Auxetic Superelastic TiNiCuCo Sputtered Thin-Films For Stretchable Electronics

Friday, May 20, 2022: 12:00 PM
Sunset Ballroom (Westin Carlsbad Resort)
Ms. Sabrina M. Curtis , Kiel University, Kiel, Germany, University of Maryland, College Park, MD
Ms. Duygu Dengiz , Kiel University, Kiel, Germany
Mr. Lars Bumke , Kiel University, Kiel, Germany
Prof. Eckhard Quandt , Kiel University, Kiel, Germany
The next generation of wearable sensors, actuators, and power microsystems require reversible elastic deformation of at least 30% - 100% macroscopic strain, to match the elasticity of human skin, while maintaining a substantial area coverage. Due to a negative Poisson’s ratio, auxetic structures are attractive for these applications because they expand (rather than contract) under applied deformation [1]. Through strategic design of the auxetic structure, a trade-off of maximum strain and area density is achieved.

Sputtered thin-film Nickel-Titanium based alloys with austenitic finish temperatures below room temperature are attractive for stretchable systems. They are capable of superelastic recovery from remarkable intrinsic strains of up to 8% due to stress induced martensitic transformations, significantly higher than strains achieved by traditional metals (~1%). Previously, superelastic TiNiCuCo thin-films were demonstrated to show ultra-low fatigue, reversibly deforming through 10 million cycles [2]. Additionally, superelastic materials exhibit exceptional mechanical strength, thermal reversibility, and decent electrical conductivity, making them ideal substrates for wearable electronics.

Here we present sputtered freestanding thin-films of TiNiCuCo superelastic materials patterned into auxetic geometries to serve as a substrate for stretchable electronics. We characterize their cyclic thermal-induced and stress-induced phase transformations as well at their electrical performance. Finally, we show auxetic TiNiCuCo films can serve as functional high-temperature substrates to enable other MEMS thin-film systems to become stretchable.

[1] Xin, et al. “Auxetic metamaterials and structures: A review” Smart Materials and Structures 27.2 (2018): 023001

[2] Chluba, C., et al. “Ultralow-fatigue shape memory alloy films. Science, 348 (6238), 1004-1007. (2015)

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