The strong strain-mediated magnetoelectric (ME) coupling found in thin-film ME heterostructures has attracted an ever-increasing interest and enables realization of a great number of integrated multiferroic devices, such as magnetometers, mechanical antennas, RF tunable inductors and filters. This paper first reviews the thin-film characterization techniques for both piezoelectric and magnetostrictive thin films, which are crucial in determining the strength of the ME coupling. After that, the most recent progress on various integrated multiferroic devices based on thin-film ME heterostructures are presented. In particular, rapid development of thin-film ME magnetometers has been seen over the past few years. These ultra-sensitive magnetometers exhibit extremely low limit of detection (sub-pT/Hz^1/2) for low-frequency AC magnetic fields, making them potential candidates for applications of medical diagnostics. Other devices reviewed in this paper include acoustically actuated nanomechanical ME antennas with miniaturized size by 1–2 orders compared to the conventional antenna; integrated RF tunable inductors with a wide operation frequency range; integrated RF tunable bandpass filter with dual H- and E-field tunability. All these integrated multiferroic devices are compact, lightweight, power-efficient, and potentially integrable with current complementary metal oxide semiconductor (CMOS) technology, showing great promise for applications in future biomedical, wireless communication, and reconfigurable electronic systems.

In recent years the delta-E effect has been used for detecting low frequency and low amplitude magnetic fields. Delta-E effect sensors utilize a forced mechanical resonator that is detuned by the delta-E effect upon application of a magnetic field. Typical frequencies of operation are from several kHz to the upper MHz regime. Different models have been used to describe the delta-E effect in those devices, but the frequency dependency has mainly been neglected. With this work we present a simple description of the delta-E effect as a function of the differential magnetic susceptibility $\chi$ of the magnetic material. We derive an analytical expression for $\chi$ that permits describing the frequency dependency of the delta-E effect of the Young’s modulus and the magnetic sensitivity. Calculations are compared with measurements on soft-magnetic ${\left({\mathrm{Fe}}_{90}{\mathrm{Co}}_{10}\right)}_{78}{\mathrm{Si}}_{12}{\mathrm{B}}_{10}$ thin films. We show that the frequency of operation can have a strong influence on the delta-E effect and the magnetic sensitivity of delta-E effect sensors. Overall, the delta-E effect reduces with increasing frequency and results in a stiffening of the Young’s modulus above the ferromagnetic resonance frequency. The details depend on the Gilbert damping. Whereas for large Gilbert damping the sensitivity continuously decreases with frequency, typical damping values result in an amplification close to the ferromagnetic resonance frequency.

A surface-acoustic-wave (SAW) magnetic-field sensor utilizing fundamental, first- and second-order Love-wave modes is investigated. A $4.5 \mathsf{\mu }\mathrm{m}$ SiO₂ guiding layer on an ST-cut quartz substrate is coated with a 200 $\mathrm{n}$ $\mathrm{m}$ (Fe₉₀Co₁₀)₇₈Si₁₂B₁₀ magnetostrictive layer in a delay-line configuration. Love-waves are excited and detected by two interdigital transducers (IDT). The delta-E effect in the magnetostrictive layer causes a phase change with applied magnetic field. A sensitivity of 1250 ${}^{°}$ / $\mathrm{m}$ $\mathrm{T}$ is measured for the fundamental Love mode at 263 $\mathrm{M}$ $\mathrm{Hz}$ . For the first-order Love mode a value of 45 ${}^{°}$ / $\mathrm{m}$ $\mathrm{T}$ is obtained at 352 $\mathrm{M}$ $\mathrm{Hz}$ . This result is compared to finite-element-method (FEM) simulations using one-dimensional (1D) and two-and-a-half-dimensional (2.5 D) models. The FEM simulations confirm the large drop in sensitivity as the first-order mode is close to cut-off. For multi-mode operation, we identify as a suitable geometry a guiding layer to wavelength ratio of $h_{\mathrm{GL}}/\lambda \approx 1.5$ for an IDT pitch of $p=12 \mathsf{\mu }\mathrm{m}$ . For this layer configuration, the first three modes are sufficiently far away from cut-off and show good sensitivity.

Two‐dimensional layered transition metal dichalcogenides (TMDCs) are promising memristive materials for neuromorphic computing systems. Despite extensive experimental work, the underlying switching mechanisms are still not understood, impeding progress in material and device functionality. This study reveals the dominant role of defect dynamics in the switching process of 2D TMDC materials. The switching process is governed by the formation and annihilation dynamics of a local vacancy depletion zone. It explains the distinct features of the device characteristics observed experimentally, including fundamentally different device behavior previously thought to originate from multiple mechanisms. Key influence factors are identified and discussed with a fully coupled and dynamic charge transport model for electrons, holes, and ionic point defects, including image‐charge‐induced Schottky barrier lowering (SBL). Thermal effects and local Joule heating are considered by coupling the transient heat transfer equation to the electronic properties. The model is validated with hysteresis and pulse measurements for various lateral 2D MoS₂‐based devices, strongly corroborating the relevance of vacancy dynamics in TMDC devices and offering a new perspective on the switching mechanisms. The insights gained from this study can be used to extend the functional behavior of 2D TMDC memristive devices in future neuromorphic computing applications.

Magnetoelectric resonators have been studied for the detection of small amplitude and low frequency magnetic fields via the delta-E effect, mainly in fundamental bending or bulk resonance modes. Here, we present an experimental and theoretical investigation of magnetoelectric thin-film cantilevers that can be operated in bending modes (BMs) and torsion modes (TMs) as a magnetic field sensor. A magnetoelastic macrospin model is combined with an electromechanical finite element model and a general description of the delta-E effect of all stiffness tensor components C_ij is derived. Simulations confirm quantitatively that the delta-E effect of the C₆₆ component has the promising potential of significantly increasing the magnetic sensitivity and the maximum normalized frequency change $\Delta f_{\mathrm{r}}$. However, the electrical excitation of TMs remains challenging and is found to significantly diminish the gain in sensitivity. Experiments reveal the dependency of the sensitivity and $\Delta f_{\mathrm{r}}$ of TMs on the mode number, which differs fundamentally from BMs and is well explained by our model. Because the contribution of C₁₁ to the TMs increases with the mode number, the first-order TM yields the highest magnetic sensitivity. Overall, general insights are gained for the design of high-sensitivity delta-E effect sensors, as well as for frequency tunable devices based on the delta-E effect.

In recent years, magnetoelectric Delta-E-effect sensors have proven the potential to detect low-frequency and low-amplitude magnetic fields, while being fully integrable. The magnetic field sensors use the magnetization-induced change of the effective Young's modulus, referred to as the Delta-E effect. Although several sensor types have been demonstrated, little is reported about the dependence of the design parameters and the resulting sensor characteristics, such as sensitivity and noise. In this Paper, we comprehensively analyze and discuss theoretically and experimentally the magnetic sensitivity and the Delta-E effect of bending-mode Delta-E-effect sensors. Analytical expressions are derived for the magnetic sensitivity and compared with the results of a more elaborate numerical mean-field model. The mean-field model additionally considers spatial variations of the magnetic properties, including the internal stray field of the real shape. Measurements are performed on state-of-the-art bending-mode Delta-E-effect sensors. We find that the Delta-E effect significantly depends on the resonance mode and, moreover, second-order bending modes increase the magnetic sensitivity compared to first-order modes. This can be explained well by the spatial variation of the internal stray field in agreement with the numerical simulations and magneto-optical measurements. Overall, we provide a comprehensive description of the magnetic sensitivity for the improvement of bending-mode Delta-E-effect sensors. We show that the weighting of local properties by the mode shape is not only key for modeling and understanding the Delta-E effect of different bending modes, but also an important factor for improving magnetic sensitivities.