Magnetic field sensors based on the delta-E effect utilize the change in the mechanical stiffness tensor of a magnetostrictive material upon applying a magnetic field, resulting in resonance detuning. Such sensors have shown the capability of detecting small amplitude and low-frequency magnetic fields. However, challenges persist in achieving high spatial resolutions and building compact arrays with millimeter-sized sensor elements. Moreover, anisotropic stress development in the magnetic layer upon releasing the resonators during the fabrication process leads to significant device-to-device performance variations [1]. Additionally, shadowing of the clamping region in cantilever-type sensors results in inhomogeneous magnetic properties, influencing sensor performance [2]. In this work, we introduce a shadow mask deposition method and a free-free microresonator design for sub-millimeter-sized ΔE-effect magnetic field sensors to minimize residual stress, achieve homogeneous magnetic properties, and improve reproducibility (Figure 1) [3]. We investigate the residual stress induced by the deposition of the FeCoSiB magnetic layer and its impact on effective magnetic anisotropy. Homogeneous magnetoelastic anisotropy below 500 J/m3 has been obtained. The sensors are evaluated regarding their sensitivity, noise, and limit of detection (LoD) in several resonance modes. The influence of excitation voltage amplitudes and magnetic bias flux density on nonlinearity and sensor performance are investigated. A noise equivalent circuit model is used to determine the contributions of different noise sources. We find that while electronic noise dominates at low excitation voltage amplitudes, magnetic noise increases at higher excitation amplitudes. An LoD ≤ 7.4±3 nT/√Hz is obtained between 10 and 1000 Hz in the third resonance mode (RM3). A high device-to-device reproducibility is achieved with a resonance frequency deviation of ≤0.2%. Overall, we present highly reproducible miniaturized ΔE-effect sensors using the proposed deposition technique and sensor design. These findings highlight the potential for fully integrated sensor arrays, with higher spatial resolution and enhanced detection limits using magnetic multilayers and compact arrays.

References

[1] A. D. Matyushov; B. Spetzler; M. Zaeimbashi; J. Zhou; Z. Qian; E. V. Golubeva; C. Tu; Y. Guo; B. F. Chen; D. Wang; A. Will-Cole; H. Chen; M. Rinaldi; J. McCord; F. Faupel; N. X. Sun Adv. Mater. Technol., 2021, 6, 2100294.

[2] B. Spetzler; E. V. Golubeva; R. M. Friedrich; S. Zabel; C. Kirchhof; D. Meyners; J. McCord; F. Faupel Sensors, 2022, 21, 2022.

[3] F. Ilgaz; E. Spetzler; P. Wiegand; F. Faupel; R. Rieger; J. McCord; B. Spetzler Sci. Rep., 2024, 14, 11075.