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International audience; We study the potential of all-electrical inductive techniques for the spectroscopy of propagating forward volume spin waves. We develop a one-dimensional model to account for the electrical signature of spin-wave reflection and transmission between inductive antennas and validate it with experiments on a perpendicularly magnetized Co/Ni multilayer. We describe the influence of the antenna geometry and antenna-to-antenna separation, as well as that of the material parameters on the line shape of the inductive signals. For a finite damping, the broadband character of the antenna emission in the wave vector space imposes to take into account the growing decoherence of the magnetization waves on their spatial propagation. The transmission signal can be viewed as resulting from two contributions: A first one from propagating spin-waves leading to an oscillatory phase of the broadband transmission coefficient and another one originating from the distant induction of ferromagnetic resonance because of the long-range stray fields of realistic antennas. Depending on the relative importance of these two contributions, the decay of the transmitted signal with the propagation distance may not be exponential and the oscillatory character of the spin-wave phase on propagation may be hidden. Our model and its experimental validation allow us to define geometrical and material specifications to be met to enable the use of forward volume spin waves as efficient information carriers.

We compare the characteristics of electrically transduced Damon-Eshbach (DESWs) and backward volume (BVSWs) configurations within the same, 30 nm thick, ferromagnetic, CoFeB waveguide. Sub-micron U-shaped antennas are used to deliver the necessary in-plane and out-of-plane RF fields. We measure the spin-wave transmission with respect to in-plane field orientation, frequency and propagation distance. Unlike DESW, BVSWs are reciprocally transduced and collected for either direction of propagation, but their ability to transport energy is lower than DESWs for two reasons. This arises first because BVSW are inductively transduced less efficiently than DESWs. Also, in the range of wavevectors (~5 rad. um-1) typically excited by our antennas, the group velocity of BVSWs stays lower than that of DESW, which leads to reduced propagation ability that impact transmission signals in an exponential manner. In contrast, the group velocity of DESWs is maximum at low fields and decreases continuously with the applied field. The essential features of the measured SW characteristics are well reciprocated by a simple, 1-D analytical model which can be used to assess the potential of each configuration., Comment: This work was funded through the FETOPEN-01-2016-2017-FET-Open research and innovation actions (CHIRON project: Grant Agreement No. 801055) and was partly supported by the French RENATECH network

A nanomechanical on-chip test platform has recently been developed to deform under a variety of loading conditions freestanding thin films, ribbons and nanowires involving submicron dimensions. The lab-on-chip involves thousands of elementary test structures from which the elastic modulus, strength, strain hardening, fracture, creep properties can be extracted. The technique is amenable to in situ transmission electron microscopy (TEM) investigations to unravel the fundamental underlying deformation and fracture mechanisms that often lead to size-dependent effects in small-scale samples. The method allows addressing electrical and magnetic couplings as well in order to evaluate the impact of large mechanical stress levels on different solid-state physics phenomena. We had the chance to present this technique in details to Jacques Friedel in 2012 who, unsurprisingly, made a series of critical and very relevant suggestions. In the spirit of his legacy, the paper will address both mechanics of materials related phenomena and couplings with solids state physics issues.

We report on the first demonstration of acoustoelectric (AE) interaction in heterogeneously integrated Lithium Niobate thin film on Silicon substrate (LNOS). The strong coupling coefficient (K2) delivers efficient excitation of Rayleigh waves, while the large permittivity and lower interface charge density of the LNOS configuration provides superior control of the semiconductor carrier density over previous approaches. Preliminary results suggest that the monolithic LNOS configuration can overcome past obstacles faced by AE technology, enabling a new era of AE-based nonreciprocal RF devices.

Letter.-- et al., Flexoelectricity allows a dielectric material to polarize in response to a mechanical bending moment and, conversely, to bend in response to an electric field. Compared with piezoelectricity, flexoelectricity is a weak effect of little practical significance in bulk materials. However, the roles can be reversed at the nanoscale. Here, we demonstrate that flexoelectricity is a viable route to lead-free microelectromechanical and nanoelectromechanical systems. Specifically, we have fabricated a silicon-compatible thin-film cantilever actuator with a single flexoelectrically active layer of strontium titanate with a figure of merit (curvature divided by electric field) of 3.33 MV−1, comparable to that of state-of-the-art piezoelectric bimorph cantilevers., The work at ICN2 was funded by an ERC Starting Grant from the EU (Project No. 308023), a National Plan grant from Spain (FIS2013-48668-C2-1-P) and the Severo Ochoa Excellence programme. The work at Cornell University was supported by the National Science Foundation (Nanosystems Engineering Research Center for Translational Applications of Nanoscale Multiferroic Systems) under grant number EEC-1160504.

Piezoelectricity and flexoelectricity are two independent but not incompatible forms of electromechanical response exhibited by nanoscale ferroelectrics. Here, we show that flexoelectricity can either enhance or suppress the piezoelectric response of the cantilever depending on the ferroelectric polarity and lead to a diode-like asymmetric (two-state) electromechanical response., The work was funded by an ERC Starting Grant from the EU (Project No. 308023), a National Plan grant from Spain (FIS2013-48668-C2-1-P) and the Severo Ochoa Excellence programme.

An on-chip internal stress-based testing device has been developed in order to deform silicon nanoribbons and nanowires up to large strains enabling high throughput of data. The fracture strain and survival probability distribution have been generated for 50-nm-thick and 50- or 500-nm-wide specimens with lengths varying between 2.5 and 10 . Fracture strains reaching up to 5% are attained in the smallest specimens, whereas 90% of the specimens survive 2.5% deformation. This testing platform opens an avenue to investigate and use electromechanical couplings appearing under large mechanical stress or large deformation.

Freestanding MEMS structures made of two long connected beams from different materials are fabricated and released in order to extract the stress-strain properties of thin films. The first material, named actuator, contains a high internal tensile stress component and, when released, pulls on the other beam. The strain in the beams is calculated based on the measurement of the displacement with respect to the reference configuration using scanning electron microscopy. The stress is estimated using two different methods. The first method, already reported, is based on the displacement of the actuator and the knowledge of its internal stress. The method which constitutes the novelty of the present study is based on the dynamic analysis of the multi-beam structures, and the determination of the stress value that corresponds to the measured resonance frequencies. The dynamic analysis is performed via two different methods: (i) the modified Rayleigh–Ritz technique and (ii) the Euler–Bernoulli beam dynamics. Results are provided for palladium thin films which deform plastically and for monocrystalline silicon thin films, exhibiting a purely elastic behavior. The results show the higher accuracy of the dynamic measurements for the estimation of the stress compared to the static method. The dynamic measurements also show that the Rayleigh–Ritz technique tends to give a higher bound for the resonance frequencies compared to the Euler–Bernoulli technique. This dynamic method extends the potential of this on-chip material testing technique which can also be adapted to stress controlled sensors applications.

Nanomechanical testing of silicon is primarily motivated toward characterizing scale effects on the mechanical behavior. “Defect-free” nanoscale silicon additionally offers a road to large deformation permitting the investigation of transport characteristics and surface instabilities of a significantly perturbed atomic arrangement. The need for developing simple and generic characterization tools to deform free-standing silicon beams down to the nanometer scale, sufficiently equipped to investigate both the mechanical properties and the carrier transport under large strains, has been met in this research through the design of a versatile lab-on-chip. The original on-chip characterization technique has been applied to monocrystalline Si beams produced from Silicon-on-Insulator wafers. The Young’s modulus was observed to decrease from 160 GPa down to 108 GPa when varying the thickness from 200 down to 50 nm. The fracture strain increases when decreasing the volume of the test specimen to reach 5% in the smallest samples. Additionally, atomic force microscope-based characterizations reveal that the surface roughness decreases by a factor of 5 when deforming by 2% the Si specimen. Proof of concept transport measurements were also performed under deformation up till 3.5% on 40-nm-thick lightly p-doped silicon beams.

A simple and versatile on-chip tensile testing method is proposed for the statistical evaluation of size effects on the mechanical strength of silicon thin films along with the simultaneous study of (from low to ultra) strain effects on the carrier transport. Mechanical results are presented on the fracture strength of micro-nano scale silicon beams, followed with a discussion on interface states and problems facing reliable nano-electronic and nano-electromechanical characterizations.

A fabrication process to characterize single crystalline silicon microbeams under uniaxial tensile stress is presented. The microbeams subjected to uniaxial tensile strain are successfully released without any stiction by the use of critical point drying tool. Based on the deformation measured using scanning electron microscope (static measurement) images, the corresponding strain and stress are calculated to plot the uniaxial tensile characteristics curve of monocrystalline silicon. Dynamic stress determination based on the measurements of flexural resonance frequency of the released beams is discussed. Finally, comparison of stress values obtained using the two methods is shown.

In this work, 100 nm-thick boron-doped silicon beams with doping levels between 1 × 1016 and 1 × 1020 cm−3 undergoing uniaxial tensile strain are investigated by Raman spectroscopy. The structures exhibit a noticeable reduction in Young's modulus (∼20%) compared with the value reported for bulk. The traditional Raman shift coefficients used to determine stress and strain in bulk structures are revised, and appropriate corrections are implemented to account for the observed changes in Young's modulus. Interestingly, the Raman shift-strain relation in silicon nanostructures with strain along the [110] direction is found to be independent of size effects and doping. In contrast, the Raman shift-stress relation is found to be highly dependent on size effects. The dependency of the Fano line-shape parameters, used to fit the Raman first order peak in structures with high levels of doping, with strain is also reported. The results are shown to be crucial to accurately determine stress and strain from Raman measurements in doped silicon nanostructures and devices with size effects.

We demonstrate correlated oxide memory devices based on proton doping and re-distribution in perovskite nickelates (RNiO3, R = Sm, Nd) that undergo filling-controlled phase transition. Switching speeds as high as 30 ns in two-terminal devices patterned by electron-beam lithography is observed. The state switching speed reported here are $\sim 300\times $ greater than what has been noted with proton-driven resistance switching to date. The ionic-electronic correlated oxide memory devices also exhibit multi-state non-volatile switching. The results are of relevance to use of quantum materials in emerging memory and neuromorphic computing.

The piezo-resistance of 100 nm-thick, [110] oriented, p-type, mono-crystalline Si beams has been investigated under large uniaxial tension up to 2 GPa using an original on-chip tensile testing set-up. The piezo-resistance coefficient (π) was found to increase by a factor of 6 compared with ∼1.5 for Si bulk, when decreasing the dopant concentration from Na ∼ 1 × 1019 cm−3 down to Na ∼ 5 × 1017 cm−3. Reduction of resistance by a factor of 5.8, higher than theoretical maximum of 4.5, is reported for Na ∼ 5 × 1017 cm−3 under a stress of 1.7 GPa, without any sign of saturation.

This work addresses the paucity of roughness measurements by reporting on roughness parameters in uniaxial strained Si beams relevant for state of the art MOSFETs, nanowire and MEMS devices, with varying degrees of strain. Roughness is characterized by high resolution AFM and strain is characterized by Raman spectroscopy. Microstructures comprising a silicon nitride actuator are used to induce a wide range of stress levels in Si beams. The microstructures also allow the comparison of surface evolution in the strain direction (along the Si beam) compared with the unstrained direction (across the Si beam). A gradual reduction in rms roughness amplitude and increase in roughness correlation length in the direction of the applied stress are found for increasing values of strain. In contrast, surface roughness in the direction perpendicular to the applied stress remained largely unchanged from the unstrained initial state.

MEMS technology is expected to play a significant role in future space missions provided the effects of radiation on the reliability of MEMS devices is well understood [1]. Radiation induced dielectric charging has been identified as a mechanism which can potentially limit the reliability of electrostatically actuated MEMS devices [2]. The response of piezoresistive and PZT actuated MEMS was also found to change after exposure to different types of radiation [3]. It is however necessary to further investigate the effect of radiation and especially neutrons on the electromechanical properties of various materials that are used in microfabrication [4]. In this work we present results from mechanical and electrical tests on different materials before and after exposure to neutrons radiation.

Simple fabrication process and extraction procedure to determine the fracture strain of monocrystalline silicone are demonstrated. Nanowires/nanoribbons in silicon are fabricated and subjected to uniaxial tensile stress along the complete length of the beams. Large strains up to 5% are measured for nanowires presenting a cross section of 50 nm x 50 nm and a length of 2.5 μm. An increase in fracture strain for silicon nanowires (NWs) with the downscaling of their volume is observed, highlighting the reduction of the defects probability as volume is decreased.

Surface roughness in uniaxially loaded strained Si has been studied experimentally using high-resolution atomic force microscopy and a microelectromechanical systems-based on-chip loading device. A reduction in rms roughness from 0.29 nm to 0.07 nm has been identified as strain increases from 0 to 2.8% (stress from 0 to 4.9 GPa). The correlation length of the roughness, also known to affect carrier mobility, increases with increasing strain up to 1.7% before reducing at larger levels of strain. These results partly explain the high-field mobility observed in strained Si, indicating that a modified correlation length should also be considered in transport modelling of strained Si.

The transport characteristics of low dimensional semiconductors like silicon nano-wires (SiNWs) rarely conform to expectations from geometry and dopant density, exhibiting significant variations as a function of different surface terminations/conditions. The association of these mechanisms with surface states and their exact influence on practical SiNW devices still remains largely unclear. Herein, we report on the influence of surface state charge distributions on SiNW transport characteristics. For this study, p-type SiNW devices with widths of 50, 100, and 2000 nm are fabricated from 25, 50, and 200 nm-thick SOI wafers. A ∼five order difference in effective carrier concentration was observed in the initial SiNWs characteristics, when comparing SiNWs fabricated with and without a thermal oxide. The removal of the surface oxide by a hydrogen fluoride (HF) treatment results in a SiNW conductance drop up to ∼six orders of magnitude. This effect is from a surface depletion of holes in the SiNW induced by positive surface charges deposited as a result of the HF treatment. However, it is observed that this charge density is transient and is dissipated with the re-growth of an oxide layer. In summary, the SiNW conductance is shown to vary by several orders of magnitude, while comparing its characteristics for the three most studied surface conditions: with a native oxide, thermal oxide and HF induced H-terminations. These results emphasize the necessity to interpret the transport characteristics of SiNWs with respect to its surface condition, during future investigations pertaining to the physical properties of SiNWs, like its piezo-resistance. As a sequel, prospects for efficiently sensing an elementary reduction/oxidation chemical process by monitoring the variation of SiNW surface potential, or in practice the SiNW conductance, is demonstrated.

The tensile response of top-down fabricated sc-Si nanobeams is inferred from the fitting of stress-strain data obtained under tensile loading conditions over a large range of deformation. The testing is performed using MEMS structures consisting of two connected beams; a highly stressed silicon-nitride (SiN) beam connected to a sc-Si specimen beam. The high tensile stress component present upon the deposition of the SiN loads the sc-Si beam once the entire structure is released. The strain and stress values are extracted independently, respectively, by scanning electron microscopy inspection and vibration frequency measurement of the released tensile MEMS structures. The tensile tests are undertaken for six thicknesses to determine the dependence of the elastic response on dimensions. The Young's modulus shows a variation of 40% for thicknesses ranging from 200 to 30 nm.

3Institute of Mechanics, Materials and Civil engineering, Universite catholique de Louvain, 1348 Louvain-la-Neuve, Belgium The characterization of the elastic, plastic and fracture behavior of nanofilms is extremely challenging, from the preparation and manipulation of specimens to the application of small loads and extraction of accurate stresses and strains. Several novel lab-on-a-chips concepts will be presented to address these challenges. The first relies on the internal stress present in one film to provide the actuation for deforming the sample film [1]. The second lab-on-a-chip relies on a macroscopic, external actuation on the silicon chip. Classical MEMS-based microfabrication procedures are used to pattern the films into special test structures and to release them from the substrate. The actuation results in uniform strain, so that data analysis is straightforward. The measurement of the displacement gives access to the stress and the strain applied to the sample, provided that the Young’s modulus and mismatch strain of the films are known. A third lab-on-chip performs the measurement of Young's The characterization of the elastic, plastic and modulus when needed. Various fracture behavior of nanofilms is extremely combinations of dimensions allow the challenging, from the preparation and characterization of different materials and manipulation of specimens to the application mechanical properties. Results obtained on of small loads and extraction of accurate both ductile and brittle nanofilms demonstrate stresses and strains. Several novel lab-on-a-the interest of these methods. chips concepts will be presented to address these challenges. The first relies on the internal stress present in one film to provide the actuation for deforming the sample film [1]. The second labon-a-chip relies on a macroscopic, external actuation on the silicon chip. modulus when needed. Various combinations of dimensions allow the characterization of different materials and mechanical properties. Results obtained on both ductile and brittle nanofilms demonstrate the interest of these methods.

The high-frequency performance of strong piezoelectric materials like Pb(Zr1– x Ti x )O3 (PZT) remains relatively less explored due to the assumption of large dielectric/ferroelectric losses at gigahertz (GHz) frequencies. Recently, the advent of magnetoelectric technology as an on-chip route to excite magnetization dynamics has provided the impetus to evaluate the electromechanical performance of PZT at microwave frequencies. In this article, we demonstrate that high-overtone bulk acoustic resonators fabricated using barium-doped PZT (BPZT) films can efficiently generate acoustic waves up to 15 GHz. The ferroelectricity of BPZT endows added functionality to the resonator in the form of voltage tunability of the electromechanical performance. We extract the piezoelectric coefficient by numerically comparing the performance of BPZT with the Mason model. The extracted piezoelectric coefficient approximately 60 pm/V agrees well with reported values on a thin-film PZT measured at low frequencies (