Highly sensitive magnetic field sensors based on sputtered thin-film magnetoelectric heterostructures are desired to have a tunable resonance frequency while maintaining a large magnetoelectric coefficient and low limit of detection . A magnetoelectric sensor will have its highest sensitivity at the mechanical resonant frequency which can be manipulated through geometrical design of the cantilever or through a gradual change in the Young’s modulus of the composite’s functional layers. In this work, we fabricate and characterize AlN / FeCoSiB thin-film magnetoelectric composites deposited on functional nickel-titanium based (NiTi-X) shape memory alloy (SMA) substrates.
Analytical calculations show the resonant frequency can be altered by 6% for an AlN (2 µm) / FeCoSiB (2 µm) / NiTi (25 µm) / Si (100 µm) magnetoelectric sensor through a temperature induced reversible solid-to-solid phase transformation of the SMA from martensite (E = 41 GPa) to austenite (E = 83 GPa). For a 2.5 mm x 20 mm cantilever the resonant frequency can be increased from 318 Hz to 340 Hz purely through this transformation. The difference in frequency between martensite and austenite becomes enhanced by increasing NiTi film thickness, eliminating the Si substrate, or alloying the NiTi with another element such as Pd, Hf, or Cu. Currently we are exploring fabrication routes to build full magnetoelectric sensors onto NiTiCu substrates for experimental verification. We will present characterization results on the effect of heat treatment and NiTiCu surface roughness on the growth and piezoelectric behavior of AlN through DBLI, XRD, AFM, and TEM methods.
 Röbisch, Volker, et al. "Pushing the detection limit of thin film magnetoelectric heterostructures." Journal of Materials Research 32.6 (2017): 1009-1019.