flexible, transparent, and portable strain sensors. When uniaxially elongated, vertical cracks were developed in the low-strain range, and beyond a critical strain, tilted cracks appeared to intersect the vertical cracks. The cracking behaviors were also dependent on Ti film thickness. The varying strain-dependent crack patterns produced a significant resistance change in response to the applied strain, particularly, in the high- and broad-strain range. For a 180-nm-thick Ti film on PDMS substrate, a gauge factor of 2 was achieved in the range of 30% to 50% strain. The operation power was extremely low. All the Ti films on PDMS substrates were transparent, highly flexible, and very easy to fabricate. These results suggest that cracked Ti films on PDMS substrates could be a viable candidate for realizing a low-cost, flexible, transparent, and portable strain sensor.
Highlights
Measuring strain accurately has become much more important since new technology fields such as health monitoring, artificial skin engineering, intelligent textile engineering, motion detection, and environment monitoring have emerged [1,2,3,4,5,6,7]
We investigated the effect of applied strain and film thickness on nanocrack generation using titanium (Ti) films on PDMS substrates
Once the cracks are initiated at the Ti/PDMS interface, they are supposed to propagate through the Ti film, but the most applied stress is likely to be consumed for PDMS surface cracking at low-strain levels
Summary
Measuring strain accurately has become much more important since new technology fields such as health monitoring, artificial skin engineering, intelligent textile engineering, motion detection, and environment monitoring have emerged [1,2,3,4,5,6,7]. Flexible materials are widely employed for these applications due to the diversity of body shapes to which the sensors are attached and the variability of strain in action. From previous works on palladium (Pd) film on a PDMS substrate, it was demonstrated that the Pd film was broken into pieces under an external or internal strain and it could be applied for highly sensitive hydrogen gas sensors [15,16,17,18]. A mechanism by which nanocracks are generated in the Pd film on PDMS substrate was proposed, and a general process on how the nanocracks generated respond to hydrogen molecules was provided [15,17]. Systematic studies on the expandability of the proposed mechanism to other metals and the crack generation behaviors dependent on the magnitude of applied strain were missing
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