Electrically modulated magnetoelectric AlN/FeCoSiB film composites for DC magnetic field sensing

Measurements of the converse magnetoelectric effect, observed for mesoscopic cantilever type magnetoelectric composites, are presented. The silicon based samples employ 2 µ m of amorphous (Fe 90 Co 10 ) 78 Si 12 B 10 film as soft magnetic, magnetostrictive phase. The piezoelectric phase consists of 2 µ m sputter deposited, highly textured aluminum nitride (AlN) in a plate capacitor arrangement. Exciting the piezoelectric phase at various frequencies leads to sharp peaks of induced voltage in a surrounding, mechanically decoupled pickup coil, corresponding to several mechanical resonances of the beam. The peak amplitude modulation can be exploited to detect DC magnetic fields. This entirely passive readout strategy is advantageous over other methods of sensitivity enhancement, typically requiring an active source of magnetic fields, thus prohibiting the construction of sensor arrays. Field dependent mechanical quality factors of up to 3800 near magnetic saturation are featured by a strong field dependence of induced voltage, reaching to 2290 V T −1 in the 20 µ T field regime. Vibrational measurements reveal a combination of the 15th flexural with a high order torsional mode as primarily active, at a resonance frequency of 520.7 kHz. This finding is supported by simple analytical estimations and literature. In unbiased operation, a linear resolution of 1.2 nT towards small 200 mHz fields is shown.