Sensor systems based on the DeltaE Effect

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Within the framework of the SFB 855, a new magnetic field sensor was developed which is based on the DeltaE Effect. It exploits the frequency shift of a cantilever, oscillating at high frequencies in the 100 kHz range, which is coated with a magnetostrictive layer whose effective Youngs modulus changes depending on the magnetic field (DeltaE effect). The sensor, which was presented in Nature as Research Highlight, allows broadband magnetic field measurements at low frequencies down to the DC range, is robust against microphony effects and mechanical noise, and provides full device integrability. In joint preparatory work, the applicants demonstrated a first fully integrated sensor where the electrical readout as well as the mechanical excitation was achieved by a single piezoelectric layer.The proposed project aims at integrating DeltaE sensors into MEMS technology and at pursuing different approaches to enhance their sensitivity. The ultimate aim are applications in magnetocardiography. Concerning the piezoelectric resonators, it is intended to utilize different sensor geometries based on bending modes as well as on longitudinal modes, which occur at substantially higher frequencies and provide better mechanical quality factors. The corresponding MEMS processes have to be developed. AlN and a modification with lower Youngs modulus for the reduction of clamping effects will be used as piezoelectric materials. Various methods are established for magnetoelectric sensors to obtain large changes in mechanical properties in a magnetic field. The applicability of these approaches to DeltaE sensors will be investigated in the present project. In addition to the well approved amorphous FeCoBSi alloys, it is also planned to use amorphous FeGaB alloys, which due to their higher coercivity and larger magnetostriction should be superior for sensors with remanent instead of an external bias field. For a better understanding of the magnetic materials, in situ magneto-optical Kerr effect measurements on the oscillating cantilever are planned in cooperation with P2. The electronics for operating the sensors will be developed along with the sensor development.