STUDY OF AlN/FSMA MAGNETOELECTRIC HETEROSTRUCTURE FOR MEMS APPLICATIONS

Abstract

In the current era, the progress of electronic technology is directly coupled with the advancement made in materials science. Magnetoelectric materials are the potential candidate for several multifunctional devices such as magnetic random-access memory, switches, magnetic sensors and tunable resonators. In these kinds of composites, the Magnetoelectric (ME) response is a product tensor property, i.e., outcome of the mechanical interaction between the magnetostrictive effect (magnetic/mechanical effect) occurring in the magnetic phase and the piezoelectric effect (mechanical/electrical effect) present in the piezoelectric phase. The ME coupling is observed in diverse structures such as bulk ceramic, two and three-phase ME composites and nanostructured thin films. However, the ME composite thin films have attracted enormous attention because different phases can be attached and designed at the atomic level with higher precision and sharp interface. Furthermore, nanostructured thin film composites enable the researchers to investigate the physical cause of the ME coupling effect at the nanoscale level. The strength of the ME coupling depends on many factors, such as interface quality, high anisotropy magnetostriction, lattice mismatching, and functional characteristics of the individual piezoelectric and magnetostrictive layers. The ideal candidates for magnetostrictive and piezoelectric layers are ferromagnetic shape memory alloys (like-NiMnIn, NiMnSb, etc.) and AlN, respectively. Ferromagnetic shape memory alloys (FSMAs) exhibit a large applied magnetic field and temperature induced strain in the temperature region during the martensite to austenite phase transition as compared to leading magnetostrictive materials such as Trefnol-D and metglas. The NiMnIn exhibits giant magnetostriction coefficient at room temperature with multiple degrees of freedom to tune its magnetostriction, i.e., by varying temperature, magnetic field, stress. On the other hand, Aluminium Nitride (AlN) is a lead-free complementary metaloxide- semiconductor (CMOS) compatible piezoelectric material with a high value of voltage piezoelectric coefficient (e33). The deposition process of AlN is also well reproducible, and its chemical compatibility is well suited with semiconductor fabrication technology. For strong coupling between ferromagnetic and piezoelectric layers in the artificial magnetoelectric heterostructure, it is desirable to fabricate high-quality thin films with a sharp interface that can be attained by several growth techniques such as molecular beam epitaxy, pulsed laser deposition, metal oxide chemical vapor deposition, sputtering.