Epoxy-free fabrication techniques for layered/2-2 magnetoelectric composite: A review

Layered or 2-2 configuration magnetoelectric (ME) composites have gained significant interest in the last few decades owing to their ease of fabrication and relatively high ME output realizable at room temperature. Conventionally, layered ME composites are fabricated by bonding the constituent magnetostrictive and piezoelectric layers via an epoxy or adhesive. Thus, the epoxied interface acts as the medium of strain transfer between the constituent layers resulting in the ME effect. However, the presence of epoxy makes the composite prone to limitations such as reduced device life due to aging epoxy, reduced strain transfer efficacy due to low stiffness of epoxy, and degradation of composite properties at elevated temperatures due to the low glass transition temperature of epoxy material. Thus, various epoxy-free methods for layered or 2-2 type ME composite fabrication have been developed in the last two decades to circumvent these limitations. These methods include co-firing technique, electroless deposition, electrodeposition, shrink-fit, and press-fit. Each of these methods has tried to mitigate the disadvantages of its predecessors, however posing its own set of limitations. This review article captures the evolutionary journey of the development of each of these aforementioned techniques in a chronological sequence by highlighting the advantages and disadvantages offered by each of them. Subsequently, a brief overview of state of the art has been provided in summary, followed by a discussion on the potential avenues that may be probed further to improve the available epoxy-free fabrication techniques for layered or 2-2 ME composites.