Search

In this work, the first surface acoustic-wave-based magnetic field sensor using thin-film AlScN as piezoelectric material deposited on a silicon substrate is presented. The fabrication is based on standard semiconductor technology. The acoustically active area consists of an AlScN layer that can be excited with interdigital transducers, a smoothing SiO2 layer, and a magnetostrictive FeCoSiB film. The detection limit of this sensor is 2.4 nT/ Hz at 10 Hz and 72 pT/ Hz at 10 kHz at an input power of 20 dBm. The dynamic range was found to span from about ± 1.7 mT to the corresponding limit of detection, leading to an interval of about 8 orders of magnitude. Fabrication, achieved sensitivity, and noise floor of the sensors are presented. [ABSTRACT FROM AUTHOR]

• Sensitivity of 35 rad/T for a SAW Magnetic Field Sensor is achieved. • Sensitivity increases with increasing magnetostrictive film thicknesses. • Magnetic hysteresis losses also increase with film thickness. • Nearly constant Limit of detection for film thicknesses between 50 nm and 300 nm. • Limit of detection is independent from sensitivity as shown analytically. In this work surface acoustic Love wave delay line magnetic field sensors with varying magnetostrictive layer thicknesses are discussed. Amorphous FeCoSiB is used as the sensitive layer with a thickness variation in the range of 25–400 nm. Each sensor is analyzed both by magneto-optical methods as well as electrical signal and noise measurements. In accordance with previously reported simulation results, the impact on the acoustically propagating wave's velocity distinctly increased with thicker magnetostrictive layers leading to magnetic sensitivities as high as 35 rad/T for a delay line coated with 400 nm thick FeCoSiB. Measurements of the sensor-intrinsic phase noise revealed distinct flicker phase noise that scales proportionally with the increase in magnetic sensitivity, thus leading to virtually constant limits of detection (LOD). Assuming that the observed flicker noise is caused by magnetic hysteresis losses due to the high-frequency excitation of the magnetic material, the LOD's independence of the magnetic sensitivity can even be shown analytically. However, it also becomes clear that such sensors need a magnetostrictive coating with a minimum thickness of at least 50 nm such that the signal-to-noise ratio is dominated by the magnetic material and not by fundamental noise contributions of the substrate. On the contrary, layers with thickness above 300 nm lead to distinct higher hysteresis losses that outrun the simultaneous increase in sensitivity, thus leading to a worse overall performance. [ABSTRACT FROM AUTHOR]