Co/Pd-based spin-valves with perpendicular magnetic anisotropy on flexible substrates. Direct deposition vs transfer-and-bonding approaches

Flexible spintronics is an emerging field of research that has received increasing attention due to the additional functionalities that are allowed (lightweight, flexibility, shape-ability, wearability) with respect to conventional rigid systems. In this work, different strategies for the fabrication of flexible spintronic devices with perpendicular magnetic anisotropy are compared, i.e., transfer-and-bonding approaches exploiting wet and dry lift-off methods, and direct deposition on flexible substrates. To evaluate the potential of the proposed strategies, Co/Pdbased giant magneto-resistive spin-valves including a synthetic antiferromagnet reference electrode were investigated. Such stacks represent a demanding model system, owing to the large number of interfaces whose quality strongly affects the overall magnetic and electric performances. The advantages and drawbacks of the different strategies are discussed to provide crucial indications for the development of flexible spintronic devices of any complexity. Based on the results, the most suitable option for achieving high-quality heterostructures on large area surfaces via direct deposition is using polyethylene naphthalate (Teonex®) tapes, provided that the processing and operating temperatures are relatively low (<525 K). On the other hand, if the process requires higher temperatures, the dry lift-off method exploiting the low adhesion between an Au underlayer and the SiOx/ Si(100) substrate is the preferred alternative.