Project A9 - Surface Acoustic Wave Magnetic Field Sensors

As part of the research in project 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/Hz^1/2 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 project A8 on modelling of design parameters as well as of the acoustic wave propagation, with project A10 on magnetic noise modelling and characterization, and with project 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:

• 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;
• 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
• 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.

Involved Researchers

Person		Role
	Prof. Dr. Eckhard Quandt Materials Science Inorganic Functional Materials	Project lead
	Dr. Fabian Lofink Microsystem Technology Fraunhofer Institute	Project lead
	M.Sc. Jana Meyer Microsystem Technology Fraunhofer Institute	Doctoral researcher
	M.Sc. Felix Weisheit Materials Science Multicomponent Materials	Doctoral researcher

Role within the Collaborative Research Centre

The CRC 1261 spans a wide range of projects: from materials research to sensor concepts to signal processing and finally to applications. Because this project deals with one of the sensor concepts, it is fully integrated within this research chain and we will have intense collaborations with materials research, sensor systems, and even with applications, especially with the transfer project. The last collaboration includes mainly the support of T1 in its measurements using SAW sensors for the localization of deep brain stimulation (DBS) and using the derived data and information for further improvement of the sensors for this application. In particular, the following close collaborations with other projects are planned:

Project-related Publications

M. Samadi, J. Schmalz, J. M. Meyer, F. Lofink, M. Gerken: Phononic-Crystal-Based SAW Magnetic-Field Sensors, SMicromachines, 14(11), 2130, 2023.

M. F. Niekiel, J. M. Meyer, H. Lewitz, A. Kittmann, M. A. Nowak, F. Lofink, D. Meyners, J.-H. Zollondz:  What MEMS Research and Development Can Learn from a Production Environment, Sensors, Dec., 23(12), 5549, 2023.

V. Schell, E. Spetzler, N. Wolff, L.Bumke, L. Kienle, J. McCord, E. Quandt, D. Meyners: Exchange Biased Surface Acoustic Wave Magnetic Field Sensors, Scientific Reports, vol. 13, no. 8446, 2023.

S. Moench, J. M. Meyer, A. Žukauskaitė, V. Lebedev, S. Fichtner, J. Su, F. Niekiel, T. Giese, L. Thormählen, E. Quandt, F. Lofink: AlScN-Based SAW Magnetic Field Sensor for Isolated Closed-Loop Hysteretic Current Control of Switched-Mode Power Converters, IEEE Sensors Letters, vol. 6, no. 10, pp. 1-4, 2022.

N. Wolff, M. R. Islam, L. Kirste, S. Fichtner, F. Lofink, A. Žukauskaitė, L. Kienle: Al1−xScxN Thin Films at High Temperatures: Sc-Dependent Instability and Anomalous Thermal Expansion, Micromachines, no. 13, issue 8 , 01282, 2022.

J. Su , S. Fichtner , M. Zubair Ghori , N. Wolff , M. R. Islam , A. Lotnyk , D. Kaden , F. Niekiel, L. Kienle, B. Wagner, F. Lofink: Growth of Highly c-Axis Oriented AlScN Films on Commercial Substrates, Micromachines , no. 13, issue 5, pp. 783, 2022.

C. Müller, P. Durdaut, R. B. Holländer, A. Kittmann, V. Schell, D. Meyners, M. Höft, E. Quandt, J. McCord: Imaging of Love Waves and Their Interaction with Magnetic Domain Walls in Magnetoelectric Magnetic Field Sensors, Advanced Electronic Materials, 2200033, 2022.

J. M. Meyer, V. Schell, J. Su, S. Fichtner, E. Yarar, F. Niekiel, T. Giese, A. Kittmann, L. Thormählen, V. Lebedev, S. Moench, A. Žukauskaitė, E. Quandt, F. Lofink: Thin-Film-Based SAW Magnetic Field Sensors, Sensors, vol. 21, no. 24, 8166, 2021.

L. Thormählen, D. Seidler, V. Schell, F. Munnik, J. McCord, D. Meyners: Sputter Deposited Magnetostrictive Layers for SAW Magnetic Field Sensors, Sensors, vol. 21, issue 24, 8386, 2021.

V. Schell, P. Durdaut, C. Müller, A. Kittmann , M. Yalaz, A. Bahr, D. Meyners, M. Höft, J. McCord, E. Quandt: Sensing Small Magnetic Fields with Surface Acoustic Waves, SAW Symposium 2021, Dresden, Germany, October 14th - 15th, 2021.

P. Durdaut, C. Müller, A. Kittmann, V. Schell, A. Bahr, E. Quandt, R. Knöchel, M. Höft, J. McCord: Phase Noise of SAW Delay Line Magnetic Field Sensors, Sensors, vol. 21, issue 16, 5631, 2021.

D. A. Bas, P. J. Shah, A. Matyushov, M. Popov, V. Schell, R. C. Budhani, G. Srinivasan, E. Quandt, N. Sun, M. R. Page: Acoustically Driven Ferromagnetic Resonance in Diverse Ferromagnetic Thin Films, IEEE Transactions on Magnetics, vol. 57, no. 2, 2021.

X. Liang, A. Matyushov, P. Hayes, V. Schell, C. Dong, H. Chen, Y. He, A. Will-Cole, E. Quandt, P. Martins, J. McCord, M. Medarde, S. Lanceros-Méndez, S. van Dijken, N. X. Sun, J. Sort: Roadmap on Magnetoelectric Materials and Devices, IEEE Transactions on Magnetics, vol. 57, issue 8, 9446997, 2021.

M.R. Islam, N. Wolff, M. Yassine, G. Schönweger, B. Christian, H. Kohlstedt, O. Ambacher, F. Lofink, L. Kienle, S. Fichtner: On the Exceptional Temperature Stability of Ferroelectric Al1-xScxN Thin Films, Applied Physics Letters, vol. 118, issue 23, 232905, 2021.

N. Wolff, S. Fichtner, B. Haas, M.R. Islam, F. Niekiel, M. Kessel, O. Ambacher, C. Koch, B. Wagner, F. Lofink, L. Kienle: Atomic Scale Confirmation of Ferroelectric Polarization Inversion in Wurtzite-Type AlScN, Journal of Applied Physics, vol. 129, issue 3, 034103, 2021.

J. Su, F. Niekiel, S. Fichtner, L. Thormaehlen, C. Kirchhof, D. Meyners, E. Quandt, B. Wagner, F. Lofink: AlScN-Based MEMS Magnetoelectric Sensor, Applied Physics Letters, vol. 117, issue 13, 132903, 2020.