Radio-frequency NEMS magnetoelectric sensors

Abstract

The effectiveness of miniaturized piezoelectric/magnetostrictive magnetometers, that operate as contour-mode resonators and exploit the ΔE effect for DC magnetic field detection, has been previously demonstrated. With thickness typically in the hundreds of nanometers, and lateral dimensions on the order of a hundred microns, these devices offer the advantages of small scale: portability, low power consumption, and the potential for high spatial resolution in magnetic sensor arrays. However, a thorough understanding of the interplay between physical parameters and magnetic properties in these magnetometers has been lacking, and realization of optimum performance has been hindered as a result. This dissertation reports on the influence of a few physical aspects of the ΔE effect magnetometers on their performance. Most prominent is the investigation of the strong effects of stress-induced curvature of the resonator plates on the total frequency response and the quality factor of the sensors. It was found that up to two orders of magnitude separated the highest and lowest observed frequency shift in otherwise identical sensors. Test results from an ensemble of devices was supplemented by magnetic domain imaging, simulations, and modeling. Furthermore, by fabricating a magnetoelectric resonator with low curvature, a record-high DC magnetic field sensitivity of 4.98 Hz/nT was achieved. Additional studies were carried out to examine the influence of resonator anchors and the association between sensor frequency and the magnitude of the ΔE effect. Results from the latter investigation were intriguing, showing a rapidly decaying ΔE effect with higher frequency. Lastly, the characterization of the magnetic noise floor and finding of the detectivity was completed on two samples. A detectivity of 8 nT/√Hz at 10 Hz was obtained.