Magnetoelectric (ME) composites are subject of great interest due to their high ME coefficients that are larger than natural multiferroics and their high sensitivity to magnetic fields at room temperature without the need of cooling. Prior investigations on ME thin film sensors using amorphous FeCoSiB as magnetostrictive and AlN as piezoelectric layer revealed a limit of detection (LOD) of a few pT/Hz^1/2 in the mechanical resonance and at room temperature. Such composites are fabricated following strict process flows dictated by the temperature sensitivity of the amorphous FeCoSiB. Accordingly FeCoSiB is deposited on top of the relatively rough, typically 2 µm thick AlN layer.
In order to further improve the LOD, a new sensor design has been investigated. Based on a new AlN deposition without intentional substrate heating  a process flow, which includes the deposition of the the amorphous FeCoSiB on the very smooth Si substrate, was developed. As a consequence, the LOD has been enhanced by almost an order of magnitude reaching 400 fT/Hz 1/2 at the mechanical resonance of the sensor (867 Hz) . Furthermore, the low temperature AlN films exhibit good piezoelectric (d33,f = 5.3±0.2 pm/V, e31,f = -1.38±0.02 C/m 2 ) and dielectric (tan δ < 0.1%) properties which additionally contribute to the improvement of the LOD.