Abstract
Delta-E effect sensors are based on magnetoelectric resonators that detune in a magnetic field due to the delta-E effect of the magnetostrictive material. In recent years, such sensors have shown the potential to detect small amplitude and low-frequency magnetic fields. Yet, they all require external magnetic bias fields for optimal operation, which is highly detrimental to their application. Here, we solve this problem by combining the delta-E effect with exchange biased multilayers and operate the resonator in a low-loss torsion mode. It is comprehensively analyzed experimentally and theoretically using various kinds of models. Due to the exchange bias, no external magnetic bias fields are required, but still low detection limits down to {{text{350 pT}} mathord{left/ {vphantom {{text{350 pT}} {sqrt {{text{Hz}}} }}} right. kern-nulldelimiterspace} {sqrt {{text{Hz}}} }} at 25 Hz are achieved. The potential of this concept is demonstrated with a new operating scheme that permits simultaneous measurement and localization, which is especially desirable for typical biomedical inverse solution problems. The sensor is localized with a minimum spatial resolution of 1 cm while measuring a low-frequency magnetic test signal that can be well reconstructed. Overall, we demonstrate that this class of magnetic field sensors is a significant step towards first biomedical applications and compact large number sensor arrays.
Highlights
The senor is fabricated starting from a 700 μm oxidized double side polished silicon wafer, covered by 50 μm polysilicon and another 650 nm oxide layer
All functional layers are deposited by magnetron sputtering from a von Ardenne CS730 S and structured by optical lithography and a combination of wet and dry etching techniques
A bottom electrode of Ta 40 nm Pt 150 nm is deposited over the whole cantilever, serving as seed layer for the following piezoelectric layer (AlN, 2 μm), which is deposited without additional heating by a pulsed DC generator as published in[31]
Summary
2 and 4 are performed six times for 4 min and averaged in the frequency domain over segments of 5 s to obtain a smooth noise floor. Each signal was measured over 1 min and averaged in the frequency domain using segments of 5 s to obtain a smooth noise floor and to better show the influence of the dual-mode operation scheme. The model cantilever consists of only two layers: one for the magnetic (FeCoSiB) layer and one substrate layer (Substrate) that includes all other layers via effective material properties.
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