Magnetoelectric sensors, which integrate magnetostrictive and piezoelectric materials, are widely used in applications such as magnetic field sensing. A promising approach involves using surface acoustic waves (SAW) generated by metal interdigital transducers (IDTs) placed on top of a piezoelectric layer. While piezoelectric single crystal substrates have been widely used for the fabrication of SAW sensors, thin-film technology offers many advantages, including greater material flexibility, improved integration, and therefore better scalability. Among the promising thin-film materials, aluminium nitride is particularly attractive due to its high wave velocity, good mechanical and dielectric properties, high thermal conductivity, and high breakdown voltage. Furthermore, alloying AlN with scandium retains these favourable material properties while significantly enhancing electromechanical coupling, [1] making AlScN an ideal piezoelectric material for SAW devices. When the SAW device in a delay line configuration is combined with a magnetostrictive film, changes in the Young’s modulus (ΔE effect) of the magnetostrictive FeCoSiB film in the presence of an external magnetic field can be detected as a phase change of the SAW, enabling highly sensitive magnetic field detection.[2] To improve the soft magnetic properties of FeCoSiB and enable the generation of different SAW modes, a smoothing layer of SiO_₂ is introduced that is smoothed by chemical mechanical polishing (Figure 1).

The impact of variations in SAW frequency and IDT design parameters (aperture, delay line length) on the sensitivity of the sensor will be presented. Possible applications include the detection of biomagnetic fields in medicine and current sensing in power electronics [3] with the advantage of a high bandwidth in the MHz range and a large dynamic range. The latest results show that thin-film SAW magnetic field sensors can reach sensitivities up to 1000 °/mT and a limit of detection of 345 pT Hz^-1/2 at 10 Hz, which is the biomagnetically interesting frequency region and up to 67 pT Hz^-1/2 at 1 kHz.