Directional Magnetic Field Response of FeCo/AlN Heterostructure Magnetoelectric Resonators

Abstract

Compact, ultra-low power magnetic field sensors are desirable for applications in multiple fields from biomedical engineering to military sensors [1,2,3]. Through direct coupling of magnetostrictive and piezoelectric strain, an on-chip sensor can be designed by exploiting the interface between thin films which can generate a charge when under an external magnetic field bias that depends not only on the magnitude of the measured field, but also the magnetic field direction enabling vector sensing capabilities. Magnetoelectric MEMS-scale heterostructures deposited in layers on silicon wafers and etched to create beams and cantilevers operating at the eletromechanical resonance were shown to work in a stress reconfigurable mode [4,5]. In this work we demonstrate magnetic field and directional response of FeC/AlN MEMS double-clamped heterostructure resonators.Through coupled strain engineering we are able to exploit the magnetic anisotropy and create a preferred axial response along the easy axis length of the suspended heterostructure beam. Resonant frequency response to the external magnetic field produces a sensitive measure of the angular dependence depending on the field vector components along the long and short axes. Figure 1a illustrates the heterostructure design of the double clamped ME MEMS structure and Figure 1b depicts a set of beams fabricated in a rosette pattern between Helmholtz coils used to apply a magnetic field to study the resonance response. The resonant peak shift with applied external magnetic field can be seen in Figure 2a where the butterfly loop has a linear slope df/dH near coercive field at 100G of 35 Hz/mT or 47 Hz/mT depending on the loop leg denoting the best bias response working point for this sensor. Polar plot of the resonance peak vs field at 15° increments can be seen in Figure 2b showing the directional response of the double clamped ME MEMS structures. Limit of detection measurements and further resonant peak angular dependence will be presented and deposition conditions will be discussed to illustrate the necessary conditions required to optimize creation of a high-quality MEMS sensor. **