ADVANCED MATERIALS & PROCESSES | OCTOBER 2025 43 incorporated as stretchable interconnects (Fig. 2) for next-generation foldable and deployable devices, or combined with piezoelectric layers in hybrid stacks that couple actuation and sensing (Fig. 3). When patterned into meta-material architectures, thin-film SMAs can conform to complex three-dimensional surfaces, making them well suited for wearable systems. Compatibility with wafer- level processing establishes applicability in emerging microelectronic and wearable platforms. Lightweight UAV and Aerospace Systems. Thin films provide deployable structures (antennas, sensors, morphing surfaces, folding wings) that require minimal volume and mass for applications such as lightweight unmanned aerial vehicles (UAVs) and other aerospace systems. Their high work density allows replacement of strain-limited piezoelectric actuators and bulky servomotors. Soft Robotics and Bio-inspired Devices. Robotic skins and wearable actuators benefit from the conformality of thin films. Patterned films bend and stretch with surrounding elastomers, enabling human-like motion, adaptive compression garments, and haptic feedback systems. FUNCTIONAL ENHANCEMENTS PROVIDED BY THIN-FILM SMAs Extended Strain Capacities. Through micro-patterning into serpentine[9], auxetic[10], or metamaterial geometries using either laser cutting or on-substrate patterning, thinfilm SMAs can achieve effective recoverable strains in the hundreds of percent, as shown in Fig. 1. Auxetic metamaterials, for instance, expand laterally under tension, enabling uniform stress distribution and enhanced fatigue resistance; serpentine traces enable elongation and bending without fracture. Multifunctionality. Thin-film SMAs serve multiple roles within a single system, providing multifunctionality that is rarely possible. A single element can simultaneously function as substrate, actuator, interconnect, or electrode[9,10]. Wire and sheet forms of SMA, by contrast, remain single-function, always requiring complementary materials to generate the desired functionalities. FORM FACTOR ADVANTAGES PVD allows direct deposition onto silicon wafers or flexible foils, to embed actuation and superelasticity within chip-scale MEMS and hybrid devices. Annealing and structuring through lithographic or laser patterning enables complex two- and three-dimensional geometries that conform to curved substrates or integrate seamlessly into multilayer stacks. Thin-film actuators contribute negligible mass when providing volumetric work densities up to 10-25 MJ/m³, and achieve high actuation frequencies[13], an especially critical combination for aerospace systems. APPLICATIONS Microelectronics and Wearables. SMA PVD thin films can be patterned into surface-mounted actuators, FEATURE Fig. 1 — PVD-fabricated SMA thin films structured into stretchable auxetic metamaterial designs, enabling conformal integration with electronics and strain capacities far beyond bulk SMA. Fig. 2 — Laboratory demonstration of a surface-mounted LED driven by PVD-fabricated TiNiCuCo thin-film SMA serpentine interconnects[9]. Fig. 3 — AlN piezoelectric thinfilm sensor composite grown on top of a TiNiCu thin-film SMA on a silicon substrate[8]. 7
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