In this presentation composite magnetoelectrics (ME) implemented as thin film systems are discussed in terms of their applicability as highly sensitive magnetic field sensors. Composite materials benefit from the advantage that their constituting phases can be optimized almost independently. Here, pulsed DC sputter deposited AlN serves as the piezoelectric component. The magnetostrictive phase is based on (Fe90Co10)78Si12B10 layers grown by magnetron sputter deposition. All functional layers are deposited with thicknesses of a few micrometers on Si cantilever structures with typical lateral dimensions of 1 mm x 3 mm and 3 mm x 25 mm.
To improve the minimum detectable magnetic field one could either increase the sensitivity given by the ME coefficient or reduce the sensor system noise governed by dielectric losses, irregular magnetization changes, acoustic interference and noise of the read-out electronics. For the cantilever design the highest sensitivities are observed for external magnetic fields with excitation frequencies matching the mechanical resonance frequency. Under such a condition, ME coefficients as large as 6900 V/cmOe and a limit of detection (LoD) below 1 pT/Hz1/2 can be measured. Our best result to date is a LoD = 500 fT/Hz1/2 at a frequency of 958 Hz using a set of two sensors for noise suppression.
Different measures such as frequency conversion techniques and the use of magnetostrictive multilayers are discussed in consideration of signal frequency range and noise level.