As part of the research in A3 in the previous funding period, it was shown that surface acoustic wave (SAW) sensors using the ΔE-effect can be used for very sensitive, broadband magnetic field sensing. These sensors are based on a patented approach using shear horizontal acoustic surface waves that are guided by a fused silica layer (Love waves) with an amorphous magnetostrictive FeCoSiB thin film on top. The velocity of these waves follows the magnetoelastic-induced changes of the shear modulus according to the magnetic field present. The delay line operation of the SAW sensor translates these changes into a phase shift. With an extremely low magnetic noise level of approximately 70 pT/Hz1/2 at 10 Hz, a bandwidth of 50 kHz and a dynamic range of 120 dB, this magnetic field sensor system shows outstanding characteristics. In addition to piezoelectric bulk crystals, polycrystalline thin-film AlScN on a silicon substrate will be investigated as a possible alternative, since its electro-acoustic coupling coefficient is clearly superior, especially in the high frequency domain. A main objective is to derive a comprehensive model for the sensitivity and the noise of magnetic field SAW sensors. This work will be performed in close collaboration with A1 on the magnetostrictive film, with A8 on modelling of design parameters as well as of the acoustic wave propagation, with A10 on magnetic noise modelling and characterization, and with B1 on the overall noise models. The major questions will include the concept and realization of the magnetostrictive component and investigations on the frequency, which is of course not independent from the magnetostrictive material of choice.
Besides this general objective, the following sub-objectives will guide the corresponding work packages, while the major results will be included in the signal-to-noise model: (1) For single crystalline SAW sensors, the choice of the piezoelectric single crystals and the material and layout of the guiding layer will be investigated as important parameters for the sensors´ performance; (2) for thin film SAW sensors, the acoustic mode and the layout of the sensor will be investigated and compared to our reference single crystalline SAW sensors; and (3) for phononic crystals, acoustic band gaps with defect-induced transmission windows as well as the micromagnetic fine-structure of the individual magnetic lattice elements will be investigated.