Distribution Of Material Characteristics In Sputter Deposited Nitinol

Sputter deposition technology for Nitinol films is a new and innovative manufacturing process for future micro-mechanical, electronic and actuator systems. New directions in qualified process control for medical implant applications of (thin)film materials should be applied to use the full process potential of this technology. Therefore, integrated and high precision material characterizations for a controlled production process should monitor and reflect Af-temperature and material integrity within high-volume manufactured batches. However, managing individual free-standing test specimen with standard test equipment and handling is challenging due to semi-finished components and design features in micrometer dimensions and required accuracy. 

In this study we investigated the spread of functional material characteristics of applied Nitinol films for Af-temperature (according to bend and free recovery) and accelerated fatigue-to-fracture testing (according to ASTM). The Nitinol actuation dynamics of distributed functional micro-test elements were analysed and optimized by finite element analysis (FEA) to achieve a flexible and wide test window with high measurement accuracy. Setup and actuation drive was tuned towards final application test parameters. A detailed correlation study with SEM analysis for integrated functional micro-test elements and free-standing elements was conducted to quantify the distributed material characteristics from several of these small elements.

From this study we can conclude that sputter deposited Nitinol (thin)film materials can be applied within the usual tolerances for functional Nitinol material characteristics (Af-Temperature +/-4°C). Results from functional micro-test elements and free-standing elements demonstrate a similar and precise homogeneity of the Nitinol films.