Dual-cathode method for sputtering magnetoelastic iron-boron films

Magnetoelastic sensors have gained attention in recent years due to their wireless nature and versatility in sensing applications, but there have been issues with fabrication, especially as sensor platform sizes approach the microscale. In this work, a dual-cathode method is presented for the co-deposition of iron and boron to produce magnetoelastic films that serve as the basis for wireless sensors. Deposition rate and film composition experiments were performed to optimize sputtering conditions for obtaining high-quality films with compositions near to the goal of 80/20 at.% iron/boron. The magnetoelasticity of films produced using this method, along with the potential of wireless sensors based upon these films, was confirmed by fabricating small (500 × 100 × 5 μm) sensor platforms and then testing for resonance using a coil and a network analyzer. These sensors were found to have resonance frequencies of around 4 kHz with Q-values, in air, of over 1000. By coating the sensor platforms with gold using a third cathode, and then annealing in a vacuum oven at 220 °C, the environmentally sensitive iron-based alloy that forms the core of the sensor platform may be protected from corrosion.