MEMS magnetic field sensor based on magnetoelectric composites

For the measurement of biomagnetic signals in the pico- and femtotesla regime superconducting interference devices (SQUIDs) are commonly used. Their major limitation comes from helium cooling which makes these sensors bulky and expensive. We show that MEMS sensors based on magnetoelectric (ME) composites could be capable as a replacement for biomagnetic measurements. Using surface micromachining processes a cantilever beam with a stack composed of SiO₂/Ti/Pt/AlN/Cr/FeCoSiB was fabricated on a 150 mm Si (1 0 0) wafer. First measurements of a rectangular micro cantilever with a thickness of 4 µm and lateral dimensions of 0.2 mm × 1.12 mm showed a giant ME coefficient α_ME = 1000 (V m⁻¹)/(A m⁻¹) in resonance at 2.4 kHz. The resulting static ME coefficient is α_ME = 14 (V m⁻¹)/(A m⁻¹). In resonance operation a sensitivity of 780 V T⁻¹ and noise levels as low as 100 pT Hz^−1/2 have been reached. (paper)